Modelling the impact of liver regeneration on hepatoblastoma patient-derived-xenograft tumor growth

BACKGROUND

Twenty percent of children with hepatoblastoma (HB) have lung metastasis at diagnosis. Treatment protocols recommend surgical removal of chemotherapy-refractory lung nodules, however no chronological order is established. As hepatectomy is followed by release of growth factors, it has been proposed that partial hepatectomy (PH) could boost local or distant residual tumor growth.

METHODS

To evaluate the impact of PH on distant tumor growth, PH was performed in mice subcutaneously implanted with a HB patient-derived xenograft (PDX). The influence of PH on tumor growth at primary site was assessed by performing PH concomitantly to HB PDXs orthotopic implantation.

RESULTS

Subcutaneously implanted HB PDX failed to show any influence of hepatectomy on tumor growth. Instead, intrahepatic tumor growth of one of the 4 HB PDXs implanted orthotopically was clearly enhanced. Cells derived from the hepatectomy-sensitive HB PDX exposed to hepatic growth factor (HGF) showed increased proliferation rate compared to cells derived from a hepatectomy-insensitive model, suggesting that the HGF/MET pathway could be one of the effectors of the crosstalk between liver regeneration and HB growth.

CONCLUSION

These results suggest that hepatectomy can contribute to HB growth in some patients, further studies will be necessary to identify biomarkers predictive of patient risk of PH-induced HB recurrence.

IMPACT

Key message: Cytokines and growth factors secreted following partial hepatectomy can contribute to intrahepatic tumor growth in some hepatoblastoma models. What does it add to the existing literature: It is the first article about the impact of liver regeneration induced by partial hepatectomy on hepatoblastoma local or distant tumoral growth in nude mice. What is the impact: It is important to identify the secreted factors that enhance tumor growth and to define biomarkers predictive of patient risk of partial hepatectomy-induced hepatoblastoma recurrence.

Development of Novel Models of Aggressive Variants of Castration-resistant Prostate Cancer

BACKGROUND

Genomic studies have identified new subsets of aggressive prostate cancer (PCa) with poor prognosis (eg, neuroendocrine prostate cancer [NEPC], PCa with DNA damage response [DDR] alterations, or PCa resistant to androgen receptor pathway inhibitors [ARPIs]). Development of novel therapies relies on the availability of relevant preclinical models.

OBJECTIVE

To develop new preclinical models (patient-derived xenograft [PDX], PDX-derived organoid [PDXO], and patient-derived organoid [PDO]) representative of the most aggressive variants of PCa and to develop a new drug evaluation strategy.

DESIGN, SETTING, AND PARTICIPANTS

NEPC (n = 5), DDR (n = 7), and microsatellite instability (MSI)-high (n = 1) PDXs were established from 51 patients with metastatic PCa; PDXOs (n = 16) and PDOs (n = 6) were developed to perform drug screening. Histopathology and treatment response were characterized. Molecular profiling was performed by whole-exome sequencing (WES; n = 13), RNA sequencing (RNA-seq; n = 13), and single-cell RNA-seq (n = 14). WES and RNA-seq data from patient tumors were compared with the models.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Relationships with outcome were analyzed using the multivariable chi-square test and the tumor growth inhibition test.

RESULTS AND LIMITATIONS

Our PDXs captured both common and rare molecular phenotypes and their molecular drivers, including alterations of BRCA2, CDK12, MSI-high status, and NEPC. RNA-seq profiling demonstrated broad representation of PCa subtypes. Single-cell RNA-seq indicates that PDXs reproduce cellular and molecular intratumor heterogeneity. WES of matched patient tumors showed preservation of most genetic driver alterations. PDXOs and PDOs preserve drug sensitivity of the matched tissue and can be used to determine drug sensitivity.

CONCLUSIONS

Our models reproduce the phenotypic and genomic features of both common and aggressive PCa variants and capture their molecular heterogeneity. Successfully developed aggressive-variant PCa preclinical models provide an important tool for predicting tumor response to anticancer therapy and studying resistance mechanisms.

PATIENT SUMMARY

In this report, we looked at the outcomes of preclinical models from patients with metastatic prostate cancer enrolled in the MATCH-R trial (NCT02517892).

Abstract 4678: Characterization of a PDX panel covering molecular diversity of non-small cell lung cancer to accelerate the development of precision therapy

Lung cancer remains the first cause of cancer-related deaths worldwide, of which Non-Small Cell Lung Cancer (NSCLC) represents more than 80% of patients with advanced disease at the time of diagnosis. NSCLC is a highly heterogenous disease, and the identification of its main actionable oncogenic drivers (i.e. EGFR, ALK, PI3K/AKT/mTOR, RET, MET, BRAF and NTRK/ROS1) and the development of specific inhibitors against these targets has transformed therapeutic care. In addition, immune-checkpoint therapy has emerged as an indispensable treatment modality, especially for patients lacking actionable oncogenic drivers, although biomarkers for predicting response to immune-checkpoint inhibition have remained elusive. Despite these new therapeutic options, NSCLC remains a lethal disease in the majority of patients due to tumor plasticity and selection leading to frequent resistance development and disease progression. Efforts are therefore needed to identify drugs and drug combinations that can prevent or overcome these resistance pathways. Patient-Derived Xenografts (PDX) models developed in immune-compromised mice recapitulate the disease more faithfully than any other in vivo model in terms of histopathologic and genomic features. They have proven their relevance in the study of pathways leading to the development and progression of cancer, to the mechanisms linked to tumor resistance and to the identification of novel effective therapies, facilitating the translation of preclinical results in the clinical setting. We describe a platform of over 35 NSCLC PDX models covering most of the molecular diversity of the disease, that have been fully characterized at the molecular level and for their response to a panel of cytotoxic chemotherapies and targeted therapies. These NSCLC PDX models have been established in immune-deficient mice from tumor biopsies collected in treatment-naïve patients or in patients having acquired resistance following an initial objective response to a variety of targeted inhibitors (EGFRi, ALKi, ROSi, BRAFi,⋯) in the MATCH-R clinical trial. In addition, 4 PDX models were established from circulating tumor cells (CTC) isolated from the blood of advanced NSCLC patients. Finally, some of these NSCLC PDX models were established in highly immunodeficient mice humanized with human PBMCs or CD34+ cells allowing testing of efficacy of bispecific T-Cell engager antibody or immune-checkpoint inhibitors. This panel of NSCLC PDX models provides a powerful preclinical platform to improve our knowledge on the mechanisms underlying resistance to treatment and to rapidly evaluate response to new treatments and translate this knowledge to the clinic.

Citation Format: Delphine Nicolle, Laura Brulle-Soumare, Katell Mevel, Ludovic Bigot, Tala Tayoun, Benjamin Besse, Françoise Farace, Luc Friboulet, Didier Decaudin, Erwan Corcuff, Anaïs Joachim, Bernard Malissen, Ana Zarubica, Hervé Luche, Jean-Gabriel Judde, Olivier Deas. Characterization of a PDX panel covering molecular diversity of non-small cell lung cancer to accelerate the development of precision therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4678.

Abstract 4677: A preclinical platform of breast cancer PDX and derived cellular models as a tool for pharmacological screening and functional studies

Despite considerable progress in understanding the biology and genetics of breast cancer, the development of effective therapies needs physiological and predictive preclinical models. In this context, breast cancer (BC) patient-derived xenograft (PDX) models have become a standard tool as they reproduce the biology of tumors of origin, in term of histology, genotype and response to chemotherapy. They have proven their relevance in the study of pathways leading to the development and progression of cancer, to the mechanisms linked to tumor resistance and to the identification of novel effective therapies. We present a preclinical platform of over 60 fully characterized BC PDX models and their in vitro cell derivatives for preclinical evaluation of new treatment modalities. Our platform consists of a PDX collection of 43 TNBC, 6 ER+, 4 HER2+, 6 Luminal B models (ER+ HER2+) and 14 cellular models derived from these PDXs, representing the variety of BC. PDX models were obtained by transplantation of post-surgery tumor specimens either by grafting of tumor fragments in the interscapular region of nude mice or by injection of tumor cells into the fat pad of NOD-Scid mice. Molecular analyses were done included gene expression, gene copy number, whole exome sequencing and IHC markers staining. In vivo drug efficacy assays were performed with standards of care as single agent or in combinations. This PDX panel mostly reflects the molecular heterogeneity of breast cancer and reproduce accurately the molecular and drug response profile of human tumors. It provides an invaluable tool for translational research. It is widely used to performed standard drug evaluation but also “Mouse Clinical Trials” (MCT) in vivo screens to provide more predictive preclinical data on single-agent or combination drug efficacy. Engrafted on highly immunodeficient mice humanized with human PBMCs or CD34+ cells, these PDX models allow bispecific T-Cell engager antibody testing or immune-checkpoint inhibitors evaluation. In addition to these PDX panel, we derived cellular models (PDXDCs) to offer a time- and cost-effective preclinical screening tool. PDXDCs were obtained from dissociated PDX tumors cultured under different media and matrix conditions. They were characterized by comparison with the parental PDX by Short Tandem Repeat (STR) profiling before performing a master bank. WES and RNASeq molecular analyses were done and in vitro drug sensitivity was compared with their parental PDX in vivo drug response. Overall, the results show that this PDXDC panel reproduced in vitro the in vivo drug response profile of the original PDXs with various therapies. This BC PDX panel and in vitro cell derivatives provide a powerful preclinical platform to improve our knowledge on BC biology and to rapidly evaluate response to new treatments and translate this knowledge to the clinic.

Citation Format: Delphine Nicolle, Aurore Gorce, Marie Tavernier, Elisabetta Marangoni, Didier Decaudin, Christophe Ginestier, Emmanuelle Charafe-Jaufret, Judith Passildas, Nina Robin, Robert Clarke, Erwan Corcuff, Anaïs Joachim, Bernard Malissen, Ana Zarubica, Hervé Luche, Jean-Gabriel Judde, Olivier Déas. A preclinical platform of breast cancer PDX and derived cellular models as a tool for pharmacological screening and functional studies. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4677.

Vav1 Selectively Down-Regulates Akt2 through miR-29b in Certain Breast Tumors with Triple Negative Phenotype

Triple negative breast cancer (TNBC) represents the most aggressive breast tumor, showing a high intrinsic variability in terms of both histopathological features and response to therapies. Blocking the Akt signaling pathway is a well-studied approach in the treatment of aggressive breast tumors. The high homology among the Akt isoforms and their distinct, and possibly opposite, oncogenic functions made it difficult to develop effective drugs. Here we investigated the role of Vav1 as a potential down-regulator of individual Akt isozymes. We revealed that the over-expression of Vav1 in triple negative MDA-MB-231 cells reduced only the Akt2 isoform, acting at the post-transcriptional level through the up-modulation of miR-29b. The Vav1/miR-29b dependent decrease in Akt2 was correlated with a reduced lung colonization of circulating MDA-MB-231 cells. In cell lines established from PDX, the Vav1 induced down-modulation of Akt2 is strongly dependent on miR-29b and occurs only in some TNBC tumors. These findings may contribute to better classify breast tumors having the triple negative phenotype, and suggest that the activation of the Vav1/miR-29b axis, precisely regulating the amount of an Akt isozyme crucial for tumor dissemination, could have great potential for driving more accurate therapies to TNBCs, often not eligible or resistant to treatments.

Abstract 176: Development of PDX-derived spheroids using LifeGel, an innovative 3D cell culture technology

One of the biggest challenges in preclinical oncology is the lack of models faithfully recapitulating the physiological and pathophysiological features of the native tumor. PDXs (Patient-Derived Xenografts), developed in immune-compromised mice, have proven their relevance in the study of aberrations leading to the development and progression of cancer, to the mechanisms linked to tumor resistance and to the identification of novel therapies. Despite being a fundamental step to generate new knowledge on cancer, the use of PDXs shows some technical disadvantages such as long engraftment time and/or low growth rate, thus raising economic and ethical concerns. Huge efforts are being done to develop cell-based alternatives systems reproducing the tumor complexity combined with suitable methods. To this aim, we have developed 50+ PDX-derived cell lines (PDXDCs) from our proprietary 200+ PDX collection. These lines are currently used as two-dimensional (2D) cultures to perform drug screening in an affordable, timewise, and cost-effective way. While well designed, drug-tailored 2D screenings can predict drug behavior in vivo, they present limitations as they are unable to reproduce cell-cell and cell-extracellular matrix interactions, two important parameters that contribute to the regulation of drug accessibility and oxygen diffusion in vivo. To encompass those limitations and give access to a wider range of experimental methods we have generated three-dimensional (3D) cell culture models by taking advantage of LifeGel technology, consisting of protein-based hydrogels that modulate matrix density and stiffness to mimic the organ of origin-specific extracellular environment. Thanks to its versatility we successfully developed spheroid cultures from PDXDCs from various indications, including breast cancer cells from different histological subtypes. Tumor cells plated on LifeGel adopted 3D spheroid-like structures in a few days. These structures showed heterogeneous morphology and size depending on the tumor type and the hydrogel composition. As spheroids can be passaged in vitro by digestion, we could easily expand them and perform drug screening that will be presented and compared to 2D and in vivo results. The aim of this project is to develop a collection of PDX-derived spheroids recapitulating PDXs characteristics. This collection will give the opportunity to perform high-content drugs screening to select the best candidate drugs to be retained for further preclinical in vivo studies.

Citation Format: Agnieszka Pietrzyk, Emilie Indersie, Olivier Deas, Jean-Gabriel Judde, Marcin Krzykawski, Stefano Cairo. Development of PDX-derived spheroids using LifeGel, an innovative 3D cell culture technology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 176.

Abstract 1951: Circulating tumor cell-derived explant models reveal DNA damage response-based therapeutic opportunities in non-small cell lung cancer

Background: DNA damage and genomic instability contribute to non-small cell lung cancer (NSCLC) etiology and progression. However, their therapeutic exploitation is disappointing. CTC-derived eXplants (CDX) offer systems for mechanistic investigation of CTC metastatic potency and biology-driven therapeutic testings. We perform in-depth molecular and functional characterization of CDX models and demonstrate that targeting defects in the DNA damage response (DDR) and genome integrity regulators impedes CTC-driven metastasis in NSCLC.

