Agents In Preclinical Models Research Articles

Neoadjuvant Interferons: Critical for Effective PD-1-Based Immunotherapy in TNBC.

The lack of targeted therapies available for triple-negative breast cancer (TNBC) patients who fail to respond to first-line chemotherapy has sparked interest in immunotherapeutic approaches. However, trials utilizing checkpoint inhibitors targeting the PD-1/PD-L1 axis in TNBC have had underwhelming responses. Here, we investigated the interplay between type I IFN signaling and the PD-1/PD-L1 axis and tested the impact of combining IFN inducers, as immune activators, with anti-PD-1, to induce an antimetastatic immune response. Using models of TNBC, we demonstrated an interplay between type I IFN signaling and tumor cell PD-L1 expression that affected therapeutic response. The data revealed that the type I IFN-inducer poly(I:C) was an effective immune activator and antimetastatic agent, functioning better than anti-PD-1, which was ineffective as a single agent. Poly(I:C) treatment induced PD-L1 expression on TNBC cells, and combined poly(I:C) and anti-PD-1 treatment prolonged metastasis-free survival in a neoadjuvant setting via the induction of a tumor-specific T-cell response. Use of this combination in a late treatment setting did not impact metastasis-free survival, indicating that timing was critical for immunotherapeutic benefit. Together, these data demonstrated anti-PD-1 as an ineffective single agent in preclinical models of TNBC. However, type I IFN inducers were effective immune activators, and neoadjuvant trials combining them with anti-PD-1 to induce a sustained antitumor immune response are warranted. Cancer Immunol Res; 5(10); 871-84. ©2017 AACR.

497P - Tumor-stroma interactions and response to targeted agents in preclinical models of colorectal cancer (CRC)

497P - Tumor-stroma interactions and response to targeted agents in preclinical models of colorectal cancer (CRC)

Abstract 1146: Biomarker-driven targeted oral treatment strategy for bladder cancer

Abstract INTRODUCTION AND OBJECTIVE: Hyaluronic acid (HA) family of molecules, HA-synthases (HAS-1,2,3), HA-receptors (CD44, RHAMM) and hyaluronidase (HYAL-1) are markers for bladder cancer (BCa) diagnosis and predicting prognosis. HA-family promotes tumor growth and metastasis by inducing epithelial mesenchymal transition (EMT). 4-Methylumbelliferone (4-MU) is an orally bioavailable dietary supplement that inhibits HA synthesis. We evaluated the expression of HA family and EMT markers in bladder tissues as well as the antitumor effects of 4-MU as a potential targeted therapeutic agent in preclinical models of BCa. METHODS: Quantitative PCR was used to measure mRNA expression of HA-family and EMT genes (β-catenin, Twist, and Snail) in 72 bladder tissue specimens (28 normal; 44 tumor); follow-up: 20.3±2.5 months; median 17 months. The effect of 4-MU (0-0.6 mM) on cell proliferation, apoptosis, intracellular signaling, and the expression of HA receptors, and EMT genes were examined in BCa cell lines by Q-PCR, immunoblotting, proximal ligation and PI-3K activity assays. Mechanism of action was analyzed by HA addition and mAkt overexpression. Effect of oral administration of 4-MU (100, 200-mg/kg) on tumor growth was analyzed in subcutaneous xenografts. RESULTS: HAS-1, -2 -3, HYAL-1 and Snail levels were 10-20-fold elevated in BCa tissues as compared to normal bladder (P<0.001). In univariate analysis, HAS-1, -2, HYAL-1 and Twist levels correlated with metastasis (P<0.001); HYAL-1 was an independent predictor of metastasis. 4-MU inhibited cell proliferation, chemotactic motility and invasion in a dose-dependent manner; 50-70% inhibition at IC50 (0.4 mM) for HA-synthesis inhibition. 4-MU induced apoptosis (>3-fold) via the death receptor pathway. 4-MU downregulated HA-signaling, specifically transcript and/or protein levels of CD44, RHAMM, p-Akt, β-catenin, pβ-catenin(S552). Snail and twist were downregulated by 2-5-fold, but pβcatenin((T41/S45), pGSK-3α/β and E-cadherin levels were increased. 4-MU also inhibited CD44/PI-3K complex formation and PI-3K activity. HA addition or myristoylated Akt expression attenuated 4-MU effects. In xenograft studies, 4-MU oral treatment abrogated tumor growth of established tumors (vehicle, day 50: 766±221 mm3; 4-MU: 128±61, day 50) by abrogating HA-synthesis. No weight loss or serum or organ toxicity was observed in treated mice. CONCULUSION: This study demonstrates that HA-family signaling is upregulated in BCa and can be specifically targeted for treatment by a non-toxic dietary supplement. Support: 7R01 CA072821-16; 7R01CA176691-03 Citation Format: Daley S. Morera, Andre Jordan, Vinata B. Lokeshwar. Biomarker-driven targeted oral treatment strategy for bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1146. doi:10.1158/1538-7445.AM2017-1146

Abstract 4038: Exploring optimal targeted combination therapies with neratinib for HER2+ breast cancer

