Selective Inhibition Of Nf1 Loss-Of-Function Driven Oncogenic Signaling In Melanomas

Abstract 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.