Abstract 2235: Implications of HVEM/BTLA/LIGHT signaling in anaplastic thyroid cancer
Authors: Chakraborty Sanjukta , Jarboe Tara , Dadafarin Sina , Geliebter Jan , Moscatello Augustine , Tiwari Raj K. 
Published: September 2020

Abstract
Thyroid cancer incidence is increasing at an alarming rate almost tripling every decade. Although the majority of thyroid tumors are treatable, about 2-3% of thyroid cancers, mainly anaplastic thyroid cancer (ATC) is refractory to mainstream therapies. Driver mutations like BRAFV600E, PI3KCAE545K prompted development of targeted therapies with kinase inhibitors for ATC, but several reports suggest development of resistance. Given the refractory nature of ATC, it is imperative to explore alternative targets using accessory cell surface molecules that modulate the tumor immune microenvironment (TIME). Immune checkpoint molecules have revolutionized the field of cancer therapeutics, but are underexplored in ATC as an alternative therapeutic target. To this end, 4 ATC cell lines 8505C, T238, SW1736 and HTh74; 3 papillary thyroid cancer (PTC) cell lines TPC-1, BCPAP and K1 and 1 follicular thyroid cancer (FTC) cell line CGTH-W-1 were screened for expression of 29 immune-checkpoint molecules by qRT PCR, immunocytochemistry, western blot and flow cytometry. We noted a differential expression of HVEM, BTLA, CD160, TIM3, LGALS9 and PD-L1 across the cell lines. The expression level of these genes was much higher in ATC cell lines compared to the rest. Expression level of HVEM was more than 30 fold higher compared to the other cell lines on average. HVEM is a member of TNFRSF which interacts with BTLA, CD160 and LIGHT in a cis or trans manner. Given the highly inflammatory nature of ATC, expression of HVEM on tumor cells was suggestive of a possible immune regulation in the TME by inflammatory cytokines. To evaluate this regulation, cells were treated with IL8 and TNFα for 24 hrs and HVEM expression was monitored on cell surface and in conditioned media. Interestingly, we observed a reduced surface expression and increased solubilization of HVEM in ATC in presence of these inflammatory cytokines. To explore possible tumor intrinsic signaling transduced by HVEM, we treated the cells with soluble form of its cognate ligand, LIGHT and observed a significant increase in pIκβ, pJNK and p-c-Jun suggestive of increased proliferative potential of these cells triggered by this interaction with LIGHT. In order to assess possible tumor intrinsic role of this molecule, we knocked down HVEM in 8505C by CRISPRi and performed clonogenic assay. HVEM knocked down cells had significantly reduced potential for clonal expansion compared to WT HVEM+ 8505C. Currently we are conducting co-culture experiments to validate its role in immunomodulation and trying to understand its regulation in case of acquired resistance against small molecule inhibitors, like vemurafenib. We believe our study has identified HVEM as an immunotherapeutic target, soluble form of which could be a potential biomarker in ATC patients.
Citation Format: Sanjukta Chakraborty, Tara Jarboe, Sina Dadafarin, Jan Geliebter, Augustine Moscatello, Raj K. Tiwari. Implications of HVEM/BTLA/LIGHT signaling in anaplastic thyroid cancer [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 2235.