Abstract Activation by amplification or overexpression of the proto-oncogene HER2 (also known as ERBB2) is associated with the development and progression of breast cancer. Neratinib is a novel, irreversible, pan-HER tyrosine kinase inhibitor which selectively inhibits EGFR, HER2 and HER4. In this preclinical study, we explored the efficacy of neratinib in combination with other clinically relevant targeted agents for optimal treatment of HER2-positive breast cancer in in vitro and in vivo models. Western blot (WB) analysis of a panel of breast cancer cell lines showed that BT-474, SKBR-3, and HCC-1954 cells displayed elevated HER2 expression levels (here denoted as HER2+), while MDA-MB-361, MDA-MB-453, and CAMA-1 breast cancer cells expressed relatively lower HER2 expression levels. Interestingly, neratinib inhibition positively correlated with HER2 expression levels as assessed by cell survival assays. The IC50 of neratinib in the HER2+ cell lines was in the 3.6 - 113nM range. Consistent with the in vitro data, treatment of a HER2+ breast cancer PDX model with neratinib single agent (p.o. 5 days/week) led to a significant dose-dependent tumor growth inhibition with tumor regressions observed at a low dose of 10 mg/kg (p<0.0001). The activity of neratinib in combination with other targeted agents was then evaluated in vitro in the HER2+ breast tumor cell lines using a Chou-Talalay method. Neratinib showed synergistic anti-proliferative activity in combination with the PI3Kα inhibitor BYL719 in all the HER2+ cell lines tested. By contrast, synergy with mTOR inhibitors (everolimus and TAK228) and with the MEK inhibitor trametinib was only observed in BT-474 and HCC-1954 cells. HCC-1954 cells had the best response to neratinib combinations among all HER2+ cell lines tested, with combination index values <0.5. Immunoblot analysis demonstrated that neratinib treatment displayed complete inhibition of HER2 phosphorylation in these cells. Substantial inhibition of downstream signaling pathways following single agent neratinib treatment was evident by reduced phosphorylation levels of AKT, S6K1, S6, 4EBP1, ERK1/2 and MEK1/2. Consistently with the cell viability data, the combination of neratinib with PI3K/Akt/mTOR and MAPK inhibitors showed a synergy on signaling blockage in these two downstream pathways respectively. Taken together this data shows that neratinib has efficacy as single agent in preclinical models of HER2+ breast tumors and its anti-proliferative activity in vitro was enhanced when combined with PI3K/Akt/mTOR and MAPK pathway inhibitors. Further studies of neratinib-based combination treatments are underway in HER2+ breast cancer xenograft and PDX models to further corroborate these findings. Citation Format: Ming Zhao, Stephen Scott, Kurt Evans, Erkan Yuca, Rashmi Murthy, Francesca Avogadri-Connors, Richard Cutler, Alshad S. Lalani, Sarina Piha-Paul, Funda Meric-Bernstam. Exploring optimal targeted combination therapies with neratinib for HER2+ breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4038. doi:10.1158/1538-7445.AM2017-4038

Abstract 4973: Discovery of LY3214996, a selective and novel ERK1/2 inhibitor with potent antitumor activities in cancer models with MAPK pathway alterations

Abstract The RAS/MAPK pathway is dysregulated in approximately 30% of human cancers, and the extracellular-signal-regulated kinases (ERK1 and ERK2) serves as key central nodes within this pathway. The feasibility and clinical impact of targeting the RAS/MAPK pathway has been demonstrated by the therapeutic success of BRAF and MEK inhibitors in BRAF V600E/K metastatic melanoma. However, resistance develops frequently through reactivation of the pathway. Therefore, simultaneous targeting of multiple effectors such as RAF, MEK and ERK in this pathway, offers a potential for enhanced efficacy while delaying and overcoming resistance. LY3214996 is a highly selective inhibitor of ERK1 and ERK2, with IC50 of 5 nM for both enzymes in biochemical assays. It potently inhibits cellular phospho-RSK1 in BRAF and RAS mutant cancer cell lines. In an unbiased tumor cell panel sensitivity profiling for inhibition of cell proliferation, tumor cells with MAPK pathway alterations including BRAF, NRAS or KRAS mutation are generally sensitivity to LY3214996. In tumor xenograft models, LY3214996 inhibits PD biomarker phospho-p90RSK1 in tumors and the PD effects are correlated with compound exposures and anti-tumor activities. LY3214996 shows either similar or superior anti-tumor activity as compared to other published ERK inhibitors in BRAF or RAS mutant cell lines and xenograft models. Oral administration of single-agent LY3214996 significantly inhibits tumor growth in vivo and is well tolerated in BRAF or NRAS mutant melanoma, BRAF or KRAS mutant colorectal, lung and pancreatic cancer xenografts or PDX models. Therefore, LY3214996 can be tailored for treatment of cancers with MAPK pathway alteration. In addition, LY3214996 has anti-tumor activity in a vemurafenib-resistant A375 melanoma xenograft model due to MAPK reactivation, may have potential for treatment of melanoma patients who have failed BRAF therapies. More importantly, LY3214996 can be combined with investigational and approved agents in preclinical models, particularly KRAS mutant models. Combination treatment of LY3214996 and CDK4/6 inhibitor abemaciclib was well tolerated and results in potent tumor growth inhibition or regression in multiple in vivo cancer models, including KRAS mutant colorectal and non-small cell lung cancers. Here, we first report the preclinical characterization of LY3214996, a novel small molecule ERK1/2 inhibitor currently in Phase I clinical trials in patients with advanced and metastatic cancers (NCT02857270). Citation Format: Shripad V. Bhagwat, William T. McMillen, Shufen Cai, Baohui Zhao, Matthew Whitesell, Lisa Kindler, Robert S. Flack, Wenjuan Wu, Karen Huss, Bryan Anderson, Xiu-Juan Yuan, Susan Jaken, Denis McCann, Brian Mathes, Andrew J. Dropsey, Jason Manro, Jennie Walgren, Eunice Yuen, Xueqian Gong, Michael J. Rodriguez, Jianping Huang, Ramon V. Tiu, Sajan Joseph, Sheng-Bin Peng. Discovery of LY3214996, a selective and novel ERK1/2 inhibitor with potent antitumor activities in cancer models with MAPK pathway alterations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4973. doi:10.1158/1538-7445.AM2017-4973

Abstract 5060: Activity of the EZH2 inhibitor tazemetostat as a monotherapy and in combination with multiple myeloma therapies in preclinical models

