Effect of interaction of glutathione S-transferases (T1 and M1) on the hematologic and cytogenetic responses in chronic myeloid leukemia patients treated with imatinib

The glutathione S-transferases (GSTs) are phase II xenobiotic metabolizing enzymes known to be involved in the detoxification of carcinogens and anticancer drugs. Individual genetic variation linked to inherited polymor- phisms of GSTT1 and GSTM1 leading to a complete loss of enzyme activity could expose subjects to develop cancer or to induce drug resistance. Indeed, despite the impressive results obtained with the imatinib, some patients with chronic myeloid leukemia (CML) fail to achieve the expected results or develop resistance. The present study aimed to examine the impact of GSTT1 and GSTM1 poly- morphisms on the response to imatinib in patients with CML. Multiplex polymerase chain reaction was used to detect the genotypes of GSTT1 and GSTM1 in 60 CML patients. We found that side effects were more frequent in patients car- rying GSTT1 null when compared to GSTT1 present carriers (31 vs. 16.6 %; v 2 = 6.2; p = 0.013). The loss of hematologic response was statistically greater in patients carrying the combined genotype GSTT1 present/GSTM1 present (26.3 %) when compared to GSTT1 null/GSTM1 present (12.8 %), GSTT1 present/GSTM1 null (8.3 %) and GSTT1 null/GSTM1 null (0 %), (v 2 = 18.85; p \ 0.001). The complete cytogenetic response was higher in patients harboring the GSTT1 null/GSTM1 null (75 %) compared with GSTT1 null/GSTM1 present (55.6 %), GSTT1 present/ GSTM1 null (50 %) and GSTT1 present/GSTM1 present (47.8). On the other hand, the frequency of none cytogenetic responders was more common in patients carrying GSTT1 present/GSTM1 present (34.8 %) when compared to other genotype combinations (v 2 = 20.99; p = 0.05). Moreover, the GSTT1 present/GSTM1 present appeared to be associated with a final dose of 600 or 800 mg of imatinib, but not sig- nificantly. Based on these findings, we find that the interac- tion between GSTT1 and GSTM1 seems to influence treatment outcome in patients with CML. Therefore, further investigations are required to confirm these results, for better genotype-phenotype correlation.