Abstract C31: Vemurafenib selectively radiosensitizes BRAF V600E mutant papillary and anaplastic thyroid carcinoma cells in vitro

Abstract

Abstract Background: BRAF mutations are oncogenic drivers which occur in about 60% of papillary thyroid cancer (PTC) as well as a significant proportion of anaplastic thyroid cancer (ATC). BRAF mutations drive MAPK signaling and treatment resistance in thyroid cancer. BRAFV600E is the most common of these mutations in PTC, and can be selectively inhibited by vemurafenib. Methods: We used a panel of PTC and ATC cell lines to assess how the presence/absence of BRAFV600E impacts radiation sensitivity. We used radiation clonogenics, comet assays, nuclear foci formation, and western blots to determine the effect of vemurafenib on PTC and ATC cell lines. Results: Analysis of radiation clonogenics revealed relative radioresistance in cell lines containing the BRAFV600E mutation versus wild-type. Vemurafenib inhibited MAPK signaling in V600E mutants, but showed no effect on BRAF wild-type cell lines. Vemurafenib pretreatment selectively radiosensitized BRAFV600E mutants, as assessed by radiation clonogenic assays. Neutral comet assays also showed that vemurafenib impairs DNA repair in BRAFV600E lines. Furthermore, γ-H2A.x westerns and nuclear foci staining indicated that vemurafenib pretreatment decreases the ability of cells to repair double-strand DNA breaks in cell lines containing the BRAFV600E mutation. Vemurafenib also appeared to alter the kinetics of nuclear foci formation and resolution of 53BP1 as well as Rad51 in these cell lines. Conclusions: From our initial results, BRAF mutations appear to be associated with radioresistance in PTC and ATC cell lines. Vemurafenib selectively radiosensitizes both PTC and ATC cells through inhibition of DNA repair mechanisms. Together, these data suggest that combining vemurafenib and radiation may improve therapeutic control for BRAFV600E mutant thyroid cancers. Citation Format: Ryan N. Robb, Linlin Yang, Moumita Chatterjee, Moto Saji, Matt Ringel, Arnab Chakravarti, Terence Williams. Vemurafenib selectively radiosensitizes BRAF V600E mutant papillary and anaplastic thyroid carcinoma cells in vitro. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C31.