SUN-312 INSIGHTS INTO THE ASSOCIATION OF CYP3A AND ABCB1 POLYMORPHISMS WITH TACROLIMUS-RELATED ADVERSE EFFECTS – VENTURING BEYOND THE CONVENTIONAL SNP-TAC LEVEL RELATIONSHIP

Abstract

Tacrolimus (Tac), an immunosuppressant used in organ transplant recipients, exhibits an interindividual pharmacokinetic variability that affects the dose required to reach the target concentration in blood. Tac requires therapeutic monitoring of blood concentrations to prevent graft rejection owing to inadequate immunosuppression with low drug levels or toxicity due to high drug levels. Tac is metabolized by two enzymes of the cytochrome P450 family, CYP3A5 and CYP3A4, in the gut and liver, and transported in the gut by P-glycoprotein (P-gp), encoded by the MDR1/ABCB1 gene. The objective of the study is to investigate the association of CYP3A5, CYP3A4 and ABCB1 gene polymorphisms and their interactions with dose-adjusted Tac trough concentration in blood and drug-induced adverse effects in South Indian renal transplant recipients. Renal transplant recipients receiving Tac as an immunosuppressant were recruited from Government Medical College, Thiruvananthapuram, Kerala, India. Tac trough concentrations(C0), dose-adjusted Tac trough concentration(C0/D), doses, concomitant medications, drug adverse effects, etc. were recorded. DNA was isolated from blood collected from patients. SNP genotyping was performed using the PCR-RFLP method. Allele, genotype frequencies and linkage disequilibrium were calculated using UNPHASED software, v3.1.7. Comparison of C0/D to genotypes by one-way Anova and linear regression, box-plot analysis and multiple regression analysis to assess the effect of gene-gene interactions were performed using SPSS v20.0. The global variation in distribution of the polymorphisms was analyzed by comparing their allelic frequencies with existing world population data. CYP3A5*3 G (*3/*3) and CYP3A4*1G GG (wt/wt) genotypes were found to be strongly associated with higher Tac C0/D on post-operative day 6. CYP3A4*1B AA also showed a significant association with higher Tac C0/D. A combination of CYP3A5*3 GG and ABCB1 3435 CC genotypes could effectively predict a higher Tac C0/D in blood. We found that CYP3A5 AND CYP3A4 non-expressers had an increased chance of developing new-onset diabetes mellitus after transplantation (NODAT) compared to expressers. Carriers of at least one copy of ABCB1 G2677T Allele G were found to be at a higher risk of developing Tac toxicity. Allele frequencies of these gene polymorphisms in our population were found to be considerably different compared to other world populations. This is the first in-depth study including various functional polymorphisms and epistatic interactions between different genes to develop a robust prognostic and predictive pharmacogenomic biomarker with clinical applicability, which can predict individuals’ response to Tac. Our data will help identify patients who might have higher/lower Tac levels based on their genotype, and those at high risk of developing Tac-related complications can be identified before their organ transplant which can help the clinician decide the initial dosage of Tac. This tailor-made therapy could minimize adverse effects due to over-dosage and graft rejection due to low drug levels. Our findings on inter-ethnic differences in allele frequencies of drug metabolizer and transporter genes underscore the need to consider population-specific genetic backgrounds when conducting pharmacogenetic analyses and clinical trials.