Targets for cancer therapy in the cell cycle pathway.

Progression through the cell cycle is a complex process that is regulated at many levels by several proteins. We are just beginning to understand how these proteins accomplish this regulation. The p16-cyclin D1.cdk4-pRb pathway is one of the most important pathways, which is altered in a majority of cancers of different types. This review focuses on some of the proteins in this pathway that offer new opportunities for drug discovery. Some guidelines to evaluate the relevance of these proteins as targets for cancer therapy and the importance of developing a combination therapy targeting multiple pathways are also discussed.