ABSTRACT:Time-dependent inhibition (TDI) of cytochrome P450 (P450) enzymes caused by new molecular entities (NMEs) is of concern because such compounds can be responsible for clinically relevant drug-drug interactions (DDI). Although the biochemistry underlying mechanism-based inactivation (MBI) of P450 enzymes has been generally understood for several years, significant advances have been made only in the past few years regarding how in vitro time-dependent inhibition data can be used to understand and predict clinical DDI. In this article, a team of scientists from 16 pharmaceutical research organizations that are member companies of the Pharmaceutical Research and Manufacturers of America offer a discussion of the phenomenon of TDI with emphasis on the laboratory methods used in its measurement. Results of an anonymous survey regarding pharmaceutical industry practices and strategies around TDI are reported. Specific topics that still possess a high degree of uncertainty are raised, such as parameter estimates needed to make predictions of DDI magnitude from in vitro inactivation parameters. A description of follow-up mechanistic experiments that can be done to characterize TDI are described. A consensus recommendation regarding common practices to address TDI is included, the salient points of which include the use of a tiered approach wherein abbreviated assays are first used to determine whether NMEs demonstrate TDI or not, followed by more thorough inactivation studies for those that do to define the parameters needed for prediction of DDI.Pharmacokinetic drug-drug interactions (DDIs) can occur when one drug alters the metabolism of a coadministered drug. The outcome is an increase or decrease in the systemic clearance and/or bioavailability, and a corresponding change in the exposure to a coadministered drug. The clinical consequences of DDIs range from lack of therapeutic efficacy of a life saving drug to severe adverse drug reactions, including fatalities. Significant drug-drug interactions can lead to termination of development of otherwise promising new therapies, withdrawal of a drug from the market, or severe restrictions/limitations on its use (Wienkers and Heath, 2005). Because of the impact on patient health and safety, DDI was the subject of a position paper in 2003 by scientists from member companies of the Pharmaceutical Research and Manufacturers of America (PhRMA) that focused on Article, publication date, and citation information can be found at

dNew regimens based on two or more novel agents are sought to shorten or simplify treatment of tuberculosis (TB). Pretomanid (PMD) is a nitroimidazole in phase 3 trials that has significant bactericidal activity alone and in combination with bedaquiline (BDQ) and/or pyrazinamide (PZA). We previously showed that the novel combination of BDQ؉PMD plus the oxazolidinone sutezolid (SZD) had sterilizing activity superior to that of the first-line regimen in a murine model of TB. The present experiments compared the activity of different oxazolidinones in combination with BDQ؉PMD with or without PZA in the same model. The 3-drug regimen of BDQ؉PMD plus linezolid (LZD) had sterilizing activity approaching that of BDQ؉PMD؉SZD and superior to that of the first-line regimen. The addition of PZA further enhanced activity. Reducing the duration of LZD to 1 month did not significantly affect the activity of the regimen. Halving the LZD dose or replacing LZD with RWJ-416457 modestly reduced activity over the first month but not after 2 months. AZD5847 and tedizolid also increased the bactericidal activity of BDQ؉PMD, but they were less effective than the other oxazolidinones. These results provide optimism for safe, short-course oral regimens for drug-resistant TB that may also be superior to the current first-line regimen for drug-susceptible TB.A pproximately half a million new cases of multidrug-resistant (MDR) tuberculosis (TB) occur annually (1). Current recommendations call for up to 2 years of treatment with second-line drugs that are poorly tolerated, toxic, more difficult to administer, and less effective than the 6-month, so-called short-course regimen for drug-susceptible TB. Regimens containing at least 6 drugs, including newer fluoroquinolones in high doses, an injectable agent, clofazimine, pyrazinamide (PZA), and high-dose isoniazid (INH), have shown potential as effective 9-month regimens in MDR-TB cases with minimal bacillary resistance to second-line drugs (2-4). However, these regimens remain quite cumbersome to administer and are not expected to be as effective in the setting of resistance to fluoroquinolones and/or injectable agents (3). Novel regimens based on 3 or more oral agents with little or no preexisting resistance would provide simpler, more universally active regimens. If such novel regimens are more effective than the current first-line regimen for drug-susceptible TB, they may shorten and simplify treatment for pulmonary TB irrespective of resistance to existing drugs.Agents from 2 novel classes recently received conditional regulatory approval for use in MDR-TB, the diarylquinoline bedaquiline (BDQ) and the nitroimidazole-derivative delamanid. Aside from some mutations known to confer cross-resistance between BDQ and clofazimine (5, 6), these agents are not known to exhibit cross-resistance with other TB drugs. We recently reported that the 3-drug regimen of BDQ plus pretomanid (PMD; formerly known as PA-824), the second nitroimidazole to enter phase 3 clinical trials, and the oxazolidinone su...

