This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Summary of information on human cyp enzymes: human p450 metabolism data

Cytochrome P450s (P450s) are subject to inhibition/inactivation by various chemically diverse agents, which may interact directly or indirectly with either the P450 prosthetic heme or the protein moiety or with both moieties. This inhibition is clinically relevant, as it can block physiological pathways as well as result in therapeutically significant beneficial or adverse effects and clinically relevant drug–drug interactions. Herein, we discuss the various chemical agents and their chemical mechanisms that lead to such reversible, quasi-irreversible, or irreversible inhibition of these enzymes. We note that such inhibition targeted at P450-dependent physiological and/or pathological processes has been ingeniously and effectively harnessed not only in the design and development of clinically relevant therapeutic agents but also of fungicides, insecticides, and herbicides.

Inhibition of Cytochrome P450 Enzymes

Angiogenesis, the formation of new blood vessels, is implicated in a number of important human diseases, including cancer, diabetic retinopathy, and rheumatoid arthritis. To identify clinically useful angiogenesis inhibitors, we assembled and screened a library of mostly Food and Drug Administration-approved drugs for inhibitors of human endothelial cell proliferation. One of the most promising and unexpected hits was itraconazole, a known antifungal drug. Itraconazole inhibits endothelial cell cycle progression at the G1 phase in vitro and blocks vascular endothelial growth factor/basic fibroblast growth factor-dependent angiogenesis in vivo. In attempts to delineate the mechanism of action of itraconazole, we found that human lanosterol 14alpha-demethylase (14DM) is essential for endothelial cell proliferation and may partially mediate the inhibition of endothelial cells by itraconazole. Together, these findings suggest that itraconazole has the potential to serve as an antiangiogenic drug and that lanosterol 14DM is a promising new target for discovering new angiogenesis inhibitors.

Inhibition of angiogenesis by the antifungal drug itraconazole.

Neonatal jaundice and liver disease

(1998). Human cytochrome P450s: selectivity and measurement in vivo. Xenobiotica: Vol. 28, No. 12, pp. 1095-1128.

Human cytochrome P450s: selectivity and measurement in vivo.

The discovery of selective lanosterol 14 alpha-demethylase inhibitors may lead to novel hypolipidemic drugs. RS-21607, (2S,4S)-cis-2[1H-imidazol-1-yl)methyl]-2-[2-(4-chlorophenyl)ethyl]-4- [[(4-aminophenyl)thio]methyl]-1,3-dioxolane, was characterized as a tight-binding, competitive inhibitor of lanosterol 14 alpha-demethylase purified from rat liver. The apparent Ki was determined to be 840 pM and found to be similar in hepatic microsomes from human, rat, and hamster. RS-21607, which contains two chiral centers, was a more effective lanosterol 14 alpha-demethylase inhibitor than its three stereoisomers. In vitro, RS-21607 had a greater affinity for lanosterol 14 alpha-demethylase than the other cytochromes P450 evaluated: CYP7, CYP27, CYP11A1, CYP19, CYP17, CYP11B1, CYP21, CYP3A4, CYP4A, CYP2D6, CYP1A2, CYP2C9, and 27-hydroxycholesterol 7 alpha-hydroxylase. The other stereoisomers were not as selective as RS-21607. Doses of 3-30 mg/kg RS-21607 given orally to hamsters caused a dose-dependent decrease in cholesterol biosynthesis with a corresponding accumulation of 24,25-dihydrolanosterol. RS-21607 inhibited the enzyme and cholesterol biosynthesis in hamster liver by 50% at 18 h following a 30 mg/kg oral dose. This was interpreted to indicate that RS-21607 is able to distribute to the site of action in hamsters and inhibit the target enzyme. In the same dose range, the plasma concentrations of testosterone, corticosterone, and progesterone, the endpoints for the cytochromes P450 involved in steroid biosynthesis, were relatively unaffected. These data show RS-21607 to be an effective and selective inhibitor of lanosterol 14 alpha-demethylase, both in vivo and in vitro. RS-21607 interacted with the purified enzyme to produce a type II binding spectrum, consistent with an interaction between the imidazole moiety and the heme. The electrostatic contribution of the imidazole binding was investigated using the desimidazole analog of RS-21607. The apparent Ki for the desimidazole compound (65 microM) was similar to the apparent Km for the substrate DHL (79 microM). Together, these data confirm that the ligand attached to the imidazole in RS-21607 is a good non-sterol substitute for DHL, i.e., binding to the enzyme with similar affinity, and that the coordination of the imidazole to the heme provides a major electrostatic contribution for the inhibition of lanosterol 14 alpha-demethylase by RS-21607. RS-21607 was also observed to increase the accumulation of 3 beta-hydroxy-24,25-dihydrolanost-8-en-32-al, the second intermediate in the multistep oxidation, but not the first intermediate. 24,25-dihydrolanost-8-ene-3 beta,32-diol.(ABSTRACT TRUNCATED AT 400 WORDS)

Shelton Ej

Papers

Selective inhibition of mammalian lanosterol 14 alpha-demethylase by RS-21607 in vitro and in vivo.