Guanylate cyclase-C agonists as peripherally acting treatments of chronic visceral pain.

Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder characterized by abdominal pain and altered bowel habit that affects ~11% of the global population. Over the past decade, preclinical and clinical studies have revealed a variety of novel mechanisms relating to the visceral analgesic effects of guanylate cyclase-C (GC-C) agonists. Here we discuss the mechanisms by which GC-C agonists target the GC-C/cyclic guanosine-3',5'-monophosphate (cGMP) pathway, resulting in visceral analgesia as well as clinically relevant relief of abdominal pain and other sensations in IBS patients. Due to the preponderance of evidence we focus on linaclotide, a 14-amino acid GC-C agonist with very low oral bioavailability that acts within the gut. Collectively, the weight of experimental and clinical evidence supports the concept that GC-C agonists act as peripherally acting visceral analgesics.

The Use of Linaclotide in Children with Functional Constipation or Irritable Bowel Syndrome: A Retrospective Chart Review.

BACKGROUND: Linaclotide is a well-tolerated and effective agent for adults with functional constipation (FC) or irritable bowel syndrome with constipation (IBS-C). However, data in children are lacking. The aim of this study is to examine the efficacy and safety of linaclotide in children. METHODS: We performed a retrospective review of children < 18 years old who started linaclotide at our institution (Nationwide Children's Hospital, Columbus, Ohio). We excluded children already using linaclotide or whom had an organic cause of constipation or abdominal pain. We recorded information on patient characteristics, medical and surgical history, symptoms, clinical response, course of treatment, and adverse events at baseline, first follow-up, and after 1 year of linaclotide use. A positive clinical response was based on the physician's global assessment of symptoms at the time of the visit as documented. RESULTS: We included 93 children treated with linaclotide for FC (n = 60) or IBS-C (n = 33); 60% were female; median age was 14.7 years (IQR 13.2-16.6). Forty-five percent of patients with FC and 42% with IBS-C had a positive clinical response at first follow-up a median of 2.5 and 2.4 months after starting linaclotide, respectively. Approximately a third of patients experienced adverse events and eventually 27% stopped using linaclotide due to adverse events. The most common adverse events were diarrhea, abdominal pain, nausea, and bloating. CONCLUSION: Nearly half of children with FC or IBS-C benefited from linaclotide, but adverse events were relatively common. Further prospective, controlled studies are needed to confirm these findings and to identify which patients are most likely to benefit from linaclotide.

Soluble guanylate cyclase stimulators and their potential use: a patent review.

Introduction: In 2013, riociguat a potent and specific stimulator of the soluble guanylyl cyclase (sGC) was approved as first in class sGC stimulator which reflected a first culmination of intense research and development efforts starting in the mid 1990ies. In the meantime, it turned out that triggering cGMP production by sGC stimulators could have a broad treatment potential. In consequence, various pharmaceutical companies are still very active in identifying novel chemistry for sGC stimulators. After the first generation of sGC stimulators like riociguat or lificiguat, new compound classes with different physicochemical and kinetic profiles were identified, like the sGC stimulators vericiguat or praliciguat.Area covered: Patent literature on sGC stimulators with a focus on recent compounds of the years 2014-2019 as on claimed use and formulations of these compounds. The information was collected from publicly available data sources only (MedLine, EmBase, Chemical Abstracts, Orbit, Dolphin).Expert Opinion: With the recent advancements reported in the patent literature, sGC stimulators might be differentiated due to tissue selectivity or route of application although exhibiting the same molecular mode of action. The indication space of these compounds is potentially very broad and multiple indications in cardiovascular diseases and beyond are under investigation.

Peripheral Guanylate Cyclase-C modulation of corticolimbic activation and corticotropin-releasing factor signaling in a rat model of stress-induced colonic hypersensitivity.

