LY3009120, a panRAF inhibitor, has significant anti-tumor activity in BRAF and KRAS mutant preclinical models of colorectal cancer

// Eliza Vakana 1, * , Susan Pratt 1, * , Wayne Blosser 1 , Michele Dowless 1 , Nicholas Simpson 2 , Xiu-Juan Yuan 3 , Susan Jaken 3 , Jason Manro 4 , Jennifer Stephens 1 , Youyan Zhang 1 , Lysiane Huber 1 , Sheng-Bin Peng 1 , Louis F. Stancato 1 1 Oncology Discovery Research, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA 2 Discovery Research, Advanced Testing Laboratory, Cincinnati, OH 45242, USA 3 Cell Technologies, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA 4 Discovery Statistics, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA * These authors contributed equally to this work Correspondence to: Louis F. Stancato, email: stancato_louis@lilly.com Keywords: RAS, RAF, signaling pathways, colorectal cancer, xenograft models Received: September 28, 2016 Accepted: December 13, 2016 Published: December 16, 2016 ABSTRACT Activating mutations in the KRAS and BRAF genes, leading to hyperactivation of the RAS/RAF/MAPK oncogenic signaling cascade, are common in patients with colorectal cancer (CRC). While selective BRAF inhibitors are efficacious in BRAF mut melanoma, they have limited efficacy in BRAF mut CRC patients. In a RAS mut background, selective BRAF inhibitors are contraindicated due to paradoxical activation of the MAPK pathway through potentiation of CRAF kinase activity. A way to overcome such paradoxical activation is through concurrent inhibition of the kinase activity of both RAF isoforms. Here, we further examined the effects of LY3009120, a panRAF and RAF dimer inhibitor, in human models of CRC with various mutational backgrounds. We demonstrate that LY3009120 induced anti-proliferative effects in BRAF mut and KRAS mut CRC cell lines through G1-cell cycle arrest. The anti-proliferative effects of LY3009120 in KRAS mut CRC cell lines phenocopied molecular inhibition of RAF isoforms by simultaneous siRNA-mediated knockdown of ARAF , BRAF and CRAF . Additionally, LY3009120 displayed significant activity in in vivo BRAF mut and KRAS mut CRC xenograft models. Examination of potential resistance to LY3009120 demonstrated RAF-independent ERK and AKT activation in the KRAS mut CRC cell line HCT 116. These findings describe the preclinical activity of a panRAF inhibitor in a BRAF mut and KRAS mut CRC setting.