HSP90 inhibitors induce GPNMB cell-surface expression by modulating lysosomal positioning and sensitize breast cancer cells to glembatumumab vedotin

Transmembrane glycoprotein NMB (GPNMB) is a prognostic marker of poor outcome in patients with triple-negative breast cancer (TNBC). Glembatumumab Vedotin, an antibody drug conjugate targeting GPNMB, exhibits variable efficacy against GPNMB-positive metastatic TNBC as a single agent. We show that GPNMB levels increase in response to standard-of-care and experimental therapies for multiple breast cancer subtypes. While these therapeutic stressors induce GPNMB expression through differential engagement of the MiTF family of transcription factors, not all are capable of increasing GPNMB cell-surface localization required for Glembatumumab Vedotin inhibition. Using a FACS-based genetic screen, we discovered that suppression of heat shock protein 90 (HSP90) concomitantly increases GPNMB expression and cell-surface localization. Mechanistically, HSP90 inhibition resulted in lysosomal dispersion towards the cell periphery and fusion with the plasma membrane, which delivers GPNMB to the cell surface. Finally, treatment with HSP90 inhibitors sensitizes breast cancers to Glembatumumab Vedotin in vivo, suggesting that combination of HSP90 inhibitors and Glembatumumab Vedotin may be a viable treatment strategy for patients with metastatic TNBC.

Unraveling Triple-Negative Breast Cancer Tumor Microenvironment Heterogeneity: Towards an Optimized Treatment Approach

Background

Recent efforts of gene expression profiling analyses recognized at least four different triple-negative breast cancer (TNBC) molecular subtypes. However, little is known regarding their tumor microenvironment (TME) heterogeneity.

Methods

Here, we investigated TME heterogeneity within each TNBC molecular subtype, including immune infiltrate localization and composition together with expression of targetable immune pathways, using publicly available transcriptomic and genomic datasets from a large TNBC series totaling 1512 samples. Associations between molecular subtypes and specific features were assessed using logistic regression models. All statistical tests were two-sided.

Results

We demonstrated that each TNBC molecular subtype exhibits distinct TME profiles associated with specific immune, vascularization, stroma, and metabolism biological processes together with specific immune composition and localization. The immunomodulatory subtype was associated with the highest expression of adaptive immune-related gene signatures and a fully inflamed spatial pattern appearing to be the optimal candidate for immune check point inhibitors. In contrast, most mesenchymal stem-like and luminal androgen receptor tumors showed an immunosuppressive phenotype as witnessed by high expression levels of stromal signatures. Basal-like, luminal androgen receptor, and mesenchymal subtypes exhibited an immune cold phenotype associated with stromal and metabolism TME signatures and enriched in margin-restricted spatial pattern. Tumors with high chromosomal instability and copy number loss in the chromosome 5q and 15q regions, including genomic loss of major histocompatibility complex related genes, showed reduced cytotoxic activity as a plausible immune escape mechanism.

Conclusions

Our results demonstrate that each TNBC subtype is associated with specific TME profiles, setting the ground for a rationale tailoring of immunotherapy in TNBC patients.

Tumour-associated macrophages drive stromal cell-dependent collagen crosslinking and stiffening to promote breast cancer aggression

Stromal stiffening accompanies malignancy, compromises treatment and promotes tumour aggression. Clarifying the molecular nature and the factors that regulate stromal stiffening in tumours should identify biomarkers to stratify patients for therapy and interventions to improve outcome. We profiled lysyl hydroxylase-mediated and lysyl oxidase-mediated collagen crosslinks and quantified the greatest abundance of total and complex collagen crosslinks in aggressive human breast cancer subtypes with the stiffest stroma. These tissues harbour the highest number of tumour-associated macrophages, whose therapeutic ablation in experimental models reduced metastasis, and decreased collagen crosslinks and stromal stiffening. Epithelial-targeted expression of the crosslinking enzyme, lysyl oxidase, had no impact on collagen crosslinking in PyMT mammary tumours, whereas stromal cell targeting did. Stromal cells in microdissected human tumours expressed the highest level of collagen crosslinking enzymes. Immunohistochemical analysis of biopsies from a cohort of patients with breast cancer revealed that stromal expression of lysyl hydroxylase 2, an enzyme that induces hydroxylysine aldehyde-derived collagen crosslinks and stromal stiffening, correlated significantly with disease specific mortality. The findings link tissue inflammation, stromal cell-mediated collagen crosslinking and stiffening to tumour aggression and identify lysyl hydroxylase 2 as a stromal biomarker.

Abstract PO-080: Predicting relapse in patients with triple negative breast cancer (TNBC) using a deep-learning approach

The abundance and/or precise location of tumor infiltrating lymphocytes (TILs), especially CD8+ T cells, can serve as a prognostic indicator in various types of solid tumors. However, it is often difficult to select an appropriate algorithm in order to stratify patients into well-defined risk groups. More importantly, patient stratification results often depends on the selection of tumor regions, where subjective judgement could affect the final results. On the other hand, machine-learning approaches can help to stratify patients in an objective and automatic fashion. Based on immunofluorescence (IF) images of CD8+ T lymphocytes and cancer cells, we develop a machine-learning approach which can predict the risk of relapse for patients with Triple Negative Breast Cancer (TNBC). Tumor-section images from 9 patients with poor outcome and 15 patients with good outcome were used as a training set. Tumor-section images of 29 patients in an independent cohort were used to test the predictive power of our algorithm. One of the key innovations is dissecting the section images into patches in a size of 640 µm x 640 µm for training and test, which allows one to make use of the information in the section images despite the small number of patients. In the test cohort, 6 (out of 29) patients who belong to the poor-outcome group were all correctly identified by our algorithm; for the 23 (out of 29) patients who belong to the good-outcome group, 17 were correctly predicted with some evidence that improvement is possible if other measures, such as the grade of tumors, are factored in. Our approach does not involve arbitrarily defined metrics and can be applied to other types of cancer in which the abundance/location of CD8+ T lymphocytes/other types of cells is an indicator of prognosis. Furthermore, we showed that using limited parts of the tumor section image for predictions would give rise to inaccurate results, which suggests that tumor heterogeneity should be carefully taken into account for a rigorous evaluation of the outcome. In summary, despite the limited number of patients, we demonstrated that the deep-learning approach can make good use information in the infiltration pattern of CD8+ T lymphocytes and thereby enable prognosis. Additional data collection efforts should be made to eventually enable a more rigorous analysis.

Citation Format: Guangyuan Yu, Xuefei Li, Ting-Fang He, Tina Gruosso, Dongmei Zuo, Margarita Souleimanova, Valentina Muñoz Ramos, Atilla Omeroglu, Sarkis Meterissian, Marie-Christine Guiot, Li Yang, Yuan Yuan, Morag Park, Peter P. Lee, Herbert Levine. Predicting relapse in patients with triple negative breast cancer (TNBC) using a deep-learning approach [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-080.