BACKGROUND: Psychological stress is a risk factor for irritable bowel syndrome, a functional gastrointestinal pain disorder featuring abnormal brain-gut connectivity. The guanylate cyclase-C (GC-C) agonist linaclotide has been shown to relieve abdominal pain in IBS-C and exhibits antinociceptive effects in rodent models of post-inflammatory visceral hypersensitivity. However, the role GC-C signaling plays in psychological stress-induced visceral hypersensitivity is unknown. Here, we test the hypothesis that GC-C agonism reverses stress-induced colonic hypersensitivity via inhibition of nociceptive afferent signaling resulting in normalization of stress-altered corticotropin-releasing factor (CRF) expression in brain regions involved in pain perception and modulation. METHODS: Adult female rats were exposed to water avoidance stress or sham stress for 10 days, and the effects of linaclotide on stress-induced changes in colonic sensitivity, corticolimbic phospho-extracellular signal-regulated kinase (pERK), and CRF expression were measured using a combination of behavioral assessments, immunohistochemistry, and qRT-PCR. KEY RESULTS: Stressed rats exhibited colonic hypersensitivity and elevated corticolimbic pERK on day 11, which was inhibited by linaclotide. qRT-PCR analysis revealed dysregulated CRF expression in the medial prefrontal cortex, paraventricular nucleus of the hypothalamus, and central nucleus of the amygdala on day 28. Dysregulated CRF expression was not affected by linaclotide treatment. CONCLUSIONS AND INFERENCES: Our results demonstrate that exposure to repeated stress induces chronic colonic hypersensitivity in conjunction with altered corticolimbic activation and CRF expression. GC-C agonism attenuated stress-induced colonic hypersensitivity and ERK phosphorylation, but had no effect on CRF expression, suggesting the analgesic effects of linaclotide occur independent of stress-driven CRF gene expression in corticolimbic circuitry.

Effects of the Soluble Guanylate Cyclase Stimulator Praliciguat in Diabetic Kidney Disease: A Randomized Placebo-Controlled Clinical Trial.

BACKGROUND AND OBJECTIVES: Impaired nitric oxide signaling through soluble guanylate cyclase has been implicated in the pathophysiology of diabetic kidney disease. Praliciguat, a soluble guanylate cyclase stimulator that amplifies nitric oxide signaling, inhibited kidney inflammation and fibrosis in animal models. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: In a phase 2 trial, 156 adults with type 2 diabetes, eGFR 30-75 ml/min per 1.73 m2, and urine albumin-creatinine ratio 200-5000 mg/g treated with renin-angiotensin system inhibitors were randomly allocated 1:1:1 to placebo, 20 mg praliciguat, or 40 mg praliciguat daily for 12 weeks. The primary efficacy and safety outcomes were change from baseline to weeks 8 and 12 in urine albumin-creatinine ratio and treatment-emergent adverse events, respectively. Other outcomes assessed were 24-hour ambulatory BP and metabolic parameters. RESULTS: Of 156 participants randomized, 140 (90%) completed the study. The primary efficacy analysis demonstrated a mean change from baseline in urine albumin-creatinine ratio of -28% (90% confidence interval, -36 to -18) in the pooled praliciguat group and -15% (-28 to 0.4) in the placebo group (difference -15%; -31 to 4; P=0.17). Between-group decreases from baseline to week 12 for praliciguat versus placebo were seen in mean 24-hour systolic BP (-4 mm Hg; -8 to -1), hemoglobin A1c (-0.3%; -0.5 to -0.03), and serum cholesterol (-10 mg/dl; -19 to -1). The incidence of treatment-emergent adverse events was similar in the pooled praliciguat and placebo groups (42% and 44%, respectively). Serious adverse events, events leading to study drug discontinuation, and events potentially related to BP lowering were reported at higher frequency in the 40-mg group but were similar in 20-mg and placebo groups. CONCLUSIONS: Praliciguat treatment for 12 weeks did not significantly reduce albuminuria compared with placebo in the primary efficacy analysis. Nonetheless, the observed changes in urine albumin-creatinine ratio, BP, and metabolic variables may support further investigation of praliciguat in diabetic kidney disease. CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER: A Study to Evaluate the Soluble Guanylate Cyclase (sGC) Stimulator IW-1973 in Diabetic Nephropathy/Diabetic Kidney Disease as Measured by Albuminuria, NCT03217591.

An update on guanylyl cyclase C in the diagnosis, chemoprevention, and treatment of colorectal cancer.