Methods: CTCs were enriched from 30 mL blood samples of 56 advanced NSCLC patients and implanted subcutaneously into Nod/Scid-IL2Rγ-/- (NSG) mice. Tumors were palpable within a median of 108 days. Among the four CDX models established, three CDX-derived cell lines (GR-CDXL1, GR-CDXL3, GR-CDXL4) were obtained. CDX and cell lines were characterized by immunofluorescence (IF), immunohistochemistry and whole-exome sequencing (WES). Chromosomal instability (CIN) and DDR activity were evaluated by IF and western blot. Gene expression was quantified by qRT-PCR. Tumorigenic potential of CDX-derived cell lines was assessed in the chick embryo chorioallantoic membrane and NSG mice engrafted intravenously. IC50 was assessed using CellTiter-Glo®.

Results: Four CDX models and three CDX-derived cell lines were established from NSCLC CTCs and recapitulated patient tumor histology (available for three patients) and response to platinum-based chemotherapy. WES analysis showed considerable mutational landscape similarity between the CDX (GR-CDXL1, GR-CDXL2, GR-CDXL3, GR-CDXL4), corresponding patient tumor biopsy and/or single CTCs. Truncal alterations in key DDR and genome integrity-related genes were prevalent across models and assessed as therapeutic targets in vitro, in ovo and in vivo. GR-CDXL1 presented homologous recombination deficiency linked to bi-allelic BRCA2 mutation, FANCA deletion and unrepaired DNA lesions post-mitosis. GR-CDXL1 cells were sensitive to PARP inhibitor (PARPi) olaparib, despite chemoresistance, which challenges the current clinical hypothesis claiming that chemosensitive NSCLC patients should respond to PARPi. Targeting CIN through centrosome clustering inhibition in GR-CDXL3 impeded tumor growth in ovo and in vivo. In GR-CDXL4, olaparib sensitivity was dictated by SLFN11 overexpression, which also correlated with increased neuroendocrine marker expression at patient disease progression, suggesting a predictive value of SLFN11 in histological transformation of NSCLC into SCLC.

Conclusion: This study unravels distinct DDR profiles as a central mechanism underpinning CTC metastatic potency. Our CDX models provide a robust platform for ex vivo drug testing of DDR-targeted strategies to expand patient categories that may benefit from precision medicine in metastatic NSCLC.

Citation Format: Tala Tayoun, Vincent Faugeroux, Marianne Oulhen, Olivier Deas, Judith Michels, Laur Brulle-Soumare, Stefano Cairo, Jean-Yves Scoazec, Virginie Marty, Agathe Aberlenc, David Planchard, Jordi Remon, Santiago Ponce, Benjamin Besse, Patricia Kannouche, Jean-Gabriel Judde, Patrycja Pawlikowska, Françoise Farace. Circulating tumor cell-derived explant models reveal DNA damage response-based therapeutic opportunities in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1951.

Abstract 1637: PDX-derived cell line platform for pharmacological screening and functional studies

Despite considerable progress in understanding the biology and genetics of cancer, the development of effective therapies is hampered by the lack of sufficient experimental models that recapitulate the genetic diversity of this disease. The recourse to patient-derived xenograft (PDX) for the evaluation of new candidate anticancer drugs is becoming the gold standard in preclinical oncology. The faithful reproduction of patients’ cancer features, and the possibility to generate a large number of models that recapitulate patient population genetic heterogeneity, confer PDXs a critical added value in the evaluation of new candidate drugs. These improved models will hopefully contribute to decrease the attrition rate observed in clinical trials, thus far unacceptably high. Over the last 15 years, we have generated and characterized a collection of 200+ PDXs from different solid tumors that accurately reproduce the histological and molecular heterogeneity of the tumors of origin. This panel has allowed for the preclinical validation of several anticancer drugs that are now used in the clinic. Although being an indispensable tool to complete preclinical studies, the use of PDX in vivo systems for large-scale screening during early drug discovery is hampered by ethical, economical and throughput burdens limiting the number of test articles being tested. To address this problem, we developed a panel of PDX-derived cell lines (PDXDCs) that we propose as a time and cost-effective medium-throughput screening tool to profile the anti-cancer activity of early test compounds. To date, 50+ PDXDCs from various indications such as breast, lung, prostate and many others have been generated and tested for their response in vitro towards standards of care and targeted anti-cancer agents matching patient clinical management. Differently from standard cell line establishment, which is obtained by expansion of a cell clone that survives in vitro plating, our cell line development technology allows for maintenance of tumor cell population heterogeneity. PDXDCs RNA and exome sequencing data faithfully match the parental PDX features, and by modulating experimental parameters, such as 2D or 3D growth conditions, drug exposure duration and endpoint read-outs, we could phenocopy in vitro the corresponding PDXs’ sensitivities to chemotherapies. These results show our PDXDCs panel is a valuable in vitro platform for drug screening to help selecting drug candidates for further validation in parental PDX models in vivo.

Citation Format: Olivier Déas, Léa Sinayen, Emilie Indersie, Kathleen Flosseau, Sophie Banis, Enora Le Ven, Jean-Gabriel Judde, Stefano Cairo. PDX-derived cell line platform for pharmacological screening and functional studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1637.

Targeting genome integrity dysfunctions impedes metastatic potency in non-small-cell lung cancer circulating tumor cell-derived eXplants

DNA damage and genomic instability contribute to non–small cell lung cancer (NSCLC) etiology and progression. However, their therapeutic exploitation is disappointing. CTC-derived explants (CDX) offer systems for mechanistic investigation of CTC metastatic potency and may provide rationale for biology-driven therapeutics. Four CDX models and 3 CDX-derived cell lines were established from NSCLC CTCs and recapitulated patient tumor histology and response to platinum-based chemotherapy. CDX (GR-CDXL1, GR-CDXL2, GR-CDXL3, GR-CDXL4) demonstrated considerable mutational landscape similarity with patient tumor biopsy and/or single CTCs. Truncal alterations in key DNA damage response (DDR) and genome integrity–related genes were prevalent across models and assessed as therapeutic targets in vitro, in ovo, and in vivo. GR-CDXL1 presented homologous recombination deficiency linked to biallelic BRCA2 mutation and FANCA deletion, unrepaired DNA lesions after mitosis, and olaparib sensitivity, despite resistance to chemotherapy. SLFN11 overexpression in GR-CDXL4 led to olaparib sensitivity and was in coherence with neuroendocrine marker expression in patient tumor biopsy, suggesting a predictive value of SLFN11 in NSCLC histological transformation into small cell lung cancer (SCLC). Centrosome clustering promoted targetable chromosomal instability in GR-CDXL3 cells. These CDX unravel DDR and genome integrity–related defects as a central mechanism underpinning metastatic potency of CTCs and provide rationale for their therapeutic targeting in metastatic NSCLC.

Abstract 595: Patterns and dynamics of genome instability drive metastatic activity in non-small cell lung cancer (NSCLC) circulating tumor cell (CTC)-derived xenograft (CDX) models

Background: CDX models have emerged as tractable systems to explore mechanisms involved in metastatic progression and tumor-initiating properties of CTCs. However, their development is challenging due to low prevalence of CTCs in patient blood. We report the genomic and functional characterization of 4 NSCLC CDX models and their derived cell lines. We focus on genome and chromosomal instability (CIN) mechanisms operating in the CDX-derived cell lines and decipher relevant therapeutic targets.

Methods: CTCs were enriched from 30mL blood samples of 58 advanced NSCLC patients and implanted subcutaneously into Nod/Scid-IL2Rγ-/- (NSG) mice. Tumors were palpable within a median of 108 days. Among the 4 CDX models established, 3 CDX-derived cell lines (GR-CDXL1, GR-CDXL3 and GR-CDXL4) were obtained. Cell lines were characterized by immunofluorescence (IF), immunohistochemistry and whole-exome sequencing (WES). CIN and DNA damage response (DDR) activity were evaluated using IF and western blot. Tumorigenic potential of CDX-derived cell lines was assessed in the chick embryo chorioallantoic membrane (CAM) and NSG mice engrafted intravenously. IC50 was assessed using CellTiter-Glo®.

Results: All CDX models had an epithelial phenotype. CDX and cell lines recapitulated the corresponding tumor histological features (available for 3 patients). WES revealed multiple copy number alterations (CNAs) in driver genes implicated in diverse genome instability mechanisms. GR-CDXL1 presented BRCA2 mutation and FANCA promoter deletion, while AKT gain was detected in GR-CDXL3 in addition to whole genome doubling. This led us to investigate the DDR in the cell lines. Homologous recombination deficiency and unrepaired DNA damage post-mitosis were observed in GR-CDXL1. GR-CDXL3 presented numerical CIN and centrosome clustering. GR-CDXL4 showed high levels of DNA damage and CIN.

CNA and functional analysis provided a biological rationale for the selection of drug candidates in pharmacological testings on the CDX-derived cell lines. The assays mirrored patients' response to chemotherapy and revealed olaparib efficiency in GR-CDXL1 and GR-CDXL4 cells, which was validated in the CAM. GR-CDXL3 cells were sensitive to phosphoinositide 3-kinase-α inhibitor alpelisib, suggesting tumor dependence on PI3K/AKT pathway. Cell lines were tumorigenic in the CAM and mice. Notably, GR-CDXL3 seeded multiple metastases, which is concordant with its distinguished CIN characteristics and WGD. In ovo and in vivo validation of candidate therapeutic strategies is ongoing and will be presented.

Conclusion: This study reveals distinct genome and CIN patterns operating in our CDX-derived cell lines that may play a critical role in CTC seeding capacity. Our CDX models offer new tools for designing therapeutic strategies targeting metastatic progression in NSCLC.

Citation Format: Tala Tayoun, Vincent Faugeroux, Marianne Oulhen, Emma Pailler, Olivier Deas, Laura Mezquita, Laura Brulle-Soumare, Stephano Cairo, Jean-Yves Scoazec, Virginie Marty, Agathe Aberlenc, Maud NgoCamus, Claudio Nicotra, David Planchard, Patricia Kannouche, Benjamin Besse, Jean-Gabriel Judde, Patrycja Pawlikowska, Françoise Farace. Patterns and dynamics of genome instability drive metastatic activity in non-small cell lung cancer (NSCLC) circulating tumor cell (CTC)-derived xenograft (CDX) models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 595.

Abstract 3014: A preclinical platform of PDX-derived cell lines as a tool for pharmacological screening and functional studies

Despite considerable progress in understanding the biology and genetics of cancer progression, the development of effective therapies against cancer need physiological and predictive preclinical models. In this context, patient-derived xenograft (PDX) models has become a standard tool as they reproduce accurately the behavior of tumor of origin, in term of histological and molecular phenotype and response to chemotherapy. Although PDXs in vivo models are indispensable for preclinical studies, they suffer from some limitations due to study costs related to tumor maintenance on mice, variable engraftment rate, growth delay and limited throughput for large-scale drug screening. To address this problem and propose a time a cost effective preclinical screening tool, we developed a panel of PDX-derived low-passage 2D cell lines as a convenient in vitro pre-screening platform to profile compound activity. Different PDX models including breast, lung, colon, melanoma, glioblastoma and hepatoblastoma were tested for their capacity to generate cell lines maintaining the characteristics of the parental PDX tumor and usable for in vitro assays. Today, we succeeded with a series of 50 PDX models with 83% success rate. Tumor cells isolated from PDX tumor tissue were cultured under different media and matrix conditions, allowing at least 5 passages in culture. A Short Tandem Repeat (STR) comparison profile was done with the parental PDX before performing a master bank. We performed short term 2D cytotoxicity assays and long term colony assays to compare cell lines in vitro drug sensitivity with their parental PDX in vivo drug response and overall, the results show that this panel reproduced the drug response profile of the original PDXs with chemotherapies, PARP inhibitors, an ADC (T-DM1) and FGFR-targeting therapies. Moreover, cellular models engrafted back onto mice showed in vivo response to chemotherapies similar to that of the parental PDX confirming the identical behavior of cell line/PDX couples. As the use of cellular models is still considered as a standard for early preclinical test to evaluate drug response before moving to in vivo assays, our PDX-derived cell line platform appeared to be a robust and relevant tool. Furthermore, since the main concern when using in vitro models is the representativeness of the results obtained when transposed to in vivo models, the similarities between cell lines and parental PDX should maximize success of further in vivo preclinical drug development.

Citation Format: Olivier Deas, Sophie Banis, Kathleen Flosseau, Lea Sinayen, Enora Le Ven, Jean-Gabriel Judde, Stefano Cairo. A preclinical platform of PDX-derived cell lines as a tool for pharmacological screening and functional studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3014.

Abstract 3016: Identification of the mechanisms of resistance to targeted therapies in advanced solid cancers

Despite progress in understanding aberrations that contribute to the development and progression of cancer, resistance to classical chemotherapeutic agents or novel targeted drugs continues to be a major problem in cancer therapy. Hence, the identification of the mechanisms underlying drug resistance acquisition is the key to explore new and efficient therapeutic pathways for patients. The MATCH-R clinical trial enrolls patients with oncogene-driven cancer who have had previous clinical response to targeted therapy and subsequently experienced disease progression under treatment. In the framework of this project, Gustave Roussy and XenTech are joining forces to develop a panel of patient-derived xenografts (PDXs) derived from biopsies collected from these patients at the stage of acquired resistance. These PDX models are being fully characterized at both molecular and pharmacological levels and used to improve knowledge on the mechanisms underlying resistance to treatment and to evaluate response to new treatments. In this perspective, the development of 75 PDX-AR (Acquired Resistance) models is planned over 3 years. To favor successful xenograft establishment, the first passages are performed without drug treatment, then all the models are maintained under the same therapeutic pressure the parental tumor was submitted to at the time of biopsy. When applying therapeutic pressure, we observed different types of response: resistance from the first passage under treatment, stabilization under treatment at the first passages and rapidly acquired resistance over passages, or sensitivity to treatment whereas the patient tumor showed progression under the same treatment. These different behaviors can be observed in PDX models developed from multiple metastases of a same patient and may reflect different mechanisms of resistance. Most interestingly, PDX models obtained from different metastatic lesions of a same patient can recapitulate the different behavior observed in this patient. This behavior is translated by either tumor progression in one PDX model and/or stabilization under treatment in another. These paired models greatly facilitate the identification of relevant mechanisms of drug resistance.We have now completed the development of a panel of 25 PDX models of various indications and exposed to a variety of last generation targeted therapies. We will discuss relevant examples of results that can be generated from this panel, with particular focus on the molecular features of models with acquired or intrinsic resistance to treatment and of paired models with different drug sensitivity. These data highlight the unique potential of the MATCH-R preclinical platform to identify resistance mechanisms and develop next generation therapeutic strategies.

