Ripretinib versus sunitinib in gastrointestinal stromal tumor: ctDNA biomarker analysis of the phase 3 INTRIGUE trial

INTRIGUE was an open-label, phase 3 study in adult patients with advanced gastrointestinal stromal tumor who had disease progression on or intolerance to imatinib and who were randomized to once-daily ripretinib 150 mg or sunitinib 50 mg. In the primary analysis, progression-free survival (PFS) with ripretinib was not superior to sunitinib. In clinical and nonclinical studies, ripretinib and sunitinib have demonstrated differential activity based on the exon location of KIT mutations. Therefore, we hypothesized that mutational analysis using circulating tumor DNA (ctDNA) might provide further insight. In this exploratory analysis (N = 362), baseline peripheral whole blood was analyzed by a 74-gene ctDNA next-generation sequencing-based assay. ctDNA was detected in 280/362 (77%) samples with KIT mutations in 213/362 patients (59%). Imatinib-resistant mutations were found in the KIT ATP-binding pocket (exons 13/14) and activation loop (exons 17/18). Mutational subgroup assessment showed 2 mutually exclusive populations with differential treatment effects. Patients with only KIT exon 11 + 13/14 mutations (ripretinib, n = 21; sunitinib, n = 20) had better PFS with sunitinib versus ripretinib (median, 15.0 versus 4.0 months). Patients with only KIT exon 11 + 17/18 mutations (ripretinib, n = 27; sunitinib, n = 25) had better PFS with ripretinib versus sunitinib (median, 14.2 versus 1.5 months). The results of this exploratory analysis suggest ctDNA sequencing may improve the prediction of the efficacy of single-drug therapies and support further evaluation of ripretinib in patients with KIT exon 11 + 17/18 mutations. ClinicalTrials.gov identifier: NCT03673501.

Mutational heterogeneity of imatinib resistance and efficacy of ripretinib vs sunitinib in patients with gastrointestinal stromal tumor: ctDNA analysis from INTRIGUE

397784

Background: Ripretinib, a switch-control tyrosine kinase inhibitor (TKI), is indicated for patients (pts) with gastrointestinal stromal tumor (GIST) who received prior treatment with ≥3 TKIs, including imatinib. Sunitinib is approved for advanced GIST after imatinib failure. Circulating tumor DNA (ctDNA) analysis may provide insight into the efficacy of these agents in second-line advanced GIST. Here, we present exploratory baseline ctDNA results from INTRIGUE. Methods: INTRIGUE is an open-label, phase 3 study that enrolled adult pts with advanced GIST who progressed on or had intolerance to imatinib (NCT03673501). Randomization was 1:1 to ripretinib 150 mg once daily (QD) or sunitinib 50 mg QD (4 wks on/2 wks off). Baseline peripheral whole blood was analyzed by Guardant360, a 74-gene ctDNA next-generation sequencing (NGS)-based assay. Only KIT mutations are reported here. Results: Of 453 pts in the overall intent-to-treat (ITT) population, 362 (80%) samples were analyzed. ctDNA was detected in 280/362 (77%), with KIT mutations detected in 213/280 (76%). Common resistance mutations were in the KIT activation loop (AL; exons 17/18; 89/213, 42%) and ATP-binding pocket (ATP-BP; exons 13/14; 81/213, 38%). Efficacy in pts with detectable ctDNA in the KIT exon 11 and overall ITT populations was consistent with the primary analysis based on tumor data used for randomization. Pts with KIT exon 11 + 17/18 (−9/13/14) mutations had superior progression-free survival (PFS), objective response rate (ORR), and overall survival (OS) with ripretinib vs sunitinib, whereas pts with exon 11 + 13/14 (−9/17/18) mutations had better PFS, ORR, and OS with sunitinib vs ripretinib (Table). Subgroup safety profiles were consistent with the primary analysis. Conclusions: While KIT ATP-BP mutations predicted clinical benefit from sunitinib vs ripretinib, pts harboring resistance mutations in the KIT AL derived meaningful clinical benefit from ripretinib but not sunitinib. This study demonstrates the value of ctDNA NGS-based sequencing of the complex landscape of KIT mutations to predict the clinical benefit of ripretinib or sunitinib as second-line therapy in pts with advanced GIST. Clinical trial information: NCT03673501 . [Table: see text]