Abstract The EZH2 inhibitor tazemetostat (EPZ-6438) is currently being evaluated in phase 2 clinical trials for the treatment of non-Hodgkin’s Lymphoma (NHL). EZH2 inhibitors have shown anti-proliferative effects in multiple preclinical models of NHL and objective clinical responses have been reported in patients with B-cell lymphomas in phase 1 and phase 2 studies of tazemetostat. Mounting evidence suggests that EZH2 is an important regulator of B cell differentiation, both in normal B-cells and in B-cell lymphoma, and may be an important mediator of cell fate in B-cell malignancies in the clinic. Consistent with its essential role in regulating B cell differentiation, recent studies have also shown a dependence on EZH2 activity in multiple myeloma (MM), a disease arising from terminally-differentiated B-cell lymphocyte plasmablasts. Frequent genetic alterations of epigenetic modulators are observed in MM, pointing towards an important role in the initiation and maintenance of this disease. Dysregulation of the H3K27 methyltransferase EZH2, its corresponding histone demethylase UTX and the H3K36 methyltransferase WHSC1 in MM suggest that disruption of the balance of histone methylation may be fundamental to MM pathogenesis in a subset of cases. Indeed, inhibition of EZH2 alone has shown potent anti-proliferative effects both in in vitro and in vivo preclinical models of MM. Here, we describe the effects of small molecule EZH2 inhibitors as monotherapy and in combination with standard of care agents in preclinical models of MM. Tazemetostat selectively inhibits intracellular H3K27 methylation in MM cell lines and elicits a robust anti-proliferative effect in 14-day assays. Following demonstration of single agent activity, we then investigated potential for combinatorial activity of tazemetostat with first and second line therapies for multiple myeloma as well as other non-approved but emerging therapies. Synergistic anti-proliferative activity was observed when tazemetostat was combined with glucocorticoid receptor agonists (dexamethasone, prednisolone), small molecule immune system modulators (lenalidomide, pomalidomide) and proteasome inhibitors (bortezomib, ixazomib) when cells were primed with tazemetostat for seven days prior to the addition of the standard of care drugs. Combination activity was also observed with an alternate treatment schedule where cells were co-treated with tazemetostat along with the combination partner for seven days. Studies with selected therapeutic modalities were expanded into in vivo xenograft models to further evaluate monotherapy and combination activity of EZH2 inhibitors in MM. Citation Format: Allison E. Drew, Vinny Motwani, John E. Campbell, Cuyue Tang, Jesse J. Smith, Richard Chesworth, Robert A. Copeland, Alejandra Raimondi, Scott Ribich. Activity of the EZH2 inhibitor tazemetostat as a monotherapy and in combination with multiple myeloma therapies in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5060. doi:10.1158/1538-7445.AM2017-5060

Prognostic relevance of Src activation in stage II-III colon cancer

Src belongs to a family of cytoplasmic tyrosine kinases that play a key role in tumor initiation and progression. Src activation has been associated with a more aggressive neoplastic phenotype and induces resistance to platinum agents in preclinical models. The aim of our study was to assess the prognostic and/or predictive value of Src activation in patients with stage II-III colon cancer. pSrc expression was assessed in paraffin-embedded tumor samples by immunohistochemistry (phospho-Y418, ab4816; Abcam). Cases were classified by staining intensity in 4 categories: no staining (0), weak (1+), moderate (2+), and intense (3+) staining. A total of 487 patients were evaluated (240 stage II, 247 stage III), of whom 298 (61%) had received adjuvant chemotherapy. Staining was absent in 78 (16%), weak in 262 (54%), moderate in 103 (21%), and intense in 44 (9%). High pSrc expression was significantly associated with decreased 5-year disease-free survival (39% versus 63% for patients with high versus low pSrc expression; hazard ratio, 0.56; P=.005) and overall survival (58% versus 74%; hazard ratio, 0.55; P=.02). Multivariate analysis confirmed pSrc expression as a significant prognostic factor both for disease-free survival and overall survival, independent of age, sex, tumor stage, bowel obstruction/perforation, or adjuvant chemotherapy. These findings illustrate the relevance of Src activation in colon cancer biology, conferring a poor prognosis to patients with early stage colon cancer regardless of adjuvant chemotherapy. Our findings may help improve prognostic stratification of patients for clinical decisions and open new avenues for potential pharmacologic manipulation that may eventually improve patients' outcomes.

Combination therapy with potent PI3K and MAPK inhibitors overcomes adaptive kinome resistance to single agents in preclinical models of glioblastoma.

Glioblastoma (GBM) is the most common and aggressive primary brain tumor. Prognosis remains poor despite multimodal therapy. Developing alternative treatments is essential. Drugs targeting kinases within the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) effectors of receptor tyrosine kinase (RTK) signaling represent promising candidates. We previously developed a non-germline genetically engineered mouse model of GBM in which PI3K and MAPK are activated via Pten deletion and KrasG12D in immortalized astrocytes. Using this model, we examined the influence of drug potency on target inhibition, alternate pathway activation, efficacy, and synergism of single agent and combination therapy with inhibitors of these 2 pathways. Efficacy was then examined in GBM patient-derived xenografts (PDX) in vitro and in vivo. PI3K and mitogen-activated protein kinase kinase (MEK) inhibitor potency was directly associated with target inhibition, alternate RTK effector activation, and efficacy in mutant murine astrocytes in vitro. The kinomes of GBM PDX and tumor samples were heterogeneous, with a subset of the latter harboring MAPK hyperactivation. Dual PI3K/MEK inhibitor treatment overcame alternate effector activation, was synergistic in vitro, and was more effective than single agent therapy in subcutaneous murine allografts. However, efficacy in orthotopic allografts was minimal. This was likely due to dose-limiting toxicity and incomplete target inhibition. Drug potency influences PI3K/MEK inhibitor-induced target inhibition, adaptive kinome reprogramming, efficacy, and synergy. Our findings suggest that combination therapies with highly potent, brain-penetrant kinase inhibitors will be required to improve patient outcomes.

Abstract S2-05: Efficacy and tolerability of veliparib (V; ABT-888) in combination with carboplatin (C) and paclitaxel (P) vs placebo (Plc)+C/P in patients (pts) with BRCA1 or BRCA2 mutations and metastatic breast cancer: A randomized, phase 2 study