Introduction: Colorectal cancer remains the second leading cause of cancer death in the United States, underscoring the need for novel therapies. Despite the successes of new targeted agents for other cancers, colorectal cancer suffers from a relative scarcity of actionable biomarkers. In this context, the intestinal receptor, guanylyl cyclase C (GUCY2C), has emerged as a promising target.Areas covered: GUCY2C regulates a tumor-suppressive signaling axis that is silenced through loss of its endogenous ligands at the earliest stages of tumorigenesis. A body of literature supports a cancer chemoprevention strategy involving reactivation of GUCY2C through FDA-approved cGMP-elevating agents such as linaclotide, plecanatide, and sildenafil. Its limited expression in extra-intestinal tissues, and retention on the surface of cancer cells, also positions GUCY2C as a target for immunotherapies to treat metastatic disease, including vaccines, chimeric antigen receptor T-cells, and antibody-drug conjugates. Likewise, GUCY2C mRNA identifies metastatic cells, enhancing colorectal cancer detection, and staging. Pre-clinical and clinical programs exploring these GUCY2C-targeting strategies will be reviewed.Expert opinion: Recent mechanistic insights characterizing GUCY2C ligand loss early in tumorigenesis, coupled with results from the first clinical trials testing GUCY2C-targeting strategies, continue to elevate GUCY2C as an ideal target for prevention, detection, and therapy.

Praliciguat inhibits progression of diabetic nephropathy in ZSF1 rats and suppresses inflammation and apoptosis in human renal proximal tubular cells.

Praliciguat, a clinical-stage soluble guanylate cyclase (sGC) stimulator, increases cGMP via the nitric oxide-sGC pathway. Praliciguat has been shown to be renoprotective in rodent models of hypertensive nephropathy and renal fibrosis. In the present study, praliciguat alone and in combination with enalapril attenuated proteinuria in the obese ZSF1 rat model of diabetic nephropathy. Praliciguat monotherapy did not affect hemodynamics. In contrast, enalapril monotherapy lowered blood pressure but did not attenuate proteinuria. Renal expression of genes in pathways involved in inflammation, fibrosis, oxidative stress, and kidney injury was lower in praliciguat-treated obese ZSF1 rats than in obese control rats; fasting glucose and cholesterol were also lower with praliciguat treatment. To gain insight into how tubular mechanisms might contribute to its pharmacological effects on the kidneys, we studied the effects of praliciguat on pathological processes and signaling pathways in cultured human primary renal proximal tubular epithelial cells (RPTCs). Praliciguat inhibited the expression of proinflammatory cytokines and secretion of monocyte chemoattractant protein-1 in tumor necrosis factor-α-challenged RPTCs. Praliciguat treatment also attenuated transforming growth factor-ß-mediated apoptosis, changes to a mesenchyme-like cellular phenotype, and phosphorylation of SMAD3 in RPTCs. In conclusion, praliciguat improved proteinuria in the ZSF1 rat model of diabetic nephropathy, and its actions in human RPTCs suggest that tubular effects may contribute to its renal benefits, building upon strong evidence for the role of cGMP signaling in renal health.

Pharmacologic Treatments for Irritable Bowel Syndrome: an Umbrella Systematic Review.

BACKGROUND AND AIMS: Multiple pharmacologic treatments are available for the management of irritable bowel syndrome (IBS), and a large body of evidence has been presented. However, the strength and credibility of the evidence have not been comprehensively evaluated. We aimed to review the systematic reviews and meta- analyses of pharmacologic treatments for IBS and evaluate the credibility of the findings. METHODS: We searched MEDLINE, Embase, and Cochrane library from inception to September 2019 for systematic reviews evaluating the effectiveness of pharmacologic treatments for IBS. We summarized relative ratios (RR), evaluated the credibility of the evidence and classified the evidence into convincing, highly suggestive, suggestive, and weak. RESULTS: We included 11 systematic reviews with 40 meta-analyses (330 randomized controlled trials and 86,459 participants) assessing 10 treatment categories and 2 drugs. Most of the pharmacologic treatments were significantly superior over placebo as reported by the included meta-analyses. The evidence for 5-hydroxytryptamine (5-HT)3 antagonists (RR=1.56, 95%CI: 1.43-1.71), antispasmodics (RR=1.19, 95%CI: 1.02-1.39), and alosetron (RR=1.46, 95%CI: 1.26-1.71) were highly suggestive for relieving global IBS symptoms. 5-HT4 agonists (RR= 1.26, 95%CI: 1.19-1.34) and guanylate cyclase-C (GCC) agonists (RR=1.73, 95%CI: 1.54-1.95) were found to give convincing evidence for the improvement of the responder rate. 5-HT3 antagonists (RR=1.32, 95%CI: 1.26-1.38) offered convincing evidence for relieving abdominal pain. CONCLUSIONS: Evidence for 5-HT3 antagonists, 5-HT4 agonists and GCC agonists, antispasmodics, and alosetron were suggestive for the treatment of IBS. However, owing to the risk of bias in randomization methods, the results for GCC should be interpreted with caution.