Characterization and Validation of Antibodies for Immunohistochemical Staining of the Chemokine CXCL12

Chemokines and their receptors have been implicated in cancer biology. The CXCL12/CXCR4 axis is essential for the homing and retention of hematopoietic stem cells in bone marrow niches, and has a significant role in neonatal development. It is also implicated in multiple facets of cancer biology including metastasis, angiogenesis/neo-vasculogenesis, and immune cell trafficking at the tumor microenvironment (TME). Immunohistochemistry (IHC) is an ideal method for investigating involvement of CXCL12 in the TME. Three antibodies were evaluated here for their suitability to stain CXCL12. Both D8G6H and K15C gave apparent specific staining in both lymphoid and tumor tissue, but with converse staining patterns. D8G6H stained cells in the parafollicular zone whereas K15C showed staining of lymphoid cells in the interfollicular zone of tonsil tissue. Using a cell line with high CXCL12 expression, TOV21G, as a positive control, it was found that D8G6H gave strong staining of TOV21G cells whereas no staining was observed with K15C indicating that D8G6H specifically stains CXCL12. Significant staining of CXCL12 in the ovarian TME using tissue microarray was observed using D8G6H. These data demonstrate the importance of antibody characterization for IHC applications, and provide further evidence for the involvement of CXCL12 in ovarian cancer biology.

Effect of FAK inhibitor defactinib on tumor immune changes and tumor reductions in a phase II window of opportunity study in malignant pleural mesothelioma (MPM)

8555

Background: Defactinib is an oral Focal Adhesion Kinase (FAK) inhibitor with preclinical activity in MPM. We assessed responses to defactinib treatment prior to planned surgical resection in naive patients with MPM. Methods: Three cohorts of 10 participants each received defactinib 400mg BID for 12, 35 and 21 days. Pre- and post-treatment blood, tumor biopsies and imaging were obtained for biomarker, immune cell and tumor response (modified RECIST, Tumor volume and SUV max) assessment. Toxicity was monitored for 30 days post treatment. Results: Between 12/2013 and 12/2017, 31 participants were registered at our center; 1 withdrew prior to intervention. Among 30 treated, 24 (80%) were male; median age 70 (47-83) years; surgery was EPP 7%, complete pleurectomy decortication (PD) 10%, extended PD 60%, partial PD 10%, unresectable 13%; MPM subtype was epithelioid 67%, biphasic 17%, sarcomatoid 17%. Expected complications of FAK inhibition, diagnostic/staging/operative procedures occurred in 83% (grade 1, 30%; grade 2, 43%; grade 3, 10%). Unexpected adverse events occurred in 77% (grade 1, 63%; grade 2, 20%; grade 3, 17% [wound-infection, prolonged QT interval, and hyperglycemia in 3% each; increased INR in 7%]; grade 5, 7% [due to progressive disease in 3%, intraoperative anaphylactoid reaction unrelated to the drug in 3%]). Objective partial response was observed in 13%, stable disease in 67%, progression in 17%. Tumor volume decreased 3-72% in 47% patients and increased 1-82% in 53%. SUV max decreased 3-69% in 50% and increased 1-61% in 50%. Biological correlates of treatment included target inhibition (75% pFAK reduction); tumor immune microenvironment changes: increased naïve (CD45RA+PD-1+CD69+) CD4 and CD8 T cells, reduced myeloid and Treg immuno-suppressive cells, reduced exhausted T cells (PD-1+CD69+), reduced peripheral MDSCs; and histological subtype change (pleomorphic or biphasic to epithelioid) in 13% of cases. Conclusions: Brief preoperative defactinib exposure was well tolerated, did not alter resectability or mortality compared to prior series, and showed evidence of therapeutic and immunomodulatory effects. Clinical trial information: NCT02004028.

