Effects of TAK-637, a tachykinin receptor antagonist, on lower urinary tract function in the guinea pig

Netupitant, a Potent and Highly Selective NK1 Receptor Antagonist, Alleviates Acetic Acid-Induced Bladder Overactivity in Anesthetized Guinea-Pigs

Introduction. Tachykinins potently contract the isolated urinary bladder from a number of animal species and play an important role in the regulation of the micturition reflex. On the guinea-pig isolated urinary bladder we examined the effects of a new potent and selective NK1 receptor antagonist (netupitant) on the contractions induced by a selective NK1 receptor agonist, SP-methylester (SP-OMe). Moreover, the effects of netupitant and another selective NK1 antagonist (L-733,060) were studied in anesthetized guinea-pigs using two experimental models, the isovolumetric bladder contractions and a model of bladder overactivity induced by intravesical administration of acetic acid (AA). Methods and Results. Detrusor muscle strips were mounted in 5 mL organ baths and isometric contractions to cumulative concentrations of SP-OME were recorded before and after incubation with increasing concentrations of netupitant. In anesthetized female guinea-pigs, reflex bladder activity was examined under isovolumetric conditions with the bladder distended with saline or during cystometry using intravesical infusion of AA. After a 30 min stabilization period, netupitant (0.1-3 mg/kg, i.v.) or L-733,060 (3-10 mg/kg, i.v.) were administered. In the detrusor muscle, netupitant produced a concentration-dependent inhibition (mean pKB = 9.24) of the responses to SP-OMe. Under isovolumetric conditions, netupitant or L-733,060 reduced bladder contraction frequency in a dose-dependent manner, but neither drug changed bladder contraction amplitude. In the AA model, netupitant dose-dependently increased intercontraction interval (ICI) but had no effect on the amplitude of micturition (AM). L-733,060 dose-dependently increased ICI also but this effect was paralleled by a significant reduction of AM. Conclusion. Netupitant decreases the frequency of reflex bladder contractions without altering their amplitude, suggesting that this drug targets the afferent limb of the micturition reflex circuit and therefore may be useful clinically in treating bladder overactivity symptoms.

Accelerated onset of the vesicovesical reflex in postnatal NGF-OE mice and the role of neuropeptides

The mechanisms underlying the postnatal maturation of micturition from a somatovesical to a vesicovesical reflex are not known but may involve neuropeptides in the lower urinary tract. A transgenic mouse model with chronic urothelial overexpression (OE) of NGF exhibited increased voiding frequency, increased number of non-voiding contractions, altered morphology and hyperinnervation of the urinary bladder by peptidergic (e.g., Sub P and CGRP) nerve fibers in the adult. In early postnatal and adult NGF-OE mice we have now examined: (1) micturition onset using filter paper void assays and open-outlet, continuous fill, conscious cystometry; (2) innervation and neurochemical coding of the suburothelial plexus of the urinary bladder using immunohistochemistry and semi-quantitative image analyses; (3) neuropeptide protein and transcript expression in urinary bladder of postnatal and adult NGF-OE mice using Q-PCR and ELISAs and (4) the effects of intravesical instillation of a neurokinin (NK)-1 receptor antagonist on bladder function in postnatal and adult NGF-OE mice using conscious cystometry. Postnatal NGF-OE mice exhibit age-dependent (R²=0.996-0.998; p≤0.01) increases in Sub and CGRP expression in the urothelium and significantly (p≤0.01) increased peptidergic hyperinnervation of the suburothelial nerve plexus. By as early as P7, NGF-OE mice exhibit a vesicovesical reflex in response to intravesical instillation of saline whereas littermate WT mice require perigenital stimulation to elicit a micturition reflex until P13 when vesicovesical reflexes are first observed. Intravesical instillation of a NK-1 receptor antagonist, netupitant (0.1μg/ml), significantly (p≤0.01) increased void volume and the interval between micturition events with no effects on bladder pressure (baseline, threshold, peak) in postnatal NGF-OE mice; effects on WT mice were few. NGF-induced pleiotropic effects on neuropeptide (e.g., Sub P) expression in the urinary bladder contribute to the maturation of the micturition reflex and are excitatory to the micturition reflex in postnatal NGF-OE mice. These studies provide insight into the mechanisms that contribute to the postnatal development of the micturition reflex.