Predicting Relapse in Patients With Triple Negative Breast Cancer (TNBC) Using a Deep-Learning Approach

The abundance and/or location of tumor infiltrating lymphocytes (TILs), especially CD8⁺ T cells, in solid tumors can serve as a prognostic indicator in various types of cancer. However, it is often difficult to select an appropriate threshold value in order to stratify patients into well-defined risk groups. It is also important to select appropriate tumor regions to quantify the abundance of TILs. On the other hand, machine-learning approaches can stratify patients in an unbiased and automatic fashion. Based on immunofluorescence (IF) images of CD8⁺ T lymphocytes and cancer cells, we develop a machine-learning approach which can predict the risk of relapse for patients with Triple Negative Breast Cancer (TNBC). Tumor-section images from 9 patients with poor outcome and 15 patients with good outcome were used as a training set. Tumor-section images of 29 patients in an independent cohort were used to test the predictive power of our algorithm. In the test cohort, 6 (out of 29) patients who belong to the poor-outcome group were all correctly identified by our algorithm; for the 23 (out of 29) patients who belong to the good-outcome group, 17 were correctly predicted with some evidence that improvement is possible if other measures, such as the grade of tumors, are factored in. Our approach does not involve arbitrarily defined metrics and can be applied to other types of cancer in which the abundance/location of CD8⁺ T lymphocytes/other types of cells is an indicator of prognosis.

Abstract 6710: AVID200, a first-in-class selective TGF-beta 1 and -beta 3 inhibitor, sensitizes tumors to immune checkpoint blockade therapies

AVID200 is a first-in-class rationally designed receptor ectodomain trap that selectively neutralizes TGF-beta 1 and -beta 3 with pM potency while sparing TGF-beta 2, thereby reducing the potential for toxicities associated with neutralization of this isoform. A Phase 1 dose-escalation clinical study of AVID200 monotherapy has recently been completed and established that the agent was well tolerated and exhibited target engagement at all dose levels tested without reaching a maximally tolerated dose.

To explore the potential of AVID200 as a combination agent with immunotherapy, expression analysis of TGF-beta isoforms across various solid tumors has been carried out and the ability of AVID200 to increase anti-tumor immunity as a single agent and in combination has been explored in vivo.

Analysis of >10,000 tumor samples from TCGA revealed that TGF-beta1 and -beta3 are the predominant isoforms expressed in solid tumors, with TGF-beta2 showing only minimal expression. This corroborates the attractiveness of TGF-beta1 and -beta3 as promising anti-cancer targets and emphasizes the need to target both isoforms simultaneously. Furthermore, AVID200 increased T-cell-mediated cytotoxicity as a single agent as well as potentiating the efficacy of immune checkpoint inhibitors (ICI) in syngeneic mouse tumor models. In line with these observations, we have found that AVID200 increases the infiltration of T-cells in the tumor microenvironment.

In conclusion, AVID200, a first-in-class, potent and selective TGF-beta trap, enhances the activity of ICI agents in vivo and holds promise as a potential novel immunotherapy combination regimen which warrants exploration in patients with solid tumor malignancies. Phase 1 clinical trials are underway in various indications.

Citation Format: Gilles Tremblay, Tina Gruosso, Jean-François Denis, Rene Figueredo, Jim Koropatnick, Maureen O'Connor-McCourt. AVID200, a first-in-class selective TGF-beta 1 and -beta 3 inhibitor, sensitizes tumors to immune checkpoint blockade therapies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6710.

Elevated V-ATPase Activity Following PTEN Loss Is Required for Enhanced Oncogenic Signaling in Breast Cancer

PTEN loss-of-function contributes to hyperactivation of the PI3K pathway and to drug resistance in breast cancer. Unchecked PI3K pathway signaling increases activation of the mechanistic target of rapamycin complex 1 (mTORC1), which promotes tumorigenicity. Several studies have suggested that vacuolar (H⁺)-ATPase (V-ATPase) complex activity is regulated by PI3K signaling. In this study, we showed that loss of PTEN elevated V-ATPase activity. Enhanced V-ATPase activity was mediated by increased expression of the ATPase H+ transporting accessory protein 2 (ATP6AP2), also known as the prorenin receptor (PRR). PRR is cleaved into a secreted extracellular fragment (sPRR) and an intracellular fragment (M8.9) that remains associated with the V-ATPase complex. Reduced PTEN expression increased V-ATPase complex activity in a PRR-dependent manner. Breast cancer cell lines with reduced PTEN expression demonstrated increased PRR expression. Similarly, PRR expression became elevated upon PTEN deletion in a mouse model of breast cancer. Interestingly, concentration of sPRR was elevated in the plasma of patients with breast cancer and correlated with tumor burden in HER2-enriched cancers. Moreover, PRR was essential for proper HER2 receptor expression, localization, and signaling. PRR knockdown attenuated HER2 signaling and resulted in reduced Akt and ERK 1/2 phosphorylation, and in lower mTORC1 activity. Overall, our study demonstrates a mechanism by which PTEN loss in breast cancer can potentiate multiple signaling pathways through upregulation of the V-ATPase complex. IMPLICATIONS: Our study contributed to the understanding of the role of the V-ATPase complex in breast cancer cell tumorigenesis and provided a potential biomarker in breast cancer.

THU0329 SAFETY, TARGET ENGAGEMENT, AND INITIAL EFFICACY OF AVID200, A FIRST-IN-CLASS POTENT AND ISOFORM-SELECTIVE INHIBITOR OF TGF-BETA 1 AND 3, IN PATIENTS WITH DIFFUSE CUTANEOUS SYSTEMIC SCLEROSIS (DCSSC): A PHASE 1 DOSE ESCALATION STUDY

Background:

AVID200 is a novel, potent TGF-beta receptor ectodomain-based trap designed to selectively neutralize TGF-beta 1 and 3. These two isoforms have been implicated as central mediators of the pathogenesis of systemic sclerosis (SSc). AVID200 avoids inhibition of TGF-beta 2, the isoform that supports normal cardiac function and hematopoiesis.

Objectives:

This first-in-human study (AVID200-01;NCT03831438) is a Phase 1, open label, multicenter, cohort dose-escalation trial designed to evaluate safety, tolerability, pharmacokinetic (PK) profile, pharmacodynamic (PD) effects, target engagement, and preliminary efficacy in patients with diffuse cutaneous SSc (dcSSc).

Methods:

Eligible patients must have dcSSc of <5 years (y) duration and a modified Rodnan Skin Score (MRSS) ≥15. AVID200 at dose levels of 1, 3, 9, or 15 mg/kg IV is administered every 2 weeks (Q2W) for 6 weeks (3 doses). Patients tolerating dosing and who have not experienced disease worsening during the initial Treatment Period may receive up to 6 additional doses Q2W (Extension Period). The ability of AVID200 to selectively sequester its target is assessed in plasma by TGF-beta quantification per ELISA and a cell-based functional readout. Expression of biomarkers of TGF-beta inhibition and genes correlating with MRSS are assessed.

