Phytochemicals as cell cycle modulators--a less toxic approach in halting human cancers

The multistep nature of cancer development provides a rationale for cancer prevention. Activation of oncogenes, inactivation of tumor suppressor genes and modulation of mitogenic signal transduction pathways are critical in cancer progression and present attractive targets for cancer prevention/intervention. In this respect, cell cycle regulation and its modulation by various natural (plant-derived) and synthetic agents are gaining widespread attention in recent years. A number of phytochemicals inhibit cell cycle progression in cancer cells, yet their clinical applications are still in infancy. The present review is focused on the modulatory effects of phytochemicals on critical cell cycle molecules, and discusses how they inhibit proliferation and/or induce apoptotic death in cancer cells.