Abstract C016: Oxidative phosphorylation is a metabolic vulnerability in chemotherapy resistant triple negative breast cancer

There is a pressing need to identify improved therapies for triple negative breast cancers (TNBC) resistant to standard chemotherapy. To identify potential molecular targets, we performed RNA sequencing of pre-treatment biopsies from 43 patients with operable TNBC who received neoadjuvant anthracycline and taxane-based chemotherapy. Ingenuity pathway analysis demonstrated that the top canonical pathway associated with higher likelihood of recurrence was higher expression of oxidative phosphorylation (OXPHOS) signature. We therefore sought to determine the efficacy of IACS-10759, a potent inhibitor of OXPHOS, in 10 TNBC patient-derived xenografts (PDX), 8 generated from chemotherapy-resistant tumors. Partial response was observed in one PDX model and prolonged disease stabilization in 5 of 10 PDXs. PDXs with higher expression of protein coding mitochondrial genes were more sensitive to IACS-10759. AXL overexpression was associated with intrinsic and acquired IACS-10759 resistance. The combination of cabozantinib, a multi-kinase inhibitor targeting AXL, with IACS-10759 significantly improved responses in TNBC PDXs. In contrast, selective AXL inhibitor BGB324 or knockdown of AXL did not enhance IACS-10759 sensitivity. In addition, an in vivo synthetic lethality screen identified CDK4, PARP1 and PARP2 as potential combination targets for IACS-10759. Palbociclib as well as talazoparib enhanced growth inhibitory effect of OXPHOS inhibition in vitro and in vivo. Our data suggests that OXPHOS is a promising target in chemoresistant TNBC. IACS-10759 is currently in Phase 1 testing, including TNBC. Further work is needed to determine the optimal biomarker-driven combination partners.

Citation Format: Kurt Evans, Stacy Moulder, Erkan Yuca, Stephen Scott, Natalia Paez Arango, Maryam Shariati, Christopher P Vellano, Turcin Saridogan, Xiaofeng Zheng, Ana Maria Gonzalez-Angulo, Ming Zhao, Xiaoping Su, Coya Tapia, Ken Chen, Argun Akcakanat, Charles M Perou, Bora Lim, Debu Tripathy, Timothy A Yap, Maria E Di Francesco, Giulio Draetta, Philip Jones, Joe Marszalek, Funda Meric-Bernstam. Oxidative phosphorylation is a metabolic vulnerability in chemotherapy resistant triple negative breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C016. doi:10.1158/1535-7163.TARG-19-C016

Abstract C036: Discovery of IACS-13909, an allosteric SHP2 inhibitor that overcomes multiple mechanisms underlying osimertinib resistance

Osimertinib, a third generation EGFR inhibitor, is a front-line therapy for EGFR mutated non-small lung cancer (NSCLC). The long-term effectiveness of osimertinib is limited by acquired resistance. Clinically identified resistance mechanisms include EGFR-dependent mechanisms such as mutations on EGFR that preclude drug binding, and EGFR-independent activation of the MAPK pathway, for instance via activation of alternate RTKs. It has also been noted that frequently a tumor from a single patient harbors more than one resistance mechanism, and the plasticity between the multiple resistance mechanisms will restrict the effectiveness of therapies targeting a single node of the oncogenic signaling network. SHP2 (Src homology 2 domain-containing phosphatase) is a phosphatase that mediates the signaling of multiple RTKs and is required for full activation of the MAPK pathway. Here we report IACS-13909 - a specific and potent allosteric inhibitor of SHP2 - suppresses the signaling of RTK/MAPK pathway. IACS-13909 potently impedes the proliferation of tumors with a broad spectrum of RTKs as the oncogenic driver. Importantly, in NSCLC models with acquired resistance to osimertinib, IACS-13909 administered as a single agent or in combination with osimertinib potently reduces tumor cell proliferation in vitro and in vivo. Together, our findings provide preclinical evidence for using a SHP2 inhibitor as a therapeutic strategy in acquired EGFR inhibitor-resistant NSCLC. Currently, a compound that potently inhibits SHP2 has been selected as the clinical development candidate and is undergoing IND-enabling studies with a projected first-in-human target of early 2020.

