Pharmacologic properties, metabolism, and disposition of linaclotide, a novel therapeutic peptide approved for the treatment of irritable bowel syndrome with constipation and chronic idiopathic constipation

Characterization of disulfide bridges containing cyclic peptide Linaclotide and its degradation products by using LC-HRMS/MS

Linaclotide (LINA) is a first-in-class guanylate cyclase agonist used for treating irritable bowel syndrome with constipation (IBS-C) and chronic idiopathic constipation. Stress degradation studies were performed to examine LINA's intrinsic stability, adhering to International Council for Harmonisation of Technical ICH) guidelines Q1A (R2). The current study endeavours to elucidate the stability behavior of LINA by exposing various stress conditions. A simple LC method was developed for effective separation of all LINA degradation products using a Waters Symmetry C18 column (150 ×4.6 mm, 3.5 µm) as the stationary phase. The generated degradation products were identified and characterized by using high-resolution mass spectrometry (LC-HRMS), MS/MS studies. The mechanistic fragmentation pathway for the seven degradation products was established and the chemical structure for the identified degradation products was elucidated. LINA was susceptible to degrade under acidic, basic, neutral, photolytic, and oxidative conditions. A total of three Pseudo DPs, DP-1, DP-2, and DP-3, were formed under acidic conditions while using methanol as the co-solvent. Additionally, degradation products (DPs) were identified: DP-4 formed under basic stress condition and DP-5 under neutral, thermal, and photolytic conditions. Furthermore, DP-6 and DP-7 were formed under oxidative stress condition. This study established the mechanistic fragmentation pathways and elucidated the chemical structures of the degradation products, offering valuable insights for generics and novel formulation drug development.

Oxytocin Analogues for the Oral Treatment of Abdominal Pain

Abdominal pain presents an onerous reality for millions of people affected by gastrointestinal disorders such as irritable bowel syndrome (IBS) and inflammatory bowel diseases (IBD). The oxytocin receptor (OTR) has emerged as a new analgesic drug target with OTR expression upregulated on colon-innervating nociceptors in chronic visceral hypersensitivity states, accessible via luminal delivery. However, the low gastrointestinal stability of OTR's endogenous peptide ligand oxytocin (OT) is a bottleneck for therapeutic development. Here, we report the development of potent and fully gut-stable OT analogues, laying the foundation for a new area of oral gut-specific peptide therapeutics. Ligand optimisation guided by structure-gut-stability-activity relationships yielded highly stable analogues (t1/2>24 h, compared to t1/2<10 min of OT in intestinal fluid) equipotent to OT (~3 nM) and with enhanced OTR selectivity. Intra-colonic administration of the lead ligand significantly reduced colonic mechanical hypersensitivity in a concentration-dependent manner in a mouse model of chronic abdominal pain. Moreover, oral administration of the lead ligand also displayed significant analgesia in this abdominal pain mouse model. The generated ligands and employed strategies could pave the way to a new class of oral gut-specific peptides to study and combat chronic gastrointestinal disorders, an area with substantial unmet medical needs.

Application of linaclotide in bowel preparation for colonoscopy in patients with constipation: A prospective randomized controlled study

BACKGROUND AND AIM

Colonoscopy plays a crucial role in the early diagnosis and treatment of colorectal cancer. Adequate bowel preparation is essential for clear visualization of the colonic mucosa and lesion detection. However, inadequate bowel preparation is common in patients with constipation, and there is no standardized preparation protocol for these patients. This study aimed to explore the effectiveness and tolerability of a pre-colonoscopy combination regimen of linaclotide and polyethylene glycol (PEG).

METHODS

In this prospective, single-center, randomized controlled trial, 322 participants were divided into two groups: a 3-L PEG + 870-μg linaclotide group (administered as a single dose for 3 days) and a 4-L PEG group. The primary endpoints were the Boston Bowel Preparation Scale (BBPS) score and the rate of adequate and excellent bowel preparation. Secondary endpoints were the rates of detection of colonic adenomas and polyps, cecal intubation rates, colonoscopy time, adverse reactions, patient satisfaction, and physician satisfaction.

RESULTS

The study included 319 patients. The 3-L PEG + linaclotide group showed significantly higher rates of adequate and excellent bowel preparation than the 4-L PEG group (89.4% vs 73.6% and 37.5% vs 25.3%, respectively; P < 0.05). The mean BBPS score for the right colon in the 3-L PEG + linaclotide group was significantly higher than that in the 4-L PEG group. There were no significant between-group differences regarding the detection rates of colonic polyps and adenomas (44.4% vs 37.7% and 23.1% vs 20.1%, respectively; P > 0.05). There were no significant between-group differences regarding cecal intubation rates, colonoscopy operation, and withdrawal times. However, patient tolerance and sleep quality were better in the 3-L PEG + linaclotide group.

CONCLUSION

The combination of 3-L PEG and 870-μg linaclotide, because of its lower volume of intake, can be considered as an alternative bowel preparation regimen for constipated patients undergoing colonoscopy, especially for the elderly.

Triscysteine disulfide-directing motifs enabling design and discovery of multicyclic peptide binders

Peptides are valuable for therapeutic development, with multicyclic peptides showing promise in mimicking antigen-binding potency of antibodies. However, our capability to engineer multicyclic peptide scaffolds, particularly for the construction of large combinatorial libraries, is still limited. Here, we study the interplay of disulfide pairing between three biscysteine motifs, and designed a range of triscysteine motifs with unique disulfide-directing capability for regulating the oxidative folding of multicyclic peptides. We demonstrate that incorporating these motifs into random sequences allows the design of disulfide-directed multicyclic peptide (DDMP) libraries with up to four disulfide bonds, which have been applied for the successful discovery of peptide binders with nanomolar affinity to several challenging targets. This study encourages the use of more diverse disulfide-directing motifs for creating multicyclic peptide libraries and opens an avenue for discovering functional peptides in sequence and structural space beyond existing peptide scaffolds, potentially advancing the field of peptide drug discovery.

Safety and efficacy of linaclotide in children aged 2-5 years with functional constipation: Phase 2, randomized study

OBJECTIVES

Linaclotide, a guanylate cyclase-C agonist, was recently approved in the United States for the treatment of children 6-17 years of age with functional constipation (FC). This study evaluated the dose-response, safety, and efficacy of 4 weeks of linaclotide compared with placebo in children 2-5 years of age with FC.

METHODS

In this phase 2, randomized, double-blind, placebo-controlled, multidose study, 35 children with FC (based on Rome III criteria) were randomized 3:1 to receive linaclotide (18, 36, or 72 μg, for groups 1, 2, and 3, respectively) and 5:1 to receive linaclotide 9, 18, 36, or 72 μg (group 4), or matching placebo. Key endpoints were the changes from baseline in overall spontaneous bowel movement (SBM) frequency (SBMs/week), stool consistency, and straining, as well as the proportion of days with fecal incontinence during the study intervention period. Adverse events (AEs) were recorded.

RESULTS

Of the randomized patients, 34 (97.1%) completed the treatment period and 33 (94.3%) completed the posttreatment period. Mean change from baseline over the treatment period for three of the four key efficacy endpoints showed greater improvement in the linaclotide 72 μg group versus placebo. A dose-response trend was seen for stool consistency in patients receiving linaclotide. Four patients randomized to linaclotide experienced treatment-emergent AEs, one of which was treatment-related (mild diarrhea). All AEs were mild or moderate and none were severe.

