Cyclin-dependent kinase inhibitors.

Cell-cycle dysregulation is one of the cardinal characteristics of neoplastic cells. For this reason, small molecule inhibitors targeting cyclin-dependent kinases (CDKs), of which flavopiridol is a prototype, have been the focus of extensive interest in cancer therapy. In addition to inhibiting cell-cycle progression, these agents exhibit a variety of other activities, including the induction of cell death. Recently, several novel mechanisms of action have been ascribed to the CDK inhibitor flavopiridol, including interference with transcription, most likely through disruption of P-TEFb (i.e. the CDK9/cyclin T complex), and induction of apoptosis, possibly a consequence of downregulation of various anti-apoptotic proteins. It has also been observed that combining CDK inhibitors with either conventional cytotoxic drugs or novel signal transduction modulators dramatically promotes neoplastic cell death in a variety of preclinical models. Efforts are underway to uncover inhibitors that selectively target specific CDKs and to develop these as a new generation of antitumour drugs. For all of these reasons, it is likely that interest in CDK inhibitors as antineoplastic agents will continue for the foreseeable future.