Results:

The first 2 dose cohorts have completed treatment: male/female 3 each, median age 61y (range 45-70), median MRSS at baseline 31 (range 23-39). Recruitment into cohort 3 is complete. AVID200 was well tolerated with no dose limiting toxicities or serious adverse events (SAEs). AEs, all considered possibly related, included single cases of Grade 1 dizziness and CPK elevation, and Grade 2 anemia. All patients demonstrated a decline in MRSS at 6 weeks by 3, 4, and 9 points in Cohort 1, and 2, 8, and 9 points in Cohort 2. Four of 6 patients demonstrated continued decrease in MRSS 12 weeks after the last dose, with all patients showing a decline in MRSS relative to baseline at this timepoint by 7, 6, and 7 points in Cohort 1 and 4, 8, and 13 points in Cohort 2. AVID200 in plasma engaged endogenous activated TGF-beta and potently neutralized signaling from exogenous TGF-beta 1 and 3, but not TGF-beta 2, across the treatment period. PD effects in skin biopsies, including expression of markers of SSc activity, TGF-beta activity, and myofibroblast-associated genes were assessed. Five of 6 patients showed decreased expression of PD biomarker genes, THBS1 and MS4A4A, comparing end of treatment biopsies to baseline, and all patients showed a decline in SERPINE1 expression, a marker gene for TGF-beta activity. Clustering of RNA-seq expression data showed close coregulation of COMP, THBS1, SERPINE1, LOXL, COL10A1, COL11A1, COL12A1, CTGF, and CDH11, suggesting that blocking TGF-beta inhibits this group of profibrotic genes. Single-cell sequencing data show that expression of these genes is upregulated by subsets of SSc fibroblasts.

Conclusion:

AVID200 at doses of 1 and 3 mg/kg was well-tolerated in this first study in dcSSc patients. Evidence of anti-fibrotic effects as indicated by rapid, persistent and clinically meaningful declines in MRSS was observed in all patients, as well as AVID200 target engagement and modulation. Recruitment into additional dose and extension cohorts is ongoing. Together, these clinical data support selective TGF-beta 1 and 3 inhibition by AVID200 as a promising therapeutic approach for dcSSc.

Disclosure of Interests:

Robert Lafyatis Grant/research support from: Forbius, Consultant of: Certa Therapeutics, Forbius, FBM Therapeutics, Robert Spiera Grant/research support from: Roche-Genetech, GSK, Boehringer Ingelheim, Chemocentryx, Corbus, Forbius, Sanofi, Inflarx, Consultant of: Roche-Genetech, GSK, CSL Behring, Sanofi, Janssen, Chemocentryx, Forbius, Mistubishi Tanabe, Robyn Domsic Consultant of: Forbius, Anna Papazoglou: None declared, Colin Ligon Grant/research support from: Forbius, Christina Mae Zinger Morse: None declared, Jean-François Denis Employee of: Forbius, Margaret Davis Employee of: Forbius, Tina Gruosso Employee of: Forbius, Gilles Tremblay Employee of: Forbius, Maureen O’Connor McCourt Employee of: Forbius, Sandra Sinclair Employee of: Forbius, Jonathan Delara Employee of: Forbius, Krista Alvarado Employee of: Forbius, Debra Wood Consultant of: Forbius, Symphogen, Paul Nadler Consultant of: Forbius, Symphogen, Karyopharm, Elizabeth Volkmann Grant/research support from: Forbius, Corbus Pharmaceuticals, Consultant of: Boehringer Ingelheim, Forbius, Speakers bureau: Boehringer Ingelheim

AVID200, first-in-class TGF-beta 1 and 3 selective and potent inhibitor: Safety and biomarker results of a phase I monotherapy dose-escalation study in patients with advanced solid tumors

3587

Background: AVID200 is a rationally designed first-in-class, selective inhibitor of transforming growth factor-beta (TGF-beta) that neutralizes TGF-beta 1 & 3 with pM potency and 4,000 fold selectivity over TGF-beta 2. TGF-beta 1 & 3 signaling has been associated with immune checkpoint inhibitor resistance and immunosuppression in the tumor microenvironment while TGF-beta 2 is required for normal cardiac function and hematopoiesis. Methods: NCT03834662 (AVID200-03) is a multicenter Phase 1 study following a standard 3 + 3 dose escalation to evaluate safety and tolerability of AVID200 given IV every 3 weeks to patients (pts) with advanced solid tumors. Peripheral target engagement was assessed in blood by ELISA and a cell-based functional assay, and in skin biopsies by immunohistochemistry (IHC). Pharmacodynamic markers of TGF-beta signal modulation and immune activation were evaluated in serum using the InflammationMAP v 1.0 (Myriad RBM) and in paired tumor biopsies by IHC and Imaging Mass Cytometry. Results: Nineteen pts (ECOG 0-1, median age 63 [range 39-77], 52.6% male) received AVID200 at 3 planned dose levels of 180 (N = 7), 550 (N = 6), and 1100 mg/m2 (N = 6) (~5, 15, and 30 mg/kg). The maximum tolerated dose was not reached. Three Grade (G) 3 treatment-related adverse events (TRAEs) were reported in 2 pts (diarrhea and lipase elevation, anemia); no > G3 TRAEs were observed. Serum exposure was dose-proportional and AVID200 sequestered all active TGF-beta 1 & 3, but not beta 2, in blood across the entire dosing period at all dose levels, providing proof-of-mechanism of AVID200. SMAD2 phosphorylation in skin biopsies was detectably reduced on Day 4 at 15 and 30 mg/kg. Pro-inflammatory markers in serum were increased on Day 8 versus baseline in a dose-dependent manner. Tumor biopsies of pts treated at 15 mg/kg showed modulation of TGF-beta signaling and immune activation. A best response of RECIST stable disease > 12 weeks was observed in 2 pts: 1 with adenoid cystic carcinoma (5 mg/kg; 8.7 months); 1 with breast carcinoma (30 mg/kg; 3.1 months). Conclusions: AVID200 was safe and well tolerated at dose levels of 5-30 mg/kg, with peripheral target engagement across the entire dosing period. AVID200 led to TGF-beta target modulation and immune activation. These data provide proof-of-principle that AVID200-mediated selective and potent inhibition of TGF-beta 1 & 3 is feasible in the clinic. The AVID200 monotherapy data warrant exploration of rational combination with a PD-(L)1 inhibitor. Clinical trial information: NCT03834662 .

Pitfalls in assessing stromal tumor infiltrating lymphocytes (sTILs) in breast cancer

Stromal tumor-infiltrating lymphocytes (sTILs) are important prognostic and predictive biomarkers in triple-negative (TNBC) and HER2-positive breast cancer. Incorporating sTILs into clinical practice necessitates reproducible assessment. Previously developed standardized scoring guidelines have been widely embraced by the clinical and research communities. We evaluated sources of variability in sTIL assessment by pathologists in three previous sTIL ring studies. We identify common challenges and evaluate impact of discrepancies on outcome estimates in early TNBC using a newly-developed prognostic tool. Discordant sTIL assessment is driven by heterogeneity in lymphocyte distribution. Additional factors include: technical slide-related issues; scoring outside the tumor boundary; tumors with minimal assessable stroma; including lymphocytes associated with other structures; and including other inflammatory cells. Small variations in sTIL assessment modestly alter risk estimation in early TNBC but have the potential to affect treatment selection if cutpoints are employed. Scoring and averaging multiple areas, as well as use of reference images, improve consistency of sTIL evaluation. Moreover, to assist in avoiding the pitfalls identified in this analysis, we developed an educational resource available at www.tilsinbreastcancer.org/pitfalls.