Deciphering ion transporters, kinases and PDZ-adaptor molecules that mediate guanylate cyclase C agonist-dependent intestinal fluid loss in vivo.

BACKGROUND: The molecular basis for heat-stable Escherichia coli enterotoxin (STa) action and its synthetic analogue linaclotide is well understood at the enterocyte level. Pharmacologic strategies to prevent STa-induced intestinal fluid loss by inhibiting its effector molecules, however, have achieved insufficient inhibition in vivo. AIMS AND EXPERIMENTAL APPROACH: To investigate whether the currently discussed effector molecules and signaling mechanisms of STa/linaclotide-induced diarrhea have similar relevance in vivo than at the enterocyte level, we studied the effect of 10-7M of the STa analogue linaclotide on short circuit current (Isc) of chambered isolated jejunal mucosa, and on the in vivo action on fluid transport in a perfused segment of proximal jejunum of anesthetized mice. The selected mice were deficient of transport (NHE3, CFTR, Slc26a3/a6), adaptor (NHERF1-3), or signal transduction molecules [cGMP-dependent kinase II (GKII)] considered to be downstream effectors after STa/linaclotide binding to guanylate cyclase C (GCC). Selective NHE3 inhibition by tenapanor was also employed. KEY RESULTS, CONCLUSIONS AND IMPLICATIONS: The comparison allowed the separation of effectors for stimulation of electrogenic anion secretion and for inhibition of electrolyte/fluid absorption in response to STa/linaclotide. The cGKII-NHERF1-CFTR and cGKII-NHERF2-NHE3 interactions are indeed major effectors of small intestinal fluid loss downstream of GCC activation in vitro and in vivo, but 50% of the linaclotide-induced fluid loss in vivo, while dependent on CFTR activation and NHE3 inhibition, does not involve cGKII, and 30% does not depend on NHERF1 or NHERF2. A combined NHERF1 and NHERF2 inhibition appears nevertheless a good pharmacological strategy against STa-mediated fluid loss.

Oral Pharmacological Activation of Hypothalamic Guanylate Cyclase 2C Receptor Stimulates Brown Fat Thermogenesis to Reduce Body Weight.

Linaclotide is a synthetic peptide approved by the FDA for the treatment of constipation-predominant irritable bowel syndrome and chronic constipation. Linaclotide binds and activates the transmembrane receptor guanylate cyclase 2C (Gucy2c). Uroguanylin (UGN) is a 16 amino acid peptide that is mainly secreted by enterochromaffin cells in the duodenum and proximal small intestine. UGN is the endogenous ligand of Gucy2c and decreases body weight in diet-induced obese (DIO) mice via the activation of the thermogenic program in brown adipose tissue. Therefore, we wanted to evaluate whether oral linaclotide could also improve DIO mice metabolic phenotype. In this study, we have demonstrated that DIO mice orally treated with linaclotide exhibited a significant reduction of body weight without modifying food intake. Linaclotide exerts its actions through the central nervous system, and more specifically, via Gucy2c receptors located in the mediobasal hypothalamus, leading to the activation of the sympathetic nervous system to trigger the thermogenic activity of brown fat stimulating energy expenditure. These findings indicate for first time that, in addition to its effects at intestinal level to treat irritable bowel syndrome with constipation and chronic constipation, linaclotide also exerts a beneficial effect in whole body metabolism.

Soluble guanylate cyclase stimulator praliciguat attenuates inflammation, fibrosis, and end-organ damage in the Dahl model of cardiorenal failure.

