PI3K-δ (XL499) Inhibitor Program

PI3K-δ is a member of the PI3K family of lipid kinases and is primarily expressed in cells of the immune system. PI3Kδ function is required for a variety of immune cell responses and is believed to be associated with auto-immune and inflammatory disorders. Inhibitors of PI3Kδ may have broad potential as anti-inflammatory agents. Exelixis discovered a series of inhibitors of PI3Kδ including XL499, which reached development compound status internally.

The program was out-licensed to Merck (known as MSD outside of the United States and Canada) in December 2011. Characterization of XL499 and related compounds in preclinical models is ongoing at Merck.