Abstract Background: Poly(ADP-ribose) polymerase (PARP) inhibitors block DNA damage repair and may thereby enhance the clinical activity of DNA-damaging chemotherapy. Homologous recombination is defective in BRCA1/2-mutated tumors, leading to more error-prone mechanisms of DNA repair and increased sensitivity to PARP inhibition. V is a potent PARP inhibitor that enhances the antitumor activity of platinum agents in preclinical models. This phase 2 trial (NCT01506609) investigated the safety and efficacy of V+C/P or V+ temozolomide (TMZ) vs Plc+C/P in pts with locally recurrent or metastatic breast cancer harboring a BRCA1 or BRCA2 mutation. Results of the V+C/P and Plc+C/P arms are presented; V+TMZ results will be presented separately. Methods: Pts ≥18 years with histologically confirmed locally recurrent or metastatic breast cancer were randomized 1:1:1 to: 1) V 40 mg BID D1–7+TMZ, 28-D cycle; 2) V 120 mg BID D1–7+C AUC 6, D3 and P 175 mg/m2, D3, 21-D cycle; or 3) Plc BID D1–7+C/P. Key eligibility criteria included deleterious BRCA1/2 mutation, ≤2 prior chemotherapies for metastatic disease, no prior platinum agent, and no CNS metastases. Randomization was stratified by hormone receptor status, prior cytotoxic therapy, and ECOG PS. The primary endpoint was progression-free survival (PFS) per RECIST 1.1 of each V arm vs Plc+C/P by independent review. Primary analysis occurred at the 112th PFS event in the V+C/P and Plc+C/P arms. Overall survival (OS), objective response rate (ORR), tolerability, and quality of life were also evaluated. Results: A total of 196 pts (193 BRCA+ per central lab) were randomized to receive double-blinded V+C/P (n=97) or Plc+C/P (n=99). Baseline demographics and disease characteristics were balanced across all treatment arms. Median study drug exposure was 10 cycles for Plc+C/P and 12 cycles for V+C/P. The V+C/P arm demonstrated numeric improvements for both PFS and OS compared to the Plc+C/P arm; improvement in ORR was statistically significant (Table 1). There was no meaningful increase of toxicity with addition of V. The most common treatment-emergent adverse events (AEs) with Plc+C/P or V+C/P were neutropenia (74%/74%), thrombocytopenia (70%/71%), and nausea (58%/71%). Grade ≥3 AEs in ≥30% of pts were neutropenia (55%/56%) and thrombocytopenia (26%/31%), respectively. There was no difference in the use of G-CSF with addition of V. Significant improvements in fatigue, pain, and insomnia (all P<0.05) were observed with V+C/P vs Plc+C/P. Conclusions: This is the first randomized phase 2 trial of a PARP inhibitor in combination with platinum-based therapy for treatment of BRCA1/2-mutated advanced breast cancer. V+C/P demonstrated significantly higher ORR and symptom improvement compared to Plc+C/P, with nonsignificant trends for improved OS and PFS. Phase 3 trials are ongoing. Table 1Efficacy (ITT population – BRCA mutation)Plc+C/P, n=98V+C/P, n=95HR (95% CI); P valuePFS(mo, 95% CI)12.3 (9.3–14.5)14.1 (11.5–16.2)0.789 (0.536–1.162); 0.231OS (mo, 95% CI)25.0 (18.1–34.8)28.5 (22.4–NR)0.725 (0.468–1.121); 0.148ORR, % (95% CI)61.3 (49.7–71.9)77.8 (66.4–86.7)P=0.027 Citation Format: Han HS, Diéras V, Robson ME, Palácová M, Marcom PK, Jager A, Bondarenko I, Citrin D, Campone M, Telli ML, Domchek SM, Friedlander M, Kaufman B, Ratajczak C, Coates A, Bonnet P, Qin Q, Qian J, Giranda VL, Shepherd SP, Isakoff SJ, Puhalla S. Efficacy and tolerability of veliparib (V; ABT-888) in combination with carboplatin (C) and paclitaxel (P) vs placebo (Plc)+C/P in patients (pts) with BRCA1 or BRCA2 mutations and metastatic breast cancer: A randomized, phase 2 study [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 S2-05.

VEGF mediated signaling in oral cancer.

Increasingly it is being realized that oral cancer arises from genetic/epigenetic mutations, dysregulations of spatio-temporally controlled signal transduction cascades and loss of apoptosis. Epidemiological studies have provided a stronger association between tobacco use (chewed and smoked) and oral cancer. Nevertheless, alcohol has also gained attention as a significant risk factor, having a multiplicative synergistic cancer promoting effect with tobacco. Vascular Endothelial Growth Factor (VEGF) mediated signaling has gained limelight because of its instrumental role in endothelial cell proliferation, survival, invasion, migration, chemotaxis of bone marrow (BM)-derived progenitor cells, vasodilation and vascular permeability. In this review we provide most recent updates on involvement of VEGF/VEGFR signaling axis in oral cancer. We partition this multi-component review into different sections and summarize latest advancements related to therapies against VEGF/VEGFR signaling axis and how microRNAs tactfully modulate VEGF and VEGFR in oral cancers. Data obtained through preclinical and clinical studies has revealed that therapeutic benefits associated with VEGF-targeted therapy are complicated in different cancers and involve myriad of mechanisms. A better understanding of VEGF/VEGFR mediated signaling in oral cancers and testing of novel therapeutic agents in preclinical models will prove to be helpful in effective translation of safest drugs from benchtop to the bedside.

Abstract 3761: The MDM2 inhibitor AMG 232 causes tumor regression and potentiates the anti-tumor activity of MEK inhibition and DNA-damaging cytotoxic agents in preclinical models of acute myeloid leukemia

Abstract AMG 232 is a potent inhibitor of the MDM2-p53 interaction and is a promising clinical candidate for treating tumors, in particular those harboring wild-type p53. AML represents a compelling indication for AMG 232 given the low rate of p53 mutation, frequent MDM2 overexpression, and unmet medical need. We evaluated the effect of AMG 232 treatment on AML tumors in vitro and in vivo, elucidated the mechanism of anti-tumor efficacy, and tested the effect of combining AMG 232 with targeted agents and chemotherapeutics. Combinations were identified based on evidence of in vitro synergy from cell based screens, or based on biological rationale and clinical opportunity with standard of care agents. Combinations evaluated included MEK inhibitors, and p53-inducing, DNA-damaging cytotoxics cytarabine, doxorubicin, and decitabine. In vitro assays demonstrated that AMG 232 as a single agent was effective at inducing cell death across a panel of p53 wild-type AML cell lines. The anti-tumor efficacy involved activation of the p53 pathway, robust inhibition of the cell cycle and induction of apoptosis. AMG 232 treatment caused AML tumor regression in vivo which was related to dose- and time-dependent induction of the p53 targets p21 and PUMA. The combination of AMG 232 and MEK inhibition resulted in synergistic tumor cell killing in vitro, and enhanced in vivo anti-tumor activity which was significantly better than either single agent. Combinations of AMG 232 with chemotherapies which induce DNA damage resulted in synergistic in vitro cell killing, and superior anti-tumor efficacy in vivo with increased induction of p53 signaling in tumors. These data support a clinical strategy for evaluating AMG 232 as a monotherapy and in combination with targeted and cytotoxic agents to treat AML patients. Citation Format: Jude R. Canon, Tao Osgood, Anne Y. Saiki, Jonathan D. Oliner. The MDM2 inhibitor AMG 232 causes tumor regression and potentiates the anti-tumor activity of MEK inhibition and DNA-damaging cytotoxic agents in preclinical models of acute myeloid leukemia. [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 3761.

