The effect of anti-tuberculosis drug pharmacokinetics on QTc prolongation

BACKGROUND

Implementation of newer anti-tuberculosis (TB) drugs may prolong the QT interval, increasing the risk of arrythmias and sudden cardiac death. The potential for cardiac adverse events has prompted recommendations for frequent cardiac monitoring during treatment. However, unknowns remain, including the association between drug concentrations and QT interval.

METHODS

An observational prospective cohort study design was used. Patients undergoing treatment for drug-resistant TB in Georgia were assessed. Serial blood samples were collected at 4-6 weeks for pharmacokinetics. Electrocardiograms were recommended to be performed monthly. A generalized estimating equation spline model was used to investigate (1) the effect difference between bedaquiline and delamanid, (2) the cumulative effect of number of anti-TB drugs, and (3) the relationship between serum drug concentrations on QTc interval.

RESULTS

Among 94 patients receiving either bedaquiline (n = 64) or delamanid (n = 30)-based treatment, most were male (82%), and the mean age was 39 years. The mean maximum QTc increase during the first six months was 37.5 ms (IQR: 17.8-56.8). Bedaquiline- and delamanid-based regimens displayed similar increased mean QTc change from baseline during drug administration (P = 0.12). Increasing number of anti-TB drugs was associated with an increased QTc (P = 0.01), but participants trended back towards baseline after drug discontinuation (P = 0.25). A significant association between AUC, Cmin, Cmax, and increased QTc interval was found for bedaquiline (months 1-6) and levofloxacin (months 1-12).

CONCLUSION

Bedaquiline- and delamanid-based regimens and increasing number of QT prolonging agents led to modest increases in the QTc interval with minimal clinical effect.

Evaluation of the inhibitory effect of quercetin on the pharmacokinetics of tucatinib in rats by a novel UPLC-MS/MS assay

CONTEXT

Tucatinib (CYP2C8 substrate) and quercetin (CYP2C8 inhibitor) are two common drugs for the treatment of cancer. However, the effect of quercetin on the metabolism of tucatinib remains unknown.

OBJECTIVE

We validated a sensitive method to quantify tucatinib levels in rat plasma based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), which was successfully employed to explore the effect of quercetin on tucatinib pharmacokinetics in rats.

MATERIALS AND METHODS

An Acquity UPLC BEH C18 column was applied to achieve the separation of tucatinib and internal standard (IS) talazoparib after protein precipitation with acetonitrile. Then, we used this assay to investigate the effect of different doses of quercetin (25, 50 and 100 mg/kg) on the exposure of orally administered tucatinib (30 mg/kg) in 24 Sprague-Dawley (SD) rats, which were randomly divided into three quercetin pre-treated groups and one control group (n = 6).

RESULTS

Our developed assay was verified in all aspects of bioanalytical method validation, involving lower limit of quantification (LLOQ), selectivity, accuracy and precision, calibration curve, extraction recovery, matrix effect and stability. After pre-treatment with 100 mg/kg quercetin, AUC_0→t, AUC_0→∞ and C_max of tucatinib were remarkably increased by 75.4%, 75.8% and 59.1% (p < 0.05), respectively, while CLz/F was decreased significantly by 47.3% (p < 0.05) when compared with oral administration of 30 mg/kg tucatinib alone. This change is dose-dependent.

CONCLUSIONS

This study will help better understand the pharmacokinetic properties of tucatinib with concurrent use with quercetin, and more clinical verifications were inspired to confirm whether this interaction has clinical significance in humans.

Pharmacokinetics and Safety of Single-dose Tedizolid Phosphate in Children 2 to <12 Years of Age

BACKGROUND

Infections with Gram-positive bacteria, including acute bacterial skin and skin structure infections (ABSSSIs), are common in children. We describe a single-dose pharmacokinetics and safety study of tedizolid phosphate, a new oxazolidinone under investigation for the treatment of ABSSSIs in children, in hospitalized participants 2 to <12 years of age.

METHODS

This open-label, multicenter, phase 1 trial (NCT02750761) enrolled hospitalized children 2 to <12 years of age receiving treatment for a confirmed/suspected Gram-positive bacterial infection. Participants were stratified by age (2 to <6 years and 6 to <12 years) to receive a single oral or intravenous dose of tedizolid phosphate. Evaluations included safety and pharmacokinetics of tedizolid phosphate and its active metabolite, tedizolid. Palatability of the oral suspension was also evaluated.

RESULTS

Thirty-two participants were enrolled and received 3-6 mg/kg of study medication. For both routes of administration, tedizolid phosphate was rapidly converted to tedizolid; median time to maximum tedizolid plasma concentration was 1-2 hours after initiation of the 1-hour intravenous infusion and 2-3 hours after oral dosing. The tedizolid mean terminal half-life was 5-6 hours and 6-7 hours for the intravenous and oral administration groups, respectively. The oral tedizolid phosphate suspension demonstrated high bioavailability comparable to that of the parenteral administration. A single dose of intravenous or oral tedizolid phosphate was well tolerated; no unexpected safety findings were observed.

CONCLUSIONS

Pharmacokinetic and safety observations provide the information necessary for the continued development of tedizolid phosphate for the treatment of Gram-positive infections in children, particularly ABSSSIs.

Quantitative determination of proxalutamide in rat plasma and tissues using liquid chromatography/tandem mass spectrometry

RATIONALE

Proxalutamide is a novel drug for the treatment of prostate cancer. However, to date, there are almost no reports on the pharmacokinetics of proxalutamide in vivo. This study developed a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method to determine the concentrations of proxalutamide in biological samples for pharmacokinetic studies.

METHODS

Chromatographic separation was achieved on a Kromasil 100-5C8 column followed by gradient elution using a Shimadzu HPLC system. MS was performed in positive ion electrospray ionization mode using a SCIEX API 4000 triple quadrupole system. A simple and rapid one-step protein precipitation method was used for sample processing, and a low sample volume of 10 μL was used for processing and analysis.

RESULTS

The method was validated to show good selectivity, sensitivity, precision, and accuracy. Good linearity (r²  > 0.99) was observed for rat plasma (range: 2-5000 ng/mL) and rat tissue homogenates (range: 2-2000 ng/mL). The extraction recovery was above 98%, and no significant matrix effect was observed. This method was successfully applied to investigate the pharmacokinetics and tissue distribution of proxalutamide in rats.

CONCLUSIONS

A rapid and sensitive LC/MS/MS method was developed and validated to determine the quantity of proxalutamide in rat plasma and tissue homogenates and to further study the pharmacokinetic parameters of proxalutamide in a rat model. The results showed that proxalutamide had good oral bioavailability and wide tissue distribution in vivo.

Design, synthesis, and evaluation of substituted 2-acylamide-1,3-benzo[d]zole analogues as agents against MDR- and XDR-MTB

N-(5-Chlorobenzo[d]oxazol-2-yl)-4-methyl-1,2,3-thiadiazole-5-carboxamideox-amide has been identified as a potent inhibitor of Mtb H37Rv, with a minimum inhibitory concentration (MIC) of 0.42 μM. In this study, a series of substituted 2-acylamide-1,3-zole analogues were designed and synthesized, and their anti-Mtb activities were analyzed. In total, 17 compounds were found to be potent anti-Mtb agents, especially against the MDR- and XDR-MTB strains, with MIC values < 10 μM. These analogues can inhibit both drug-sensitive and drug-resistant Mtb. Four representative compounds were selected for further profiling, and the results indicate that compound 18 is acceptably safe and has favorable pharmacokinetic (PK) properties. In addition, this compound displays potent activity against Gram-positive bacteria, with MIC values in the range of 1.48-11.86 μM. The data obtained herein suggest that promising anti-Mtb candidates may be developed via structural modification, and that further research is needed to explore other compounds.

Preclinical profile and phase I clinical trial of a novel androgen receptor antagonist GT0918 in castration-resistant prostate cancer

PURPOSE

We conducted preclinical experiments and phase I clinical trial to investigate the safety, pharmacokinetics (PK) and antitumour effects of GT0918 in castration-resistant prostate cancer (CRPC).

EXPERIMENTAL DESIGN

An androgen receptor (AR) competitive binding assay was performed, followed by evaluation of GT0918 on AR protein expression. The efficacy of GT0918 was investigated in a castration-resistant xenograft model. A phase I dose-escalation study of GT0918 in CRPC was also carried out to evaluate its safety, PK and antitumour efficacy.

RESULTS

GT0918 was demonstrated to inhibit the binding of androgen to AR more potently than MDV3100, and to effectively reduce the AR protein level. GT0918 inhibited the transcriptional activity of wild-type AR and AR with clinically relevant ligand-binding domain mutations. Furthermore, GT0918 significantly inhibited the growth of prostate cancer. A total of 16 patients was treated with GT0918 at five dose levels. Among these 16 patients, 10 and 2 patients, respectively, completed a three-cycle and six-cycle treatment, in which MTD was not reached. All the treatment-related adverse events were grade I, including hypercholesterolemia, hypertriglyceridemia, fatigue and anaemia. PK parameters showed that drug exposure increased with dose proportionally from 50 to 300 mg and a saturation was observed between 300 and 400 mg. PSA declines of ≥30% and ≥50% were, respectively, observed in six and two cases. All the 12 patients with metastatic soft tissue lesions confirmed stable disease.

CONCLUSIONS

GT0918, a full AR antagonist without agonist effect, has high binding affinity to AR with AR protein down-regulation activity. GT0918 is demonstrated to be well tolerated with a favourable PK profile and exhibits promising antitumour activity in CRPC. CLINICALTRIALS: gov identifier CTR20150501.

