Biological characterization of ETP-46321 a selective and efficacious inhibitor of phosphoinositide-3-kinases

Inhibitors of PI3K signaling are of great therapeutic interest in oncology. The phosphoinositide-3-kinase signaling pathway is activated in a variety of solid and non-solid tumors. We have identified an imidazopyrazine derivative, ETP-46321, as a potent inhibitor of PI3Kα \( {\text{K}}_{\text{i}}^{\text{app}} = {2}.{\text{4 nM}} \). The compound was 6 times less potent towards PI3Kδ and more than 200 and 60 times less potent at inhibiting PI3Kβ and PI3Kγ and did not significantly inhibit the related phosphoinositide-3-kinase-related protein kinase family kinases mTOR or DNA PK (IC₅₀’s > 5 μM), or an additional 287 protein kinases that were screened. ETP-46321 inhibited PI3K signaling in treated tumor cell lines, induced cell cycle arrest and inhibited VEGF-dependent sprouting of HUVEC cells. The compound was anti-proliferative and synergized with both cytotoxic and targeted therapeutics. The compound induced a reduction in the phosphorylation of Akt in U87 MG xenografts after a single treatment. The growth of colon and lung cancinoma HT-29 and A549 xenografts was delayed by once a day treatment with ETP-46321. The compound synergized with Doxotaxel in a model of ovarian cancer.