sb-590885 and Neoplasms

Oncogenic BRAF kinase deregulates the ERK signaling pathway in a large number of human tumors. FDA-approved BRAF inhibitors for BRAFV600E/K tumors have provided impressive clinical responses extending survival of melanoma patients. However, these drugs display paradoxical activation in normal tissue with BRAFWT due to RAF transactivation and priming, acquired drug resistance, and limited clinical effectiveness in non-V600 BRAF-dependent tumors, underscoring the urgent need to develop improved BRAF inhibitors. This review provides an overview of recent structural and biochemical insights into the mechanisms of BRAF regulation by BRAF inhibitors that are linked to their clinical activity, clinical liabilities, and medicinal chemistry properties. The effectiveness and challenges of structurally diverse next generation RAF inhibitors currently in preclinical and clinical development are discussed, along with mechanistic insights for developing more effective RAF inhibitors targeting different oncogenic BRAF conformations.

Topics: Animals; Drug Discovery; Humans; Mutation; Neoplasms; Protein Kinase Inhibitors; Proto-Oncogene Proteins B-raf

Oncogenic BRAF alleles are both necessary and sufficient for cellular transformation, suggesting that chemical inhibition of the activated mutant protein kinase may reverse the tumor phenotype. Here, we report the characterization of SB-590885, a novel triarylimidazole that selectively inhibits Raf kinases with more potency towards B-Raf than c-Raf. Crystallographic analysis revealed that SB-590885 stabilizes the oncogenic B-Raf kinase domain in an active configuration, which is distinct from the previously reported mechanism of action of the multi-kinase inhibitor, BAY43-9006. Malignant cells expressing oncogenic B-Raf show selective inhibition of mitogen-activated protein kinase activation, proliferation, transformation, and tumorigenicity when exposed to SB-590885, whereas other cancer cell lines and normal cells display variable sensitivities or resistance to similar treatment. These studies support the validation of oncogenic B-Raf as a target for cancer therapy and provide the first evidence of a correlation between the expression of oncogenic BRAF alleles and a positive response to a selective B-Raf inhibitor.

Topics: Alleles; Animals; Blotting, Western; Cell Line, Tumor; Cell Movement; Cell Proliferation; Crystallization; Crystallography, X-Ray; Extracellular Signal-Regulated MAP Kinases; Female; HT29 Cells; Humans; Imidazoles; Mice; Mice, Nude; Models, Molecular; Molecular Structure; Mutation; Neoplasms; Phosphorylation; Protein Conformation; Protein Kinase Inhibitors; Proto-Oncogene Proteins B-raf; Xenograft Model Antitumor Assays