ABSTRACT:This article describes an in vitro investigation of the inhibition of cytochrome P450 (P450) 2C9 by a series of flavonoids made up of flavones (flavone, 6-hydroxyflavone, 7-hydroxyflavone, chrysin, baicalein, apigenin, luteolin, scutellarein, and wogonin) and flavonols (galangin, fisetin, kaempferol, morin, and quercetin). With the exception of flavone, all flavonoids were shown to inhibit CYP2C9-mediated diclofenac 4-hydroxylation in the CYP2C9 RECO system, with K i value <2.2 M. In terms of the mechanism of inhibition, 6-hydroxyflavone was found to be a noncompetitive inhibitor of CYP2C9, whereas the other flavonoids were competitive inhibitors. Computer docking simulation and constructed mutants substituted at residue 100 of CYP2C9.1 indicate that the noncompetitive binding site of 6-hydroxyflavone lies beside Phe100, similar to the reported allosteric binding site of warfarin. The other flavonoids exert competitive inhibition through interaction with the substrate binding site of CYP2C9 accessed by flurbiprofen. These results suggest flavonoids can participate in interactions with drugs that act as substrates for CYP2C9 and provide a possible molecular basis for understanding cooperativity in human P450-mediated drug-drug interactions.Flavonoids are polyphenolic secondary metabolites that are widely distributed in higher plants and ingested by humans in their regular food (Kuhnau, 1976;Bravo, 1998). Flavones and flavonols are two major classes of flavonoids (Table 1). Flavonols are present in a variety of fruits and vegetables, whereas flavones are mainly found in cereals and herbs (Hertog et al., 1993;Bravo, 1998;Peterson and Dwyer, 1998). In the West, the estimated daily intake of both flavonols and flavones is in the range 20 to 50 mg per day (Cermak and Wolffram, 2006). However, given the growing demand for food supplements or herbal remedies containing flavonoids, and given that in some countries flavonoids are commonly used as therapeutic agents (2008 State Food and Drug Administration RPC, http://app1.sfda.gov. cn/datasearch/face3/dir.html), it is likely that some individuals are exposed to relatively high levels of flavonoids. This points to a need for more information on the safety and potential toxicity of flavonoids.In the early 1980s, several studies reported the effects of flavonoids on the activity of hepatic cytochrome P450 (P450) enzymes (Buening et al., 1981;Lasker et al., 1982). Since then, the ability of flavonoids to inhibit isoforms of CYP450, particularly CYP1A1 and CYP1A2, has been extensively confirmed (Cermak and Wolffram, 2006). Several clinical studies have reported that some flavonoids have the capacity to alter drug metabolism in vivo (Peng et al., 2003;Rajnarayana et al., 2003;Choi et al., 2004). However, for CYP2C9, which ranks among the most important drug-metabolizing enzymes in humans and hydroxylates 10 to 20% of commonly prescribed drugs (Kirchheiner and Brockmöller, 2005), only two flavones, luteolin and baicalein, and one flavonol, quercetin, have been found to ...

This study suggests that this novel CYP2C9 allele was correlated with reduced plasma clearance of drugs that are substrates for CYP2C9.

ABSTRACT:CYP2C9 is an important member of the cytochrome P450 enzyme superfamily with some 12 CYP2C9 alleles (*1-*12) being previously reported. Recently, we identified a new CYP2C9 allele with a Leu90Pro mutation in a and 12% compared with wild type. In a subsequent clinical study, the AUC of lornoxicam was increased by 1.9-fold and its oral clearance (CL/F) decreased by 44% in three CYP2C9*1/*13 subjects, compared with CYP2C9*1/*1 individuals. This suggests that the CYP2C9*13 allele is associated with decreased enzymatic activity both in vitro and in vivo.

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BackgroundPancreatic cancer is a highly malignant disease with an extremely poor prognosis. Histone deacetylase inhibitors (HDACIs) have shown promising antitumor activities against preclinical models of pancreatic cancer, either alone or in combination with chemotherapeutic agents. In this study, we sought to identify clinically relevant histone deacetylases (HDACs) to guide the selection of HDAC inhibitors (HDACIs) tailored to the treatment of pancreatic cancer.MethodologyHDAC expression in seven pancreatic cancer cell lines and normal human pancreatic ductal epithelial cells was determined by Western blotting. Antitumor interactions between class I- and class II-selective HDACIs were determined by MTT assays and standard isobologram/CompuSyn software analyses. The effects of HDACIs on cell death, apoptosis and cell cycle progression, and histone H4, alpha-tubulin, p21, and γH2AX levels were determined by colony formation assays, flow cytometry analysis, and Western blotting, respectively.ResultsThe majority of classes I and II HDACs were detected in the pancreatic cancer cell lines, albeit at variable levels. Treatments with MGCD0103 (a class I-selective HDACI) resulted in dose-dependent growth arrest, cell death/apoptosis, and cell cycle arrest in G2/M phase, accompanied by induction of p21 and DNA double-strand breaks (DSBs). In contrast, MC1568 (a class IIa-selective HDACI) or Tubastatin A (a HDAC6-selective inhibitor) showed minimal effects. When combined simultaneously, MC1568 significantly enhanced MGCD0103-induced growth arrest, cell death/apoptosis, and G2/M cell cycle arrest, while Tubastatin A only synergistically enhanced MGCD0103-induced growth arrest. Although MC1568 or Tubastatin A alone had no obvious effects on DNA DSBs and p21 expression, their combination with MGCD0103 resulted in cooperative induction of p21 in the cells.ConclusionOur results suggest that classes I and II HDACs are potential therapeutic targets for treating pancreatic cancer. Accordingly, treating pancreatic cancer with pan-HDACIs may be more beneficial than class- or isoform-selective inhibitors.