Pilocarpine-Induced Effects on Salivary Secretion as a Pharmacological Biomarker for Cholinergic Parasympathetic Activation.

Pilocarpine-induced salivary secretion could serve as a nontherapeutic target engagement biomarker in a clinical setting to test the activity of an M3 positive allosteric modulator (PAM). The potentiating effect on the reactivity of the M3 receptor to the agonistic effect of pilocarpine would support the mechanism of action of an M3 PAM in a variety of therapeutic areas. The aim of this study was to determine the optimal pilocarpine dose needed for evaluation of this potentiating effect. Therefore, the effects of pilocarpine on salivary secretion rate and its pharmacokinetics were explored at single doses of 2.5, 5, and 10 mg of pilocarpine or placebo. The study also explored the test-retest variability of the pilocarpine-induced effects on salivary secretion. Pilocarpine caused a reproducible, dose-related increase in overall and maximum salivary secretion rate, in line with pilocarpine exposure. Oral doses of pilocarpine from 2.5 to 10 mg were safe and well tolerated, consistent with the published safety profile. These results support the use of pilocarpine in single-dose pharmacological challenge studies. The recommended dose for evaluating M3 PAM activity would be between 2.5 and 5 mg, showing a small increase in salivary secretion rate with room for further increase due to PAM activation.

Are there different patterns of detrusor overactivity which are clinically relevant? ICI-RS 2018.

INTRODUCTION: Different patterns of detrusor overactivity (DO) have been described and included in several standardization terminology documents. However, it is unclear if these different patterns have any clinical significance. METHODS: This is a report of the proceedings of Proposal 3: "Are there different patterns of detrusor overactivity which are clinically relevant?" from the annual International Consultation on Incontinence-Research Society (ICIRS) meeting, which took place from 14 to 16 June 2018, in Bristol, UK. RESULTS: We have collected and discussed, as a committee, the evidence about different urodynamic (UD) patterns of detrusor overactivity and their potential clinical significance. We reviewed the important previous basic research and clinical studies and compiled summaries. The discussion focused on clinical relevance of different UD patterns of DO and what further research is required. CONCLUSIONS: There are several UD definitions of patterns of detrusor overactivity, however the clinical relevance of these definitions remains unclear. Future research should concentrate on defining the pattern of DO in relation to clinical diagnosis, gender, age, and treatment outcomes.

The efficacy of mirabegron in the treatment of urgency and the potential utility of combination therapy.

Urgency is the prevalent and most bothersome symptom of overactive bladder (OAB) and the treatment of urgency is the primary objective in the management of OAB. Urgency has a major impact on other symptoms of OAB and culminates in an increased frequency of micturition and reduced volume voided, which may contribute to shorter intervals between the need to void. Antimuscarinic agents and mirabegron, a ß3-adrenoceptor agonist, constitute the main oral pharmacotherapeutic options for the treatment of urgency and other OAB symptoms. The reduction of urgency and other OAB symptoms significantly improve health-related quality of life. This review will explore the distinct mechanisms of action and effects of antimuscarinic agents and mirabegron, in relation to their effect on the pathophysiology of urgency. The review will also provide an overview of the various validated measurements of urgency and the numerous clinical trials regarding antimuscarinic agent monotherapy, mirabegron monotherapy, or combination treatment with mirabegron added on to the antimuscarinic agent solifenacin. A narrative review of the literature relating to pathophysiology of urgency, the validated measurements of urgency, and clinical trials relating to the pharmacological treatment of urgency. Antimuscarinic agent monotherapy, mirabegron monotherapy, or combination treatment with mirabegron added on to the antimuscarinic agent solifenacin statistically significantly reduce the symptoms of urgency compared with placebo. Combination therapy with mirabegron added on to solifenacin also statistically significantly reduces the symptoms of severe urgency compared with antimuscarinic agent monotherapy. A critique of the clinical benefits of combination therapy is also provided. Combination therapy provides an alternative treatment in patients with OAB that includes urgency who respond poorly to first-line monotherapy and who may otherwise often move on to more invasive treatments.

An Exploratory Study in Healthy Male Subjects of the Mechanism of Mirabegron-Induced Cardiovascular Effects.

