Pharmacological properties and procognitive effects of ABT-288, a potent and selective histamine H3 receptor antagonist.

Blockade of the histamine H(3) receptor (H(3)R) enhances central neurotransmitter release, making it an attractive target for the treatment of cognitive disorders. Here, we present in vitro and in vivo pharmacological profiles for the H(3)R antagonist 2-[4'-((3aR,6aR)-5-methyl-hexahydro-pyrrolo[3,4-b]pyrrol-1-yl)-biphenyl-4-yl]-2H-pyridazin-3-one (ABT-288). ABT-288 is a competitive antagonist with high affinity and selectivity for human and rat H(3)Rs (K(i) = 1.9 and 8.2 nM, respectively) that enhances the release of acetylcholine and dopamine in rat prefrontal cortex. In rat behavioral tests, ABT-288 improved acquisition of a five-trial inhibitory avoidance test in rat pups (0.001-0.03 mg/kg), social recognition memory in adult rats (0.03-0.1 mg/kg), and spatial learning and reference memory in a rat water maze test (0.1-1.0 mg/kg). ABT-288 attenuated methamphetamine-induced hyperactivity in mice. In vivo rat brain H(3)R occupancy of ABT-288 was assessed in relation to rodent doses and exposure levels in behavioral tests. ABT-288 demonstrated a number of other favorable attributes, including good pharmacokinetics and oral bioavailability of 37 to 66%, with a wide central nervous system and cardiovascular safety margin. Thus, ABT-288 is a selective H(3)R antagonist with broad procognitive efficacy in rodents and excellent drug-like properties that support its advancement to the clinical area.

Structure-activity studies of novel cyanoguanidine ATP-sensitive potassium channel openers for the treatment of overactive bladder.

A series of novel cyanoguanidine derivatives was designed and synthesized. Condensation of N-(1-benzotriazol-1-yl-2,2-dichloropropyl)-substituted benzamides with N-(substituted-pyridin-3-yl)-N'-cyanoguanidines furnished N-{2,2-dichloro-1-[N'-(substituted-pyridin-3-yl)-N''-cyanoguanidino]propyl}-substituted benzamide derivatives. These agents were glyburide-reversible potassium channel openers and hyperpolarized human bladder cells as assessed by the FLIPR membrane potential dye (KATP-FMP). These compounds were also potent full agonists in relaxing electrically stimulated pig bladder strips, an in vitro model of overactive bladder. The most active compound 9 was evaluated for in vivo efficacy and selectivity in a pig model of bladder instability. Preliminary pharmacokinetic studies in dog demonstrated excellent oral bioavailability and a t1/2 of 15 h. The synthesis, SAR studies, and biological properties of these agents are discussed.

Discovery and metabolic stabilization of potent and selective 2-amino-N-(adamant-2-yl) acetamide 11beta-hydroxysteroid dehydrogenase type 1 inhibitors.

Starting from a rapidly metabolized adamantane 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) inhibitor 22a, a series of E-5-hydroxy-2-adamantamine inhibitors, exemplified by 22d and (+/-)-22f, was discovered. Many of these compounds are potent inhibitors of 11beta-HSD1 and are selective over 11beta-HSD2 for multiple species (human, mouse, and rat), unlike other reported species-selective series. These compounds have good cellular potency and improved microsomal stability. Pharmacokinetic profiling in rodents indicated moderate to large volumes of distribution, short half-lives, and a pharmacokinetic species difference with the greatest exposure measured in rat with 22d. One hour postdose liver, adipose, and brain tissue 11beta-HSD1 inhibition was confirmed with (+/-)-22f in a murine ex vivo assay. Although 5,7-disubstitued-2-adamantamines provided greater stability, a single, E-5-position, polar functional group afforded inhibitors with the best combination of stability, potency, and selectivity. These results indicate that adamantane metabolic stabilization sufficient to obtain short-acting, potent, and selective 11beta-HSD1 inhibitors has been discovered.

2,4-diaminopyrimidine derivatives as potent growth hormone secretagogue receptor antagonists.

Ghrelin, a gut-derived orexigenic hormone, is an endogenous ligand of the growth hormone secretagogue receptor (GHS-R). Centrally administered ghrelin has been shown to cause hunger and increase food intake in rodents. Inhibition of ghrelin actions with ghrelin antibody, peptidyl GHS-R antagonists, and antisense oligonucleosides resulted in weight loss and food intake decrease in rodents. Here we report the effects of GHS-R antagonists, some of which were potent, selective, and orally bioavailable. A structure-activity relationship study led to the discovery of 8a, which was effective in decreasing food intake and body weight in several acute rat studies.

Discovery and pharmacological evaluation of growth hormone secretagogue receptor antagonists.

