Appendix Human and Rat Liver Cytochromes P450: Functional Markers, Diagnostic Inhibitor Probes, and Parameters Frequently Used in P450 Studies Maria Almira Correia The tables in this appendix summarize the rel­ different P450 isoforms included in its evaluation ative functional selectivities of substrates and as well as the range of substrate/inhibitor concen­ inhibitors for the major human and rat liver trations tested. Second, substrates and inhibitors C3^ochrome P450 isoforms (P450s). These hepatic determined to be "relatively selective" for a human isoforms are well recognized to catalytically par­ liver isoform, may not necessarily be so for its rat ticipate in the metabolism of chemically diverse liver ortholog, and vice versa. Third, the relative endo- and xenobiotics including drugs, and in the metabolic contribution of a P450 isoform to the case of human liver P450s to thus contribute to in vivo hepatic metabolism of a given drug is directly clinically adverse drug-drug interactions. Conse­ proportional to the relative hepatic microsomal quently, these P450s are the targets of intense abundance of that isoform and its affinity for that scrutiny in the pharmaceutical screening of exist­ compound, irrespective of its in vitro high meta­ ing or novel chemical agents of potential clinical bolic profile assessed under "optimized" condi­ relevance for drug development. At a more basic tions. This issue arises because recent advances in level, these tables provide information on estab­ recombinant P450 technology have made unprece­ lished and/or potential diagnostic tools for the dented amounts of purified human liver enzymes identification and/or characterization of the meta­ readily available for comparative in vitro charac­ bolic role of each individual P450 in the disposition terization of drug metabolism, at relative P450 of an as yet uncharacterized xeno- or endobiotic. concentrations that may be irrelevant in vivo. Three critical issues are however worth considera­ Furthermore, this abundance albeit highly desir­ tion before use of these experimental probes: First, able, has nevertheless also sidelined the compara­ as discussed in Chapter 7 (Inhibition of Cytochrome tive characterization of rat liver orthologs of newly P450 Enzymes), given the vast diversity of P450 discovered human P450 isoforms. Thus, in some isoforms and their differential active-site affinities cases (i.e., CYPIBI), better characterized func­ for a given compound, the "relative" selectivity tional probes are available for the human liver of a substrate or inhibitor probe for a given P450 enzyme than for its rat counterpart. In addition to isoform is entirely defined by the number of the functional probe information, a table with Maria Almira Correia • Departments of Cellular and Molecular Pharmacology, Pharmaceutical Chemistry, and Biopharmaceutical Sciences and the Liver Center, University of California, San Francisco, CA. Cytochrome P450: Structure, Mechanism, and Biochemistry, 3e, edited by Paul R. Ortiz de Montellano Kluwer Academic / Plenum Publishers, New York, 2005. 619 620 M.A. Correia some signature P450 spectral characteristics and Biology (Volume 107, Cytochrome P450 parameters commonly used in P450 studies has Protocols)^, Chapter 7 (Inhibition of Cytochromes been included as a quick reference guide. P450), and Chapter 10 (Human Cytochrome P450 It is to be noted that the tables in this appendix Ervz^mQs). Last, but not the least, I wish to partic­ have been compiled with practical utility rather ularly acknowledge Prof S. Rendic for having pro­ than comprehensiveness as the overall objective. vided access to his regularly tipdated human P450 Much more comprehensive coverage is available in metabolism database through the Gentest website several excellent books and reviews on human and during the preparation of this Appendix. Wherever rat liver P450s that are gratefully acknowledged as feasible, the literature citations in this appendix the sources of some of the information presented have favored those providing methodological herein^"^^. In particular, the reader is referred to details, assay modifications, and/or controversial the series Methods in Enzymology (Volumes 10, information, sometimes at the expense of accurate 52, 206, 272, and 357)3-^, Methods in Molecular chronological reporting of the literature. 