Pharmacology and metabolism of renzapride : a novel therapeutic agent for the potential treatment of irritable bowel syndrome

Regional brain activation during rectal distention and attenuation with alosetron in a nonhuman primate model of irritable bowel syndrome

Greater understanding of the mechanism that mediates visceral pain and hypersensitivity associated with irritable bowel syndrome (IBS) would facilitate the development of effective therapeutics to manage these symptoms. An objective marker associated with the underlying mechanisms of visceral pain and hypersensitivity could be used to guide therapeutic development. The current study examined brain activation evoked by rectal distention with functional magnetic resonance imaging (fMRI) in a cynomolgus macaque model of visceral hypersensitivity. Male, cynomolgus macaques underwent five four-week treatments of dextran sodium sulfate (DSS)-distilled water (DW), which induced mild-moderate colitis with remission during each treatment cycle. Balloon rectal distention (RD) was performed under anesthesia 14 weeks after the final DSS-DW treatment. Colonoscopy confirmed the absence of colitis prior to the start of RD. In naïve, untreated macaques, 10, 20 and 30 ml RD did not evoke brain activation. However, insular cortex/somatosensory II cortex and cerebellum were significantly activated in DSS-treated macaques at 20 and 30 ml rectal distention. Intra-rectal pressure after DSS treatment was not significantly different from that of naïve, untreated macaques, indicating lack of alteration of rectal functioning following DSS-treatment. Treatment with 5-HT3 receptor antagonist alosetron (p.o.) reduced distension-evoked brain activation and decreased intra-rectal pressure. The current findings demonstrated activation of brain regions to RD following DSS treatments which was not present in naïve macaques, suggesting visceral hypersensitivity. Brain activation in turn was reduced by alosetron, which could underlie the analgesic effect alosetron in IBS patients.

The role of serotonergic, adrenergic and dopaminergic receptors in antidepressant-like effect

Depression is a serious global illness, becoming more and more common in developed countries. Because of specific symptoms it is considered as a leading cause of disability all over the world with a high death factor due to suicides. There are many antidepressants used in the therapy, but still more than 30% of patients do not respond to the treatment. The heterogeneous nature of the illness and its complex, unclear aetiology may be responsible for these difficulties. Next to the main monoaminergic hypothesis of depression there are also many other approaches connected with the pathophysiology of the disease, including hypothalamic-pituitary-adrenal axis dysregulation, dopaminergic, cholinergic, glutamatergic or GABA-ergic neurotransmission. Nevertheless, it can be unambiguously stated that serotonergic, noradrenergic and dopaminergic systems are precisely connected with pathogenesis of depression, and should be therefore considered as valuable targets in patients' treatment. Bearing that in mind, this review presents the role of serotonergic, adrenergic and dopaminergic receptors in antidepressant-like effect.

The safety of novel drugs used to treat irritable bowel syndrome

INTRODUCTION

Irritable bowel syndrome (IBS) is a chronic gastrointestinal (GI) disorder with a high prevalence. Besides efficacy, the safety of each drugs used to treat GI disorders is an important issue in the drug development process.

AREAS COVERED

This article reviews all Phase I to IV clinical trials or case reports with results related to the safety of novel GI drugs. The drugs are currently approved or under evaluation for approval.

EXPERT OPINION

Most of the reported adverse events were related to the GI tract with mild-to-moderate severity. Diarrhea was significantly higher versus placebo following use of linaclotide and renzapride, similar to that of constipation with ramosetron. Lubiprostone, linaclotide and rifaximin with low systemic bioavailability have less adverse events and exert more advantageous results. Asimadoline acts peripherally on κ-opioid receptors and is not associated with CNS side effects. As lubiprostone and linaclotide cause dose-dependent adverse events, starting the treatment with the lowest effective doses is advised. Ramosetron is under evaluation for diarrhea-predominant IBS due to its acceptable safety and tolerability, besides its efficacy. Rifaximin, asimadoline and renzapride are still in need of more long-term studies regarding their safety.