The discovery and pharmacological evaluation of potent, selective, and orally bioavailable growth hormone secretagogue receptor (GHS-R) antagonists are reported. Previously, 2,4-diaminopyrimidine-based GHS-R antagonists reported from our laboratories have been shown to be dihydrofolate reductase (DHFR) inhibitors. By comparing the X-ray crystal structure of DHFR docked with our GHS-R antagonists and GHS-R modeling, we designed and synthesized a series of potent and DHFR selective GHS-R antagonists with good pharmacokinetic (PK) profiles. An amide derivative 13d (Ca2+ flux IC50 = 188 nM, [brain]/[plasma] = 0.97 @ 8 h in rat) showed a 10% decrease in 24 h food intake in rats, and over 5% body weight reduction after 14-day oral treatment in diet-induced obese (DIO) mice. In comparison, a urea derivative 14c (Ca2+ flux IC50 = 7 nM, [brain]/[plasma] = 0.0 in DIO) failed to show significant effect on food intake in the acute feeding DIO model. These observations demonstrated for the first time that peripheral GHS-R blockage with small molecule GHS-R antagonists might not be sufficient for suppressing appetite and inducing body weight reduction.

Cardiovascular disease in chronic kidney failure: the role of VDR activators.

Vitamin D3 is modified by vitamin D3 25-hydroxylase in the liver, and by 25-hydroxyvitamin D3 1alpha-hydroxylase (CYP27B1) in the kidney, to form the active metabolite 1alpha,25-dihydroxyvitamin D3. Several vitamin D receptor (VDR) activators, including paricalcitol and calcitriol, are currently available for the treatment of hyperparathyroidism secondary to chronic kidney disease (CKD). CKD patients encounter a much higher risk of cardiovascular disease than do members of the general public, and recent clinical observations have shown that VDR activator therapy provides survival benefit for CKD patients in the rank order of paricalcitol > calcitriol > no VDR activator therapy, independent of parathyroid hormone, phosphorus and calcium. One possible explanation for this observation is that VDR activators exert a positive impact on cardiovascular functions. Studies in animals with disrupted genes involved in the vitamin D signaling pathway have provided some interesting data. For example, in mice lacking VDR or CYP27B1, it was found that in addition to the expected phenotype (hypocalcemia, secondary hyperparathyroidism and osteomalacia), expression of renin or atrial natriuretic peptide was elevated. The mice also developed hypertension and cardiac hypertrophy. Gene expression profiling studies have revealed that VDR may play a role in regulating smooth-muscle-cell (SMC) proliferation, thrombosis, fibrinolysis and vessel relaxation. Paricalcitol and calcitriol are equally potent at suppressing plasminogen activator inhibitor-1 synthesis and inhibiting cellular proliferation in human coronary artery SMCs. The effect of VDR activators on the modulation of renin expression and vascular functions may be factors that contribute to reduced mortality and morbidity risk in VDR-activator-treated CKD patients. In this review, we discuss recent preclinical and clinical data regarding the role of VDR and its ligands in the cardiovascular system.

Differential effects of Vitamin D analogs on bone formation and resorption.

Deficiency in Vitamin D and its metabolites leads to a failure in bone formation primarily caused by dysfunctional mineralization, suggesting that Vitamin D analogs might stimulate osteoblastic bone formation and mineralization. In this study, we compare the effect of selected Vitamin D analogs and active metabolite, 1alpha,25-dihydroxyvitamin D(3), 19-nor-1alpha, 25-dihydroxyvitamin D(2), and 1alpha-hydroxyvitamin D(2) or 1alpha,25-dihydroxyvitamin D(2) on bone formation and resorption. In a mouse calvariae bone primary organ culture system, all Vitamin D analogs and metabolite tested-stimulated collagen synthesis in a dose-dependent manner and 19-nor-1alpha, 25-dihydroxyvitamin D(2) was the most efficacious among three. 19-nor-1alpha, 25-dihydroxyvitamin D(2) and 1alpha,25-dihydroxyvitamin D(2) showed similar potencies and 1alpha,25-dihydroxyvitamin D(3) was less potent than others. Osteocalcin was also up-regulated in a dose-dependent manner, suggesting that the three Vitamin D analogs have the equal potencies on bone formation. 25-Hydroxyvitamin D-24-hydroxylase expression was induced in a dose-dependent manner and 19-nor-1alpha, 25-dihydroxyvitamin D(2) was less potent than other two compounds. In a mouse calvariae organ culture, all induced a net calcium release from calvariae in a dose-dependent manner, but the potency is in the order of 1alpha,25-dihydroxyvitamin D(2) congruent with1alpha,25-dihydroxyvitamin D(3)>19-nor-1alpha, 25-dihydroxyvitamin D(2). In a Vitamin D/calcium-restricted rat model, all caused an elevation in serum calcium in a dose-dependent manner. There is no significant difference between 1alpha,25-dihydroxyvitamin D(3) and 1alpha-hydroxyvitamin D(2) in potencies, but 19-nor-1alpha, 25-dihydroxyvitamin D(2) is at least 10-fold less potent than the other two compounds. Our results suggest that Vitamin D analogs have direct effects on bone resorption and formation, and 19-nor-1alpha, 25-dihydroxyvitamin D(2) may be more effective than 1alpha,25-dihydroxyvitamin D(3) and 1alpha-hydroxyvitamin D(2) on stimulating anabolic bone formation.