This article is available online at http://dmd.aspetjournals.org ABSTRACT:1-Aminobenzotriazole (ABT) has been extensively used as a nonspecific inhibitor of cytochromes P450 (P450s) in animals for mechanistic studies, and antipyrine (AP) has been used as a probe for hepatic oxidative metabolic capacity determination in vivo. The method of use of ABT has been variable from lab to lab due largely to unknown pharmacokinetics of ABT itself and incomplete information on various P450s inhibited. The oral pharmacokinetic profiles of ABT were generated in rats, dogs, and monkeys in the dose range of 5 to 200 mg/kg. The results showed that after single oral doses of 50 mg/kg in rats, and 20 mg/kg in dogs and monkeys, the plasma concentrations were high and were sustained for over 24 h. In vitro, inhibition of various expressed P450s upon 30-min preincubation with ABT (0-500 M) showed that CYP1A2, 2B6, 2C9, 2C19, 2D6, and 3A4 were inhibited in a dose-dependent manner. The intravenous pharmacokinetics of AP also was affected in a dose-dependent manner in all species, treated 2 h earlier with ABT. Thus, the plasma clearance of AP was inhibited by 88% in rats pretreated with 50 mg/kg ABT and 96% in dogs and 83% in monkeys pretreated with 20 mg/kg ABT. Based on these data in rats, dogs, and monkeys, and the established safety profile of ABT in rats dosed up to 100 mg/kg, a pretreatment at 2 h with a single oral dose of ABT at 100 mg/kg in rats (providing 93% inhibition) and 20 mg/kg in dogs and monkeys effectively inhibited the clearance of the probe compound. ABT1 has been extensively used as a nonspecific inhibitor of cytochromes P450 in animals for mechanistic studies (Mico et al., 1988;Huijzer et al., 1989;Mugford and Tarloff, 1995;Su et al., 1998;Constan et al., 1999;Marczylo and Ioannides, 1999). The method of use of ABT has been quite variable from lab to lab, for example, single versus multiple dosing of animals prior to the test compound, p.o. versus i.v. route of administration, different pretreatment times, and different dose levels. Moreover, the pharmacokinetics of ABT in different species have not been reported. Also there is incomplete information in the literature on the inhibition of P450s by ABT (Knickle and Bend, 1992;Su et al., 1998;Di Re et al., 1999). To provide a guideline for the pretreatment regimen of ABT, 1) single dose oral pharmacokinetic studies were conducted in rats, dogs, and monkeys at several dose levels; 2) in vitro inhibition of various recombinant P450s by ABT was determined; and 3) the effect of selected doses of ABT on the intravenous pharmacokinetics of antipyrine, a probe for measuring efficiency of hepatic oxidative metabolism, was determined. The results from these studies are described in this report. Materials and MethodsABT and antipyrine (AP) were obtained from Sigma-Aldrich (St. Louis, MO). Single oral dose pharmacokinetics of ABT, in 0.5% aqueous methylcellulose, were studied in fasted male Sprague-Dawley rats at 10, 50, and 200 mg/kg (n Ն 3) and in Beagle dogs and Cynomolus m...

