Investigation of Drug-Drug Interactions Between Ritobegron, a Selective ß3 -Adrenoceptor Agonist, With Probenecid in Healthy Men.

We evaluated the effects of probenecid, a potent organic anion transporter 1 (OAT1) and OAT3 inhibitor, on the pharmacokinetics and safety of ritobegron, a selective ß3 -adrenoceptor agonist, in healthy men. Twelve healthy men were administered a single oral dose of ritobegron (20 mg) alone or in combination with probenecid 2 hours before administration of ritobegron. In the combination sequence, additional doses of probenecid were administered 4 and 10 hours after the administration of ritobegron. Probenecid increased the Cmax of KUC-7322, an active form of ritobegron, and the AUC0-48 h by 1.39 and 2.93 times, respectively. Probenecid prolonged the t1/2 of KUC-7322 from 1.6 to 3.4 hours and decreased the renal clearance and cumulative fraction of KUC-7322 excreted in urine from 18.5 to 4.9 L/h and from 64.7% to 49.7%, respectively. Coadministration of probenecid did not influence adverse events, blood pressure, pulse rate, or heart rate relative to ritobegron alone. Although probenecid inhibited renal tubule secretion of KUC-7322 via OAT3 and increased KUC-7322 exposure, it did not influence adverse effects or vital signs. Therefore, clinically significant drug-drug interactions are unlikely to occur when probenecid is administered in combination with OAT3 inhibitors or substrates.

Species differences in the metabolism of ritobegron in vitro and assessment of potential interactions with transporters and cytochrome P450 enzymes.

Ritobegron, a selective ß3-adrenoceptor agonist, is the prodrug of the active compound, KUC-7322. We investigated species differences in its metabolism in vitro and the potential for drug-drug interactions with ritobegron. In rat, dog, monkey, and human liver microsomes, ritobegron was not metabolized by cytochrome P450 enzymes (CYPs). KUC-7322 was the only metabolite observed. Hydrolysis of ritobegron to KUC-7322 was likely catalyzed by carboxylesterases in human liver microsomes. The maximum velocity of the reaction (V(max))/Michaelis-Menten constant (K(m)) for hydrolysis of ritobegron to KUC-7322 was much higher in rat serum than those in other species. There were also species differences in the conjugation of KUC-7322. Sulfate conjugates of ritobegron were detected in all species, whereas glucuronide and glutathione conjugates of KUC-7322 were only observed in rat liver subcellular fractions. Ritobegron and KUC-7322 did not affect the CYP-mediated metabolism of probe substrates in human liver microsomes and organic anion transporter 1 (OAT1)-, OAT2-, OAT3-, organic cation transporter 2 (OCT-2)-, OCT3-, or organic cation/carnitine transporter 1 (OCTN1)-mediated uptake of probe substrates in S2 cells. Ritobegron, but not KUC-7322, inhibited P-glycoprotein-mediated digoxin transport in Caco-2 cells. Significant uptake of KUC-7322 was observed in OAT3-expressing S2 cells. Therefore, CYP-mediated drug-drug interactions are not likely when ritobegron is administered with CYP substrates or inhibitors. Ritobegron may increase the plasma concentrations of P-glycoprotein substrates, such as digoxin, and the plasma concentration of KUC-7322 may increase when it is administered in combination with OAT inhibitors such as probenecid.

Absorption, disposition, metabolism, and excretion of ritobegron (KUC-7483), a novel selective ß3-adrenoceptor agonist, in rats.