Pharmacological characterization of urinary bladder smooth muscle contractility following partial bladder outlet obstruction in pigs.

Partial bladder outlet obstruction of the pig is considered as a valuable preclinical model for evaluating the profile of compounds for the treatment of bladder overactivity. In this study, we characterized the pharmacological properties of isolated bladder smooth muscle from pigs following partial outlet obstruction and its sensitivity to potassium channel openers. Bladder strips from obstructed animals showed significantly lower maximal efficacy (E(max)) and sensitivity to stimulation by ATP and carbachol, but not to those evoked by serotonin, compared to age-matched controls. Tissue strips from obstructed animals also showed a 2.5-fold increase in the potency and significantly reduced maximum response following K+ depolarization. With respect to spontaneous activity, bladder strips from control strips demonstrated little spontaneous phasic activity at all preloads examined. In contrast, bladder strips from obstructed animals showed large preload-dependent increases in spontaneous phasic activity at preload values of 16-32 g. The potencies of K(ATP) channel openers to relax carbachol-evoked contractions showed a good 1:1 correlation (r(2)=0.90) between obstructed and control bladder strips. These studies demonstrate that obstructed pig bladders show enhanced spontaneous phasic activity especially at elevated preloads, which may underlie unstable myogenic bladder contractions reported in cystometrographic measurements in vivo. The impaired responses to electrical field stimulation could be attributed to reduced efficacies and/or lower sensitivities of muscarinic and purinergic signaling pathways. K(ATP) channel sensitivities remain essentially unimpaired in the obstructed bladder and could be effectively modulated by openers with potential for the treatment of overactive bladder secondary to outlet obstruction.

Synthesis and structure-activity relationships of a novel series of 2,3,5,6,7,9-hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-dioxide K(ATP) channel openers: discovery of (-)-(9S)-9-(3-bromo-4-fluorophenyl)-2,3,5,6,7,9- hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-dioxide (A-278637), a potent K(ATP) opener that selectively inhibits spontaneous bladder contractions.

Structure-activity relationships were investigated on a novel series of sulfonyldihydropyridine-containing K(ATP) openers. Ring sizes, absolute stereochemistry, and aromatic substitution were evaluated for K(ATP) activity in guinea pig bladder cells using a fluorescence-based membrane potential assay and in a pig bladder strip assay. The inhibition of spontaneous bladder contractions in vitro was also examined for a select group of compounds. All compounds studied showed greater potency to inhibit spontaneous bladder contractions relative to their potencies to inhibit contractions elicited by electrical stimulation. In an anesthetized pig model of myogenic bladder overactivity, compound 14 and (-)-cromakalim 1 were found to inhibit spontaneous bladder contractions in vivo at plasma concentrations lower than those that affected hemodynamic parameters. Compound 14 showed approximately 5-fold greater selectivity than 1 in vivo and supports the concept that bladder-selective K(ATP) channel openers may have utility in the treatment of overactive bladder.

Zotarolimus, a novel sirolimus analogue with potent anti-proliferative activity on coronary smooth muscle cells and reduced potential for systemic immunosuppression.

Sirolimus (rapamycin) is an immunosuppressant used in preventing allograft rejection and in drug-eluting stents to prevent restenosis after angioplasty. Zotarolimus, an analogue of sirolimus, was designed to have a shorter in vivo half-life. Zotarolimus was found to be mechanistically similar to sirolimus in having high-affinity binding to the immunophilin FKBP12 and comparable potency for inhibiting in vitro proliferation of both human and rat T cells. Rat pharmacokinetic studies with intravenous dosing demonstrated terminal elimination half-lives of 9.4 hours and 14.0 hours for zotarolimus and sirolimus, respectively. Given orally, T1/2 values were 7.9 hours and 33.4 hours, respectively. Consistent with its shorter duration, zotarolimus showed a corresponding and statistically significant 4-fold reduction in potency for systemic immunosuppression in 3 rat disease models. Pharmacokinetic studies in cynomolgus monkey underpredicted the half-life difference between zotarolimus and sirolimus apparent from recent clinical data. In vitro inhibition of human coronary artery smooth muscle cell proliferation by zotarolimus was comparable to sirolimus. Drug-eluting stents for local delivery of zotarolimus to the vessel wall of coronary arteries are in clinical development. The pharmacological profile of zotarolimus suggests it may be advantageous for preventing restenosis with a reduced potential for causing systemic immunosuppression or other side effects.