P856 AVID200, first-in-class TGF-beta1 and beta3 selective inhibitor: results of a phase 1 monotherapy dose escalation study in solid tumors and evidence of target engagement in patients

Background

AVID200 is a rationally designed first-in-class receptor ectodomain trap that inhibits transforming growth factor-beta (TGF-beta) isoforms -beta1 and -beta3 with pM potency. TGF-beta signaling is highly immunosuppressive in the tumor microenvironment and has been associated with immune checkpoint inhibitor resistance.1-4 TGF-beta1 and -beta3 are most closely associated with cancer progression whereas TGF-beta2 is required for normal cardiac function and hematopoiesis. Accordingly, selective targeting of TGF-beta1 and -beta3 by AVID200 may improve the efficacy of immunotherapy while avoiding toxicities associated with earlier generations of non-selective TGF-beta inhibitors.

Methods

This open-label, multicenter Phase 1 study (NCT03834662) evaluated safety, tolerability and dose-limiting toxicities (DLTs) of sequential escalating doses of AVID200 (Q3W IV) to establish the recommended Phase 2 dose. Patients with documented, locally advanced or metastatic solid tumors without other treatment options were eligible. The primary objective was safety and tolerability; secondary objectives included preliminary anti-tumor activity, pharmacokinetics (PK), and assessment of pharmacodynamic biomarkers indicative of target modulation. PK was assessed by enzyme immunoassay. Ability of AVID200 to selectively sequester and neutralize its target was assessed by TGF-beta quantification per ELISA, as well as cell-based IL-11 release functional evaluation of TGF-beta signal inhibition. In addition, phosphorylation of SMAD2, a downstream target of TGF-beta, was assessed by immunohistochemistry in skin biopsies at screening and Cycle 1, Day 4 (C1D4).

Results

Enrollment to all planned cohorts is complete: A total of 13 patients with ECOG 0-1 received AVID200 across the three planned dose levels of 180 (N=7), 550 (N=3), and 1100 mg/m2 (N=3) (~5, 15, and 30 mg/kg). The MTD was not reached. Grade 3 study drug-related AEs were reported in two patients (diarrhea, lipase elevation); no related Grade 4 or 5 AEs were observed. Serum exposure was dose-proportional. AVID200 sequestered circulating endogenous active TGF-beta at all dose levels. Moreover, AVID200 in patient plasma potently neutralized TGF-beta1- and -3 – but not -beta2 – mediated signaling. SMAD2 phosphorylation in skin biopsies was detectably reduced at C1D4 across all dose levels. Three of nine patients evaluated for response had a best response of stable disease (SD), including one prolonged SD which was ongoing at six months at time of writing.

Conclusions

AVID200 has been well tolerated as monotherapy and engaged its target in patients providing proof-of-principle that selective and potent inhibition of TGF-beta1 and -beta3 is feasible in the clinic. The results warrant evaluation of AVID200 in combination with anti-PD(L)1 and other anti-cancer therapies.

Acknowledgements

We would like to thank all participating patients, their families and caretakers as well as staff members at the clinical sites.

Trial Registration

Clinicaltrials.gov NCT03834662

Ethics Approval

The study was approved by START-Midwest‘s IRB (approval number STMW2018.19), University Health Network‘s Research Ethics Board (approval number 18-6104), and The University of Texas MD Anderson Cancer Center‘s IRB (approval number 2018-1079).

References

Mariathasan S, Turley SJ, Nickles D, et al. TGFβ attenuates tumour response to PD-L1 blockade by contributing to exclusion of T cells. Nature 2018; 554:544–548.

Chakravarthy A, Khan L, Bensler NP, Bose P, De Carvalho DD. TGF-β-associated extracellular matrix genes link cancer-associated fibroblasts to immune evasion and immunotherapy failure. Nat Commun 2018; 9:4692.

Tauriello DVF, Palomo-Ponce S, Stork D, et al. TGFβ drives immune evasion in genetically reconstituted colon cancer metastasis. Nature. 2018; 554:538–543.

Zhao F, Evans K, Xiao C, et al. Stromal Fibroblasts Mediate Anti–PD-1 Resistance via MMP-9 and Dictate TGFβ Inhibitor Sequencing in Melanoma. Cancer Immunol Res 2018; 6:1459–1471.

Abstract B65: Mathematical modeling studies on spatial profiles of tumor-infiltrating T cells

Activated cytotoxic T lymphocytes have been demonstrated to be able to kill antigen-specific cancer cells via various mechanisms. Not surprisingly, stronger infiltration of cytotoxic T cells into tumor/tumor-cell clusters generally associates with better prognosis, which has been demonstrated in various cancers. There have been efforts on quantifying the distribution of cytotoxic T cells on the whole tumor level. On the other hand, a solid tumor is usually composed of many tumor-cell clusters as well as stroma in gaps between those clusters. It has been noticed that T cells can be mostly localized in the stromal regions of a solid tumor. Therefore, it is also important to quantify the spatial pattern of T cells on the tumor-cell cluster level and further investigate the mechanism underlying the observed limited infiltration. In our work, we quantified the spatial distribution of CD8+ T cells with respect to their distance to the boundary of individual tumor-cell clusters. Generally, we observed that: i) patients differ in infiltration at the cluster level; ii) for most samples, T cells mainly accumulate outside the tumor-cell clusters; iii) for some samples T cells can effectively infiltrate the tumor-cell clusters; and iv) for other samples, the T-cell infiltration profile is intermediate. This last possibility reveals a non-monotonic distribution of T cells, i.e., a drop of T-cell density at the boundary coupled with a second accumulation of T cells at the center of tumor-cell clusters. Based on the quantified CD8+ T-cell profiles on the tumor-cell cluster level, we constructed mathematical models to test two hypothesized contributors affecting the spatial distribution of CD8+ T cells: a physical motility barrier set up by the ECM fibers in the stroma and a biochemical inhibitor ultimately due to the cancer cells inside the tumor-cell clusters. Mathematical models that only include physical barrier effects can qualitatively capture some (but not all) spatial features of the T-cell profiles. However, there is one significant shortcoming: the physical barrier scenario predicts that the profiles observed should be transient and hence eventually T cells should infiltrate all tumors. This appears inconsistent with simple time-scale estimates. A biochemical model focusing on T-cell repulsion can give rise to the observed spatial profiles as steady-state solutions; the different patterns correspond to different properties of cancer cells in different patients. We therefore favor this modeling framework. Of course, a definitive test would require experiments that would enable us to study the infiltration of T cells in a time-dependent manner or alternatively perturb possible mechanisms with drugs to directly test their effects on the infiltration pattern of T cells.

Citation Format: Tina Gruosso, Morag Park, Herbert Levine, Xuefei Li. Mathematical modeling studies on spatial profiles of tumor-infiltrating T cells [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B65.

