Plexxikon and Merck to Collaborate on Combination Study Evaluating Investigational Immuno-oncology Regimen

PRESS RELEASE

BERKELEY, Calif., and KENILWORTH, N.J. — May 7, 2015 — Plexxikon Inc., a member of Daiichi Sankyo Group, and Merck (NYSE:MRK), known as MSD outside the US and Canada, through a subsidiary, today announced a collaborative clinical trial that will evaluate the combination of PLX3397, Plexxikon’s investigational CSF-1R inhibitor, and KEYTRUDA^® (pembrolizumab), Merck’s anti-PD-1 therapy, which provides the potential for a double blockade of cancer-induced immune suppression. The Phase 1/2 trial will enroll patients with advanced melanoma and multiple other solid tumors with the goal of determining the safety and tolerability of the combination therapy. The trial is expected to begin enrollment by mid-year.

“We are excited to evaluate PLX3397 in combination with KEYTRUDA, as each agent is designed to attack cancer cells in different ways. Cancer cells use multiple tactics to evade host immune responses, and the combination of these two agents is being investigated to re-activate anti-tumor immunity using distinct and complementary mechanisms,” stated Gideon Bollag, Ph.D, chief executive officer of Plexxikon, a member of the Daiichi Sankyo Group. “Importantly, both PLX3397 and KEYTRUDA have potential application in multiple types of cancer.”

“We are at an important juncture in the advancement of immuno-oncology, and this is why Merck is focused on this area of breakthrough science,” stated Dr. Eric Rubin, therapeutic area head, oncology early-stage development, Merck Research Laboratories. “Given the promising data observed with KEYTRUDA and PLX3397, we are eager to see how combining these medicines may be complementary in increasing the immune response.”