Antitumor properties of RAF709, a highly selective and potent inhibitor of RAF kinase dimers, in tumors driven by mutant RAS or BRAF

Resistance to the RAF inhibitor vemurafenib arises commonly in melanomas driven by the activated BRAF oncogene. Here we report antitumor properties of RAF709, a novel ATP-competitive kinase inhibitor with high potency and selectivity against RAF kinases. RAF709 exhibited a mode of RAF inhibition distinct from RAF monomer inhibitors such as vemurafenib, showing equal activity against both RAF monomers and dimers. As a result, RAF709 inhibited MAPK signaling activity in tumor models harboring either BRAFV600 alterations or mutant N- and KRAS-driven signaling, with minimal paradoxical activation of wild-type RAF. In cell lines and murine xenograft models, RAF709 demonstrated selective antitumor activity in tumor cells harboring BRAF or RAS mutations compared to cells with wild-type BRAF and RAS genes. RAF709 demonstrated a direct pharmacokinetic/pharmacodynamic relationship in in vivo tumor models harboring KRAS mutation. Further, RAF709 elicited regression of primary human tumor derived xenograft models with BRAF, NRAS or KRAS mutations with excellent tolerability. Our results support further development of inhibitors like RAF709, which represents a next generation RAF inhibitor with unique biochemical and cellular properties that enables antitumor activities in RAS mutant tumors.

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