Abstract C62: Identification of GSK2126458, a highly potent inhibitor of phosphoinositide 3‐kinase (PI3K) and the mammalian target of rapamycin (mTOR)

Phosphoinositide 3‐kinase (PI3K) is a critical regulator of cell growth and transformation and its signaling pathway is one of the most commonly mutated pathways in human cancer. The mammalian target of rapamycin (mTOR), a class IV PI3K protein kinase, is also a central regulator of cell growth, and mTOR inhibitors are believed to augment the antiproliferative efficacy of the PI3K/AKT pathway. GSK1059615, our first PI3K clinical compound, progressed to a dose escalation study in patients with refractory malignancies. Following the discovery of GSK1059615, we sought to identify a second inhibitor with improved potency, selectivity, and pharmacokinetics. Key to our approach to achieving the desired levels of PI3K activity was to pursue structure‐based design utilizing crystallography of the more amenable PI3K as a surrogate protein. Following a chemistry lead optimization effort, the pyridylsulfonamide GSK2126458 was identified as a highly potent, orally bioavailable, pan‐PI3K and mTOR inhibitor (PI3K app K i = 19 pM; mTORC1 app K i = 180 pM; mTORC2 app K i = 300 pM). Consistent with potent PI3K and mTORC2 enzyme inhibition, GSK2126458 decreased cellular levels of phosphorylated AKT (BT474 pAKT IC 50 = 180 pM) and inhibited cell proliferation in a large panel of cancer cell lines ( e.g. BT474 growth IC 50 = 2 nM). GSK2126458 showed good exposure in four pre‐clinical animal species and exhibited in vivo activity in both pharmacodynamic and tumor growth efficacy models. GSK2126458 is being evaluated currently in human clinical trials for the treatment of cancer. The discovery, design, and optimization of GSK2126458 and related analogs will be presented. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C62.