CONCLUSIONS

Linaclotide was well tolerated in this pediatric population and an efficacy trend was seen with linaclotide 72 μg versus placebo.

Examining linaclotide for the treatment of chronic idiopathic constipation

INTRODUCTION

Chronic idiopathic constipation (CIC) is characterized by infrequent bowel movements and hard stools lasting for at least three months or longer. This disease affects 8-12% of the US population and 10-17% of the world population. Treatment and management involve identifying the primary cause, changing dietary habits, and adequate physical activity. Linaclotide is a guanylate cyclase-agonist acting locally in the luminal surface of the intestinal enterocyte leading to a signal transduction cascade, activation of the cystic fibrosis transmembrane conductance regulator (CFTR), thus increasing secretion of chloride and bicarbonate into the intestinal lumen with eventual increased intestinal fluid and faster transit time.

AREAS COVERED

We reviewed multiple studies and did a thorough literature review on CIC including its pathophysiology. Through this literature review, we were able to discuss and give the context and rationale for drug regimens indicated for CIC.

EXPERT OPINION

The era we live in right now is akin to nutrient-rich and fertilized soil as knowledge and resources are abundant. The opportunities and potential are endless. Constipation being more extensively studied, our understanding of medications and diseases broadens, leading to novel medications being discovered. Linaclotide is a pioneer in this aspect and can pave the way for future generations.

Clinical effects of chemical drugs, fecal microbiota transplantation, probiotics, dietary fiber, and acupuncture in the treatment of chronic functional constipation: a systematic review and network meta-analysis

Currently, there are increasingly diverse treatment modalities for chronic functional constipation (CFC). This study aims to compare the relative efficacy and safety of chemical drugs, fecal microbiota transplantation (FMT), probiotics, dietary fiber, and acupuncture in the treatment of patients with CFC. We searched relevant randomized controlled trials (RCTs) published in five databases up to November 2023. Network meta-analysis (NMA) was carried out using R Studio 4.2.1. Cumulative ranking probability plots, assessed through the surface under the cumulative ranking (SUCRA), were employed to rank the included drugs for various outcome measures. We included a total of 45 RCT studies with 17 118 patients with CFC. From the SUCRA values and NMA results FMT showed the best utility in terms of clinical efficacy, Bristol stool form scale scores, patient assessment of constipation quality of life scores, and the treatment modality with the lowest ranked incidence of adverse effects was electroacupuncture. Subgroup analysis of the chemotherapy group showed that sodium A subgroup analysis of the chemical group showed that sodium picosulfate 10 mg had the highest clinical efficacy. FMT is more promising in the treatment of CFC and may be more effective in combination with the relatively safe treatment of acupuncture.

Natural products from the human microbiome: an emergent frontier in organic synthesis and drug discovery

Often referred to as the "second genome", the human microbiome is at the epicenter of complex inter-habitat biochemical networks like the "gut-brain axis", which has emerged as a significant determinant of cognition, overall health and well-being, as well as resistance to antibiotics and susceptibility to diseases. As part of a broader understanding of the nexus between the human microbiome, diseases and microbial interactions, whether encoded secondary metabolites (natural products) play crucial signalling roles has been the subject of intense scrutiny in the recent past. A major focus of these activities involves harvesting the genomic potential of the human microbiome via bioinformatics guided genome mining and culturomics. Through these efforts, an impressive number of structurally intriguing antibiotics, with enhanced chemical diversity vis-à-vis conventional antibiotics have been isolated from human commensal bacteria, thereby generating considerable interest in their total synthesis and expanding their therapeutic space for drug discovery. These developments augur well for the discovery of new drugs and antibiotics, particularly in the context of challenges posed by mycobacterial resistance and emerging new diseases. The current landscape of various synthetic campaigns and drug discovery initiatives on antibacterial natural products from the human microbiome is captured in this review with an intent to stimulate further activities in this interdisciplinary arena among the new generation.

An insight into the pharmacology of cysteine/methionine containing peptide drugs

Since last century, peptides have emerged as potential drugs with >90 FDA approvals for various targets with several in the pipeline. Sulphur, in peptides is present either as thiol (-SH) from Cys or thioether from Met. In this review, all the peptides approved by FDA since 2000 containing sulphur have been included. Among them ∼50 % contains disulphide bridges. This clearly demonstrates the significance of disulphide bonds in peptide drugs. This can be achieved synthetically by using orthogonal protecting groups (PGs) for -SH. These PGs are compatible with Solid Phase Peptide Synthesis (SPPS), which is still the method of choice for peptide synthesis. The orthogonal PGs used for Cys thiol side chain protecting for disulphide bond formation have been included which are currently in use both by academia and industry from small scale to large scale synthesis. In addition, the details of the FDA approved drugs containing Cys and Met (or both) have also been discussed.

The evolutionary divergence of receptor guanylyl cyclase C has implications for preclinical models for receptor-directed therapeutics

Mutations in receptor guanylyl cyclase C (GC-C) cause severe gastrointestinal disease, including meconium ileus, early onset acute diarrhea, and pediatric inflammatory bowel disease that continues into adulthood. Agonists of GC-C are US Food and Drug Administration-approved drugs for the treatment of constipation and irritable bowel syndrome. Therapeutic strategies targeting GC-C are tested in preclinical mouse models, assuming that murine GC-C mimics human GC-C in its biochemical properties and downstream signaling events. Here, we reveal important differences in ligand-binding affinity and GC activity between mouse GC-C and human GC-C. We generated a series of chimeric constructs of various domains of human and mouse GC-C to show that the extracellular domain of mouse GC-C contributed to log-orders lower affinity of mouse GC-C for ligands than human GC-C. Further, the Vmax of the murine GC domain was lower than that of human GC-C, and allosteric regulation of the receptor by ATP binding to the intracellular kinase-homology domain also differed. These altered properties are reflected in the high concentrations of ligands required to elicit signaling responses in the mouse gut in preclinical models and the specificity of a GC inhibitor towards human GC-C. Therefore, our studies identify considerations in using the murine model to test molecules for therapeutic purposes that work as either agonists or antagonists of GC-C, and vaccines for the bacterial heat-stable enterotoxin that causes watery diarrhea in humans.

Defatted hempseed meal altered the metabolic profile of fermented yogurt and enhanced the ability to alleviate constipation in rats

BACKGROUND

Hempseeds (Cannabis sativa L.) are rich in easily digestible proteins, fats, polyunsaturated fatty acids, and insoluble fiber and are of high nutritional value. Probiotics have been found to relieve constipation, which solves a health problem that constantly troubles a lot of people. Therefore, the changes in the metabolites of fermented yogurt with or without 10% defatted hempseed meal (10% SHY or 0% SHY respectively) were studied and their laxative effects were examined through animal experiments.

