Targeted delivery of biologic and other antineoplastic agents.

This review summarizes several strategies under investigation for targeted delivery of antineoplastic agents to tumor cells, which avoids normal tissue damage. Monoclonal antibodies remain the molecules of choice for targeted therapy, and several improvements to immunotargeting are discussed. These improvements include the use of novel radioisotopes, cytokines, new linkers for chemotherapeutic drugs, more potent drugs, and improved immunotoxins. Bifunctional antibodies, in which one antigen-binding site recognizes a tumor-associated antigen and the other an antineoplastic agent, have been investigated for radioimmunotherapy and for the activation of cytotoxic cells for targeted immunotherapy. The activation of relatively nontoxic prodrugs by antibody-enzyme conjugates is increasingly being investigated in an effort to reduce the systemic toxicity associated with conventional chemotherapy. Finally, the use of liposomes as carriers of drugs or as activators of macrophages is described.