antineoplastic /-nē′ōplas″tik/ [Gk, anti + neos, new, plasma, something formed] , 1. pertaining to a substance, procedure, or measure that prevents the proliferation of cells. 2. a chemotherapeutic agent that controls or kills cancer cells. Drugs used in the treatment of cancer are cytotoxic but are generally more damaging to dividing cells than to resting cells. Cycle-specific antineoplastic agents are more effective in killing proliferating cells than resting cells, and phase-specific agents are most active during a specific phase of the cell cycle. Most anticancer drugs prevent the proliferation of cells by inhibiting the synthesis of deoxyribonucleic acid (DNA) by various mechanisms. Alkylating agents, such as mechlorethamine HCl derivatives, ethylenimine derivatives, and alkyl sulfonates, interfere with DNA replication by causing cross-linking of DNA strands and abnormal pairing of nucleotides. Antimetabolites exert their action by interfering with the formation of compounds required for cell division. Methotrexate, folic acid analog, and 5-fluorouracil, a pyrimidine analog, inhibit enzymes required for the formation of the essential DNA constituent thymidine. 6-Mercaptopurine, a hypoxanthine analog, and 6-thioguanine, an analog of guanine, interfere with the biosynthesis of purines. VinBLAStine sulfate and vinCRIStine sulfate, alkaloids derived from the periwinkle plant, disrupt cell division by interfering with the formation of the mitotic spindle. Antineoplastic antibiotics, such as DOXOrubicin HCl, daunomycin, and mitomycin, block or inhibit DNA synthesis; dactinomycin and plicamycin interfere with ribonucleic acid synthesis. Cytotoxic chemotherapeutic agents may be administered via the oral or intravenous route or by infusion. All have untoward and unpleasant side effects and are potentially immunosuppressive and dangerous. Estrogens and androgens, although not considered antineoplastic agents, frequently cause tumor regression when administered in high doses to patients with hormone-dependent cancers.