Abstract 568: FAK/PYK2 inhibition enhances immune checkpoint inhibitor efficacy

Although durable responses to single agent immune checkpoint inhibitors have been reported, additional approaches are needed to improve upon this therapeutic benefit. Combinations of immunotherapy agents with tumor microenvironment modulators have the potential to overcome barriers that tumor cells develop to evade the immune system, and provide benefit to a greater proportion of patients. Focal Adhesion Kinase (FAK) and its family member, PYK2, are potentially valuable targets due to their roles in regulating key cellular populations in the tumor microenvironment. In addition to targeting cancer stem cells, the FAK/PYK2 dual inhibitors, VS-6063 and VS-4718, have been shown to inhibit monocyte-derived macrophages, reduce tumor-associated macrophages in xenograft models, and promote a CD8+ T cell-mediated anti-tumor response in squamous cell carcinoma models.

We now report that the combination of VS-4718 with an anti-PD-1 mAb shows improved efficacy over anti-PD-1 mAb alone and extends survival of MC38 syngeneic tumor bearing animals. Analysis of MC38 tumors at day 12 of treatment revealed a significant increase in the CD8+ T cells/Treg ratios in tumors in the VS-4718 + anti-PD-1 combination group, providing a mechanistic understanding for the enhanced efficacy of this combination.

To explore additional combination options, we tested the combination of VS-4718 with anti-4-1BB in the MC38 model. Consistent with what was observed with the anti-PD-1 combination, VS-4718 also enhanced the efficacy of an anti-4-1BB mAb.

To further delineate direct effect of FAK inhibition on human T cells, in vitro T cell proliferation assays were conducted. VS-6063 and VS-4718 dose-dependently stimulated proliferation of CD8+ cytotoxic T cells isolated from healthy donors. This is in distinct contrast to other protein kinase inhibitors, such as the SRC inhibitor dasatinib which impaired the proliferation of CD8+ cytotoxic T cells. In addition, both VS-4718 and VS-6063 decreased CD8+ T cell exhaustion markers, and increased T cell-mediated tumor cell killing in vitro.

These data provide a rationale for clinical trials in cancer patients to test whether a FAK/PYK2 inhibitor in combination with an immune checkpoint inhibitor could increase the breadth of responsive tumor types, increase the number of responders, and confer more durable anti-tumor responses.

Citation Format: Yan Wang, Jennifer E. Ring, Kam Sprott, David T. Weaver, Jonathan A. Pachter. FAK/PYK2 inhibition enhances immune checkpoint inhibitor efficacy. [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 568.

Abstract 974: FAK inhibitors VS-6063 and VS-4718 target cancer stem cells: Implications for TNBC sequential and combination therapies

Cancer stem cells (CSCs), a subpopulation of tumor cells characterized by tumor-initiating capability and resistance to chemotherapy, are an underlying cause of tumor progression and metastasis. In breast cancer, CSCs can be identified by aldehyde dehydrogenase 1 (ALDH) or CD44+/CD24- expression separately, although combination of ALDH, CD44+, and CD24- together may better describe the CSC population in breast cancer. Neoadjuvant chemotherapy has been shown to lead to an increase in CSCs in locally advanced breast cancer (Alamgeer et al., 2014, Br. Can. Res. 16:R14) which is associated with a significantly worse prognosis. It is also evident that stem-like features of tumor cells are present in metastatic breast cancer (Yu et al., 2013, Science 339:580) indicating that targeting of CSCs may be valuable in metastatic disease. VS-6063 and VS-4718 are orally bioavailable, potent and selective inhibitors of Focal Adhesion Kinase (FAK). These agents preferentially target CSCs in preclinical models and are currently in clinical development.

