Preclinical characterization of PWT33597, a dual inhibitor of PI3-kinase alpha and mTOR.

Abstract

4485: Phosphoinositide-3-kinase (PI3K) is an important mediator of tumor cell growth, survival and proliferation. In particular, PI3K alpha is important for signaling downstream of receptor tyrosine kinases and is also frequently amplified or mutationally activated in tumors, suggesting that selective inhibitors of this isoform may have therapeutic utility in the treatment of cancer. Downstream of PI3K, the mTOR kinase also plays a critical role in cellular growth and metabolism, and inhibitors of mTOR have demonstrated clinical benefit in several tumor types. We report here the discovery and characterization of PWT33597, a dual inhibitor of PI3K alpha and mTOR. PWT33597 inhibits PI3K alpha and mTOR in biochemical assays with IC50 values of 19 and 14 nM respectively, and is approximately 10-fold selective with respect to PI3K gamma and PI3K delta. Profiling of PWT33597 against 442 protein kinases (Ambit Kinomescan) revealed little or no cross-reactivity with either serine/threonine or tyrosine kinases, and there was little cross-reactivity with an additional panel of 64 pharmacologically relevant targets. In NCI-H460 and HCT116 tumor cells with mutationally activated PI3K alpha, PWT33597 inhibits phosphorylation of PI3K and mTOR pathway proteins with cellular IC50 values similar to its biochemical IC50 values. PWT33597 has good pharmacokinetic properties in multiple preclinical species, is not extensively metabolized in vivo and shows little potential for interaction with cytochrome P450 enzymes. Following a single oral dose in vivo, PWT33597 shows durable inhibition of PI3K and mTOR pathway signaling in xenograft tumors. High compound distribution into tumors and potent anti-tumor activity has been observed in multiple tumor xenograft models with activated PI3K/mTOR pathways. Also, administration of PWT33597 in mice is associated with transient increases in plasma insulin, consistent with an effect on PI3K/AKT signaling. A robust PK/PD relationship has been defined, which will guide interpretation of the planned phase I clinical study. IND-enabling studies with PWT33597 are currently in progress.