RESULTS

Amino acids and peptides, terpene glycosides, carbohydrates, lineolic acids, and fatty acids were found to be the major contributors to the discrimination of the metabolic profile between 0% SHY and 10% SHY. The differentially accumulated metabolites may lead to the discrepancy in the yogurt's functionality. Animal experiments showed that the 10% SHY treatment prevented constipation by increasing feces number, fecal water content, and small intestinal transit rate and reducing inflammatory injury in loperamide-induced constipated rats. Further analysis of the gut microbiota revealed that 10% SHY gavage increased the relative abundances of the Lactobacillus, Allobaculum, Turicibacter, Oscillibacter, Ruminococcus, and Phascolarctobacterium genera in the constipated rats, whereas Akkermansia, Clostridium_XIVa, Bacteroides, Staphylococcus, and Clostridium_IV were decreased. The combination of defatted hempseed meal and probiotics was found to be effective in relieving constipation, probably due to the enriched amino acids and peptides, such as Thr-Leu and lysinoalanine through correlation analysis.

CONCLUSION

Our findings indicated that defatted hempseed meal in yogurt altered the metabolic profile and effectively alleviated constipation in rats, which is a promising therapeutic candidate for constipation. © 2023 Society of Chemical Industry.

Intestinal neuropod cell GUCY2C regulates visceral pain

Visceral pain (VP) is a global problem with complex etiologies and limited therapeutic options. Guanylyl cyclase C (GUCY2C), an intestinal receptor producing cyclic GMP(cGMP), which regulates luminal fluid secretion, has emerged as a therapeutic target for VP. Indeed, FDA-approved GUCY2C agonists ameliorate VP in patients with chronic constipation syndromes, although analgesic mechanisms remain obscure. Here, we revealed that intestinal GUCY2C was selectively enriched in neuropod cells, a type of enteroendocrine cell that synapses with submucosal neurons in mice and humans. GUCY2Chi neuropod cells associated with cocultured dorsal root ganglia neurons and induced hyperexcitability, reducing the rheobase and increasing the resulting number of evoked action potentials. Conversely, the GUCY2C agonist linaclotide eliminated neuronal hyperexcitability produced by GUCY2C-sufficient - but not GUCY2C-deficient - neuropod cells, an effect independent of bulk epithelial cells or extracellular cGMP. Genetic elimination of intestinal GUCY2C amplified nociceptive signaling in VP that was comparable with chemically induced VP but refractory to linaclotide. Importantly, eliminating GUCY2C selectively in neuropod cells also increased nociceptive signaling and VP that was refractory to linaclotide. In the context of loss of GUCY2C hormones in patients with VP, these observations suggest a specific role for neuropod GUCY2C signaling in the pathophysiology and treatment of these pain syndromes.

Randomised clinical trial: effects of MD-7246 on irritable bowel syndrome with diarrhoea

BACKGROUND

MD-7246, a delayed-release formulation of linaclotide, is designed to target the ileocaecal junction and caecum with the aim of relieving abdominal pain independently of bowel function.

AIMS

To evaluate the efficacy, safety and dose-response of MD-7246 in patients with irritable bowel syndrome with diarrhoea (IBS-D).

METHODS

A randomised, double-blind, phase 2 clinical trial enrolled adult patients with IBS-D (Rome IV criteria). Patients were randomised to placebo or once-daily oral MD-7246 300, 600 or 1200 μg for 12 weeks. Abdominal and bowel symptoms were assessed daily. Key efficacy endpoints were change from baseline in abdominal pain and responder rates for a 30% reduction in abdominal pain in 6/12 weeks. Additional abdominal pain responder and exploratory bowel function endpoints were also assessed.

RESULTS

Among the 388 randomised patients, there was no significant difference in mean change from baseline in abdominal pain between the MD-7246 300 μg, 600 μg and 1200 μg groups and placebo (-1.93, -1.58, -1.95 and - 2.01, respectively; p > 0.05 for each group vs placebo). The abdominal pain responder rates in the MD-7246 groups were similar to or lower than those in the placebo group. All doses of MD-7246 had a minimal effect on bowel function and were generally well tolerated.

CONCLUSIONS

MD-7246 at the doses studied did not improve abdominal pain relative to placebo in an IBS-D patient population. Similarly, most additional efficacy endpoints showed no improvement with MD-7246 relative to placebo.

Design and Measurement of Drug Tissue Concentration Asymmetry and Tissue Exposure-Effect (Tissue PK-PD) Evaluation

The "free drug hypothesis" assumes that, in the absence of transporters, the steady state free plasma concentrations equal to that at the site of action that elicit pharmacologic effects. While it is important to utilize the free drug hypothesis, exceptions exist that the free plasma exposures, either at C_max, C_trough, and C_average, or at other time points, cannot represent the corresponding free tissue concentrations. This "drug concentration asymmetry" in both total and free form can influence drug disposition and pharmacological effects. In this review, we first discuss options to assess total and free drug concentrations in tissues. Then various drug design strategies to achieve concentration asymmetry are presented. Last, the utilities of tissue concentrations in understanding exposure-effect relationships and translational projections to humans are discussed for several therapeutic areas and modalities. A thorough understanding in plasma and tissue exposures correlation with pharmacologic effects can provide insightful guidance to aid drug discovery.

Ex silico engineering of cystine-dense peptides yielding a potent bispecific T cell engager

Cystine-dense peptides (CDPs) are a miniprotein class that can drug difficult targets with high affinity and low immunogenicity. Tools for their design, however, are not as developed as those for small-molecule and antibody drugs. CDPs have diverse taxonomic origins, but structural characterization is lacking. Here, we adapted Iterative Threading ASSEmbly Refinement (I-TASSER) and Rosetta protein modeling software for structural prediction of 4298 CDP scaffolds and performed in silico prescreening for CDP binders to targets of interest. Mammalian display screening of a library of docking-enriched, methionine and tyrosine scanned (DEMYS) CDPs against PD-L1 yielded binders from four distinct CDP scaffolds. One was affinity-matured, and cocrystallography yielded a high-affinity (K_D = 202 pM) PD-L1-binding CDP that competes with PD-1 for PD-L1 binding. Its subsequent incorporation into a CD3-binding bispecific T cell engager produced a molecule with pM-range in vitro T cell killing potency and which substantially extends survival in two different xenograft tumor-bearing mouse models. Both in vitro and in vivo, the CDP-incorporating bispecific molecule outperformed a comparator antibody-based molecule. This CDP modeling and DEMYS technique can accelerate CDP therapeutic development.

On the Utility of Chemical Strategies to Improve Peptide Gut Stability

Inherent susceptibility of peptides to enzymatic degradation in the gastrointestinal tract is a key bottleneck in oral peptide drug development. Here, we present a systematic analysis of (i) the gut stability of disulfide-rich peptide scaffolds, orally administered peptide therapeutics, and well-known neuropeptides and (ii) medicinal chemistry strategies to improve peptide gut stability. Among a broad range of studied peptides, cyclotides were the only scaffold class to resist gastrointestinal degradation, even when grafted with non-native sequences. Backbone cyclization, a frequently applied strategy, failed to improve stability in intestinal fluid, but several site-specific alterations proved efficient. This work furthermore highlights the importance of standardized gut stability test conditions and suggests defined protocols to facilitate cross-study comparison. Together, our results provide a comparative overview and framework for the chemical engineering of gut-stable peptides, which should be valuable for the development of orally administered peptide therapeutics and molecular probes targeting receptors within the gastrointestinal tract.