Etoxazole stereoselective determination, bioaccumulation, and resulting oxidative stress in Danio rerio (zebrafish)

An environmentally-friendly and fast analytical method for the stereoselective determination of etoxazole was developed and then applied to estimate stereoselective bioaccumulation and elimination in zebrafish using SFC-MS/MS. Optimal enantioseparation conditions were determined using a Chiralpak IG-3 column and CO₂/MeOH mobile phase (80/20, v/v), at 3.0 mL/min within 1 min, 30°Me and 18 MPa. A modified QuEChERS method was developed for zebrafish sample pretreatment, and mean recoveries were 88.43-110.12% with relative standard deviations ranging from 0.32 to 5.34%. The enantioselectives of etoxazole enantiomers in zebrafish during uptake and depuration phases were evaluated. Significant enantioselective bioaccumulation was observed, with preferential accumulation of (-)-R-etoxazole compared to its antipode, during uptake at both low and high exposure concentrations. The toxic effects of etoxazole on zebrafish were further explored, and activities of antioxidant enzymes were determined in liver of zebrafish. Significant changes were observed in the SOD and GST activities and in the MDA levels, which indicated the occurrence of oxidative stress in liver of zebrafish. The toxic effects exhibited time- and dose-dependent properties. These results can facilitate the accurate risk evaluation of etoxazole and provide basic knowledge for further study of biotoxicity mechanisms.

Exposure and response analysis of aleglitazar on cardiovascular risk markers and safety outcomes: An analysis of the AleCardio trial

AIMS

The AleCardio trial aimed to characterize the efficacy and safety of peroxisome proliferator-activated receptor-αγ agonist aleglitazar in patients with type 2 diabetes mellitus and acute coronary syndrome. The trial terminated early because of futility and safety signals. We evaluated whether the safety signals could be attributed to increased exposure to aleglitazar.

MATERIALS AND METHODS

The AleCardio trial enrolled 7226 patients to receive aleglitazar 150 μg or matching placebo on top of standard care. A population pharmacokinetic analysis was conducted in a pharmacokinetic substudy to identify covariates that explained interindividual variability in exposure. Subsequently, the effect of these covariates on surrogate and clinical outcomes was assessed in the full patient population.

RESULTS

Concomitant administration of clopidogrel was identified as a covariate that influenced the apparent clearance of aleglitazar. Patients using clopidogrel had a mean predicted area under the plasma-concentration-time curve (AUC_0-24 ) of 174.7 ng h/mL (SD: ±112.9 ng h/mL) versus 142.2 ng h/mL (SD: ±92.6 ng h/mL) in patients without clopidogrel. The effect of aleglitazar compared with placebo on HbA1c, haemoglobin, serum creatinine and adiponectin was modified by concomitant clopidogrel use (P for interaction 0.007, 0.002, <0.001 and < 0.001, respectively).

CONCLUSIONS

Concomitant use of clopidogrel was identified as a covariate that explained interindividual variability in exposure to aleglitazar. Patients using clopidogrel showed an additional lowering of HbA1c, at the expense of an additional decrease in haemoglobin, and an increase in serum creatinine and adiponectin. Clopidogrel is a moderate inhibitor of CYP2C8. Because aleglitazar is metabolized by CYP2C8, a pharmacokinetic interaction could explain differences in exposure and response to aleglitazar.

Delamanid Central Nervous System Pharmacokinetics in Tuberculous Meningitis in Rabbits and Humans

Central nervous system tuberculosis (TB) is devastating and affects vulnerable populations. Multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculous meningitis (TBM) specifically are nearly uniformly fatal, with little information being available to guide the treatment of these patients. Delamanid (DLM), a nitro-dihydro-imidazooxazole, is a new, well-tolerated anti-TB drug with a low MIC (1 to 12 ng/ml) against Mycobacterium tuberculosis It is used for the treatment of pulmonary MDR-TB, but pharmacokinetic (PK) data for DLM in the central nervous system (CNS) of patients with TBM are not available. In the present study, we measured DLM concentrations in the brain and cerebrospinal fluid (CSF) of six rabbits with and without experimentally induced TBM receiving single-dose DLM. We report the steady-state CSF concentrations from three patients receiving DLM as part of multidrug treatment who underwent therapeutic drug monitoring. Drug was quantified using liquid chromatography-tandem mass spectrometry. In rabbits and humans, mean concentrations in CSF (in rabbits, 1.26 ng/ml at 9 h and 0.47 ng/ml at 24 h; in humans, 48 ng/ml at 4 h) were significantly lower than those in plasma (in rabbits, 124 ng/ml at 9 h and 14.5 ng/ml at 24 h; in humans, 726 ng/ml at 4 h), but the estimated free CSF/plasma ratios were generally >1. In rabbits, DLM concentrations in the brain were 5-fold higher than those in plasma (means, 518 ng/ml at 9 h and 74.0 ng/ml at 24 h). All patients with XDR-TBM receiving DLM experienced clinical improvement and survival. Collectively, these results suggest that DLM achieves adequate concentrations in brain tissue. Despite relatively low total CSF drug levels, free drug may be sufficient and DLM may have a role in treating TBM. More studies are needed to develop a fuller understanding of its distribution over time with treatment and clinical effectiveness.

Colloidal Drug Aggregate Stability in High Serum Conditions and Pharmacokinetic Consequence

Colloidal drug aggregates have been a nuisance in drug screening, yet, because they inherently comprise drug-rich particles, they may be useful in vivo if issues of stability can be addressed. As the first step toward answering this question, we optimized colloidal drug aggregate formulations using a fluorescence-based assay to study fulvestrant colloidal formation and stability in high (90%) serum conditions in vitro. We show, for the first time, that the critical aggregation concentration of fulvestrant depends on media composition and increases with serum concentration. Excipients, such as polysorbate 80, stabilize fulvestrant colloids in 90% serum in vitro for over 48 h. Using fulvestrant and an investigational pro-drug, pentyloxycarbonyl-( p-aminobenzyl) doxazolidinylcarbamate (PPD), as proof-of-concept colloidal formulations, we demonstrate that the in vivo plasma half-life for stabilized colloids is greater than their respective monomeric forms. These studies demonstrate the potential of turning the nuisance of colloidal drug aggregation into an opportunity for drug-rich formulations.

Synthesis and preclinical evaluation of [¹⁸F]FCHC for neuroimaging of fatty acid amide hydrolase

PURPOSE

Fatty acid amide hydrolase (FAAH), a catabolic enzyme which regulates lipid transmitters in the endocannabinoid system, is an avidly sought therapeutic and positron emission tomography (PET) imaging target for studies involving addiction and neurological disorders. We report the synthesis of a new fluorine-18-labeled FAAH inhibitor, trans-3-(4, 5-dihydrooxazol-2-yl)phenyl-4-[(18)F]fluorocyclohexylcarbamate ([(18)F]FCHC), and its evaluation in rat brain.

PROCEDURES

The synthesis of [(18)F]FCHC was conducted via a 3-step, 1-pot reaction, resulting in uncorrected radiochemical yields between 10 and 20% (n = 5) relative to [(18)F]fluoride, with specific activities of >5 Ci/μmol at the end of the synthesis. The radiosynthesis was seamlessly automated using a commercial radiofluorination apparatus. Ex vivo biodistribution and preliminary PET imaging studies were carried out in male Sprague-Dawley rats.

RESULTS

Rat brain biodistribution at 2 min post-injection showed a standard uptake value of 4.6 ± 0.1 in the cortex, which increased to 7.8 ± 0.1 at 40 min. Pretreatment with the selective FAAH inhibitor URB597 reduced uptake of radioactivity in all brain regions by >90%, with 98 % blockade in the FAAH-rich cortex. PET imaging was consistent with biodistribution studies.

CONCLUSIONS

[(18)F]FCHC appears to be a highly sensitive (18)F-labeled radiotracer for imaging FAAH in the central nervous system, and these results warrant further imaging in nonhuman primates.

Tedizolid: a novel oxazolidinone with potent activity against multidrug-resistant gram-positive pathogens

Tedizolid phosphate is a novel oxazolidinone prodrug (converted to the active form tedizolid by phosphatases in vivo) that has been developed and recently approved (June 2014) by the United States FDA for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) caused by susceptible Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). Tedizolid is an oxazolidinone, but differs from other oxazolidinones by possessing a modified side chain at the C-5 position of the oxazolidinone nucleus which confers activity against certain linezolid-resistant pathogens and has an optimized C- and D-ring system that improves potency through additional binding site interactions. The mechanism of action of tedizolid is similar to other oxazolidinones and occurs through inhibition of bacterial protein synthesis by binding to 23S ribosomal RNA (rRNA) of the 50S subunit of the ribosome. As with other oxazolidinones, the spontaneous frequency of resistance development to tedizolid is low. Tedizolid is four- to eightfold more potent in vivo than linezolid against all species of staphylococci, enterococci, and streptococci, including drug-resistant phenotypes such as MRSA and vancomycin-resistant enterococci (VRE) and linezolid-resistant phenotypes. Importantly, tedizolid demonstrates activity against linezolid-resistant bacterial strains harboring the horizontally transmissible cfr gene, in the absence of certain ribosomal mutations conferring reduced oxazolidinone susceptibility. With its half-life of approximately 12 h, tedizolid is dosed once daily. It demonstrates linear pharmacokinetics, has a high oral bioavailability of approximately 90 %, and is primarily excreted by the liver as an inactive, non-circulating sulphate conjugate. Tedizolid does not require dosage adjustment in patients with any degree of renal dysfunction or hepatic dysfunction. Studies in animals have demonstrated that the pharmacodynamic parameter most closely associated with the efficacy of tedizolid is fAUC(0-24h)/MIC. In non-neutropenic animals, a dose-response enhancement was observed with tedizolid and lower exposures were required compared to neutropenic cohorts. Two Phase III clinical trials have demonstrated non-inferiority of a once-daily tedizolid 200 mg dose for 6-10 days versus twice-daily 600 mg linezolid for the treatment of ABSSSIs. Both trials used the primary endpoint of early clinical response at 48-72 h; however, one trial compared oral formulations while the other initiated therapy with the parenteral formulation and allowed oral sequential therapy following initial clinical response. Throughout its development, tedizolid has demonstrated that it is well tolerated and animal studies have shown a lower propensity for neuropathies with long-term use than its predecessor linezolid. Data from the two completed Phase III clinical trials demonstrated that the studied tedizolid regimen (200 mg once daily for 6 days) had significantly less impact on hematologic parameters as well as significantly less gastrointestinal treatment-emergent adverse effects (TEAEs) than its comparator linezolid. As with linezolid, tedizolid is a weak, reversible MAO inhibitor; however, a murine head twitch model validated to assess serotonergic activity reported no increase in the number of head twitches with tedizolid even at doses that exceeded the C max in humans by up to 25-fold. Tyramine and pseudoephedrine challenge studies in humans have also reported no meaningful MAO-related interactions with tedizolid. With its enhanced in vitro activity against a broad-spectrum of Gram-positive aerobic bacteria, convenient once-daily dosing, a short 6-day course of therapy, availability of both oral and intravenous routes of administration, and an adverse effect profile that appears to be more favorable than linezolid, tedizolid is an attractive agent for use in both the hospital and community settings. Tedizolid is currently undergoing additional Phase III clinical trials for the treatment of hospital-acquired bacterial pneumonia (HABP) and ventilated nosocomial pneumonia (VNP).

