Targeted Therapy for BRAFV600E Malignant Astrocytoma

Abstract

Purpose: Malignant astrocytomas (MA) are aggressive central nervous system tumors with poor prognosis. Activating mutation of BRAF (BRAF^V600E) has been reported in a subset of these tumors, especially in children. We have investigated the incidence of BRAF^V600E in additional pediatric patient cohorts and examined the effects of BRAF blockade in preclinical models of BRAF^V600E and wild-type BRAF MA. Experimental Design: BRAF^V600E mutation status was examined in two pediatric MA patient cohorts. For functional studies, BRAF^V600E MA cell lines were used to investigate the effects of BRAF shRNA knockdown in vitro, and to investigate BRAF pharmacologic inhibition in vitro and in vivo. Results: BRAF^V600E mutations were identified in 11 and 10% of MAs from two distinct series of tumors (six of 58 cases total). BRAF was expressed in all MA cell lines examined, among which BRAF^V600E was identified in four instances. Using the BRAF^V600E-specific inhibitor PLX4720, pharmacologic blockade of BRAF revealed preferential antiproliferative activity against BRAF^V600E mutant cells in vitro, in contrast to the use of shRNA-mediated knockdown of BRAF, which inhibited cell growth of glioma cell lines regardless of BRAF mutation status. Using orthotopic MA xenografts, we show that PLX4720 treatment decreases tumor growth and increases overall survival in mice-bearing BRAF^V600E mutant xenografts, while being ineffective, and possibly tumor promoting, against xenografts with wild-type BRAF. Conclusions: Our results indicate a 10% incidence of activating BRAF^V600E among pediatric MAs. With regard to implications for therapy, our results support evaluation of BRAF^V600E-specific inhibitors for treating BRAF^V600E MA patients. Clin Cancer Res; 17(24); 7595–604. ©2011 AACR.