Deregulation of kinase activity has emerged as a major mechanism by which cancer cells evade normal physiological constraints on growth and survival. To date, 11 kinase inhibitors have received US Food and Drug Administration approval as cancer treatments, and there are considerable efforts to develop selective small molecule inhibitors for a host of other kinases that are implicated in cancer and other diseases. Herein we discuss the current challenges in the field, such as designing selective inhibitors and developing strategies to overcome resistance mutations. This Review provides a broad overview of some of the approaches currently used to discover and characterize new kinase inhibitors.

The mammalian target of rapamycin (mTOR) kinase is the catalytic subunit of two functionally distinct complexes, mTORC1 and mTORC2, that coordinately promote cell growth, proliferation, and survival. Rapamycin is a potent allosteric mTORC1 inhibitor with clinical applications as an immunosuppressant and anti-cancer agent. Here we find that Torin1, a highly potent and selective ATP-competitive mTOR inhibitor that directly inhibits both complexes, impairs cell growth and proliferation to a far greater degree than rapamycin. Surprisingly, these effects are independent of mTORC2 inhibition and are instead because of suppression of rapamycin-resistant functions of mTORC1 that are necessary for cap-dependent translation and suppression of autophagy. These effects are at least partly mediated by mTORC1-dependent and rapamycin-resistant phosphorylation of 4E-BP1. Our findings challenge the assumption that rapamycin completely inhibits mTORC1 and indicate that direct inhibitors of mTORC1 kinase activity may be more successful than rapamycin at inhibiting tumors that depend on mTORC1.

Summary Embryonic stem cells (ESCs) of mice and humans have distinct molecular and biological characteristics, raising the question whether an earlier ‘naive’ state of pluripotency may exist in humans. Here we took a systematic approach to identify small molecules that support self-renewal of naive human ESCs based on maintenance of endogenous OCT4 distal enhancer activity, a molecular signature of ground state pluripotency. Iterative chemical screening identified a combination of five kinase inhibitors that induces and maintains OCT4 distal enhancer activity when applied directly to conventional human ESCs. These inhibitors generate human pluripotent cells in which transcription factors associated with the ground state of pluripotency are highly upregulated and bivalent chromatin domains are depleted. Comparison with previously reported naive human ESCs indicates that our conditions capture a distinct pluripotent state in humans that closely resembles mouse ESCs. This study presents a framework for defining the culture requirements of naive human pluripotent cells.