Genotype-dependent cooperation of ionizing radiation with BRAF inhibition in BRAF V600E-mutated carcinomas.
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 BRAF-V600E 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.
Department of Radiation Oncology, University of California, San Francisco, 1600 Divisadero Street, Suite H-1031, San Francisco, CA, 94143-1708, USA.
Tina
T
Dasgupta
Daphne A
DA
Haas-Kogan
Xiaodong
X
Yang
Aleksandra
A
Olow
Daniel X
DX
Yang
Ashley
A
Gragg
Lisa A
LA
Orloff
Sue S
SS
Yom
D000970:Antineoplastic Agents / Q000008:administration & dosage*; D002277:Carcinoma / Q000188:drug therapy* / Q000235:genetics / Q000532:radiotherapy*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival; D003131:Combined Modality Therapy; D005838:Genotype; D006801:Humans; D007211:Indoles / Q000008:administration & dosage*; D009154:Mutation; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage*; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors* / Q000235:genetics; D011836:Radiation Tolerance / Q000187:drug effects; D011839:Radiation, Ionizing; D013449:Sulfonamides / Q000008:administration & dosage*
D000970:Antineoplastic Agents; D007211:Indoles; C528407:PLX 4720; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf