Assessment of Pain Perception in Irritable Bowel Syndrome: Towards an Optimal Definition of Rectal Hypersensitivity

rats were subjected to restraint stress by placing them in individual wire-mesh cages. Fecal pellets were collected during the 2 hr stress period and the wet weight was determined. Results: RQ-00310941 displayed high affinity for the human recombinant 5-HT2B receptor with a Ki value of 2.0 nM, and also showed >2000-fold selectivity against more than 60 GPCRs ion-channels and enzymes. The cell-based functional assay demonstrated that RQ00310941 was potent antagonist against the human 5-HT2B receptor (IC50=17 nM). The TNBS-induced decrease in the distal colon sensitivity was dose dependently suppressed by oral administration of RQ-00310941at doses of 0.1, 0.3 and 1 mg/kg (% Inh: -2, 32, 61%, respectively). RQ-00310941 at 1, 3, and 10 mg/kg, p.o. inhibited the restraint stress-induced defecation in TNBS-treated rats in a dose-dependent manner (% Inh: 2, 35, 95%, respectively). In addition, high dose of RQ-00310941 (30 mg/kg) did not affect normal defecation in naïve rats. Alosetron, a 5-HT3 receptor antagonist, was effective in visceral hypersensitivity and abnormal defecation in TNBS-treated rats at clinically relevant dose (0.01-0.03 mg/kg), but also significantly inhibited spontaneous defecation at 0.03 mg/kg. Conclusion: RQ00310941 exhibited highly selective and potent antagonistic activity against the human 5HT2B receptor. The results observed In Vivo suggest that RQ-00310941 will be a useful therapeutic agent for D-IBS and mixed IBS in which there is a low risk of ischemic colitis or severe constipation observed with 5-HT3 antagonists. Mo1307 Assessment of Pain Perception in Irritable Bowel Syndrome: Towards an Optimal Definition of Rectal Hypersensitivity Samefko Ludidi, José M. Conchillo, Daniel Keszthelyi, Mark van Avesaat, Daisy Jonkers, Ad Masclee Background: Visceral hypersensitivity is considered a hallmark of irritable bowel syndrome (IBS) and is present in up to 60% of IBS patients. A rectal barostat test is frequently used to investigate intestinal sensitivity in IBS. This test allows discrimination between IBS patients and healthy controls (HC) based on pain perception. However, there is no consensus regarding the procedure of testing visceral sensitivity and threshold or normal values. Aim of the present study was therefore to assess the optimal threshold and cut-off to detect altered visceral perception (hypersensitivity and allodynia) in IBS, by standardised rectal distensions. Methods: Barostat data of 126 IBS patients (38±1.3 years) according to Rome III criteria and 30 HC (37±3.1 years) were analysed for visceral pain perception. The rectal barostat procedure consisted of intermittent staircase distensions between 0-50 mmHg above MDP, with increments of 3 mmHg. Participants scored pain at 100mm visual analogue scales (VAS). Based on perception data in IBS and HC, area under receiver operating characteristic curve (AUC); sensitivity (SEN); specificity (SPE); positive predictive value (PPV) and positive likelihood ratio (LR+) were calculated. This resulted in a cut-off point (i.e. combination of pressure step and VAS-score for pain) for optimal discrimination between IBS and HC. VAS-scores above this cut-off optimum were defined as hypersensitive, VASscores below this cut-off optimum but above the cut-off for first sensation (VAS of 10mm) were defined as allodynic. Results: Diarrhoea-, constipation-predominant and mixed stool type were found in 50, 29 and 21% of IBS patients, respectively. Five pressure steps with corresponding cut-off values had AUC > 0.75 (Table 1). The cut-off that allowed optimal discrimination between IBS and HC was found to be 26mmHg with a VAS-score >20mm (i.e. pain threshold), based on sensitivity (0.64), specificity (0.90), AUC (0.77), PPV (0.96) and LR+ (6.3). Using this criterion, 63.5% of IBS patients and 10.0% of HC were hypersensitive, whereas allodynia percentages in these groups were 11.1% and 6.6%, respectively. Conclusion: Threshold and cut-off values during rectal barostat procedure to a large extent determine hypersensitivity percentages amongst IBS patients. When using the barostat as a descriptive or diagnostic tool for IBS, international standardisation of the distension protocol is required. With this study, we have shown that 26mmHg at VAS>20mm is most optimal for the detection of visceral hypersensitivity in IBS patients, compared to healthy controls during rectal barostat. Table 1: five most accurate pressure steps and VAS-scores for hypersensitivity in IBS