Abstract 3209: CRLX101, an investigational nanoparticle-drug conjugate of camptothecin, demonstrates synergy with immunotherapy agents in preclinical models

Abstract CRLX101, an investigational nanoparticle-drug conjugate (NDC) containing the payload camptothecin, is currently being clinically evaluated in multiple treatment-refractory solid tumors. CRLX101 has been shown preclinically to be active in many different tumor types as a dual inhibitor of topoisomerase 1 and hypoxia-inducible factor 1α (HIF-1α). It has a long circulation half-life and has been shown pre-clinically to release camptothecin in a slow and prolonged manner in tumors. Camptothecin itself was identified as an active anti-tumor agent preclinically but was not developed clinically due to its poor tolerability in patients. The development of CRLX101, which has not shown significant toxicity in over 300 patients to date, offers a unique opportunity to improve cancer treatment in a meaningful way. Recent publications have suggested that tumor expression of the immune-suppressive molecule PD-L1 is controlled by HIF-1α. Since CRLX101 is a potent inhibitor of HIF-1α, it is possible that CRLX101 behaves as an inhibitor of the PD-1/PD-L1 axis in vivo. We therefore hypothesized that a combination of CRLX101 with agents that are being investigated in combination with the anti PD-1 antibody would lead to increased efficacy. Indole diamine oxygenase (IDO) inhibitors are a new class of drugs that decrease tumor-induced immune suppression and are currently being evaluated in the clinic with anti-PD-1 antibodies. Using syngeneic tumor models, we tested the combination of CRLX101 with three different IDO inhibitors. Treatment of the B16.F10 melanoma model with IDO inhibitors NLG919, INCB024360 or indoximod had no effect on tumor growth while CRLX101 as monotherapy showed moderate anti-tumor activity. When CRLX101 was combined with any of the three IDO inhibitors, the anti-tumor activity was greatly improved compared to monotherapy. Similar results were noted in other syngeneic tumor models. This improved combination response was not observed in IDO inhibitor combinations with the clinically approved topoisomerase inhibitor irinotecan, suggesting that CRLX101 provides a unique advantage in this context. Interestingly, CRLX101/IDO inhibitor combination was also superior to the combination of anti-PD-1 antibody and IDO inhibitor. These data suggest that CRLX101 in combination with IDO inhibitors can successfully block host-mediated immune-suppression to enhance anti-tumor immunity, and this combination may therefore show improved therapeutic activity in the clinic. We therefore plan to explore the immune-specific effects of CRLX101 as well as the mechanistic basis for the observed combination response, and use that information to guide CRLX101 clinical strategy in the setting of chemo-immunotherapy regimens. Citation Format: Douglas Lazarus, Christian Peters, Adam Stockmann, Scott Eliasof, Lata Jayaraman. CRLX101, an investigational nanoparticle-drug conjugate of camptothecin, demonstrates synergy with immunotherapy agents in preclinical models. [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 3209.

A Phase 1b Study of Venetoclax (ABT-199/GDC-0199) in Combination with Decitabine or Azacitidine in Treatment-Naive Patients with Acute Myelogenous Leukemia Who Are ≥ to 65 Years and Not Eligible for Standard Induction Therapy

A Phase 1b Study of Venetoclax (ABT-199/GDC-0199) in Combination with Decitabine or Azacitidine in Treatment-Naive Patients with Acute Myelogenous Leukemia Who Are ≥ to 65 Years and Not Eligible for Standard Induction Therapy

Bortezomib (Velcade), Thalidomide, Dexamethasone and Panobinostat (VTD-P) Is a Safe, Well Tolerated and Efficacious Regimen for Patients with Relapsed Multiple Myeloma: Preliminary Results of the Muk-Six Trial

