Pharmacogenetic Analysis of Polymorphisms in Pharmacological Pathway of Vincristine, Doxorubicine and Dexamethasone (VAD Regimen) To Predict Response in Patients with Multiple Myeloma.

Combination of vincristine, doxorubicin and dexamethasone (VAD regimen) is a widely-used, effective and economic initial treatment of multiple myeloma (MM). However, between 30 and 50% of MM patients do not respond to VAD, and exposure to VAD may induce multi-drug resistance. Therefore, in the era of emerging novel therapies for MM, there is a need for pre-treatment identification of potential responders to VAD. Importantly, all three VAD components have common steps in their pathways of transport and metabolism, thus even modest inherited alteration caused by single nucleotide polymorphisms (SNP) may influence VAD efficacy an toxicity. The aim of this study was to investigate whether analysis of common functional SNP in drug transporter P-glycoprotein gene (MDR1 or ABCB1), phase I cytochrome P450A metabolizing enzymes genes (CYP3A4 and CYP3A5), phase II glutathione S-transferase P metabolizing enzyme gene (GSTP1) as well as in glucocorticoid receptor gene NR3C1 can be useful to predict response to VAD in MM. Fifty-two uniformly treated MM patients were investigated for 8 common SNPs including MDR1 exon 12 C1236T, MDR1 exon 21 G2677T/A, MDR1 exon 26 C3435T, CYP3A4*1B, CYP3A5*3, GSTP1 A313G as well as NR3C1 bcl I and NR3C1 N363S polymorphisms. Genotypes were identified using direct sequencing or RFLP methods. The response to VAD was estimated after administration of 3 courses of VAD, and patients who achieved complete or partial remission of MM were assigned as responders to VAD. In the cohort of included MM patients there were 39/52 (75%) responders to VAD. The analysis of the prognostic impact of the genotyped SNPs showed that carriers of P-glycoprotein gene MDR1 2677G allele had a significantly greater probability of achievement of the response to VAD as compared to the non-carriers, odds ratio(OR)=8.0, 95% confidence interval (95%CI)= 1.2–52.9, Fisher exact test p=0.031). Moreover, the predictive effect of MDR1 2677G allele was further increased by the presence of glucocorticoid receptor NR3C1 gene 363N allele. The carriers of both MDR1 2677G and NR3C1 363N alleles had 8.4-fold greater probability to achieve complete or partial remission with 3 courses of VAD (OR=8.40, 95% CI=1.8–40.0, p=0.008). Taken together, these data support the hypothesis that analysis of common functional polymorphisms in drug transporters, metabolizing enzymes and receptors may be useful for individualization of the initial therapy of MM. Particularly MDR1 G2677T/A and NR3C1 N363S SNPs can be considered as determinants of response to VAD therapy.