Robert Houle

Pitavastatin is a more sensitive and selective organic anion‐transporting polypeptide 1B clinical probe than rosuvastatin

AIMS Rosuvastatin and pitavastatin have been proposed as probe substrates for the organic anion-transporting polypeptide (OATP) 1B, but clinical data on their relative sensitivity and selectivity to OATP1B inhibitors are lacking. A clinical study was therefore conducted to determine their relative suitability as OATP1B probes using single oral (PO) and intravenous (IV) doses of the OATP1B inhibitor rifampicin, accompanied by a comprehensive in vitro assessment of rifampicin inhibitory potential on statin transporters. METHODS The clinical study comprised of two separate panels of eight healthy subjects. In each panel, subjects were randomized to receive a single oral dose of rosuvastatin (5 mg) or pitavastatin (1 mg) administered alone, concomitantly with rifampicin (600 mg) PO or IV. The in vitro transporter studies were performed using hepatocytes and recombinant expression systems. RESULTS Rifampicin markedly increased exposures of both statins, with greater differential increases after PO vs. IV rifampicin only for rosuvastatin. The magnitudes of the increases in area under the plasma concentration-time curve were 5.7- and 7.6-fold for pitavastatin and 4.4- and 3.3-fold for rosuvastatin, after PO and IV rifampicin, respectively. In vitro studies showed that rifampicin was an inhibitor of OATP1B1 and OATP1B3, breast cancer resistance protein and multidrug resistance protein 2, but not of organic anion transporter 3. CONCLUSIONS The results indicate that pitavastatin is a more sensitive and selective and thus preferred clinical OATP1B probe substrate than rosuvastatin, and that a single IV dose of rifampicin is a more selective OATP1B inhibitor than a PO dose.

Discovery of MK-7246, a selective CRTH2 antagonist for the treatment of respiratory diseases

In this manuscript we wish to report the discovery of MK-7246 (4), a potent and selective CRTH2 (DP2) antagonist. SAR studies leading to MK-7246 along with two synthetic sequences enabling the preparation of this novel class of CRTH2 antagonist are reported. Finally, the pharmacokinetic and metabolic profile of MK-7246 is disclosed.

Evaluation of human hepatocyte incubation as a new tool for metabolism study of androstenedione and norandrostenedione in a doping control perspective

Human hepatocyte incubations were used to study the metabolism of precursors of testosterone and nortestosterone and to evaluate qualitatively the correlation between in vitro and published in vivo urinary metabolic profiles. Both phase I and phase II biotransformations were observed in vitro: oxidoreduction at C-3 and C-17, reduction at C-4,5, hydroxylation at C-6 beta and C-16, glucuronidation and sulfation. All major metabolites detected in urine following oral administration of androstenedione and norandrostenedione were present in human hepatocyte incubations. The good correlation between in vitro and in vivo metabolic profiles indicates that hepatocyte incubations can be a useful tool to identify and characterize metabolites that could be potential urinary markers for detection of steroid abuse by athletes.

Azaindoles as potent CRTH2 receptor antagonists

A new class of 7-azaindole analogs of MK-7246 as potent and selective CRTH2 antagonists is reported. The SAR leading to the identification of the optimal azaindole regioisomer as well as the pharmacokinetics and off-target activities of the most potent antagonists are disclosed.

USE OF A BENZYLOXY-SUBSTITUTED LACTONE CYCLOOXYGENASE-2 INHIBITOR AS A SELECTIVE FLUORESCENT PROBE FOR CYP3A ACTIVITY IN PRIMARY CULTURED RAT AND HUMAN HEPATOCYTES

