New anticancer agents: taxol, camptothecin analogs, and anthrapyrazoles

Taxol, an agent with a unique mechanism of action, has been shown to be highly active in patients with refractory ovarian cancer and may well have significant activity in other malignancies such as breast and lung cancer. The camptothecin analogs, another unique class of agents, have demonstrated antitumor activity in phase I and II trials. Finally, the anthrapyrazoles are intercalating agents with clinical activity in breast cancer and a toxicity profile that may permit increased dose intensity using colony-stimulating factor support. While this review focuses on these three drug classes, a number of other agents with apparently unique mechanisms of antitumor activity and unusual dose-limiting toxicities are in earlier development. These include antimetabolites; inhibitors of DNA, RNA, or protein synthesis; differentiating agents; agents that inhibit tumor growth by binding to growth factors; and agents whose mechanism of action is best classified as unknown.