Predictive Models of CYP3A4 Heteroactivation: In Vitro-in Vivo Scaling and Pharmacophore Modeling

Abstract

Although activation of CYP3A4 is frequently observed in vitro, predictive computational-based models and methods for in vitro-in vivo scaling are scarce. It has been previously shown that in vitro CYP3A4 heteroactivation of carbamazepine (CBZ)-epoxide (ep) formation can be associated with the clinical drug interaction between felbatame and CBZ. The previously reported prediction methodology is applied here to an additional set of in vitro CYP3A4 heteroactivators, some exerting this effect at concentrations relevant in vivo. The antimalarial artemisinin potently increases CBZ-ep formation by a maximum of 500% at 300 M. Testosterone and progesterone activates by a maximum of 1680 and 920%, respectively, at 150 M, and quinidine causes a 130% increase at 300 M. The predicted maximum in vivo decrease in steady-state concentration of carbamazepine (Css CBZ ) at saturating effector concentrations is 85 to 90% for testosterone and progesterone, 75% for artemisinin, and 45% for quinidine. The corresponding predicted in vivo increase in Css CBZ-ep is 50, 60, 55, and 30% for artemisinin, testosterone, progesterone, and quinidine, respectively. At effector concentrations relevant in vivo, the Css CBZ change is predicted to Յ20% for testosterone, artemisinin, and quinidine and Յ10% for progesterone, with a concomitant Css CBZ-ep increase of 12% for testosterone and Յ10% for progesterone, artemisinin, and quinidine. Structure-heteroactivation relationships were evaluated by generating a pharmacophore. The model includes two hydrogen bond acceptor features separated by hydrophobic features. Internal predictivity is high, and heteroactivation of an external test set correlate to observed in vitro heteroactivation.Inhibition of cytochromes P450 is a well known phenomena in vitro and has been shown to translate to decreases in P450-mediated metabolism in vivo, sometimes leading to clinically relevant drug-drug interactions (Lin and Lu, 1998). Quantitative prediction of the in vivo relevance of P450 inhibition based on in vitro data has also become an integral part of drug discovery and is based on methods that are continuously validated by comparison with in vivo observations (Ito et al., 2004). An increased number of attempts have also been made at producing computational models of P450 inhibition (Afzelius et al., 2001;Ekins et al., 2001).Extensive observations, however, suggest that apart from inhibition, modulation of cytochromes P450 can also occur by activation, a phenomenon that if translated to in vivo events is also a potential source of drug-drug interactions. The in vivo effects of P450 heteroactivation would be observed as an increased clearance of the affected drug, similar to the changes observed by P450 induction, except that the time course of the interaction would not be determined by the rate of synthesis and turnover of P450 enzyme but by the halflives of the interacting drugs. Activation of CYP3A4 has been extensively studied in vitro and based on site-directed mutagenesis studies (Khan et al., 2002), ...

Heterotropic Activation of the Midazolam Hydroxylase Activity of CYP3A by a Positive Allosteric Modulator of mGlu5: In Vitro to In Vivo Translation and Potential Impact on Clinically Relevant Drug-Drug Interactions

“…Although the metabolism of a particular substrate by a P450 enzyme is best described employing Michaelis-Menten kinetics, there are many instances of substrate-enzyme interactions that follow more atypical kinetic profiles, such as homotropic or heterotropic activation, substrate inhibition, partial inhibition, or biphasic metabolism (Korzekwa et al, 1998;Hutzler and Tracy, 2002;Atkins, 2005;Egnell et al, 2005). One of the earliest demonstrations of the ability of a P450 activator (i.e., perpetrator) to enhance the metabolism of a concomitantly administered compound (i.e., victim) was the CYP3A4-mediated hydroxylation of benzo [a]pyrene by a-naphthoflavone reported by Shou et al (1994).…”

Blood-Brain Barrier P450 Enzymes and Multidrug Transporters in Drug Resistance: A Synergistic Role in Neurological Diseases

“…Generally, first generation AEDs differ substantially from second generation AEDs in terms of metabolic transformation pathways (Phase I and II) and drug-to-drug interactions [9,37,42,43] . Both first and second generation AED undergo Phase II metabolism.…”

“…Generally, first generation AEDs differ substantially from second generation AEDs in terms of metabolic transformation pathways (Phase I and II) and drug-to-drug interactions [9,37,42,43]. For example, carbamazepine (first generation AED) is a substrate and an inducer of hepatic CYP3A4 [26,[38][39][40]44] while phenytoin serum levels are determined by CYP2C9 and CYP2C19 [38,44,45].…”

“…In particular, P450 phase I enzymes (e.g., CYP3A4/5 and CYP2C9/19) are responsible for the hepatic metabolism of first generation AEDs and some second generation ones [26,[37][38][39][40]. Phase II enzymes such as glutathione-S-transferase (GSTs), sulfotransferase and UDP-glucuronosyl-transferase (UGTs) are responsible for the metabolic clearance of both first and second generation AEDs [41].Generally, first generation AEDs differ substantially from second generation AEDs in terms of metabolic transformation pathways (Phase I and II) and drug-to-drug interactions [9,37,42,43] . Both first and second generation AED undergo Phase II metabolism.…”

A Screen of Approved Drugs Identifies the Androgen Receptor Antagonist Flutamide and Its Pharmacologically Active Metabolite 2-Hydroxy-Flutamide as Heterotropic Activators of Cytochrome P450 3A In Vitro and In Vivo

“…Although heterotropic activation or inhibition of the CYP3A family enzymes (as well as the CYP2C family) has received significant in vitro investigative attention (Hutzler and Tracy, 2002), little in the way of in vivo translation has been realized due to the lack of suitable animal models where the phenomenon has translated effectively (Tang et al, 1999;Hutzler et al, 2001). In addition, although the preponderance of in vitro atypical kinetics, such as heterotropic activation, is vast and there are established structure-activity relationship (SAR) data within common pharmacophores (Egnell et al, 2003a(Egnell et al, , 2005Henshall et al, 2008), there are no real predictive trends across therapeutic drug classes (Hutzler and Tracy, 2002;Hutzler et al, 2005).…”