Drug-Drug Interactions Evaluated by a Highly Active Reconstituted Native Human Cytochrome P4503A4 and Human NADPH-Cytochrome P450 Reductase System

Abstract

Catalytic activities of native human CYP3A4-mediated reactions as well as drug interactions were directly evaluated by isolated reconstituted human CYP3A4: NADPH-cytochrome P450 reductase systems. The SDS-PAGE pure CYP3A4 and human NADPH-cytochrome P450 reductase had been incorporated into a binary vesicular phospholipid system of dilauroyl-phosphatidyl-choline and phosphatidyl-serine which had proven to achieve optimal nifedipine oxidase activity (19.6 nmol nifedipine oxidized x min(-1) x nmol CYP3A4(-1)). The IC50 values of ketoconazole (CAS 65 277-42-1) (approximately 3 micromol/l), quinidine (CAS 56-54-2) (approximately 5 micromol/l), mifepristone (CAS 84 371-65-3) (-8 micromol/l), 17alpha-ethinylestradiol (CAS 57-63-6) (approximately 17 micromol/l), cimetidine (CAS 51 481-61-9) (approximately 46 micromol/l), FK 506 (tacrolimus) (CAS 104 987-11-3) (approximately 53 micromol/l), naringenin (CAS 480-41-1) (approximately 87 micromol/l), and cyclosporine A (CAS 59 865-13-3) (approximately 90 micromol/l) indicate that all these drugs have an inhibitory effect on nifedipine (CAS 21 829-25-4) metabolism, whereas the drug quinine (CAS 130-95-0) did not elicit any significant inhibition.

Drug–drug interactions and cooperative effects detected in electrochemically driven human cytochrome P450 3A4

“…The inhibition data obtained are shown in Figure 4. The results reported are in good agreement with the previously published data where ketoconazole exhibits a high inhibitory capacity (IC 50 = 135 ± 10 nM) [25,26] with respect to the less potent inhibitor cimetidine (IC 50 = 80 ± 5 µM) [24]. The highest measured IC 50 was that of diclofenac (311 ± 20 µM) inline with this drug being a weak mechanism-based inhibitor [21].…”

“…In particular, in the case of the mechanismbased inhibitor diclofenac, a 15min pre-incubation was applied in the absence of substrate, due to the known fact that P450 3A4 converts this drug into its product 5'-hydroxydiclofenac, that acts as the inhibitor [21]. Conversely, pre-incubation was not required for ketoconazole or cimetidine since they are not mechanism-based inhibitors of P450 3A4 [22][23][24]. The inhibition data obtained are shown in Figure 4.…”

Effectiveness of Sirolimus in Combination with Cyclosporine against Chronic Rejection in a Pediatric Liver Transplant Patient

“…22) In addition, the apparent IC 50 values of tacrolimus and cyclosporine on for CYP3A4 inhibition were determined to be 53 µm and 90 µm, respectively. 23) However, the target trough concentration of tacrolimus was approximately 10 µg/mL and that of cyclosporine was approximately 180 µg/mL in this case. Therefore, the inhibitory effect of cyclosporine on CYP3A4-mediated sirolimus metabolism would be stronger than that of tacrolimus in clinical use.…”