Citation Format: Olivier Deas, Emilie Dassé, Laura Brulle-Soumare, Katell Mevel, Ludovic Bigot, Yohann Loriot, Fabrice André, Jean-Charles Soria, Benjamin Besse, Enora Le Ven, Stefano Cairo, Luc Friboulet, Jean-Gabriel Judde. Identification of the mechanisms of resistance to targeted therapies in advanced solid cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3016.

Abstract 2038: A non-canonical, cell-autonomous STING function protects breast cancer cells from intrinsic and genotoxic-induced DNA instability

Several studies have recently indicated the activation of the immune system against tumor cells as well as the targeting of cancer cell DNA damage repair mechanisms as effective strategies to target tumor growth. STING is a well-known DNA sensor of innate immunity mostly characterized as a transmembrane protein of various cytoplasmic organelles that senses cytosolic DNA as a danger signal and triggers inflammatory responses. A current cancer immunotherapy strategy relies on the use of STING agonists to boost the patient's immune system through a cytokine-mediated recruitment of immune cells that infiltrate and kill tumor cells. However, the role of the STING pathway in cancer is far to be fully understood as there is otherwise accumulating evidence that activation of the cGAS-STING pathway can have a deleterious outcome. We recently showed that genotoxic treatment of breast cancer PDXs and cell lines triggered the STING pathway. Genetic inhibition of this pathway in MCF7 cells increased genotoxic treatment efficacy by promoting cell death and delaying cell colony regrowth, indicating that STING pathway intrinsically promotes cell resistance to treatment. In this study, we show that STING silencing decreased cell viability in a panel of classical or PDX-derived breast cancer cell lines irrespective of their ER status and of the genotoxic treatment received. Cell fractionation indicates that part of the STING pool intrinsically resides in the nucleus of various malignant and non-malignant cells. Fluorescence and electron microscopy show that STING partly resides at the inner membrane of the nucleus, and mass-spectrometry analysis revealed that STING interacts with core proteins of the non-homologous end joining (NHEJ) DNA damage repair (DDR) complex. STING promotes NEHJ-related protein assembly with chromatin, and its silencing decreases DDR and cell viability, while STING overexpression protects cancer cells from genotoxic treatment. STING involvement in DDR is independent of the classical STING-TBK1-IFN inflammatory response, thus identifying a new functional pathway for STING. STING nuclear localization was confirmed in a panel of breast cancer patient-derived xenografts and in surgical samples from breast cancer patients that received neoadjuvant chemotherapy. Evaluation of the impact of STING expression on patient outcome via the Kaplan Meier plotter show that overall STING expression level is positively correlated with favorable outcome in breast cancer patients, however high STING expression in breast and ovarian cancer patients treated with adjuvant chemotherapy is associated with poor prognosis. These findings place STING at the crossroad of DDR and immune surveillance, two major pathways for tumorigenesis and tumor survival.

Citation Format: Laura Cheradame, Ida Chiara Guerrera, Julie Gaston, Alain Schmitt, Vincent Jung, Marion Pouillard, Nina Radosevic-Robin, Mauro Modesti, Jean-Gabriel Judde, Vincent Goffin, Stefano Cairo. A non-canonical, cell-autonomous STING function protects breast cancer cells from intrinsic and genotoxic-induced DNA instability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2038.

Targeting the Vav1/miR‑29b axis as a potential approach for treating selected molecular subtypes of triple‑negative breast cancer

MicroRNA (miR)‑29b has been reported to play a controversial role in breast cancer, particularly triple‑negative breast cancer (TNBC). Based on our previous data revealing that the PU.1‑mediated expression of miR‑29b in cells from acute myeloid leukemia is sustained by Vav1, the potential role of this multidomain protein in modulating miR‑29b levels in breast tumor cells, in which Vav1 is ecstopically expressed and shows a nuclear accumulation, was investigated. Breast cancer cell lines with various phenotypes and patient‑derived xenograft‑derived TNBC cells were subjected to Vav1 modulation and reverse transcription quantitative PCR of miR‑29b levels. The recruitment of CCAAT enhancer binding protein α (CEBPα) to miR‑29b promoters was investigated by quantitative chromatin immunoprecipitation assays. It was found that Vav1 was essential for the recovery of mature miR‑29b in breast cancer cell lines, and that it promoted the expression of the miRNA in TNBC cells of the mesenchymal molecular subtype by sustaining the transcription of the miR‑29b1/a cluster mediated by CEBPα. The present results suggest that Vav1 is a crucial modulator of miR‑29b expression in breast tumor cells, and this finding may help identify strategies that may be useful in the management of TNBC by targeting the Vav1/miR‑29b axis, as there is a lack of molecular‑based treatments for TNBC.

Abstract PS17-52: A preclinical platform of breast cancer PDX-derived cell lines as a tool for pharmacological screening and functional studies

Despite considerable progress in understanding the biology and genetics of breast cancer progression, the development of effective therapies need physiological and predictive preclinical models. In this context, breast cancer patient-derived xenograft (PDX) models has become a standard tool as they reproduce accurately the behavior of tumor of origin, in term of histological and molecular phenotype and response to chemotherapy. Although PDXs in vivo models are indispensable for preclinical studies, they suffer from some limitations due to study costs related to tumor maintenance on mice, variable engraftment rate, growth delay and limited throughput for large-scale drug screening.To address this problem and propose a time and cost effective preclinical screening tool, we developed a panel of breast cancer PDX-derived low-passage 2D cell lines as a convenient in vitro pre-screening platform to profile compound activity.30 different breast cancer PDX models including TNBC, HER2+ and ER+ were tested for their capacity to generate cell lines maintaining the characteristics of the parental PDX tumor and usable for in vitro assays.Today, we succeeded with a series of 14 PDX models.Tumor cells isolated from PDX tumor tissue were cultured under different media and matrix conditions, allowing at least 5 passages in culture. A Short Tandem Repeat (STR) comparison profile was done with the parental PDX before performing a master bank. We succeeded in establishing a panel of 14 PDX-derived cellular models (14/30 = 46% success rate).We performed short term 2D cytotoxicity assays and long term colony assays to compare cell lines in vitro drug sensitivity with their parental PDX in vivo drug response and overall, the results show that this panel reproduced the drug response profile of the original PDXs with chemotherapies, PARP inhibitors, an ADC (T-DM1) therapies.Moreover, cellular models engrafted back onto mice showed in vivo response to chemotherapies similar to that of the parental PDX confirming the identical behavior of cell line / PDX couples.As the use of cellular models is still considered as a standard for early preclinical test to evaluate drug response before moving to in vivo assays, our breast cancer PDX-derived cell line platform appeared to be a robust and relevant tool. Furthermore, since the main concern when using in vitro models is the representativeness of the results obtained when transposed to in vivo models, the similarities between cell lines and parental PDX should maximize success of further in vivo preclinical drug development.

Citation Format: Stefano Cairo, Olivier Deas, Sophie Banis, Kathleen Flosseau, Enora Le Ven, Jean-Gabriel Judde. A preclinical platform of breast cancer PDX-derived cell lines as a tool for pharmacological screening and functional studies [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-52.

MEK activation modulates glycolysis and supports suppressive myeloid cells in TNBC

Triple-negative breast cancers (TNBCs) are heterogeneous and aggressive, with high mortality rates. TNBCs frequently respond to chemotherapy, yet many patients develop chemoresistance. The molecular basis and roles for tumor cell-stromal crosstalk in establishing chemoresistance are complex and largely unclear. Here we report molecular studies of paired TNBC patient-derived xenografts (PDXs) established before and after the development of chemoresistance. Interestingly, the chemoresistant model acquired a distinct KRASQ61R mutation that activates K-Ras. The chemoresistant KRAS-mutant model showed gene expression and proteomic changes indicative of altered tumor cell metabolism. Specifically, KRAS-mutant PDXs exhibited increased redox ratios and decreased activation of AMPK, a protein involved in responding to metabolic homeostasis. Additionally, the chemoresistant model exhibited increased immunosuppression, including expression of CXCL1 and CXCL2, cytokines responsible for recruiting immunosuppressive leukocytes to tumors. Notably, chemoresistant KRAS-mutant tumors harbored increased numbers of granulocytic myeloid-derived suppressor cells (gMDSCs). Interestingly, previously established Ras/MAPK-associated gene expression signatures correlated with myeloid/neutrophil-recruiting CXCL1/2 expression and negatively with T cell-recruiting chemokines (CXCL9/10/11) across patients with TNBC, even in the absence of KRAS mutations. MEK inhibition induced tumor suppression in mice while reversing metabolic and immunosuppressive phenotypes, including chemokine production and gMDSC tumor recruitment in the chemoresistant KRAS-mutant tumors. These results suggest that Ras/MAPK pathway inhibitors may be effective in some breast cancer patients to reverse Ras/MAPK-driven tumor metabolism and immunosuppression, particularly in the setting of chemoresistance.

Chloroquine Triggers Cell Death and Inhibits PARPs in Cell Models of Aggressive Hepatoblastoma

Background: Hepatoblastoma (HB) is the most common pediatric liver malignancy. Despite advances in chemotherapeutic regimens and surgical techniques, the survival of patients with advanced HB remains poor, underscoring the need for new therapeutic approaches. Chloroquine (CQ), a drug used to treat malaria and rheumatologic diseases, has been shown to inhibit the growth and survival of various cancer types. We examined the antineoplastic activity of CQ in cell models of aggressive HB. Methods: Seven human HB cell models, all derived from chemoresistant tumors, were cultured as spheroids in the presence of relevant concentrations of CQ. Morphology, viability, and induction of apoptosis were assessed after 48 and 96 h of CQ treatment. Metabolomic analysis and RT-qPCR based Death Pathway Finder array were used to elucidate the molecular mechanisms underlying the CQ effect in a 2-dimensional cell culture format. Quantitative western blotting was performed to validate findings at the protein level. Results: CQ had a significant dose and time dependent effect on HB cell viability both in spheroids and in 2-dimensional cell cultures. Following CQ treatment HB spheroids exhibited increased caspase 3/7 activity indicating the induction of apoptotic cell death. Metabolomic profiling demonstrated significant decreases in the concentrations of NAD⁺ and aspartate in CQ treated cells. In further investigations, oxidation of NAD⁺ decreased as consequence of CQ treatment and NAD⁺/NADH balance shifted toward NADH. Aspartate supplementation rescued cells from CQ induced cell death. Additionally, downregulated expression of PARP1 and PARP2 was observed. Conclusions: CQ treatment inhibits cell survival in cell models of aggressive HB, presumably by perturbing NAD⁺ levels, impairing aspartate bioavailability, and inhibiting PARP expression. CQ thus holds potential as a new agent in the management of HB.

Genetic characterization of a unique neuroendocrine transdifferentiation prostate circulating tumor cell-derived eXplant model

Transformation of castration-resistant prostate cancer (CRPC) into an aggressive neuroendocrine disease (CRPC-NE) represents a major clinical challenge and experimental models are lacking. A CTC-derived eXplant (CDX) and a CDX-derived cell line are established using circulating tumor cells (CTCs) obtained by diagnostic leukapheresis from a CRPC patient resistant to enzalutamide. The CDX and the derived-cell line conserve 16% of primary tumor (PT) and 56% of CTC mutations, as well as 83% of PT copy-number aberrations including clonal TMPRSS2-ERG fusion and NKX3.1 loss. Both harbor an androgen receptor-null neuroendocrine phenotype, TP53, PTEN and RB1 loss. While PTEN and RB1 loss are acquired in CTCs, evolutionary analysis suggest that a PT subclone harboring TP53 loss is the driver of the metastatic event leading to the CDX. This CDX model provides insights on the sequential acquisition of key drivers of neuroendocrine transdifferentiation and offers a unique tool for effective drug screening in CRPC-NE management.

Abstract 2122: Generation of a fully characterized preclinical PDX panel to accelerate the identification of next generation treatments for patients with acquired resistance to targeted therapies

The last 20 years have witnessed the identification of an increasing number of actionable oncogenic drivers and the development and clinical use of specific inhibitors against these targets. Unfortunately, patients treated with targeted therapies consistently develop resistance and progression under treatment. Hence, important scientific, pharmaceutical and medical research efforts are directed towards understanding the mechanisms of acquired resistance to explore new therapeutic pathways.

The MATCH-R clinical trial enrolls patients with oncogene-driven cancer who have had previous clinical response to targeted therapy and subsequently experienced disease progression. In the framework of this project, Gustave Roussy and XenTech are joining forces to develop a panel of patient-derived xenografts (PDXs) derived from biopsies collected from these patients at the stage of acquired resistance. These PDX models will be fully characterized at molecular and pharmacological level and used to improve knowledge on the mechanisms underlying resistance to treatment and to evaluate response to new treatments.

In this perspective, the development of 75 PDX-AR (Acquired Resistance) models is planned over 3 years. All the models are maintained under the same therapeutic pressure the parental tumor was submitted to at the time of biopsy, and will be subjected to extensive phenotypic and genotypic characterization.