To explore the role of ß1 -adrenoceptors (ARs) in the heart rate response to the selective ß3 -adrenoceptor agonist mirabegron, 12 young male volunteers received single oral doses of the nonselective ß1/2 -AR antagonist propranolol (160 mg), the selective ß1 -AR antagonist bisoprolol (10 mg), or placebo on days 1 and 5 of each period in a 3-period crossover study. On day 5, dosing was followed by a supratherapeutic dose of mirabegron (200 mg). Vital signs, impedance cardiography, and plasma renin activity were collected. Mirabegron increased heart rate and systolic blood pressure and reduced stroke volume, whereas cardiac output and diastolic blood pressure were unaffected. Mirabegron-induced changes were attenuated by propranolol and bisoprolol. The data indicate that mirabegron has a positive chronotropic effect at supratherapeutic concentrations, which is at least partly mediated by stimulation of ß1 -AR.

Translational science approach for assessment of cardiovascular effects and proarrhythmogenic potential of the beta-3 adrenergic agonist mirabegron.

INTRODUCTION: Translational assessment of cardiac safety parameters is a challenge in clinical development of beta-3 adrenoceptor agonists. The preclinical tools are presented that were used for assessing human safety for mirabegron. METHODS: Studies were performed on electrical conductance at ion channels responsible for cardiac repolarization (IKr, IKs, Ito, INa, and ICa,L), on QT-interval, subendocardial APD90, Tpeak-end interval, and arrhythmia's in ventricular dog wedge tissue in vitro and on cardiovascular function (BP, HR, and QTc) in conscious dogs. RESULTS: In conscious dogs, mirabegron (0.01-10mg/kg, p.o.) dose-dependently increased HR, reduced SBP but DBP was unchanged. Propranolol blocked the decrease in SBP and attenuated HR increase at 100mg/kg mirabegron. Mirabegron, at 30, 60, or 100mg/kg, p.o., had no significant effect on the QTc interval. In paced dog ventricular wedge, neither mirabegron nor metabolites M5, M11, M12, M14, and M16 prolonged QT, altered transmural dispersion of repolarization, induced premature ventricular contractions, or induced ventricular tachycardia. Mirabegron nor its metabolites inhibited IKr, IKs, Ito INa, or ICa,L at clinically relevant concentrations. DISCUSSION: Up to exposure levels well exceeding human clinical exposure no discernible effects on ion channel conductance or on arrhythmogenic parameters in ventricular wedge resulted for mirabegron, or its main metabolites, confirming human cardiac safety findings. In vivo, dose-related increases in HR with effects markedly higher than seen clinically, was mediated in part by cross-activation of beta-1 adrenoceptors. This non-clinical cardiac safety test program therefore proved predictive for human cardiac safety for mirabegron.

ß3-Adrenoceptor agonists for overactive bladder syndrome: Role of translational pharmacology in a repositioning clinical drug development project.

ß3-Adrenoceptor agonists were originally considered as a promising drug class for the treatment of obesity and/or type 2 diabetes. When these development efforts failed, they were repositioned for the treatment of the overactive bladder syndrome. Based on the example of the ß3-adrenoceptor agonist mirabegron, but also taking into consideration evidence obtained with ritobegron and solabegron, we discuss challenges facing a translational pharmacology program accompanying clinical drug development for a first-in-class molecule. Challenges included generic ones such as ligand selectivity, species differences and drug target gene polymorphisms. Challenges that are more specific included changing concepts of the underlying pathophysiology of the target condition while clinical development was under way; moreover, a paucity of public domain tools for the study of the drug target and aspects of receptor agonists as drugs had to be addressed. Nonetheless, a successful first-in-class launch was accomplished. Looking back at this translational pharmacology program, we conclude that a specifically tailored and highly flexible approach is required. However, several of the lessons learned may also be applicable to translational pharmacology programs in other indications.

ß3-Adrenoceptor-mediated relaxation of rat and human urinary bladder: roles of BKCa channels and Rho kinase.

