Abstract 625: Selective inhibition of NF1 loss-of-function driven oncogenic signaling in melanomas

Oncogenic activation of the MAPK signaling pathway occurs across >90% of melanomas, motivating the clinical evaluation of MAPK-targeted therapies in these tumors. However, only BRAFV600E/K-mutated melanomas show consistent clinical responses to MAPK-targeted therapies. Inactivation of the tumor suppressor gene neurofibromin 1 (NF1) is among the mechanisms that drive hyperactivated RAS signaling in >10% of melanomas. These tumors, however, have variable dependency on RAS-mediated pathways, such as MAPK and PI3K/mTOR, and thus exhibit inconsistent sensitivity to targeted inhibitors of these pathways. It is of paramount importance, therefore, to identify new therapeutic strategies to block tumor cell growth or improve MAPK- or PI3K-targeted therapy response in NF1 loss-of-function (NF1LoF) melanomas. To identify actionable vulnerabilities in NF1LoF melanoma cells, we apply a systematic approach, combining multiplexed high-throughput immunofluorescence microscopy, single-cell measurements and computational analysis, to study the responses of differentially mutated human melanoma cell lines to a variety of RAS-related pathway inhibitors. Our analysis led to the identification of a multi-kinase inhibitor, MTX-216, which is efficacious in induction of tumor cell death and inhibition of NF1LoF melanoma growth both in vitro and in vivo, but does not exhibit cytotoxicity in BRAFV600E melanomas and wild-type melanocytes. Single-cell analysis of downstream RAS-mediated signaling markers (e.g. phospho-S6) and proliferation markers (e.g. Ki-67) demonstrated cell-to-cell heterogeneity in NF1LoF melanoma cells treated with commercially available kinase inhibitors, resulting in incomplete drug responses. MTX-216 reduces this single-cell variability, providing evidence that co-suppression of signaling and proliferation pathways is correlated with drug-induced cytotoxicity. Our systematic analysis, together with ongoing studies to uncover the mechanism of action of MTX-216 in NF1LoF melanomas, has the potential to identify new and effective treatment strategies for NF1-mutant melanomas.

Citation Format: Cara Abecunas, Mohammad Fallahi-Sichani, Judith Leopold, Christopher Whitehead, Elizabeth Ziemke. Selective inhibition of NF1 loss-of-function driven oncogenic signaling in melanomas [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 625.

Abstract 2931: MTX-211, a dual and selective inhibitor of EGFR and PI3 kinase, shows promising activity in combination with MEK inhibition in preclinical models of pancreatic cancer

Pancreatic cancer is one of the deadliest forms of cancer, with median 5-year survival rates less than 10%. This disease is recalcitrant to chemotherapeutic approaches and recently approved therapies afford only modest improvements in survival. KRAS is the most commonly mutated gene in pancreatic tumors with an incidence rate exceeding 90%. Despite intensive efforts, KRAS has remained undruggable. Kinases acting both upstream and downstream of RAS continue to be exploited for the development of novel agents to attenuate signaling through this critical oncogene. While EGFR and MEK inhibitor monotherapies have been evaluated in the clinic for the treatment of pancreatic cancer, efficacy has been modest despite their relevance to MAP kinase (MAPK) pathway-altered tumors. Novel therapies are urgently needed to address adaptive signaling mechanisms that diminish the effectiveness of kinase-targeted approaches. MTX-211 is a first-in-class dual inhibitor of PI3K and EGFR kinase with a promising pharmaceutical profile and proven ability to potentiate the effectiveness of MEK inhibitor therapy in KRAS mutant colorectal tumors. The present study was undertaken to extend our evaluation of MTX-211 to include pancreatic cancer model systems. We have found that MTX-211 exhibits low micromolar potency against an extensive panel of primary models of pancreatic cancer and is highly synergistic with the MEK inhibitor trametinib. Preliminary data suggest that this synergy is driven by the ability of MTX-211 to target compensatory transcriptional activation of HER3 that occurs in response to MEK inhibition. A genetically engineered KRAS and p53 mutant (KPC) mouse model was transduced with a lentiviral construct encoding a caspase reporter, which was used to show that the combination of MTX-211 and trametinib elicited a significant increase in apoptosis over single agent controls. Results from an animal study conducted with the KPC model further showed that the combination of MTX-211 and trametinib significantly slowed growth of these aggressive tumors. Employing both KPC and patient-derived xenograft models of pancreatic cancer, efforts are underway to optimize therapeutic outcome in response to MTX-211-based combination treatment regimens.

Citation Format: Christy Frankowski-McGregor, Joel Maust, Elizabeth Ziemke, Rachel Mumby, Amy Delaney, Alnawaz Rehemtulla, Christopher Whitehead, Judith S. Sebolt-Leopold. MTX-211, a dual and selective inhibitor of EGFR and PI3 kinase, shows promising activity in combination with MEK inhibition in preclinical models of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2931.