Citation Format: Yuting Sun, Brooke A Meyers, Sarah B Johnson, Angela L Harris, Barbara Czako, Jason B Cross, Paul G Leonard, Faika Mseeh, Maria E Di Francesco, Connor A Parker, Qi Wu, Christopher A Bristow, Jason P Burke, Caroline C Carrillo, Christopher L Carroll, Qing Chang, Ningping Feng, Sonal Gera, Gao Guang, Justin Kwang-Lay Huang, Yongying Jiang, Zhijun Kang, Jeffrey J Kovacs, Xiaoyan Ma, Pijus K Mandal, Timothy McAfoos, Robert A Mullinax, Michael D Peoples, Vandhana Ramamoorthy, Sahil Seth, Erika Suzuki, Christopher Conrad Williams, Simon S Yu, Andy M Zuniga, Giulio F Draetta, Joseph R Marszalek, Timothy P Heffernan, Nancy E Kohl, Philip Jones. Discovery of IACS-13909, an allosteric SHP2 inhibitor that overcomes multiple mechanisms underlying osimertinib resistance [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C036. doi:10.1158/1535-7163.TARG-19-C036

A Novel Mitochondrial Inhibitor Blocks MAPK Pathway and Overcomes MAPK Inhibitor Resistance in Melanoma

PURPOSE

The purpose of this study is to determine if inhibition of mitochondrial oxidative phosphorylation (OxPhos) is an effective strategy against MAPK pathway inhibitor (MAPKi)-resistant BRAF-mutant melanomas.Experimental Design: The antimelanoma activity of IACS-010759 (OPi), a novel OxPhos complex I inhibitor, was evaluated in vitro and in vivo. Mechanistic studies and predictors of response were evaluated using molecularly and metabolically stratified melanoma cell lines. ¹³C-labeling and targeted metabolomics were used to evaluate the effect of OPi on cellular energy utilization. OxPhos inhibition in vivo was evaluated noninvasively by [¹⁸F]-fluoroazomycin arabinoside (FAZA) PET imaging.

RESULTS

OPi potently inhibited OxPhos and the in vivo growth of multiple MAPKi-resistant BRAF-mutant melanoma models with high OxPhos at well-tolerated doses. In vivo tumor regression with single-agent OPi treatment correlated with inhibition of both MAPK and mTOR complex I activity. Unexpectedly, antitumor activity was not improved by combined treatment with MAPKi in vitro or in vivo. Signaling and growth-inhibitory effects were mediated by LKB1-AMPK axis, and proportional to AMPK activation. OPi increased glucose incorporation into glycolysis, inhibited glucose and glutamine incorporation into the mitochondrial tricarboxylic acid cycle, and decreased cellular nucleotide and amino acid pools. Early changes in [¹⁸F]-FAZA PET uptake in vivo, and the degree of mTORC1 pathway inhibition in vitro, correlated with efficacy.

CONCLUSIONS

Targeting OxPhos with OPi has significant antitumor activity in MAPKi-resistant, BRAF-mutant melanomas, and merits further clinical investigation as a potential new strategy to overcome intrinsic and acquired resistance to MAPKi in patients.

Abstract 2900: Dissection of clonal heterogeneity unmasks pre-existing chemoresistance and new metabolic vulnerabilities in pancreatic cancer