Reduced nitric oxide (NO) and a decrease in cGMP signaling mediated by soluble guanylate cyclase (sGC) has been linked to the development of several cardiorenal diseases. Stimulation of sGC is a potential means for enhancing cGMP production in conditions of reduced NO bioavailability. The purpose of our studies was to determine the effects of praliciguat, a clinical-stage sGC stimulator, in a model of cardiorenal failure. Dahl salt-sensitive rats fed a high-salt diet to induce hypertension and organ damage were treated with the sGC stimulator praliciguat to determine its effects on hemodynamics, biomarkers of inflammation, fibrosis, tissue function, and organ damage. Praliciguat treatment reduced blood pressure, improved cardiorenal damage, and attenuated the increase in circulating markers of inflammation and fibrosis. Notably, praliciguat affected markers of renal damage at a dose that had minimal effect on blood pressure. In addition, liver fibrosis and circulating markers of tissue damage were attenuated in praliciguat-treated rats. Stimulation of the NO-sGC-cGMP pathway by praliciguat attenuated or normalized indicators of chronic inflammation, fibrosis, and tissue dysfunction in the Dahl salt-sensitive rat model. Stimulation of sGC by praliciguat may present an effective mechanism for treating diseases linked to NO deficiency, particularly those associated with cardiac and renal failure. Praliciguat is currently being evaluated in patients with diabetic nephropathy and heart failure with preserved ejection fraction.

The guanylate cyclase C agonist linaclotide ameliorates the gut-cardio-renal axis in an adenine-induced mouse model of chronic kidney disease.

BACKGROUND: Cardiorenal syndrome is a major cause of mortality in patients with chronic kidney disease (CKD). However, the involvement of detrimental humoral mediators in the pathogenesis of cardiorenal syndrome is still controversial. Trimethylamine-N-oxide (TMAO), a hepatic metabolic product of trimethylamine generated from dietary phosphatidylcholine or carnitine derived by the gut microbiota, has been linked directly with progression of cardiovascular disease and renal dysfunction. Thus, targeting TMAO may be a novel strategy for the prevention of cardiovascular disease and chronic kidney disease. METHODS: Linaclotide, a guanylate cyclase C agonist, was administered to adenine-induced renal failure (RF) mice and changes in renal function and levels of gut-derived uremic toxins, as well as the gut microbiota community, were analyzed using metabolomic and metagenomic methods to reveal its cardiorenal effect. RESULTS: Linaclotide decreased the plasma levels of TMAO at a clinically used low dose of 10 µg/kg in the adenine-induced RF mouse model. At a high concentration of 100 µg/kg, linaclotide clearly improved renal function and reduced the levels of various uremic toxins. A reduction in TMAO levels following linaclotide treatment was also observed in a choline-fed pro-atherosclerotic model. Linaclotide ameliorated renal inflammation and fibrosis and cardiac fibrosis, as well as decreased the expression of collagen I, transforming growth factor-ß, galectin-3 (Gal-3) and ST2 genes. Plasma levels of Gal-3 and ST2 were also reduced. Because exposure of cardiomyocytes to TMAO increased fibronectin expression, these data suggest that linaclotide reduced the levels of TMAO and various uremic toxins and may result in not only renal, but also cardiac, fibrosis. F4/80-positive macrophages were abundant in small intestinal crypts in RF mice, and this increased expression was decreased by linaclotide. Reduced colonic claudin-1 levels were also restored by linaclotide, suggesting that linaclotide ameliorated the 'leaky gut' in RF mice. Metagenomic analysis revealed that the microbial order Clostridiales could be responsible for the change in TMAO levels. CONCLUSION: Linaclotide reduced TMAO and uremic toxin levels and could be a powerful tool for the prevention and control of the cardiorenal syndrome by modification of the gut-cardio-renal axis.

Plecanatide for the treatment of chronic idiopathic constipation in adult patients.

Introduction. Chronic idiopathic constipation (CIC) is a functional gastrointestinal disorder that is associated with an increased healthcare cost and an abnormally poor quality of life. Plecanatide is a natural analog to the peptide agonist of the guanylate cyclase-C (GC-C) receptor, uroguanylin. The conversion of guanosine 5-triphosphate to cyclic guanosine monophosphate results in an increased bowel fluid secretion. Plecanatide is a promising new agent for CIC unresponsive to current therapeutic regimes.Areas covered. A comprehensive online search of Medline and the Science Citation Index was made using the keywords 'plecanatide', 'guanylate cyclase-C agonists', and 'constipation', in various combinations. We reviewed the pharmacodynamics, pharmacokinetics, and metabolism of this agent, and the most significant studies regarding the clinical efficacy and safety of plecanatide in CIC therapy.Expert opinion. Experimental studies showed that plecanatide was significantly better than placebo in reducing CIC severity, straining, stool consistency, bowel movements and quality of life. Apart from limited cases of diarrhea, no serious adverse events were reported. However, few data are available on its long-term safety. Furthermore, patients' affordability of plecanatide can be limited by its costs. Finally, this new agent with a different way of action can be proposed in patients refractory to common therapy.