Previous studies suggest that the large-conductance Ca(2+)-activated K(+) (BKCa) channel and Rho-kinase play major roles in the control of urinary bladder tone. Here, we investigated their involvement in ß-adrenoceptor (AR)-mediated relaxation of rat and human bladder. Concentration-response curves of isoprenaline and mirabegron-induced bladder relaxation were generated against passive tension and KCl- and carbachol-induced tone, in the absence or presence of the BKCa channel inhibitor iberiotoxin (100 nM) or the Rho-kinase inhibitor Y27,632 (1 µM). Myosin light chain (MLC) phosphorylation was studied by Western blot. In rat, iberiotoxin only slightly altered isoprenaline- and mirabegron-induced relaxation against KCl-induced tone but attenuated relaxation by both agonists against carbachol-induced tone. Y27,632 enhanced isoprenaline- or mirabegron-induced relaxation only against carbachol-induced tone. In humans, iberiotoxin slightly enhanced relaxation by both agonists against carbachol-induced pre-contraction. Y27,632 did not change isoprenaline-induced relaxation but enhanced that by mirabegron. Under passive tension, MLC phosphorylation was markedly reduced by both ß-AR agonists, an effect insensitive to Y27,632. In the presence of carbachol, both ß-AR agonists increased MLC phosphorylation, an effect reduced by Y27,632 only in the presence of 1 µM carbachol. These results indicate that the extent of BKCa channel and Rho-kinase involvement in relaxation induced by ß-AR agonists depends on pre contractile stimulus and species.

The actions of prolonged exposure to cholinergic agonists on isolated bladder strips from the rat.

The present study was done to explore the cholinergic systems operating in the wall of the isolated rat bladder. In a first set of experiments, bladder strips in vitro were subjected to cumulative concentration-response curve (CRC) to non-selective muscarine agonist carbachol or the partially M2>M3 selective agonist arecaidine to establish optimal concentration to be used thereafter. In a second set of experiments, the effects of drugs (solifenacin, isoproterenol, and mirabegron) were tested on urinary bladder contraction induced by the non-selective muscarinergic agonist carbachol. For both agonists, the contractile responses are qualitatively similar: an initial transient rise in tension followed by complex bursts of high-frequency small 'micro'-contractions superposed on a tonic contraction, with immediate transient 'rebound' contraction after the agonist is washed from the preparation. This rebound contraction is greater with carbachol than arecaidine. Components of the responses to cholinergic stimulation, notably the micro-contractions, were found to be differently stimulated and inhibited by the M3>M2 selective antagonist solifenacin and by the ß-adrenoceptor agonists isoprenaline and mirabegron. A physiological role for the muscarinic dependent phasic contractions and the micro-anatomical elements that might be involved are not known but may be related to non-voiding activity observed during filling cystometry in conscious animals related to afferent discharge and possibly sensation. Furthermore, suggestions for the potential impact of these findings and design of further studies in relation to bladder physiology, pharmacology, and pathology are discussed.

Detrusor underactivity: Pathophysiological considerations, models and proposals for future research. ICI-RS 2013.

AIMS: Detrusor underactivity, resulting in either prolonged or inefficient voiding, is a common clinical problem for which treatment options are currently limited. The aim of this report is to summarize current understanding of the clinical observation and its underlying pathophysiological entities. METHODS: This report results from presentations and subsequent discussion at the International Consultation on Incontinence Research Society (ICI-RS) in Bristol, 2013. RESULTS AND CONCLUSIONS: The recommendations made by the ICI-RS panel include: Development of study tools based on a system's pathophysiological approach, correlation of in vitro and in vivo data in experimental animals and humans, and development of more comprehensive translational animal models. In addition, there is a need for longitudinal patient data to define risk groups and for the development of screening tools. In the near-future these recommendations should lead to a better understanding of detrusor underactivity and its pathophysiological background. Neurourol. Urodynam. 33:591-596, 2014. © 2014 Wiley Periodicals, Inc.

The novel ß3-adrenoceptor agonist mirabegron reduces carbachol-induced contractile activity in detrusor tissue from patients with bladder outflow obstruction with or without detrusor overactivity.

