Selective inhibition of human cytochrome P450 3A4 by N-[2(R)-hydroxy-1(S)-indanyl]-5-[2(S)-(1,1-dimethylethylaminocarbonyl)-4-[(furo[2,3-B]pyridin-5-yl) methyl]piperazin-1-yl]-4(S)-hydroxy-2(R)-phenylmethylpentanamide and P-glycoprotein by valspodar in gene transfectant systems
I. Kawahara et al., Selective inhibition of human cytochrome P450 3A4 by N-[2(R)-hydroxy-1(S)-indanyl]-5-[2(S)-(1,1-dimethylethylaminocarbonyl)-4-[(furo[2,3-B]pyridin-5-yl) methyl]piperazin-1-yl]-4(S)-hydroxy-2(R)-phenylmethylpentanamide and P-glycoprotein by valspodar in gene transfectant systems, DRUG META D, 28(10), 2000, pp. 1238-1243
Our previous report showed that L754.394 and valspodar (PSC833) are potent
inhibitors of midazolam hydroxylation in human jejunum microsomes and vecto
rial transport of vinblastine in Caco-2 cells, respectively. In the present
study, to directly examine the interactions of these compounds as well as
other substrates with CYP3A4 and P-glycoprotein (P-gp), we performed in vit
ro inhibition studies using recombinant CYP3A4-expressed microsomes and an
MDR1-transfected cell line, LLC-MDR1, respectively. In CYP3A4-expressed mic
rosomes, both L754.394 and ketoconazole, at a concentration less than 0.5 m
u M, are the most potent inhibitors of the formation of 1'-hydroxymidazolam
, a major metabolite of midazolam formed by CYP3A4. The greatest inhibitory
effect on the transcellular transport of digoxin in LLC-MDR1 cells was obs
erved in the presence of valspodar (< 0.1 mu M), followed by verapamil. Fro
m a comparison of the IC50 values, it was shown that L754.394 and valspodar
exhibited the highest selectivity for CYP3A4 and P-gp, respectively. To de
monstrate such specificity, both midazolam hydroxylation and digoxin transp
ort were observed in CYP3A4 transfected Caco-2 cells, which coexpress both
P-gp and CYP3A4, in the presence or absence of L754.394 (0.5 mu M) and vals
podar (1.0 mu M). L754.394 almost completely inhibited midazolam hydroxylat
ion, but not digoxin transport, whereas almost complete inhibition of digox
in transport was observed in the presence of valspodar, but inhibition of t
he hydroxylation was minimal. Thus, the present study has demonstrated that
L754.394 has a specific inhibitory effect on CYP3A4, whereas valspodar is
specific for P-gp.