Identification of Inhibitors of the Kinase Activity of Oncogenic V600E BRAF in an Enzyme Cascade High-Throughput Screen

Abstract

The Cancer Genome Project has identified several oncogenic mutations in BRAF that represent important opportunities for cancer drug discovery. The V600EBRAF mutation accounts for approximately 90% of the mutations identified. A strong case has emerged from molecular, cellular, and structural studies for the identification and development of inhibitors of this mutated BRAF protein. The authors have developed and run a high-throughput screen to find inhibitors of V600EBRAF using an enzyme cascade assay in which oncogenic BRAF activates MEK1, which in turn activates ERK2, which then phosphorylates the transcription factor ELK1. A phosphospecific antibody, Europium-labeled secondary antibody, and a time-resolved fluorescent readout were used to measure phosphorylation of ELK1. Overall assay variation was 12.4%. The assay was used to screen 64,000 compounds with an overall Z′ factor of 0.58 ± 0.12. A series of 3,5, di-substituted pyridines were identified as inhibitors of the cascade assay. These compounds did not inhibit a shortened activated MEK1 to ELK1 cascade but were active (0.5-27.9 μM) in a V600EBRAF assay and represent a potential starting point for future drug discovery and development.