Cyclin-dependent kinases as cellular targets for antiviral drugs

Cyclin-dependent kinases (cdks) are required for replication of viruses that replicate only in dividing cells, such as adeno- and papillomaviruses. Recently, cdks have been shown to be required also for replication of viruses that can replicate in non-dividing cells, such as HIV-1 and herpes simplex virus types 1 and 2 (HSV-1 and -2). In these experiments, pharmacological cdk inhibitors (PCIs) were shown to have potent antiviral activity in vitro against HIV-1, HSV-1 and -2, human cytomegalovirus, varicella-zoster virus, and to inhibit specific functions of other viruses. Since two PCIs, flavopiridol and roscovitine, are proving to be non-toxic in human clinical trials against cancer, PCIs may be useful as antivirals. As significant advantages, PCIs are active in vitro against many viruses, including drug-resistant strains of HIV-1 and HSV-1, and mutant strains of HIV-1 or HSV-1 resistant to PCIs have not been identified in spite of intense efforts. Furthermore, the antiviral effects of a PCI and a conventional antiviral drug are additive. The aetiopathogenesis of several diseases, such as Kaposi's sarcoma, HPV-induced cervical carcinoma and HIV-associated nephropathy (HIVAN), among others, includes replication or expression of proteins by viruses that require cdks. Thus, PCIs could target both the aetiological agent (the virus) and the pathogenic mechanisms (cell replication). Two important questions regarding the antiviral activities of PCIs are the focus of current research efforts, (i) the identity of the specific cdks that mediate the antiviral activities of PCIs, and (ii) whether PCIs have antiviral activity in vivo at non-toxic doses.