title: Inactivation of O6-alkylguanine DNA alkyltransferase as a means to enhance chemotherapy.
abstract: DNA adducts at the O6-position of guanine are a result of the carcinogenic, mutagenic and cytotoxic actions of methylating and chloroethylating agents. The presence of the DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT) renders cells resistant to the biological effects induced by agents that attack at this position. O6-Benzylguanine (O6-BG) is a low molecular weight substrate of AGT and therefore, results in sensitizing cells and tumors to alkylating agent-induced cytotoxicity and antitumor activity. Presently, chemotherapy regimens of O6-BG in combination with BCNU, temozolomide and Gliadel are in clinical development. Other ongoing clinical trials include expression of mutant AGT proteins that confer resistance to O6-BG in bone marrow stem cells, in an effort to reduce the potential enhanced toxicity and mutagenicity of alkylating agents in the bone marrow. O6-BG has also been found to enhance the cytotoxicity of agents that do not form adducts at the O6-position of DNA, including platinating agents. O6-BG's mechanism of action with these agents is not fully understood; however, it is independent of AGT activity or AGT inactivation. A better understanding of the effects of this agent will contribute to its clinical usefulness and the design of better analogs to further improve cancer chemotherapy.
authors.affiliation: Department of Medicine, Committee on Cancer Biology, Committee on Clinical Pharmacology and Pharmacogenomics, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Cara A
authors.initials: CA
authors.lastname: Rabik
authors.forename: Maria Chidiamara
authors.initials: MC
authors.lastname: Njoku
authors.forename: M Eileen
authors.initials: ME
authors.lastname: Dolan
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use; D018906:Antineoplastic Agents, Alkylating / Q000008:administration & dosage / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D045643:DNA Repair Enzymes / Q000037:antagonists & inhibitors*; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000627:therapeutic use; D006147:Guanine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000627:therapeutic use; D006412:Hematopoietic Stem Cells / Q000187:drug effects; D006801:Humans; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000037:antagonists & inhibitors*; D017671:Platinum Compounds / Q000627:therapeutic use
chemical_list: D000970:Antineoplastic Agents; D018906:Antineoplastic Agents, Alkylating; D004791:Enzyme Inhibitors; D017671:Platinum Compounds; C064976:O(6)-benzylguanine; D006147:Guanine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D045643:DNA Repair Enzymes