KIBRA (WWC1) Is a Metastasis Suppressor Gene Affected by Chromosome 5q Loss in Triple-Negative Breast Cancer

Triple-negative breast cancers (TNBCs) display a complex spectrum of mutations and chromosomal aberrations. Chromosome 5q (5q) loss is detected in up to 70% of TNBCs, but little is known regarding the genetic drivers associated with this event. Here, we show somatic deletion of a region syntenic with human 5q33.2–35.3 in a mouse model of TNBC. Mechanistically, we identify KIBRA as a major factor contributing to the effects of 5q loss on tumor growth and metastatic progression. Re-expression of KIBRA impairs metastasis in vivo and inhibits tumorsphere formation by TNBC cells in vitro. KIBRA functions co-operatively with the protein tyrosine phosphatase PTPN14 to trigger mechanotransduction-regulated signals that inhibit the nuclear localization of oncogenic transcriptional co-activators YAP/TAZ. Our results argue that the selective advantage produced by 5q loss involves reduced dosage of KIBRA, promoting oncogenic functioning of YAP/TAZ in TNBC.

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Reduced KIBRA expression is associated with chr 5q loss in breast cancer

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Restoring Kibra expression inhibits metastatic dissemination in mice

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KIBRA impairs the self-renewal capacity of triple-negative breast cancer cells

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KIBRA blocks mechanotransduction signals required for YAP/TAZ activation

Spatially distinct tumor immune microenvironments stratify triple-negative breast cancers

Understanding the tumor immune microenvironment (TIME) promises to be key for optimal cancer therapy, especially in triple-negative breast cancer (TNBC). Integrating spatial resolution of immune cells with laser capture microdissection gene expression profiles, we defined distinct TIME stratification in TNBC, with implications for current therapies including immune checkpoint blockade. TNBCs with an immunoreactive microenvironment exhibited tumoral infiltration of granzyme B+CD8+ T cells (GzmB+CD8+ T cells), a type 1 IFN signature, and elevated expression of multiple immune inhibitory molecules including indoleamine 2,3-dioxygenase (IDO) and programmed cell death ligand 1 (PD-L1), and resulted in good outcomes. An "immune-cold" microenvironment with an absence of tumoral CD8+ T cells was defined by elevated expression of the immunosuppressive marker B7-H4, signatures of fibrotic stroma, and poor outcomes. A distinct poor-outcome immunomodulatory microenvironment, hitherto poorly characterized, exhibited stromal restriction of CD8+ T cells, stromal expression of PD-L1, and enrichment for signatures of cholesterol biosynthesis. Metasignatures defining these TIME subtypes allowed us to stratify TNBCs, predict outcomes, and identify potential therapeutic targets for TNBC.

Abstract P4-06-03: Unravelling triple-negative breast cancer tumor microenvironment heterogeneity using an integrative multiomic analysis

Introduction: Triple negative breast cancer (TNBC) constitute 10-20% of all breast cancers and is associated with a worse prognosis and limited treatment options. Recent trials evaluating immune checkpoint blockade in TNBC demonstrated encouraging results for a subset of patients. TNBC is highly heterogeneous and its tumour microenvironment (TME) has been recognized as a critical determinant of its behavior and clinical outcome. Genome-wide gene expression profiling analyses have already improved our understanding of the complexity of this disease and have defined 6 different molecular subtypes namely Basal-like 1 (BL1), basal-like 2 (BL2), immunomodulatory (IM), mesenchymal (M), mesenchymal stem-like (MSL) and luminal androgen receptor (LAR), exhibiting distinct biological and clinical characteristic.

In this study, we aim to dissect the molecular diversity of the TME and more specifically to assess the immune landscape according to TNBC molecular subtypes.

Methods: A cohort of 485 TNBC patient with publicly available data (RNA-Seq and Illumina HT-12 v3) from the METABRIC and the TCGA consortia were used in the gene expression analysis. Gene signatures reflecting different features or cellular components (immune, stromal, angiogenesis, lymphangiogenesis, hypoxia, metabolism) of the TME were used to evaluate multiple biological processes known to contribute to tumorogenesis. A compendium of 17 immune specific gene signatures and T cell localisation classification were used to evaluate the immune composition and spatial pattern of immune infiltrates. All parameters were compared using a logistic regression model to evaluate their relative contribution according to each molecular subtype.

Results: Our analyses demonstrated that each molecular subtype exhibits different TME profiles, as well as specific immune composition and localisation. IM tumors were associated with the highest expression of immune-related gene signatures, enriched with adaptive immune cells and with a fully inflamed spatial pattern. MSL tumors were mostly associated with the expression of Lymphangiogenesis and Stromal TME signatures. They also exhibited some immune activity through the expression of immune gene signatures capturing innate immune and adaptive immunosuppressive cells. This subtype was mainly associated with margin restricted and to some extent with fully inflamed spatial pattern. BL1 tumors were associated with the expression of Metabolism TME signatures, along with fully inflamed and stroma restricted spatial pattern. To a lesser extent, this subtype was also associated with activated DC and CD4 Tem cells. LAR and M tumors exhibited an immune cold phenotype. They were associated with Stromal and Metabolism TME signatures, enriched in margin restricted spatial pattern and negatively associated with every immune cells.

Conclusions: Our results demonstrate for the first time the huge heterogeneity that characterizes the TME of TNBCs. Identification of specific TME profiles could help to design more rationale and appropriate synergistic therapeutic combinations targeting TME elements in this high-risk disease.

Citation Format: Bareche Y, Buisseret L, Gruosso T, Girard E, Venet D, Dupont F, Desmedt C, Park M, Rothé F, Stagg J, Sotiriou C. Unravelling triple-negative breast cancer tumor microenvironment heterogeneity using an integrative multiomic analysis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-06-03.

Inhibition of the Stromal p38MAPK/MK2 Pathway Limits Breast Cancer Metastases and Chemotherapy-Induced Bone Loss

The role of the stromal compartment in tumor progression is best illustrated in breast cancer bone metastases, where the stromal compartment supports tumor growth, albeit through poorly defined mechanisms. p38MAPKα is frequently expressed in tumor cells and surrounding stromal cells, and its expression levels correlate with poor prognosis. This observation led us to investigate whether inhibition of p38MAPKα could reduce breast cancer metastases in a clinically relevant model. Orally administered, small-molecule inhibitors of p38MAPKα or its downstream kinase MK2 each limited outgrowth of metastatic breast cancer cells in the bone and visceral organs. This effect was primarily mediated by inhibition of the p38MAPKα pathway within the stromal compartment. Beyond effectively limiting metastatic tumor growth, these inhibitors reduced tumor-associated and chemotherapy-induced bone loss, which is a devastating comorbidity that drastically affects quality of life for patients with cancer. These data underscore the vital role played by stromal-derived factors in tumor progression and identify the p38MAPK-MK2 pathway as a promising therapeutic target for metastatic disease and prevention of tumor-induced bone loss.Significance: Pharmacologically targeting the stromal p38MAPK-MK2 pathway limits metastatic breast cancer growth, preserves bone quality, and extends survival. Cancer Res; 78(19); 5618-30. ©2018 AACR.