Introduction: VTD is an effective regimen for patients with multiple myeloma and forms a backbone for the addition of novel agents. The MUK-six trial aimed to improve the efficacy by adding Panobinostat, a now FDA approved pan-histone deacetylase inhibitor that demonstrated synergy with proteasome inhibition and immunomodulatory agents in pre-clinical models. We have previously reported the phase 1 dose finding part which determined the MTD of panobinostat with VTD to be 20mg. Here we present the efficacy results from the recommended dose (RD) expansion phase (primary end point) and safety, tolerability data for all patients during the induction phase of the study.Methods: MUK-six was a multi-centre UK Phase I/IIa trial for patients with relapsed and relapsed/ refractory myeloma who had received between 1 and 4 prior lines of therapy. Subjects received VTD-P (bortezomib 1.3mg/2sc days 1 and 8, thalidomide 100mg daily (50mg if pre-existing neuropathy), dexamethasone 20mg days 1, 2, 8, 9 and panobinostat 20mg days 1, 3, 5, 8, 10, 12) every 3 weeks for up to 16 cycles (induction) followed by 1 year of panobinostat maintenance. Those planned for autologous stem cell transplantation (ASCT) received a minimum of 6 cycles of VTD-P. All patients treated with VTD-P received venous thrombosis prophylaxis as per institutional practice. Responses were assessed using modified IWG uniform response criteria and toxicity graded by CTCAE V4.0.Results: 46 patients were treated at the RD and were of a median age of 60 years (41-76). 80.4% had received one prior line of therapy (range 1-4), 71.7% had prior bortezomib and 39.2% prior thalidomide. Most patients were ISS 1 (60.9%), 45.7% had adverse FISH lesions at baseline, 8.7% had 17p deletion. 6 patients remain on treatment at the time of this abstract. 51.3% of patients came off study to proceed to ASCT.The overall response rate (≥PR) for patients receiving at least one dose of panobinostat was 91.3%, ≥VGPR 45.7% (CR 6.5%, VGPR 39.1%, PR 45.7%). The ≥VGPR rate for those with standard FISH was 52.1% vs 42.9% for adverse FISH. Those treated at first relapse had higher overall responses to those treated later in their disease course (≥PR 94.6% vs 77.8%). Responses were independent of prior bortezomib exposure (≥PR 90.9%, ≥VGPR 45.5% vs PR≥92.3%, ≥VGPR 46.2%).Treatment was generally well tolerated, with a mean panobinostat dose of 17.4mg (86.8% of the RD) delivered across all cycles. 32.1% of those starting at 50mg thalidomide stopped the drug due to toxicity, and 52.6% of those starting at 100mg required dose reductions/stopping. 46 serious adverse events were reported in 27 patients which were mainly infections (17/46, 37.0%). The commonest grade 3-4 toxicities reported for all 57 patients were: neutropenia (14, 24.6%), hypophosphatemia (11, 19.3%), thrombocytopenia (8, 14.1%) and diarrhoea (6, 10.5%). Of note there were no reports of ≥ grade 3 neuropathy. The most frequent grade 1-2 toxicities were fatigue (50, 87.7%), neuropathy (43, 75.5%), constipation (35, 61.4%), diarrhoea (35, 61.4%), bone pain (33, 57.9%), and nausea (27, 47.4%). 2 patients withdrew consent due to toxicity.Conclusions: This study demonstrated that panobinostat can be safely given in combination with VTD and appears highly effective with a response rate of 91.3%, ≥VGPR 45.6% despite 72% having previous bortezomib. This regimen was well tolerated, in particular the incidence of diarrhoea, neuropathy and asthenia/fatigue appeared lower than that observed in the PANORAMA 2 trial (San Miguel et al., 2014). It is possible that the incorporation of a low intensity subcutaneous bortezomib schedule (2 doses every 3 weeks) contributed to the lesser toxicity.Acknowledgments: This trial was part of the Myeloma UK Clinical Trial Network, ISRCTN: 59395590. DisclosuresPopat:Janssen: Honoraria. Off Label Use: Panobinostat: use outside of FDA licence, not yet EU approved. Kishore:Celgene: Other: Conference Sponsorship; Jazz pharma: Other: Conference Sponsorship. Oakervee:Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Yong:Janssen: Honoraria; Autolous: Consultancy; Amgen: Honoraria; BMS: Honoraria; Takeda: Honoraria; Novartis: Consultancy. Cook:Sanofi: Consultancy, Honoraria, Speakers Bureau; Jazz Pharma: Consultancy, Honoraria, Speakers Bureau; Amgen: Consultancy, Honoraria, Speakers Bureau; Chugai: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Honoraria, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau. Cavenagh:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

SGN-CD33A in Combination with Hypomethylating Agents Is Highly Efficacious in Preclinical Models of AML

Acute myeloid leukemia (AML) remains a therapeutic challenge. Long-term survival rates, in particular for older AML patients, remain poor, highlighting the need for improved and well-tolerated treatment options. AML patients who are unfit for high dose chemotherapy in the US are often prescribed hypomethylating agents (azacitidine or decitabine) although the efficacy of these agents in this population was modest (Estey, Leukemia 2013).SGN-CD33A is a CD33-directed antibody drug conjugate (ADC) that is comprised of a cysteine-engineered anti-CD33 antibody, a cleavable dipeptide linker that is highly stable in circulation, and a PBD dimer that binds DNA with high intrinsic affinity. The ADC is active as a single agent in preclinical models of AML that are characteristically resistant to chemotherapy (multi-drug-resistant, MDR-positive) (Sutherland et al. Blood 2013). In the present study, we tested the activity of SGN-CD33A in combination with hypomethylating agents (HMA), azacitidine or decitabine. We hypothesized that the combination of SGN-CD33A with an HMA will have greater impact on the DNA repair pathway in leukemic cells, furthering the processes of apoptosis and cell death. MDR-positive AML cells were treated for 96 hours with SGN-CD33A and each of the HMAs alone and in combination, evaluating both simultaneous as well as sequential administration. Enhanced tumor cell killing was observed when AML cells were treated concomitantly with the combination of SGN-CD33A and an HMA or pre-treated with HMAs prior to the addition of SGN-CD33A.Superior anti-leukemic activity of subtherapeutic doses of SGN-CD33A in combination with HMAs was observed in mouse xenograft models generated with MDR-positive AML cell lines. In the difficult to treat HEL9217 model, decitabine or a single dose of 200 mcg/kg SGN-CD33A delayed tumor growth, while significant reductions in tumor growth were observed for the combination treatment (p=0.0001). Improved antitumor activity in this model was also observed for SGN-CD33A in combination with azacitidine. SGN-CD33A in combination with decitabine significantly reduced tumor burden compared to either agent alone in the TF1-α AML model (p=0.0002). Similarly, sequenced dosing of azacitidine followed by a subtherapeutic dose of 30 mcg/kg SGN-CD33A in mice bearing KG-1 xenografts delivered greater antitumor activity compared to the individual agents (p=0.0001).To investigate the mechanism underlying the enhancement in antileukemic activity, we looked at the impact of HMAs alone and in combination with SGN-CD33A on myeloid marker expression, PBD drug release, and impact on the DNA damage and apoptotic pathways. In AML cell lines that did not show improved cytotoxic activity with the combination of SGN-CD33A and HMA, HMA treatment appeared to have no positive effect on the cell surface levels of CD33. However in responsive cell lines such as TF1-α, HMA treatment resulted in time- and dose-dependent increases in the levels of CD33. Significant increases in expression were observed between 2 and 4 days with decitabine and after 4 days with azacitidine. In addition, more PBD dimer drug from SGN-CD33A was incorporated into DNA in HMA treated cells. Concomitant, the treatment of AML cells with the combination of SGN-CD33A and HMA resulted in greater DNA damage and apoptosis as shown by the increased levels of the early DNA damage marker, γH2AX, and the formation of cleaved PARP, an apoptosis marker, compared to either agent alone. Studies are in progress to investigate the effects on other components of the DNA repair and cell cycle pathways.These findings demonstrate that SGN-CD33A can be successfully combined with hypomethylating agents to deliver marked antitumor activity in preclinical drug-resistant models of AML. DisclosuresSutherland:Seattle Genetics, Inc.: Employment. Yu:Seattle Genetics, Inc.: Employment. O'Day:Seattle Genetics,Inc: Employment. Alley:Seattle Genetics,Inc.: Employment. Anderson:Seattle Genetics, Inc.: Employment. Emmerton:Seattle Genetics, Inc.: Employment. Zeng:Seattle Genetics, Inc.: Employment. O'Meara:Seattle Genetics, Inc: Employment, Equity Ownership. Feldman:Seattle Genetics,Inc: Employment. Kennedy:Seattle Genetics,Inc: Employment, Equity Ownership, Honoraria, Speakers Bureau. Ryan:Seattle Genetics, Inc.: Employment. Benjamin:Seattle Genetics, Inc: Employment.