Intravesical PAC1 Receptor Antagonist, PACAP(6-38), Reduces Urinary Bladder Frequency and Pelvic Sensitivity in NGF-OE Mice

Chronic NGF overexpression (OE) in the urothelium, achieved through the use of a highly urothelium-specific uroplakin II promoter, stimulates neuronal sprouting in the urinary bladder, produces increased voiding frequency and non-voiding contractions, and referred somatic sensitivity. Additional NGF-mediated pleiotropic changes might contribute to increased voiding frequency and pelvic hypersensitivity in NGF-OE mice such as neuropeptide/receptor systems including PACAP(Adcyap1) and PAC1 receptor (Adcyap1r1). Given the presence of PAC1-immunoreactive fibers and the expression of PAC1 receptor expression in bladder tissues, and PACAP-facilitated detrusor contraction, whether PACAP/receptor signaling contributes to increased voiding frequency and somatic sensitivity was evaluated in NGF-OE mice. Intravesical administration of the PAC1 receptor antagonist, PACAP(6-38) (300 nM), significantly (p ≤ 0.01) increased intercontraction interval (2.0-fold) and void volume (2.5-fold) in NGF-OE mice. Intravesical instillation of PACAP(6-38) also decreased baseline bladder pressure in NGF-OE mice. PACAP(6-38) had no effects on bladder function in WT mice. Intravesical administration of PACAP(6-38) (300 nM) significantly (p ≤ 0.01) reduced pelvic sensitivity in NGF-OE mice but was without effect in WT mice. PACAP/receptor signaling contributes to the increased voiding frequency and pelvic sensitivity observed in NGF-OE mice.

Activation of neurokinin-1 receptors increases the excitability of guinea pig dorsal root ganglion cells

The suppression of overactive bladder symptoms in patients and overactive bladder reflexes in animal models by neurokinin (NK)-1 receptor antagonists raises the possibility that these drugs target sensory neurons. This mechanism was evaluated by examining the interactions between a specific NK-1 agonist, [Sar(9),Met(O(2))(11)]-substance P (Sar-Met-SP), and a potent NK-1 antagonist, netupitant (NTP), on small size (20-30 μm) dissociated L6 and S1 dorsal root ganglion (DRG) neurons from female guinea pigs. Current-clamp recording revealed that Sar-Met-SP (1 μM) elicited membrane depolarization (average 8.05 ± 1.38 mV) in 27% (18 of 65) of DRG neurons. In 74% of the remaining neurons (35 of 47) Sar-Met-SP decreased the rheobase for action potential (AP) generation and increased the response to a suprathreshold stimulus (3 times rheobase) without changing the membrane potential. Sar-Met-SP also induced changes in the action potential (AP) wave form, including 1) an increase in overshoot (average 5 mV, n = 35 neurons), 2) a prolongation of AP duration (from 4.64 to 5.29 ms, n = 34), and 3) a reduction in the maximal rate of AP repolarization. NTP (200 nM) reversed the Sar-Met-SP-induced changes. Ca(2+) imaging showed that application of Sar-Met-SP (1 μM) decreased the tachyphylaxis induced by repeated application of capsaicin (0.5 μM), an effect blocked by pretreatment with NTP (200 nM). These results raise the possibility that activation of NK-1 receptors in primary sensory neurons plays a role in the generation of overactive bladder and that block of NK-1 receptors in these neurons may contribute to efficacy of NK-1 antagonists in the treatment of overactive bladder symptoms.

Novel 3-phenylpiperidine-4-carboxamides as highly potent and orally long-acting neurokinin-1 receptor antagonists with reduced CYP3A induction

The synthesis and biological evaluation of a series of novel 3-phenylpiperidine-4-carboxamide derivatives are described. These compounds are generated by hybridization of the substructures from two types of tachykinin NK(1) receptor antagonists. Compound 42 showed high metabolic stability and excellent efficacy in the guinea-pig GR-73637-induced locomotive activity assay at 1 and 24h after oral administration. It also exhibited good pharmacokinetic profiles in four animal species, and a low potential in a pregnane X receptor induction assay.