Profile of delamanid for the treatment of multidrug-resistant tuberculosis

New approaches to the treatment of multidrug-resistant and extensively drug-resistant tuberculosis (TB) are badly needed. Not only is the success rate of current treatment regimens suboptimal but existing regimens require multiple drugs and lengthy courses and may lead to significant toxicities. The treatment landscape is beginning to shift, however, with the recent approvals of the new TB drugs bedaquiline and delamanid. Delamanid, a dihydro-imidazooxazole, has been shown to have excellent activity against Mycobacterium tuberculosis in both in vitro and in murine TB models. It has also recently been reported to improve rates of sputum culture conversion in patients with multidrug-resistant TB when added to an optimized background regimen. Although generally well tolerated, delamanid has been associated with QT prolongation, which may be of particular clinical concern when paired with other TB drugs that may also have this effect, most notably the fluoroquinolones. Ongoing studies will help to clarify delamanid's role in the treatment of drug-resistant TB.

Simulation of the Impact of Atropisomer Interconversion on Plasma Exposure of Atropisomers of an Endothelin Receptor Antagonist

BMS-207940, a potent endothelin receptor antagonist, exists as rapidly interconverting atropisomers. The plasma interconversion t(1/2) is approximately 2.5 hours at 400 microg/mL under room temperature and decreases to < 0.1 hours at 20 microg/mL, making it extremely difficult to conduct pharmacokinetic studies of individual atropisomers. The pharmacokinetics of the 50/50 racemate of BMS-207940 in humans were reasonably described by a one-compartmental model with an apparent terminal elimination t(1/2) of 15 hours. Given the above rates, simulations were conducted based on a one-compartmental model to explore the possible range of individual rates of atropisomer elimination and potential difference in plasma exposure to the two atropisomers. Simulations demonstrated that the elimination rates of the individual atropisomers are bounded between 0 and 0.046 h(-1) and between 0.046 and 0.092 h(-1), respectively. The estimation of the upper bounds for atropisomer elimination rate constants is robust and relatively insensitive to the rate of atropisomer interconversion compared to the rate of racemate elimination. Simulations of the administration of a single atropisomer or the 50/50 racemate, based on all the possible scenarios of individual atropisomer elimination, showed little difference in plasma exposure to the two atropisomers. Potential differences in plasma exposure to the two atropisomers depend, to a larger extent, on the ratio of the rate of atropisomer interconversion versus racemate elimination and, to a lesser extent, on the conformation of atropisomers administered. When atropisomer interconversion is 10-fold or more rapid than racemate elimination, the largest possible difference in plasma exposure between the two atropisomers is below 20%, regardless of the route and conformation of the atropisomer(s) administered.

Design novel dual agonists for treating type-2 diabetes by targeting peroxisome proliferator-activated receptors with core hopping approach

Owing to their unique functions in regulating glucose, lipid and cholesterol metabolism, PPARs (peroxisome proliferator-activated receptors) have drawn special attention for developing drugs to treat type-2 diabetes. By combining the lipid benefit of PPAR-alpha agonists (such as fibrates) with the glycemic advantages of the PPAR-gamma agonists (such as thiazolidinediones), the dual PPAR agonists approach can both improve the metabolic effects and minimize the side effects caused by either agent alone, and hence has become a promising strategy for designing effective drugs against type-2 diabetes. In this study, by means of the powerful “core hopping” and “glide docking” techniques, a novel class of PPAR dual agonists was discovered based on the compound GW409544, a well-known dual agonist for both PPAR-alpha and PPAR-gamma modified from the farglitazar structure. It was observed by molecular dynamics simulations that these novel agonists not only possessed the same function as GW409544 did in activating PPAR-alpha and PPAR-gamma, but also had more favorable conformation for binding to the two receptors. It was further validated by the outcomes of their ADME (absorption, distribution, metabolism, and excretion) predictions that the new agonists hold high potential to become drug candidates. Or at the very least, the findings reported here may stimulate new strategy or provide useful insights for discovering more effective dual agonists for treating type-2 diabetes. Since the “core hopping” technique allows for rapidly screening novel cores to help overcome unwanted properties by generating new lead compounds with improved core properties, it has not escaped our notice that the current strategy along with the corresponding computational procedures can also be utilized to find novel and more effective drugs for treating other illnesses.

Delamanid for multidrug-resistant pulmonary tuberculosis

BACKGROUND

Delamanid (OPC-67683), a nitro-dihydro-imidazooxazole derivative, is a new antituberculosis medication that inhibits mycolic acid synthesis and has shown potent in vitro and in vivo activity against drug-resistant strains of Mycobacterium tuberculosis.

METHODS

In this randomized, placebo-controlled, multinational clinical trial, we assigned 481 patients (nearly all of whom were negative for the human immunodeficiency virus) with pulmonary multidrug-resistant tuberculosis to receive delamanid, at a dose of 100 mg twice daily (161 patients) or 200 mg twice daily (160 patients), or placebo (160 patients) for 2 months in combination with a background drug regimen developed according to World Health Organization guidelines. Sputum cultures were assessed weekly with the use of both liquid broth and solid medium; sputum-culture conversion was defined as a series of five or more consecutive cultures that were negative for growth of M. tuberculosis. The primary efficacy end point was the proportion of patients with sputum-culture conversion in liquid broth medium at 2 months.

RESULTS

Among patients who received a background drug regimen plus 100 mg of delamanid twice daily, 45.4% had sputum-culture conversion in liquid broth at 2 months, as compared with 29.6% of patients who received a background drug regimen plus placebo (P=0.008). Likewise, as compared with the placebo group, the group that received the background drug regimen plus 200 mg of delamanid twice daily had a higher proportion of patients with sputum-culture conversion (41.9%, P=0.04). The findings were similar with assessment of sputum-culture conversion in solid medium. Most adverse events were mild to moderate in severity and were evenly distributed across groups. Although no clinical events due to QT prolongation on electrocardiography were observed, QT prolongation was reported significantly more frequently in the groups that received delamanid.

CONCLUSIONS

Delamanid was associated with an increase in sputum-culture conversion at 2 months among patients with multidrug-resistant tuberculosis. This finding suggests that delamanid could enhance treatment options for multidrug-resistant tuberculosis. (Funded by Otsuka Pharmaceutical Development and Commercialization; ClinicalTrials.gov number, NCT00685360.).

Phase 2, randomized, double-blind, dose-ranging study evaluating the safety, tolerability, population pharmacokinetics, and efficacy of oral torezolid phosphate in patients with complicated skin and skin structure infections

Torezolid (TR-700) is the active moiety of the prodrug torezolid phosphate ([TP] TR-701), a second-generation oxazolidinone with 4- to 16-fold greater potency than linezolid against Gram-positive species including methicillin-resistant Staphylococcus aureus (MRSA). A double-blind phase 2 study evaluated three levels (200, 300, or 400 mg) of oral, once-daily TP over 5 to 7 days for complicated skin and skin structure infections (cSSSI). Patients 18 to 75 years old with cSSSI caused by suspected or confirmed Gram-positive pathogens were randomized 1:1:1. Of 188 treated patients, 76.6% had abscesses, 17.6% had extensive cellulitis, and 5.9% had wound infections. S. aureus, the most common pathogen, was isolated in 90.3% of patients (139/154) with a baseline pathogen; 80.6% were MRSA. Cure rates in clinically evaluable patients were 98.2% at 200 mg, 94.4% at 300 mg, and 94.4% at 400 mg. Cure rates were consistent across diagnoses, regardless of lesion size or the presence of systemic signs of infection. Clinical cure rates in patients with S. aureus isolated at baseline were 96.6% overall and 96.8% for MRSA. TP was safe and well tolerated at all dose levels. No patients discontinued treatment due to an adverse event. Three-stage hierarchical population pharmacokinetic modeling yielded a geometric mean clearance of 8.28 liters/h (between-patient variability, 32.3%), a volume of the central compartment of 71.4 liters (24.0%), and a volume of the peripheral compartment of 27.9 liters (35.7%). Results of this study show a high degree of efficacy at all three dose levels without significant differences in the safety profile and support the continued evaluation of TP for the treatment of cSSSI in phase 3 trials.

Development of a fast LC-MS/MS method for quantification of rilmenidine in human serum: elucidation of fragmentation pathways by HRMS

Rilmenidine is an alpha 2 adrenoreceptor agonist used in the treatment of mild and moderate hypertension. In this study, a fast and accurate liquid chromatographic method with tandem mass spectrometric detection has been validated in order to assure quantification of rilmenidine in human serum. The fragmentation pathway of protonated rilmenidine was studied using high-resolution mass spectrometry (HRMS). This study compared selectivity, linearity, accuracy, precision, extraction efficiency, matrix effect and sensitivity using common liquid-liquid extraction (LLE) and solid-phase extraction (SPE) procedures. The limit of quantitation for both extraction techniques was 0.1 ng/ml. Several differences between the LLE and SPE have been observed in terms of linearity, accuracy, precision and matrix effect. Additionally, the advantages of SPE included less manual work load and increased recovery of rilmenidine in human serum to approximately 80% (LLE, 57%). The developed method involving SPE was found to be accurate (relative error (RE) < 5%), reproducible (relative standard deviation, RSD < 7%), robust and suitable for quantitative analysis of rilmenidine in serum samples obtained from patients under antihypertensive treatment.