Targeting ADAM17 inhibits human colorectal adenocarcinoma progression and tumor-initiating cell frequency

ADAM17 (a disintegrin and metalloproteinase 17)/TACE (TNFα converting enzyme) has emerged as a potential therapeutic target in colorectal cancer (CRC) and other cancers, due in part to its role in regulating various tumor cell surface proteins and growth factors and cytokines in the tumor microenvironment. The emergence of MEDI3622, a highly potent and specific antibody-based ADAM17 inhibitor, has allowed testing of the concept that targeting ADAM17 may be an important new therapeutic approach for CRC patients. We demonstrate that MEDI3622 is highly efficacious on tumor growth in multiple human CRC PDX models, resulting in improved survival of animals bearing tumor xenografts. MEDI3622 was further found to impact Notch pathway activity and tumor-initiating cells. The promising preclinical activity seen here supports further clinical investigation of this treatment approach to improve therapeutic outcome for patients diagnosed with metastatic CRC, including patients with KRAS-mutant tumors for whom other therapeutic options are currently limited.

Abstract 975: Monoclonal antibody targeting of ADAM17 is an effective treatment for metastatic colorectal cancer resulting in tumor growth control and reductions of cancer stem cells

ADAM17/TACE (TNFα converting enzyme) has been implicated to play a role in the drug resistance of colorectal cancers. The present study addresses the hypothesis that MEDI3622, a specific ADAM17 monoclonal antibody known to possess both human and mouse cross reactivity, represents a viable therapeutic strategy to improve outcome in the treatment of metastatic colorectal cancer (mCRC). We have generated both in vitro and in vivo data in patient-derived CRC models to provide compelling support for further exploration of this treatment strategy. A heterogeneous panel of low passage colorectal patient-derived xenografts (PDX) has been established from biospecimens procured during patient surgeries conducted at University of Michigan. All xenograft models have been genomically profiled and their histologies mimicked those observed in the original samples. As anticipated, approximately half of these models harbor an oncogenic KRAS mutation and exhibit widely differing histologies, consistent with the heterogeneity encountered in the clinic. Efficacy testing of MEDI3622 has shown that this agent significantly impaired tumor growth in 3 of the 5 PDX models examined, including one model that is KRASMT. Furthermore, cancer stem cell function in these CRC models is negatively impacted by MEDI3622, reducing tumor initiation frequencies in tumor re-implantation studies at the conclusion of treatment. Therefore our results suggest that a monoclonal antibody approach that targets ADAM17 may provide an attractive therapeutic strategy for the treatment of metastatic colorectal cancer both by reducing tumor growth and inhibiting cancer stem cells.

Citation Format: Joseph Dosch, Elizabeth Ziemke, Theodore Welling, Karin Hardiman, Juidth Sebolt-Leopold, Emil Michelotti, Robert Hollingsworth, Elaine Hurt. Monoclonal antibody targeting of ADAM17 is an effective treatment for metastatic colorectal cancer resulting in tumor growth control and reductions of cancer stem 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 975. doi:10.1158/1538-7445.AM2015-975

Abstract 4541: Dual targeting of CDK4 and MEK as a combination treatment strategy for metastatic colorectal cancer

Aberrant hyperactivation of KRAS plays a prominent role in tumor initiation and progression of a broad spectrum of human malignancies. The incidence of KRAS mutations is especially high in colorectal cancers, where it occurs at a frequency of roughly 50%. The present study addresses the hypothesis that dual targeting of CDK4 and MEK represents a viable treatment strategy for the subpopulation of colorectal cancers exhibiting hyperactivated KRAS signaling. We have generated both in vitro and in vivo data in highly passaged colorectal xenograft models to provide compelling support for further exploration of this combination treatment strategy. We have now turned to the study of primary human models that are anticipated to be more predictive of ultimate clinical activity in patients. A heterogeneous panel of low passage colorectal patient-derived xenografts (PDX) has been established from biospecimens procured during patient surgeries conducted at our institution (n=12). All xenograft models have been genomically profiled and their histologies mimicked those observed in the original samples. As anticipated, approximately half of these models harbor an oncogenic KRAS mutation and exhibit widely differing histologies, consistent with the heterogeneity encountered in the clinic. Immunoblotting analysis has further revealed that that the majority (>80%) are positive for both phosphorylated RB and constitutive pERK expression and are therefore candidates for treatment regimens combining inhibitors of CDK4 and MEK. Employing the CDK4 inhibitor palbociclib and multiple MEK inhibitors, in vivo efficacy studies are ongoing against our colorectal PDX panel. Preliminary data have shown a higher frequency of regressions in the combination arm compared to either single agent arm at the respective maximum tolerated doses. Our results therefore suggest that combined inhibition of CDK4 and MEK may provide an attractive therapeutic strategy for the treatment of colorectal cancer.

Citation Format: Elizabeth Ziemke, Joseph Dosch, Amrith Shettigar, Shanshan Wan, Theodore Welling, Karin Hardiman, Judith Sebolt-Leopold. Dual targeting of CDK4 and MEK as a combination treatment strategy for metastatic colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4541. doi:10.1158/1538-7445.AM2014-4541