To favor successful xenograft establishment, the first two passages are performed without drug treatment, which is applied from the third passage on. When doing so, we observed 3 types of response: some models showed resistance from the first passage under treatment, some showed stabilization under treatment at the first passages and rapidly acquired resistance over passages, and others showed sensitivity to treatment, whereas the patient tumor showed progression under the same treatment. These different behaviors might be due to different mechanisms of resistance, irreversible for the former, reversible for the two latter, as well as to suboptimal correlation of the clinical dose with the one used in mice.

An example of such discrepancies has been found in two models of NSCLC PDX obtained from two metastases from a patient treated by a ROS1 and ALK inhibitor. While LCx-MR135PD2-AR PDX does not respond to the treatment, the LCx-MR135PD1 model is highly sensitive. As both metastases were progressing under treatment in the patient, molecular and pharmacological comparative analysis of these two models will investigate these discrepancy and provide important insights into the mechanisms of resistance to such inhibitors.

Overall, the MatchR PDX project will provide a unique preclinical platform to identify resistance mechanisms to current targeted therapies and to develop next generation therapeutic strategies.

Citation Format: Olivier Déas, Ludovic Bigot, Emilie Dasse, Guillaume Lang, Yohann Loriot, Fabrice Andre, Jean-Charles Soria, Benjamin Besse, Stefano Cairo, Marie Tavernier, Katell Mevel, Enora Le Ven, Jean-Gabriel Judde, Luc Friboulet. Generation of a fully characterized preclinical PDX panel to accelerate the identification of next generation treatments for patients with acquired resistance to targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2122.

Abstract 1511: MEK activation modulates immunosuppressive MDSCs and metabolic phenotypes in TNBC

Triple-negative breast cancers (TNBCs) are highly heterogeneous and aggressive, with high mortality rates. Although TNBC is typically more responsive to chemotherapy than other breast cancer subtypes, many patients develop chemo-resistance. The molecular processes between tumor and stromal cells involved in developing chemo-resistance are under-explored. Here we report studies of paired TNBC patient-derived xenografts (PDX) established before and after chemo-resistance. Despite significant genetic similarities, the chemo-resistant PDX model harbored a rare constitutively-active KRASQ61R mutation which was not present in the chemo-naive PDX. Further analysis demonstrated that the chemo-resistant KRAS-mutant model exhibited altered gene expression changes including increased expression of CXCR2-ligands CXCL1 and CXCL2, which are responsible for recruiting immune cells to tumors. These expression patterns were largely inhibited in vivo by MEK inhibitor (MEKi) treatment. Moreover, in breast cancer cell lines, CXCL1, CXCL2, and granulocyte macrophage-colony stimulating factor (CSF2, stimulates granulocyte and macrophage differentiation from hematopoietic precursor cells, including immunosuppressive myeloid cells) transcripts were also downregulated by MEKi. Notably, chemo-resistant KRAS-mutant tumors harbored increased Gr1+ and Arginase-1+ cells, consistent with recruitment of immunosuppressive M2-like macrophages and/or myeloid-derived suppressor cells (MDSCs), which was inhibited by MEKi. Further experiments demonstrate that CD45+CD11b+Ly6G+ MDSC accumulation in tumors can be inhibited by MEKi treatment alone, or by CXCR2 inhibition, suggesting that the effects of MEK inhibition on MDSC recruitment are CXCL1/2-dependent. Confirming the translational relevance of these findings, in >200 murine and >1000 human breast tumors, Ras/MAPK transcriptional activity correlated with myeloid-recruiting CXCL1/2 expression and negatively with T-cell recruiting chemokines (CXCL9/10/11), even in the absence of activating KRAS mutations. The association with Ras/MAPK activity was also confirmed using immunofluorescence to quantify MHC-II-low myeloid cells in 80 post-chemotherapy TNBC tumors. Importantly, MEKi and chemotherapy combination treatment reversed immunosuppressive cell accumulation and metabolic phenotypes exemplified by altered optical redox ratios (NAD(P)H/FAD) in the chemo-resistant KRAS mutant tumors, resulting in tumor growth suppression in mice. MEKi treatment also reduced redox ratios in 3D cultures of breast cancer cell lines further suggesting that MEK inhibition targets multiple oncogenic processes in breast cancer. These results suggest that Ras/MAPK pathway inhibitors may be effective in some breast cancer patients to reverse Ras/MAPK-driven tumor metabolism and immunosuppression, particularly in the setting of chemo-resistant disease.

Citation Format: Derek A. Franklin, Joe T. Sharick, Paula I. Ericsson-Gonzalez, Violeta Sanchez, Phillip T. Dean, Susan R. Opalenik, Stefano Cairo, Jean-Gabriel Judde, Michael T. Lewis, Jenny C. Chang, Melinda E. Sanders, Rebecca S. Cook, Melissa C. Skala, Jennifer Bordeaux, Jehovana Orozco Bender, Christine Vaupel, Gary Geiss, Douglas Hinerfeld, Justin M. Balko. MEK activation modulates immunosuppressive MDSCs and metabolic phenotypes in TNBC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1511.

Abstract 3810: Establishment of an in vitro assay that phenocopies tumor response to PARP inhibitors in vivo

Poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPi) have recently emerged as therapeutic options for patients with homologous recombination-deficient (HRD) breast or ovarian cancer, two heterogeneous diseases associated with high mortality rates. As shown in several clinical studies, patient response to PARPi is invariably followed by eventual mid-long term resistance and progression under treatment. The molecular processes contributing to PARPi-resistance are at present under-explored. Therefore, a huge effort is being made to better understand how to overcome resistance and to identify ad-hoc combinations with other targeted therapies to improve tumor response and extend progression-free survival. We have previously published the PARPi-response profile of a panel of 40 breast cancer (BC) patient-derived xenografts (PDXs). The models tested showed heterogeneous response to PARPi, and only partial association with the genomic status of BRCA genes, the only currently acknowledged clinical marker to select patients that can benefit from PARPi administration. Although these models are ideal preclinical tools for the evaluation of drug combinations to improve tumor response to PARPi as single agent, the use of these models for early preclinical evaluation of combination efficacy is not straightforward in reason of the limited throughput and of the ethical issue with respect of the 3Rs. The use of cellular models is still considered as a standard early preclinical test to evaluate drug response before moving to in vivo assays. However, the main concern when using in vitro models is the representativeness of the results obtained when transposed to in vivo models. In this study, we have setup an in vitro assay that recapitulates the response to PARPi observed in vivo in our BC PDXs, with particular focus on the models that show resistance to PARPi. To this aim we generated 9 cellular models from 9 BC PDX models: HBCx-2, HBCx-3, HBCx-6, HBCx-8, HBCx-9, HBCx-17, HBCx-19, HBCx-39 and T174. Two cellular models (HBCx-3, and HBCx-19) were established from ER+ BC PDX and 7 from ER- BC PDXs and two models, HBCx-8 and HBCx-17, harbor BRCA1 and BRCA2 mutation, respectively. Seven out of 9 models are resistant to PARPi in vivo, with HBCx-6 PDX showing partial tumor regression and HBCx-17 PDX showing tumor stabilization upon treatment. Several different 2D-culture experimental conditions, namely different cell growth conditions, drug concentrations, duration of cell exposure to drugs, time points and readouts, have been tested to evaluate response to olaparib. The results showed that a 2D colony assay is the best experimental strategy to faithfully evaluate tumor cell sensitivity, minimizing the false positive results when compared to the in vivo data.. This cell panel will be used to identify combination of PARPi with a library of FDA-approved targeted therapy to identify the treatments to be moved forward in vivo.

Citation Format: Olivier Déas, Romain Rousseau, Sophie Banis, Kathleen Flosseau, Enora Le Ven, Jean-Gabriel Judde, stefano cairo. Establishment of an in vitro assay that phenocopies tumor response to PARP inhibitors in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3810.

Abstract 3107: A scientific task force to generate proof-of-concept data packages for clinical trials in pediatric cancers: The hepatoblastoma example

Identification of new treatments for relapsing pediatric cancer is an unmet clinical need and a societal challenge. Hepatoblastoma (HB) is a rare tumor that constitutes the most frequent form of childhood liver cancer. Current improvement in medical care allows 80% of children to survive this disease, but no second line treatment is available at relapse, so that 20% will not survive. Patient population small size and very low mutation rate besides beta-catenin activating mutation, which is at present undruggable, make HB an orphan disease. Very few anti-cancer drugs evaluated for adult diseases are investigated in the pediatric population, with 12 drugs approved for adult cancers every year against 6 drugs approved in childhood cancer since 1978. The need of incentives to encourage pharmaceutical industry to invest in this field has been well received by the European and US medicine agencies, and recent modification to regulations on adult and pediatric oncology drug development are expected to induce pharmaceutical companies to test their new compounds in the pediatric setting. Parallel to this initiative, it is imperative that the scientific community develops research tools and scientific rational to assist drug development as well as repositioning of drugs already approved in adult cancers. To this aim, in collaboration with the International Childhood Liver Tumour Strategy Group (SIOPEL) and the network of hospitals in the Paris area (AP-HP), XenTech has launched in 2010 the development of a panel of HB patient-derived xenografts (HB-PDXs). To date, 26 HB-PDXs have been established from 80 engraftments from patients at surgery after chemotherapy or at relapse. As these models were established from tumor cells that either evaded chemotherapy or promoted local and distant metastases, they present a biological surrogate of the recurrent disease. From these PDXs, 9 cellular models have been established to allow the exploration of the functional mechanisms of tumor growth and resistance to treatment, as well as to facilitate drug screening. This project is receiving worldwide participation from the HB scientific community including clinicians, academic researchers and parents associations. Thanks to this joint effort all the models are now fully characterized at the molecular level, PDXs pharmacological profiling has been done and is currently ongoing for many of these models, and PDXs and cellular models are being used from a growing number of collaborators to perform 3D culture, to improve our knowledge on the HB biology and to identify new drugs. The ambition of this project is to generate a reference preclinical platform that will be used for research purposes by the academic community and as a testing site for biotechs and pharmaceutical companies to accelerate the identification of anti-cancer therapies for children with aggressive HB.

Citation Format: Carolina Armengol, Roland Kappler, Liqin Zhu, Nikolai Timchenko, Dina Kats, Charles Keller, Lisa Howard, Christophe Grosset, Delphine Nicolle, Olivier Déas, Martina Pigazzi, Laurence Brugières, Charlotte Mussini, Louise Galmiche-Rolland, Christophe Chardot, Sophie Brancereau, Jean-Gabriel Judde, Stefano Cairo. A scientific task force to generate proof-of-concept data packages for clinical trials in pediatric cancers: The hepatoblastoma example [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3107.

A RAD51 assay feasible in routine tumor samples calls PARP inhibitor response beyond BRCA mutation

Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) are effective in cancers with defective homologous recombination DNA repair (HRR), including BRCA1/2-related cancers. A test to identify additional HRR-deficient tumors will help to extend their use in new indications. We evaluated the activity of the PARPi olaparib in patient-derived tumor xenografts (PDXs) from breast cancer (BC) patients and investigated mechanisms of sensitivity through exome sequencing, BRCA1 promoter methylation analysis, and immunostaining of HRR proteins, including RAD51 nuclear foci. In an independent BC PDX panel, the predictive capacity of the RAD51 score and the homologous recombination deficiency (HRD) score were compared. To examine the clinical feasibility of the RAD51 assay, we scored archival breast tumor samples, including PALB2-related hereditary cancers. The RAD51 score was highly discriminative of PARPi sensitivity versus PARPi resistance in BC PDXs and outperformed the genomic test. In clinical samples, all PALB2-related tumors were classified as HRR-deficient by the RAD51 score. The functional biomarker RAD51 enables the identification of PARPi-sensitive BC and broadens the population who may benefit from this therapy beyond BRCA1/2-related cancers.

Heterogeneous expression of EPCAM in human circulating tumour cells from patient-derived xenografts

Background

We aim to characterize the heterogeneous circulating tumour cells (CTCs) in peripheral blood, independently of physical or immunological purification, by using patient-derived xenografts (PDXs) models. CTC studies from blood generally rely on enrichment or purification. Conversely, we devised a method for the inclusive study of human cells from blood of PDX models, without pre-selection or enrichment.

Methods

A qRT-PCR assay was developed to detect human and cancer-related transcripts from CTCs in PDXs. We quantified the EPCAM and keratins CTC markers, in a PDX cohort of breast cancer. The murine beta actin gene was used for normalization. Spearman's rho coefficients were calculated for correlation.

Results

We demonstrated, for the first time, that we can quantify the content of CTCs and the expression of human CTC markers in PDX blood using human-specific qRT-PCR. Our method holds strong potential for the study of CTC heterogeneity and for the identification of novel CTC markers.

Conclusions

The identification and the relative quantification of the diverse spectrum of CTCs in patients, irrespective of EPCAM or other currently used markers, will have a great impact on personalized medicine: unrestricted CTCs characterization will allow the early detection of metastases in cancer patients and the assessment of personalized therapies.

Abstract 5600: Establishment and characterization of a unique circulating tumor cells-derived xenograft (CDX) in prostate cancer

Background: The rarity of in vivo and in vitro human prostate cancer (PCa) models has hampered progress in understanding disease pathogenesis, metastatic progression and drug resistance mechanisms. Using CTCs from a leukapheresis product of a patient with advanced PCa, we report the establishment of a CDX and an in vitro cell line derived from this CDX. The phenotypic and molecular characterization of patient tumor-biopsies, CTCs, CDX and CDX-derived cell-line are presented.

Methods: Leukapheresis was performed in seven patients with advanced castration-resistant prostate cancer (CRPC). CTCs from the seven leukapheresis products were enriched by RosetteSep and implanted in Nod/Scid-IL2Rγ-/-mice. The CDX tumor was propagated in successive generations of mice. All samples, including eight tumor-biopsies performed at diagnosis two years prior leukapheresis and CTCs isolated at the single cell level during leukapheresis were characterized by immunofluorescence, immunohistochemistry, and whole-exome sequencing (WES).