1. The selectivity of eight chemical inhibitors has been extensively evaluated with 10 cDNA-expressed human cytochrome P450 isoforms (CYP). The results indicate that sulphaphenazole, quinidine and alpha-naphthoflavone are selective inhibitors of CYP2C9 (IC50 = 0.5-0.7 microM), CYP2D6 (0.3-0.4 microM) and CYP1A (0.05-5 microM) respectively on the basis of the IC50, which are much lower than those of other P450 isoforms (> 10-fold). 2. Ketoconazole exhibited potent inhibition of both CYP3A4-catalysed metabolism of phenanthrene, testosterone, diazepam (IC50 = 0.03-0.5 microM) and CYP1A1-catalysed deethylation of 7-ethoxycoumarin (0.33 microM). The selectivity of ketoconazole for other P450s was highly related to the concentration used. 3. Diethyldithiocarbamate, orphenadrine and furafylline were shown separately to be less selective inhibitors of CYP2E1, CYP2B6 and CYP1A isoforms by a broad range of IC50 that overlap those observed with other P450 isoforms. 4. Furafylline, quinidine and alpha-naphthoflavone activated CYP3A4-catalysed phenanthrene metabolism by 1.7-, 2- and 15-fold respectively. 5. The selectivity of orphenadrine and ketoconazole was further examined by using inhibitory monoclonal antibodies (MAb). Inhibitory MAb specific for the individual P450 isoforms may be of greater value than chemical inhibitors.

Western and Chinese artists have different traditions in representing the world in their paintings. While Western artists start since the Renaissance to represent the world with a central perspective and focus on salient objects in a scene, Chinese artists concentrate on context information in their paintings, mainly before the mid-19th century. We investigated whether the different typical representations influence the aesthetic preference for traditional Chinese and Western paintings in the different cultural groups. Traditional Chinese and Western paintings were presented randomly for an aesthetic evaluation to Chinese and Western participants. Both Chinese and Western paintings included two categories: landscapes and people in different scenes. Results showed a significant interaction between the source of the painting and the cultural group. For Chinese and Western paintings, a reversed pattern of aesthetic preference was observed: while Chinese participants gave higher aesthetic scores to traditional Chinese paintings than to Western paintings, Western participants tended to give higher aesthetic scores to traditional Western paintings than to Chinese paintings. We interpret this observation as indicator that personal identity is supported and enriched within cultural belongingness. Another important finding was that landscapes were more preferable than people in a scene across different cultural groups indicating a universal principle of preferences for landscapes. Thus, our results suggest that, on the one hand, the way that artists represent the world in their paintings influences the way that culturally embedded viewers perceive and appreciate paintings, but on the other hand, independent of the cultural background, anthropological universals are disclosed by the preference of landscapes.

Synchronizing neural processes, mental activities, and social interactions is considered to be fundamental for the creation of temporal order on the personal and interpersonal level. Several different types of synchronization are distinguished, and for each of them examples are given: self-organized synchronizations on the neural level giving rise to pre-semantically defined time windows of some tens of milliseconds and of approximately 3 s; time windows that are created by synchronizing different neural representations, as for instance in aesthetic appreciations or moral judgments; and synchronization of biological rhythms with geophysical cycles, like the circadian clock with the 24-hr rhythm of day and night. For the latter type of synchronization, an experiment is described that shows the importance of social interactions for sharing or avoiding common time. In a group study with four subjects being completely isolated together for 3 weeks from the external world, social interactions resulted both in intra- and interindividual circadian synchronization and desynchronization. A unique phenomenon in circadian regulation is described, the "beat phenomenon," which has been made visible by the interaction of two circadian rhythms with different frequencies in one body. The separation of the two physiological rhythms was the consequence of social interactions, that is, by the desire of a subject to share and to escape common time during different phases of the long-term experiment. The theoretical arguments on synchronization are summarized with the general statement: "Nothing in cognitive science makes sense except in the light of time windows." The hypothesis is forwarded that time windows that express discrete timing mechanisms in behavioral control and on the level of conscious experiences are the necessary bases to create cognitive order, and it is suggested that time windows are implemented by neural oscillations in different frequency domains.

