Nuclear receptor activation by antiretroviral drugs used in the treatment of HIV disease with implications for xenobiotic and endobiotic processes

Abstract

Genotyping: DNA was isolated from whole blood of 1013 HIV-patients and genotyped commercially for 37 single nucleotide polymorphisms (SNPs) and one 3-basepair insertion in genes of relevance for drug interactions: NR1I2 (PXR), CYP3A4, CYP2B6 and ABCB1 (MDR1). An in-house quality control was carried out by PCR-RFLP. 22 polymorphisms (out of 29 detected) were found at significantly different (P ≤ 0.05) allele frequencies between Caucasians and Sub-Saharan Africans (chi-square with Fisher's Exact Test). A comparison of our Sub-Saharan African population with available data from other studies of African American subjects revealed significantly different allele frequencies of four SNPs. Antiretroviral (ARV) induction of nuclear receptor-mediated transcription of cytochrome P450 (CYP450) enzymes: The inductive ability of sixteen ARVs on CYP3A4 and CYP2B6 promoter activity via pregnane X receptor (PXR) or constitutive androstane receptor (CAR) was explored in vitro using luciferase reporter assays with HepG2 cells. Normalised results were compared to untreated cells by one-way ANOVA with Dunnett's post hoc analysis, P < 0.05 indicated significant difference. PXR- mediated CYP3A4 promoter activity was induced by (mean fold change ± S.E.M): Fosamprenavir (13.5 ± 3.9), lopinavir (7.5 ± 2.7), nelfinavir (5.6 ± 2.3), tipranavir (9.9 ± 3.4) and efavirenz (5.7 ± 3.3). PXR- mediated CYP2B6 promoter activity was increased by lopinavir (11.4 ± 10.0), darunavir (6.1 ± 0.4), efavirenz (4.7 ± 2.3) and abacavir (2.3 ± 0.6). CAR-mediated CYP3A4 promoter activity was induced only by abacavir (2.5 ± 1.0), while CAR-mediated CYP2B6 promoter activity was increased by fosamprenavir (3.4 ± 3.2), lopinavir (3.0 ± 1.3) and tipranavir (4.8 ± 2.4).