Pharmacokinetics of DA-7218, a new oxazolidinone, and its active metabolite, DA-7157, after intravenous and oral administration of DA-7218 and DA-7157 to rats

DA-7218 (a prodrug of DA-7157), a new oxazolidinone, was hydrolysed via phosphatase to form its active metabolite, DA-7157, in rats. The pharmacokinetic parameters of DA-7218 and DA-7157 were evaluated after intravenous (5, 10 and 20 mg kg−1) and oral (20, 50 and 100 mg kg−1) administration of DA-7218 to rats. DA-7218 and DA-7157 exhibited dose-proportional pharmacokinetics after both intravenous and oral administration of DA-7218 to rats. The stability of DA-7218 and DA-7157, blood partition of DA-7157, and the plasma protein binding of DA-7157 were also evaluated. DA-7218 was unstable in rat blood, plasma, bile and liver homogenates, but DA-7157 was stable, suggesting that DA-7218 is hydrolysed via phosphatase. DA-7157 rapidly reached equilibrium between plasma and blood cells, and the mean equilibrium plasma-to-blood cells ratio was 3.18, indicating that binding of DA-7157 to blood cells was not considerable. The protein binding of DA-7157 in fresh rat plasma was 93.4%.

Pharmacokinetics of muraglitazar (BMS-298585), a dual peroxisome proliferator-activated receptors (PPAR) α and γ activator, in mice, rats, dogs, and monkeys

The pharmacokinetic parameters of muraglitazar, a novel dual-activator of the peroxisome proliferator-activated receptors (PPAR) alpha and gamma, were determined in mice, rats, dogs, and monkeys after intravenous and oral administration. In the mouse, rat, and monkey the absolute oral bioavailability of muraglitazar ranged from 64 to 88%, and in the dog oral bioavailability was approximately 18%. The systemic clearance values of muraglitazar in the mouse, rat, dog, and cynomolgus monkey were 1.2, 3.0, 12.3 and 1.2 ml min-1 kg-1, respectively. The terminal elimination half-life was 2.4 h in dogs and 7.3 h in rats. The terminal elimination half-life could not be determined in the mouse and monkey because the sampling interval did not adequately cover the terminal elimination phase. Muraglitazar appears to be distributed outside of the vasculature, with the steady-state volume of distribution being approximately twofold that of the vascular volume in rats and dogs, and approximately twofold that of the total body water in mice. The systemic plasma clearance of muraglitazar in humans was predicted to be approximately 12-14 ml min-1 kg-1 based on allometry or by scaling of in vitro clearance parameters. Overall, the pharmacokinetic parameters of muraglitazar in preclinical species were acceptable for the advancement of the compound as a clinical candidate.

Bioequivalence evaluation of rilmenidine in healthy volunteers

The bioavailability of two rilmenidine tablet formulations was compared in healthy male (17) and female (8) subjects, aged 18 to 36 years, during a laboratory-blind, randomized, two-treatment, two-period, cross-over study under fasting conditions. In each treatment phase subjects received a single dose of 1.544 mg rilmenidine dihydrogen phosphate (CAS 85409-38-7), equivalent to 1 mg rilmenidine (CAS 54187-04-1). Consecutive dosing was separated by a drug-free wash-out period of 7 d. Following each dosing, serial venous blood samples were collected over a period of 48 h for the determination of plasma rilmenidine concentrations by means of a validated LCMS/MS method. The most frequently reported drug-related adverse events were dizziness and headache ranging from mild to moderate in intensity. The geometric mean C(max) of rilmenidine for the reference and test products was 3.73 and 3.97 ng/ml, respectively. The corresponding geometric mean AUC(0-infinity)) was 34.0 and 35.1 ng x h/ml. T(max) for both products under investigation appeared at 1.33 h. The test product was shown to be bioequivalent to the reference product with respect to all pharmacokinetic variables investigated.

Application of structure–metabolism relationships in the identification of a selective endothelin A antagonist, BMS-193884, with favourable pharmacokinetic properties

1. Based on binding affinity, 2'-amino-N-(3,4-dimethyl-5-isoxazolyl)-4'-(2-methylpropyl)[1,1'-biphenyl]-2-sulfonamide (2) was identified as an initial lead in a programme to identify selective endothelin (ET) receptor antagonists. However, the compound was extensively metabolized in preclinical animal species and human in vitro systems due to oxidative biotransformation. 2. To optimize this structural class, the site of metabolism of 2 was determined. This allowed for focussed structure-activity and structure-metabolism studies aimed at finding more metabolically stable analogues that maintained potency. New analogues were screened for their ET binding characteristics and their stability in rat and human liver microsomes. 3. The use of the microsomal stability screen was tested by the determination of the pharmacokinetic parameters of select analogues. A good correlation was found between reduced rates of rat microsomal metabolism and reduced clearance in the rat. 4. N-(3,4-dimethyl-5-isoxazolyl)-4'-(2-oxazolyl)[1,1'-biphenyl]-2-sulfonamide (3) was identified as an analogue with improved in vitro properties and further studies revealed that the compound had improved pharmacokinetic properties. 5. N-[[2'-[[(3,4-dimethyl-5-isoxazolyl)amino]sulfonyl]-4-(2-oxazolyl)[1,1'-biphenyl]-2-yl]methyl]acetamide (4) was subsequently identified as a compound with superior in vitro properties compared with compound 3, but when tested in vivo it had a substantially increased rate of clearance. Further studies demonstrated that the clearance of this closely related structural analogue was not dictated by metabolic processes, but was mediated by transport-mediated direct biliary excretion. 6. The utility of screening for in vitro liver microsomal stability as part of the lead optimization process for compounds with metabolic liabilities was shown. It was also shown that relatively small molecular changes can dramatically change the disposition of closely related analogues and care must be used when screening for a single property.

Mass defect filtering on high resolution LC/MS data as a methodology for detecting metabolites with unpredictable structures: identification of oxazole-ring opened metabolites of muraglitazar

This study describes the application of the mass defect filter method for the detection of two unpredicted oxazole-ring opened metabolites of muraglitazar in the feces of humans following oral administration. Unlike other muraglitazar metabolites, these metabolites formed little to no protonated ions, and the NH(4)(+) or Na(+) adduct ions that were formed were weak and not discernible from fecal interferences even after background subtraction. With mass defect filtering on high resolution LC/MS data, the resulting total ion chromatogram and the simplified mass spectra allowed for the identification and characterization of these metabolite ions, and their structures were confirmed by synthesis.

Synthesis, biodistribution and excretion of radiolabeled poly(2-alkyl-2-oxazoline)s

Here we report on the preparation of well defined water-soluble poly(2-methyl-2-oxazoline) and poly(2-ethyl-2-oxazoline) terminally equipped with a chelator (N,N',N'',N'''-tetraazacylododecane-1,4,7,10-tetraacetic acid (DOTA)) for radionuclide labeling. The tissue distribution and excretion of (111)In-labeled poly(2-alkyl-2-oxazoline)s were studied in mice. We found that the hydrophilic polymers do not accumulate in tissues and are rapidly cleared from the blood pool, predominantly by glomerular filtration in the kidneys. In contrast only a small fraction is excreted via the hepatobiliary tract. Only minimal amounts of poly(2-alkyl-2-oxazoline)s are taken up by the reticuloendothelial system (RES). Scintigraphic studies revealed the feasibility of in vivo imaging of (111)In-labeled poly(2-oxazoline)s. Since additional functionalities for targeting can readily be introduced into poly(2-oxazoline)s via functional monomer units, these compounds fulfill fundamental requirements for an application as carrier molecules in radionuclide therapy.

Rodent Carcinogenicity Profile of the Antidiabetic Dual PPAR α and γ Agonist Muraglitazar

The carcinogenic potential of muraglitazar, a dual human peroxisome proliferator-activated receptor alpha/gamma agonist, was evaluated in 2-year studies in mice (1, 5, 20, and 40 mg/kg) and rats (1, 5, 30, and 50 mg/kg). Benign gallbladder adenomas occurred at low incidences in male mice at 20 and 40 mg/kg (area under the curve [AUC] exposures > or = 62 times human exposure at 5 mg/day) and were considered drug related due to an increased incidence of gallbladder mucosal hyperplasia at these doses. There was a dose-related increased incidence of transitional cell papilloma and carcinoma of the urinary bladder in male rats at 5, 30, and 50 mg/kg (AUC exposures > or = 8 times human exposure at 5 mg/day). At 30 and 50 mg/kg, the urinary bladder tumors were accompanied by evidence of increased urine solids. Subsequent investigative studies established that the urinary bladder carcinogenic effect was mediated by urolithiasis rather than a direct pharmacologic effect on urothelium. Incidences of subcutaneous liposarcoma in male rats and subcutaneous lipoma in female rats were increased at 50 mg/kg (AUC exposures > or = 48 times human exposure at 5 mg/day) and attributed, in part, to persistent pharmacologic stimulation of preadipocytes. Toxicologically relevant nonneoplastic changes in target tissues included thinning of cortical bone in mice and hyperplastic and metaplastic adipocyte changes in mice and rats. Considering that muraglitazar is nongenotoxic, the observed tumorigenic effects in mice and rats have no established clinical relevance since they occurred at either clinically nonrelevant exposures (gallbladder and adipose tumors) or by a species-specific mechanism (urinary bladder tumors).