Results: Based on CellSearch® counts in leukapheresis products, the estimated median number of engrafted CTCs was 697 (range: 10-19988). A mouse engrafted with 19988 CTCs developed a tumor within 193 days. Immunohistochemistry performed on the CDX and two tumor-biopsies indicated that the CDX and biopsies were positive for EpCAM, CK5/6/8/18, negative for CK7 and vimentin, and weakly positive for synaptophysin. While biopsies expressed PSA and the androgen receptor, the CDX was negative for both indicating tumor evolution. In contrast to tumor biopsies, the CDX strongly expressed Ki67, NSE and chromogranin, evidencing emergence of a neuroendocrine phenotype. The in vitro cell line established by culturing dissociated CDX cells for five months, grew in microspheres and expressed epithelial and ALDH and CD133 cancer stem-cell markers. By WES, a high degree of intra-tumor heterogeneity was observed in the eight tumor biopsies and CTCs as already reported in this tumor type. Only 2.8% (58/2087) and 2.3% (49/2087) of the mutations present in the tumor biopsies were identified in CTCs and the CDX respectively, indicating that a very few number of mutations have the potential to support the dissemination and tumorigenic activity of CTC. Trunk mutations in TP53, NF1 and LRP1B genes were identified in all samples including the CDX while PTEN gene loss was acquired lately and detected only in CTCs and the CDX. Mutational similarity of the CDX and the in vitro cell line was 91%. The analysis of copy number variations is ongoing in all samples and will be presented.

Conclusion: We report the first PCa CDX model, demonstrating the tumorigenicity of CTCs from CRPC. This CDX model represents a unique tool to identify clonal mutations associated with the tumor-initiating capacity of CTCs and explore the genetic and phenotypic basis of metastasis and drug resistance in advanced CRPC.

Citation Format: Vincent Faugeroux, Emma Pailler, Olivier Deas, Virginie Marty, Kamélia Alexandrova, Kiki Andree, Jean-Yves Scoazec, Nikolas Stoecklein, Nicolo Manaresi, Dominique Tramalloni, Maud Ngo-Camus, Claudio Nicotra, Leon Terstappen, Valérie Lapierre, Karim Fizazi, Yohann Loriot, Jean-Gabriel Judde, Françoise Farace. Establishment and characterization of a unique circulating tumor cells-derived xenograft (CDX) in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5600.

Abstract 2811: High IFN/STAT-related gene expression is associated with sensitivity to PARP inhibitors of triple negative breast cancer

Triple negative breast cancer (TNBC) comprises 15-20% of all breast cancers, and carries increased risk of distant metastasis, early relapse and short post-recurrence survival. TNBC shares clinical and pathological features with hereditary BRCA1/2-related breast cancers. In TNBCs, besides mutation-associated BRCA inactivation occurring by loss of heterozygosity (LOH) in about 15% of the cases, dysregulation in the homologous-recombination (HR)-dependent DNA-repair pathway has been attributed to a number of mechanisms. PARP1 and PARP2, two important regulators of the DNA base-excision-repair pathway, have emerged as therapeutic targets for TNBC. Indeed, a subset of TNBC patients is responsive to PARP inhibitors (PARPi), a class of novel therapeutic agents that inhibits the function of several PARP family members. Pathogenic BRCA1/2 mutations, and other genomic markers have been proposed as molecular markers to identify tumors with homologous recombination deficiency (HRD) that are more likely to be sensitive to PARPi. However, these tests lack specificity as less than half of TNBC patients harboring BRCA-mutated or HRD-positive tumors are responsive to PARP inhibitors, and a number of TNBC patients without BRCA1/2 mutations are responsive to PARP inhibitors.

In the present study, we investigated the antitumor activity of PARPi in a panel of 28 TNBC patient-derived xenograft PDX models. Responses were correlated with BRCA1/2, with HRD status and with other HRD markers, and GSEA analysis was run to compare gene expression profile of PARP inhibitor-sensitive vs resistant TNBC PDXs.

Among the gene signatures differentially expressed we identified the IFN/STAT signature as upregulated in tumors sensitive to PARPi. We previously described that TNBC PDXs that respond to a genotoxic stress induce activation of the IFN/STAT pathway. Therefore we hypothesized that a significant fraction of tumors scoring HRD positive (by BRCA mutation or genomic scarring assay) may have reverted back to a phenotype of HR competency, making them refractory to PARP inhibition. In this scenario, IFN/STAT-related gene expression might be a feature of HRD-positive tumors in which HR deficiency has not been compensated and is still effective, resulting in PARP inhibitor sensitivity. Inclusion of this parameter strongly ameliorated the predictive power of the HRD assay, with decreased rate of false-positives (28.6% for IFN/STAT signature + HRD versus 52.9% for HRD alone) and overall misclassification reduced to only 5/28 PDXs (17.6% for IFN/STAT signature + HRD versus 32.1% for HRD alone).

This study suggests that high IFN/STAT-related gene expression can be a strong marker of persistent tumor instability and improve the performance of HRD-based PARPi efficacy predictive scores.

Citation Format: Stefano Cairo, Olivier Déas, Truong-an Tran, Jean-Gabriel Judde. High IFN/STAT-related gene expression is associated with sensitivity to PARP inhibitors of triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2811.

Abstract 2147: Development of preclinical models to accelerate the identification of next generation treatments for patients with acquired resistance to targeted therapies

The last 20 years have witnessed the identification of an increasing number of druggable oncogenic drivers and the development and clinical use of specific inhibitors against these targets. Unfortunately, patients treated with targeted therapies consistently develop resistance and progression under treatment. Hence, important scientific, pharmaceutical and medical research efforts are directed towards understanding the mechanisms of acquired resistance to explore new therapeutic pathways.

The MATCH-R clinical trial enrolls patients with oncogene-driven cancer who have had previous clinical response to targeted therapy and subsequently experienced disease progression. In the framework of this project, Gustave Roussy and XenTech are joining forces to develop a panel of patient-derived xenografts (PDXs) derived from biopsies collected from these patients at the stage of acquired resistance. These PDX models will be used to improve knowledge on the mechanisms underlying resistance to treatment and to evaluate response to new treatments.

In this perspective, the development of 75 PDX-AR (Active Resistance) models is planned over 3 years. All the models are maintained under the same therapeutic pressure the parental tumor was submitted to at the time of biopsy, and will be subjected to extensive phenotypic and genotypic characterization.

The following models have been established so far:

• ENDx-MR-004-AR (endometrial): resistant to the combination of MEK and MDM2 inhibitors;

• LCx-MR-007-AR: (NSCLC): resistant to third generation EGFR inhibitor (osimertinib);

• UREx-MR-015A-AR (ureter) and VEx-MR-086A-AR (bladder): resistant to a FGFR inhibitor (erdafitinib);

• PARx-MR-010-AR (parotid): resistant to a NOTCH Inhibitor;

• TCx-MR-122-AR (colon): resistant to an ATR inhibitor.

To favor successful xenograft establishment, the first two passages were performed without drug treatment, which was applied from the third passage on. When doing so, some models showed resistance from the first passage under treatment, whereas others showed stabilization under treatment at the first passages and rapidly acquired resistance over passages. These different behaviors might underlie different mechanisms of resistance, irreversible (monoclonal) for the former, reversible (polyclonal) for the latter.

Parallel to the development of UREx-MR-015A-AR, we developed the UREx-MR-015B-SD (stable disease) model from a biopsy collected from a different metastasis in the same patient, but stabilized by the therapy. Comparative analysis of these two models will provide important insights into the mechanisms of resistance to FGFR inhibitors. The MATCH-R PDX project will provide a unique preclinical platform for identifying resistance mechanisms to current targeted therapies and developing next generation therapeutic strategies.

Citation Format: Olivier Déas, Ludovic Bigot, Guillaume Lang, Yohann Loriot, Fabrice Andre, Jean Charles Soria, Benjamin Besse, Stefano Cairo, Marie Tavernier, Katell Mevel, Enora Le Ven, Jean-Gabriel Judde, Luc Friboulet. Development of preclinical models to accelerate the identification of next generation treatments for patients with acquired resistance to targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2147.

Abstract 4628: Tailoring personalized strategies for children with treatment-refractory liver cancer

Tumour heterogeneity is probably the reason for different sensitivity to the same treatment in patients. Therefore, we urgently need to develop tools to help assign the right treatment to the right patient. This is particularly challenging for paediatric cancers. Hepatoblastoma (HB) is the most frequent malignant embryonal tumor of the liver in childhood. About 25% of HB patients will develop metastatic disease which is associated with a poor prognosis. Because of the small number of patients eligible for enrollment, clinical trials in most of cases could not provide clinicians with statistically significant results. In oncology, preclinical data are generally poorly predictive of treatment efficacy in patients, probably due to oversimplification of tumor biology and underrepresentation of the genetic tumor heterogeneity observed in patients. To face this issue, we have launched a program to generate patient-derived xenografts, the gold standard in preclinical oncology, from surgical tissue from HB patients after chemotherapy, at relapse and from local and distant metastases. Therefore, the models developed are representative of relapsing, metastatic HB. So far, a panel of 24 HB PDXs models has been established. From these models 10 cell lines could be established so far to be used for large-scale in vitro screening of anticancer compound libraries. The aim of this project is to combine in vitro and in vivo drug screening to provide strong preclinical rationale to the development of novel therapeutic options for children with HB, and to identify candidate biomarkers predictive of tumor response. In vitro screening of a HB PDX-derived cells with a library of 60 compounds corresponding to treatments already available in the clinic lead us to identify 4 compounds with very strong cytotoxic activity on HB cells. One of them, Volasertib, a PLK1 inhibitor, was selected to be tested in the HB PDX the cells were derived from. The in vivo study compared the effect of volasertib as single agent or in combination with irinotecan to irinotecan alone or in combination with temozolomide. The results showed that high dose volasertib induce tumor regression with efficacy comparable to irinotecan/temozolomide combination. Following these encouraging results, Volasertib was tested in the complete panel of HB PDX-derived cells, and the majority of them showed strong sensitivity to the drug. This sensitivity was associated with specific molecular alterations that might be used as biomarkers to predict tumor sensitivity. Overall, these results suggest that volasertib could be an effective second line treatment for children with recurrent HB, and that this platform could be a very important preclinical tool to foster translational research in HB.

Citation Format: Stefano Cairo, Bénédicte Noblet, Samuel Rasmussen, Matthew N. Svalina, Katell Mevel, Enora Le Ven, Delphine Nicolle, Olivier Déas, Charlotte Mussini, Sophie Branchereau, Jean-Gabriel Judde, Charles Keller. Tailoring personalized strategies for children with treatment-refractory liver cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4628.

Abstract 2597: Development and characterization of novel non-small cell lung cancer (NSCLC) circulating tumor cells (CTCs)-derived xenograft (CDX) models

Background: CDX models are expected to provide crucial information on mechanisms involved in metastatic progression, tumor-initiating properties of CTCs and the development of drug resistance. However, excepted for small-cell lung cancer (SCLC), CDX models are very difficult to develop. Here, we report the establishment, phenotypic and molecular characterization of four NSCLC CDX models and three in vitro cell lines derived from these CDXs.

Methods: CTCs were enriched by RosetteSep from 30 ml blood samples and implanted subcutaneously into Nod/Scid-IL2Rγ-/- (NSG) mice. CDXs were phenotypically and genetically characterized by immunofluorescence, immunohistochemistry and whole-exome sequencing (WES). CDX-derived cell lines were established after mouse fibroblast depletion using classical culture medium. Standard conditions were used for IC50 determination.

Results: Between January 2014 and June 2017, CTCs from 58 NSCLC patients with advanced metastatic disease were implanted into NSG mice resulting in the establishment of four CDXs. All had an epithelial phenotype. Based on CellSearch® counts, median and mean numbers of engrafted CTCs were 9 and 693 respectively (range, 0-17,694). GR-CDXL1, GR-CDXL2, GR-CDXL3, GR-CDXL4 were established starting from 3500, 35, 330, and 1102 CTCs respectively. Measurable tumors were obtained between 100 and 200 days after CTC implantation and were maintained by successive transplantations in NSG mice. Three in-vitro cell lines were established from GR-CDXL1, GR-CDXL3 and GR-CDXL4 tumors, and expressed an epithelial phenotype and CSC-markers such as ALDH, CD133 and CD90. Immunohistochemistry with epithelial and neuroendocrine markers, TTF1 and Ki67 indicated that CDXs and CDX-derived cell lines were representative of the corresponding patient tumor specimens (available in three patients). WES indicated 86%, 93%, 82% mutational similarity between GR-CDXL2, GR-CDXL3 and GR-CDXL4 and the corresponding tumor biopsies. The mutational similarity of GR-CDXL1, GR-CDXL3 and GR-CDXL4 and their corresponding in vitro cell lines was 24%, 83% and 84% respectively. WES of individual CTCs isolated at the time of CTC implantation is ongoing. In in vitro cytotoxicity assays, CDX-derived cell lines mirrored the patient's responsiveness to cisplatin and paclitaxel chemotherapy. The results of ongoing in vivo drug efficacy assays and of mutational tree analyses reconstructing the phylogenic evolution of tumor biopsies, CTCs, CDX and cell lines will be presented.

Conclusion: This study revealed considerable similarities between CDXs and their corresponding patient tumor biopsies. These NSCLC CDX models represent unique tools to identify clonal mutations associated with the tumor-initiating capacity of CTCs and explore the genetic and phenotypic basis of metastasis and drug resistance associated with advanced NSCLC.

Citation Format: Vincent Faugeroux, Emma Pailler, Olivier Deas, Judith Michels, Laura Mezquita, Laura Brulle-Soumare, Stefano Cairo, Jean-Yves Scoazec, Virginie Marty, Pauline Queffelec, Maud Ngo-Camus, Claudio Nicotra, David Planchard, Patricia Kannouche, Benjamin Besse, Jean-Gabriel Judde, Françoise Farace. Development and characterization of novel non-small cell lung cancer (NSCLC) circulating tumor cells (CTCs)-derived xenograft (CDX) models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2597.

