Cancer drug discovery is one of the most rapidly changing areas of pharmaceutical research. Uncontrolled proliferation is a hallmark of cancer cells. Over the past two decades, it has become increasingly clear that in many human cancers, hyperactivity of Cyclin Dependent Kinases (CDKs) is one of the mechanisms underlying the physiological hyper-proliferation. CDKs are serine/threonine protein kinases, which play an important role in cell-cycle regulation. Their sequential activation ensures, the correct timing and ordering of events required for cell cycle progression. Therefore, inhibition of CDKs, through the insertion of small molecules into its ATP binding pocket has emerged as a potential therapy method for cancers. Consequently, a number of small molecules with CDK inhibitory properties have been developed. Many of these have been evaluated as potent inhibitors and some are currently in clinical-trials for various types of cancer. This review reports various CDK inhibitors, natural as well as small molecules, along with their reported activities for various CDKs. It will highlight the potential for the development of novel anti-cancer molecules.

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Oral administration of Pueraria tuberosa D.C. root extract to male rats (100 mg=rat per day) for the period of 60 days did not cause body weight loss, whereas the weights of testes, epididymides, seminal vesicle, and ventral prostate were significantly reduced. The production of step-19 spermatids was reduced by 63.7% in P. tuberosa-treated rats. The population of preleptotene spermatocytes and secondary spermatocytes were decreased by 61 and 72%, respectively. The seminiferous and Leydig cell nuclear area were reduced significantly (p < 0.001) when compared to controls. The number of mature Leydig cells was significantly reduced. Treated rats showed significant (p < 0.001) reduction in the sperm concentration of testes and cauda epididymides. The sperm motility of the cauda epididymides was also reduced significantly (p < 0.001). The Pueraria treatment reduced the fertility of male rats by 100%. A significant fall in the total protein and sialic acid contents of the testes, epididymides, seminal vesicle, and ventral prostate as well as glycogen contents of testes was also observed. Fructose in seminal vesicle was lowered non-significantly, whereas testicular cholesterol was elevated in comparison to controls.