Pharmacogenetic Markers of Treatment Response of Imatinib Mesylate in Chronic Myeloid Leukemia Brazilian Patients

The treatment of chronic myeloid leukemia (CML) was revolutionized by the introduction of imatinib mesylate (IM). However, approximately 20% of patients are non-responsive and interpatient variability in response to IM is still a phenomenon lacking explanation. Single nucleotide polymorphisms (SNPs) located in genes encoding proteins involved in IM pharmacokinetics are potentially involved in the causes of this variation. In this study, we investigated the association of SNPs in the genes encoding IM metabolizing enzymes CYP3A4 (rs35599367 and rs2740574) and CYP3A5 (rs776746) and efflux transporter proteins ABCB1 (rs3213619, rs1128503, rs2032582 and rs1045642), ABCG2 (rs2231142) and ABCC4 (rs9561765) with response to treatment and with IM plasma through levels and hair concentrations. The analyzed sample was constituted of 182 CML patients on IM treatment. DNA samples were genotyped for the nine SNPs using real-time polymerase chain reaction. Hair and plasma trough IM concentrations were measured through liquid chromatography coupled to mass spectrometry methods. Clinical response was defined according to the European Leukemia Net guidelines. The number of responders to standard IM therapy was 104. A trend to a higher frequency of CYP3A4 *22 (rs35599367) allele carriers was observed among responders to IM (12.5 vs. 3.4% of non-responders, P = 0.087), although no significant differences in plasma or hair concentrations between genotypes were found. Pharmacogenetics may become a valuable approach to optimize therapy with IM in CML, but many factors still need to be clarified to make possible its application in clinical practice.