Antineoplastic agents vinca alkaloid

Based on comparative studies of the relative gonadal toxicity of several antineoplastic agents in experimental models and humans, the vinca alkaloids vinblastine and vincristine have negligible potency for killing stem cells. Permanent recovery of sperm counts and preserved ovarian function, depending on the patient s age at the time of... 

Vinca alkaloids (vincristine, vinblastine, vinorelbine) are derived from the periwinkle plant (Vinca rosea). These agents work by binding to tubulin at a site different than colchicine or paclitaxel. They block polymerization, which prevents the formation of the mitotic spindle, and are used as antineoplastic agents. Taxanes produce a stabilization of microtubules similar to colchicine, but by a different mechanism, and also halt cells in metaphase. Paclitaxel (taxol) is the taxane used clinically. It is derived from the bark of the pacific yew. Taxol disrupts several microtubule-based functions as completely as inhibitors of polymerization, emphasizing the importance of assembly/disassembly balance in microtubule function. Recently, it has been found that paclitaxel also binds to and inhibits the function of a protein called bcl-2, an inhibitor of one or more pathways involved in mediating apoptosis. PaclitaxeTs interference with this function promotes apoptosis in addition to its microtubule-related inhibition of cell division. 

List the two major vinca alkaloids used as antineoplastic agents. 

The periwinkle plant (Vinca rosa), which is indigenous to Florida, has yielded several indole alkaloids. Two with antineoplastic properties are the dimeric indole-dihydroindole derivatives vinblastine (Velban ) and vincristine (Oncovin ). These agents bind to tubulin, arresting mitosis at the metaphase. 

So far about 72 alkaloids have been isolated from Vinca rosea Liim, genus Catharanthus roseus (Family Apocynaceae). Out of these 24 dimeric alkaloids only six possess antineoplastic activity but specifically two i.e., vincristine, vinblastine, are used clinically in human neoplasms. These are cell-cycle specific agents. 

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