CrosstalkNet: A Visualization Tool for Differential Co-expression Networks and Communities

Variations in physiological conditions can rewire molecular interactions between biological compartments, which can yield novel insights into gain or loss of interactions specific to perturbations of interest. Networks are a promising tool to elucidate intercellular interactions, yet exploration of these large-scale networks remains a challenge due to their high dimensionality. To retrieve and mine interactions, we developed CrosstalkNet, a user friendly, web-based network visualization tool that provides a statistical framework to infer condition-specific interactions coupled with a community detection algorithm for bipartite graphs to identify significantly dense subnetworks. As a case study, we used CrosstalkNet to mine a set of 54 and 22 gene-expression profiles from breast tumor and normal samples, respectively, with epithelial and stromal compartments extracted via laser microdissection. We show how CrosstalkNet can be used to explore large-scale co-expression networks and to obtain insights into the biological processes that govern cross-talk between different tumor compartments.Significance: This web application enables researchers to mine complex networks and to decipher novel biological processes in tumor epithelial-stroma cross-talk as well as in other studies of intercompartmental interactions. Cancer Res; 78(8); 2140-3. ©2018 AACR.

Abstract PD6-05: Distinct tumor microenvironments stratify triple negative breast cancer into immune subtypes

Background:

Triple negative breast cancer (TNBC) are especially difficult to treat effectively. While only 20-30% of TNBC patients respond to chemotherapy in the neoadjuvant setting, overall outcome remains poor for non-responding patients. Engaging the immune system promises optimal personalized cancer therapy as mounting evidence suggests that immune-checkpoint inhibitor immunotherapies may become a therapeutic option for TNBC patients. The presence of CD8+ T cells, a crucial component of the cytotoxic arm of the adaptive immune response, is associated with good clinical outcome in TNBC patients. Specifically, it is the efficient CD8+ T cell invasion and infiltration in the tumor that is associated with good outcome. On the other hand, some tumors accumulate CD8+ T cells in the tumor-associated stroma with poor infiltration in the tumor epithelium. These patients show poor outcome. As CD8+ T cell infiltration in the tumor is a crucial step to mount an efficient anti-tumor response, we thus wondered how the tumor microenvironment affects CD8+ T cell invasion into the tumor epithelial compartment of the TNBC tumors.

Methods:

To identify potential stroma-dependent mechanisms that potentiate or inhibit CD8+ T cells invasion into the tumor epithelium, we coupled analysis of spatial patterns of CD8+ T cell localization by Immunohistochemistry (IHC) andperformed gene expression profiling of laser-capture microdissected tumor-associated stroma (as well as matched epithelium and bulk tumor) from 38 TNBC chemotherapy-naive primary cases. GSEA-based Metasignatures were derived from bulk tumor gene expression data from our cohort. To investigate the compartment of origin of the pathways identified via the Metasignatures, the (LCM)-derived tumor stromal and epithelial gene expression were analyzed.

Results:

CD8+ T cell quantification in different compartments of the tumor identify 3 main subgroups of TNBC based on CD8+ T cell localization. Importantly we developed a 2-step classification scheme based on CD8+ T cell localization. We developed metasignatures following our 2 steps classification and identified key bulk tumor metasignatures that showed prognostic value in an independent cohort. In addition the matched LCM gene expression from the tumor epithelium and stromal compartments allowed us to identify the compartment of origin.

Importantly, while 1 group of TNBC tumor was showing a significant anti-tumor response, the 2 other groups showed absence of such environment. The 2 non inflamed immune subtypes showed distinct phenotypes and biologies associated with poor anti-tumor response that we validated by immunohistochemistry and fluorescence. These results highlight different potential mecanisms that lead to immune evasion and allow us to stratify TNBC into immune subgroups.

Citation Format: Gruosso T, Gigoux M, Bertos N, Manem VS, Zuo D, Saleg SM, Souleimanova M, Zhao H, Johnson RM, Monette A, Muñoz Ramos V, Hallett MT, Stagg J, Lapointe R, Omeroglu A, Meterissian S, Buisseret L, Van den Eyden G, Salgado R, Guiot M-C, Haibe-Kains B, Park M. Distinct tumor microenvironments stratify triple negative breast cancer into immune subtypes [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD6-05.

Identification of Interacting Stromal Axes in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a molecularly heterogeneous cancer that is difficult to treat. Despite the role it may play in tumor progression and response to therapy, microenvironmental (stromal) heterogeneity in TNBC has not been well characterized. To address this challenge, we investigated the transcriptome of tumor-associated stroma isolated from TNBC (n = 57). We identified four stromal axes enriched for T cells (T), B cells (B), epithelial markers (E), or desmoplasia (D). Our analysis method (STROMA4) assigns a score along each stromal axis for each patient and then combined the axis scores to subtype patients. Analysis of these subtypes revealed that prognostic capacity of the B, T, and E scores was governed by the D score. When compared with a previously published TNBC subtyping scheme, the STROMA4 method better captured tumor heterogeneity and predicted patient benefit from therapy with increased sensitivity. This approach produces a simple ontology that captures TNBC heterogeneity and informs how tumor-associated properties interact to affect prognosis. Cancer Res; 77(17); 4673-83. ©2017 AACR.

Abstract P4-03-08: Mechanisms of CD8+ T cell immunosuppression in triple negative breast cancer

Triple negative breast cancer (TNBC), defined as tumors lacking expression of the estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), are especially difficult to treat effectively. While ER+ and HER2+ breast cancer subtypes can be treated with Tamoxifen and Herceptin, respectively, there are no targeted therapies for TNBC patients. Furthermore, while only 20-30% of TNBC patients respond to chemotherapy in the neoadjuvant setting, overall outcome remains poor for non-responding patients. However, mounting evidence suggests that immune-checkpoint inhibitor immunotherapies may be especially promising for TNBC patients. We and others have shown that the presence of CD8+ T cells, a crucial component of the cytotoxic arm of the adaptive immune response, is a sign of good clinical outcome in TNBC patients. However, good outcome only correlates with CD8 +T cell invasion of the tumor parenchyma. Some patients had an accumulation of CD8+ T cells in the surrounding tumor-associated stroma, but not the tumor epithelia, and these patients responded as poorly as patients with no CD8 T cells at all. Yet how cancer associated fibroblasts (CAFs), the dominant cell type of the tumor-associated stroma, affects CD8+ T cell invasion into the tumor epithelia is still poorly understood. To identify potential stroma-dependent mechanisms which potentiate or inhibit CD8+ T cells invasion into the tumor epithelia, we performed gene expression profiling of laser-capture microdissected tumor-associated stroma (and matched epithelia) from 38 TNBC cases. Here we identify several stromal and epithelial canonical pathways as well as biomarkers that are associated with and may explain the accumulation of CD8 T cells outside of the tumor epithelia.

Citation Format: Gruosso T, Gigoux M, Bertos N, Zuo D, Manem V, Monette A, Lapointe R, Haibe-Kains B, Park M. Mechanisms of CD8+ T cell immunosuppression in triple negative breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-03-08.