Urothelial carcinogenesis in the urinary bladder of male rats treated with muraglitazar, a PPAR alpha/gamma agonist: Evidence for urolithiasis as the inciting event in the mode of action

Muraglitazar, a PPARalpha/gamma agonist, dose-dependently increased urinary bladder tumors in male Harlan Sprague-Dawley (HSD) rats administered 5, 30, or 50 mg/kg/day for up to 2 years. To determine the mode of tumor development, male HSD rats were treated daily for up to 21 months at doses of 0, 1, or 50 mg/kg while being fed either a normal or 1% NH4Cl-acidified diet. Muraglitazar-associated, time-dependent changes in urine composition, urothelial mitogenesis and apoptosis, and urothelial morphology were assessed. In control and treated rats fed a normal diet, urine pH was generally > or = 6.5, which facilitates formation of calcium-and magnesium-containing solids, particularly in the presence of other prolithogenic changes in rat urine. Urinary citrate, an inhibitor of lithogenesis, and soluble calcium concentrations were dose dependently decreased in association with increased calcium phosphate precipitate, crystals and/or microcalculi; magnesium ammonium phosphate crystals and aggregates; and calcium oxalate-containing thin, rod-like crystals. Morphologically, sustained urothelial cytotoxicity and proliferation with a ventral bladder predilection were noted in treated rats by month 1 and urinary carcinomas with a similar distribution occurred by month 9. Urothelial apoptotic rates were unaffected by muraglitazar treatment or diet. In muraglitazar-treated rats fed an acidified diet, urine pH was invariably < 6.5, which inhibited formation of calcium-and magnesium-containing solids. Moreover, dietary acidification prevented the urothelial cytotoxic, proliferative, and tumorigenic responses. Collectively, these data support an indirect pharmacologic mode of urinary bladder tumor development involving alterations in urine composition that predispose to urolithiasis and associated decreases in urine-soluble calcium concentrations.

Analysis of 3,5-dichloroaniline as a biomarker of vinclozolin and iprodione in human urine using liquid chromatography/triple quadrupole mass spectrometry

The fungicides vinclozolin and iprodione are widely used in agriculture. These pesticides are dicarboximide fungicides containing the common moiety 3,5-dichloroaniline (3,5-DCA). It has been suggested that low-level exposures to such compounds may be associated with adverse health effects such as endocrine disruption. In this study a method using liquid chromatography/triple quadrupole mass spectrometry (LC/MS/MS) was developed for the analysis of 3,5-DCA as a biomarker of exposure to these fungicides in human urine. The urine samples were treated by basic hydrolysis to degrade the fungicides, their metabolites and conjugates to 3,5-DCA. The 3,5-DCA was then extracted using toluene and derivatized using pentafluoropropionic anhydride (PFPA). Analysis of the derivative was carried out using selected reaction monitoring (SRM) in the negative ion mode. Quantification of the derivative was performed using [(13)C(6)]-labeled 3,4-DCA as an internal standard with good precision and linearity in the range 0.1-200 ng/mL urine. The limit of detection was determined to be 0.1 ng/mL. The metabolites in urine were found to be stable during storage at -20 degrees C. To validate 3,5-DCA as a biomarker the method was applied in a human experimental exposure to iprodione and vinclozolin. Two healthy volunteers received 200 microg single oral doses of each pesticide followed by urine sampling during 72-120 h post-exposure. Between 78-107% of the dose was recovered as 3,5-DCA in the urine after exposure.

A potent immunomodulatory compound, (S,R)-3-Phenyl-4,5-dihydro-5-isoxazole acetic acid, prevents spontaneous and accelerated forms of autoimmune diabetes in NOD mice and inhibits the immunoinflammatory diabetes induced by multiple low doses of streptozotocin in CBA/H mice

(S,R)-3-Phenyl-4,5-dihydro-5-isoxasole acetic acid (VGX-1027) is an isoxazole compound that exhibits various immunomodulatory properties. The capacity of VGX-1027 to prevent interleukin (IL)-1beta plus interferon-gamma-induced pancreatic islet death in vitro prompted us to evaluate its effects on the development of autoimmune diabetes in preclinical models of human type 1 diabetes mellitus (T1D). Administration of VGX-1027 to NOD mice with spontaneous or accelerated forms of diabetes induced either by injection of cyclophosphamide or by transfer of spleen cells from acutely diabetic syngeneic donors markedly reduced the cumulative incidence of diabetes and insulitis. In addition, VGX-1027 given either i.p. or p.o. to CBA/H mice made diabetic with multiple low doses of streptozotocin successfully counteracted the development of destructive insulitis and hyperglycemia. The animals receiving VGX-1027 exhibited reduced production of the proinflammatory mediators tumor necrosis factor-alpha, IL-1beta, macrophage migration inhibitory factor, and inducible nitric-oxide synthase-mediated nitric oxide generation in both pancreatic islets and peripheral compartments. These results indicate that VGX-1027 probably exerts its antidiabetogenic effects by limiting cytokine-mediated immunoinflammatory events, leading to inflammation and destruction of pancreatic islets. VGX-1027 seems worthy of being considered as a candidate drug in the development of new therapeutic strategies for the prevention and early treatment of T1D.

Comparative Metabolism of Radiolabeled Muraglitazar in Animals and Humans by Quantitative and Qualitative Metabolite Profiling

Muraglitazar (Pargluva), a dual alpha/gamma peroxisome proliferator-activated receptor (PPAR) activator, has both glucose- and lipid-lowering effects in animal models and in patients with diabetes. This study describes the in vivo and in vitro comparative metabolism of [(14)C]muraglitazar in rats, dogs, monkeys, and humans by quantitative and qualitative metabolite profiling. Metabolite identification and quantification methods used in these studies included liquid chromatography/mass spectrometry (LC/MS), LC/tandem MS, LC/radiodetection, LC/UV, and a newly described mass defect filtering technique in conjunction with high resolution MS. After oral administration of [(14)C]muraglitazar, absorption was rapid in all species, reaching a concentration peak for parent and total radioactivity in plasma within 1 h. The most abundant component in plasma at all times in all species was the parent drug, and no metabolite was present in greater than 2.5% of the muraglitazar concentrations at 1 h postdose in rats, dogs, and humans. All metabolites observed in human plasma were also present in rats, dogs, or monkeys. Urinary excretion of radioactivity was low (<5% of the dose) in all intact species, and the primary route of elimination was via biliary excretion in rats, monkeys, and humans. Based on recovered doses in urine and bile, muraglitazar showed a very good absorption in rats, monkeys, and humans. The major drug-related components in bile of rats, monkeys, and humans were glucuronides of muraglitazar and its oxidative metabolites. The parent compound was a minor component in bile, suggesting extensive metabolism of the drug. In contrast, the parent drug and oxidative metabolites were the major components in feces, and no glucuronide conjugates were found, suggesting that glucuronide metabolites were excreted in bile and hydrolyzed in the gastrointestinal tract. The metabolites of muraglitazar resulted from both glucuronidation and oxidation. The metabolites in general had greatly reduced activity as PPARalpha/gamma activators relative to muraglitazar. In conclusion, muraglitazar was rapidly absorbed, extensively metabolized through glucuronidation and oxidation, and mainly eliminated in the feces via biliary excretion of glucuronide metabolites in all species studied. Disposition and metabolic pathways were qualitatively similar in rats, dogs, monkeys, and humans.

(R)-3‘-(3-Methylbenzo[b]thiophen-5-yl)spiro[1-azabicyclo[2,2,2]octane-3,5‘-oxazolidin]-2‘-one, a Novel and Potent α7 Nicotinic Acetylcholine Receptor Partial Agonist Displays Cognitive Enhancing Properties

Recent studies have suggested that the alpha7 nicotinic acetylcholine receptors play important roles in learning and memory. Herein, we describe our research of the structure-activity relationships (SAR) in a series of (S)-spiro[1-azabicyclo[2.2.2]octane-3,5'-oxazolidin]-2'-ones bearing various bicyclic moieties to discover novel alpha7 receptor agonists. Through a number of SAR studies on the series, we have found out that inhibition of CYP 2D6 isozyme, which was a primary obstacle for the previously identified compound, was avoidable by the introduction of bicyclic moieties. Chemical optimization of the series led to the identification of a novel and potent alpha7 nicotinic acetylcholine receptor partial agonist 23. This compound not only possessed high binding affinity (K(i) = 3 nmol/L) toward the alpha7 receptor but also showed agonistic activity even at a concentration of 0.1 micromol/L. In addition, compound 23 improved cognition in several rat models, which might suggest the potential of the alpha7 receptor partial agonist for the treatment of neurological disorders including cognitive dysfunction.

Pharmacodynamics of a new cephalosporin, PPI-0903 (TAK-599), active against methicillin-resistant Staphylococcus aureus in murine thigh and lung infection models: identification of an in vivo pharmacokinetic-pharmacodynamic target

PPI-0903 is a new cephalosporin with broad-spectrum activity, including beta-lactam-resistant Streptococcus pneumoniae and Staphylococcus aureus. We used the neutropenic murine thigh and lung infection models to examine the pharmacodynamic characteristics of PPI-0903. Serum drug levels following four fourfold-escalating single doses of PPI-0903 were measured by microbiologic assay. In vivo postantibiotic effects (PAEs) were determined after doses of 1.56, 6.25, 25, and 100 mg/kg of body weight in mice infected with S. pneumoniae ATCC 10813, S. aureus ATCC 29213, or Escherichia coli ATCC 25922. Dose fractionation studies over a 24-h dose range of 0.39 to 1,600 mg/kg were administered every 3, 6, 12, or 24 hours. Nonlinear regression analysis was used to determine which pharmacokinetic-pharmacodynamic (PK-PD) index (total and free 65% drug) best correlated with CFU/thigh at 24 h. Similar to other beta-lactam antibiotics, PPI-0903 produced short to modest in vivo PAEs with either S. pneumoniae or E. coli. The percent time that serum concentrations were above the MIC (%T>MIC) was the PK-PD index that best correlated with efficacy (R2=84 to 88% for the three organisms, compared with 9 to 41% for peak/MIC and 30 to 82% for the area under the concentration-time curve/MIC). In subsequent studies we used the neutropenic murine thigh infection model to determine if the magnitude of the free-drug % T>MIC needed for efficacy of PPI-0903 varied among pathogens (including resistant strains). Mice infected with one of five isolates of S. pneumoniae, four isolates of S. aureus, or four gram-negative bacilli were treated for 24 h with 0.10 to 400 mg/kg of PPI-0903 every 6 h. A sigmoid dose-response model was used to estimate the doses (mg/kg/24 h) required to achieve a net bacteriostatic affect over 24 h and to produce a reduction in the burden of organisms from the start of therapy by 1 and 2 log10 CFU/thigh. MICs ranged from 0.008 to 1 microg/ml.Mean free-drug %T >MICs the standard deviation associated with the static effect endpoint for S. pneumoniae, S. aureus, and gram-negative isolates were 39±9, 26±8, and 47±8, respectively [corrected]. Methicillin and penicillin resistance did not alter the magnitude of free-drug %T>MIC required for efficacy. The free-drug %T>MIC necessary for efficacy was slightly reduced in animals with normal neutrophil counts. Treatment effect was similar in both the thigh and lung infection models. The pharmacodynamic characteristics of PPI-0903 are similar to those of other compounds within the cephalosporin class.

