ABSTRACT:CYP51 fulfills an essential requirement for all cells, by catalyzing three sequential mono-oxidations within the cholesterol biosynthesis cascade. Inhibition of fungal CYP51 is used as a therapy for treating fungal infections, whereas inhibition of human CYP51 has been considered as a pharmacological approach to treat dyslipidemia and some forms of cancer. This study has demonstrated the potential for ligand-based computational pharmacophore modeling of human CYP51 and enables a high-throughput screening system for drug discovery and data base mining.

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Diabetic dyslipidemia requires simultaneous treatment with hypoglycemic agents and lipid-modulating drugs. We recently described glycogen phosphorylase inhibitors that reduce glycogenolysis in cells and lower plasma glucose in ob/ob mice ( J. Med. Chem. , 41: 2934, 1998). In evaluating the series prototype, CP-320626, in dogs, up to 90% reduction in plasma cholesterol was noted after 2 week treatment. Cholesterol reductions were also noted in ob/ob mice and in rats. In HepG2 cells, CP-320626 acutely and dose-dependently inhibited cholesterolgenesis without affecting fatty acid synthesis. Inhibition occurred together with a dose-dependent increase in the cholesterol precursor, lanosterol, suggesting that cholesterolgenesis inhibition was due to lanosterol 14 ␣ -demethylase (CYP51) inhibition. In ob/ob mice, acute treatment with CP-320626 resulted in a decrease in hepatic cholesterolgenesis with concomitant lanosterol accumulation, further implicating CYP51 inhibition as the mechanism of cholesterol lowering in these animals. CP-320626 and analogs directly inhibited rhCYP51, and this inhibition was highly correlated with HepG2 cell cholesterolgenesis inhibition ( R 2 ‫؍‬ 0.77). These observations indicate that CP-320626 inhibits cholesterolgenesis via direct inhibition of CYP51, and that this is the mechanism whereby CP-320626 lowers plasma cholesterol in experimental animals. Dual-action glycogenolysis and cholesterolgenesis inhibitors therefore have the potential to favorably affect both the hyperglycemia and the dyslipidemia of type 2 diabetes.

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New chemical entities are routinely screened in vitro and in vivo for their ability to induce cytochrome P450s (CYP), other drug-metabolizing enzymes and possibly transporters in an attempt to more accurately predict clinical parameters such as drug-drug interactions and clearance in humans. Some of these potential therapeutic agents can cause induction of the metabolism of another molecule or auto-induction thereby increasing their own metabolism and elimination, as well as potentially any molecules metabolized by the same enzyme(s). Key CYPs in the 1A, 2B, 2C, and 3A families have all been shown to be inducible. It would be clearly advantageous to know the potential for a compound to induce drug metabolizing enzymes or transporters prior to clinical development, and many in vitro systems have been developed for this purpose. Newer computational technologies are also being applied in order to attempt to predict induction from the molecular structure alone before a molecule is even synthesized or tested. This review will cover the various in vitro and in silico methods developed for prediction of key inducers of CYPs and other proteins, as well as the limitations of such technologies and applications in the future.