Abstract IA23: Deconvolution of the triple-negative breast cancer microenvironment

Breast cancer heterogeneity is one of the principal obstacles both to predicting outcome and to determining an effective course of treatment for this disease. Although genomic technologies have been used to gain a better understanding, by identifying gene expression signatures associated with clinical outcome and breast cancer subtypes, relatively little is known about heterogeneity in the tumor microenvironment. It is now accepted that changes in the normal cells that constitute the tumor microenvironment (TME) play important roles in determining cancer progression and ultimate outcome. We and others have established that an immune gene expression signature correlates with good outcome in triple negative breast cancer (TNBC), yet fails to accurately predict outcome in all patients. Examining stromal heterogeneity in TNBC has identified four distinct stromal clusters, three of which are prognostic, contain distinct immune signatures and a signature of fibrosis. Lymphocytic infiltration and access to tumor parenchyma is not well understood due to high levels of spatial heterogeneity within tumors. We show that location of CD8+T cells is strongly influenced by TME subtypes and identify gene expression signatures predictive of distinct CD8+T cell localization and patient outcome. Since mounting evidence suggests that immune-checkpoint inhibitor immunotherapies may be promising for only a subset of TNBC patients, highlights the importance of understanding how the TME influences CD8+T cell location.

Citation Format: Sadiq Saleh, Tina Gruosso, Mathieu Gigoux, Nicholas Bertos, Atilla Omeroglu, Dongmei Zuo, Sarkis Meterissian, Michael Hallett, Morag Park. Deconvolution of the triple-negative breast cancer microenvironment. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr IA23.

Abstract A15: Mechanisms of CD8+ T cell immunosuppression in triple negative breast cancer

Triple negative breast cancer (TNBC), defined as tumors lacking expression of the estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), are especially difficult to treat effectively. While ER+ and HER2+ breast cancer subtypes can be treated with Tamoxifen and Herceptin, respectively, there are no targeted therapies for TNBC patients. Furthermore, while only 20-30% of TNBC patients respond to chemotherapy in the neoadjuvant setting, overall outcome remains poor for non-responding patients. However, mounting evidence suggests that immune-checkpoint inhibitor immunotherapies may be especially promising for TNBC patients. We and others have shown that the presence of CD8+ T cells, a crucial component of the cytotoxic arm of the adaptive immune response, is a sign of good clinical outcome in TNBC patients. However, good outcome only correlates with CD8+ T cell invasion of the tumor parenchyma. Here we show that some patients have an accumulation of CD8+ T cells in the surrounding tumor-associated stroma, but not the tumor epithelium, and these patients responded as poorly as patients with no CD8+ T cells at all. Yet how cancer associated fibroblasts (CAFs), a dominant cell type of the tumor-associated stroma, affects CD8+ T cell invasion into the tumor epithelium is still poorly understood.

To identify potential stroma-dependent mechanisms that potentiate or inhibit CD8+ T cells invasion into the tumor epithelium, we performed gene expression profiling of laser-capture microdissected tumor-associated stroma (and matched epithelium) from 56 TNBC cases. Here we identify several key stromal features that may explain the accumulation of CD8+ T cells outside of the tumor epithelium. Preliminary data by immunohistochemistry and immunofluorescence validate some key stromal features and decipher the implication of other immune cell types in CD8+ T cells lack of tumor epithelium infiltration. These key stromal features that impair CD8+ T cell infiltration into the tumor in some patients might explain the relative low efficiency of immunotherapies in TNBC patients (20% of patients respond). One could speculate that targeting these key stromal features would allow a significant CD8+ T cell infiltration into the tumor and thus sensitize patients to immunotherapies.

Citation Format: Tina Gruosso, Mathieu Gigoux, Nicholas Bertos, Sadiq Saleh, Atilla Omeroglu, Dongmei Zuo, Hong Zhao, Margarita Souleimanova, Valerie Weaver, Sarkis Meterissian, Michael Hallett, Morag Park. Mechanisms of CD8+ T cell immunosuppression in triple negative breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A15.

Abstract 720: Novel prognostic stromal subtypes in triple-negative breast cancer

Breast cancer is a heterogeneous disease in terms of presentation, morphology, molecular profile and response to therapy. Gene expression profiling has identified intrinsic molecular subtypes that are associated with clinical markers (ER, PR, HER2) as well as prognosis and survival. However, it is well established that the intrinsic molecular profiles of breast tumors are not sufficient to perfectly predict disease outcome. Increasing evidence indicates that characteristics of the breast stroma influence tumor progression and response to therapy. Previous work in our lab has demonstrated that gene expression signatures in human stroma can predict outcome of breast cancer patients independently of clinical parameters and molecular subtypes. In this study, we expand our findings by focusing on a previously underrepresented subset of breast tumors that have no detectable ER, PR or HER2 (termed Triple-Negative, TN). TN tumors, which represent approximately 15% of all breast cancers, are typically associated with poor outcome. However, the contribution of the stroma to the underlying heterogeneity of TN breast cancer and its corresponding influence on therapeutic response is not well understood. To address this, we isolated TN tumor epithelial and stromal tissues by laser capture microdissection and subjected them to gene expression profiling. Class discovery revealed distinct gene-clusters (stromal properties) which are associated with prognosis in TNBC whole tumor samples. Analysis of the genes comprising each stromal property suggests that the properties primarily represent the prevalence of distinct cell types, namely T cells, B cells, activated fibroblasts, and myoepithelial cells. Importantly, these properties are not mutually exclusive, i.e. some tumors are associated with multiple stromal properties. While confirming the heterogeneity of TN-associated stroma, this also indicates that a multi-parameter classification better reflects the true nature of the tumor microenvironment. This project provides the first integrated in-depth analysis of the contribution of tumor stromal processes to TN disease heterogeneity, and positions the tumor microenvironment for therapeutic intervention.

Citation Format: Crista Thompson, Sadiq M. Saleh, Nicholas Bertos, Mathieu Gigoux, Tina Gruosso, Margarita Souleimanova, Hong Zhao, Michael T. Hallett, Morag Park. Novel prognostic stromal subtypes in 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 720.

Chronic oxidative stress promotes H2AX protein degradation and enhances chemosensitivity in breast cancer patients

Anti‐cancer drugs often increase reactive oxygen species (ROS) and cause DNA damage. Here, we highlight a new cross talk between chronic oxidative stress and the histone variant H2AX, a key player in DNA repair. We observe that persistent accumulation of ROS, due to a deficient JunD‐/Nrf2‐antioxidant response, reduces H2AX protein levels. This effect is mediated by an enhanced interaction of H2AX with the E3 ubiquitin ligase RNF168, which is associated with H2AX poly‐ubiquitination and promotes its degradation by the proteasome. ROS‐mediated H2AX decrease plays a crucial role in chemosensitivity. Indeed, cycles of chemotherapy that sustainably increase ROS reduce H2AX protein levels in Triple‐Negative breast cancer (TNBC) patients. H2AX decrease by such treatment is associated with an impaired NRF2‐antioxidant response and is indicative of the therapeutic efficiency and survival of TNBC patients. Thus, our data describe a novel ROS‐mediated regulation of H2AX turnover, which provides new insights into genetic instability and treatment efficacy in TNBC patients.