Microsomal epoxide hydrolase (mEH) is a conserved enzyme that is known to hydrolyze many drugs and carcinogens, and a few endogenous steroids and bile acids. mEH-null mice were produced and found to be fertile and have no phenotypic abnormalities thus indicating that mEH is not critical for reproduction and physiological homeostasis. mEH has also been implicated in participating in the metabolic activation of polycyclic aromatic hydrocarbon carcinogens. Embryonic fibroblast derived from the mEH-null mice were unable to produce the proximate carcinogenic metabolite of 7,12-dimethylbenz[a]anthracene (DMBA), a widely studied experimental prototype for the polycylic aromatic hydrocarbon class of chemical carcinogens. They were also resistant to DMBA-mediated toxicity. Using the two-stage initiation-promotion skin cancer bioassay, the mEH-null mice were found to be highly resistant to DMBA-induced carcinogenesis. In a complete carcinogenesis bioassay, the mEH mice were totally resistant to tumorigenesis. These data establish in an intact animal model that mEH is a key genetic determinant in DMBA carcinogenesis through its role in production of the ultimate carcinogenic metabolite of DMBA, the 3,4-diol-1,2-epoxide.Microsomal epoxide hydrolase (mEH) 1 is a critical phase I biotransformation enzyme that catalyzes hydrolysis of a large number of epoxide intermediates (1, 2). mEH is highly conserved in different mammalian species, is expressed in the embryo (3-5) and multiple organs, and is active toward some endogenous epoxy-steroids (6) and bile acids (7) thus suggesting that it plays a critical physiological role. mEH is usually thought to play a pivotal role in protection against the toxicity of reactive epoxide intermediates, because metabolism of epoxides by this enzyme results in the production of less reactive and less toxic dihydrodiol intermediates of drugs such as phenytoin and carbamazepine (8, 9) and epoxides of environmental toxins (10, 11). In contrast to this protective effect, mEH is thought to be required for the metabolic activation of the potent carcinogen 7,12-dimethylbenz[a]anthracene (DMBA), a widely studied experimental prototype for the polycylic aromatic hydrocarbon class of chemical carcinogens (12). P450s and mEH metabolize DMBA to both inert metabolites and metabolites that are electrophilic and capable of producing DNA adducts (Fig. 1). Cytochrome P450 CYP1B1 oxidizes DMBA to the 3,4-epoxide (13). This is followed by hydrolysis of the epoxide by mEH to the proximate carcinogenic metabolite, DMBA-3,4-diol. This metabolite can be further oxidized by either CYP1A1 or CYP1B1 to the principal ultimate carcinogenic metabolite, DMBA-3,4-diol-1,2-epoxide, that is capable of producing DNA adducts (14 -17). Other ring hydroxylations and methyl hydroxylations of DMBA result in inactive metabolites that do not bind DNA. Based on this scheme, mEH should be a critical enzyme in the pathway leading to the carcinogenic activity of DMBA. However a role for mEH in DMBA carcinogenesis has not been established i...

Abstract. Metabolism-related liabilities continue to be a major cause of attrition for drug candidates in clinical development. Such problems may arise from the bioactivation of the parent compound to a reactive metabolite capable of modifying biological materials covalently or engaging in redox-cycling reactions leading to the formation of other toxicants. Alternatively, they may result from the formation of a major metabolite with systemic exposure and adverse pharmacological activity. To avert such problems, biotransformation studies are becoming increasingly important in guiding the refinement of a lead series during drug discovery and in characterizing lead candidates prior to clinical evaluation. This article provides an overview of the methods that are used to uncover metabolism-related liabilities in a preclinical setting and offers suggestions for reducing such liabilities via the modification of structural features that are used commonly in drug-like molecules.