[Pharmacological and clinical profile of linaclotide (Linzess®), a novel therapeutic agent for irritable bowel syndrome with constipation and chronic constipation].

Linaclotide (Linzess® tablets 0.25 mg) is a guanylate cyclase-C (GC-C) agonist with high selectivity and binding affinity to GC-C. In Japan, linaclotide was approved for 〝irritable bowel syndrome with constipation (IBS-C)〟 in December 2016 and 〝chronic constipation (CC) (excluding constipation due to organic disease)〟 in August 2018. Non-clinical studies demonstrated that linaclotide binding to GC-C increases intracellular cyclic guanosine monophosphate (cGMP), resulting in increased fluid secretion and gastrointestinal transit. In rats with colonic hyperalgesia, but not in normal rats, linaclotide suppressed the visceral nociceptive response, mediated by increased submucosal cGMP. In clinical studies in Japan, improvements were observed in the responder rates for global assessment of IBS symptom relief, complete spontaneous bowel movements in patients with IBS-C, and the frequency of spontaneous bowel movement in patients with CC, which were maintained during long-term treatment. Additionally, abdominal bloating, which has been associated with lower quality of life (QOL) and lower satisfaction with other approved therapies, and IBS QOL were improved throughout treatment with linaclotide. Diarrhea, a consequence of linaclotide's mechanism of action, was observed during the clinical studies, but was generally controllable by decreasing the linaclotide dose. No drug resistance was observed during the clinical studies, unlike some other approved agents. These results of non-clinical and clinical studies demonstrate that linaclotide can improve constipation, various abdominal symptoms, and QOL with a favorable safety profile in patients with IBS-C and CC.

Linaclotide for the treatment of chronic constipation.

INTRODUCTION: Chronic constipation (CC) is a common gastrointestinal disorder with limited treatment options. Linaclotide is a potent peptide agonist of the guanylate cyclase-C receptor. This action activates intracellular conversion of guanosine 5-triphosphate to cyclic guanosine monophosphate resulting in the stimulation of intestinal fluid secretion. Linaclotide is a promising new agent for refractory constipation. Areas covered: All published articles regarding the development, clinical efficacy, and safety of linaclotide in treating CC were reviewed. Pharmacodynamics, pharmacokinetics, and metabolism of this secretagogue agent were examined. Clinical studies showed that linaclotide increases the number of spontaneous bowel movements and stool consistency scores. Overall, patients reported relief from abdominal discomfort and severity of constipation. Finally, linaclotide has a good safety profile, with diarrhea being the main side effect. Expert opinion: Linaclotide appears to be a well-tolerated and effective agent for patients with CC, and could be effectively combined with other drugs in patients with refractory constipation. However, data on the efficacy and safety of linaclotide in pediatric patients and in opioid-induced constipation are currently limited and more studies need to be undertaken.

Oral treatment with plecanatide or dolcanatide attenuates visceral hypersensitivity via activation of guanylate cyclase-C in rat models.

