Exelixis, Inc. has agreed to a request from GlaxoSmithKline (GSK) to initiate its review of XL880 before the compound reaches proof-of-concept. Exelixis expects to deliver the appropriate diligence information to GSK in mid-September, at which point GSK will begin its review to determine whether or not to select XL880 for further development and commercialization. Both companies have agreed to expedite the review of XL880 in order to build on its position as a leading MET inhibitor, which is believed to be the most advanced in clinical development.

Under the terms of the product development and commercialization agreement between the parties, GSK's review period would have otherwise commenced once proof-of-concept data became available. In addition, the companies have initiated preliminary transition activities in the event that GSK decides to select XL880 for further clinical development and commercialization.

"We are extremely pleased that GSK has asked us to expedite its review process for XL880. This request reflects the high level of excitement around both the compound and the therapeutic potential of MET inhibition," said George A. Scangos, Ph.D., president and chief executive officer of Exelixis. "Our recently reported data from the XL880 Phase 1 trial at the 2007 ASCO Annual Meeting underscore our belief that XL880 is the most advanced MET inhibitor in clinical development, and we and GSK are committed to building upon this leadership position."

XL880 has attractive pharmaceutical properties, with high solubility and oral bioavailability. In preclinical studies, XL880 inhibited its targets with nanomolar potency, and retained potent activity against mutationally activated forms of MET found in hereditary papillary renal cell carcinomas. The compound also demonstrated dose-dependent tumour growth inhibition in models of breast cancer, colorectal cancer, non-small cell lung cancer, and glioblastoma, and has been shown to cause substantial tumour regression in all models tested. Significantly, a single dose of XL880 completely inhibited tumour growth for 21 days in a glioblastoma model.

Exelixis, Inc. is a development-stage biotechnology company dedicated to the discovery and development of novel small molecule therapeutics for the treatment of cancer and other serious diseases. The company is leveraging its fully integrated drug discovery platform to fuel the growth of its development pipeline, which is primarily focused on cancer.