Transport of fluorescent chenodeoxycholic acid via the human organic anion transporters OATP1B1 and OATP1B3

This study sought to clarify the contributions of organic anion-transporting polypeptide (OATP) 1B1 and 1B3 to the liver uptake of chenodeoxycholic acid (CDCA). We synthesized a fluorescent version of CDCA, chenodeoxychilyl-(Nepsilon-NBD)-lysine (CDCA-NBD), to characterize transporter-mediated uptake. CDCA-NBD is efficiently transported by OATP1B1 and OATP1B3 with high affinities. The Michaelis-Menten constants for CDCA-NBD uptake by OATP1B1 and OATP1B3 were 1.45 +/- 0.39 microM and 0.54 +/- 0.09 microM, respectively. By confocal laser scanning microscopy, CDCA-NBD, which is taken up by OATP1B1 and OATP1B3, was observed to localize to the cytosol. We also examined the transport of newly synthesized fluorescent bile acids. NBD-labeled bile acids, including cholic acid, deoxycholic acid, lithocholic acid, and ursodeoxycholic acid, were all transported by OATP1B1 and OATP1B3. CDCA-NBD exhibited the highest rate of transport of the five NBD-labeled bile acids examined in OATP1B1- and OATP1B3-expressing cells. Our results suggest that OATP1B1 and OATP1B3 play important roles in CDCA uptake into the liver. Fluorescent bile acids are useful tools to characterize the uptake properties of membrane transporters.

Muraglitazar: an agent for the treatment of type 2 diabetes and associated dyslipidemia

Many studies indicate that postprandial metabolic abnormalities, such as hyperglycemia and dyslipidemia, which are exaggerated and prolonged in type 2 diabetes, are important risk factors for cardiovascular disease. Different pharmacotherapies have been developed to specifically target these risk factors associated with type 2 diabetes. The peroxisome proliferator-activated receptor (PPAR) agonists, which are potent insulin sensitizers, have been the focus of much research during the past decade. Since their development, PPAR agonists have emerged as an important target for the treatment of insulin resistance and dyslipidemia. The more recent development of agonists that selectively target both the alpha and gamma PPARs has provided a potential treatment of global risk in patients with the metabolic syndrome or type 2 diabetes. Muraglitazar is a non-thiazolidinedione, oxybenzylglycine dual PPARalpha/gamma agonist that is in advanced clinical development for the treatment of type 2 diabetes and its associated dyslipidemia. This article summarizes the available clinical data on the efficacy and safety of muraglitazar in patients with type 2 diabetes.

BIOTRANSFORMATION OF CARBON-14-LABELED MURAGLITAZAR IN MALE MICE: INTERSPECIES DIFFERENCE IN METABOLIC PATHWAYS LEADING TO UNIQUE METABOLITES

Muraglitazar (Pargluva; Bristol-Myers Squibb), a dual alpha/gamma peroxisome proliferator-activated receptor activator, is under development for treatment of type 2 diabetes. This study describes the biotransformation profile of carbon-14-labeled muraglitazar in plasma, urine, feces, and bile samples from male CD-1 mice [intact and bile duct cannulation (BDC)] after single oral doses of 1 and 40 mg/kg. The major drug-related component circulating in mouse plasma was the parent compound for up to 4 h postdose. Similar to excretion profiles of muraglitazar in humans, monkeys, and rats, urinary excretion was the minor and fecal excretion via the biliary route was the major elimination pathway for muraglitazar in mice. The parent compound was a minor component in urine, bile, and feces, indicating that muraglitazar was extensively metabolized in mice. Major biotransformation pathways of muraglitazar in mice included taurine conjugate formation, acyl glucuronidation, hydroxylation, and O-dealkylation. In addition to those metabolites previously identified in humans, monkeys, and rats (M1-M21), several unique metabolites identified in mice included taurine conjugates (M24, M25, M26a,b,c, and M31), oxazole-ring-opened metabolites (M27 and M28), glutathione conjugates (M29a,b and M30), a dihydroxylated metabolite (M32), hydroxylated metabolites (M33 and M35), and a dehydrogenated metabolite (M34). The taurine conjugate of muraglitazar, M24, was a major metabolite in mice, accounting for 12 to 15% of the total dose in BDC mice or 7 to 12% of the total dose in intact mice. None of these taurine and glutathione conjugates were found in the bile samples of humans, monkeys, or rats.

Assessment of dose proportionality of muraglitazar after repeated oral dosing in rats via a sparse sampling methodology

Muraglitazar is an alpha/gamma-dual peroxisome proliferator-activated receptor (PPAR) agonist. This study evaluated the single- and multiple-dose oral toxicokinetics of muraglitazar in rats at doses of 3, 30 and 300 mg/kg/day. In total, 15 rats/gender/dose group received muraglitazar every day for 1 month. On both day 1 and day 28, blood samples were obtained at 0.5, 2, 4, 6, 8 and 24 h post-dose, followed by LC/MS analysis. In order to minimize blood loss in the rats, a sparse sampling approach was used to delineate the toxicokinetics. The peak plasma concentration (C(max)) and area under the plasma concentration-time curve (TAUC(0-t)) values for muraglitazar increased in a proportion less than the increment in dose. As the dose increased in the ratio 1:10:100, the C(max) for muraglitazar in male and female rats increased in the ratio of 1:10.3:58.6 and 1:15.3:75.3 on day 1, and 1:5.9:28.1 and 1:13.3:37.3 on day 28, respectively. The corresponding TAUC(0-t) values for males and females were in the ratio of 1:10.2:131 and 1:12.4:131 on day 1, and 1:9.5:93.4 and 1:11.8:94.3 on day 28, respectively. The results indicate that muraglitazar exhibits a dose dependent toxicokinetics in rats and the systemic exposure of muraglitazar was decreased on day 28 compared with day 1.

Preclinical pharmacokinetics and metabolism of 6-(4-(2,5-difluorophenyl)oxazol-5-yl)-3-isopropyl-[1,2,4]-triazolo[4,3-a]pyridine, a novel and selective p38α inhibitor: identification of an active metabolite in preclinical species and human liver microsomes

The disposition of 6-(4-(2,5-difluorophenyl)oxazol-5-yl)-3-isopropyl-[1,2,4]-triazolo[4,3-a]pyridine (1), a potent and selective inhibitor of mitogen activated protein (MAP) kinase p38alpha, was characterized in several animal species in support of its selection for preclinical safety studies and potential clinical development. 1 demonstrated generally favorable pharmacokinetic properties in all species examined. Following intravenous (i.v.) administration, 1 exhibited low volumes of distribution at steady state (Vd(ss)) ranging from 0.4-1.3 l/kg (2.4-26 l/m(2)) in the rat, dog and monkey. Systemic plasma clearance was low in cynomolgus monkeys (6.00 ml/min/kg, 72.0 ml/min/m(2)) and Sprague-Dawley rats (7.65+/-1.08 ml/min/kg, 45.9+/-6.48 ml/min/m(2) in male rats and 3.15+/-0.27 ml/min/kg, 18.9+/-1.62 ml/min/m(2) in female rats) and moderate in beagle dogs (12.3+/-5.1 ml/min/kg, 246+/-102 ml/min/m(2)) resulting in plasma half-lives ranging from 1 to 5 h in preclinical species. Moderate to high bioavailability of 1 was observed in rats (30-65%), dogs (87%) and monkeys (40%) after oral (p.o.) dosing consistent with the in vitro absorption profile of 1 in the Caco-2 permeability assay. In rats, the oral pharmacokinetics were dose dependent over the dose range studied (5, 50 and 100 mg/kg). The principal route of clearance of 1 in rat, dog, monkey and human liver microsomes and in vivo in preclinical species involved oxidative metabolism mediated by cytochrome P450 enzymes. The major metabolic fate of 1 in preclinical species and humans involved hydroxylation on the isopropyl group to yield the tertiary alcohol metabolite 2. In human liver microsomes, this transformation was catalysed by CYP3A4 as judged from reaction phenotyping analysis using isozyme-specific inhibitors and recombinant CYP enzymes. Metabolite 2 was also shown to possess inhibitory potency against p38alpha in a variety of in vitro assays. 1 as well as the active metabolite 2 were moderately to highly bound to plasma proteins (f(u) approximately 0.1-0.33) in rat, mouse, dog, monkey and human. 1 as well as the active metabolite 2 did not exhibit competitive inhibition of the five major cytochrome P450 enzymes namely CYP1A2, 2C9, 2C19, 2D6 and 3A4 (IC(50)>50 microM). Overall, these results indicate that the absorption, distribution, metabolism and excretion (ADME) profile of 1 is relatively consistent across preclinical species and predict potentially favorable pharmacokinetic properties in humans, supporting its selection for toxicity/safety assessment studies and possible investigations in humans as an anti-inflammatory agent.