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.

Impact of Intrinsic and Extrinsic Factors on the Pharmacokinetics of Peptides: When Is the Assessment of Certain Factors Warranted?

Peptides are short chains of 2 to 50 amino acids (molecular weight of less than 10 kDa) linked together by peptide bonds. As therapeutic agents, peptides are of interest because the body naturally produces many different peptides. Short-chain peptides have many advantages as compared with long-chain peptides (e.g., low toxicity). The first peptide corticotropin was approved in 1952 for multiple inflammatory diseases and West syndrome. Since then, more than 60 peptides have been approved by the FDA. Pharmacokinetics (PK) is widely used in modern-day drug development for designing a safe and efficacious dose to treat a wide variety of diseases. There are, however, several factors termed as “intrinsic” or “extrinsic” which can influence the PK of a drug, and as a result, one has to adjust the dose in a patient population. These intrinsic and extrinsic factors can be described as age, gender, disease states such as renal and hepatic impairment, drug–drug interaction, food, smoking, and alcohol consumption. It is well known that these intrinsic and extrinsic factors can have a substantial impact on the PK of small molecules, but for macromolecules, the impact of these factors is not well established. This review summarizes the impact of intrinsic and extrinsic factors on the PK of peptides.

Phase I double-blind, placebo-controlled trial of dolcanatide (SP-333) 27 mg to explore colorectal bioactivity in healthy volunteers

Guanylyl cyclase C (GUCY2C) is a tumor-suppressing receptor silenced by loss of expression of the 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. Previous studies revealed that linaclotide, an oral GUCY2C agonist formulated for gastric release, did not persist to activate guanylyl cyclase signaling in the distal rectum. Dolcanatide is an investigational oral uroguanylin analog, substituted with select D amino acids, for enhanced stability and extended persistence to activate GUCY2C in small and large intestine. However, the ability of oral dolcanatide to induce a pharmacodynamic (PD) response by activating GUCY2C in epithelial cells of the colorectum in humans remains undefined. Here, we demonstrate that administration of oral dolcanatide 27 mg daily for 7 d to healthy volunteers did not activate GUCY2C, quantified as accumulation of its product cyclic GMP, in epithelial cells of the distal rectum. These data reveal that the enhanced stability of dolcanatide, with persistence along the rostral-caudal axis of the small and large intestine, is inadequate to regulate GUCY2C across the colorectum to prevent tumorigenesis. These results highlight the importance of developing a GUCY2C agonist for cancer prevention formulated for release and activity targeted to the colorectum.

Chronic Refractory Constipation in Children: Think Beyond Stools

Chronic refractory constipation (CRC) is defined as children who are unable to pass stools in spite of being on maximum laxative therapy and require daily rectal stimulation in the form of enemas or suppositories to pass stools for >3 months. Children are often referred for treatment of refractory constipation that may result from uncontrolled underlying disease or ineffective treatment. Constipated children can be managed by a variety of medical therapeutic options that yield satisfying results in most cases. However, a subset of constipated children fails to benefit from conventional treatments. On treatment failure or on suspicion of organic disease the patient should be referred for further evaluation. Treatment options for treatment-resistant patients are presented. Pharmalogical and non-pharmalogical treatment modalities are reviewed and an algorithm for refractory constipation in children are presented.

Efficacy of Linaclotide in Reducing Abdominal Symptoms of Bloating, Discomfort, and Pain: A Phase 3B Trial Using a Novel Abdominal Scoring System

INTRODUCTION

Linaclotide improves abdominal pain and constipation in patients with constipation-predominant irritable bowel syndrome (IBS-C). Patients report additional bothersome abdominal symptoms of bloating and discomfort. The intention of this study was to evaluate linaclotide's efficacy in relieving IBS-C-related abdominal symptoms (bloating, discomfort, and pain) using a novel multi-item Abdominal Score (AS).

METHODS

Patients with IBS-C with abdominal pain ≥3 (0-10 scale) were randomized to linaclotide 290 μg or placebo daily for 12 weeks. The AS, derived from the Diary for IBS Symptoms-Constipation, is the average of abdominal bloating, discomfort, and pain at their worst (0 = none, 10 = worst possible). The primary end point was overall change from baseline (CFB) in AS. Secondary end points included CFB in 12-week AS evaluated using cumulative distribution function and 6-week/12-week AS responder (AS improvement ≥2 points for ≥6-week/12-week).

RESULTS

Overall, 614 patients (mean age 46.7 years; 81% female) were randomized. All prespecified end points showed significant benefit of linaclotide vs placebo. The mean overall CFB AS reduction for linaclotide was -1.9 vs -1.2 for placebo (P < 0.0001); the 6-week/12-week AS responder rate was 40.5% for linaclotide vs 23.4% for placebo (odds ratio = 2.2 [95% confidence interval, 1.55-3.12; P < 0.0001]). Diarrhea was the most common treatment-emergent adverse event (linaclotide = 4.6%, placebo = 1.6%).

DISCUSSION

Linaclotide significantly reduced multiple abdominal symptoms important to patients with IBS-C (bloating, discomfort, and pain) compared with placebo, as measured by a novel multi-item AS. The AS, derived from the Diary for IBS Symptoms-Constipation, should be considered for use in future IBS-C clinical studies to measure clinically meaningful improvements beyond traditional end points.

Plant-Derived Cyclotides Modulate κ-Opioid Receptor Signaling

Cyclotides are plant-derived disulfide-rich peptides comprising a cyclic cystine knot, which confers remarkable stability against thermal, proteolytic, and chemical degradation. They represent an emerging class of G protein-coupled receptor (GPCR) ligands. In this study, utilizing a screening approach of plant extracts and pharmacological analysis we identified cyclotides from Carapichea ipecacuanha to be ligands of the κ-opioid receptor (KOR), an attractive target for developing analgesics with reduced side effects and therapeutics for multiple sclerosis (MS). This prompted us to verify whether [T20K]kalata B1, a cyclotide in clinical development for the treatment of MS, is able to modulate KOR signaling. T20K bound to and fully activated KOR in the low μM range. We then explored the ability of T20K to allosterically modulate KOR. Co-incubation of T20K with KOR ligands resulted in positive allosteric modulation in functional cAMP assays by altering either the efficacy of dynorphin A1-13 or the potency and efficacy of U50,488 (a selective KOR agonist), respectively. In addition, T20K increased the basal response upon cotreatment with U50,488. In the bioluminescence resonance energy transfer assay T20K negatively modulated the efficacy of U50,488. This study identifies cyclotides capable of modulating KOR and highlights the potential of plant-derived peptides as an opportunity to develop cyclotide-based KOR modulators.

