Abstract 5192: Selection of radiosensitizers based on HRAS mutation in head and neck cancer

Abstract

Abstract Purpose/Objective(s): The ability of activated HRAS to promote radiation resistance and predict for sensitivity to potential radiosensitizers was tested in a head and neck cancer model system. Materials/Methods: Mutations in HRAS, KRAS, and NRAS were analyzed using cBioPortal in a head and neck cancer cohort. The Illumina TruSeq Amplicon Cancer panel was used to screen a panel of head and neck cancer cell lines for mutations in RAS-family genes. Cell growth and radiation survival was assessed by clonogenic survival assay. Immunoblots were used to confirm target activation/knockdown in overexpression and knockdown studies. A tumor control dose 50% (TCD50) assay was employed to investigate radiosensitization of a mutated-HRAS head and neck cancer cell line in a flank xenograft model in nude mice. Results: Activating mutations in one of the three RAS genes are seen in 5-10% of head and neck cancer patients. Mutations in HRAS represent over 50% of these. Screening our panel of head and neck cancer cell lines identified a canonical activating mutation in HRAS (i.e. G12V) in SCC22B. Consistent with known roles for activated HRASG12V, SCC22B is relatively insensitive to both cetuximab and radiation. Using both in vitro and in vivo studies, cetuximab exhibited no ability to radiosensitize SCC22B. Cetuximab treatment decreased AKT, but not ERK activation. Direct inhibition pathways downstream of HRAS by selumetinib (MEK/ERK) or BEZ235 (PI3K/MTOR) decreased target protein activation and resulted in significant growth inhibition compared to control (p<0.05). Treatment with either selumetinib or BEZ235 radiosensitized HRASG12V expressing cells (SER 1.3-1.8) but had more modest effects on cells with wildtype HRAS. siRNA knockdown of HRAS radiosensitized SCC22B, but not SCC1 or SCC6 cells relative to non-targeting control. Overexpression of HRASG12V conferred relative radioresistance in wildtype cell lines. In vivo assessment of the radiosensitizing effects of these compounds (TCD50) is pending. Conclusion: More than 5% of head and neck cancers harbor activating mutations in one of the RAS family of genes. These mutations lead to resistance to cetuximab, either as a single agent, or as a radiosensitizer. Inhibition of downstream targets such as the MEK/ERK and PI3K/MTOR pathways can radiosensitize tumors harboring activating mutations in HRAS. Identification of additional mutation/drug combinations that result in radiosensitization may be valuable to advance the design of personalized radiation therapy. Citation Format: Michael M. Fisher, Adam D. Swick, Kwangok P. Nickel, Randall J. Kimple. Selection of radiosensitizers based on HRAS mutation in head and neck cancer [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 5192. doi:10.1158/1538-7445.AM2017-5192