title: Time- and NADPH-dependent inhibition of cytochrome P450 3A4 by the cyclopentapeptide cilengitide: significance of the guanidine group and accompanying spectral changes.
abstract: Cilengitide is a stable cyclic pentapeptide containing an Arg-Gly-Asp motif responsible for selective binding to αVβ3 and αVβ5 integrins. The candidate drug showed unexpected inhibition of cytochrome P450 (P450) 3A4 at high concentrations, that is, a 15-mM concentration caused attenuation of P450 3A4 activity (depending on the probe substrate): 15-19% direct inhibition, 10-23% time-dependent inhibition (30-minute preincubation), and 54-60% metabolism-dependent inhibition (30-minute preincubation). The inactivation efficiency determined with human liver microsomes was 0.003 ± 0.001 min(-1) mM(-1) and was 0.04 ± 0.01 min(-1) mM(-1) with baculovirus-based microsomes containing recombinant P450 3A4. Neither heme loss nor covalent binding to apoprotein could explain the observed reductions in residual activity. Slowly forming type II difference spectra were observed, with maximum spectral changes after 2 hours. Binding to both reduced and oxidized P450 3A4 was observed, with apparent Kd values of 0.66 μM and 6 μM. The significance of the guanidine group in inhibition was demonstrated using ligand binding spectral changes and inactivation assays with guanidine analogs (debrisoquine, N-acetylarginine-O-methyl ester) and the acetylated ornithine derivative of cilengitide. The observed inhibition could be explained by direct inhibition, plus by formation of stable complexes with both ferric and ferrous forms of heme iron and to some extent by the formation of reactive species capable to react to the protein or heme. Formation of the complex required time and NADPH and is attributed to the guanidino group. Thus, the NADPH-dependent inhibition is considered to be mainly due to the formation of a stable complex rather than the formation of reactive species.
authors.affiliation: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee (M.B., F.P.G.); Merck-Serono, RBM S.p.A. Istituto di Ricerche Biomediche A. Marxer, Colleretto Giacosa, Torino, Italy (L.B., S.R.); Merck-Serono, Global Early Development, Darmstadt, Germany (H.D.); and Merck-Serono, Global Early Development, Darmstadt/Global DMPK, Grafing, Germany (A.F., D.G.).
authors.forename: Mirza
authors.initials: M
authors.lastname: Bojić
authors.affiliation: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee (M.B., F.P.G.); Merck-Serono, RBM S.p.A. Istituto di Ricerche Biomediche A. Marxer, Colleretto Giacosa, Torino, Italy (L.B., S.R.); Merck-Serono, Global Early Development, Darmstadt, Germany (H.D.); and Merck-Serono, Global Early Development, Darmstadt/Global DMPK, Grafing, Germany (A.F., D.G.).
authors.forename: Luca
authors.initials: L
authors.lastname: Barbero
authors.affiliation: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee (M.B., F.P.G.); Merck-Serono, RBM S.p.A. Istituto di Ricerche Biomediche A. Marxer, Colleretto Giacosa, Torino, Italy (L.B., S.R.); Merck-Serono, Global Early Development, Darmstadt, Germany (H.D.); and Merck-Serono, Global Early Development, Darmstadt/Global DMPK, Grafing, Germany (A.F., D.G.).
authors.forename: Hugues
authors.initials: H
authors.lastname: Dolgos
authors.affiliation: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee (M.B., F.P.G.); Merck-Serono, RBM S.p.A. Istituto di Ricerche Biomediche A. Marxer, Colleretto Giacosa, Torino, Italy (L.B., S.R.); Merck-Serono, Global Early Development, Darmstadt, Germany (H.D.); and Merck-Serono, Global Early Development, Darmstadt/Global DMPK, Grafing, Germany (A.F., D.G.).
authors.forename: Achim
authors.initials: A
authors.lastname: Freisleben
authors.affiliation: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee (M.B., F.P.G.); Merck-Serono, RBM S.p.A. Istituto di Ricerche Biomediche A. Marxer, Colleretto Giacosa, Torino, Italy (L.B., S.R.); Merck-Serono, Global Early Development, Darmstadt, Germany (H.D.); and Merck-Serono, Global Early Development, Darmstadt/Global DMPK, Grafing, Germany (A.F., D.G.).
authors.forename: Dieter
authors.initials: D
authors.lastname: Gallemann
authors.affiliation: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee (M.B., F.P.G.); Merck-Serono, RBM S.p.A. Istituto di Ricerche Biomediche A. Marxer, Colleretto Giacosa, Torino, Italy (L.B., S.R.); Merck-Serono, Global Early Development, Darmstadt, Germany (H.D.); and Merck-Serono, Global Early Development, Darmstadt/Global DMPK, Grafing, Germany (A.F., D.G.).
authors.forename: Simona
authors.initials: S
authors.lastname: Riva
authors.affiliation: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee (M.B., F.P.G.); Merck-Serono, RBM S.p.A. Istituto di Ricerche Biomediche A. Marxer, Colleretto Giacosa, Torino, Italy (L.B., S.R.); Merck-Serono, Global Early Development, Darmstadt, Germany (H.D.); and Merck-Serono, Global Early Development, Darmstadt/Global DMPK, Grafing, Germany (A.F., D.G.) f.guengerich@vanderbilt.edu.
authors.forename: F Peter
authors.initials: FP
authors.lastname: Guengerich
mesh_terms: D000328:Adult; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D019791:Guanidine / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006801:Humans; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D012910:Snake Venoms / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D012910:Snake Venoms; D006418:Heme; C422910:Cilengitide; D009249:NADP; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D019791:Guanidine