Muscarinic M3 positive allosteric modulator ASP8302 enhances bladder contraction and improves voiding dysfunction in rats.

OBJECTIVES: Muscarinic M3 (M3 ) receptors mediate cholinergic smooth muscle contraction of the bladder. Current drugs targeting bladder M3 receptors for micturition disorders have a risk of cholinergic side effects due to excessive receptor activation and insufficient selectivity. We investigated the effect of ASP8302, a novel positive allosteric modulator (PAM) of M3 receptors, on bladder function in rats. METHODS: Modulation of carbachol-induced increases in intracellular Ca2+ was assessed in cells expressing rat muscarinic receptors. Potentiation of bladder contractions was evaluated using isolated rat bladder strips and by measuring intravesical pressure in anesthetized rats. Conscious cystometry was performed to investigate the effects on residual urine volume and voiding efficiency in rat voiding dysfunction models induced by the α1 -adrenoceptor agonist midodrine and muscarinic receptor antagonist atropine, and bladder outlet obstruction. To assess potential side effects, the number of stools and tracheal insufflation pressure were measured in conscious and anesthetized rats, respectively. RESULTS: ASP8302 demonstrated PAM effects on the rat M3 receptor in cell assays, and augmented cholinergic bladder contractions both in vivo and in vitro. ASP8302 improved voiding efficiency and reduced residual urine volume in two voiding dysfunction models as effectively as distigmine bromide, but unlike distigmine bromide did not affect the number of stools or tracheal insufflation pressure. CONCLUSIONS: Our results in rats indicate that ASP8302 improves voiding dysfunction by potentiating bladder contraction with fewer effects on cholinergic responses in other organs, and suggest a potential advantage over current cholinomimetic drugs for treating micturition disorders caused by insufficient bladder contraction.

Modulation of urinary frequency via type 1 lysophosphatidic acid receptors: Effect of the novel antagonist ASP6432 in conscious rats.

Bladder dysfunctions associated with benign prostatic hyperplasia are not sufficiently alleviated by current pharmacotherapies. Lysophosphatidic acid (LPA) is a phospholipid with diverse biological effects. LPA modulates prostate and urethral contraction via the type 1 LPA (LPA1) receptor, suggesting the potential of the LPA1 receptor as a therapeutic target. However, the role of LPA and the LPA1 receptor in bladder function has not been studied in vivo. We investigated the effects of LPA and the novel LPA1 receptor antagonist ASP6432 (potassium 1-(2-{[3,5-dimethoxy-4-methyl-N-(3-phenylpropyl)benzamido]methyl}- 1,3-thiazole-4-carbonyl)- 3-ethyl-2,2-dioxo-2λ6-diazathian-1-ide) on the micturition reflex in conscious rats using cystometry. Intravenous infusion of LPA decreased the micturition interval and threshold pressure with no apparent changes in baseline pressure or maximum intravesical pressure. ASP6432 inhibited the LPA-induced decrease in MI. In contrast, ASP6432 had no effect on the LPA-induced decrease in threshold pressure. Similarly, ASP6432 had no effect on either baseline pressure or maximum intravesical pressure. We also evaluated the effect of ASP6432 on the urinary frequency induced by the nitric oxide synthase inhibitor L-Nω-nitro arginine methyl ester (L-NAME). Intravenous L-NAME administration decreased the micturition interval. ASP6432 dose-dependently reversed the L-NAME-induced decrease in micturition interval. Our findings demonstrate for the first time that LPA causes bladder overactivity in rats. ASP6432 inhibited the LPA- and L-NAME-induced decrease in micturition interval, suggesting a significant role for the LPA1 receptor in regulating the functional capacity of the bladder. Our results also suggest the potential of ASP6432 as a novel therapy for the treatment of bladder dysfunction associated with lower urinary tract diseases.

ASP6432, a type 1 lysophosphatidic acid receptor antagonist, reduces urethral function during urine voiding and improves voiding dysfunction.

