Received for publication September 4, 2007.
Revised March 4, 2008.
Accepted for publication March 5, 2008.

Intestinal human colon adenocarcinoma cell line, LS180, is an excellent model to study PXR- but not CAR-mediated CYP3A4 and MDR1 induction: studies with Anti-HIV Protease Inhibitors

Abstract

Lack of an established cell line model to study induction of cytochrome P450s (CYPs) and drug transporters poses a challenge in predicting in vivo drug-drug interactions. Although not well characterized, LS180 cells could be an excellent cell line to study induction of CYPs and transporters because they express PXR. Therefore, as part of a larger study of in vitro to in vivo prediction of inductive drug interactions, we determined induction of various CYPs and drug transporters by the anti-HIV protease inhibitors (PIs) and the prototypic inducer, rifampin, in LS180 cells. Amongst these proteins, the various PIs significantly induced (n=3-5) only CYP3A4 and MDR1 transcripts (2-50 fold). CYP3A4 activity (1'-OH midazolam formation) was increased (2-fold) by rifampin (10 µM) but was reduced by the PIs (1.5-7 fold). Surprisingly, CAR1 was not found to be expressed in these cells. Additionally, using a reporter assay, we found that PIs did not activate CAR3 but significantly activated PXR (2-24 fold) which correlated well with induction of CYP3A4 and MDR1 transcripts (~ r = 0.9). Furthermore, in a PXR-knockdown stable LS180 cell line, induction of CYP3A4 and MDR1 mRNA, following treatment with PIs and rifampin, was significantly reduced (1.4-5 fold) when compared with that in PXR non-silenced cells. Based on these data, we conclude that LS180 cells could be used as a readily available, high throughput cell line to screen for PXR-mediated induction of CYP3A4 and MDR1 transcripts. These data also indicate that the majority of the PIs are likely to produce intestinal drug-drug interactions by inactivating or inhibiting CYP3A enzymes even though they induce CYP3A4 and MDR1 transcripts via PXR.

Key words: CAR, CYP induction, cytochrome P450 regulation, drug interactions, in vitro-in vivo prediction, p-glycoprotein, PXR, RXR, SXR, transporters

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