Here we report that VS-6063 and VS-4718 preferentially target CSCs in multiple breast cancer models. Ex vivo treatment of explants from human breast tumors with either VS-6063 or VS-4718 decreased the proportion of CSCs in contrast to paclitaxel treatment which increased the proportion of CSCs. In an MDA-MB-231 mouse xenograft model, in vivo treatment with VS-6063 decreased CSCs by more than 6-fold as demonstrated by limiting dilution transplantation assay. Consistent with the notion that CSCs are responsible for cancer relapse after chemotherapy, VS-6063 and VS-4718 substantially delayed tumor growth following cessation of paclitaxel or cisplatin treatment in models of TNBC, including a patient-derived xenograft. Furthermore, using an imaging-based 4T1-luciferase TNBC orthotopic model, both VS-6063 and VS-4718 inhibited metastatic outgrowth or induced regression of metastases after primary tumor resection, whereas metastases progressed in all animals in the vehicle control group.

A multiplex assay for multiple CSC markers (ALDH1, CD44 and CD24) was developed and validated in biopsies of primary patient tumors and matched lymph node biopsies taken pre- and post-neoadjuvant chemotherapy. CSCs, represented by the ALDH+ and/or CD44+/CD24- populations were present at detectable levels in a high fraction of triple negative breast cancer primary tumors.

In summary, CSCs are readily detectable in primary breast cancers at surgery, and VS-6063 and VS-4718 diminish the CSC subpopulation in vitro, ex vivo and in xenograft models. This critical subpopulation of CSCs is detectable in residual tumors after neoadjuvant therapy, and may also be present in metastatic disease. CSC-targeted agents such as VS-6063 or VS-4718 should be clinically tested in these breast cancer settings to potentially delay time to relapse and improve patient outcome.

Citation Format: Vihren N. Kolev, Kam Sprott, Qunli Xu, Jonathan A. Pachter, David T. Weaver. FAK inhibitors VS-6063 and VS-4718 target cancer stem cells: Implications for TNBC sequential and combination therapies. [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 974. doi:10.1158/1538-7445.AM2015-974

DNA repair biomarkers XPF and phospho-MAPKAP kinase 2 correlate with clinical outcome in advanced head and neck cancer

BACKGROUND

Induction chemotherapy is a common therapeutic option for patients with locoregionally-advanced head and neck cancer (HNC), but it remains unclear which patients will benefit. In this study, we searched for biomarkers predicting the response of patients with locoregionally-advanced HNC to induction chemotherapy by evaluating the expression pattern of DNA repair proteins.

METHODS

Expression of a panel of DNA-repair proteins in formalin-fixed paraffin embedded specimens from a cohort of 37 HNC patients undergoing platinum-based induction chemotherapy prior to definitive chemoradiation were analyzed using quantitative immunohistochemistry.

RESULTS

We found that XPF (an ERCC1 binding partner) and phospho-MAPKAP Kinase 2 (pMK2) are novel biomarkers for HNSCC patients undergoing platinum-based induction chemotherapy. Low XPF expression in HNSCC patients is associated with better response to induction chemoradiotherapy, while high XPF expression correlates with a worse response (p = 0.02). Furthermore, low pMK2 expression was found to correlate significantly with overall survival after induction plus chemoradiation therapy (p = 0.01), suggesting that pMK2 may relate to chemoradiation therapy.

CONCLUSIONS

We identified XPF and pMK2 as novel DNA-repair biomarkers for locoregionally-advanced HNC patients undergoing platinum-based induction chemotherapy prior to definitive chemoradiation. Our study provides insights for the use of DNA repair biomarkers in personalized diagnostics strategies. Further validation in a larger cohort is indicated.