Pharmacological Inhibition of the Voltage-Gated Sodium Channel NaV1.7 Alleviates Chronic Visceral Pain in a Rodent Model of Irritable Bowel Syndrome

The human nociceptor-specific voltage-gated sodium channel 1.7 (hNa_V1.7) is critical for sensing various types of somatic pain, but it appears not to play a primary role in acute visceral pain. However, its role in chronic visceral pain remains to be determined. We used assay-guided fractionation to isolate a novel hNa_V1.7 inhibitor, Tsp1a, from tarantula venom. Tsp1a is 28-residue peptide that potently inhibits hNa_V1.7 (IC₅₀ = 10 nM), with greater than 100-fold selectivity over hNa_V1.3-hNa_V1.6, 45-fold selectivity over hNa_V1.1, and 24-fold selectivity over hNa_V1.2. Tsp1a is a gating modifier that inhibits Na_V1.7 by inducing a hyperpolarizing shift in the voltage-dependence of channel inactivation and slowing recovery from fast inactivation. NMR studies revealed that Tsp1a adopts a classical knottin fold, and like many knottin peptides, it is exceptionally stable in human serum. Remarkably, intracolonic administration of Tsp1a completely reversed chronic visceral hypersensitivity in a mouse model of irritable bowel syndrome. The ability of Tsp1a to reduce visceral hypersensitivity in a model of irritable bowel syndrome suggests that pharmacological inhibition of hNa_V1.7 at peripheral sensory nerve endings might be a viable approach for eliciting analgesia in patients suffering from chronic visceral pain.

Improving the Gastrointestinal Stability of Linaclotide

High susceptibility to proteolytic degradation in the gastrointestinal tract limits the therapeutic application of peptide drugs in gastrointestinal disorders. Linaclotide is an orally administered peptide drug for the treatment of irritable bowel syndrome with constipation (IBS-C) and abdominal pain. Linaclotide is however degraded in the intestinal environment within 1 h, and improvements in gastrointestinal stability might enhance its therapeutic application. We therefore designed and synthesized a series of linaclotide analogues employing a variety of strategic modifications and evaluated their gastrointestinal stability and pharmacological activity at its target receptor guanylate cyclase-C. All analogues had substantial improvements in gastrointestinal half-lives (>8 h vs linaclotide 48 min), and most remained active at low nanomolar concentrations. This work highlights strategic approaches for the development of gut-stable peptides toward the next generation of orally administered peptide drugs for the treatment of gastrointestinal disorders.

Single- and Multiple-Dose Pharmacokinetics and Pharmacodynamics of PN-943, a Gastrointestinal-Restricted Oral Peptide Antagonist of α4β7, in Healthy Volunteers

PN‐943 is an orally stable, gastrointestinal‐restricted peptide that binds specifically to α4ß7 integrin on leukocytes, blocking leukocyte trafficking to and activation in the gut, inhibiting colon inflammation and reducing signs and symptoms of active ulcerative colitis. Two pharmacokinetic/pharmacodynamic studies were conducted in healthy volunteers. Study 1 was a first‐in‐human study with 40 male subjects receiving PN‐943, 100 to 1400 mg or placebo, as single doses and 57 male subjects receiving PN‐943, 100 to 1000 mg or placebo, as multiple doses. Study 2 was a randomized, crossover study comparing multiple doses of 450‐mg PN‐943 twice daily as a liquid solution and as an immediate‐release tablet in 10 subjects. No subjects discontinued due to treatment‐emergent adverse events. Consistent with the gastrointestinal‐restricted nature of the peptide, systemic exposure was minimal; there was an approximate dose‐proportional increase in area under the plasma concentration–time curve. There was minimal accumulation with once‐daily dosing and an absence of time‐dependent changes in pharmacokinetics. Administration of PN‐943 after a high‐fat meal reduced peak plasma concentration and area under the plasma concentration–time curve. There was minimal (<0.1%) urinary excretion of intact drug, and there was a dose‐related increase in fecal excretion of intact PN‐943. Dose‐dependent increases in blood receptor occupancy and reduction in blood receptor expression were observed, supporting target engagement. Twice‐daily dosing resulted in sustained receptor occupancy with low plasma fluctuations (143%). PN‐943 was generally well tolerated following single and multiple oral doses with low systemic exposure. Twice‐daily dosing resulted in sustained pharmacokinetics and pharmacodynamics, supporting further investigation in efficacy studies.

Trends in peptide drug discovery

Since the introduction of insulin almost a century ago, more than 80 peptide drugs have reached the market for a wide range of diseases, including diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain. In this Perspective, we summarize key trends in peptide drug discovery and development, covering the early efforts focused on human hormones, elegant medicinal chemistry and rational design strategies, peptide drugs derived from nature, and major breakthroughs in molecular biology and peptide chemistry that continue to advance the field. We emphasize lessons from earlier approaches that are still relevant today as well as emerging strategies such as integrated venomics and peptide-display libraries that create new avenues for peptide drug discovery. We also discuss the pharmaceutical landscape in which peptide drugs could be particularly valuable and analyse the challenges that need to be addressed for them to reach their full potential.

[Efficacy and Safety of Linaclotide in Elderly Patients]

The efficacy and safety of linaclotide in elderly patients are poorly understood. Herein, we aimed to assess the efficacy and safety of linaclotide in elderly patients in real-world setting. We retrospectively enrolled consecutive patients who started linaclotide therapy at Sapporo Medical University Hospital from October 1, 2017 to December 31, 2019. The efficacy and safety of linaclotide were examined in relation to various factors, including age (<65 or ≥65 years) and dose (0.25 or 0.5 mg/d). Fifty-two patients were enrolled, 60% of whom were over 65 years old and 40% were female. Thirty-six patients received a linaclotide dose of 0.25 mg/d. The most common side effect was diarrhea, but there was no difference in the incidence of diarrhea between the elderly (64.5%) and non-elderly patients (42.9%, p=0.130). No significant difference was observed with respect to improvement in constipation in the elderly (83.9%) and non-elderly patients (71.4%, p=0.318). Additionally, the difference in efficacy of linaclotide in patients who received a reduced dose (80.6%) vs. those who received the recommended dose (75.0%) was not statistically significant (p=0.719). Multivariate analysis revealed that age, gender, and dose were not associated with diarrhea induced by linaclotide treatment. However, concurrent treatment with constipation-inducing medications [odds ratio (OR) 5.79, p=0.047] and linaclotide monotherapy (OR 11.1, p=0.040) were both risk factors contributing to diarrhea. Linaclotide is effective and safe for use in elderly patients. The incidence of diarrhea may increase when linaclotide is administered alone or concurrently used with medications that cause constipation.

Randomized Trial of 2 Delayed-Release Formulations of Linaclotide in Patients With Irritable Bowel Syndrome With Constipation

INTRODUCTION

Immediate-release (IR) formulation of linaclotide 290 μg improves abdominal pain and constipation (APC) in patients with irritable bowel syndrome (IBS) with constipation. Delayed-release (DR) formulations were developed on the premise that targeting the ileum (delayed-release formulation 1 [DR1]) or ileocecal junction and cecum (MD-7246, formerly DR2) would modulate linaclotide's secretory effects while preserving pain relief effects.

METHODS

This phase 2b study randomized patients with IBS with constipation to placebo or 1 of 7 once-daily linaclotide doses (DR1 30, 100, or 300 μg; MD-7246 30, 100, or 300 μg; or IR 290 μg) for 12 weeks. Key efficacy endpoints were change from baseline in abdominal pain and complete spontaneous bowel movement frequency, and 6/12-week combined APC+1 responder rate.

