Abstract 3656: Implication for checkpoint therapeutics: Expression of co-stimulatory and co-inhibitory molecules in melanoma cells
Authors: Maniyar Rachana R. , Chakraborty Sanjukta , Tuli Neha , Rahoma Ghada Ben , Singh Sarnath , Geliebter Jan , Wallack Marc , Tiwari Raj K. 
Published: July 2017

Melanoma is one of the deadliest forms of skin cancer, with a dim prognosis when metastasized, leading to the highest number of skin cancer related deaths. In recent years there has been a focus on the use of checkpoint inhibitor therapies like anti-CTLA-4, anti-PD-1 and anti-PD-L1 to treat melanoma. PD-L1, HVEM and VISTA expression on cancer cells has been shown to promote immune evasion and tumor survival. CTLA-4, when engaged on tumor cells leads to their apoptosis and LIGHT signaling leads to recruitment of T cells and effective tumor clearance. Thus, since these molecules do not function in isolation, we need to consider tissue pleiotropy and the expression of co-stimulatory and co-inhibitory molecules on tumor tissue. Our laboratory has characterized and established five primary patient derived melanoma cell lines, MEL-2, MEL-V, 3MM, KFM and GLM-2. In an effort to understand tumor tissue pleiotropy, we conducted a comprehensive expression pattern screening of eight co-inhibitory and ten co-stimulatory molecules by RT-PCR. Among others, VISTA, a CD4+ T cell suppressor, HVEM, an immune evasion regulator, LAG3 and TIM3, potential immune checkpoint targets, were seen to be differentially expressed in these primary cell lines. Current therapies target CTLA-4, PD-1 and PD-L1, which also exhibit varying expression in our primary cell lines, pointing to the importance of considering tissue expression of these molecules when administering these novel immunotherapies. Additionally, 80% of melanoma patients are positive for the BRAFV600E genetic lesion and are administered vemurafenib (PLX4032), an inhibitor of the overactive mutated BRAF. Our in vitro studies show that treatment with PLX4032, changed the expression of CTLA-4 and PD-L1 in these primary cells. We observed a decrease in PD-L1 protein expression in MEL-V and GLM-2 and an increase in PD-L1 protein expression in MEL-2 and KFM, the four BRAFV600E positive cell lines. CTLA-4 protein expression demonstrated an upward trend on treatment with PLX4032. This synergy observed between treatment with drugs targeting genetic lesions and the expression of immunomodulatory molecules warrants characterization of tumor biopsies prior to designing an effective combinatorial therapy regime. Our long term goal is to optimize combinatorial immune and drug therapies directed against both co-stimulators and checkpoint inhibitors.

Citation Format: Rachana R. Maniyar, Sanjukta Chakraborty, Neha Tuli, Ghada Ben Rahoma, Sarnath Singh, Jan Geliebter, Marc Wallack, Raj K. Tiwari. Implication for checkpoint therapeutics: Expression of co-stimulatory and co-inhibitory molecules in melanoma cells [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 3656. doi:10.1158/1538-7445.AM2017-3656