Abstract 919: Endogenous STING inhibition induces breast cancer cell death

Several studies have recently indicated the (re)activation of the immune system against tumor cells as an effective strategy to inhibit tumor growth. A current cancer immunotherapy strategy proposes the use of STING agonists to boost the patient's immune system through the cytokine-mediated enhancement of tumor infiltration and killing by immune cells. We recently showed that genotoxic treatment in vitro of the ER-positive breast cancer cell line MCF7 triggered the STING pathway. Of interest, genetic inhibition of this pathway increased genotoxic treatment efficacy by promoting cell death and delaying cell colony regrowth, indicating that STING pathway intrinsically promotes MCF7 cell resistance to treatment. While STING is commonly described as an endoplasmic reticulum resident protein that localizes to Golgi and/or perinuclear vesicles upon activation, we showed that STING is constitutively present in the nucleus of MCF7 cells and, upon activation, forms nuclear foci that co-localize with gH2AX at DNA breaks. The aim of this study was to investigate whether these observations could be extended to cell lines derived from human breast cancer xenografts that are more representative of the disease.

To this aim, STING pathway was monitored in HBCx-3 (derived from the homonymous parental ER-positive breast cancer PDX) and HBCx-39 (derived from the homonymous triple negative breast cancer PDX) cells using cell fractionation, western blot, immunofluorescence and viability assays. Similarly to what we observed in MCF7 cells, STING was invariably present in the cytoplasm as well as the nucleus of HBCx cells. In these models, STING formed clusters together with gH2AX at DNA breaks even in the absence of genotoxic treatment. Finally, we showed that STING silencing decreased cell viability of HBCx-3 and HBCx-39 cells irrespective of genotoxic treatment. Interestingly, another ER-positive PDX-derived cell line (HBCx-19) and two well-known triple negative breast cancer cell lines (BT20 and HCC1937) showed similar sensitivity to STING downregulation in a siRNA screening assay.

These studies show that STING clustering at DNA breaks in the nucleus is a general feature of breast cancer cells, and that the STING pathway is a cell-intrinsic mechanism of cell survival of many breast cancer cell lines including those derived from patient-derived xenografts. Our preliminary results indicate that STING-gH2AX foci can also be observed in the nucleus of TC122A cells derived from a human colon tumor xenograft, suggesting this mechanism may be common to other types of cancer.

To gain insight into the potential antagonistic roles of STING pathway modulation in tumors in vivo, we have transduced MCF7 and PDX-derived cell lines with an inducible shRNA directed against STING, and are evaluating the impact of STING inhibition or activation on tumor growth in immune cells-humanized PDX models.

Citation Format: Laura Cheradame, Hery Ratsima, Olivier Déas, Jean-Gabriel Judde, Vincent Goffin, stefano cairo. Endogenous STING inhibition induces breast cancer cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 919.

Abstract 1718: Tumor immune gene profile before and after various targeted therapies in NSCLC PDXs

Introduction: The blockade of immune checkpoints with antibodies directed against CTLA-4, PD-1 and PD-L1 molecules, is now entering in the current management of non-small cell lung cancer (NSCLC) patients; those tumors are heterogeneous regarding driver oncogenes, which predict the efficacy of targeted therapies (TT). In this context, our study aimed to define the relationship between conventional TT used in NSCLC and the dynamic expression of immune genes.

Experimental procedure: Eight different NSCLC Patient-Derived Xenografts (PDXs) with defined mutations, were grafted in immunodeficient mice which were then treated by various TT (Table). About 3 tumors per group were collected at the end of the in vivo experiments. The expression of human and mouse genes, using species-specific primers was determined by qPCR and normalized to the expression of the human or mouse Total Binding Protein gene. Basal gene expression, predictive markers of response and resistance to tested therapies, as well as pharmacodynamics (PD) markers were analyzed.

Results: Basal immune gene expression analysis revealed various immune profiles in this panel of NSCLC PDXs, with clustering of both models and genes. Predictive and pharmacodynamics markers underlined the impact of human HLA class I and II gene expression in the response to erlotinib and everolimus (HLA-A, HLA-DRA, and HLA-DRB); of B7-H3 (CD276), PDL1 (CD274) and Tigit (PVRIG) in the response to erlotinib; and of TNFSF7 (CD70) and TNFSF9 in the response to BKM120. PD markers showed that PDL1, B7-H3, and Tigit expression was highly impacted by everolimus, erlotinib, and BKM120 treatments, respectively. Complete gene expression results can be presented at the meeting.

Conclusions: Using NSCLC PDXs, we have identified specific tumor immune profiles and a set of genes involved in the response to TT. Moreover, PD analysis of immune markers reveals potential combinations of TT with immune checkpoints blockade that may have important translational value.

NSCLC PDXsLCF4LCF9LCF12LCF15LCF25LCF29ML1ML5HistologyAdenocarcinomaXXXXXXXLarge cellsXMUTATIONSEGFRXXKRASXXPi3KCAXXXTREATMENTS (Targets)Cetuximab (1)EGFRXXXXErlotinib (2)EGFRXXXXAfatinib (3)EGFR/HER2XXXXBKM120 (4)Pi3KXXXXXXXXEverolimus (5)mTORC1XXXXSelumetinib (6)MEK1/2XXXXXXXX1 + 2/XXXX1 + 3/XXXX1 + 4/X2 + 4/X3 + 4/X5 + 6/XXXX

Citation Format: Elodie Montaudon, Sophie Vacher, Wilfrid Richer, Ahmed Dahmani, Caroline Guibaudet, Olivier Déas, Stefano Cairo, Ludmilla De Plater, Marine Dubois, Fariba Némati, Christine Sedlik, Jean-Gabriel Judde, Nicolas Girard, Ivan Bieche, Eliane Piaggio, Didier Decaudin. Tumor immune gene profile before and after various targeted therapies in NSCLC PDXs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1718.

MiR-205 as predictive biomarker and adjuvant therapeutic tool in combination with trastuzumab

Trastuzumab is the standard treatment for HER2+ breast cancer (BC) patients, and even though it significantly improved their clinical outcome, 50% of them do not benefit from this drug and disease recurs, underlining the need of reliable predictive biomarkers and new therapeutic strategies. Strikingly, despite all the molecular analyses performed to identify the escape mechanisms behind this resistance, it still represents a question point. MiRNAs have been correlated with occurrence and progression of human cancer, and their potential as clinical tools has emerged in the last years. We previously reported that oncosuppressive miR-205 targets HER3, thus increasing the responsiveness to TKIs lapatinib and gefitinib in preclinical models.

Here we demonstrate that HER3 inhibition by miR-205 ectopic expression or siRNA-mediated silencing improves the responsiveness to Trastuzumab in vitro in HER2+ BC cell lines, and that this effect is exerted through impairment of AKT-mediated pathway. Moreover, evaluating a series of 52 HER2+ BC patients treated with adjuvant Trastuzumab, we observed that higher miR-205 expression is significantly associated with better outcome (disease-free survival).

In summary, our data indicate that miR-205 could predict Trastuzumab efficacy and that its modulation might be useful as adjuvant treatment to improve the response to the drug.

An NF90/NF110-mediated feedback amplification loop regulates dicer expression and controls ovarian carcinoma progression

Reduced expression of DICER, a key enzyme in the miRNA pathway, is frequently associated with aggressive, invasive disease, and poor survival in various malignancies. Regulation of DICER expression is, however, poorly understood. Here, we show that NF90/NF110 facilitates DICER expression by controlling the processing of a miRNA, miR-3173, which is embedded in DICER pre-mRNA. As miR-3173 in turn targets NF90, a feedback amplification loop controlling DICER expression is established. In a nude mouse model, NF90 overexpression reduced proliferation of ovarian cancer cells and significantly reduced tumor size and metastasis, whereas overexpression of miR-3173 dramatically increased metastasis in an NF90- and DICER-dependent manner. Clinically, low NF90 expression and high miR-3173-3p expression were found to be independent prognostic markers of poor survival in a cohort of ovarian carcinoma patients. These findings suggest that, by facilitating DICER expression, NF90 can act as a suppressor of ovarian carcinoma.

Intracellular STING inactivation sensitizes breast cancer cells to genotoxic agents

Activation of the IFN/STAT1 pathway is closely associated with drug response and recurrence of breast cancer treated by chemotherapy. The aim of the current study was to elucidate the molecular mechanisms involved upstream and downstream of this pathway in order to identify distinct entities that might be manipulated to improve treatment efficacy. Four breast cancer cell lines (T-47D, MCF7, MDA-MB-231 and HBCx-19 established from the eponymous PDX) were treated in vitro with mafosfamide, a DNA damage inducer. In two of these cell lines (MCF7 and HBCx-19), genotoxic treatment upregulated type I IFN expression leading to paracrine activation of IFN/STAT1 signaling pathway after 6–8 days. We show that STING, a well-characterized inducer of IFN in immune cells, is rapidly triggered in MCF7 cells under genotoxic stress and forms nuclear foci that co-localize with phosphorylated IRF-3 and γH2AX. STING silencing abrogated chemotherapy-induced type I IFN production and signaling and potentiated genotoxic treatment efficacy as it promoted cell death extent and delayed cell colony regrowth. Similar results were obtained after silencing PARP12, one selected gene of the IFN/STAT1 pathway fingerprint. In summary, this study provides the first demonstration of STING activation in breast cancer cells. Our data suggest that genotoxic-induced, STING-mediated type I IFN signaling is a cell-intrinsic mechanism of breast cancer cell survival and regrowth.

Association of FGFR1 with ERα Maintains Ligand-Independent ER Transcription and Mediates Resistance to Estrogen Deprivation in ER+ Breast Cancer

Purpose:FGFR1 amplification occurs in approximately 15% of estrogen receptor-positive (ER⁺) human breast cancers. We investigated mechanisms by which FGFR1 amplification confers antiestrogen resistance to ER⁺ breast cancer.Experimental Design: ER⁺ tumors from patients treated with letrozole before surgery were subjected to Ki67 IHC, FGFR1 FISH, and RNA sequencing (RNA-seq). ER⁺/FGFR1-amplified breast cancer cells, and patient-derived xenografts (PDX) were treated with FGFR1 siRNA or the FGFR tyrosine kinase inhibitor lucitanib. Endpoints were cell/xenograft growth, FGFR1/ERα association by coimmunoprecipitation and proximity ligation, ER genomic activity by ChIP sequencing, and gene expression by RT-PCR.Results: ER⁺/FGFR1-amplified tumors in patients treated with letrozole maintained cell proliferation (Ki67). Estrogen deprivation increased total and nuclear FGFR1 and FGF ligands expression in ER⁺/FGFR1-amplified primary tumors and breast cancer cells. In estrogen-free conditions, FGFR1 associated with ERα in tumor cell nuclei and regulated the transcription of ER-dependent genes. This association was inhibited by a kinase-dead FGFR1 mutant and by treatment with lucitanib. ChIP-seq analysis of estrogen-deprived ER⁺/FGFR1-amplified cells showed binding of FGFR1 and ERα to DNA. Treatment with fulvestrant and/or lucitanib reduced FGFR1 and ERα binding to DNA. RNA-seq data from FGFR1-amplified patients' tumors treated with letrozole showed enrichment of estrogen response and E2F target genes. Finally, growth of ER⁺/FGFR1-amplified cells and PDXs was more potently inhibited by fulvestrant and lucitanib combined than each drug alone.Conclusions: These data suggest the ERα pathway remains active in estrogen-deprived ER⁺/FGFR1-amplified breast cancers. Therefore, these tumors are endocrine resistant and should be candidates for treatment with combinations of ER and FGFR antagonists. Clin Cancer Res; 23(20); 6138-50. ©2017 AACR.

Abstract 3856: Identification of circulating tumour cells in breast cancer patient-derived xenograft models

Metastases from primary tumours accounts for the great majority of cancer-related deaths. This process is thought to involve a series of sequential steps, with the release of circulating tumour cells (CTCs) into the blood stream. CTCs have been detected in the peripheral blood of patients with advanced cancers of different origin and in some localized cancers. Recently, liquid biopsy focusing on the analysis of CTCs has received enormous attention because of its obvious clinical implications for personalized medicine. Clinical applications of CTCs detection include early detection of cancer, prediction of the risk for metastatic relapse or progression, monitoring the effects of systemic therapies, and stratification of patients based on the detection of therapeutic targets on resistance mechanisms. To date, only few data are available about the numbers of these cells, their molecular and biological heterogeneity, and their significance. CTCs comprise a minute fraction of mononucleated cells in the circulation, posing a serious challenge for any analytical system. Multiple technologies have been developed for CTC capture, but there is still a critical need for increased sensitivity in rare tumour cell isolation within blood specimens. Most of the current CTC detection techniques rely on antibody-based capture of cells, and epithelial markers have been frequently used to distinguish cancer cells from normal blood cells. However, the phenotypic changes that occur in CTCs, due predominantly to the epithelial-mesenchymal transition process, could be responsible for the failure to detect them in blood samples. We describe a novel approach for the identification of molecular markers to detect CTCs in peripheral blood of patient-derived xenograft (PDX) models. We analyzed the transcriptome in more than 10,000 samples of primary and metastatic tumours deposited in public databases, and identified a small set of cancer-specific genes coding for membrane protein. Putative markers were assayed by reverse transcription PCR with species-specific primers in blood samples from breast cancer PDXs, testing their ability to detect human CTCs. Thus, we identified human membrane proteins, which can be used for CTC monitoring in peripheral blood. The use of multiple targets for CTC capture and identification increases the sensitivity of CTC detection, allowing the isolation of all heterogeneous CTCs subpopulations.

Citation Format: Chiara Agnoletto, Linda Minotti, Marco Galasso, Fabio Corrà, Federica Baldassari, Stefano Cairo, Jean-Gabriel Judde, Aurelie Sauvage, Olivier Deas, Lorenzo Pasquali, Stefano Volinia. Identification of circulating tumour cells in breast cancer patient-derived xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3856. doi:10.1158/1538-7445.AM2017-3856

Abstract 90: STING colocalizes with gamma-H2AX upon treatment of breast cancer cells with genotoxics: A new role in DNA repair

One of the current tumor immunotherapy strategies involves the use of STING agonist, a well-known inducer of interferon (IFN) signaling in the immune system, to promote tumor-rejection. However, recent evidence also indicates that constitutive activation of IFN signaling in the tumor may lead to a bad outcome. For instance, increased expression of IFN- stimulated genes (ISGs) at time of surgery was associated with early breast cancer recurrence, and an IFN-related DNA damage resistance signature (IRDS) was identified as a predictive marker of recurrence after radiotherapy. Thus, IFNs secreted into the tumor microenvironment may have complex opposite effects on tumor behavior and response to treatment.