RESULTS

Overall, 532 patients were randomized; mean age was 45.1 years, and most were women (83.3%) and White (64.7%). All linaclotide DR1 and MD-7246 groups experienced greater improvements in abdominal pain from baseline and vs placebo throughout treatment. Linaclotide DR1 and IR led to numerically greater improvements from baseline in complete spontaneous bowel movement frequency and higher APC+1 responder rates compared with placebo; MD-7246 results were similar to placebo. Diarrhea was the most common adverse event with DR1 and IR; rates were similar between MD-7246 and placebo.

DISCUSSION

Altering the site of drug delivery in the intestine might uncouple linaclotide's pain relief from secretory effects. Persistent, modest abdominal pain improvement with limited impact on bowel symptom parameters, as seen across MD-7246 doses, warrants further study of MD-7246 as a novel treatment for abdominal pain, regardless of IBS subtype.

Uncontrolled, Open-Label Pre-Dinner Administration of Elobixibat in Japanese Adults with Chronic Constipation: A Retrospective Chart Review

BACKGROUND

Elobixibat has been approved as a new therapeutic drug for chronic constipation. Only the pharmacological efficacy and safety profile of pre-breakfast administration of elobixibat had been previously demonstrated.

OBJECTIVE

We evaluated the efficacy and safety profile of pre-dinner administration of elobixibat in patients with functional constipation in a retrospective observational study.

METHODS

Patients aged 20 years or older diagnosed with functional constipation by the Rome IV criteria from June 1, 2018, to January 17, 2019. The evaluation time points were at the start and 1, 2, 4, and 8 weeks after treatment. The primary end point was frequency of spontaneous bowel movements per week. The secondary end points were changes in Bristol Stool Form Scale score, onset time required for spontaneous defecation after administration, percent of patients with spontaneous defecation within 24 hours and 48 hours after the first administration, improvement of abdominal pain or abdominal bloating evaluated by a visual analog scale, and total score and each subscore of the Japanese-Translated Version of Patient Assessment of Constipation Quality of Life Questionnaire.

RESULTS

Pre-dinner administration of elobixibat was associated with significantly increased frequency of spontaneous bowel movements and improved Bristol Stool Form Scale score at 1, 2, 4, and 8 weeks after treatment. The mean onset time until spontaneous defecation after treatment was 4 to 5 hours, which was earlier than that by conventional constipation treatment drugs and almost constant within an individual during the treatment period. Spontaneous defecation was achieved by 85.4% within 24 hours and 90.2% within 48 hours after the first administration. Elobixibat also improved patients' quality of life, which was evaluated by the Japanese-Translated Version of Patient Assessment of Constipation Quality of Life Questionnaire without adverse events.

CONCLUSIONS

Pre-dinner administration of elobixibat improved constipation, abdominal pain and bloating, and patient quality of life by management of fixed defecation. (Curr Ther Res Clin Exp. 2020; 81:XXX-XXX).

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-β, 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.

Miniproteins as a Powerful Modality in Drug Development

Miniproteins are a diverse group of protein scaffolds characterized by small (1-10 kDa) size, stability, and versatility in drug-like roles. Coming largely from native sources, they have been widely adopted into drug development pipelines. While their structures and capabilities are diverse, the approaches to their utilization share more similarities with each other than with more widely used modalities (e.g., antibodies or small molecules). In this review, we highlight recent advances in miniprotein-based approaches to otherwise poorly addressed clinical needs, including structure-based and functional characterization. We also summarize their unique screening strategies and pharmacology considerations. Through a greater understanding of the unique properties that make them attractive for drug design, miniproteins can be effectively utilized against targets that are intractable by other approaches.

Appropriate Use of Laxatives in the Older Person

Constipation is a common condition, affecting up to half of all older adults during their lifetime. Untreated constipation has significant impacts, decreasing quality of life and potentially leading to urinary and/or faecal incontinence, faecal impaction and, in severe cases, hospitalisation. The increased constipation prevalence among older populations is multifactorial, with a number of age-related factors contributing to the rise in prevalence with aging. Laxatives are the mainstay of constipation management and are commonly used among older populations for both treatment and prevention of constipation. A range of laxative types including bulk forming agents, softeners and emollients, osmotic agents, stimulants, and the newer prokinetic and secretory agents are available. Despite laxatives being freely available without prescription in many countries and commonly used by older individuals, evidence regarding the effectiveness or safety of most laxatives in older populations is lacking. Additionally, age-related changes increase the risk of adverse effects associated with laxatives, such as electrolyte disturbances, among older persons. Caution must be taken when extrapolating recommendations for general adult populations to older populations. Laxative choice for older individuals should be tailored after careful assessment and consideration of comorbid conditions, concomitant medications and the potential for adverse effects.

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.

Physiology of Electrolyte Transport in the Gut: Implications for Disease

We now have an increased understanding of the genetics, cell biology, and physiology of electrolyte transport processes in the mammalian intestine, due to the availability of sophisticated methodologies ranging from genome wide association studies to CRISPR-CAS technology, stem cell-derived organoids, 3D microscopy, electron cryomicroscopy, single cell RNA sequencing, transgenic methodologies, and tools to manipulate cellular processes at a molecular level. This knowledge has simultaneously underscored the complexity of biological systems and the interdependence of multiple regulatory systems. In addition to the plethora of mammalian neurohumoral factors and their cross talk, advances in pyrosequencing and metagenomic analyses have highlighted the relevance of the microbiome to intestinal regulation. This article provides an overview of our current understanding of electrolyte transport processes in the small and large intestine, their regulation in health and how dysregulation at multiple levels can result in disease. Intestinal electrolyte transport is a balance of ion secretory and ion absorptive processes, all exquisitely dependent on the basolateral Na⁺ /K⁺ ATPase; when this balance goes awry, it can result in diarrhea or in constipation. The key transporters involved in secretion are the apical membrane Cl^- channels and the basolateral Na⁺ -K⁺ -2Cl^- cotransporter, NKCC1 and K⁺ channels. Absorption chiefly involves apical membrane Na⁺ /H⁺ exchangers and Cl^- /HCO₃ ^- exchangers in the small intestine and proximal colon and Na⁺ channels in the distal colon. Key examples of our current understanding of infectious, inflammatory, and genetic diarrheal diseases and of constipation are provided. © 2019 American Physiological Society. Compr Physiol 9:947-1023, 2019.

Design and Synthesis of Cross-Link-Dense Peptides by Manipulating Regioselective Bisthioether Cross-Linking and Orthogonal Disulfide Pairing

Existing disulfide-rich peptides, both naturally occurring and de novo designed, only represent a tiny amount of the possible sequence space because natural evolution and de novo design only keep sequences that are structurally approachable by correct disulfide pairings. To bypass this limitation for designing new peptide scaffolds beyond the natural sequence space, we dedicate to developing novel disulfide-rich peptides with predefined disulfide pairing patterns irrelevant to primary sequences. However, most of these designed peptides still suffer from disulfide rearrangements to at least one to three possible isomers. Here, we report a general and reliable strategy for the design and synthesis of a range of structurally diverse cross-link-dense peptide (CDP) scaffolds with two orthogonal disulfide bonds and a bisthioether bridge that are not subject to disulfide isomerizations. Altering the pattern of cysteine and penicillamine generates hundreds of different CDP scaffolds tolerant to extensive sequence manipulations. This work thus provides many useful scaffolds for the design of functional molecules such as protein binders with improved proteolytic stability (e.g., designed by epitope grafting).