Adaptive drug-resistance mechanisms allow human tumors to evade treatment through selection and expansion of treatment-resistant clones. Modeling the functional heterogeneity of tumors can unmask critical contributions of distinct tumor cell sub-populations toward identifying rational drug combinations. Here, studying clonal evolution of tumor cells derived from human pancreatic tumors, we demonstrate that in vitro adherent cultures and in vivo tumors are maintained by a common set of long term self-renewing tumorigenic cells that can be used to establish clonal replica tumors (CRTs), large cohorts of animals bearing human tumors with identical clonal composition. Using CRTs to conduct quantitative assessments of clonal dynamics and adaptive responses to therapeutic challenge over time, we uncovered that the tumorigenic compartment of pancreatic tumors maintains a multitude of functionally heterogeneous subpopulations of cells with differential degrees of sensitivity to therapeutics. High-throughput isolation and deep characterization of unique clonal lineages showed genetic and transcriptomic diversity underlying the functionally diverse subpopulations, positioning the origins of tumor heterogeneity within the long-term self-renewing compartment. Molecular annotation of gemcitabine-naïve clonal lineages with distinct responses to treatment in the context of CRTs generated signatures that can predict the response to chemotherapy and exposed pre-existing functional mechanisms of clonal resistance, primarily associated to DNA damage tolerance and mitochondrial respiration (OXPHOS). Further transcriptomic and metabolic characterization of residual tumor cells in patient derived xenograft models as well as in patients after chemoradiation showed that resistant cells that contribute to tumor relapse are metabolically rewired to upregulate OXPHOS. Combining a novel inhibitor of oxidative phosphorylation (IACS-10759) developed at the MD Anderson Institute for Applied Cancer Science, and currently in phase I clinical trial in acute myeloid leukemia and solid tumors, with standard of care drugs drastically reduces tumor clonal complexity, underscoring the promise of inhibiting mitochondrial respiration as a new therapeutic strategy to prolong patient survival by eradicating resistant clones that survive chemoradiation. Our study, correlating genomic and transcriptomic traits with specific functional phenotypes, uncovered new mechanisms that underlie intra-tumor sub-clonal heterogeneity, influence treatment response to drugs and sustain tumor relapse.

Citation Format: Sahil Seth, Chieh-Yuan Li, Sara Loponte, I-Lin Ho, Denise Corti, Luigi Sapio, Edoardo Del Poggetto, Michael Peoples, Tatiana Karpinets, Frederick S. Robinson, Shan Jiang, Prasanta Dutta, Joseph Marszalek, Maria E. Di Francesco, Timothy P. Heffernan, Virginia Giuliani, Pratip K. Bhattacharya, Giannicola Genovese, Andrew Futreal, Giulio Draetta, Andrea Viale, Alessandro Carugo. Dissection of clonal heterogeneity unmasks pre-existing chemoresistance and new metabolic vulnerabilities in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2900.

Abstract A050: Intratumoral delivery of a novel STING agonist synergizes with checkpoint blockade to regress multifocal pancreatic cancer

Immunosuppressive myeloid populations including tumor-associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC) are abundant within pancreatic adenocarcinoma (PDAC) tumors and play critical roles in constraining cytotoxic T-cell function in the tumor microenvironment. We hypothesized that intratumoral engagement of innate pathogen recognition receptors such as Stimulator of Interferon Genes (STING) could induce proinflammatory polarization of the myeloid stroma and liberate the antitumor T-cell response to regress refractory PDAC tumors in the presence of checkpoint blockade.We developed and characterized a novel cyclic dinucleotide (CDN) STING agonist IACS-8803, and found that 8803 activates downstream STING signaling in both human (THP-1) and murine (J774) myeloid reporter cells with over 10-fold greater potency than ML-RR-S2-CDA, the first-in-class CDN currently undergoing clinical evaluation (NCT02675439, NCT03172936). Intratumoral delivery of 8803 into subcutaneous B16 melanoma and PDAC tumors additionally revealed a greater capacity to induce tumor regression relative to ML-RR-S2-CDA. In order to evaluate the specific effects of 8803 on the phenotype and function of suppressive myeloid populations, we generated in vitro polarized human M2 macrophages and murine bone marrow-derived MDSC. Upon exposure to 8803, we observe downregulation of M2 markers CD163, LAP/TGF-β, and Arginase on human M2 macrophages, concomitant with upregulation of M1 markers CD86, CD80, and IL-6. Additionally, 8803-stimulated murine MDSC exhibit reduced T-cell suppressive capacity compared to unstimulated MDSC. In these studies, we consistently observe that the magnitude of phenotypic and functional repolarization by 8803 is superior to that of ML-RR-S2-CDA as well as other known CDN, 2’3’-cGAMP and c-di-GMP. Therefore, we describe IACS-8803 as a novel, highly potent STING agonist with the capacity to induce inflammatory repolarization in suppressive myeloid cells of both human and murine origin. We next investigated the capacity for intratumoral delivery of IACS-8803 to sensitize murine pancreatic cancer to checkpoint blockade and to mobilize systemic immunity against disseminated lesions. We utilized mT4-2D, a novel pancreatic cancer cell line from Kras+/LSL-G12D Tp53+/LSL-R172H Pdx1-Cre tumor organoids. We isolateda single cell clone of mT4-2D with reduced in vivo growth kinetics (termed mT4-LS), as well as a clone that maintains the aggressive nature of the parental line (termed mT4-LA). Mice bearing 10-day established orthotopic and subcutaneous mT4-LS tumors received standard regimens of αCTLA-4, αPD-1, or combined αCTLA-4/αPD-1 in the presence or absence of 8803 CDN injected into the orthotopic pancreatic tumor. We find single-agent treatment with 8803, αCTLA-4, αPD-1, or αCTLA-4/αPD-1 can cure 40-60% of mice of both orthotopic and subcutaneous tumors in this system; however, combining 8803 with checkpoint blockade completely eradicates both injected and distal mT4-LS tumors in all mice. We replicated these studies using the highly aggressive and refractory mT4-LA model, and found that combination therapy with intra-pancreatic 8803 and systemic αCTLA-4/αPD-1 significantly extends survival compared to 8803 or αCTLA-4/αPD-1 alone (p=0.001, p=0.0086, respectively). Analysis of treated mT4-LA tumors by flow cytometry reveals that combination therapy enhances the cytotoxic potential of CD8 T-cells at both injected and uninjected lesions, and promotes dendritic cell proliferation within the pancreatic milieu. These studies provide a preclinical rationale for pursuing the use of STING-activating CDN as a localized approach to sensitize refractory PDAC tumors to checkpoint blockade immunotherapy.