Efficacy and tolerability of renzapride in irritable bowel syndrome: a meta-analysis of randomized, controlled clinical trials including 2528 patients

INTRODUCTION

By targeting different subtypes of 5-hydroxytryptamine (5HT) receptors in the gastrointestinal (GI) tract, several drugs have been introduced for the management of irritable bowel syndrome (IBS). Renzapride is a full agonist for 5HT4 receptor and an antagonist to 5HT2b and 5HT3 receptors which is thought a promising therapeutic agent for constipation predominant IBS (C-IBS) patients due to its accelerating effect on the GI tract. In this meta-analysis, our aim was to evaluate the efficacy and tolerability of renzapride in the management of IBS.

MATERIAL AND METHODS

A search was done from 1992 to February 2013 for placebo-controlled trials that investigated the efficacy of renzapride in IBS.

RESULTS

Relative risk (RR) for clinical efficacy in IBS patients treated for 5 weeks or less comparing renzapride to placebo was 1.07 (95% CI = 0.89-1.29, p = 0.38). This value for IBS patients treated for more than 5 weeks was 1.04 (95% CI = 0.78-1.239, p = 0.77). The RR for clinical efficacy in IBS patients treated with renzapride (4 mg) for 5 weeks or less and more than 5 weeks in comparison to placebo was 1.2 (95% CI = 0.97-1.48, p = 0.1) and 1.16 (95% CI = 0.98-1.37, p = 0.08), respectively, which were statistically non-significant but clinically important. The analysis of tolerability demonstrated that amongst different reported adverse effects, renzapride caused diarrhea more than placebo (RR = 1.61 with a 95% CI = 1.16-2.24, p = 0.004). The RR for withdrawals from renzapride compared to placebo was 1.58 (95% CI = 1.26-2.07, p = 0.0007).

CONCLUSIONS

Renzapride is not superior to placebo in relieving IBS symptoms and causes significant incidences of diarrhea and drop-outs due to adverse effects in treated patients vs. placebo. Thus, this medicine might be a cost burden to patients without providing good effectiveness.

Systematic review: cardiovascular safety profile of 5-HT(4) agonists developed for gastrointestinal disorders

BACKGROUND

The nonselective 5-HT(4) receptor agonists, cisapride and tegaserod have been associated with cardiovascular adverse events (AEs).

AIM

To perform a systematic review of the safety profile, particularly cardiovascular, of 5-HT(4) agonists developed for gastrointestinal disorders, and a nonsystematic summary of their pharmacology and clinical efficacy.

METHODS

Articles reporting data on cisapride, clebopride, prucalopride, mosapride, renzapride, tegaserod, TD-5108 (velusetrag) and ATI-7505 (naronapride) were identified through a systematic search of the Cochrane Library, Medline, Embase and Toxfile. Abstracts from UEGW 2006-2008 and DDW 2008-2010 were searched for these drug names, and pharmaceutical companies approached to provide unpublished data.

RESULTS

Retrieved articles on pharmacokinetics, human pharmacodynamics and clinical data with these 5-HT(4) agonists, are reviewed and summarised nonsystematically. Articles relating to cardiac safety and tolerability of these agents, including any relevant case reports, are reported systematically. Two nonselective 5-HT(4) agonists had reports of cardiovascular AEs: cisapride (QT prolongation) and tegaserod (ischaemia). Interactions with, respectively, the hERG cardiac potassium channel and 5-HT(1) receptor subtypes have been suggested to account for these effects. No cardiovascular safety concerns were reported for the newer, selective 5-HT(4) agonists prucalopride, velusetrag, naronapride, or for nonselective 5-HT(4) agonists with no hERG or 5-HT(1) affinity (renzapride, clebopride, mosapride).

CONCLUSIONS

5-HT(4) agonists for GI disorders differ in chemical structure and selectivity for 5-HT(4) receptors. Selectivity for 5-HT(4) over non-5-HT(4) receptors may influence the agent's safety and overall risk-benefit profile. Based on available evidence, highly selective 5-HT(4) agonists may offer improved safety to treat patients with impaired GI motility.

Investigational agents for the irritable bowel syndrome

IMPORTANCE OF THE FIELD

Irritable bowel syndrome (IBS) is a common disorder with significant health and economic consequences. The etiology of IBS is complex and appears to be multifactorial. Traditional IBS therapies have been directed primarily at the relief of individual symptoms but have been largely disappointing. This has triggered the search for newer treatment strategies with improved patient outcomes.

