The Restriction Point in Cancer
Cancer can be seen as a disruption of normal restriction point function, as cells continually and inappropriately reenter the cell cycle, and do not enter G0. Mutations at many steps in the pathway towards the restriction point can result in cancerous growth of cells. Some of the genes most commonly mutated in cancer include Cdk’s and CKI’s; overactive Cdk’s or underactive CKI’s lower the stringency of the restriction point, allowing more cells to bypass senescence.
The restriction point is an important consideration in the development of new drug therapies. Under normal physiological conditions, all cell proliferation is regulated by the restriction point. This can be exploited and used as a way to protect non-cancerous cells from chemotherapy treatments. Chemotherapy drugs typically attack cells that are proliferating rapidly. By using drugs that inhibit completion of the restriction point, such as growth factor receptor inhibitors, normal cells are prevented from proliferating, and are thus protected from chemotherapy treatments.
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