Using patient-derived xenograft (PDX) models, we previously showed that the IFN/STAT1 pathway was activated within breast cancer cells in response to chemotherapy and that this pathway may be involved in treatment resistance and recurrence. The aim of this study was to elucidate the mechanisms by which IFN-signaling is triggered in breast cancer cells following chemotherapy and how its activation leads to tumor survival and recurrence. To this aim, the breast cancer cell line MCF7 was treated in vitro with mafosfamide and the activity of different IFN pathway effectors was monitored using western blot, immunofluorescence and cell fractionation techniques.

We found that in breast cancer cells, similarly to what is observed in immune cells, type I IFN expression is triggered in a STING-dependent manner. STING silencing abrogated chemotherapy-induced type I IFN production and signaling, while potentiating genotoxic treatment efficacy by promoting cell death and delaying cell colony regrowth. Surprisingly, while STING is described as an endoplasmic reticulum resident protein that relocalizes to perinuclear vesicles upon activation in immune cells, we showed that STING is constitutively present in the nucleus of breast cancer cells and, under activation, forms nuclear clusters that co-localize with gH2AX at DNA breaks.

This study provides the first demonstration of STING activation in breast cancer cells and describes a potential new role for the nuclear form of STING in DNA damage response. Our data suggest that genotoxic stress-induced STING activation is a cell-intrinsic mechanism of breast cancer cell survival and regrowth. Whether STING pro-survival role is IFN-dependent (through the activation of given ISGs), IFN-independent (through its involvement in the DNA damage response) or both is currently under investigation.

Citation Format: Laura Cheredame, Julie Gaston, Vanessa Yvonnet, Olivier Deas, Marie-Françe Poupon, Jean-Gabriel Judde, Vincent Goffin, Stefano Cairo. STING colocalizes with gamma-H2AX upon treatment of breast cancer cells with genotoxics: A new role in DNA repair [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 90. doi:10.1158/1538-7445.AM2017-90

Abstract 4936: Modelling clinical issues by using patient-derived xenografts: Evaluation of partial hepatectomy on hepatoblastoma intrahepatic and distant growth

Hepatoblastoma (HB) is a rare disease that represents the most frequent liver malignancy during childhood. HB incidence is approximately 1.5 cases per million children less than 15-years old in Western countries.

HB is histologically classified as epithelial or mixed depending on the presence of mesenchymal component. The most common epithelial components are the embryonal and fetal phenotype, reminiscent of at early or late stages of liver development. The improvement of the clinical management in the last 30 years has allowed 5-year survival rate to pass from 35 to 80%,due to the introduction of cisplatin-based chemotherapy. More than 50% of tumors are either inoperable or are metastatic at diagnosis. Neoadjuvant chemotherapy allows tumor size reduction and sometimes leads to complete regression of pulmonary metastasis.

In Europe, the SIOPEL (International Childhood Liver Tumors Strategy Group) protocols recommend the use of cisplatinum-based neoadjuvant chemotherapy followed by surgery and adjuvant chemotherapy. All international studies recommend resecting all the metastases remaining after neoadjuvant chemotherapy, however, to date no indication is provided that defines whether metatases removal must take place before or after primary tumor resection by partial or total hepatectomy.

As liver regeneration is a complex process that involves the expression and release of numerous factors that induce cell hypertrophy and proliferation, the risk that hepatectomy-induced release of regenerating factors might help the survival and proliferation of microscopic intrahepatic or distant tumor cells leads several clinicians to perform hepatectomy only after the removal of all detectable metastases.

To challenge this paradigm, we used a panel of HB patient-derived xenograft and evaluated the impact of partial hepatectomy on intrahepatic and extrahepatic tumor growth. Partial hepatectomy performed either concomitantly with interscapular implantation of HB-217 xenograft, a model established from a patient with intrahepatic recurrence, or at the time of tumor appearance in mice failed to increase tumor growth. When hepatectomy was realized on several HB models concomitantly with either intrahepatic injection of bioluminescent HB cells derived from HB PDXs or by tumor fragments’ direct implantation, one of these models, HB-243, also a model established from a patient with intrahepatic recurrence, showed increased tumor growth in mice concomitantly subjected to partial hepatectomy.

These results suggest that increased tumor growth induced by hepatectomy can occur in HB, albeit heterogeneously. We are now evaluating the molecular features of this hepatectomy-sensitive model and the impact of different cytokines on HB-243 PDX-derived tumor cells. The aim of this study will be to identify molecular markers and drivers of tumor sensitivity to hepatectomy.

Citation Format: Marianna Cornet, Anais Delaitre Delattre, Laura Brulle Soumare, Victorine Boissay, Thierry Tordjmann, Antoinette Lemoine, Olivier Deas, Jean-Gabriel Judde, Sophie Branchereau, Stefano Cairo. Modelling clinical issues by using patient-derived xenografts: Evaluation of partial hepatectomy on hepatoblastoma intrahepatic and distant growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4936. doi:10.1158/1538-7445.AM2017-4936

Patient-derived mouse xenografts from pediatric liver cancer predict tumor recurrence and advise clinical management

Identification of new treatments for relapsing pediatric cancer is an unmet clinical need and a societal challenge. Liver cancer occurrence in infancy, 1.5 for million children per year, falls far below the threshold of interest for dedicated drug development programs, and this disease is so rare that it is very difficult to gather enough children into a phase II clinical trial. Here, we present the establishment of an unprecedented preclinical platform of 24 pediatric liver cancer patient-derived xenografts (PLC-PDXs) from 20 hepatoblastomas (HBs), 1 transitional liver cell tumor (TCLT), 1 hepatocellular carcinoma, and 2 malignant rhabdoid tumors. Cytogenetic array and mutational analysis of the parental tumors and the corresponding PLC-PDXs show high conservation of the molecular features of the parental tumors. The histology of PLC-PDXs is strikingly similar to that observed in primary tumors and recapitulates the heterogeneity of recurrent disease observed in the clinic. Tumor growth in the mouse is strongly associated with elevated circulating alpha-fetoprotein (AFP), low rate of necrosis/fibrosis after treatment, and gain of chromosome 20, all indicators of resistance to chemotherapy and poor outcome. Accordingly, the ability of a tumor to generate PLC-PDX is predictive of poor prognosis. Exposure of PLC-PDXs to standards of care or therapeutic options already in use for other pediatric malignancies revealed unique response profiles in these models. Among these, the irinotecan/temozolomide combination induced strong tumor regression in the TCLT and in a model derived from an AFP-negative relapsing HB.

CONCLUSION

These results provide evidence that PLC-PDX preclinical platform can strongly contribute to accelerate the identification and diversification of anticancer treatment for aggressive subtypes of pediatric liver cancer. (Hepatology 2016;64:1121-1135).

Abstract 633: Gene-expression characterization of bioluminescent PDX in orthotopic and ectopic models of pancreatic cancer and metastatic triple-negative breast cancer

Background: Patient derived xenografts (PDX) are regarded as the gold-standard for translational preclinical cancer research due to their preservation of tumor heterogeneity and propagation in vivo. Similarly, grafting human tumor cells of a particular tissue origin into the corresponding orthotopic context enhances translational accuracy; with recapitulation of tumor::microenvironment biology, as well as more accurate tumor progression kinetics and metastasis, a s well as for systemic delivery of therapies as compared to traditional subcutaneous xenografts. Bioluminescent luciferase-reporters into traditional cancer cell lines has allowed for in-life imaging of tumor growth kinetics in real-time, within obfuscated internal organs, improving experimental precision. We have reported on the development and validation of bioluminescent pancreatic cancer and breast cancer PDX in clinically recapitulative orthotopic models. Here, we characterize these bioluminescent PDX by gene-expression profiling; comparing orthotopic and ectopically propagated bioluminescent PDX to their non-transduced parental PDX counterparts.

Methods: Pancreatic (PANx-005-Luc) or metastatic breast (HBCx-14-Luc) PDXs stably transduced with lentiviral luciferase were dissociated and implanted orthotopically into pancreas or mammary fat pad respectively or subcutaneously into the flank of NOD scid gamma (NSG) mice. Likewise, the parental reporter-free PANx-005 or HBCx-14 PDX were implanted subcutaneously into NSG mice. For luciferase-expressing PDX implanted orthotopically, tumor growth was monitored in-life (Xenogen IVIS® Lumina Series III instrument (IVIS)). For the PANx-005-Luc, orthotopic tumors were harvested at a mean tumor radiance (TR) of 2.53 × 106 + 1.63 × 106 ph/s, while ectopic luciferase-transduced and parental tumors were harvested at a mean tumor volume of 530 + 337mm3. For the HBCx-14-Luc, orthotopic tumors were harvested individually when TR reached 6.5 × 109 ph/s while ectopic luciferase-transduced or parental tumors were harvested when tumor volumes reached 1500 + 362.5mm3. Tumor samples were fixed in 10% neutral buffered formalin and embedded in paraffin-blocks for histological analysis. RNA was extracted from all tumors and full-coverage human genome gene-expression profiling was performed. Major differences observed in microarray data was validated via quantitative biochemical assays.

Results: Stable expression of lentiviral luciferase did not result in significant gene-expression changes to PDX lines, while site of implantation altered some gene-expression characteristics of the PDX.

Conclusions: The introduction of an integrating stable bioluminescent reporter does not significantly alter the gene-expression characteristics of PANx-005 or HBCx-14 PDX. Site of implantation plays a role in gene-expression of PDX tumor models.

Citation Format: Benjamin G. Cuiffo, Olivier Deas, Ingrid Rankin, Gregory D. Lyng, Stephano Cairo, Katie Pedrick, Alexandra Kury, Enora Le Ven, Jean-Gabriel Judde, Stephen T. Sonis. Gene-expression characterization of bioluminescent PDX in orthotopic and ectopic models of pancreatic cancer and metastatic triple-negative breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 633.

Activation of IFN/STAT1 signalling predicts response to chemotherapy in oestrogen receptor-negative breast cancer

Background:

Oestrogen receptor-negative (ER−) breast cancer is intrinsically sensitive to chemotherapy. However, tumour response is often incomplete, and relapse occurs with high frequency. The aim of this work was to analyse the molecular characteristics of residual tumours and early response to chemotherapy in patient-derived xenografts (PDXs) of breast cancer.

Methods:

Gene and protein expression profiles were analysed in a panel of ER− breast cancer PDXs before and after chemotherapy treatment. Tumour and stromal interferon-gamma expression was measured in xenografts lysates by human and mouse cytokine arrays, respectively.

Results:

The analysis of residual tumour cells in chemo-responder PDX revealed a strong overexpression of IFN-inducible genes, induced early after AC treatment and associated with increased STAT1 phosphorylation, DNA-damage and apoptosis. No increase in IFN-inducible gene expression was observed in chemo-resistant PDXs upon chemotherapy. Overexpression of IFN-related genes was associated with human IFN-γ secretion by tumour cells.

Conclusions:

Treatment-induced activation of the IFN/STAT1 pathway in tumour cells is associated with chemotherapy response in ER− breast cancer. Further validations in prospective clinical trials will aim to evaluate the usefulness of this signature to assist therapeutic strategies in the clinical setting.

Abstract A9: Bioluminescent orthotopic PDX models of primary pancreatic cancer and residual/metastatic breast cancer predict efficacy of standard of care and experimental treatments

Background: Only 5% of investigational anti-cancer agents are ultimately clinically successful. This may be attributed in part to the historical preclinical use of human cell lines that poorly recapitulate tumor heterogeneity in imperfect xenograft models. To model critical influences of tissue environment on tumor behavior and therapeutic response, heterogeneous patient-derived xenografts (PDX) can be assayed following implantation at orthotopic sites in rodents. Challenges to this approach include inaccessibility of certain organs or inability to track residual or metastatic disease. To address these problems, we utilized pancreatic (PANx-005) or metastatic breast (HBCx-14) PDXs transduced with stable bioluminescent reporters in efficacy studies of standard of care (SOC) and experimental treatments in clinically recapitulative models.

Methods: Freshly excised PDXs were transduced with lentiviral vectors stably expressing luciferase, and implanted orthotopically into NOD scid gamma (NSG) mice. For our primary pancreatic cancer model, the pancreas was surgically exposed, and ∼2.5 × 106 PANx-005-Luc cells were inoculated directly. Post-op, tumor growth was monitored in-life (Xenogen IVIS® Lumina Series III instrument (IVIS)). Mice were randomized into treatment groups when mean tumor radiance (TR) reached 3.0 × 106 photons/sec. Control animals received no treatment; SOC groups received either focused fractionated radiation (12 Gy as 3×4 Gy fractions, Q5D (SRT)) or gemcitabine (75 mg/kg, 2QWx4, i.p.), and the experimental group received (+)-JQ-1 BET bromodomain inhibitor (50 mg/kg, QD, i.p.). For the residual/metastatic breast cancer model, ∼1.5 × 106 HBCx-14-Luc were injected directly into the 4th inguinal mammary fat pad. Tumor growth and response were monitored throughout the study by IVIS. When individual TR reached 7.5 × 109 photons/sec, the primary tumor was resected and the animal enrolled into a treatment group to be treated for residual/metastatic disease. Control animals received no treatment; SOC groups received either SRT, capacetabine (540 mg/kg QDx5/ 1week rest, p.o.) or docetaxel (20 mg/kg, Q3Wx2, i.p.); while experimental animals received (+)-JQ-1 (50 mg/kg, QD, i.p.).