In silico prediction of Ebola Zaire GP(1,2) immuno-dominant epitopes for the Balb/c mouse.

BackgroundEbola is a Filovirus (FV) that induces a highly communicable and deadly hemorrhagic fever. Currently, there are no approved vaccines to treat FV infections. Protection from FV infection requires cell mediated and humoral immunity. Glycoprotein GP1,2 Fc Zaire, a recombinant FV human Fc fusion protein, has been shown to confer protection against mouse adapted Zaire Ebola virus. The present studies are focused upon identifying immunodominant epitopes using in silico methods and developing tetramers as a diagnostic reagent to detect cell mediated immune responses to GP1,2 Fc.MethodsThe GP1,2 Ebola Zaire sequence from the 1976 outbreak was analyzed by both BIMAS and SYFPEITHI algorithms to identify potential immuno-dominant epitopes. Several peptides were synthesized and screened in flow-based MHC stability studies. Three candidate peptides, P8, P9 and P10, were identified and, following immunization in Balb/c mice, all three peptides induced IFN-γ as detected by ELISpot and intracellular staining.ResultsSignificantly, P8, P9 and P10 generated robust cytotoxic T-cell responses (CTL) as determined by a flow cytometry-based Caspase assay. Antigen specific cells were also detected, using tetramers. Both P9 and P10 have sequence homology with highly conserved regions of several strains of FV.ConclusionsIn sum, three immunodominant sequences of the Ebola GP1,2 have been identified using in silico methods that may confer protection against mouse adapted Ebola Zaire. The development of tetramer reagents will provide unique insight into the potency and durability of medical countermeasure vaccines for known bioterrorism threat agents in preclinical models.

Abstract 576: Development and analytical validation of a novel assay for tissue detection of hyaluronan in the tumor microenvironment to select patients for molecularly targeted pancreatic cancer therapies

Abstract Background: Hyaluronan (HA), a glycosaminoglycan distributed in the extracellular matrix, is frequently upregulated in cancer and correlates with disease progression. Administration of a first-in-class PEGylated recombinant human hyaluronidase (PEGPH20) depletes HA, unmasks HA around tumor cells and decreases tumor interstitial fluid pressure, increasing accessibility to systemically administered agents in preclinical models. PEGPH20 recently received Orphan Drug designation in pancreatic ductal adenocarcinoma (PDA) in the USA. We report the development and analytical validation of a novel prototype assay for a companion diagnostic to select patients with PDA for molecularly targeted therapies with PEGPH20. Design: A recently described biotinylated recombinant immunoadhesin (HTI-601, Jadin 2014) was adapted for use in an immunohistochemistry-based assay on formalin-fixed paraffin-embedded tissue. Sensitivity, specificity, and within-laboratory precision studies were performed in a research mode and then at a central laboratory on a validation set of approximately 200 tumor and normal tissues under GCP conditions. Both pathologist scoring and operator-assisted image analysis (positive pixel count for strong positive pixels) were evaluated. Results: Analytical sensitivity studies identified an optimal probe dilution of 0.417 μg/mL on an immunostainer based on dynamic range in 4 human tumor xenografts containing differential levels of HA. The frequency of high HA observed was 62.7% of archival PDA (N = 75). During analytical specificity, 5.1% of 75 PDA and 3 normal adjacent tissue samples had faint or focal staining after pre-digestion with recombinant PH20 hyaluronidase. No cross-reactivity was identified in 99 normal human tissues across a panel of histotypes; only 1 (1.0%) colon sample had staining of macrophages. Within-laboratory precision among three observers’ annotations had average%CVs as follows: between day 4.8%, between run 12.2%, and repeatability 16.6%. Conclusion: The sensitivity, specificity and within-laboratory precision of the prototype assay using image analysis are acceptable. The frequency of high HA expression is similar to other studies in the literature. Cross-reactivity was focal and faint so is unlikely to interfere. Subset analysis showed contributions to%CV to be higher for HAlow than HAmedium or HAhigh samples as expected. These findings warrant further evaluation of HTI-601 staining on biopsies for PEGPH20-associated therapies in clinical studies. Citation Format: Arnold B. Gelb, Ping Jiang, Laurence Jadin, Daniel C. Maneval, H. Michael Shepard. Development and analytical validation of a novel assay for tissue detection of hyaluronan in the tumor microenvironment to select patients for molecularly targeted pancreatic cancer 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 576. doi:10.1158/1538-7445.AM2015-576

Abstract 4426: A 13 mer LNA miR-221 inhibitor restores drug sensitivity in melphalan-refractory multiple myeloma cells