Abstract 3507: Multiparameter CTC characterization using dual capture microfluidic chips

Circulating tumor cells (CTCs) have become increasingly acceptable as a prognostic marker in stratifying metastatic cancer patients for treatment and as a predictive marker in monitoring therapeutic response. CTC enumeration is an established prognostic marker (gold standard) in metastatic prostate, breast and colorectal cancer. However, due to the heterogeneity with respect to CTC phenotypic expression, epithelial-mesenchymal transition, and morphologic variability of different cancer cells, it is impossible to simply use the counts of well defined cells to characterize a wide spectrum of cancer status and progression. In addition, manual counting of CTCs also introduces operator bias on the size, shape and expression levels. We have developed an automated CTC characterization system that extracts enumeration, cell morphology and expression level of all intact, irregular and fragmented CTCs in an automatic fashion. A multiparameter classification model was then developed to characterize patient clinical outcome. Whole blood from advanced stage cancer patients and non-diseased controls was processed through anti-EpCAM antibody coated OnQChipsTM. Chips were imaged at low magnification on a fully calibrated rapid automated platform. Captured CTC candidate events were processed by an automated CTC detection algorithm using a set of spatial and spectral features to initially remove non-cellular events and then to indentify CTC subclasses. All CTC subclasses as well as artifact classes were manually labeled and verified at high magnification by trained imaging technologists. Manual labels were used to assess performance of the automated algorithms. A multivariate model based on CART (Classification and Regression Trees) was used for the classifier development. A total of 27 prostate cancer patients and 33 normal controls with 7.5mL blood samples per patient were used to develop and validate the initial techniques. The preliminary results show that the automated CTC event detection algorithm achieved a sensitivity of 96% and specificity of 89%. The CTC subclass classification algorithm achieved classification accuracy from 82% to 95% across all subclasses. The algorithms were N-fold cross-validated with 80/20 random sampling. The preliminary clinical model achieved sensitivity and specificity values of 90% and 82% respectively for patient vs. normal classification. A method for automated patient CTC classification and clinical model has been developed. The performance data from all classification algorithms is very encouraging. The multivariate patient model discriminates cancer patients from normal donor samples with high sensitivity and specificity. Future work includes incorporation of image-based features as well as clinical patient data into the model to improve sensitivity and specificity and address specific clinical needs.

Citation Format: Chunsheng Jiang, Oleg Gusyatin, David Tims, Aladin Milutinovic, Kam Sprott, Michael Stocum. Multiparameter CTC characterization using dual capture microfluidic chips. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3507. doi:10.1158/1538-7445.AM2013-3507

Abstract 5108: Capture and enumeration of mesenchymal CTCs on the OnQChip platform

Circulating tumor cells (CTCs) are cancer cells that disseminate from the primary tumor and enter the blood. While cells in the primary tumor are generally epithelial in nature, as they become migratory and invasive, changes such as loss of epithelial markers (ie: EpCAM and cytokeratin (CK)) and a switch to a mesenchymal phenotype (EMT) often occur. CTC platforms must be flexible in capturing and identifying cells, and not limited to the use of only epithelial markers. Dual modal capture on the OnQChip provides this flexibility, allowing for CTC isolation based on size and independent of surface marker expression in addition to specific antibody mediated capture targeting markers such as EpCAM. For cell lines ranging in EpCAM expression, the OnQChip captures 90% or greater of mid to high EpCAM expressing cells, and 79% or greater of very low EpCAM expressing cells. Due to the OnQChip's gradient design, distinct capture patterns related to EpCAM levels are observed, allowing for capture location to be informative about EpCAM expression. When Hs578T cells, a mesenchymal model with very little EpCAM and CK, are prestained around 79% of spiked cells are enumerated on the OnQChip, but when the same cells are not prestained and only CK staining is used, 0-2% of spiked cells are counted. When two new mesenchymal staining markers are incorporated alongside CK, 60-80% of spiked Hs578T cells are now enumerated, translating to a 75-100% staining efficiency of captured cells. Although very few cells are visualized with CK alone, pooling CK staining with mesenchymal staining shows increased staining intensity compared to mesenchymal staining alone, highlighting benefits of a multi-marker staining panel for visualizing cells with low expression of several different markers, likely the case for subpopulations of cells at different stages of the EMT. On a population of 44 prostate cancer samples, an increase of 28.5, 8.2, 12.7, and 7.6 in the mean number of total, intact, irregular, and fragmented CTCs, respectively, was observed with staining for CK plus the mesenchymal markers as compared to CK staining alone. Specifically, 70.5%, 18.2%, 50%, and 38.6% of patients showed an increase of 5 or more, and 40.9%, 9.1%, 31.8%, and 25% showed an increase of 10 or more, total, intact, irregular, and fragmented CTCs, respectively, when mesenchymal staining was included. Additionally, a few case studies from this population for which serial draws during treatment were obtained indicate changes in the ratio of CTCs enumerated with staining for CK plus mesenchymal markers compared to CK only, suggesting the ratio of mesenchymal to epithelial like CTCs may reflect a clinical outcome. Our data suggests that the OnQChip's ability to capture CTCs based on size independent of surface marker expression and inclusion of two new stains, allow for capture and enumeration of mesenchymal CTCs that would be missed by platforms incorporating only epithelial markers such as EpCAM and CK.