Effectiveness and tolerability of linaclotide in the treatment of IBS-C in a "real-life" setting: Results from a Portuguese single-center study

BACKGROUND

Although linaclotide has been approved to treat moderate to severe IBS-C, no data are available on its effectiveness and tolerability in patients in a real-life setting.

METHODS

A prospective single-center study of the effectiveness and tolerability of linaclotide was carried out on patients (n = 40) with moderate to severe IBS-C, all fulfilling the Rome IV criteria. Clinical information was recorded using a dietary questionnaire at baseline, and 3 and 6 months after initiating treatment. The end-points to measure effectiveness included abdominal pain and bloating (11-NRS), the number of bowel movements and patient satisfaction. Tolerability was assessed through the frequency of adverse events.

KEY RESULTS

In terms of efficacy, an improvement in abdominal pain and in the intensity of bloating was evident in the cohort after 6 months of linaclotide therapy. The proportion of patients with moderate or severe symptoms of bloating fell from 93.3% to 33.3% and those with pain from 93.4% to 20%. Weekly bowel movements also improved and accordingly, 97% of the patients were moderately or very satisfied with the treatment. At the end of the study, diarrhea was the most frequent adverse event (10%), although it was considered mild in 66.7% of these subjects and moderate in 33.3%. A lack of efficacy (n = 3) and excessive diarrhea (n = 7) were motives for discontinuing the treatment.

CONCLUSIONS AND INFERENCES

Linaclotide proved to be a safe and effective drug to reduce the main symptoms of IBS-C in everyday clinical practice, with an improvement comparable to that seen in clinical trials.

pDobz/pDobb protected diaminodiacid as a novel building block for peptide disulfide-bond mimic synthesis

The diaminodiacid strategy has been widely studied in the chemical synthesis of peptide disulfide bond mimics. Diaminodiacid building blocks, which are key intermediates, are currently under the spotlight. However, one technical bottleneck inherent in existing building blocks is the contamination problem caused by the heavy metal reagents during the deprotection process, which makes the peptides less suitable for pharmaceutical use. Herein, we describe the successful development of a p-dihydroxyborylbenzyloxycarbonyl pinacol ester (pDobz)- and p-dihydroxyborylbenzyl pinacol ester (pDobb)-based novel diaminodiacid building block that can be easily deprotected via mild treatment with amine oxide. Its efficiency and practicability were also confirmed by the total synthesis of contryphan-Vn disulfide bond mimic. The results suggested that this novel diaminodiacid building block has satisfactory Fmoc SPPS compatibility, yet only required a facile, rapid, and metal-free deprotection process. We believe this novel diaminodiacid building block could promote further development of the diaminodiacid strategy.

The total synthesis of a contryphan-Vn disulfide bond mimic utilizing a novel pDobz/pDobb based diaminodiacid building block via the diaminodiacid strategy.

High-dose linaclotide is effective and safe in patients with chronic constipation: A phase III randomized, double-blind, placebo-controlled study with a long-term open-label extension study in Japan

BACKGROUND

A previous phase II dose-ranging study of linaclotide in a Japanese chronic constipation (CC) population showed that 0.5 mg was the most effective dose. This study aimed to verify the hypothesis that 0.5 mg of linaclotide is effective and safe in Japanese CC patients.

METHODS

This was a Japanese phase III randomized, double-blind, placebo-controlled (part 1), and long-term, open-label extension (part 2) study of linaclotide. CC patients (n = 186) diagnosed using the Rome III criteria were randomly assigned to linaclotide 0.5 mg (n = 95) or placebo (n = 91) for a 4-week double-blind treatment period in part 1, followed by an additional 52 weeks of open-label treatment with linaclotide in part 2. The primary efficacy endpoint was the change from baseline in weekly spontaneous bowel movement (SBM) frequency at the first week. Secondary endpoints included responder rate for complete SBM (CSBM), changes in stool consistency, and severity of straining.

KEY RESULTS

Part 1: Change in weekly mean SBM frequency in the first week of treatment with linaclotide (4.02) was significantly greater than that with placebo (1.48, P < 0.001). Linaclotide produced a higher CSBM responder rate (52.7%) compared to placebo (26.1%, P < 0.001). Part 2: Patients continued to show improved SBM frequency with linaclotide. Through parts 1 and 2, the most common drug-related adverse event was mild and occasionally moderate diarrhea.

CONCLUSIONS AND INFERENCES

The results of this study indicate that a linaclotide dose of 0.5 mg/day is effective and safe in Japanese CC patients.

Dose-finding study of linaclotide in Japanese patients with chronic constipation: A phase II randomized, double-blind, and placebo-controlled study

BACKGROUND

Based on the previous phase II/III studies of irritable bowel syndrome with constipation (IBS-C) in Japan that demonstrated the efficacy and safety of linaclotide 0.5 mg/d, we evaluated linaclotide at doses of 0.5 mg/d and lower in the treatment of Japanese patients with chronic constipation (CC).

METHODS

This was a phase II randomized, double-blind, placebo-controlled, dose-finding study of linaclotide for Japanese patients with CC (n = 382, 64 men, 318 women, age 20-75). After a baseline period of two weeks, patients were randomized to receive placebo (n = 80), or 0.0625 mg (n = 82), 0.125 mg (n = 71), 0.25 mg (n = 73) or 0.5 mg (n = 76) of linaclotide during a two-week treatment period. The primary efficacy endpoint was change from baseline in weekly spontaneous bowel movement (SBM) frequency during the first week. Secondary endpoints included complete SBM (CSBM) responder rates and IBS-QOL. Safety and adverse events were also evaluated.

KEY RESULTS

The change in SBM frequency during the first week (mean) was 3.89, 3.11, 3.87, and 3.85 for 0.0625 mg, 0.125 mg, 0.25 mg, and 0.5 mg for linaclotide, significantly higher than for placebo (1.91, P < 0.05). The CSBM responder, which is an important parameter, showed the greatest improvement at the 0.5 mg during the 2 week. The most frequent adverse event in the linaclotide groups was diarrhea.

CONCLUSIONS & INFERENCES

Our results suggest that 0.0625, 0.125, 0.25, and 0.5 mg/d are effective doses of linaclotide for treating CC in Japanese patients. ClinicalTrials.gov: NCT02425722, supported by Astellas Pharma, Inc.

Pharmacokinetics of Toxin-Derived Peptide Drugs

Toxins and venoms produced by different organisms contain peptides that have evolved to have highly selective and potent pharmacological effects on specific targets for protection and predation. Several toxin-derived peptides have become drugs and are used for the management of diabetes, hypertension, chronic pain, and other medical conditions. Despite the similarity in their composition (amino acids as the building blocks), toxin-derived peptide drugs have very profound differences in their structure and conformation, in their physicochemical properties (that affect solubility, stability, etc.), and subsequently in their pharmacokinetics (the processes of absorption, distribution, metabolism, and elimination following their administration to patients). This review summarizes and critically analyzes the pharmacokinetic properties of toxin-derived peptide drugs: (1) the relationship between the chemical structure, physicochemical properties, and the pharmacokinetics of the specific drugs, (2) the major pharmacokinetic properties and parameters of these drugs, and (3) the major pharmacokinetic variability factors of the individual drugs. The structural properties of toxin-derived peptides affect their pharmacokinetics and pose some limitations on their clinical use. These properties should be taken into account during the development of new toxin-derived peptide drugs, and for the efficient and safe use of the clinically approved drugs from this group in the individual patients.

