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Invest New Drugs (2013) 31:11361141 DOI 10.1007/s10637-013-9928-9
PRECLINICAL STUDIES
Genotype-dependent cooperation of ionizing radiationwith BRAF inhibition in BRAF V600E-mutated carcinomas
Tina Dasgupta & Daphne A. Haas-Kogan &
Xiaodong Yang & Aleksandra Olow & Daniel X. Yang &
Ashley Gragg & Lisa A. Orloff & Sue S. Yom
Received: 21 October 2012 /Accepted: 7 January 2013 /Published online: 26 January 2013 # Springer Science+Business Media New York 2013
Summary Background A substantial proportion of solid tumors carry the BRAF V600E mutation, which causes activation of the MEK/MAPK pathway and is a poor prognostic indicator. Patients with locally advanced human cancers are often treated with external beam radiation therapy. Given the association of Raf overactivation with radioresistance, we hypothesized that, in BRAF V600E-mutated carcinomas, there would be combinatorial activity between radiation and PLX4720, a specific BRAF V600E-inhibitor. Methods Two BRAF V600E-mutated cancer cell lines and one BRAFV600E wildtype (WT) cancer cell line were obtained. We performed cell viability assays and clonogenic assays using combinations of radiation and PLX4720. We assessed MEK and MAPK phosphorylation at different PLX4720 concentrations with western blotting, and cell cycle progression was evaluated by flow cytometry. Results Our results show combinatorial, additive activity between radiation and PLX4720 in BRAF V600E-mutated cell lines, but not in the BRAF WT line. In BRAF V600E-mutated cells, there was a PLX4720
concentration-dependent decrease in MEK and MAPK phosphorylation. In cells with BRAF V600E mutations, PLX4720 caused cell cycle arrest at G1, and, when combined with radiation, caused a combined G1 and G2 cell cycle arrest; this pattern of cell cycle effects was not seen in the BRAF WT cell line. Conclusions These data suggest additive, combinatorial activity between radiation and PLX4720 in cancers carrying BRAF V600E mutations. Our data has potential for translation into the multimodality treatment of BRAF V600E-mutated cancers.
Keywords BRAF V600E . PLX4720 . PLX4032 . vemurafenib . Radiosensitization
Introduction
BRAF is a member of the RAF family of proteins and plays a major role in signal transduction of extracellular signals to intracellular targets. As a receptor tyrosine kinase (RTK) is bound by a ligand, it undergoes an intracellular conformation change to cause autophosphorylation of the RTK, which subsequently commences a phosphorylation cascade. In this way, Ras is activated, and subsequently phosphorylates Raf, one...