Targeted Therapy for BRAF Malignant Astrocytoma

Running title: Targeting BRAF V600E in Malignant Astrocytoma We declare no conflict of interest (or relationship that would be suspected of constituting conflicts) at the time of submission. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Malignant astrocytoma (MA) is the most common histopathologic subclassification for primary central nervous system cancer, and the outcome for patients with MA is dismal. In the current study we demonstrate a 10% incidence of BRAF V600E in pediatric MAs, and demonstrate that a BRAF small molecule inhibitor has substantial activity against intracranial xenografts established from BRAF V600E MA cells, while being ineffective against intracranial xenografts established from wild-type BRAF MA cells. This finding suggests that patients with BRAF V600E MA can be effectively treated with BRAF-specific small molecule inhibitors. Because there is a clinically approved analogue for the BRAF inhibitor we have used in our studies, we anticipate these results to have immediate impact with regard to stimulating clinical trial evaluation of BRAF small molecule inhibitors for treating patients with BRAF V600E MA. Acknowledgements: We thank David Ellison (St Jude) and Sabine Mueller (UCSF) for help in compiling clinical data, and Brian West and Gideon Bollag at Plexxikon Inc. for providing drug and technical assistance. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Abstract Purpose. Malignant astrocytomas (MAs) 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 percent of MAs from two distinct series of tumors (6 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 anti-proliferative activity against BRAF V600E mutant cells in vitro, in contrast to the …