GLUCURONIDATION AS A MAJOR METABOLIC CLEARANCE PATHWAY OF 14C-LABELED MURAGLITAZAR IN HUMANS: METABOLIC PROFILES IN SUBJECTS WITH OR WITHOUT BILE COLLECTION

The metabolism and disposition of 14C-labeled muraglitazar (Pargluva), a novel dual alpha/gamma peroxisome proliferator-activated receptor activator, was investigated in eight healthy male subjects with and without bile collection (groups 1 and 2) after a single 20-mg oral dose. Bile samples were collected for 3 to 8 h after dosing from group 2 subjects in addition to the urine and feces collection. In plasma, the parent compound was the major component, and circulating metabolites, including several glucuronide conjugates, were minor components at all time points. The exposure to parent drug (Cmax and area under the plasma concentration versus time curve) in subjects with bile collection was generally lower than that in subjects without bile collection. The major portion of the radioactive dose was recovered in feces (91% for group 1 and 51% for group 2). In addition, 40% of the dose was recovered in the bile from group 2 subjects. In this 3- to 8-h bile, the glucuronide of muraglitazar (M13, 15% of dose) and the glucuronides of its oxidative metabolites (M17a,b,c, M18a,b,c, and M20, together, 16% of dose) accounted for approximately 80% of the biliary radioactivity; muraglitazar and its O-demethylated metabolite (M15) each accounted for approximately 4% of the dose. In contrast, fecal samples only contained muraglitazar and its oxidative metabolites, suggesting hydrolysis of biliary glucuronides in the intestine before fecal excretion. Thus, the subjects with and without bile collection showed different metabolic profiles of muraglitazar after oral administration, and glucuronidation was not observed as a major pathway of metabolic clearance from subjects with the conventional urine and fecal collection, but was found as a major elimination pathway from subjects with bile collection.

Structural elucidation of human oxidative metabolites of muraglitazar: use of microbial bioreactors in the biosynthesis of metabolite standards

Muraglitazar (Pargluva), a dual alpha/gamma peroxisome proliferator-activated receptor activator, is currently in clinical development for treatment of type 2 diabetes. This study describes the structural elucidation of the human oxidative metabolites of muraglitazar through the use of a combination of microbial bioreactors, NMR and accurate mass analyses, and organic synthesis. Plasma, urine, and feces were collected from six healthy subjects following oral administration of 14C-labeled muraglitazar (10 mg, 100 microCi) and pooled samples were analyzed. Approximately 96% of the recovered radioactive dose was found in the feces and 3.5% in the urine. The parent compound represented >85% of the radioactivity in plasma. The fecal radioactivity was distributed among 16 metabolites (M1-M12, M14-M16, and M8a) and the parent drug, of which hydroxylation and O-demethylation metabolites (M5, M10, M11, M14, and M15) represented the prominent human metabolites. The urinary radioactivity was distributed into several peaks including muraglitazar glucuronide (M13) and the parent drug. Low concentrations of metabolites in human samples prevented direct identification of metabolites beyond liquid chromatographic (LC)-mass spectrometric analysis. Microbial strains Cunninghamella elegans and Saccharopolyspora hirsuta produced muraglitazar metabolites that had the same high performance liquid chromatography retention times and the same tandem mass spectrometric (MS/MS) properties as the corresponding human metabolites. The microbial metabolites M9, M10, M11, M14, M15, and M16 were isolated and analyzed by NMR. Based on these LC-MS/MS and NMR analyses, and organic synthesis, the structures of 16 human oxidative metabolites were identified. The oxidative metabolism of muraglitazar was characterized by hydroxylation, O-demethylation, oxazolering opening, and O-demethylation/hydroxylation, as well as O-dealkylation and carboxylic acid formation. This study demonstrated the utility of microbial bioreactors for the identification of metabolites.

Discovery of new diphenyloxazole derivatives containing a pyrrolidine ring: orally active prostacyclin mimetics. Part 2

Synthetic and biological evaluation of novel diphenyloxazole derivatives containing a pyrrolidine ring, as a prostacyclin mimetic without the PG skeleton, are described. Asymmetric reduction of a ketone using a chiral Ru complex and reductive amination by NaBH(4) produces four isomers of the tetrahydronaphthalene ring and the pyrrolidine ring with high stereoselectivity. FR193262 (4), (R,R)-diphenyloxazolyl pyrrolidine derivative, displays high potency and agonist efficacy at the IP receptor and has good bioavailability in rats and dogs.

Metabolism investigation leading to novel drug design: orally active prostacyclin mimetics. Part 4

A metabolism study of FR181157 (1) led to the discovery of new oxazole derivatives as active metabolites. The metabolite 6 with an epoxy ring exhibited high anti-aggregative potency with an IC(50) of 5.8 nM and potent binding affinity for the human recombinant IP receptor with a K(i) value of 6.1 nM and selectivity for human IP receptor over all other members of the human prostanoid receptor family.

Synthesis and biodistribution of (11)C-GW7845, a positron-emitting agonist for peroxisome proliferator-activated receptor-{gamma}

The goal of this study was to synthesize and evaluate in vivo the peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist (11)C-GW7845 ((S)-2-(1-carboxy-2-{4-[2-(5-methyl-2-phenyloxazol-4-yl)ethoxy]phenyl}ethylamino)benzoic acid methyl ester) ((11)C-compound 1). PPARgamma is a member of a family of nuclear receptors that plays a central role in the control of lipid and glucose metabolism. Compound 1 is an analog of tyrosine (inhibitor constant, 3.7 nmol/L), which is an inhibitor of experimental mammary carcinogenesis.

METHODS

Protection of the carboxylic acid moiety of compound 1 was effected by treatment with N,N-dimethylformamide di-tert-butyl acetal to provide compound 2. Hydrolysis of the carbomethoxy group of compound 2 provided the benzoic acid (compound 3) that served as an immediate precursor to radiolabeling. Compound 3 underwent treatment with (11)C-methyl iodide followed by high-performance liquid chromatography to produce a radioactive peak sample that coeluted with a standard sample of compound 1. Analysis of biodistribution was undertaken by injecting male CD-1 mice via the tail vein with 6.03 MBq (163 microCi, 2.55 microg/kg) of (11)C-compound 1. To determine the tumor uptake of the radiotracer, 6 female SCID mice bearing MCF-7 xenografts were injected via the tail vein with 10.5 MBq (283 microCi, 0.235 microg/kg) of (11)C-compound 1.

RESULTS

(11)C-Compound 1 was synthesized at an 8% radiochemical yield in 29 min with an average specific radioactivity of 1,222 GBq/micromol (33,024 mCi/micromol; n = 6) at the end of synthesis. Spleen (target)-to-muscle uptake and tumor-to-muscle uptake ratios were 3.1 and 1.5, respectively, but this uptake could not be blocked with unlabeled compound 1 at 2 mg/kg.

CONCLUSION

Further structural modification, perhaps to generate a less lipophilic tyrosine analog, will be necessary to enable receptor-mediated PPARgamma imaging by this class of agents.

Fluorescent Kabiramides: New Probes to Quantify Actin in Vitro and in Vivo

We present the design, synthesis, and biochemical and spectroscopic characterization of five functional fluorescent conjugates of kabiramide C (KabC), a small molecule biomimetic of gelsolin. The tetramethylrhodamine (TMR), rhodol green (RG), IC5, dapoxyl (DAP), and fluorescein diester (FDE) conjugates of KabC bind specifically to actin at the barbed end in a 1:1 complex. These probes are shown to function in an indistinguishable manner to the unmodified KabC. Various modalities of the fluorescence emission of these KabC probes, including fluorescence anisotropy and fluorescence resonance energy transfer, are used for the development of assays for the rapid determination of G-actin concentration in solution. The TMR-KabC and FDE-KabC probes are cell permeable and provide unique imaging information on the distribution and dynamics of actin filament within living cells.

Acute inhibition of cardiac monoamine oxidase A after tobacco smoke inhalation: validation study of [11C]befloxatone in rats followed by a positron emission tomography application in baboons

The in vivo characteristics of [11C]befloxatone were assessed in myocardium of rats and monkeys. A complete multicompartmental model was developed to quantify monkey cardiac monoamine oxidase A (MAO-A) binding sites using positron emission tomography (PET) and was applied to assess the acute effects of inhalation of tobacco smoke. Unknown compounds contained in tobacco smoke inhibit brain MAO. In vitro, befloxatone inhibits selectively, competitively, and reversibly MAO-A in human tissues. [11C]Befloxatone (1.85 MBq) was i.v. injected into rats. Animals were sacrificed, dissected, and samples were assessed for radioactivity. Another group of rats was pretreated with clorgyline (10 mg/kg i.v.). Monkeys were injected with [11C]befloxatone (222-370 MBq), and the chest was imaged with PET for 2 h. Presaturation and displacement experiments were performed using unlabeled befloxatone. For quantification of myocardial binding sites (Bmax), [11C]befloxatone was first injected as a tracer dose (2.7-9.3 nmol) and 20 min later injected as a mixture of labeled and unlabeled befloxatone (labeled, 10.3-41.9 nmol; unlabeled, 407-765 nmol). In rodents, cardiac uptake was high (3.39 +/- 0.5% injected dose/g tissue) and strongly inhibited (80%) by clorgyline. In monkeys, administration of unlabeled befloxatone displaced 85% of cardiac radioactivity. Bmax was found to be 208 +/- 13 pmol ml(-1) tissue. Inhalation of tobacco smoke decreased Bmax: 150 +/- 6.2 pmol ml(-1), whereas nicotine did not. [11C]Befloxatone allows a good visualization of the heart. Cardiac MAO-A Bmax was quantified and a clear effect of acute inhalation of tobacco smoke was evidenced. Therefore, a single cigarette can interfere with the cardiac turnover of catecholamines.