Current pharmacotherapies for voiding dysfunctions are in need of improvement. Lysophosphatidic acid (LPA) is a phospholipid that contracts the urethra by activating type 1 LPA receptors (LPA1). However, the role of LPA1 in regulating urethral tonus during urine voiding which primarily affects the voiding function has not been investigated. To elucidate the role of LPA1 in the regulation of urethral tonus during urine voiding, we investigated the effects of ASP6432, a novel LPA1 antagonist, and the α1-adrenoceptor antagonist tamsulosin on urethral perfusion pressure (UPP) at the filling phase (UPPbase) and the minimum UPP at the voiding phase (UPPnadir) in anesthetized rats under isovolumetric conditions. We further evaluated the effects of ASP6432 and tamsulosin on voiding dysfunction characterized by changes in post-void residual urine (PVR) and voiding efficiency (VE) induced by the nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) in conscious rats using single cystometry. ASP6432 dose-dependently decreased UPPbase and UPPnadir, while tamsulosin reduced UPPbase but did not change UPPnadir. ASP6432 dose-dependently suppressed the L-NAME-induced increase in PVR and decrease in VE, whereas tamsulosin did not affect either PVR or VE. We demonstrate that ASP6432 reduced UPPnadir and ameliorated L-NAME-induced voiding dysfunction, neither of which were affected by tamsulosin. Our study results suggest that LPA1 has a significant role in regulating urethral tonus during urine voiding, and highlight the potential of ASP6432 for improving voiding dysfunctions associated with various lower urinary tract diseases.

Effect of Selective Prostaglandin E2 EP2 Receptor Agonist CP-533,536 on Voiding Efficiency in Rats with Midodrine-Induced Functional Urethral Obstruction.

OBJECTIVES: We investigated the effect of the selective prostaglandin E2 EP2 receptor agonist CP-533,536 on voiding efficiency in rats with midodrine-induced functional urethral obstruction. METHODS: The effect of CP-533,536 (0.03-0.3 mg/kg, intravenous [i.v.]) on urethral perfusion pressure (UPP) was investigated in anesthetized rats pre-treated with midodrine (1 mg/kg, i.v.), which forms an active metabolite that acts as an α1 -adrenoceptor agonist. The effect of CP-533,536 (0.03-0.3 mg/kg, i.v.) on cystometric parameters was also investigated in anesthetized rats. In addition, the effect of CP-533,536 (0.03-0.3 mg/kg, i.v.) on residual urine volume (RV) and voiding efficiency (VE) was investigated in conscious rats treated with midodrine (1 mg/kg, i.v.). RESULTS: CP-533,536 dose-dependently decreased UPP elevated by midodrine in anesthetized rats. In contrast, CP-533,536 did not affect maximum voiding pressure, intercontraction interval, or intravesical threshold pressure. In conscious rats, midodrine (1 mg/kg, i.v.) markedly increased RV and reduced VE. CP-533,536 dose-dependently ameliorated increases in RV and decreases in VE induced by midodrine. CONCLUSIONS: These results suggest that a selective EP2 receptor agonist could ameliorate the elevation of RV and improve the reduction of VE in rats with functional urethral obstruction caused by stimulation of α1 -adrenoceptors. The mechanism of action might be not potentiation of bladder contraction but rather preferential relief of urethral constriction.

Antiemetic effect of a potent and selective neurokinin-1 receptor antagonist, FK886, on cisplatin-induced acute and delayed emesis in ferrets.