AIM: To investigate the effects of plecanatide and dolcanatide on maintenance of paracellular permeability, integrity of tight junctions and on suppression of visceral hypersensitivity. METHODS: Transport of fluorescein isothiocyanate (FITC)-dextran was measured to assess permeability across cell monolayers and rat colon tissues. Effects of plecanatide and dolcanatide on the integrity of tight junctions in Caco-2 and T84 monolayers and on the expression and localization of occludin and zonula occludens-1 (ZO-1) were examined by immunofluorescence microscopy. Anti-nociceptive activity of these agonists was evaluated in trinitrobenzene sulfonic acid (TNBS)-induced inflammatory as well as in non-inflammatory partial restraint stress (PRS) rat models. Statistical significance between the treatment groups in the permeability studies were evaluated using unpaired t-tests. RESULTS: Treatment of T84 and Caco-2 monolayers with lipopolysaccharide (LPS) rapidly increased permeability, which was effectively suppressed when monolayers were also treated with plecanatide or dolcanatide. Similarly, when T84 and Caco-2 monolayers were treated with LPS, cell surface localization of tight junction proteins occludin and ZO-1 was severely disrupted. When cell monolayers were treated with LPS in the presence of plecanatide or dolcanatide, occludin and ZO-1 were localized at the cell surface of adjoining cells, similar to that observed for vehicle treated cells. Treatment of cell monolayers with plecanatide or dolcanatide without LPS did not alter permeability, integrity of tight junctions and cell surface localization of either of the tight junction proteins. In rat visceral hypersensitivity models, both agonists suppressed the TNBS-induced increase in abdominal contractions in response to colorectal distension without affecting the colonic wall elasticity, and both agonists also reduced colonic hypersensitivity in the PRS model. CONCLUSION: Our results suggest that activation of GC-C signaling might be involved in maintenance of barrier function, possibly through regulating normal localization of tight junction proteins. Consistent with these findings, plecanatide and dolcanatide showed potent anti-nociceptive activity in rat visceral hypersensitivity models. These results imply that activation of GC-C signaling may be an attractive therapeutic approach to treat functional constipation disorders and inflammatory gastrointestinal conditions.

Linaclotide inhibits colonic and urinary bladder hypersensitivity in adult female rats following unpredictable neonatal stress.

BACKGROUND: Irritable bowel syndrome (IBS) and bladder pain syndrome (BPS) are female-predominant, chronic functional pain disorders that are associated with early life stress (ELS) and therapeutic options for such patients remain limited. Linaclotide, a guanylate cyclase-C (GC-C) agonist, relieves abdominal pain and bowel symptoms in adult patients suffering from IBS with constipation. Here, we test the hypothesis that linaclotide will reverse colon and bladder hyperalgesia in a female-specific rodent model of adverse early life experience. METHODS: Neonatal rats were exposed to an odor-attachment learning paradigm of early life stress (ELS). In adulthood, the effect of linaclotide (3 µg kg-1  d-1 , p.o.) on colonic and bladder sensitivity was assessed via quantification of the visceromotor response to colorectal distension and the frequency of withdrawal responses to the application of von Frey hairs to the suprapubic region. In another cohort of rats, the effect of linaclotide on ELS-induced colonic and bladder permeability was investigated via measurements of transepithelial electrical resistance (TEER). KEY RESULTS: Rats exposed to unpredictable ELS exhibited colonic and bladder hypersensitivity that was significantly reduced by linaclotide compared to vehicle-treated controls. Colonic and bladder tissue isolated from adult rats exposed to unpredictable ELS exhibited a decrease in colonic and bladder TEER that was reversed by linaclotide. CONCLUSIONS AND INFERENCES: Our results demonstrate that neonatal rats exposed to unpredictable ELS develop increased sensitivity and permeability of the colon and bladder in adulthood through a mechanism involving activation of peripheral GC-C signaling.

Cyclic-GMP-Elevating Agents Suppress Polyposis in ApcMin mice by Targeting the Preneoplastic Epithelium.

The cGMP signaling axis has been implicated in the suppression of intestinal cancers, but the inhibitory mechanism and the extent to which this pathway can be targeted remains poorly understood. This study has tested the effect of cGMP-elevating agents on tumorigenesis in the ApcMin/+ mouse model of intestinal cancer. Treatment of ApcMin/+ mice with the receptor guanylyl-cyclase C (GCC) agonist linaclotide, or the phosphodiesterase-5 (PDE5) inhibitor sildenafil, significantly reduced the number of polyps per mouse (67% and 50%, respectively). Neither of the drugs affected mean polyp size, or the rates of apoptosis and proliferation. This was possibly due to increased PDE10 expression, as endogenous GCC ligands were not deficient in established polyps. These results indicated that the ability of these drugs to reduce polyp multiplicity was primarily due to an effect on nonneoplastic tissues. In support of this idea, ApcMin/+ mice exhibited reduced levels of endogenous GCC agonists in the nonneoplastic intestinal mucosa compared with wild-type animals, and this was associated with crypt hyperplasia and a loss of goblet cells. Administration of either sildenafil or linaclotide suppressed proliferation, and increased both goblet cell numbers and luminal apoptosis in the intestinal mucosa. Taken together, the results demonstrate that targeting cGMP with either PDE5 inhibitors or GCC agonists alters epithelial homeostasis in a manner that reduces neoplasia, and suggests that this could be a viable chemoprevention strategy for patients at high risk of developing colorectal cancer. Cancer Prev Res; 11(2); 81-92. ©2018 AACR.

