Rational design and physiological selection of a RAF pathway inhibitor that disrupts angiogenesis and tumor growth

AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA 2490 Identification of therapeutic kinase inhibitors via high throughput screening using recombinant catalytic kinase domains at low ATP concentration often yields high affinity ATP mimetics that lack specificity, thereby producing unwanted side effects. We identified an inhibitor of endothelial cell RAF signaling by applying a rational design approach using a novel amino-triazole scaffold designed to stabilize B-RAF in the inactive state. We selected RAF pathway inhibitors in an endothelial cell-based model followed by further selection in a Tg( fli1-EGFP) zebrafish embryogenesis model, allowing us to identify potent anti-angiogenic compounds. Our lead compound, KG5, disrupts the association of B- and C-RAF in endothelial cells and prevents endothelial cell lumen formation during angiogenesis. In addition to RAF, KG5 inhibited PDGFRbeta in smooth muscle cells but failed to interfere with a wide variety of other kinases. While structurally similar to the multikinase inhibitor Sorafenib, KG5 does not compete for ATP yet it readily disrupts RAF signaling in tumor cells and endothelial cells. Evidence is provided that KG5 is an orally-active RAF pathway inhibitor that blocks angiogenesis and tumor growth in orthotopic models of pancreatic carcinoma and renal cell carcinoma, as well as a V600E BRAF expressing melanoma.