Discovery of Diphenyloxazole and Nδ-Z-Ornithine Derivatives as Highly Potent and Selective Human Prostaglandin EP4Receptor Antagonists

Two novel classes of diphenyloxazole and Ndelta-Z-ornithine derivatives as highly potent and selective EP(4) antagonists have been discovered. The optimized diphenyloxzole 8 and Ndelta-Z-ornithine 11 effectively competed with [(3)H]PGE(2) binding to human recombinant EP(4), with K(i) values of 0.30 nM and 0.91 nM, respectively, and were selective for all members of the human prostanoid receptor family. 8 was shown to exhibit good pharmacokinetic properties in rats and dogs and potent inhibitory activity toward in vitro PGE(2)-promoted IgE synthesis.

Discovery and evaluation of 2-anilino-5-aryloxazoles as a novel class of VEGFR2 kinase inhibitors

A series of derivatives of 2-anilino-5-phenyloxazole (5) has been identified as inhibitors of VEGFR2 kinase. Herein we describe the structure-activity relationship (SAR) of this novel template. Optimization of both aryl rings led to very potent inhibitors at both the enzymatic and cellular levels. Oxazole 39 had excellent solubility and good oral PK when dosed as the bis-mesylate salt and demonstrated moderate in vivo efficacy against HT29 human colon tumor xenografts. X-ray crystallography confirmed the proposed binding mode, and comparison of oxazoles 39 and 46 revealed interesting differences in orientation of 2-pyridyl and 3-pyridyl rings, respectively, attached at the meta position of the 5-phenyl ring.

P-glycoprotein plays a role in the oral absorption of BMS-387032, a potent cyclin-dependent kinase 2 inhibitor, in rats

PURPOSE

BMS-387032, a novel cyclin-dependent kinase 2 inhibitor, is currently in phase I clinical trials for anticancer therapy. The oral bioavailability of BMS-387032 has been found to be about 31% in rats. Absorption and first-pass metabolism were evaluated as possible reasons for the incomplete oral bioavailability in rats.

METHODS

Male Sprague-Dawley rats were given single doses of BMS-387032 intraarterially (9.1 mg/kg), orally (9.1 mg/kg), or intraportally (10 mg/kg). The routes of excretion of BMS-387032 after intravenous dosing were investigated in bile-duct-cannulated rats. The rate of metabolism of BMS-387032 was investigated in liver microsomes. The permeability of BMS-387032 was evaluated using Caco-2 cells, an in vitro model of the intestinal epithelium. To determine if BMS-387032 was a P-glycoprotein substrate, brain uptake studies were conducted in P-glycoprotein knockout versus wildtype mice.

RESULTS

The exposure in rats after an intraportal dose was similar to that after an intraarterial dose, indicating that absorption may play a greater role than liver first-pass metabolism in the low oral bioavailability seen in rats. After an intravenous dose, the percent of dose excreted unchanged in the urine and bile over a 9-h period was 28% and 11%, respectively. In vitro studies in rat liver microsomes showed low rates of metabolism of BMS-387032. The Caco-2 cell permeability of BMS-387032 was <15 nm/s in the apical to basolateral direction, and 161 nm/s in the basolateral to apical direction, indicating that it may be a substrate for an intestinal efflux transporter. A P-glycoprotein binding assay showed that BMS-387032 might be a P-glycoprotein modulator. Brain penetration studies in mice showed brain levels of BMS-387032 about 3.5-fold higher in P-glycoprotein knockout mice than in wildtype mice, providing evidence of BMS-387032 being a P-glycoprotein substrate.

CONCLUSIONS

Poor absorption may be playing a greater role than extensive first-pass metabolism in the incomplete oral bioavailability of BMS-387032 seen in rats. The efflux transporter, P-glycoprotein, may be responsible for limiting absorption, as BMS-387032 appears to be a substrate of P-glycoprotein.

[Rilmenidine sympatholytic activity preserves mental and orthostatic sympathetic response and epinephrine secretion]

BACKGROUND

Heightened central sympathetic nervous outflow is common in essential hypertension, contributing to hypertension development and perhaps also to complications. Acute sympathetic nervous activation is a proven trigger for adverse cardiovascular events. Accordingly, antihypertensive drugs inhibiting sympathetic outflow represent a theoretically attractive therapeutic option.

OBJECTIVES

To study the sympatholytic and blood pressure lowering activity of the imidazoline binding agent rilmenidine at rest and during reflex sympathetic activation.

DESIGN AND METHODS

The HERA study (Hyperium Effect on the sympathetic Reflex activation and Adrenaline) is a randomised, double-blind, 6-week cross-over trial, with a 1-week placebo run-in period, two 2-week active treatment intervals (rilmenidine 1 mg bid, placebo) and intervening one week placebo wash-out. In 15 hypertensive patients, noradrenaline and adrenaline plasma kinetics and intra-arterial blood pressure measurements were performed at rest, after mental stress (difficult mental arithmetic) and during head-up tilting, at the end of the 2-week dosing periods.

RESULTS

The noradrenaline spillover rate, indicative of whole body sympathetic activity, was reduced 35% by rilmenidine at rest (p<0.01) and remained significantly lower during mental stress and tilting, although the increases in noradrenaline spillover with both stimuli were preserved. The effects on intraarterial blood pressure ran in parallel, a fall in supine resting pressure, but no reduction in BP rise during mental stress and a lack of fall in BP with tilting. On placebo, adrenaline secretion was 162 +/- 27 ng/min (mean, SE) at rest, increased by 77 +/- 42 ng/min with mental stress (p=0.019) and was unchanged with tilting. Rilmenidine left adrenaline secretion untouched under all conditions.

CONCLUSIONS

This study confirms a sympatholytic effect of rilmenidine during supine rest but demonstrates that sympathetic responses during mental stress and tilting are preserved, the latter underlying a perhaps surprising absence of postural hypotension on the drug. The absence of suppression of reflexive sympathetic responses contrasts with the effects of rilmenidine in experimental animals, and emphasises the previously demonstrated unique importance in humans of suprabulbar noradrenergic neuronal projections from the brainstem, which are inhibited by imidazoline binding agents, in regulating tonic sympathetic activity in essential hypertension. Sympathetic nervous inhibition with rilmenidine contrasted with an absence of suppression of the secretion of adrenaline affirming that here, as elsewhere, sympathetic nervous and adrenal medullary function can be disconnected.

Chronic treatment with rilmenidine in spontaneously hypertensive rats: differences between two schedules of administration

Rilmenidine is one of the lead compounds of the second generation of centrally acting antihypertensive drugs. In the first part of this study, 2 routes of administration of chronic treatment (1 month) with rilmenidine were compared. In conscious and pentobarbital-anesthetized spontaneously hypertensive rats (SHR), rilmenidine was delivered intraperitoneally either 250 microg/kg b.i.d. or 500 microg/kg/d infusion by means of minipumps. The possibility of rilmenidine-induced desensitization of central (brain cortex) and/or peripheral (kidney) alpha2-adrenoreceptors was studied in saturation experiments with the classic alpha2-adrenergic antagonist [H]rauwolscine. In the second part of this study, the cardiovascular and cardiac antihypertrophic effects of the most efficient procedure were investigated. The discontinuous administration of the drug was more effective than infusion. In rats treated with rilmenidine b.i.d., mean blood pressure was reduced by nearly 15% when no reduction occurred in SHRs treated with minipumps. With the first schedule of administration, plasma concentration of the drug reached a maximum of approximately 30 ng/ml when it was only 12 ng/ml with the continuous infusion of the same dose. Anesthesia with pentobarbital potentiated the antihypertensive effect of rilmenidine in rats treated discontinuously and unmasked an antihypertensive action in rats receiving the drug with minipumps. In saturation binding experiments, no significant changes in adrenergic receptors were observed in kidney membrane preparations. In contrast, in brain cortical membranes a reduction by about 50% of the Bmax of [H]rauwolscine value was observed in rats treated discontinuously with rilmenidine. In contrast, a 400% increase of the Bmax was observed in the brain of rats treated with minipumps. Over the one-month period of the second study, the discontinuous treatment with the 500 microg/kg/d dose of rilmenidine was still able to reduce blood pressure, at least at the peak concentration time, but did not induce any significant reduction of the ventricular mass. In conclusion, rilmenidine has only weak antihypertensive effects in conscious SHRs, even at doses higher than those that are active in rabbits and humans. As a consequence, it lacks significant cardiac antihypertrophic effects in this species. Pharmacokinetic data show that the rapid plasma withdrawal of this drug may explain this particular feature in rats.

N-(Cycloalkylamino)acyl-2-aminothiazole Inhibitors of Cyclin-Dependent Kinase 2. N-[5-[[[5-(1,1-Dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-4- piperidinecarboxamide (BMS-387032), a Highly Efficacious and Selective Antitumor Agent

N-Acyl-2-aminothiazoles with nonaromatic acyl side chains containing a basic amine were found to be potent, selective inhibitors of CDK2/cycE which exhibit antitumor activity in mice. In particular, compound 21 [N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-4-piperidinecarboxamide, BMS-387032], has been identified as an ATP-competitive and CDK2-selective inhibitor which has been selected to enter Phase 1 human clinical trials as an antitumor agent. In a cell-free enzyme assay, 21 showed a CDK2/cycE IC(50) = 48 nM and was 10- and 20-fold selective over CDK1/cycB and CDK4/cycD, respectively. It was also highly selective over a panel of 12 unrelated kinases. Antiproliferative activity was established in an A2780 cellular cytotoxicity assay in which 21 showed an IC(50) = 95 nM. Metabolism and pharmacokinetic studies showed that 21 exhibited a plasma half-life of 5-7 h in three species and moderately low protein binding in both mouse (69%) and human (63%) serum. Dosed orally to mouse, rat, and dog, 21 showed 100%, 31%, and 28% bioavailability, respectively. As an antitumor agent in mice, 21 administered at its maximum-tolerated dose exhibited a clearly superior efficacy profile when compared to flavopiridol in both an ip/ip P388 murine tumor model and in a s.c./i.p. A2780 human ovarian carcinoma xenograft model.