The pharmacokinetic profile of ritobegron, a novel, selective ß3-adrenoceptor agonist, was investigated in rats. Ritobegron, an ethyl ester prodrug of the active compound KUC-7322, or KUC-7322 itself was orally administered (10 mg/kg). Ethyl esterification resulted in a 10-fold increase in the area under the plasma concentration-time curve (AUC(0-t)), as compared to KUC-7322. Following intravenous administration of KUC-7322 (1 mg/kg), total blood clearance was 1.36 L/h/kg, suggesting that intrinsic hepatic clearance is the rate-limiting step in KUC-7322 excretion. When ritobegron was orally administered (0.3, 1, 3, and 10 mg/kg), plasma concentrations of KUC-7322 rapidly increased and reached a maximum concentration (C(max)) at 0.25 to 0.31 h. KUC-7322 levels rapidly decreased, with a half-life (t 1/2) of 0.42 to 1.37 h thereafter. AUC(0-t) did not show a dose-dependent increase. The bioavailability of KUC-7322 was estimated to be 4%. Following oral administration of [14C]ritobegron (3 mg/kg), radioactivity concentrations in tissues rapidly increased and declined in parallel with changes in plasma concentration. In most of tissues, excluding the liver, kidney, urinary bladder, stomach and small intestine, radioactivity concentrations were lower than that in plasma. In plasma, bile, urine, and feces, KUC-7322 and its glucuronide, sulfate, and glutathione conjugates were detected. The glucuronide conjugate of KUC-7322 was the predominant metabolite in bile, plasma, and urine, and KUC-7322 was predominant in feces. Ritobegron was not detected in any of the samples. The cumulative excretion of radioactivity in urine and feces were 28.7% and 68.3% of the dose, respectively, up to 120 h after administration.

Functional investigation of ß-adrenoceptors in human isolated detrusor focusing on the novel selective ß3-adrenoceptor agonist KUC-7322.

This study aimed to characterize the ß-adrenoceptor (ß-AR) subtype mediating relaxation of isolated human bladder strips and to explore relaxation by the novel ß3-AR-selective agonist KUC-7322 for its relaxant effect on the human isolated detrusor and for its effect on the carbachol (CCh)-induced contractile response. In two parallel studies, relaxation of isolated human bladder strips was tested for the ß-AR agonists isoproterenol, clenbuterol, BRL 37344, and KUC-7322. For the isoproterenol and KUC-7322 responses, antagonism by CGP 20712A, ICI 118551, and SR59230A was determined. The potency and efficacy of the reference agonists for detrusor relaxation was in line with their known ß3-AR activity. KUC-7322 relative to isoproterenol was a full agonist with a pEC(50) of 5.95 ± 0.09 and 5.92 ± 0.11 in the two studies. SR59230A exhibited antagonism of the expected potency against isoproterenol (apparent pK (B) 7.2) but not against KUC-7322. Neither isoproterenol nor KUC-7322 nor forskolin significantly attenuated CCh-induced contraction. These results suggest that KUC-7322 displays full agonistic activity in relaxing the human detrusor without inhibiting the contraction induced by cholinergic stimulation. These characteristics, if proven in vivo, may be beneficial for the treatment of overactive bladder, as increased bladder capacity with a negligible effect on voiding contractions may be anticipated.

Bladder selectivity of the novel ß3-agonist ritobegron (KUC-7483) explored by in vitro and in vivo studies in the rat.

We performed in vitro and in vivo experiments to evaluate the pharmacological profile of ritobegron and its effects on the bladder in rats. ß(3)-AR selectivity was assessed using CHO cells expressing various subtypes of the human ß-adrenoceptor (AR). Effects on isolated organs were evaluated using the organ-bath method. Effects on intravesical pressure, heart rate, and mean blood pressure were evaluated in urethane-anesthetized rats. Ritobegron increased cAMP accumulation in a concentration-dependent manner in CHO cells expressing any one of three human ß-AR, its selectivity for ß(3)-AR being 301-fold and 32-fold higher versus ß(1)-AR and ß(2)-AR, respectively. Ritobegron decreased the resting tension of the isolated bladder in a concentration-dependent manner (EC(50), 7.7 × 10(-8) mol/L; maximal relaxation, 97.0 %), and the ß(3)-AR antagonist SR58894A produced a parallel rightward-shift of this concentration-response curve without altering the maximal response [pK(B) value, 6.43]. Ritobegron concentration-dependently increased atrial rate and decreased myometrial contractions in vitro, and its selectivity for the bladder was 2,078-fold higher versus the atria and 14-fold higher versus the uterus. In vivo, ritobegron induced a dose-dependent decrease in intravesical pressure (ED(50) 0.4 mg/kg), without affecting heart rate and only slightly lowering mean blood pressure. Thus, ritobegron displayed potent and selective ß(3)-AR agonistic activity toward transfected human ß-AR and exhibited a high selectivity for the bladder versus other organs in rats. Moreover, it decreased intravesical pressure with minimal effects on the cardiovascular system in anesthetized rats. These results suggest that ritobegron shows promise as a potential agent for the treatment of overactive bladder.