ß(3)-Adrenoceptors are major players in detrusor relaxation and have been suggested as a new putative target for the treatment of overactive bladder syndrome. We determined the effects of mirabegron (YM178), a novel ß(3)-adrenoceptor agonist, on carbachol-induced tone in isolated human detrusor preparations from patients with bladder outflow obstruction (BOO) with and without detrusor overactivity (DO), and from patients with normal bladder function. We compared the effects to those of isoprenaline, a non-selective ß-adrenoceptor agonist. Detrusor specimens were obtained from patients with benign prostatic hyperplasia undergoing cystoscopy and from patients undergoing radical prostatectomy/cystectomy (in total 33 donors). Detrusor contractility was evaluated by organ bath studies and strips were incubated with carbachol (1µM) to induce and enhance tension. Both mirabegron and isoprenaline reduced carbachol-induced tone in tissues from all groups. Isoprenaline decreased tension with higher potency than mirabegron in normal, BOO and BOO+DO detrusor strips with pIC(50) values of 7.49 ± 0.16 vs. 6.23 ± 0.26 (P=0.0002), 6.89 ± 0.34 vs. 6.04 ± 0.31 (P=0.01), and 6.57 ± 0.20 vs. 5.41 ± 0.08 (P<0.0001, n=4), respectively. The maximal relaxant effect of isoprenaline and mirabegron in the normal, BOO and BOO+DO detrusor was 37.7 ± 14.4% and 36.1 ± 23.3%, 14.4 ± 12.2% vs. 33.4 ± 21.0% and 18.3 ± 10.0% vs. 28.3 ± 12.2% (n=4, P>0.05), respectively. Mirabegron and isoprenaline reduced carbachol-induced tone in both normal bladders and obstructed bladder with and without DO. Isoprenaline had higher potency than mirabegron, but the efficacy of mirabegron effect was the same as that of isoprenaline.

Modulation of non-voiding activity by the muscarinergic antagonist tolterodine and the ß(3)-adrenoceptor agonist mirabegron in conscious rats with partial outflow obstruction.

UNLABELLED: Experimental urethral obstruction in rats alters micturition patterns with non-voiding activity (NVA) during filling cystometry, showing similarity to that observed in human detrusor overactivity. Several drug classes with therapeutic potential in overactive bladder in humans have been tested in this model in rats, rabbits or guinea pigs, but no detailed analysis of drug effects on cystometric patterns has been published. The present study uses a rat model of overactivity with partial bladder outflow obstruction (BOO) in combination with the procedures to analyse NVA to study the effects of the anticholinergic drug tolterodine and the novel ß(3)-adrenoceptor agonist mirabegron. The current data for the first time show that NVA in rats with BOO is sensitive to both the muscarinergic antagonist tolterodine and the ß(3)-adrenoceptor agonist mirabegron, but with clear differences between the two drugs: during progression of bladder filling, tolterodine affected both the amplitude and frequency of NVA whereas mirabegron affected primarily the frequency. In addition, tolterodine dose-dependently reduced voiding contractions, while mirabegron did not. A model is proposed to account for these observations where both agents act on a 'pacemaker-like' mechanism which is sensitive to cholinergic excitatory and beta-adrenergic inhibitory inputs. Such concepts could provide insights into the nature of overactive bladder and the site of action of key therapeutic drugs. OBJECTIVE: To investigate the hypothesis that tolterodine and the ß(3)-adrenoceptor agonist mirabegron exert their actions on the motor component of the motor/sensory system in the bladder wall: non-voiding activity (NVA). MATERIALS AND METHODS: The present study used standard cystometric techniques and a conscious rat model of partial bladder outflow obstruction (BOO). A single dose of either tolterodine (0.01, 0.1 0.3 or 1.0 mg/kg) or mirabegron (0.03, 0.1, 0.3, 1.0 or 3.0 mg/kg) was given i.v. to each animal. RESULTS: In the dose ranges used, tolterodine reduced the voiding contraction amplitude, whereas mirabegron did not. Non-voiding activity consisted of small (<0.6 mmHg) and large (>0.6 mmHg) transients. As a fill progressed, both tolterodine and mirabegron reduced the cumulative activity of the large non-voiding contractions, but had little effect on the small transients. Tolterodine affected both the amplitude and frequency of NVA, whereas mirabegron affected primarily the frequency. CONCLUSIONS: Non-voiding activity is sensitive to muscarinergic antagonists and ß(3)-adrenoceptor agonists, but there are clear differences between the two drugs. A model is proposed to account for these observations where both agents act on a 'pacemaker-like' mechanism with cholinergic excitatory and adrenergic inhibitory inputs. Such concepts may provide insights into the nature of overactive bladder and the site of action of key therapeutic drugs.