The antiemetic effect of a potent and selective neurokinin-1 (NK1) receptor antagonist, FK886 ([3,5-bis(trifluoromethyl)phenyl][(2R)-2-(3-hydroxy-4-methylbenzyl)-4-{2-[(2S)-2-(methoxymethyl)morpholin-4-yl]ethyl}piperazin-1-yl]methanone dihydrochloride), on cisplatin-induced acute and delayed emesis in ferrets was studied. Intravenous administration of FK886 dose-dependently inhibited cisplatin (10 mg/kg)-induced acute emesis with a minimum effective dose (MED) of 0.32 mg/kg. In the same study, oral FK886 administered 8 h prior to cisplatin also dose-dependently inhibited the acute emesis during the 4-h observation period with an MED of 3.2 mg/kg. Further, when given by repeated oral administration of ≥1.6 mg/kg at 12-h intervals, the first dose being administered 1 min before cisplatin, FK886 significantly decreased the number of emetic responses in cisplatin (5 mg/kg)-induced delayed emesis. In the same study, oral FK886 (3.2 mg/kg) repeatedly administrated at 12-h intervals, the first dose being administered 36 h post cisplatin, also significantly attenuated the delayed emesis. Pharmacokinetic data in ferrets showed that plasma FK886 reached a maximum concentration within 0.5 h of administration, suggesting rapid oral absorption. In addition, rapid brain penetration of FK886 was suggested by complete and near complete inhibition of GR73632- and copper sulfate-induced emesis, respectively, by low-dose intravenous FK886 administered shortly before the emetogens. These results suggest that FK886 is an orally available NK1 receptor antagonist which is effective against both the acute and delayed emesis induced by cisplatin. Because of its therapeutic efficacy on the delayed emesis and rapid brain distribution after oral administration, FK886 may have potential as an antiemetic agent that can be used for interventional treatment of chemotherapy-induced delayed emesis.

Antiemetic effects of a potent and selective neurokinin-1 receptor antagonist, FK886, on cisplatin- and apomorphine-induced emesis in dogs.

The antiemetic properties of a novel neurokinin-1 (NK1) receptor antagonist, FK886 ([3,5-bis(trifluoromethyl)phenyl][(2R)-2-(3-hydroxy-4-methylbenzyl)-4-{2-[(2S)-2-(methoxymethyl)morpholin-4-yl]ethyl}piperazin-1-yl]methanone dihydrochloride), were studied in dog models of cisplatin- and apomorphine-induced emesis. Intravenously administered FK886 (0.32-1 mg/kg) significantly inhibited cisplatin-induced acute emesis during the 5-h observation period. Nearly complete inhibition was observed at 1 mg/kg. At an equivalent dose range, orally administered FK886 also significantly inhibited emesis, indicating good oral absorption. Similarly, FK886 inhibited apomorphine-induced emetic responses effectively following both intravenous and oral administration. The effects were long lasting, with 1.6 mg/kg of FK886 completely blocking apomorphine-induced retching and vomiting after a 12-h pretreatment period. Furthermore, FK886 showed rapid onset of antiemetic activity after oral administration. At doses of 0.32 mg/kg or more, a pretreatment time of 0.5 h was sufficient for complete inhibition of apomorphine-induced emetic responses. This fast onset after oral administration was supported by pharmacokinetic data, which demonstrated plasma levels of FK886 after oral administration reached levels similar to those 30 min after intravenous administration. These results suggest that FK886 has excellent antiemetic properties in dogs, and that its rapid-onset and long-lasting properties might make it a promising antiemetic agent.

Pharmacological properties of FK886, a new, centrally active neurokinin-1 receptor antagonist.