The neurokinin-1 antagonist activity of maropitant, an antiemetic drug for dogs, in a gerbil model

Maropitant is a novel synthetic nonpeptide neurokinin type 1 (NK1) selective receptor antagonist, recently developed for use in the dog as an antiemetic. The in vivo functional activity of maropitant was investigated in the gerbil foot-tapping model, to determine the ability of maropitant to penetrate the central nervous system and inhibit foot-tapping induced by the selective NK1 agonist GR73632. In comparison with CP-122,721, a previously characterized NK1 receptor antagonist, maropitant (1 mg/kg by s.c. injection) was found to inhibit foot-tapping for significantly longer (P < 0.01). Inhibition of foot-tapping by maropitant was 100% at 2 h and approximately 50% at 8 h postdosing. The mean brain:plasma concentration ratio at 8 h post-treatment was 3.59. These data demonstrate the central functional action of maropitant as a selective and potent NK1 receptor antagonist and help to support and explain its clinical potential as a broad-spectrum antiemetic agent.

Current and emerging investigational medical therapies for the treatment of overactive bladder

Overactive bladder (OAB) is a chronic distressing condition characterised by urinary urgency with or without urge incontinence, usually with frequency (voiding at least eight times daily) and nocturia. It affects millions of people worldwide independent of age, sex and race. The prevalence increases with age and is relatively higher in women compared with men. The treatment of OAB is aimed at reducing the debilitating symptoms so as to improve the overall quality of life for patients. Anticholinergic agents targeting the muscarinic receptors in the bladder represent the mainstay of pharmacotherapy for the treatment of OAB. Besides their status as the current standard of care, use of antimuscarinic drugs is limited by certain side effects, particularly dry mouth and constipation; therefore, various attempts have been made to improve the organ selectivity of these drugs to overcome the side effects. These include the development of new antimuscarinic agents with structural modifications and the use of innovative drug delivery methods. The advancement in the drug delivery systems extends to the long-term therapeutic efficacy with improved tolerability and patient compliance; however, future prospective therapies are aimed at novel targets with novel mechanisms of action, including beta3-adrenoceptor agonists, K+ channel openers, 5-HT modulators and botulinum toxin, which are currently under different stages of clinical development. Among other investigational therapies, neurokinin receptor antagonists, alpha-adrenoceptor antagonists, nerve growth factor inhibitors, gene therapy and stem cell-based therapies are of considerable interest. The future for the development of new modalities for the treatment of OAB looks promising.

Animal models in urological disease and sexual dysfunction

There are several conditions associated with dysfunction of the lower urinary tract or which result in a reduction in the ability to engage in satisfactory sexual function and result in significant bother to sufferers, partners and/or carers. This review describes some of the animal models that may be used to discover safe and effective medicines with which to treat them. While alpha adrenoceptor antagonists and 5-alpha-reductase inhibitors deliver improvement in symptom relief in benign prostatic hyperplasia sufferers, the availability of efficacious and well-tolerated medicines to treat incontinence is less well served. Stress urinary incontinence (SUI) has no approved medical therapy in the United States and overactive bladder (OAB) therapy is limited to treatment with muscarinic antagonists (anti-muscarinics). SUI and OAB are characterised by high prevalence, a growing ageing population and a strong desire from sufferers and physicians for more effective treatment options. High patient numbers with low presentation rates characterizes sexual dysfunction in men and women. The introduction of Viagra in 1998 for treating male erectile dysfunction and the success of the phosphodiesterase type 5 inhibitor class (PDE5 inhibitor) have indicated the willingness of sufferers to seek treatment when an effective alternative to injections and devices is available. The main value of preclinical models in discovering new medicines is to predict clinical outcomes. This translation can be established relatively easily in areas of medicine where there are a large number of drugs with different underlying pharmacological mechanisms in clinical usage. However, apart from, for example, the use of PDE5 inhibitors to treat male erectile dysfunction and the use of anti-muscarinics to treat OAB, this clinical information is limited. Therefore, current confidence in existing preclinical models is based on our understanding of the biochemical, physiological, pathophysiological and psychological mechanisms underlying the conditions in humans and how they are reflected in preclinical models. Confidence in both the models used and the pharmacological data generated is reinforced if different models of related aspects of the same disorder generate confirmatory data. However, these models will only be fully validated in retrospect once the pharmacological agents they have helped identify are tested in humans.

DIFFERENTIAL EFFECTS OF ACTIVATION OF PERIPHERAL AND SPINAL TACHYKININ NEUROKININ 3 RECEPTORS ON THE MICTURITION REFLEX IN RATS

PURPOSE

We clarified the roles of tachykinin neurokinin (NK)3 receptors in the bladder or spinal cord for control of the micturition reflex in rats.