Effects of ritobegron (KUC-7483), a novel selective ß3-adrenoceptor agonist, on bladder function in cynomolgus monkey.

We evaluated the pharmacological profile of ritobegron [KUC-7483; (-)-ethyl 2-[4-(2-{[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino}ethyl)-2,5-dimethylphenyloxy]acetate monohydrochloride] and its effects on the bladder in cynomolgus monkeys by in vitro and in vivo experiments. In vitro, ritobegron decreased the resting tension of the isolated bladder in a concentration-dependent manner (EC(50) 8.2 ± 2.3 × 10(-7) M; maximal relaxation 88.7 ± 3.7%). The ß(3)-adrenoceptor (AR) antagonist 3-(2-allylphenoxy)-1-[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-(2S)-2-propanol hydrochloride (SR58894A) produced a rightward shift of this concentration-response curve without altering the maximal response (pK(B) value 6.56 ± 0.35). In isolated atria, ritobegron increased the atrial rate only at high concentrations (EC(50) 6.5 ± 1.2 × 10(-5) M). Ritobegron had no effect on tracheal contraction at concentrations from 10(-9) to 10(-4) M, and even at the highest concentration tested, 10(-3) M, the maximal relaxation it induced was only 26.7 ± 8.1%. Tests of the selectivity of ritobegron for the bladder gave values of 79.3- and 1200-fold higher versus atria and trachea, respectively. In the in vivo study ritobegron significantly decreased intravesical pressure (ED(50) 1.44 mg/kg) without affecting either mean blood pressure or heart rate. In conclusion, ritobegron displayed potent and selective ß(3)-AR agonistic activity and relaxed the monkey isolated bladder, and in vivo it decreased intravesical pressure without affecting cardiovascular parameters. These results suggest that ritobegron may be a promising potential agent for the treatment of overactive bladder.

Effects of ritobegron (KUC-7483), a novel ß3-adrenoceptor agonist, on both rat bladder function following partial bladder outlet obstruction and on rat salivary secretion: a comparison with the effects of tolterodine.

The objective of this study was to investigate the effects of the ß3-adrenoceptor (AR) agonist ritobegron on rat bladder function following partial bladder outlet obstruction and on rat salivary secretion. In addition, the effects of ritobegron were compared with those of the anti-muscarinic agent tolterodine. After a 6-week partial bladder outlet obstruction (BOO), drug effects on bladder functions were evaluated using cystometrography. Effects on carbachol (CCh)-induced salivary secretion were evaluated in urethane-anesthetized rats. Ritobegron significantly decreased the frequency of non-voiding contractions (NVC), while both ritobegron and tolterodine each significantly decreased the amplitude of NVC. Ritobegron had no effect on either the micturition pressure (MP) or the residual volume (RV). In contrast, tolterodine dose-dependently decreased MP and increased RV. Ritobegron had no effect on CCh-induced salivary secretion, whereas tolterodine dose-dependently decreased it. Ritobegron decreased both the frequency and amplitude of NVC, which is similar to its effect on the contractions associated with detrusor overactivity (DO) in patients with an overactive bladder (OAB), without affecting MP, RV, or CCh-induced salivary secretion. Although tolterodine reduced the amplitude of NVC, it also markedly increased RV and significantly inhibited CCh-induced salivary secretion. These results suggest that use of ritobegron, a ß3-AR agonist, is unlikely to lead to the residual urine and dry mouth symptoms that are associated with anti-muscarinic drugs, and that ritobegron may hold promise as a safe and effective agent for OAB treatment.