Mo1305 DA-6886 is a Novel 5-HT4 Receptor Agonist With Increased Colonic Motor Activity in Mice Min Jung Lee, Sunghak Choi, Kang Hun Cho, Hyun Min Park, Hyun Jung Sung, Sun Ho Choi, Weonbin Im Purpose: DA-6886, the gastrointestinal prokinetic agent is a novel 5-HT4 receptor agonist being developed for the treatment of constipation-predominant irritable bowel syndrome (IBS-C). The objectives of this study were to investigate the In Vitro pharmacological profile and In Vivo gastrointestinal activity. Methods: 5-HT4 binding affinity was assessed in competitive radioligand binding assays. Total cellular cAMP in human 5-HT4 receptor-expressing cells was quantified using homogenous time-resolved fluorescence method. Cell viability was measured in AGS and Caco-2 cell line using MTS assay. The 5-HT4 receptor-mediated relaxation was evaluated using tunica muscularis mucosae from the rat isolated esophagus. The colonic transit was measured in normal ICR mice as well as mice with loperamideinduced constipation. Results: DA-6886 had a high binding affinity to 5-HT4 receptors, with mean pKi of 7.55, 7.19, 7.39 and 7.76 for the human 5-HT4a, 5-HT4b, 5-HT4d and guinea pig 5-HT4, respectively that translates to functional agonist activity in total cellular cAMP assay. DA-6886 produced 5-HT4 receptor-mediated relaxation of the rat isolated oesophagus (EC50 value of 181nM). In the normal ICR mice, oral administration of DA6886 significantly enhanced colonic transit in a dose-dependent manner. In the loperamideinduced constipation mouse model, 2 mg/kg of DA-6886 resulted in marked stimulation of colonic transit, similar to 10 mg/kg of tegaserod. DA-6886 did not show hERG binding activity and cytotoxicity of human gastrointestinal cells at concentrations up to 10 uM. Conclusions: DA-6886 is a potent 5-HT4 agonist with increased colonic transit activity in normal mice as well as constipation-induced mice, which may be effective for the treatment of gastrointestinal motor disorders such as IBS-C and chronic constipation. Mo1306

Mo1308

The Novel 5-HT2B Receptor Antagonist, RQ-00310941, Attenuates Visceral Hypersensitivity and Abnormal Defecation in Rat Models Nobuyuki Takahashi, Kazuyuki Inagaki, Kana Taniguchi, Yoshiko Sakaguchi, Kiyoshi Kawamura

Lubiprostone Treatment in Patients With Irritable Bowel Syndrome With Constipation for up to 16 Weeks Duration Raymond M. Panas, Vince Lin, Ryuji Ueno