MATERIALS AND METHODS

In female rats under urethane anesthesia repetitive bladder contractions were elicited by saline infusion into the bladder through intravesical bladder catheters. The effects of peripheral receptor activation were first examined by topical application of the tachykinin NK3 receptor agonist [MePhe]-NKB (Calbiochem, Darmstadt, Germany) in normal rats and rats pretreated with capsaicin (Sigma Chemical Co., St. Louis, Missouri) 4 days before the experiments. Subsequently the effects of spinal NK3 receptor activation were examined by intrathecal administration of [MePhe]-NKB via implanted intrathecal catheters. The effects of the tachykinin NK3 receptor antagonist SB235375 and the opioid receptor antagonist naloxone on changes in bladder activity induced by [MePhe]-NKB were also investigated.

RESULTS

Topical application of [MePhe]-NKB onto the bladder surface decreased intercontraction intervals and bladder capacity, and increased baseline bladder pressure in dose dependent fashion. [MePhe]-NKB induced bladder overactivity was inhibited by simultaneous topical administration of SB235375 or by capsaicin pretreatment. In contrast, intrathecal injection of [MePhe]-NKB increased intercontraction intervals in dose dependent fashion and at a high dose it induced overflow incontinence or inefficient voiding. These inhibitory effects of [MePhe]-NKB in the spinal cord were antagonized by the intrathecal injection of SB235375 or naloxone.

CONCLUSIONS

These results indicate that the tachykinin NK3 receptor mediated neural control of the micturition reflex has dual actions depending on the location of receptor activation. Activation of tachykinin NK3 receptors located in the bladder can induce bladder overactivity at least in part via the activation of capsaicin sensitive C-fiber afferents, while tachykinin NK3 receptor activation in the spinal cord can inhibit the micturition reflex through an opioid mechanism.

Tachykinins and tachykinin receptors: effects in the genitourinary tract

Tachykinins (TKs) are a family of peptides involved in the central and peripheral regulation of urogenital functions through the stimulation of TK NK1, NK2 and NK3 receptors. At the urinary system level, TKs locally stimulate smooth muscle tone, ureteric peristalsis and bladder contractions, initiate neurogenic inflammation and trigger local and spinal reflexes aimed to maintain organ functions in emergency conditions. At the genital level, TKs are involved in smooth muscle contraction, in inflammation and in the modulation of steroid secretion by the testes and ovaries. TKs produce vasodilatation of maternal and fetal placental vascular beds and appear to be involved in reproductive function, stress-induced abortion, and pre-eclampsia. The current data suggest that the genitourinary tract is a primary site of action of the tachykininergic system.

Tachykinins as modulators of the micturition reflex in the central and peripheral nervous system

In the normal urinary bladder, tachykinins (TKs) are expressed in a population of bladder nociceptors that is sensitive to the excitatory and desensitizing effects of capsaicin (i.e., capsaicin-sensitive primary afferent neurons (CSPANs)). Several endobiotics or xenobiotics excite CSPANs and release TKs and other mediators at both the peripheral and spinal cord level. The peripheral release of TKs determines a set of responses (known as neurogenic inflammation) that includes vasodilatation, plasma protein extravasation, smooth muscle contraction and stimulation of afferent nerves. Following chronic inflammation, both immune cells and capsaicin-resistant sensory neurons can de novo express TKs: whether these pools of TKs are releasable and contribute to inflammatory processes is presently unsettled. At the spinal cord level, the release of TKs contributes in determining an altered pattern of vesicourethral reflexes in response to nociceptive stimulation of the bladder by conveying: (a) the afferent transmission to supraspinal sites, and (b) descending or sensory inputs to the sacral parasympathetic nucleus (SPN). Recent evidence also attribute a synergetic role of TKs in the supraspinal modulation of the sensory arm of the micturition reflex. The overall available information suggests that TK receptor antagonists may affect bladder motility/reflexes which occur during different pathological states, while having little influence on the normal motor bladder function.