AREAS COVERED IN THIS REVIEW

Enhanced knowledge about the putative pathophysiology of IBS has allowed the identification of new mechanistic targets for treatment. Our aim is to review emerging and promising drugs in the treatment of IBS based on disease pathophysiology. Data were extracted using Medline and PubMed search engines until January 2010. Abstracts were identified through 'Web of Science' and abstract supplements of major gastrointestinal scientific meetings. Drugs were classified according to mechanism of action and those with efficacy in trials involving human subjects examined.

WHAT THE READER WILL GAIN

Additional insight into the pathophysiology as well as current and prospective treatments of IBS.

TAKE HOME MESSAGE

A multitude of putative drug targets have been identified and some novel treatments have progressed through to human clinical trials, but very few will be approved for the market in the near future. Moreover, and in keeping with the complex and multifactorial nature of this syndrome, it is unlikely that there will be one dominant and universally effective form of therapy for all IBS patients.

[New drugs for the treatment of constipation]

This review introduces new therapeutic options in the treatment of chronic idiopathic constipation and irritable bowel syndrome with constipation. Therefore, prucalopride and lubiprostone are discussed including their mechanisms and side effects. In addition, other substances that are currently under evaluation such as renzapride and linaclotide are described, since recent results showed a significant effect in patients with constipation. Thus, after the withdrawal of tegaserod due to cardiac side effects, new potent drugs are now available for the treatment of constipation.

Pharmacological management of constipation

The approach of this review is to give a pragmatic approach to using laxatives, based on a combination of what is known about mechanism of action and the available literature on evidence.

The role of serotonin in irritable bowel syndrome: implications for management

Irritable bowel syndrome (IBS) is a poorly understood, common, chronic condition characterized by -abdominal discomfort associated with altered bowel habits in the absence of structural or biochemical abnormalities. Despite the significant economic and personal burden associated with IBS, treatment options remain limited. Serotonin is recognized as a key neurotransmitter in intestinal secretory, sensory, and motor function. Although the pathophysiology of IBS is incompletely understood, there is evidence that abnormalities in brain-gut signaling and serotonin metabolism play a role. This article reviews the evidence that serotonin, one of the better-understood neurotransmitters with respect to its role in human central and intestinal physiology, plays a role in IBS. Serotonin signaling is discussed, with a focus on receptor subtypes and the therapeutic agents that target these receptors. Evidence that IBS is associated with perturbations in serotonin metabolism at various steps in the signaling pathway is also addressed, along with the limitations on alteration in serotonin metabolism as the sole explanation for the constellation of symptoms observed in patients with IBS.

The in vitro pharmacological profile of TD-5108, a selective 5-HT(4) receptor agonist with high intrinsic activity

The in vitro pharmacological profile of TD-5108, a novel, selective 5-HT(4) receptor agonist, was compared to that of clinically efficacious gastroprokinetic 5-HT(4) receptor agonists. TD-5108 produced an elevation of cyclic adenosine monophosphate in human embryonic kidney 293 cells expressing the human recombinant 5-HT(4(c)) (h5-HT(4(c))) receptor (pEC(50) = 8.3) and 5-HT(4) receptor-mediated relaxation of the rat esophagus (pEC(50) = 7.9) and contraction of the guinea pig colon (pEC(50) = 7.9). In all in vitro assays, TD-5108 was a high intrinsic activity agonist, unlike tegaserod, mosapride, and cisapride which, in the majority of test systems, had lower intrinsic activity. TD-5108 had high affinity (pK (i) = 7.7) and selectivity (> or =25-fold) for h5-HT(4(c)) receptors over other biogenic amine receptors. TD-5108 was >500-fold selective over other 5-HT receptors (including h5-HT(2B) and h5-HT(3A)) and, at 3 microM, had no effect on human ether-à-go-go-related gene K+ channels. In conclusion, TD-5108 is a selective 5-HT(4) receptor agonist in vitro. The high intrinsic activity and preferential binding of TD-5108 to 5-HT4 over other 5-HT receptors may result in an improved clinical profile for the treatment of gastrointestinal disorders of reduced motility.