Tamsulosin shows a higher unbound drug fraction in human prostate than in plasma: a basis for uroselectivity?

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: The efficacy-tolerability profile of tamsulosin in patients with benign prostatic hyperplasia (BPH) is assumed to be associated both with the α1-adrenoceptor selectivity profile of the drug and a small peak : trough ratio in the plasma pharmacokinetic (PK) profile. Tamsulosin is highly bound to plasma proteins, notably α1-acid glycoprotein (AGP). This protein is a high-affinity binding protein and AGP plasma concentration was found to influence the therapeutic (unbound) plasma concentrations for high-AGP-binding drugs. WHAT THIS STUDY ADDS: The study actually assessed unbound tamsulosin concentrations in both blood plasma and prostate tissue and reported that the unbound tamsulosin concentrations after multiple dosing in men with BPH, were much higher in prostate than in blood plasma. The assumption is put forward that differential free drug concentrations in prostate and blood plasma may contribute to the relative 'uroselectivity' of tamsulosin. AIM: The aim of this small patient study was to investigate tamsulosin concentrations in prostate and plasma samples in order to identify potential differences in the pharmacokinetics (PK) in plasma and prostate contributing to its pharmacodynamic activity profile in patients. METHODS: Forty-one patients with benign prostatic hyperplasia (BPH) scheduled for open prostatectomy were given tamsulosin 0.4 mg for 6-21 days in order to reach steady-state PK. Patients were randomized over four groups to allow collection of plasma and tissue samples at different time points after last dose administration. Samples were collected during surgery and assayed for tamsulosin HCl. The free fraction (f(u)) of tamsulosin was determined by ultracentrifugation of plasma and prostate tissue spiked with (14)C-tamsulosin. RESULTS: C(max) in plasma at 4.4 h for total tamsulosin was 15.2 ng ml(-1) and AUC(0,24 h) was 282 ng ml(-1) h, while for prostate C(max) at 11.4 h post-dose was 5.4 ng ml(-1) and AUC(0,24 h) was 120 ng ml(-1) h. AUC(0,24 h) for total tamsulosin in prostate was 43% of the plasma AUC(0,24 h). f(u) was 0.4 % for plasma and 59.1% for prostate. Therefore calculated on unbound tamsulosin, a ratio of 63 resulted for prostate vs. plasma C(max) concentrations. CONCLUSIONS: These data indicate that in patients with confirmed BPH the amount of tamsulosin freely available in the target tissue (prostate) is much higher than in plasma.

Specific pharmacokinetic aspects of the urinary tract.

This chapter reviews the evidence for "specific" pharmacokinetics playing a role in currently marketed drugs intended to treat lower urinary tract (LUT) symptoms. Principles of drug targeting include intrinsic properties of drugs or organs as well as drug formulations to modify drug release or to create confinement of drug presence. Prodrugs and specific formulations to deliver high drug concentrations at the site(s) of action as well as other ways to manipulate drug distribution to achieve enrichment in target tissues are considered. In overactive bladder (OAB), specific formulations for oxybutynin have been introduced to reduce the level of side effects of the active drug. Extended release tablet formulations and a topical gel formulation have been introduced, with efficacy similar to immediate release (IR) tablets, but with a reduction in anticholinergic adverse effects. However, these modifications have not led to outstanding performance parameters compared to other anticholinergic drugs marketed as IR formulations. Urinary excretion is discussed as potential mechanism for targeting LUT symptoms, but no strong indications appear to exist that this mechanism would contribute for currently available drugs. Intravesical administration of drugs is not a preferred option and only considered for drugs like botulinum toxin, where the inconvenient application compensates for a reasonable degree of long-term efficacy in severe refractory OAB. Alpha acid glycoprotein binding is discussed as a potential factor to influence drug tissue distribution, and it is concluded that there is reasonable evidence that for tamsulosin this mechanism is responsible for the difference in free fraction of the drug observed in plasma and prostate, which could contribute to its relative absence of blood pressure effects in patients with LUT symptoms related to benign prostate hyperplasia (LUTS-BPH). The principle of irreversible inhibition of type II 5α-reductase as a tool to develop drugs to reduce prostatic levels of dihydrotestosterone is employed by both dutasteride and finasteride for treatment of LUTS-BPH. Of the mechanisms discussed, the principles employed for the 5α-reductase blockers and tamsulosin in this respect can be considered relatively specific for its urological indication.