Citation Format: Keith D. Merdek, Kam Sprott, Chunsheng Jiang, Michael Stocum, Glenn Bubley, Walter Carney. Capture and enumeration of mesenchymal CTCs on the OnQChip platform. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5108. doi:10.1158/1538-7445.AM2013-5108

Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

DNA repair protein biomarkers associated with time to recurrence in triple-negative breast cancer

PURPOSE

To evaluate the prognostic utility of immunohistochemical assessment of key proteins in multiple DNA repair pathways in triple-negative breast cancer (TNBC; estrogen receptor negative, progesterone receptor negative, and HER2/neu negative by immunohistochemistry).

EXPERIMENTAL DESIGN

Archived clinically annotated tumor specimens from 112 women with TNBC were immunostained with antibodies against DNA repair proteins and scored using digital image analysis. The cohort was divided into training and test sets for development of a multiantibody model. Scores were combined with clinical data to assess association with outcome.

RESULTS

Low XPF (P = 0.005), pMK2 (P = 0.01), MLH; P = 0.002), and FANCD2 (P = 0.001) were each associated with shorter time to recurrence (TTR) in univariate analysis. A 4-antibody model could segregate high-risk and low-risk groups on the basis of TTR in both the training (relative risk [RR] = 3.52; P = 9.05E-07) and test (RR 2.67; P = 0.019) cohorts.

CONCLUSIONS

DNA repair proteins may be useful as prognostic markers in TNBC. Further study in larger, uniformly treated cohorts with additional clinical parameters is warranted.

Akt-RSK-S6 kinase signaling networks activated by oncogenic receptor tyrosine kinases

Receptor tyrosine kinases (RTKs) activate pathways mediated by serine-threonine kinases, such as the PI3K (phosphatidylinositol 3-kinase)-Akt pathway, the Ras-MAPK (mitogen-activated protein kinase)-RSK (ribosomal S6 kinase) pathway, and the mTOR (mammalian target of rapamycin)-p70 S6 pathway, that control important aspects of cell growth, proliferation, and survival. The Akt, RSK, and p70 S6 family of protein kinases transmits signals by phosphorylating substrates on an RxRxxS/T motif (R, arginine; S, serine; T, threonine; and x, any amino acid). We developed a large-scale proteomic approach to identify more than 300 substrates of this kinase family in cancer cell lines driven by the c-Met, epidermal growth factor receptor (EGFR), or platelet-derived growth factor receptor alpha (PDGFRalpha) RTKs. We identified a subset of proteins with RxRxxS/T sites for which phosphorylation was decreased by RTK inhibitors (RTKIs), as well as by inhibitors of the PI3K, mTOR, and MAPK pathways, and we determined the effects of small interfering RNA directed against these substrates on cell viability. Phosphorylation of the protein chaperone SGTA (small glutamine-rich tetratricopeptide repeat-containing protein alpha) at serine-305 was essential for PDGFRalpha stabilization and cell survival in PDGFRalpha-dependent cancer cells. Our approach provides a new view of RTK and Akt-RSK-S6 kinase signaling, revealing previously unidentified Akt-RSK-S6 kinase substrates that merit further consideration as targets for combination therapy with RTKIs.

