Natural products in anticancer therapy.

Many pharmaceutical agents have been discovered by screening natural products from plants, animals, marine organisms and microorganisms. Vincristine, irinotecan, etoposide and paclitaxel are examples of plant-derived compounds that are being employed in cancer treatment, and dactinomycin, bleomycin and doxorubicin are anticancer agents derived from microbial sources. Citarabine is an example of an anticancer agent originating from a marine source. Other agents originating from marine sources are bryostatin-1, aplidine, dolastatin 10 and ET-743, which have recently entered phase I and II clinical trials.