RT Journal Article SR Electronic T1 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 JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 2066 OP 2075 DO 10.1124/dmd.113.052662 VO 41 IS 12 A1 Anna L. Blobaum A1 Thomas M. Bridges A1 Frank W. Byers A1 Mark L. Turlington A1 Margrith E. Mattmann A1 Ryan D. Morrison A1 Claire Mackie A1 Hilde Lavreysen A1 José M. Bartolomé A1 Gregor J. MacDonald A1 Thomas Steckler A1 Carrie K. Jones A1 Colleen M. Niswender A1 P. Jeffrey Conn A1 Craig W. Lindsley A1 Shaun R. Stauffer A1 J. Scott Daniels YR 2013 UL http://dmd.aspetjournals.org/content/41/12/2066.abstract AB Allosteric modulation of G protein-coupled receptors has gained considerable attention in the drug discovery arena because it opens avenues to achieve greater selectivity over orthosteric ligands. We recently identified a series of positive allosteric modulators (PAMs) of metabotropic glutamate receptor 5 (mGlu5) for the treatment of schizophrenia that exhibited robust heterotropic activation of CYP3A4 enzymatic activity. The prototypical compound from this series, 5-(4-fluorobenzyl)-2-((3-fluorophenoxy)methyl)-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine (VU0448187), was found to activate CYP3A4 to >100% of its baseline intrinsic midazolam (MDZ) hydroxylase activity in vitro; activation was CYP3A substrate specific and mGlu5 PAM dependent. Additional studies revealed the concentration-dependence of CYP3A activation by VU0448187 in multispecies hepatic and intestinal microsomes and hepatocytes, as well as a diminished effect observed in the presence of ketoconazole. Kinetic analyses of the effect of VU0448187 on MDZ metabolism in recombinant P450 or human liver microsomes resulted in a significant increase in Vmax (minimal change in Km) and required the presence of cytochrome b5. The atypical kinetics translated in vivo, as rats receiving an intraperitoneal administration of VU0448187 prior to MDZ treatment demonstrated a significant increase in circulating 1- and 4-hydroxy- midazolam (1-OH-MDZ, 4-OH-MDZ) levels compared with rats administered MDZ alone. The discovery of a potent substrate-selective activator of rodent CYP3A with an in vitro to in vivo translation serves to illuminate the impact of increasing intrinsic enzymatic activity of hepatic and extrahepatic CYP3A in rodents, and presents the basis to build models capable of framing the clinical relevance of substrate-dependent heterotropic activation.