Citation Format: Casey R. Ager, Maria E. Di Francesco, Philip Jones, Michael A. Curran. Intratumoral delivery of a novel STING agonist synergizes with checkpoint blockade to regress multifocal pancreatic cancer [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A050.

Abstract 2831: Collateral lethality: A new target for personalized oncology

Large-scale genomic profiling efforts, such as The Cancer Genome Atlas (TCGA) have painted an unprecedentedly detailed picture of the genetic alterations that underlie carcinogenesis, yet the key challenge remains as to how to turn this information into actionable therapies. Genomic deletions are a frequent event in diverse cancers, which inactivate a limited number of tumor suppressor genes (“driver”-events) but frequently include many chromosomal neighbors as “passengers”, some of which play critical but redundant roles in normal cellular housekeeping. The overall hypothesis we propose to test is that collateral deletions of such “passenger” genes can be utilized as novel targets of synthetic lethality, an idea which we term “collateral lethality." The large number of passenger deleted genes, playing diverse functions in cell homeostasis, offers a rich repertoire of pharmacologically targetable vulnerabilities presenting novel opportunities for the development of personalized anti-neoplastic therapies. We have provided in vitro proof-of-principal of a collaterally deleted glycolytic gene Enolase 1 (ENO1) at the 1p36 tumor suppressor locus in glioblastoma (GBM), that leads to dramatic sensitization to inhibition of the redundant paralogue, ENO2. The next step is to take this concept to the clinic. Our overall goal is to generate a clinical candidate Enolase inhibitor for tumors with ENO1-deletions, like GBM for which there is no other treatment option and the therapeutic benefit could be quite substantial.

Citation Format: Yu-Hsi Lin, Naima Hammoudi, Nikunj Satani, Jeffrey Ackroyd, Sunada Khadka, Dimitra Georgiou, Joe Marszalek, Yuting Sun, Marina Protopopova, Maria E. Di Francesco, Barbara Czako, Alan Y. Wang, Ronald A. DePinho, Florian L. Muller. Collateral lethality: A new target for personalized oncology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2831.

Abstract A39: Pomhex, a cell-permeable high potency enolase inhibitor with utility for collateral lethality treatment of cancer

