DNA damage induced by doxorubicin is not associated with individual GSTM1 and GSTT1 polymorphisms Free

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Interindividual variability in efficacy and toxicity of drug therapy may result from genetic polymorphisms, the majority of them associated to drug metabolizing enzymes as well as for DNA repair enzymes. Glutathione S-transferases (GSTs) are phase II reaction enzymes that catalyze the conjugation of electrophilic compounds with glutathione. This may contribute to the detoxification of some chemotherapy drugs including doxorubicin (Dox). This drug is an anthracycline antibiotic widely used in the treatment of various types of cancer, but the mechanisms of antineoplasic action are complex and not yet fully understood. Since GSTs have been thoroughly associated with the susceptibility to various diseases as well as for the chemotherapy outcome, we hypothesize if the genotoxic response observed after the incubation of human lymphocytes from healthy individuals with Dox could be correlated with the GST genotype. For this purpose, we studied the induction of micronuclei, as a measure of induction of DNA damage, by Dox in vitro,using the cytokinesis blocked micronucleus assay. A dose dependent increase in the micronucleei (MN) formation in human lymphocytes in vitro was observed for concentrations up to 100 nM of Dox. For higher concentrations Dox induced cytotoxicity was evident, with a marked decrease in the % binucleated cells (%BN) as well as in the Nuclear Division Index (NDI). A reference concentration of 50 nM Dox was afterwards selected for the analysis of MN. Two completely independent experiments were carried out on 14 healthy non smokers individuals, from both sexes. The results obtained showed a large interindividual variation concerning the increase of MN levels induced by Dox. In fact, the ‰ of micronucleated binucleated cells (‰ MNBN) varied from 11.0 up to 55.5. Considering this large variation, for all the participants involved in this study individual GSTM1 and GSTT1 genotypes were determined by Multiplex PCR. The results obtained showed that GSTM1 null individuals have a higher increase of ‰ MNBN when compared with GSTM1 non null individuals (30.1 versus 22.5), but the difference does not reach the statistical significance. Additionally, GSTT1 gene delection does not seem to influence the genotoxicity of Dox. These results do not support a strong influence of GSTM1 and GSTT1 polymorphisms in the induction of DNA damage by Dox. However, we can not exclude that other polymorphisms in genes associated with the metabolic fate of Dox or with the repair of DNA lesion induced by this compound, might explain the interindividual variation observed in this study.