title: Melanoma cells show a heterogeneous range of sensitivity to ionizing radiation and are radiosensitized by inhibition of B-RAF with PLX-4032.
abstract: OBJECTIVE
  To assess the relative radiosensitivities of a large collection of melanoma cell lines and to determine whether pharmacologic inhibition of mutant B-RAF with PLX-4032 can radiosensitize B-Raf+ melanoma cells.
  
  
  METHODS
  A large collection of melanoma cell lines (n=37) were treated with 0-8Gy IR and clonogenic survival assays used to generate survival curves to rank relative radiosensitivities among the cell lines. The ability of a B-RAF inhibitor, PLX-4032, to radiosensitize highly radioresistant B-Raf+ cells was also assessed by clonogenic cell survival and spheroid invasion assays and the effects of treatment on the cell cycle assessed by FACS.
  
  
  RESULTS
  Melanoma cell lines displayed a very large, heterogeneous range of SF2 values (1.002-0.053) with a mean of 0.51. Cell lines with surviving fractions of 0.29 or less at SF2 and SF4 were observed at a high frequency of 18.9% and 70.2%, respectively. Treatment of B-Raf+ cells with the B-RAF inhibitor PLX-4032 in combination with radiation provided enhanced inhibition of both colony formation and invasion, and radiosensitized cells through an increase in G(1) arrest.
  
  
  CONCLUSIONS
  Our data suggest that melanomas are not uniformly radioresistant with a significant subset displaying inherent radiosensitivity. Pharmacologic inhibition of B-RAF with PLX-4032 effectively radiosensitized B-Raf+ melanoma cells suggesting that this combination approach could provide improved radiotherapeutic response in B-Raf+ melanoma patients.
authors.affiliation: Department of Pathology and Laboratory Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, NC 27599, USA.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Sambade
authors.forename: Eldon C
authors.initials: EC
authors.lastname: Peters
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Thomas
authors.forename: William K
authors.initials: WK
authors.lastname: Kaufmann
authors.forename: Randall J
authors.initials: RJ
authors.lastname: Kimple
authors.forename: Janiel M
authors.initials: JM
authors.lastname: Shields
mesh_terms: D015153:Blotting, Western; D045744:Cell Line, Tumor; D005434:Flow Cytometry; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D008545:Melanoma / Q000473:pathology*; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors* / Q000235:genetics; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013449:Sulfonamides / Q000494:pharmacology*; D000077484:Vemurafenib
chemical_list: D007211:Indoles; D011838:Radiation-Sensitizing Agents; D013449:Sulfonamides; D000077484:Vemurafenib; D048493:Proto-Oncogene Proteins B-raf