Linaclotide activates guanylate cyclase-C/cGMP/protein kinase-II-dependent trafficking of CFTR in the intestine.

The transmembrane receptor guanylyl cyclase-C (GC-C), expressed on enterocytes along the intestine, is the molecular target of the GC-C agonist peptide linaclotide, an FDA-approved drug for treatment of adult patients with Irritable Bowel Syndrome with Constipation and Chronic Idiopathic Constipation. Polarized human colonic intestinal cells (T84, CaCo-2BBe) rat and human intestinal tissues were employed to examine cellular signaling and cystic fibrosis transmembrane conductance regulator (CFTR)-trafficking pathways activated by linaclotide using confocal microscopy, in vivo surface biotinylation, and protein kinase-II (PKG-II) activity assays. Expression and activity of GC-C/cGMP pathway components were determined by PCR, western blot, and cGMP assays. Fluid secretion as a marker of CFTR cell surface translocation was determined using in vivo rat intestinal loops. Linaclotide treatment (30 min) induced robust fluid secretion and translocation of CFTR from subapical compartments to the cell surface in rat intestinal loops. Similarly, linaclotide treatment (30 min) of T84 and CaCo-2BBe cells increased cell surface CFTR levels. Linaclotide-induced activation of the GC-C/cGMP/PKGII signaling pathway resulted in elevated intracellular cGMP and pVASPser239 phosphorylation. Inhibition or silencing of PKGII significantly attenuated linaclotide-induced CFTR trafficking to the apical membrane. Inhibition of protein kinase-A (PKA) also attenuated linaclotide-induced CFTR cell surface trafficking, implying cGMP-dependent cross-activation of PKA pathway. Together, these findings support linaclotide-induced activation of the GC-C/cGMP/PKG-II/CFTR pathway as the major pathway of linaclotide-mediated intestinal fluid secretion, and that linaclotide-dependent CFTR activation and recruitment/trafficking of CFTR from subapical vesicles to the cell surface is an important step in this process.

Bioactivity of Oral Linaclotide in Human Colorectum for Cancer Chemoprevention.

Guanylate cyclase C (GUCY2C) is a tumor-suppressing receptor silenced by loss of expression of its luminocrine hormones guanylin and uroguanylin early in colorectal carcinogenesis. This observation suggests oral replacement with a GUCY2C agonist may be an effective targeted chemoprevention agent. Linaclotide is an FDA-approved oral GUCY2C agonist formulated for gastric release, inducing fluid secretion into the small bowel to treat chronic idiopathic constipation. The ability of oral linaclotide to induce a pharmacodynamic response in epithelial cells of the colorectum in humans remains undefined. Here, we demonstrate that administration of 0.87 mg of oral linaclotide daily for 7 days to healthy volunteers, after oral colon preparation with polyethylene glycol solution (MoviPrep), activates GUCY2C, resulting in accumulation of its product cyclic (c)GMP in epithelial cells of the cecum, transverse colon, and distal rectum. GUCY2C activation by oral linaclotide was associated with homeostatic signaling, including phosphorylation of vasodilator-stimulated phosphoprotein and inhibition of proliferation quantified by reduced Ki67-positive epithelial cells. In the absence of the complete oral colonoscopy preparation, linaclotide did not alter cGMP production in epithelial cells of the colorectum, demonstrating that there was an effect related to the laxative preparation. These data show that the current FDA-approved formulation of oral linaclotide developed for small-bowel delivery to treat chronic idiopathic constipation is inadequate for reliably regulating GUCY2C in the colorectum to prevent tumorigenesis. The study results highlight the importance of developing a novel GUCY2C agonist formulated for release and activity targeted to the large intestine for colorectal cancer prevention. Cancer Prev Res; 10(6); 345-54. ©2017 AACR.