The benzyloxy-substituted lactone cyclooxygenase-2 inhibitor DFB [3-[(3,4-difluorobenzyl)oxy]-5,5-dimethyl-4-[4-(methylsulfonyl)phenyl]furan-2(5H)-one] is metabolized in human and rat liver microsomal incubations and hepatocytes to a fluorescent metabolite, DFH [3-hydroxy-5,5-dimethyl-4-[4-(methylsulfonyl)phenyl]furan-2(5H)-one]. This process is CYP3A-mediated in both species, as demonstrated by incubations with recombinant CYP3A enzymes and experiments with inhibitory antibodies. Measurement of DFH fluorescence can be used as a rapid readout of CYP3A activity following microsomal or cultured hepatocyte incubations. In rat and human hepatocytes treated with prototypical inducers, the formation of DFH was linear for the first 30 min, with no secondary metabolism of DFH, such as phase II glucuronidation, observed at early time points. Using a panel of four prototypical inducers (phenobarbital, dexamethasone, phenytoin, and rifampicin), the correlation between testosterone 6beta-hydroxylation in cultured human hepatocytes and CYP3A enzyme level in cell lysate was confirmed. DFB debenzylation was then shown to correlate well with testosterone 6beta-hydroxylation in hepatocytes treated with these four inducers. Primary cultured rat and human hepatocyte induction assays were optimized for 24- and 96-well plates, respectively. Controls were established to evaluate whether test compounds demonstrate time-dependent CYP3A inhibition to avoid false negative results. Thus, the use of DFB, a fluorogenic CYP3A-selective probe substrate, affords a fast, efficient, and robust assay for the measurement of CYP3A induction in both rat and human cultured primary hepatocytes.

Addressing time-dependent CYP 3A4 inhibition observed in a novel series of substituted amino propanamide renin inhibitors, a case study

Time-dependent inhibitors of CYPs have the potential to perpetrate drug-drug interactions in the clinical setting. After finding that several leading compounds in a novel series of substituted amino propanamide renin inhibitors inactivated CYP3A4 in an NADPH-dependent and time-dependent manner, a search to identify the cause of this liability was initiated. Extensive SAR revealed that the amide bridge present in compound 1 as a possible culprit. Through the installation of a metabolic soft spot distal to this moiety, potent renin inhibitors with improved CYP profile were identified.

Design and optimization of a substituted amino propanamide series of renin inhibitors for the treatment of hypertension.

The discovery and SAR of a new series of substituted amino propanamide renin inhibitors are herein described. This work has led to the preparation of compounds with in vitro and in vivo profiles suitable for further development. Specifically, challenges pertaining to oral bioavailability, covalent binding and time-dependent CYP 3A4 inhibition were overcome thereby culminating in the identification of compound 50 as an optimized renin inhibitor with good efficacy in the hypertensive double-transgenic rat model.

Renin inhibitors for the treatment of hypertension: Design and optimization of a novel series of pyridone-substituted piperidines

An SAR campaign aimed at decreasing the overall lipophilicity of renin inhibitors such as 1 is described herein. It was found that replacement of the northern appendage in 1 with an N-methyl pyridone and subsequent re-optimization of the benzyl amide handle afforded compounds with in vitro and in vivo profiles suitable for further profiling. An unexpected CV toxicity in dogs observed with compound 20 led to the employment of a time and resource sparing rodent model for in vivo screening of key compounds. This culminated in the identification of compound 31 as an optimized renin inhibitor.

Renin inhibitors for the treatment of hypertension: Design and optimization of a novel series of tertiary alcohol-bearing piperidines

The design and optimization of a novel series of renin inhibitor is described herein. Strategically, by committing the necessary resources to the development of synthetic sequences and scaffolds that were most amenable for late stage structural diversification, even as the focus of the SAR campaign moved from one end of the molecule to another, highly potent renin inhibitors could be rapidly identified and profiled.

New indole amide derivatives as potent CRTH2 receptor antagonists.

A new series of indole amide acting as hCRTH2 receptor ligands had been explored and are described herein. Several amide derivatives displaying low nanomolar activity in hCRTH2 binding and whole blood assays were identified. They were found to behave as a full antagonists, exhibiting good selectivity over related prostaglandin receptors. Also, prototypical compounds in this novel series which displayed acceptable CYP profiles and were orally bioavailable in rats were identified.