title: DNA topoisomerase I-targeting drugs as radiation sensitizers.
abstract: Combination chemoradiation, alone or as an adjuvant to surgery, has been shown to improve treatment outcomes in a number of human malignancies, but may be limited by normal tissue toxicities. A primary challenge in radiation oncology is the development of drugs that can selectively enhance the cytotoxicity of ionizing radiation against tumor cells. Mammalian DNA topoisomerase I is the major cytotoxic target of a number of newly developed anticancer drugs that have shown efficacy against solid tumors, including colon cancer, ovarian cancer, lung cancer, cancer of the head and neck, and pediatric cancers. Topoisomerase I-targeting drugs exert their cytotoxic effect by producing enzyme-mediated DNA damage, rather than by directly inhibiting enzyme catalytic activity. DNA topoisomerase I recently has been established as a biochemical mediator of radiosensitization in cultured mammalian cells by camptothecin derivatives. Interestingly, this sensitization appears to be schedule-dependent, cell cycle phase-specific, cell line-dependent, and not strictly dependent on drug cytotoxicity. Clinical chemoradiation trials using camptothecin derivatives are currently ongoing. Future studies aimed at better understanding the underlying mechanisms of molecular radiosensitization with topoisomerase I-targeting drugs are pivotal to the clinical application of these agents, as well as in guiding the development of more effective radiosensitizers.
authors.affiliation: Drug Discovery Laboratory, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: A Y
authors.initials: AY
authors.lastname: Chen
authors.forename: H
authors.initials: H
authors.lastname: Choy
authors.forename: M L
authors.initials: ML
authors.lastname: Rothenberg
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology* / Q000627:therapeutic use; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology* / Q000627:therapeutic use; D002453:Cell Cycle / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000532:radiotherapy; D003131:Combined Modality Therapy; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000532:radiotherapy; D006801:Humans; D000077146:Irinotecan; D008175:Lung Neoplasms / Q000188:drug therapy / Q000532:radiotherapy; D009369:Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000532:radiotherapy; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology* / Q000627:therapeutic use; D019772:Topotecan / Q000494:pharmacology* / Q000627:therapeutic use
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D004791:Enzyme Inhibitors; D011838:Radiation-Sensitizing Agents; D000077146:Irinotecan; D019772:Topotecan; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin