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.
Once thought to be an artifact of microsomal systems, atypical kinetics with cytochrome P450 (CYP) enzymes have been extensively investigated in vitro and found to be substrate and species dependent. Building upon increasing reports of heterotropic CYP activation and inhibition in clinical settings, we screened a compound library of clinically approved drugs and various probe compounds to identify the frequency of heterotropism observed with different drug classes and the associated CYP enzymes thereof (1A2, 2C9, 2D6, and 3A4/5). Results of this screen revealed that the prescribed androgen receptor antagonist flutamide activated the intrinsic midazolam hydroxylase activity of CYP3A in human hepatic microsomes (66%), rat and human hepatocytes (36 and 160%, respectively), and in vivo in male Sprague-Dawley rats (>2-fold, combined area under the curve of primary rat in vivo midazolam metabolites). In addition, a screen of the pharmacologically active metabolite 2-hydroxy-flutamide revealed that this principle metabolite increased CYP3A metabolism of midazolam in human microsomes (30%) and hepatocytes (110%). Importantly, both flutamide and 2-hydroxy-flutamide demonstrated a pronounced increase in the CYP3A-mediated metabolism of commonly paired medications, nifedipine (antihypertensive) and amiodarone (antiarrhythmic), in multispecies hepatocytes (100% over baseline). These data serve to highlight the importance of an appropriate substrate and in vitro system selection in the pharmacokinetic modeling of atypical enzyme kinetics. In addition, the results of our investigation have illuminated a previously undiscovered class of heterotropic CYP3A activators and have demonstrated the importance of selecting commonly paired therapeutics in the in vitro and in vivo modeling of projected clinical outcomes.
Departments of Pharmacology (A.L.B., F.W.B., T.M.B., C.W.L., P.J.C., C.W.L, J.S.D) and Chemistry (C.W.L), Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, Tennessee (C.W.L.) annie.blobaum@vanderbilt.edu.
Anna L
AL
Blobaum
Departments of Pharmacology (A.L.B., F.W.B., T.M.B., C.W.L., P.J.C., C.W.L, J.S.D) and Chemistry (C.W.L), Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, Tennessee (C.W.L.).
Frank W
FW
Byers
Departments of Pharmacology (A.L.B., F.W.B., T.M.B., C.W.L., P.J.C., C.W.L, J.S.D) and Chemistry (C.W.L), Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, Tennessee (C.W.L.).
Thomas M
TM
Bridges
Departments of Pharmacology (A.L.B., F.W.B., T.M.B., C.W.L., P.J.C., C.W.L, J.S.D) and Chemistry (C.W.L), Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, Tennessee (C.W.L.).
Charles W
CW
Locuson
Departments of Pharmacology (A.L.B., F.W.B., T.M.B., C.W.L., P.J.C., C.W.L, J.S.D) and Chemistry (C.W.L), Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, Tennessee (C.W.L.).
P Jeffrey
PJ
Conn
Departments of Pharmacology (A.L.B., F.W.B., T.M.B., C.W.L., P.J.C., C.W.L, J.S.D) and Chemistry (C.W.L), Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, Tennessee (C.W.L.).
Craig W
CW
Lindsley
Departments of Pharmacology (A.L.B., F.W.B., T.M.B., C.W.L., P.J.C., C.W.L, J.S.D) and Chemistry (C.W.L), Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, Tennessee (C.W.L.).
J Scott
JS
Daniels
D059002:Androgen Receptor Antagonists / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D004353:Drug Evaluation, Preclinical / Q000379:methods; D020536:Enzyme Activators / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D005485:Flutamide / Q000378:metabolism* / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D008297:Male; D051379:Mice; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013552:Swine; D013556:Swine, Miniature
D059002:Androgen Receptor Antagonists; D020536:Enzyme Activators; D005485:Flutamide; D051544:Cytochrome P-450 CYP3A