(-)-(9S)-9-(3-Bromo-4-fluorophenyl)-2,3,5,6,7,9-hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-dioxide (A-278637): a novel ATP-sensitive potassium channel opener efficacious in suppressing urinary bladder contractions. II. in vivo characterization.

ATP-sensitive potassium (K(ATP)) channel openers (KCOs) have been shown to inhibit spontaneous myogenic contractile activity of the urinary bladder, a mechanism hypothesized to underlie detrusor instability and symptoms of overactive bladder. However, the therapeutic utility of KCOs has been limited by a lack of differentiation of bladder versus vascular effects. In this study, we evaluated the in vivo potency and bladder selectivity of (-)-(9S)-9-(3-bromo-4-fluorophenyl)-2,3,5,6,7,9-hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-dioxide (A-278637), a novel dihydropyridine KCO, in a pig model of detrusor instability secondary to partial bladder outlet obstruction. For comparison, we profiled two KCOs, ((R)-4-[3,4-dioxo-2-(1,2,2-trimethyl-propylamino)-cyclobut-1-enylamino]-3-ethyl-benzonitrile (WAY-133537) and (S)-N-(4-benzoylphenyl)-3,3,3-trifluro-2-hydroxy-2-methyl-propionamide (ZD6169), reported previously to have improved bladder selectivity in vivo and a calcium channel blocker, nifedipine. Effective doses of A-278637, WAY-133537, ZD6169, and nifedipine to inhibit unstable contraction area under the curve by 35% and to decrease mean arterial pressure by 10% were 4.2 and 12, 109 and 51, 661 and 371, and 136 and 30 nmol/kg i.v., yielding corresponding bladder selectivity ratios of 3, 0.5, 0.6, and 0.2. Therefore, A-278637 was approximately 5- to 6-fold more bladder-selective than the other KCOs and 15-fold more selective than nifedipine, the latter approximately 4.5-fold vascular-selective. The potency of KCOs to inhibit unstable contraction in vivo was accurately predicted by their potency to inhibit spontaneous contractile activity of pig detrusor strips in vitro. These results indicate that A-278637, with enhanced potency and bladder selectivity compared with the other compounds evaluated, could serve as a useful tool in the investigation of smooth muscle K(ATP) channel openers as novel therapeutic agents for the treatment of overactive bladder.

Effects of ATP-sensitive K+ channel openers and tolterodine on involuntary bladder contractions in a pig model of partial bladder outlet obstruction.

AIMS: To compare in vivo the efficacy, potency, and bladder-vascular selectivity of ATP-sensitive potassium channel openers (KCOs), YM934 and (-)-cromakalim to a muscarinic antagonist, tolterodine in a novel partial outlet obstructed pig model. METHODS: Partially obstructed female Landrace pigs were implanted with telemetry transmitters to allow the continuous measurement of intravesical, abdominal and arterial pressures. A subcutaneous port catheter was used to adjust bladder volume. Bladder and arterial pressure were simultaneously monitored under isoflurane anesthesia before and after increasing i.v. doses of test compounds. RESULTS: Under anesthesia, voiding was completely inhibited, but spontaneous, nonvoiding bladder contractions were observed with mean amplitude of 16 +/- 1 cm H(2)O, duration of 35 +/- 2 seconds, and intercontraction interval of 43 +/- 4 seconds (n = 25). YM934 and (-)-cromakalim both caused dose-dependent decreases in bladder contraction area under the curve (AUC) with effective doses to inhibit AUC by 35% of 3.6 and 14.9 nmol/kg, i.v., respectively. However, concomitant reductions in mean arterial pressure of 12 and 13% were also observed. Tolterodine did not inhibit spontaneous bladder contractions at doses up to 100 nmol/kg, i.v. corresponding to plasma concentrations up to 41 ng/mL. CONCLUSIONS: The superior efficacy of KCOs to inhibit spontaneous bladder contractions relative to tolterodine support the hypothesis that KCOs may provide an alternate therapeutic mechanism to treat symptoms of overactive bladder if bladder-vascular selectivity can be sufficiently improved. The minimally invasive model described herein appears useful in the preclinical evaluation of potential therapeutics targeted to treat the overactive bladder.