Abstract The onset of resistance to melphalan (MF) in Multiple Myeloma (MM) patients adversely affects disease outcome. Presently there is increasing evidence on the pivotal role of microRNA (miRNAs) in mediating drug-resistance. We here investigated the effect of an original LNA inhibitor of microRNA-221 (LNA-i-miR-221), in restoring sensitivity to MF in MM cells. LNA-i-miR-221 has been previously demonstrated as anti-tumor agent in preclinical models of MM. We studied the MF-sensitizing effect of LNA-i-miR-221 on MM cells in vitro and in vivo. MiR-221/222 expression inversely correlated with MF-sensitivity in a panel of 6 MM cell lines. Noteworthy, LNA-i-miR-221 overcame MF-resistance in vitro significantly enhancing apoptotic cell death as demonstrated by activation/cleavage of caspase-8, caspase-9 and caspase-3, as well as by PARP cleavage and by histone H2AX (γ-H2AX) phosphorylation. Importantly, the synergistic activity of LNA-i-miR-221 with MF affected cell survival even in the presence of bone marrow stromal cells (BMSCs). Gene expression profiling (GEP) comparing treated and untreated MF-sensitive and -resistant MM cell lines was performed to investigate genes and pathways significantly affected by combinatory treatment. Based on the GEP findings, we confirmed by Western Blot that the growth impairment occurred together with up-regulation of pro-apoptotic BBC3/PUMA protein, a target of miR-221/222 which we validated by luciferase assay in our system. Moreover, GEP analysis showed modulation of drug-influx -efflux transporters such as L-type amino acid transporter 1 (LAT1) and multidrug resistance associated protein 1 (MRP1/ABCC1) which was confirmed by Western Blot analysis. Indeed, LNA-i-miR-222 led to a reduction of the Side Population in MF-resistant cells as assessed by Hoechst dye exclusion assay. Finally, treatment of human MM xenografts in SCID/NOD mice with LNA-i-miR-221 plus MF induced a marked antitumor effect, which again occurred together with BBC3/PUMA and MRP1/ABCC1 proteins modulation in retrieved tumors. Taken together, our findings provide proof-of-concept that LNA-i-miR-221 overcomes MF-resistance of MM cells, providing the rationale for clinical translation of LNA-i-miR-221/MF combination in MM patients. Citation Format: Annamaria Gulla, Maria Teresa Di Martino, Maria Eugenia Gallo Cantafio, Eugenio Morelli, Nicola Amodio, Cirino Botta, Maria Rita Pitari, Santo Giovanni Lio, Pierosandro Tagliaferri, Pierfrancesco Tassone. A 13 mer LNA miR-221 inhibitor restores drug sensitivity in melphalan-refractory multiple myeloma cells. [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 4426. doi:10.1158/1538-7445.AM2015-4426

Abstract BS2-2: Targeting the LIFR-Hippo-YAP pathway as an anti-metastatic strategy

Abstract Deregulation of signaling pathways that control organ size, such as the Hippo-YAP pathway, can lead to tumor formation and metastatic progression. Several upstream regulators are known to provide inputs feeding into the core Hippo pathway. However, the cell membrane receptors that activate the MST (the mammalian Hippo homolog)-LATS-YAP phosphorylation cascade are elusive. Although G-protein-coupled receptors have been found to regulate LATS and YAP phosphorylation, they act in a Hippo-independent manner and do not regulate MST. Combining high-throughput RNA sequencing, functional characterization, mechanistic studies, and clinical validation, we identified leukemia inhibitory factor receptor (LIFR) as a novel breast cancer metastasis suppressor downstream of the miR-9 microRNA and upstream of Hippo signaling. We found that LIFR suppresses metastasis by promoting cell membrane localization of the adaptor protein Scribble, leading to activation of a Hippo kinase cascade and functional inactivation of the transcriptional co-activator YAP. We found that LIFR is commonly downregulated in human breast cancer, and that loss of LIFR in non-metastatic stage I-III breast tumors was highly associated with poor metastasis-free, recurrence-free, and overall survival outcomes in approximately 1,000 patients. Recently, we generated Lifr conditional knockout (cKO) mice to determine whether genetic deletion of Lifr in the breast and other organs leads to increased organ size, tumorigenesis, and metastasis. Notably, we confirmed that Hippo signaling is shut down in Lifr-deficient adult mouse tissues and primary mouse embryonic fibroblasts. The phenotypic characterization of these mice is under way. In preliminary analyses, we indeed observed enlarged organs in Lifr cKO mice, which is what is expected from inactivation of Hippo signaling. These results further validated LIFR as a receptor that triggers the Hippo pathway. We aim to make translational advances on this finding. By delineating the appropriate cutoffs, detection of LIFR could be implemented in the clinic as a prognostic marker of metastatic relapse. We are also developing therapeutic agents to target the miR-9-LIFR-Hippo-YAP pathway as new anti-metastatic strategies. miR-9 antagomirs and LIFR ligands (such as LIF) could be useful for tumors with downregulation but not complete loss of LIFR, whereas agents targeting the functional YAP targets, such as CTGF, may be useful for tumors with either downregulation or complete loss of LIFR. Recently, we established collaboration with FibroGen to develop a human CTGF-neutralizing antibody (FG-3019) as an anti-metastatic agent in preclinical models of breast cancer. We will also investigate whether the blood level of CTGF can serve as a prognostic marker for metastatic relapse and a predictive marker to select patients that would benefit from FG-3019 treatment. These studies will likely facilitate biomarker-driven personalization of breast cancer metastasis prevention and treatment. Citation Format: Li Ma. Targeting the LIFR-Hippo-YAP pathway as an anti-metastatic strategy [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr BS2-2.

O6.4 - VX-970, selective inhibitor of ataxia telangiectasia and Rad3-related (ATR) protein

ABSTRACT Background: ATR is a critical regulator of the homologous recombination DNA repair pathway and the cellular response to replication stress. Inhibition of ATR is predicted to selectively enhance the sensitivity of tumor cells, in which DNA repair is often compromised, to standard of care DNA damaging agents, while relatively sparing non-tumor cells which have DNA repair mechanisms to compensate for the loss of ATR. VX-970 is a potent and selective inhibitor of ATR with a Ki Results: VX-970 substantially increases the cytotoxic activity of multiple DNA damaging agents in a broad panel of tumor cell lines, with minimal increase in non-tumor cell cytotoxicity. VX-970 markedly synergizes with cytotoxic agents in mouse xenograft models of several tumor types. At concentrations of VX-970 which inhibit tumor growth, phosphorylation of the downstream biomarker, Chk1, is observed, as is up-modulation of markers of unrepaired double strand DNA breaks, including gamma-H2AX. VX-970 is currently in two phase 1 clinical trials which employ standard 3 + 3 dose escalations in subjects with advanced solid tumors to determine the tolerability of escalating doses of VX-970, administered intravenously, in combination with gemcitabine, cisplatin or carboplatin. Conclusions: VX-970 is an inhibitor of ATR that enhances the activity of DNA damaging agents in pre-clinical models, and is in phase 1 clinical development.