Examination of the paradoxical lack of responsiveness of the guinea-pig vas deferens to tyramine.

1. The isolated superfused vas deferens from the guinea-pig was more sensitive to the contractile action of noradrenaline than that from the rat. Tyramine had about 10% of the potency of noradrenaline on the rat vas deferens, but had no contractile activity on the guinea-pig vas deferens (potency less than 0.1% of noradrenaline). 2. The response of the guinea-pig vas deferens to noradrenaline was not affected by tyramine in a concentration that produced a clear contractile response of the rat vas deferens. 3. Noradrenaline and tyramine released less radioactivity from guinea-pig than from rat vasa deferentia in which noradrenergic transmitter stores had been labelled with 3H-noradrenaline. In vasa deferentia from either species, tyramine released less radioactivity than noradrenaline. 4. Pretreatment with the monoamine oxidase inhibitor iproniazid increased the amount of radioactivity released by tyramine from vasa deferentia of both species, increased the contractile response of the rat vas deferens to tyramine, and resulted in the appearance of a contractile response to tyramine in the guinea-pig vas deferens. 5. alpha-methyltyramine, which is not a substrate for monoamine oxidase, had about the same potency as tyramine in releasing radioactivity from vasa deferentia of both species, and in contracting the rat vas deferens, but was virtually without contractile activity on the guinea-pig vas deferens. 6. Pretreatment with iproniazid resulted in the appearance of a contractile response to alpha-methyltyramine in the guinea-pig vas deferens. 7. Pretreatment with iproniazid resulted in change in the composition of the radioactivity released by tyramine, with an increase in the proportion of noradrenaline and a decrease in the proportion of deaminated products. There was also an increase in the amount of endogenous noradrenaline released by tyramine. 8. It was concluded that the main factor accounting for the lack of reactivity of the guinea-pig vas deferens to tyramine is intraneuronal metabolism of the noradrenaline displaced by it.

[Therapy of orthostatic dysregulation with gepefrin. Study with continuous telemetric blood pressure monitoring]. / Therapie der orthostatischen Dysregulation mit Gepefrin. Studie mit telemetrischen kontinuierlichen Blutdruckregistrierungen.

The action of the new pressor agent gepefrine (D form of 3-hydroxyphenyl-2-aminopropan) was evaluated in 16 patients with typical clinical symptoms of orthostatic adjustment disorders. The blood pressure measured in the brachial artery (percutaneous puncture and catheterisation according to the Seldinger technique) and the electrocardiogram were transmitted by telemetry and continuously documented under standard conditions at rest, on standing and during a step test. One hour after oral administration of 30 mg or 45 mg gepefrine the blood pressure increased significantly at rest and more markedly on standing and during the step test. Gepefrine led to a reduction in pathological orthostatic regulation during the early phase as well as to the prevention of subjective and objective signs of orthostatic adjustment disorder during the late phase. Patients with insufficient rise in blood pressure during the step test (80 watts) showed after gepefrine a distinct tendency towards normalisation and the regression of subjective states of exhaustion. Gepefrine caused on average no substantive alternations in heart rate during all phases of the investigation. Complications or side-effects due to the method or the medicament were not observed.

Accumulation of radioiodinated tyrosine derivatives in the adrenal medulla and in melanomas.

Because tyrosine and dopa can be regarded as precursors of adrenomedullary hormones and melanin, radioiodinated derivatives of these compounds were tested for their accumulation in the adrenal medulla and in melanomas of various animal species. The highest level of accumulation in the adrenal medulla was attained in mice and rats with iodinated beta-hydroxy-alpha-methyltyramine, and in melanomas of mice with iodinated alpha-methyltyrosine. The results could not be reproduced to the same extent in other species.