Abstract 714: A case for combining immunotherapy and targeted small molecule inhibitors: Immunoregulation by primary melanoma cells

Abstract

Abstract Metastatic melanoma, leads to the highest number of skin cancer related deaths. Checkpoint inhibitor therapy has witnessed a high success rate in melanoma patients with anti-CTLA-4 and anti-PD-1. However, checkpoint inhibitor molecules and their compensatory stimulatory counterparts are widely expressed on T cells and antigen presenting cells suggesting a robust redundancy in these molecules as clinical targets. Some of these molecules that include CTLA-4, PD-1, HVEM, VISTA, 41-BB, OX-40 and CD226 are also expressed on tumor cells. Their role in regulating an immune response whether it is cell killing or immune evasion remains to be elucidated. We isolated and characterized five primary patient derived melanoma cell lines: MEL-2, MEL-V, 3MM, KFM and GLM2. We screened these cells for the expression of a comprehensive panel of twenty-five co-stimulatory and co-inhibitory molecules by RT-PCR which revealed significant heterogeneity in expression of these molecules compared to normal adult melanocytes under normal conditions; underscoring the importance of understanding tumor tissue pleiotropy prior to designing a therapeutic regimen. Surprisingly, inhibitory molecules including PD-1, VISTA and LAIR1 and stimulatory molecules including 4-1BB, HVEM and ICOS were upregulated differentially in these cell lines by metabolic stress brought on by starvation conditions. Some of these molecules were restored to basal levels of expression on treatment with 10μM vemurafenib (PLX4032), a BRAFV600E inhibitor, for 24 hours. However the treatment led to concurrent upregulation of molecules such as LAG3, BTLA, CD226 and TIM1, suggesting a compensatory mechanism that could aid melanoma adaptation and escape from immune recognition. Exposing melanoma cells to classical activated dendritic cell cytokines, IL-6 and IL-12, led to a differential expression of these molecules. Additionally, experiments using tumor lysate loaded dendritic cells to study activation revealed an ability to modulate immune activation correlating with unique stimulatory and inhibitory molecule expression profile of each primary cell line. Our results underscore the importance of understanding the profile of co-stimulatory and co-inhibitory molecules expressed in tumor cells. With eighty percent of melanoma patients being positive for the BRAFV600E lesion, we make a case for designing a combinatorial therapeutic regimen, with targeted immunotherapies as well as targeting specific genetic lesions with small molecule inhibitors. Citation Format: Rachana R. Maniyar, Sanjukta Chakraborty, Neha Y. Tuli, Ghada Ben Rahoma, Sarnath Singh, Marc Wallack, Jan Geliebter, Raj K. Tiwari. A case for combining immunotherapy and targeted small molecule inhibitors: Immunoregulation by primary melanoma cells [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 714.