Concentration-dependent effects of cyclase inhibitor treatments on
PXR-responsive reporter expression in HepG2 cells. HepG2 cells were
transiently transfected with pSG5-hPXR1, XREM-CYP3A4-Luc, and pRL-CMV and then
incubated for 24 h with medium alone or containing 10–8 to 3
× 10–5 M Ro 48-8071 (A) or with medium containing 0.1%
DMSO or 10–8 to 10–5 M BIBX 79 or U18666A
(B). After treatment, cells were harvested for measurement of firefly and
Renilla luciferase activities. Normalized (firefly/Renilla)
values are expressed as -fold changes ± S.D. (n = 3
wells/treatment group) relative to the appropriate negative control group
(i.e., medium alone for Ro 48-8071; DMSO-treated for BIBX 79 and U18666A).
Concentration-response data were fit to sigmoid relationships, and
EC50 values with 95% confidence intervals (CIs) are shown. *,
p < 0.05 and **, p < 0.01 versus negative control.