MAP3K8/TPL-2/COT is a potential predictive marker for MEK inhibitor treatment in high-grade serous ovarian carcinomas

Ovarian cancer is a silent disease with a poor prognosis that urgently requires new therapeutic strategies. In low-grade ovarian tumours, mutations in the MAP3K BRAF gene constitutively activate the downstream kinase MEK. Here we demonstrate that an additional MAP3K, MAP3K8 (TPL-2/COT), accumulates in high-grade serous ovarian carcinomas (HGSCs) and is a potential prognostic marker for these tumours. By combining analyses on HGSC patient cohorts, ovarian cancer cells and patient-derived xenografts, we demonstrate that MAP3K8 controls cancer cell proliferation and migration by regulating key players in G1/S transition and adhesion dynamics. In addition, we show that the MEK pathway is the main pathway involved in mediating MAP3K8 function, and that MAP3K8 exhibits a reliable predictive value for the effectiveness of MEK inhibitor treatment. Our data highlight key roles for MAP3K8 in HGSC and indicate that MEK inhibitors could be a useful treatment strategy, in combination with conventional chemotherapy, for this disease.

Abstract A69: The immunological environment in triple negative breast cancer; impact on clinical outcomes towards a prognostic clinical test

It is now accepted that changes in the normal cells that constitute the tumor microenvironment (TME) play important roles in determining cancer progression and ultimate outcome. We and others have established that an immune signature, and more recently that the ability of CD8+ T cells to infiltrate the tumor bed, are correlated with good outcome in triple negative breast cancer. Importantly, since the cytotoxic effector functions of CD8+ T cells are mainly contact-dependent, the tumor microenvironment may act to inhibit access to the epithelial tumor bed, leading to uncontrolled tumor growth. Therefore, in order to determine the role that the TME plays on mediating the entry of CD8+ T cells into the epithelial tumor bed, our group performed laser-capture microdissection to separate the tumor epithelial compartment from the surrounding tumor-associated stroma from the primary tumor of 56 triple negative breast cancer patients and followed by gene expression profiling. Our aims are to provide clinical validation of predicted CD8+ T cell localisation based on our bioinformatic analysis, test our predictions that the identified stroma signature correlates with CD8+ T cell retention in other cohort of TN breast cancer patients and develop suitable markers of this stroma, and develop a muliplex based assay integrating CD8+ T cell localisation with stromal markers suitable for a retrospective study to validate predictions with outcome. Using gene expression profiling, our data have identified a canonical gene expression signature which correlates with retention of CD8+ T cells in the stroma and poor outcome. Thus, our results demonstrate that gene expression analysis of clinical triple negative breast cancer samples can predict the location of CD8+ T cells within the tumor and in turn the outcome.

Citation Format: Mathieu Gigoux, Tina Gruosso, Nicholas Bertos, Sadiq Saleh, Atilla Omeroglu, Hong Zhao, Margarita Souleimanova, Sarkis Meterissian, Michael Hallett, Morag Park. The immunological environment in triple negative breast cancer; impact on clinical outcomes towards a prognostic clinical test. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr A69.

Abstract LB-200: Loss of the scaffold protein Kibra in a mouse model of triple-negative breast cancer

Introduction: Targeted therapies in breast cancer rely on tumor cell expression of Estrogen and/or HER2 receptors. Triple negative breast cancers (TNBCs), lacking these receptors, have no targeted therapies. We have developed a preclinical murine model expressing a naturally occurring oncogenic variant of the Met receptor in the mammary gland combined with loss of function of the tumour suppressor p53 (MMTV-Met;Trp53fl/+;Cre). This model recapitulates many features of TNBC at the level of gene expression, pathological markers and genomic alterations. Notably, this model spontaneously undergoes loss of a genomic region syntenic with human chromosome 5q which is lost in up to 70% of human TNBCs (Turner et al., 2010). This provides an opportunity for us to identify and study potential driver genes for this breast cancer subtype.

Experimental procedures: Approximately 80% of MMTV-Met;Trp53fl/+;Cre mammary tumors have a mesenchymal pathology that recapitulates key features of TNBC. Array CGH profiling showed a consistent loss of chromosome 11:31.35-58.2Mb, syntenic with human 5q31.1 and 5q33.1-35.3. Analysis of mouse model expression profiling data confirmed decreased expression of 83 genes within this region. Comparison with human breast cancers within the TCGA dataset further highlighted 14 of these genes with significantly decreased expression in humans with the TNBC subtypes ‘Basal’ and ‘Claudin-low’. One of these genes, WWC1, undergoes heterozygous deletion in 49% of human Basal breast cancers (TCGA, Nature 2012) and has also been associated with Claudin-low cancers (Moleirinho et al., 2013). WWC1, also known as Kibra, encodes a scaffold protein that positively regulates the Hippo tumor suppressor pathway. We used both Kibra knockdown and over-expression to understand the functional consequences of Kibra-loss.

Results: MMTV-Met solid carcinoma cells retain both Kibra expression and epithelial characteristics typical of human luminal breast cancers (Ponzo et al., 2009). Kibra depletion by siRNA in these cells led to weakening of cell-cell junctions and colony dispersal, as well as decreased cortical actin and increased membrane protrusions, consistent with epithelial-to-mesenchymal transition (EMT). Mice injected with Kibra shRNA-tumor cells developed secondary lesions at sites distant to the mammary gland. By comparison, re-expression of Kibra in MMTV-Met;Trp53fl/+ cell lines and human TNBC cells led to morphological changes consistent with an EMT reversal, including loss of actin rich protrusions. Furthermore, re-expressing Kibra impaired proliferation in vitro and decreased tumorigenicity in vivo. Globally, our results strongly suggest that Kibra loss plays a significant role in TNBC development and metastasis and is a candidate driver gene for Chr5q loss.

Citation Format: Jennifer France Knight, Tina Gruosso, Danielle Angeline de Verteuil, Sadiq Saleh, Robert Lesurf, Hong Zhao, Ryan Davis, Dongmei Zuo, Robert Cardiff, Jeffrey Gregg, Michael Hallett, Morag Park. Loss of the scaffold protein Kibra in a mouse model of triple-negative breast cancer. [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 LB-200. doi:10.1158/1538-7445.AM2015-LB-200

Ovarian cancer emerging subtypes: role of oxidative stress and fibrosis in tumour development and response to treatment

Epithelial ovarian cancer is a silent disease of usually late diagnosis and poor prognosis. Currently treatment options are limited and mainly consist of surgery followed by taxol- and platinum-based chemotherapy. Patient response to treatment is difficult to predict and there is a serious need for anticipating tumour response and orientating medical choices. In that aim, recent researches have focused on molecular aspects of ovarian tumours that could help patient stratification. We review here published discoveries in that field. We emphasize that signatures, defined by combining miRNA and transcriptomic data, enlighten important aspects of ovarian cancer biology and reliably stratify patients. The miR-200-dependent "Oxidative stress" and "Fibrosis" signatures are promising in patient stratification for defining oriented therapeutic strategies. Indeed, the "Stress" patients survive longer than the "Fibrosis" patients, who exhibit partial debulking and incomplete response to chemotherapy. Interestingly, these two subgroups might benefit from specifically targeted therapeutic approaches, as discussed here.