The effect of tamsulosin on the response of the rabbit bladder to partial outlet obstruction.

AIM: To determine if tamsulosin treatment prevents or decreases the incidence and severity of outlet obstruction-induced bladder dysfunction in rabbits. MATERIALS AND METHODS: Male New Zealand White rabbits were treated with tamsulosin or vehicle for 4 weeks with treatments initiated 1 week prior to sham or obstruction surgery. Cystometry was done on anesthetized rabbits 21 days after surgery. The bladders were then removed, weighed, and prepared for in vitro whole bladder studies. Responses to 32 Hz field stimulation (FS), carbachol, phenylephrine, and KCl were measured. RESULTS: Obstruction resulted in a significant increase in bladder weight, which was unchanged by tamsulosin treatment and a significant increase in micturition pressure in the vehicle-treated group but not in the tamsulosin-treated group. Compliance was significantly decreased in both obstructed groups. The vehicle-treated obstructed rabbits had a very sharp increase in intravesical pressure as the bladder reached capacity; this was not seen in the tamsulosin-treated obstructed rabbits. Tamsulosin did not change the pattern of modifications in contractile responses induced by bladder outlet obstruction. CONCLUSIONS: In vitro responses of vehicle and tamsulosin-treated obstructed rabbit groups in this study were similar. A greater micturition pressure was found for the vehicle-treated obstructed group than for the tamsulosin-treated obstructed group, which was probably due to decreased urethral resistance in the latter. On a functional basis, the higher compliance at capacity and decreased micturition pressure in the tamsulosin-treated obstructed group would be considered beneficial for bladder function.

Effects of alpha 1-adrenergic receptor subtype selective antagonists on lower urinary tract function in rats with bladder outlet obstruction.

PURPOSE: Antagonists of alpha 1-adrenergic receptors (alpha 1ARs) relieve obstructive and irritative symptoms in patients with bladder outlet obstruction. However, to our knowledge mechanisms underlying the relief of irritative symptoms remain unknown. Because bladder alpha 1dARs are up-regulated in some rats with bladder outlet obstruction, we investigated the effect of the alpha 1aAR antagonist 5-methyl urapidil (5MU) vs the alpha 1a/alpha 1dAR antagonist tamsulosin on urinary frequency in obstructed rats. MATERIALS AND METHODS: Baseline frequency was measured using a chronic micturition recording system and then obstruction (40 rats) or sham obstruction surgery (11 rats) was performed. After 6 weeks frequency was reassessed, followed by subcutaneous implantation of osmotic pumps to deliver 5MU, tamsulosin or vehicle for 1 week. Upon the completion of drug treatment urinary frequency was again measured and the pressor response to the alpha 1AR agonist phenylephrine was documented. RESULTS: Obstructed bladder mass was an average of 4.9 times greater than bladder mass in sham operated rats (p <0.001). Urinary frequency was elevated in obstructed rats with a bladder mass of greater than 500 mg vs all rats with a bladder mass of under 255 mg (p = 0.01). Of rats with a bladder mass of greater than 500 mg frequency was decreased in those treated with tamsulosin (p = 0.03) but not in those treated with 5MU. Tamsulosin and 5MU inhibited the pressor response to phenylephrine. CONCLUSIONS: Urinary frequency is increased in rats with a bladder mass of greater than 500 mg. The combined alpha 1a/alpha 1dAR antagonist tamsulosin decreases urinary frequency more than the alpha 1aAR selective antagonist 5MU. This finding supports the hypothesis that the alpha 1dAR is important for mediating irritative symptoms.