Glycolysis inhibition is an active area of investigation for the treatment of cancer. However, few compounds have progressed beyond the cell culture stage. We have recently demonstrated that genomic passenger deletion of the glycolytic enzyme Enolase 1 (ENO1) leaves gliomas harboring such deletions solely reliant on ENO2, rendering them exquisitely sensitive to enolase inhibitors Collateral Lethality. However, the tool compound that we employed for these in vitro studies, Phosphonoacetohydroxamate (PhAH), has very poor pharmacological properties and was ineffective in vivo. We recently reported that a structural analogue of PhAH, the natural phosphonate antibiotic SF2312, is a high potency inhibitor of Enolase. While more potent than PhAH, SF2312 remains poorly cell permeable. Here, we generated a Pivaloyloxymethyl (POM) ester pro-drug derivative of SF2312, termed POMSF, which increased the potency in cell based systems by ~50-fold. POMSF is selectively active against ENO1-deleted glioma cells in culture at ~19 nM, versus μM for SF2312. However, POMSF displayed poor aqueous stability. A derivative of POMSF, termed POMHEX, showed greater stability and its active form, HEX, showed 4-fold preference for ENO1 over ENO2. Labeled 13C-glucose tracing shows that POMHEX inhibits glycolysis at the Enolase step in all cell lines tested, but with ~100-fold greater potency in ENO1-deleted lines. POMHEX selectively killed ENO1-deleted glioma cells with an IC50 <30nM, whilst non-deleted cells could readily tolerate μM levels of inhibitor. As such, POMHEX was selected for in vivo experiments. Using an orthotopic intracranial xenografted model where tumor growth and response to therapy are monitored by MRI, we show that POMHEX is capable of eradicating intracranial ENO1-deleted tumors, with mice remaining recurrence-free even after treatment discontinuation. Taken together, these results reinforce that glycolysis is a viable target and provide in vivo proof-of-principal for the concept of using passenger deletions as targetable vulnerabilities in personalized cancer therapy.

Citation Format: Yu-Hsi Lin, Nikunj Satani, Naima Hammoudi, Federica Pisaneschi, Paul Leonard, David Maxwell, Zhenghong Peng, Todd Link, Lee IV R. Gilbert, Ananth Bosajou, Duoli Sun, Joe Marszalek, Yuting Sun, John S. McMurray, Pijus K. Mandal, Maria E. Di Francesco, Barbara Czako, Alan Wang, William Bornmann, Ronald A. DePinho, Florian Muller. Pomhex, a cell-permeable high potency enolase inhibitor with utility for collateral lethality treatment of cancer [abstract]. In: Proceedings of the AACR Precision Medicine Series: Opportunities and Challenges of Exploiting Synthetic Lethality in Cancer; Jan 4-7, 2017; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2017;16(10 Suppl):Abstract nr A39.

Abstract 3837: Passenger deletion of ENO1 as a collateral lethality target in cancer

Large scale genomic characterization efforts such as TCGA have painted an unprecedentedly detailed picture of the genetic alterations that underlie tumorigenesis. Yet, the majority of genetic alterations are passenger rather than driver events and are considered unactionable. We have previously proposed that passenger or collateral deletions could serve as pharmacologically targetable vulnerabilities Collateral Lethality, in case passenger genes are homozygously deleted and member of a paralogous gene family carrying out an essential housekeeping function. We have presented proof-of-principal, whereby passenger deletion of the glycolytic gene Enolase 1 (ENO1) as part of the 1p36-tumor suppressor locus, renders glioma cells harboring such deletions highly sensitive to ablation of its redundant paralogue, ENO2. While our original analysis identified ENO1-homozygous deletions in Glioblastoma (GBM), recent bioinformatics analyzes, backed by immunohistochemistry, show that ENO1-homozygous deletions also occur in Hepatocellular Carcinoma and Cholangiocarcinoma. In GBM, multisector analysis of primary and recurrent tumors, indicate that ENO1 deletion is an early event which is homogenously distributed through the primary tumor and persist during recurrence. To pharmacologically exploit ENO1-deletion, we have pursued two approaches. First, we have synthesized cell-permeable prodrug derivatives of the natural Enolase inhibitor SF2312. The lead compound, POMHEX, shows potent killing of ENO1-deleted glioma cells in the low nM range while ENO1-restored isogenic or normal cells can tolerate μM doses. POMHEX has a short half-life yet can eradicate intracranial xenografted ENO1-deleted tumors, provided extensive breakdown of the blood-brain barrier. Our second approach to targeting ENO1-deletion consisted of chemical biology screening of drug libraries for the ability to kill ENO1-deleted but not isogenic rescued cells. We find that ENO1-deleted cells show a dramatic sensitization to inhibitors of the mitochondrial electron transport chain. These include tool compounds such as rotenone as well as compounds not previously associated with mitochondria, such as Mubritinib and an experimental anti-neoplastic agent previously described as a HIF1-inhibitor, now known to inhibit mitochondrial Complex I. The latter agent shows potent activity against ENO1-deleted intracranial xenografts. The likely cause for this sensitivity is the inability of ENO1-deleted cells to compensatory upregulate glycolysis in response mitochondrial inhibition, the typical response of ENO1-intact glioma cells and normal cells. Together, these data indicate that passenger deletion of ENO1 is an encouraging drug-target and provide support for collateral lethality as a viable therapeutic strategy, which, given the large number of passenger deletions in the cancer genome, may be broadly applicable.

