Modulation of O6-alkylating agent induced clastogenicity by enhanced DNA repair capacity of bone marrow cells.
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.
Chinnasamy
N
N
CRC Section of Haemopoietic Cell, Paterson Institute for Cancer Research, Christine Hospital NHS Trust, Mancester M20 4BX, UK.
Fairbairn
L J
LJ
Laher
J
J
Willington
M A
MA
Rafferty
J A
JA
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
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