Development of a novel PI3Kα/CDK7 potent hybrid inhibitor for Cancer treatment.

Phosphatidylinositol 3-kinase alpha (PI3Kα) and cyclin-dependent kinase 7 (CDK7) play key roles in the growth of multiple cancers. PI3Kα indirectly activates and enhances CDK7 expression. Our preliminary findings from screening recombinant PI3Kα on the Kinome Array showed that it may directly activate CDK7 and presents promising targets for the development of novel drugs with dual inhibition. In this work, we designed and synthesized two hybrids, HY3 and HY5, employing the strategy of combining the cores of Alpelisib and SY-5609, known selective inhibitors of PI3Kα and CDK7, respectively. HY3 showed 98% inhibition against CDK7 and 10% against PI3Kα. 10-point titration of HY3 was determined against CDK7 with an IC50 = 10.8 nM. We then developed a potent hybrid inhibitor (HY5) employing X-ray structure-based drug design. HY5 showed dual inhibition, 87% inhibition with IC50 of 87.9 nM against PI3Kα and 89% inhibition with IC50 of 638 nM against CDK7. We also screened HY5 for cytotoxicity against HCT116, SKOV3 and MCF7 cells exhibiting IC50s of 360 nM, 490 nM, and 820 nM, respectively. To compare selective killing of cancer cells, we tested HY5 against several normal cell lines: human fibroblast (WI-38), retinal pigmented epithelial cells (RPE), mouse embryonic cell line (10 T1/2), and canine kidney (MDCK). HY5 was significantly less toxic against WI-38 and showed similar toxicity against 10 T1/2, RPE and MDCK cells at 5, 10 and 20 μM which is comparable to the Alpelisib + SY-5609 combination. HY5 showed high selectivity for MCF7 cells where 80% were killed at 1 μM compared to only 10-50% of normal cells at 20 μM.