The pharmacological properties of the novel neurokinin-1 (NK(1)) receptor antagonist FK886, ([3,5-bis(trifluoromethyl)phenyl][(2R)-2-(3-hydroxy-4-methylbenzyl)-4-{2-[(2S)-2-(methoxymethyl)morpholin-4-yl]ethyl}piperazin-1-yl]methanone dihydrochloride), were studied. FK886 potently inhibited the binding of [(125)I]Bolton-Hunter-labeled substance P ([(125)I]BH-SP; 100 pM) to human NK(1) receptors expressed in Chinese hamster ovary (CHO) cells (IC(50)=0.70 nM). It also possessed high affinities for dog, ferret, gerbil and guinea pig NK(1) receptors, but not for rat NK(1) receptor. FK886 was highly selective for the NK(1) receptor, with 250- and >20000-fold selectivity for human NK(1) over NK(2) and NK(3), respectively. Further, it did not inhibit radioligand binding at 54 different sites, including receptors, ion channels and transporters. FK886 inhibited substance P (3.2 nM)-induced inositol phosphate formation in human NK(1) receptor-expressing CHO cells (IC(50)=1.4 nM) without stimulating NK(1) receptors. The antagonism exerted by FK886 against human NK(1) receptor was insurmountable in saturation binding experiments, with both the affinity and B(max) of [(125)I]BH-SP being significantly reduced. After intravenous administration, FK886 (0.01-0.1 mg/kg) dose-dependently inhibited the foot-tapping behavior induced by intracerebroventricular administration of a selective NK(1) receptor agonist, GR73632 (10 pmol), in gerbils, with significant inhibition being observed at doses of 0.032-0.1 mg/kg, indicating excellent brain penetration. The brain penetration of FK886 was further demonstrated by the cerebral distribution of radioactivity after intravenous injection of radiolabeled FK886. Taken together, these results demonstrate that FK886 is a potent, highly selective and centrally active, insurmountable antagonist of the NK(1) receptor, and suggest that FK886 antagonizes various NK(1) receptor-mediated biological effects in the central nervous system.

Inhibitory effect of zacopride on Cisplatin-induced delayed emesis in ferrets.

We evaluated the antiemetic effect of zacopride, a potent 5-HT3-receptor antagonist with 5-HT4-receptor agonist properties, on delayed emesis caused by cisplatin (5 mg/kg, i.p.) in ferrets, compared with granisetron, a selective 5-HT3-receptor antagonist. Multiple intravenous injections of zacopride at 1 mg/kg, a dose that completely inhibited acute emesis caused bycisplatin (10 mg/kg, i.v.), significantly reduced delayed emesis. Granisetron (3.2 mg/kg) also reduced delayed emesis but this failed to reach statistical significance. The present study suggests that a combined 5-HT3-receptor antagonist/5-HT4-receptor agonist, like zacopride, may be useful against both acute and delayed emesis induced by cancer chemotherapy.

Antiemetic activity of FK1052, a 5-HT3- and 5-HT4-receptor antagonist, in Suncus murinus and ferrets.

We investigated the effect of FK1052 [(+)-8,9-dihydro-10-methyl-7-[(5-methyl-1H-imidazol-4-yl)methyl]pyrido[1,2-a]indol-6(7H)-one hydrochloride], a 5-HT3- and 5-HT4-receptor antagonist, on the emesis induced by motion stimuli, copper sulfate, or cisplatin in either Suncus murinus or ferrets and also clarified the role of the 5-HT3 and 5-HT4 receptors in these models. In Suncus murinus, oral administration of FK1052 (100 microg/kg) completely prevented emesis induced by cisplatin (18 mg/kg, i.p.). Intraperitoneal injection of scopolamine (10 mg/kg) and promethazine (32 mg/kg), but not FK1052 (1 mg/kg), significantly reduced the emetic responses by motion stimuli. In ferrets, copper sulfate (40 mg/kg, p.o.)-induced emesis was moderately prevented by FK1052 (3.2 mg/kg), but not by granisetron (3.2 mg/kg). Cisplatin-induced acute (10 mg/kg, i.v.) and delayed (5 mg/kg, i.p.) emesis were significantly reduced by single and multiple intravenous injection of both FK1052 (3.2 mg/kg) and granisetron (3.2 mg/kg), respectively. The present study suggests that FK1052 may be useful against both acute and delayed emesis induced by cancer chemotherapy. Moreover, it is suggested that blockades of 5-HT3 and 5-HT4 receptors are not relevant to the control of motion sickness; and furthermore, it suggested that blocking 5-HT4 receptors in addition to 5-HT3 receptors does not have an additional effect on the control of cisplatin-induced emesis, but that 5-HT4 receptors are at least partly involved in the mechanism of emesis induced by copper sulfate.

Diphenidol has no actual broad antiemetic activity in dogs and ferrets.