Background: Irritable bowel syndrome (IBS) is a chronic, relapsing and potentially disabling bowel disorder characterized by the presence of abdominal pain/discomfort and abnormal defecation. 5-HT2B receptors are located both to smooth muscles and neurons of the myenteric plexus in human colon, and 5-HT2B receptors mediate 5-HT-evoked contraction of the longitudinal smooth muscle. Therefore, it has been recently suggested that 5-HT2B receptor antagonism could play a role in modulating colonic motility and sensory signaling in the gut. RQ-00310941 is a novel, potent and selective 5-HT2B receptor antagonist. In the present study, we have characterized the In Vitro pharmacology of RQ-00310941. Furthermore, we assessed the effects of RQ-00310941 on visceral hypersensitivity and stressinduced abnormal defecation in TNBS-treated rats. Methods: In Vitro functional activity of RQ-00310941 was evaluated in calcium mobilization assay using stably expressed human 5-HT2B receptor. Visceral hypersensitivity was induced by an injection of TNBS into the lumen of the proximal colon. Colorectal distension was regulated by an electronic barostat. The colonic pain threshold was determined as the lowest pressure required to elicit behavioral signs of abdominal pain. The defecation response was measured in TNBS-treated rats. The

INTRODUCTION: Treatment of irritable bowel syndrome with constipation (IBS-C) is challenging given the diversity of symptoms reported by patients with this disorder. Lubiprostone (8 mcg BID) has been shown to provide safe and effective relief for patients with IBS-C in two Phase 3 studies. AIM: To evaluate abdominal and bowel symptoms through 16 weeks duration inclusive of a 4-week randomized withdrawal of active treatment. METHODS: Patients were randomized in a 2:1 ratio to receive lubiprostone (L) or placebo (P) for a 12week treatment period (Period I). At the end of Period I, L group patients were randomly re-assigned in a 1:1 ratio to receive lubiprostone (LL) or placebo (LP) for a 4-week withdrawal period (Period II). Baseline criteria for patients to be included in the analyses were as follows: < 3 spontaneous bowel movements (SBMs)/week, ≥ 25% of SBMs associated with moderate or greater straining, and ≥ 25% of SBMs having hard or very hard stool consistency. Outcomes included stool consistency, abdominal discomfort/pain, and SBM frequency. Weekly mean changes from baseline during Period I were analyzed to compare L group with P group. Similar between-group comparison analyses were performed for Period II. RESULTS: 258 patients (L group=170, P group=88) met analysis criteria for Period I. At Period II, L group

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AGA Abstracts

AGA Abstracts

patients with CC. METHODS: The AEs from 14 Phase II/III, double-blind, placebo (PLA)controlled trials (duration 4-12 weeks; PRU dose 0.5-4mg q.d.) in patients with CC were pooled, and different AE categories were compared between elderly and adults. RESULTS: 2717 patients were treated with PRU (exposure: 406 patient-yrs), of which 564 were ≥65 yrs (exposure: 63 patient-yrs). Exposure time to 2mg (recommended dose for adults) was 165 pt-yrs (n=938); exposure to 1mg (recommended dose for elderly) was 8 pt-yrs (n= 113). In the elderly, the incidence of the different AE categories was comparable between PRU and PLA, and comparable to those seen in adults except for serious AEs (SAEs). SAEs were reported at a higher rate in elderly (most commonly infections, infestations or respiratory disorders), with no difference observed between PRU and PLA (Table). Three elderly patients died, 2 on PRU, due to pneumonia or bronchitis (not considered related to study medication) and 1 on PLA due to arrhythmia/myocardial infarction. Most common AEs with PRU in both age groups were gastrointestinal symptoms (nausea, diarrhea, abdominal pain) and headache. Results in subgroups of patients 65-75 yrs and patients ≥75 yrs were similar to those observed in the whole group of elderly patients. The proportion of patients on PRU discontinuing therapy among the elderly and adults was similar. The incidence of cardiovascular AEs of interest (palpitations, corrected QT interval-related AEs, and ventricular arrhythmias) was comparable in both age groups, as well as for PRU and PLA. Cardiac ischemia and atrial arrhythmia-related AEs were more common in elderly, but their incidence was not different for PRU and PLA. The majority of ischemic and atrial rhythm-related AEs were reported by the investigator as unrelated to the study medication or doubtful. CONCLUSIONS: In 14 double-blind, PLA-controlled, Phase II/III trials of PRU, the safety and AE profiles were similar relative to PLA in adult and elderly patients with CC.