Results: Tumor seeding approached 100% in both models. Growth kinetics resembled clinical indications, including rapid growth and lung metastases for the HBCx-14 tumors, and slower growth of PANCx-005 tumors. Efficacies of individual treatments recapitulated clinical responses: HBCx-14 tumors were high responders to capecitabine and (+)-JQ-1, and low-responders to docetaxel, while PANx-005 tumors displayed high response to (+)-JQ-1 and lower response to gemcitabine.

Conclusions: The translational predictivity of preclinical cancer models is enhanced by the use of human PDXs that preserve tumor heterogeneity, are assayed at orthotopic sites, and are utilized in models that recapitulate clinical situations (e.g. treatment of residual disease vs primary tumor). The use of stable bioluminescent reporters in such assays greatly enhances precision in monitoring tumor growth and treatment response. Currently available preclinical oncology models are more recapitulative, precise and predictive than ever before, and appear poised to engender improved translational success.

Citation Format: Benjamin G. Cuiffo, Olivier Deas, Gregory D. Lyng, Stephano Cairo, Enora Le Ven, Jean-Gabriel Judde, Stephen T. Sonis. Bioluminescent orthotopic PDX models of primary pancreatic cancer and residual/metastatic breast cancer predict efficacy of standard of care and experimental treatments. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A9.

Abstract A103: Cell-autonomous activation of the interferon/STAT1 pathway in response to genotoxic treatment

Identification of the mechanisms of tumor resistance remains an unmet need in oncology. Among the reasons for this challenging issue is the lack of reliable preclinical models that represent inter and intra-patient tumor heterogeneity observed in the clinic. Patient-derived xenografts (PDXs) consist in grafting human cancer samples into immunocompromised mice directly after patient surgery. Since each PDX faithfully recapitulates patient's tumor genetics, these preclinical models well represent the intrinsic heterogeneity of cancer. We took advantage of the large collection of breast cancer PDXs held at XenTech to address the mechanisms of tumor response to treatment vs tumor recurrence. Upon receiving chemotherapy, some breast cancer PDXs (the 'responders') undergo tumor shrinkage, whereas others continue to grow (the 'non-responders'). Comparative transcriptomic profiling of laser-microdissected cancer cells showed that the reduction of tumor volume in responders was closely associated to the over-expression of genes related to the interferon (IFN)/signal transducer and activator of transcription 1 (STAT1) pathway.

Using mouse versus human cytokine arrays we observed that activation of this pathway was associated with the secretion of ligands of human origin (cancer) rather than with ligands secreted from the nude mice residual immune system. Next, we screened a large number of cell lines to identify in vitro cell models able to mimic cell-autonomous induction of the IFN/STAT1 signature after genotoxic treatment. Both an immortalized cell line and a primary culture dissociated from a responder PDX were shown to activate the IFN/STAT1 pathway and to express the cognate gene signature after treatment with mafosfamide (the active metabolite of cyclophosphamide used in the clinic). Expression analyses (qPCR) confirmed induction of IFN type I elements by cell models. Conditioned medium collected from mafosfamide-treated cancer cells was able to activate luciferase reporter genes harboring ISRE (interferon stimulated response elements) and GAS (gamma interferon activated sequence) response elements, meaning that active ligands of the IFN/STAT1 pathways were secreted. Accordingly, STAT1 gene silencing (siRNA) resulted in markedly attenuated gene signature expression after mafosfamide treatment. The addition of conditioned medium significantly reduced mafosfamide-induced cancer cell death suggesting that the over-expression of the IFN/STAT1 pathway may ultimately have protective effect on cancer cell viability.

In conclusion, this study supports that cell-autonomous activation of the IFN/STAT1 pathway is a surrogate biomarker of initial tumor shrinkage in response to genotoxics, and suggests that it may play a role in tumor resistance to treatment.

Citation Format: Julie Gaston, Laura Cheradame, Marie-Emmanuelle Legrier, Olivier Déas, Myriam Lassalle, Enora Le Ven, Jean-Gabriel Judde, Vincent Goffin, Stefano Cairo. Cell-autonomous activation of the interferon/STAT1 pathway in response to genotoxic treatment. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A103.

The sialyl-glycolipid stage-specific embryonic antigen 4 marks a subpopulation of chemotherapy-resistant breast cancer cells with mesenchymal features

Introduction

Chemotherapy resistance resulting in incomplete pathologic response is associated with high risk of metastasis and early relapse in breast cancer. The aim of this study was to identify and evaluate biomarkers of treatment-resistant tumor cells.

Methods

We performed a cell surface marker screen in triple-negative breast cancer patient-derived xenograft models treated with standard care genotoxic chemotherapy. Global expression profiling was used to further characterize the identified treatment-resistant subpopulations.

Results

High expression of sialyl-glycolipid stage-specific embryonic antigen 4 (SSEA4) was found in residual tumor cells surviving chemotherapy and in samples from metastatic patients who relapsed after neoadjuvant chemotherapy. Gene and microRNA (miRNA) expression profiling linked SSEA4 positivity with a mesenchymal phenotype and a deregulation of drug resistance pathways. Functional assays demonstrated a direct link between epithelial–mesenchymal transition (EMT) and SSEA4 expression. Interestingly, SSEA4 expression, EMT, and drug resistance seemed to be regulated posttranscriptionally. Finally, high expression of CMP-N-acetylneuraminate-β-galactosamide-α-2,3-sialyltransferase 2 (ST3GAL2), the rate-limiting enzyme of SSEA4 synthesis, was found to be associated with poor clinical outcome in breast and ovarian cancer patients treated with chemotherapy.

Conclusions

In this study, we identified SSEA4 as highly expressed in a subpopulation of tumor cells resistant to multiple commonly used chemotherapy drugs, as well as ST3GAL2, the rate-limiting enzyme of SSEA4 synthesis, as a predictive marker of poor outcome for breast and ovarian cancer patients undergoing chemotherapy. Both biomarkers and additionally identified regulatory miRNAs may be used to further understand chemoresistance, to stratify patient groups in order to avoid ineffective and painful therapies, and to develop alternative treatment regimens for breast cancer patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0652-6) contains supplementary material, which is available to authorized users.

Abstract 4317: The sialyl-glycolipid SSEA4 marks a subpopulation of chemotherapy-resistant breast cancer cells with mesenchymal features

Currently, the main option for systemic therapy of high-risk breast cancer is chemotherapy, with an overall poor efficacy and severe side effects. Chemotherapy-resistance and incomplete pathologic response associate with risk of metastasis and early relapse in breast cancer.

In order to characterize treatment-resistant tumor cells, we performed a cell surface marker screen in 4 triple-negative breast cancer patient-derived xenograft (PDX) models that respond well to adriamycin/cyclophosphamide-based chemotherapy but fail to reach complete pathological response. We used multi-parameter flow cytometry to screen for the expression of a set of 45 cell surface markers during the course of chemotherapy. This set of markers represented both proteins involved in stem cell function and proteins known to be over-expressed in stem cells or cancer stem cell sub-populations.

We identified the sialyl-glycolipid SSEA4 as a constant marker of chemotherapy-resistant cancer cells in all four models. In addition, SSEA4 expression was found higher in 3 out of 4 TNBC PDXs that are de novo resistant to neo-adjuvant chemotherapy compared to sensitive TNBC PDXs. Two cell populations with different percentage of SSEA4-positive (SSEA4+) cells and with different growth characteristics were identified in a PDX model. When treated with genotoxic compounds, the cell population with higher SSEA4+ expression showed increased resistance to chemotherapy, indicating this post-translational modification as potential marker of tumor resistance. Comparison of SSEA4+ and SSEA4-negative (SSEA4-) tumor cells from TNBC PDX models by global gene expression profiling showed overexpression of mesenchymal-associated genes in SSEA4+ tumor cells and a deregulation of drug resistance pathway-associated genes and miRNAs. In addition, high expression of ST3 beta-galactoside alpha-2,3-sialyltransferase 2 (ST3GAL2), the enzyme catalyzing the last step of SSEA4 synthesis, was found associated with poor outcome in breast and ovarian cancer patients treated with chemotherapy.

Thus, we propose SSEA4 as a novel marker of epithelial-mesenchymal transition associated with chemoresistance, and ST3GAL2 expression as a predictive marker for tumor chemoresistance associated with poor outcome in breast and ovarian cancer patients. Both biomarkers and additionally identified regulatory miRNAs may be used to further understand chemoresistance and to develop alternative treatment regimens for breast and ovarian cancer patients.

Citation Format: Andrea Aloia, Evgeniya Petrova, Stefan Tomiuk, Ute Bissels, Sophie Banis, Olivier Deas, Silvia Rüberg, Bernhard Gerstmayer, David Agorku, Jean-Gabriel Judde, Andreas Bosio, Stefano Cairo, Olaf T. Hardt. The sialyl-glycolipid SSEA4 marks a subpopulation of chemotherapy-resistant breast cancer cells with mesenchymal features. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4317. doi:10.1158/1538-7445.AM2015-4317

Abstract P5-06-04: The PARP inhibitor niraparib demonstrated activity in patient-derived triple-negative breast cancer xenograft models with high homologous recombination deficiency (HRD) score

Triple negative breast cancer (TNBC), which comprises 15% of all breast cancers, has a poor prognosis and currently lacks effective treatment. TNBCs are highly proliferative, genomically unstable and share molecular characteristics with that of BRCA1/2 mutation driven breast cancer. Poly(ADP-ribose) polymerase-1 (PARP) is a key DNA repair enzyme that mediates single strand break (SSB) repair through the base excision repair (BER) pathway. PARP inhibitors have been demonstrated to selectively kill tumor cells that harbor BRCA1 and BRCA2 mutations. In addition, pre-clinical and preliminary clinical data suggest that PARP inhibitors are selectively cytotoxic for tumors with homologous recombination repair deficiency caused by dysfunction of genes other than BRCA1 or BRCA2.

Niraparib is a potent, orally active PARP inhibitor that is being evaluated in Phase 3 clinical studies for ovarian cancer and BRCA related breast cancer. Previously, we demonstrated that a subset of basal breast cancer (BBC) patient-derived xenograft (PDX) models responded robustly to single agent niraparib treatment. To understand the selectivity observed, the samples from a collection of 37 BBC PDX models have been subjected to homologous recombination deficiency (HRD) analysis. HRD analysis is a DNA-based assay that is capable of detecting homologous recombination deficiency independent of its etiology. Genome-wide SNP data was generated from a custom Agilent SureSelect XT capture followed by sequencing on an Illumina HiSeq2500. SNP data was analyzed using three algorithms (LOH, TAI and LST scores), and the final HRD score is the sum of the LOH+TAI+LAST scores.

Niraparib’s antitumor activity was investigated in patient derived BBC models with various HRD scores. The correlation between niraparib efficacy, HRD score and BRCA deficiency will be discussed.

Citation Format: Yan Wang, Stefano Cairo, Olivier Deas, Anne-Renee Hartman, Joshua Jones, Alexander Gutin, Jerry Lanchbury, Zaina Sangale, Cara Solimeno, Jean-Gabriel Judde, Kirsten Timms, Keith Wilcoxen. The PARP inhibitor niraparib demonstrated activity in patient-derived triple-negative breast cancer xenograft models with high homologous recombination deficiency (HRD) score [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-06-04.

Abstract 204: Understanding breast cancer resistance to chemotherapy: Characterization of cancer cell sub-populations in residual and relapsed tumors

Tumor recurrence fueled by residual tumor cells having survived chemotherapy represents the principal cause of breast cancer treatment failure. Triple-negative breast cancer (TNBC) is a heterogeneous disease at both molecular and cellular level, and the presence of different tumor cell sub-populations is likely the reason for this heterogeneity and for the incomplete response to neoadjuvant chemotherapy observed for most TNBC. To identify and isolate tumor cell sub-populations that resist to chemotherapy, we used a panel of 45 antibody fluorochrome conjugates in combination with multi-parameter flow cytometry to screen for the expression of a set of cell surface markers during the course of tumor chemotherapy. This set of markers represented both proteins involved in stem cell function and proteins known to be over-expressed in stem cells or cancer stem cell sub-populations. As a source of tumor samples, we used a panel of TNBC patient-derived xenografts (PDXs). These tumor models are known to preserve the morphology, molecular characteristics and drug response profile of the original patient tumors. We used TNBC PDX models to reproduce in vivo chemotherapy-induced tumor regression and relapse. Tumor dissociation, depletion of mouse cells and multi-parameter flow cytometry allowed us to measure the percentage of marker expression only in the fraction of human tumor cells.

We found that the expression of most of markers was very heterogeneous among the different TNBC models analyzed. In residual tumors, we observed enrichment or depletion of several cell populations expressing stem and cancer stem cell markers such as CD44+ and CD133/1+. Interestingly, in the majority of relapsed tumors, the percentage of these marker-positive cells shifted back to pre-treatment levels. Moreover, the percentage of certain tumor cell sub-populations was higher in untreated chemotherapy-resistant tumors compared to untreated chemotherapy-sensitive ones. To study the properties of enriched tumor cells sub-populations, we coupled cell separation of marker-positive tumor cells to large scale molecular analysis. Microarray-based gene expression analysis of sorted tumor cells revealed cell sub-populations with up-regulated signaling pathways related to stem cell function, cell migration or EMT. Further in vivo and in vitro assays with sorted sub-populations are currently being performed to search for possible functional role of selected markers during tumor resistance to chemotherapy and initiation of tumor relapse.

In summary, by coupling PDX and cell surface marker screening technologies, we have identified distinct tumor cell sub-populations which are associated with tumor resistance to chemotherapy. We believe that this approach will help gaining knowledge of tumor cell adaptation and selection in response to chemotherapy, which will ultimately lead to design tailored treatments for TNBCs.

Citation Format: Andrea Aloia, Evgeniya Petrova, Olivier Deas, Sophie Banis, Enora Le Ven, Andreas Bosio, Olaf Hardt, Stefano Cairo, Jean-Gabriel Judde. Understanding breast cancer resistance to chemotherapy: Characterization of cancer cell sub-populations in residual and relapsed tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 204. doi:10.1158/1538-7445.AM2014-204