Anaplastic thyroid cancer(ATC) is a rare but extremely aggressive form of endocrine malignancy that accounts for only 1-2% of total thyroid cancer cases but responsible for 20-30% of annual mortality from thyroid cancer in the USA. Genetic lesion landscape in ATC is not conducive to multiple targeted therapies. BRAF mutation is one of the dominant genetic lesions observed in 30-40% of ATC cases and 98% of them are BRAFV600E positive. Due to the limited therapeutic efficacy of BRAFV600E inhibitor vemurafenib, identification of novel therapeutic candidates would provide a viable alternative. Immunecheckpoint therapies have showed huge promise in recent years but are relatively underexplored in ATC patients. To this end, 4 ATC cell lines 8505C, T238, SW1736 and HTh74; 3 PTC cell lines TPC-1, BCPAP and K1 and 1 FTC cell line CGTH-W-1 were screened for expression of 29 immune-checkpoint molecules by qRT PCR with or without 10μM vemurafenib treatment for 24 hrs. Initial screening revealed a differential expression level of the transcripts among the cells. Vemurafenib treatment further up regulated expression of CD160, HVEM, BTLA, TIM3 and galectin9 in cell lines positive for BRAFV600E mutation (8505C, SW1736, BCPAP) and the ones harboring an additional PIK3CA mutation (T238, K1). This observation was further confirmed by immunocytochemistry. CD160 was not detected in any of the cell lines except for K1, TPC-1 and NTHY at protein level. Flow cytometry confirmed presence of BTLA, HVEM and TIM3 on the surface of these tumor cells which would enable them to engage their cognate ligands on T cells and suppress antitumor immune response. Western blots confirmed upregulation of BTLA, HVEM, TIM3 and galectin 9 in response to vemurafenib in both BRAFV600E positive cell lines and HTh74. Expression of these molecules were also validated by immunohistochemistry in patient samples. In an effort to evaluate the functional activity of these immunecheckpoint molecules, co-culture studies were done. Both HVEM and BTLA showed immunomodulatory capability and were capable of redirecting T cell differentiation towards a suppressive phenotype. Preclinical studies with combination of BRAFV600E or PI3K inhibitor and antagonistic antibodies against these molecules are currently underway. This study has identified two novel immune checkpoint molecules in ATC and might provide viable therapeutic targets.

Citation Format: Sanjukta Chakraborty, Rachana R. Maniyar, Sina Dadafarin, Ghada Ben Rahoma, Sarnath Singh, Augustine Moscatello, Jan Geliebter, Raj K. Tiwari. Combinatorial immune checkpoint inhibitor therapy in anaplastic thyroid 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 3237.

©2019 American Association for Cancer Research.
2019
American Association for Cancer Research.