Pharmacology of the lower urinary tract

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the urinary bladder, urethra, and external urethral sphincter. This activity is in turn controlled by neural circuits in the brain, spinal cord, and peripheral ganglia. Various neurotransmitters, including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in the neural regulation of the lower urinary tract. Injuries or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce voiding dysfunctions such as urinary frequency, urgency, and incontinence or inefficient voiding and urinary retention. This chapter will review recent advances in our understanding of the pathophysiology of voiding disorders and the targets for drug therapy.

Effect of TAK-637, a tachykinin NK1-receptor antagonist, on lower urinary tract function in cats

The effect of TAK-637 ((aR,9R)-7-[3,5-bis(trifluoromethyl)benzyl]-8,9,10,11-tetrahydro-9-methyl-5-(4-methylphenyl)-7H[1,4]diazocino[2,1g][1,7]naphthyridine-6,13-dione), a tachykinin NK1-receptor antagonist, on lower urinary tract function was investigated in cats. TAK-637 (0.1, 0.3, 1 and 3 mg/kg, i.v.) produced a dose-dependent increase in bladder capacity without any significant reduction in voiding efficiency in decerebrate cats. The maximal increase in bladder capacity was 94%. By contrast, oxybutynin at 1 and 3 mg/kg (i.v.) produced a 18% and 35% increase in bladder capacity, respectively, with a 47% and 45% reduction in voiding efficiency. TAK-637 (3 mg/kg, i.v.) did not inhibit the micturition reflex induced by electrical stimulation of the rostral brainstem near the locus coeruleus, indicating that it does not impair the well-organized micturition reflex (bladder contraction and urethral relaxation). These results suggest that TAK-637 increases bladder storage capability without inhibiting the voiding function of the lower urinary tract, presumably by inhibiting the afferent pathway of the micturition reflex, rather than the efferent pathway.

Possible site of action of TAK-637, a tachykinin NK(1) receptor antagonist, on the micturition reflex in guinea pigs

TAK-637((aR,9R)-7-[3,5-bis(trifluoromethyl)benzyl]-8,9,10, 11-tetrahydro-9-methyl-5-(4-methylphenyl)-7H-[1,4]diazocino[2,1-g] [1,7]naphthyridine-6,13-dione) is a novel tachykinin NK(1) receptor antagonist that has been shown to inhibit the micturition reflex in guinea pigs. The aim of this study was to clarify its mechanism of action in guinea pigs. TAK-637 inhibited the spinal vesico-vesical reflex induced by electrical stimulation of the proximal cut end of the pelvic nerve in spinal animals, but not bladder contractions induced by electrical stimulation of the distal cut end of the nerve. Furthermore, TAK-637 had no effect on carbachol- or electrical field stimulation-induced contractions of isolated bladder muscle strips in an organ bath, whereas drugs used for abnormally frequent micturition inhibited both contractions. These results suggest that TAK-637 inhibits the micturition reflex by acting, at least in part, on the spinal cord, and its mechanism of action clearly differs from those of antimuscarinics or spasmolytics.

Effects of TAK-637, a tachykinin receptor antagonist, on the micturition reflex in guinea pigs

The effects of a new tachykinin NK(1) receptor antagonist, (aR, 9R)-7-[3,5-bis(trifluoromethyl)benzyl]-8,9,10, 11-tetrahydro-9-methyl-5-(4-methylphenyl)-7H-[1,4]diazocino[2,1-g] [1, 7]naphthyridine-6,13-dione (TAK-637), on the micturition reflex were compared with those of drugs used for abnormally frequent micturition or incontinence. TAK-637 showed a characteristic effect on the distension-induced rhythmic bladder contractions in guinea pigs. The systemic administration of TAK-637 decreased the number but not the amplitude of the distension-induced rhythmic bladder contractions. A similar effect was observed in animals in which the spinal cord had been severed. TAK-637 also inhibited the micturition reflex induced by topical application of capsaicin onto the surface of bladder dome. From these results, it is concluded that TAK-637 inhibits sensory transmissions from the bladder evoked by both physiological and nociceptive stimuli by blocking tachykinin NK(1) receptors, possibly at the level of the spinal cord. On the other hand, the other drugs such as oxybutynin, tolterodine, propiverine, and inaperisone showed no effects on the frequency of the distension-induced rhythmic bladder contractions but decreased the contraction amplitude. Therefore, TAK-637 may represent a new class of drugs, which would be effective for abnormally frequent micturition without causing voiding difficulties due to decreased voiding pressure.