Akt and 14-3-3 control a PACS-2 homeostatic switch that integrates membrane traffic with TRAIL-induced apoptosis

TRAIL selectively kills diseased cells in vivo, spurring interest in this death ligand as a potential therapeutic. However, many cancer cells are resistant to TRAIL, suggesting the mechanism mediating TRAIL-induced apoptosis is complex. Here we identify PACS-2 as an essential TRAIL effector, required for killing tumor cells in vitro and virally infected hepatocytes in vivo. PACS-2 is phosphorylated at Ser437 in vivo, and pharmacologic and genetic studies demonstrate Akt is an in vivo Ser437 kinase. Akt cooperates with 14-3-3 to regulate the homeostatic and apoptotic properties of PACS-2 that mediate TRAIL action. Phosphorylated Ser437 binds 14-3-3 with high affinity, which represses PACS-2 apoptotic activity and is required for PACS-2 to mediate trafficking of membrane cargo. TRAIL triggers dephosphorylation of Ser437, reprogramming PACS-2 to promote apoptosis. Together, these studies identify the phosphorylation state of PACS-2 Ser437 as a molecular switch that integrates cellular homeostasis with TRAIL-induced apoptosis.

DNA repair protein biomarkers in triple negative breast cancer

Abstract #1064

Introduction: Triple negative breast tumors form a distinct, aggressive, subgroup of breast cancers that exhibit a high degree of genomic instability and have many phenotypic similarities to BRCA1 deficient tumors. These observations suggest that aberrant DNA repair may be involved in triple negative tumor carcinogenesis. We profiled tumor DNA repair capacity using immunohistochemistry in order to develop prognostic biomarkers and suggest targets for novel therapies.
 Methods: We identified 143 previously treated women with triple negative breast cancers and used their archived, formalin-fixed, paraffin-embedded primary excision biopsies to create a tissue microarray (TMA). The TMA was stained using antibodies against proteins in various DNA repair pathways including XPF, FANCD2, PAR, MLH1, and MK2. Stained tissue was evaluated using machine-based image analysis and scoring that represented both the intensity and quantity of positive tumor nuclei. Biomarker scores and clinical data were assessed for correlations with outcome. Patients were randomized into training and test cohorts for the development of a multiple marker model. A set of critical threshold marker values were determined that maximally separated the training samples into low and high risk recurrence groups. Training set thresholds and marker combinations were applied towards the test set. Kaplan-Meier and Cox proportional hazards were used to test time to recurrence.
 Results: Clinical data for 115 patients with primary treatment data was available with a median follow up of 58 months. There were 37 recurrences: 18 were distant first, 12 were local first and 7 were simultaneous. Low XPF (p=0.002), pMK2 (p=0.02), MLH (p<0.001) and FANCD2 (p=0.05) were associated with shorter time to recurrence. In the training cohort, the high-risk group defined by a four marker model had a relative risk of recurrence of 3.0 (p<0.00001) and shorter median time to recurrence than the low risk group (13.1 months versus not reached). This was superior to single markers and to other markers such as P53 (p = 0.02) or Ki67 (p = 0.07). In the test set, the model produced similar results with a relative risk of 2.1 (p=0.029) for the high-risk group and shorter median time to recurrence (14.1 months versus not reached).
 Conclusions: Triple negative breast cancers show variable expression of proteins involved in DNA repair. Levels of four DNA repair proteins correlated significantly with recurrence free survival, and were used to develop a DNA repair profile model in a training set which was prognostic in a test set. DNA repair biomarker panels may be useful as prognostic or predictive indicators as well as suggest possible targets for novel therapies such as PARP inhibition. Further study of the model in another validation set with other clinical variables is warranted.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1064.