003P Brighton
Winter Meeting December 2008 |
Nuclear receptor-mediated expression of CYP3A4 and CYP2B6 by antiretrovirals - implications for prediction of drug interaction potential
Jenny Svard1, Paul Spiers1, Fiona Mulcahy2, Martina Hennessy1
1Trinity College, Dublin, Ireland, 2St James’s Hospital, Dublin, Ireland
Unpredictable drug interactions remain a complication of complex antiretroviral (ARV) regimens. ARVs may stimulate expression of CYP3A4 and CYP2B6 via pregnane X receptor (PXR) and constitutive androstane receptor (CAR), with implications for drug disposition and interaction potential. However, data on differential effects of ARV subclasses used alone and in combinations for these pathways remain incomplete; many newer agents have not been tested and the effect of low dose RTV has not been studied. This study investigates the role of nuclear receptors PXR and CAR in the regulation of CYP3A4 and 2B6 by ARVs and examines if ritonavir (RTV) “boosting” alters the response.
HepG2 cells were transfected with nuclear receptor, luciferase construct and internal standard plasmids. Dual-luciferase reporter assays were performed following 48h ARV drug exposure (RTV, fosamprenavir (FOS), indinavir (IND), lopinavir (LPV), nelfinavir (NFV), saquinavir (SQV), abacavir (ABC), tenofovir (TFV), efavirenz (EFV) and nevirapine (NVP)). Combinations with low dose RTV were also assessed. Drug-induced expression of the target gene constructs was normalised to the internal standard and compared to untreated controls by one-way ANOVA with Dunnett's post hoc analysis.
Fold increase of induction compared to untreated cells (mean ± SEM, * = P<0.05) presented in Table 1.
| TABLE 1 | Drug | Conc (μM) | PXR/CYP3A4 | CAR/CYP3A4 | PXR/CYP2B6 | CAR/CYP2B6 |
| PIs |
RTV |
1 |
2.2 ± 0.4 |
0.0 ± 0.2 |
1.3 ± 0.4 |
0.0 ± 0.2 |
| FOS |
13 |
18.3 ± 2.8* |
0.8 ± 0.5 |
3.6 ± 1.6 |
0.6 ± 0.9 |
| FOS/r |
13/1 |
8.6 ± 1.1* |
0.5 ± 0.1 |
6.2 ± 1.4* |
0.6 ± 0.6 |
| IDV |
15 |
1.5 ± 0.6 |
0.2 ± 0.4 |
0.9 ± 0.1 |
0.5 ± 0.6 |
| LPV |
16 |
9.8 ± 1.9* |
0.1 ± 0.1 |
6.6 ± 2.3* |
0.5 ± 0.4 |
| LPV/r |
16/1 |
9.0 ± 3.3* |
0.1 ± 0.1 |
19.0 ± 0.9* |
4.0 ± 1.3* |
| NFV |
6 |
7.0 ± 1.6* |
-0.7 ± 0.1 |
4.9 ± 1.5* |
-0.6 ± 0.1 |
| SQV |
4 |
4.3 ± 1.8 |
0.2 ± 0.1 |
0.6 ± 0.2 |
1.1 ± 1.0 |
| SQV/r |
4/1 |
4.0 ± 0.5 |
0.2 ± 0.0 |
5.2 ± 0.6* |
1.5 ± 0.8 |
| NRTIs |
ABC |
5 |
1.9 ± 0.1 |
3.5 ± 1.5* |
1.5 ± 0.6 |
1.4 ± 0.0 |
| TFV |
1 |
-0.1 ± 0.3 |
0.0 ± 0.3 |
0.0 ± 0.2 |
0.0 ± 0.6 |
| NNRTIs |
EFV |
10 |
7.2 ± 2.4* |
-0.1 ± 0.4 |
3.7 ± 1.5 |
0.3 ± 0.7 |
| NVP |
7.5 |
0.6 ± 0.4 |
0.2 ± 0.5 |
0.4 ± 0.2 |
0.4 ± 0.4 |
PXR is the main modulator of ARV induction of CYP3A4 and 2B6. However, ABC and LPV/r significantly induce CYP450 expression in a CAR-dependent system. RTV alone produced no effect, although in combination with both SQV and LPV increased PXR-mediated CYP2B6 expression without further change in 3A4 expression. In contrast, FOS/r increased CYP2B6 but decreased 3A4 expression. Altered binding affinities to responsive elements or conformational changes in binding sites may be involved. This warrants further study as these effects are likely to contribute to the unpredictable nature of drug interactions. Based on these results continued single drug testing is of limited value.
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