Previous studies showed that diphenidol was effective on emetogens-induced pica, eating of non-nutritive substances, in rats, a model analogous to emesis in other species. We evaluated the actual antiemetic activity of diphenidol against four emetic stimuli in the dog and ferret, animals that possess an emetic reflex. In dogs, emetic responses to apomorphine were significantly prevented by diphenidol (3.2 mg/kg, i.v.), whereas diphenidol (3.2 mg/kg, i.v. x 2) showed a weak inhibition to the vomiting evoked by cisplatin. In ferrets, diphenidol (10 mg/kg, i.p.) exhibited a weak antiemetic activity on the emesis induced by copper sulfate and had no activity on emesis by loperamide. On the other hand, CP-122,721, a NK1-receptor antagonist, significantly reduced the emetic episodes to all four stimuli. These results suggest that the prediction of antiemetic activity of compounds in animals lacking an emetic reflex does not always correspond with actual antiemetic activity.

Contribution of tachykinin receptor subtypes to micturition reflex in guinea pigs.

The aim of the present study was to determine the role of tachykinin in the micturition reflex in guinea pigs. We investigated the effects of tachykinin NK(1) receptor antagonists, GR205171 ([2-methoxy-5-(5-trifluoromethyl-tetrazol-1-yl)-benzyl]-(2S-phenyl-piperidin-3S-yl)-amine), CP99994 ((+), (2R, 3R)-3-(2-methoxybenzyl-amino)-2-phenylpiperidine) and FK888 (N(2)-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl) carbonyl-L-prolyl]-N-methyl-N-phenylmethyl-3-(2-naphthyl)-L-alaninamide), the tachykinin NK(2) receptor antagonist, SR48968 ((+)-N-methyl-[4-(4-acetylamino-4-phenyl piperidino)-2-(3, 4-dichloro-phenyl)butyl] benzamide), and the tachykinin NK(3) receptor antagonist, SB223412 ((S)-(-)-N-(alpha-ethylbenzyl)-3-hydroxy-2-phenylquinoline-4-carboxamide) on rhythmic bladder contraction. GR205171 and CP99994 but not SR48968 or SB223412 reduced bladder contraction frequency. FK888 inhibited the frequency very slightly at the highest dose tested. The distribution of tachykinin NK(1) receptor antagonists to the central nervous system after intravenous administration was examined using an ex vivo binding assay. GR205171 was distributed to the brain and spinal cord, but the tachykinin NK(1) receptor antagonist, FK888, was not. These results suggest that tachykinin NK(1) receptors, which are located in the central nervous system, play an important role in micturition in guinea pigs.

Resiniferatoxin antagonizes cisplatin-induced emesis in dogs and ferrets.

We evaluated the antiemetic activity of resiniferatoxin, an ultrapotent capsaicin analogue, on cisplatin- and apomorphine-induced emesis in dogs, and on cisplatin-induced acute and delayed emesis in ferrets. In the dog, resiniferatoxin (10 microg/kg, s.c.) 30 min before the injection of cisplatin markedly prevented acute emesis induced by cisplatin. When animals were given resiniferatoxin (10 microg/kg, s.c.) 24 h prior to cisplatin, the emesis was still inhibited, but not significantly. Resiniferatoxin (10 microg/kg, s.c.) 30 min before the administration of apomorphine also significantly reduced the emetic responses induced by apomorphine in dogs. In the ferret, resiniferatoxin (10 microg/kg, s.c.) 30 min prior to cisplatin completely inhibited acute emesis caused by cisplatin (10 mg/kg, i.p.). When ferrets were given resiniferatoxin (10 microg/kg, s.c.) 16 h prior to cisplatin, the emesis was still significantly inhibited. Cisplatin (5 mg/kg, i.p.) induced both acute (0-24 h) and delayed (24-72 h) phase emesis, and a single injection of resiniferatoxin (10 microg/kg, s.c.) at 36 h after cisplatin significantly reduced subsequent emetic responses during the 36-72 h period. These results suggest that resiniferatoxin-related vanilloids may be useful drugs against both acute and delayed emesis induced by cancer chemotherapy.