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W o ^ .2 o o^ ts ^ 4^ 3 -« O fl I U •s g 11 i Si 8 Is It CO > o 1 " _o o ^_^ I 2^ I II til £^1 PQ (N PH 00 o m ^ I/) in r-- TH < PQ CM < <U T^T ^1 m m Si iiij SlIJlH lIlJI Human and Rat Liver Cytochromes P450 623 »^ >^ o ed o O o -S. o . o lis c 1^^ T3 S s= 5 OH •2II •-^ O T3 <:|.^ ^ J*- ^ o £.§ ;^'5 2 o2 a. •S B , . > ^ «3 ex I D ON is ^ OTS ^ O p o ^ ^a 3 . CM . -5 ^ •-d W N 72 g •o' o""^ O ?'^ 3 (N O ^^ ^ ,—^ 13 «2 "flj "o O lo gj S.2 c^ o^ -O c3 ^ .1^ •-^ fl .1 ^^g ^ 3;-5^2:: 2LVON . .^-' o c I oo ;i O cp Os^ § -^ ^. JIJCN ^ r r- a —"—' 03'—"—i"- "S P^ OO -^ ^ t^ rr^^ eg c^ .g .£2 ^ ci -i-"^(-(M-Hj< >"-' <O J fli^' ^ q^'i^ nj^^ fli^^ i5i5§^| .^ u m ^^ p^ P^Cci 624 M.A. Correia Table A.2. Human Liver P450s: Chemical Structures of Diagnostic Substrate and Inhibitor Probes P450S Substrate^ Inhibitor^ CYP1A2 OH O Galangin (3, 5,7-trihydroxyflavone)^ ^^ CH3CH2' Ethoxyresorufin^o^^ Furafylline (MBI/S)3^ ^2 ^H—COCH3 CYP2A6 NH. o^^o .HCl Coumarin'^ Tranylcypromine'^' '*^^^ x)^ (R)-(+)Menthofuran (MBI/S)"^ Human and Rat Liver Cytochromes P450 625 Table A.2. (continued) P450s Substrate^ Inhibitor^ CYP2B6 O' XH3 (S)-Mephenytoin^^ 2-PMADA^'^52 Bupropion hydrochloride^' 3-PIVIDIA^ 9-Ethynylphenanthrene (MBI/S)^^^ /CI ,x^^\^Sv ' J. Ticlopidine (MBI/S)' CYP2C8 ^^^ JD OH CH \==/ NH Taxol (paclitaxel) ^^^^ CYP2C9 ^"•-v/fv^^ O CI Tolbutamide ^ Tienilicacid(MBI/Sp,73 626 M.A. Correia Table A.2. (continued) P450s Substrate^ Inhibitor^ COOH '^-vjhQ" Diclofenac ^^ ^"^ Sulfaphenazole^ CYP2C18 3-[2, 3-Dichloro-4-(2-thenoyl)phenoxy]- propan-1-or^ CYP2C19 (S)-Mephenytoin7i^4,8o^i (+)-A/-3-Benzyl-nirvanol'^' (+)-A/-3-Benzyl-phenobarbital^ CYP2D6 4 > NH . II N—C—NH2 Debrlsoqulne^^^^ Quinidlne^^9,9o Human and Rat Liver Cytochromes P450 627 Table A.2. (continued) P450S Substrate" Inhibitor^ \>—CH—CH2—NH—C—CHg CH3 (+/-) Bufuralor SCH66712^^96 c„.o^J>-o CH3O -^^^ Dextromethorphan Hydrobromide^"^ ^^ Paroxetine (l\/IBI/Qlf CYP2E1 H 1> CH3 Chlorzoxazone 97-99 4-l\/lethylpyrazole^^9^^^ (CH3)2N—N=0 (CH3CH2)2N-C-SH yV-Nitrosodimethylamine^^^^°^ Diethyldithiocarbamate^^ ^^^ ^^^ CYP3A4 CH3 CH3 X Testosterone^o^^^^ Azamulin"^ 628 M.A. Correia Table A.2. (continued) P450s Substrate^ Inhibitor^ OH CH3^.^-^^OCH3 I >CH3 H3C CH3 ^ H3C' ^O ^ OH I/CH3 OHCH3 \^^^0C0CH3 6CH3 Erythromycin 116,117 ^^3 Troleandomycin (MBI/QO^i^ ^^^ H3CO2C Nifedipine' Gestodene (MBI/S) KetoconazoleA18,48' , 115, 122 Human and Rat Liver Cytochromes P450 629 Table A.2. (continued) P450s Substrate^ Inhibitor^ f<::^=^^^^N-0CH3 V-OCOCHa H3C CH3 Midazolam'' Diltiazam (MBI/QI)^ ^^e CYP3A5 %^ Midazolam^ 128,129,131 OCH3 Aflatoxin BV 630 M.A. Correia Table A.2. (continued) P450S Substrate^ Inhibitor^ CYP3A7 HO3SO DHEA-Sulfate' CYP4A11 COOH COOH Laurie acid ^ 17-0DYA(MBI/S)> ^^N^^N'°" HET0016^^^^^2 ~\- COOH \ H 10-IDA^^ 141 Human and Rat Liver Cytochromes P450 631 Table A.2. (continued) P450S Substrate^ Inhibitor^ CYP4F2 OH COOH 10-UDYA(MBI/Sr CYP4F12 OOH Arachidonic acid^"^^ CYP7A1 Cholesterol^ CYP8B1 3-One-4-ene-7a-hydroxycholesterol 632 M.A. Correia Table A.2. (continued) Additional literature references are listed in Table A.2. "Arrow(s) indicate(s) the substrate position(s) oxidized by that particular P450 isoform, enabling the assay of the corresponding oxidized metabolite(s) as its relatively selective functional probe(s). *The arrow indicates the inhibitor site that is metabolically activated by that P450 isoform resulting in mechanism- based inactivation (MBI) of the enzyme that is either irreversible (suicide, S) or quasi-irreversible (QI). ^Inhibitor acts competitively by coordinating to the P450 heme-iron and/or ligation to the protein at the active site. ^2-PMADA, 2-isopropenyl-2-methyladamantane. ^3-PMDIA, 3-isopropenyl-3-methyldiadamantane. ^SCH66712, 5-fluoro-2-[4-[(2-phenyl-1 H-imidazol-5-yl)methyl]-1 -piperazinyl]pyrimidine. ^A metabolic intermediate complex (MIC) observed only with CYP3A4 but not CYPs 3A5 and 3A7. ^Given their —89% sequence similarity, CYP3A4 and CYP3A5 have similar functional and inhibitory profiles. However, CYP3A5 may be distinguished from CYP3A4 by its higher metabolic ratio of midazolam 1 '-/4-hydroxyla- tion, aflatoxin Bl 8,9-epoxidation to 3a-hydroxylation, and alprazolam 4-/1'-hydroxylation, as well as by its inabil­ ity to form a diltiazam-MIC. Mifepristone has also been found to distinguish between the two CYP3A isoforms.