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 outlicensed to Merck in December 2011. Characterization of XL499 and related compounds in preclinical models is ongoing at Merck.