Citation Format: Yu-Hsi Lin, Nikunj Satani, Naima Hammoudi, Joe Marszalek, Yuting Sun, Marina Protopopova, Maria E. Di Francesco, Barbara Czako, Alan Wang, Ronald A. DePinho, Florian L. Muller. Passenger deletion of ENO1 as a collateral lethality target in 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 3837.

Abstract C183: Pomhex: a cell-permeable high potency Enolase inhibitor with in vivo anti-neoplastic activity

Glycolysis inhibition is an active area of investigation in cancer. However, few compounds have progressed beyond the cell culture stage. We have recently demonstrated that genomic passenger deletion of the glycolytic enzyme Enolase 1 (ENO1) leaves gliomas harboring such deletions with less than 10% of normal enzymatic activity, rendering them exquisitely sensitive to enolase inhibitors. However, the tool compound that we employed for these in vitro studies, Phosphonoacetohydroxamate (PhAH), has very poor pharmacological properties and was ineffective in vivo. We performed a SAR studies to increase inhibitor specificity towards ENO2 as well as pro-druging to increase cell permeability. The lead compound generated by these efforts, termed POMHEX, is selectively active against ENO1-deleted glioma cells in culture at ∼35nM (versus μM for PhAH). Using an orthotopic intracranial xenografted model where tumor growth and response to therapy are monitored by MRI, we show that POMHEX is capable of eradicating intracranial ENO1-deleted tumors, with mice remaining recurrence-free even after treatment discontinuation. Taken together, these results reinforce that glycolysis is a viable target and provide in vivo proof-of-principal for the concept of using passenger deletions as targetable vulnerabilities in cancer therapy.

Citation Format: Yu-Hsi Lin, Joe Marszalek, Yuting Sun, Naima Hammoudi, Paul Leonard, David Maxwell, Nikunj Satani, Peng Zhang, Todd Link, Gilbert Lee, Maria E. Di Francesco, Barbara Czako, Alan Y. Want, Ronald A. DePinho, Florian L. Muller. Pomhex: a cell-permeable high potency Enolase inhibitor with in vivo anti-neoplastic activity. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C183.

Genetic events that limit the efficacy of MEK and RTK inhibitor therapies in a mouse model of KRAS-driven pancreatic cancer

Mutated KRAS (KRAS*) is a fundamental driver in the majority of pancreatic ductal adenocarcinomas (PDAC). Using an inducible mouse model of KRAS*-driven PDAC, we compared KRAS* genetic extinction with pharmacologic inhibition of MEK1 in tumor spheres and in vivo. KRAS* ablation blocked proliferation and induced apoptosis, whereas MEK1 inhibition exerted cytostatic effects. Proteomic analysis evidenced that MEK1 inhibition was accompanied by a sustained activation of the PI3K-AKT-MTOR pathway and by the activation of AXL, PDGFRa, and HER1-2 receptor tyrosine kinases (RTK) expressed in a large proportion of human PDAC samples analyzed. Although single inhibition of each RTK alone or plus MEK1 inhibitors was ineffective, a combination of inhibitors targeting all three coactivated RTKs and MEK1 was needed to inhibit proliferation and induce apoptosis in both mouse and human low-passage PDAC cultures. Importantly, constitutive AKT activation, which may mimic the fraction of AKT2-amplified PDAC, was able to bypass the induction of apoptosis caused by KRAS* ablation, highlighting a potential inherent resistance mechanism that may inform the clinical application of MEK inhibitor therapy. This study suggests that combinatorial-targeted therapies for pancreatic cancer must be informed by the activation state of each putative driver in a given treatment context. In addition, our work may offer explanative and predictive power in understanding why inhibitors of EGFR signaling fail in PDAC treatment and how drug resistance mechanisms may arise in strategies to directly target KRAS.