The inducibility of a cytochrome P450 isoform, CYP2E1 (cyp2e-1), was compared in colonic epithelium of selected inbred mice. Mice were chosen for study on the basis of reported susceptibility to 1,2-dimethylhydrazine (DMH)-induced colorectal tumor formation. DBA/2J (resistant), C57BL/6J (intermediate) and SWR/J (susceptible) mice were exposed to acetone (1% v/v) in drinking water for 10 days. SWR/J mice sustained the largest increase in colonic cyp2e-1, although protein levels, assessed by Western analysis, were markedly increased in mucosal tissue obtained from C57BL/6J mice as well. Further evidence for colonic cyp2e-1 induction is supported by elevated (3.5-fold) chlorzoxazone 6-hydroxylase activity in response to acetone. To more fully characterize these changes in colon, the tumor-sensitive SWR/J mice were chosen for further evaluation. Mice were treated with a panel of agents established to induce this protein in liver, including isoniazid (0.1% v/v) and ethanol (10% v/v) in drinking water and pyrazole (300 mg/kg), given intraperitoneally. With the exception of ethanol, each compound produced a marked (1.5- to 3-fold) elevation of cyp2e-1 in colon and liver. Overall balance between phase I and II metabolism may be a critical factor in determining tumor susceptibility. Therefore, glutathione S-transferase (GST) activity was also examined. In liver, basal GST levels varied less than 2-fold between strains, while in colon, levels were 5-10% of corresponding hepatic levels. Although acetone treatment did not significantly alter hepatic GST, a 30-60% decline in activity was observed in colons of SWR/J and C57BL/6J mice. Further examination of colonic GST revealed compound-specific effects. Ethanol exposure markedly (60%) lowered GST levels in colon, whereas pyrazole produced a 2-fold increase. None of these agents significantly altered hepatic GST activity. These studies demonstrate the ability of mouse colon to undergo an increase in immunoreactive cyp2e-1 in response to a panel of xenobiotics known to elevate this protein in liver. Further characterization of cyp2e-1 and GSTs in inbred mice may provide important information on the role of colonocytes in direct activation of ingested procarcinogens to DNA-reactive metabolites.

1. Transgenic mice were evaluated with six human cytochrome P450 (CYP) selective probe substrates, as little is known about their metabolism in the mouse. Mouse strains characterized include C57BL/SJL, FVB/N, mdr 1a/1b (-/-), ob/ob and ACCA. 2. Human CYP probe substrates used for characterization of mouse CYP activities included bufuralol, testosterone, dextromethorphan, phenacetin, diclofenac and S-mephenytoin. Activities were compared with those obtained in human liver microsomes and in human recombinant enzyme preparations. All transgenic mouse strains showed similar apparent K(m) with bufuralol, testosterone and dextromethorphan which compared favourably with those observed in human liver microsomes. 3. K(m) for phenacetin O-deethylase and S-mephenytoin 4'-hydroxylation were more variable across strains and in some cases demonstrated biphasic kinetics. Phenacetin O-deethylase activity was low in all mouse strains except FVB/N and mdr 1a/1b (-/-). Diclofenac 4-hydroxylation did not occur to any significant extent in the five strains of mouse evaluated here. 4. The findings suggest the validity of using five of the probes for transgenic mouse hepatic CYP characterization and gross comparison with data generated with human CYP.

Acetaminophen is an analgesic and antipyretic which causes liver toxicity in humans and experimental animals with overdose. Acetaminophen (APAP) covalent binding to a cytosolic protein of approximately 58 kDa (58-ABP) has been associated with target organ toxicity. Since hepatic content of 58-ABP varies, studies were conducted to determine if this influences APAP binding to other target proteins. In the liver, the amount of 58-ABP varied with individual male CD-1 mice, but in kidneys of the same mice there was no such variability in 58-ABP content. All male A/J mice tested had comparatively little detectable 58-ABP in liver cytosol. Similarly, female CD-1 mice had low 58-ABP content compared to males; however, administration of testosterone propionate to females significantly increased 58-ABP content in liver cytosol. At 4 hr after challenge of mice from the above-described groups with 600 mg APAP/kg, cytosolic covalent binding to proteins was determined by Western blot analysis with anti-APAP antibody. The Western blots were then stripped of antibody and blocking agents and reprobed with antibody prepared against purified 58-ABP (anti-58-ABP). In the liver, the level of APAP bound to the 58-ABP target corresponded with 58-ABP content. In cases where 58-ABP was poorly expressed, APAP adducts to other protein targets were more prominently detected. In the kidneys of the male CD-1 mice 58-ABP arylation by APAP varied little among animals, reflecting the relatively consistent levels of renal 58-ABP. These data suggest that binding to the 58-ABP may spare other potential targets of APAP electrophile attach and support a role of the 58-ABP as a preferred target of APAP electrophile in cytosol.