title: Modulation of O6-alkylating agent induced clastogenicity by enhanced DNA repair capacity of bone marrow cells.
abstract: The murine bone marrow micronucleus assay has been used to examine (1) the potentiation of fotemustine and streptozotocin induced-clastogenicity by the O6-alkylguanine-DNA alkyltransferase (ATase) inactivator O6-benzylguanine (O6-beG) and (2) the level of protection afforded against this potentiation by retrovirus-mediated expression of an O6-beG-resistant mutant of human ATase (haTPA/GA) in mouse bone marrow. Both fotemustine and streptozotocin induced significantly higher levels of micronucleated polychromatic erythrocytes (p < 0.001 for the highest doses studied) compared to those seen in vehicle-treated animals. The number of micronuclei produced by either agent was dramatically elevated by pretreatment with O6-beG (p < 0.001). Furthermore, in myeloablated mice reconstituted with bone marrow expressing the O6-beG-resistant hATPA/GA as a result of retroviral gene transfer, the frequency of micronucleus formation following exposure of mice to otherwise clastogenic doses of fotemustine or streptozotocin, in the presence of O6-beG, wash highly significantly reduced (p < 0.001 for both agents) relative to that in mock transduced controls. These data clearly implicate O6-chloroethyl- and O6-methylguanine as clastogenic lesions in vivo and establish ATase as a major protective mechanism operating to reduce the frequency of such damage. The potentiation of drug induced clastogenicity by O6-beG suggests that the clinical use of this inactivator in combination with O6-alkylating agents, could substantially increase the risk of therapy related malignancy. Nevertheless the use of hATPA/GA as a protective mechanism via gene therapy may overcome this risk.
authors.affiliation: CRC Section of Haemopoietic Cell, Paterson Institute for Cancer Research, Christine Hospital NHS Trust, Mancester M20 4BX, UK.
authors.forename: N
authors.initials: N
authors.lastname: Chinnasamy
authors.forename: L J
authors.initials: LJ
authors.lastname: Fairbairn
authors.forename: J
authors.initials: J
authors.lastname: Laher
authors.forename: M A
authors.initials: MA
authors.lastname: Willington
authors.forename: J A
authors.initials: JA
authors.lastname: Rafferty
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors / Q000235:genetics; D000477:Alkylating Agents / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects* / Q000378:metabolism*; D016026:Bone Marrow Transplantation; D004260:DNA Repair / Q000187:drug effects*; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D005260:Female; D015870:Gene Expression; D006147:Guanine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008297:Male; D051379:Mice; D015162:Micronucleus Tests; D009153:Mutagens / Q000008:administration & dosage / Q000494:pharmacology*; D009154:Mutation; D009607:Nitrosourea Compounds / Q000008:administration & dosage / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000008:administration & dosage / Q000494:pharmacology; D013311:Streptozocin / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D000477:Alkylating Agents; D004791:Enzyme Inhibitors; D009153:Mutagens; D009607:Nitrosourea Compounds; D009943:Organophosphorus Compounds; C064976:O(6)-benzylguanine; D013311:Streptozocin; D006147:Guanine; D019883:Alkyl and Aryl Transferases; C050956:DNA alkyltransferase; C054368:fotemustine