Linaclotide improves gastrointestinal transit in cystic fibrosis mice by inhibiting sodium/hydrogen exchanger 3

Gastrointestinal dysfunction in cystic fibrosis (CF) is a prominent source of pain among patients with CF. Linaclotide, a guanylate cyclase C (GCC) receptor agonist, is a US Food and Drug Administration-approved drug prescribed for chronic constipation but has not been widely used in CF, as the cystic fibrosis transmembrane conductance regulator (CFTR) is the main mechanism of action. However, anecdotal clinical evidence suggests that linaclotide may be effective for treating some gastrointestinal symptoms in CF. The goal of this study was to determine the effectiveness and mechanism of linaclotide in treating CF gastrointestinal disorders using CF mouse models. Intestinal transit, chloride secretion, and intestinal lumen fluidity were assessed in wild-type and CF mouse models in response to linaclotide. CFTR and sodium/hydrogen exchanger 3 (NHE3) response to linaclotide was also evaluated. Linaclotide treatment improved intestinal transit in mice carrying either F508del or null Cftr mutations but did not induce detectable Cl^- secretion. Linaclotide increased fluid retention and fluidity of CF intestinal contents, suggesting inhibition of fluid absorption. Targeted inhibition of sodium absorption by the NHE3 inhibitor tenapanor produced improvements in gastrointestinal transit similar to those produced by linaclotide treatment, suggesting that inhibition of fluid absorption by linaclotide contributes to improved gastrointestinal transit in CF. Our results demonstrate that linaclotide improves gastrointestinal transit in CF mouse models by increasing luminal fluidity through inhibiting NHE3-mediated sodium absorption. Further studies are necessary to assess whether linaclotide could improve CF intestinal pathologies in patients. GCC signaling and NHE3 inhibition may be therapeutic targets for CF intestinal manifestations. NEW & NOTEWORTHY Linaclotide's primary mechanism of action in alleviating chronic constipation is through cystic fibrosis transmembrane conductance regulator (CFTR), negating its use in patients with cystic fibrosis (CF). For the first time, our findings suggest that in the absence of CFTR, linaclotide can improve fluidity of the intestinal lumen through the inhibition of sodium/hydrogen exchanger 3. These findings suggest that linaclotide could improve CF intestinal pathologies in patients.

Chronic linaclotide treatment reduces colitis-induced neuroplasticity and reverses persistent bladder dysfunction

Irritable bowel syndrome (IBS) patients suffer from chronic abdominal pain and extraintestinal comorbidities, including overactive bladder (OAB) and interstitial cystitis/painful bladder syndrome (IC-PBS). Mechanistic understanding of the cause and time course of these comorbid symptoms is lacking, as are clinical treatments. Here, we report that colitis triggers hypersensitivity of colonic afferents, neuroplasticity of spinal cord circuits, and chronic abdominal pain, which persists after inflammation. Subsequently, and in the absence of bladder pathology, colonic hypersensitivity induces persistent hypersensitivity of bladder afferent pathways, resulting in bladder-voiding dysfunction, indicative of OAB/IC-PBS. Daily administration of linaclotide, a guanylate cyclase-C (GC-C) agonist that is restricted to and acts within the gastrointestinal tract, reverses colonic afferent hypersensitivity, reverses neuroplasticity-induced alterations in spinal circuitry, and alleviates chronic abdominal pain in mice. Intriguingly, daily linaclotide administration also reverses persistent bladder afferent hypersensitivity to mechanical and chemical stimuli and restores normal bladder voiding. Linaclotide itself does not inhibit bladder afferents, rather normalization of bladder function by daily linaclotide treatment occurs via indirect inhibition of bladder afferents via reduced nociceptive signaling from the colon. These data support the concepts that cross-organ sensitization underlies the development and maintenance of visceral comorbidities, while pharmaceutical treatments that inhibit colonic afferents may also improve urological symptoms through common sensory pathways.

Gut Movements: A Review of the Physiology of Gastrointestinal Transit

The well-regulated mechanisms of intestinal transit favor aboral movement of intestinal contents during the formation of normal stool. Electrical pacemakers initiate mechanical smooth muscular propulsion under regulation by the enteric nervous system-a function of the "brain-gut axis." Several unique intestinal motor patterns function in concert to enhance the activities of intestinal transit. Development of pharmacologic targets of intestinal transit mechanisms afford clinicians control in the management of functional gastrointestinal disorders. This review highlights the important physiologic events of intestinal transit, discusses selected pharmacologic and neuromodulators involved in these processes, and provides relevant clinical correlates to physiologic events.

Demonstration of differences in colonic volumes, transit, chyme consistency, and response to psyllium between healthy and constipated subjects using magnetic resonance imaging

BACKGROUND

In functional gastrointestinal disorders a lack of objective biomarkers limits evaluation of underlying mechanisms. We aimed to demonstrate the utility of magnetic resonance imaging for this task using psyllium, an effective constipation treatment, in patients and controls.

METHODS

Two crossover studies: (i) adults without constipation (controls, n = 9) took three treatments in randomized order for 6 days - maltodextrin (placebo), psyllium 3.5 g t.d.s and 7 g t.d.s., (ii) adults with chronic constipation (patients, n = 20) took placebo and psyllium 7 g t.d.s. for 6 days. MRI was performed fasting and postprandially on day 6. Measurements included small bowel and ascending colon water content, colonic volume, transit time, and MR relaxometry (T1, T2) to assess colonic chyme. Stool water percentage was measured.

RESULTS

7 g psyllium t.d.s. increased fasting colonic volumes in controls from median 372 mL (IQR 284-601) to 578 mL (IQR 510-882), and in patients from median 831 mL (IQR 745-934) to 1104 mL (847-1316), P < .05. Mean postprandial small bowel water was higher in controls and patients after 7 g psyllium t.d.s. vs placebo. Whole gut transit was slower in patients than controls (P < .05). T1 of the descending colon chyme (fasting) was lower in patients (213 ms, 176-420) than controls (440 ms, 352-884, P < .05) on placebo, but increased by 7 g psyllium t.d.s. (590 ms, 446-1338), P < .001. Descending colon T1 correlated with baseline stool water content and stool frequency on treatment.

CONCLUSIONS AND INFERENCES

MRI measurements can objectively demonstrate the mode of action of therapy targeting intestinal fluid content in constipation.

Guanylate cyclase-C as a therapeutic target in gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs) and IBDs are two of the most prevalent disorders of the GI tract and consume a significant proportion of healthcare resources. Recent studies have shown that membrane-bound guanylate cyclase-C (GC-C) receptors lining the GI tract may serve as novel therapeutic targets in the treatment of FGIDs and IBDs. GC-C receptor activation by its endogenous paracrine hormones uroguanylin and guanylin, and the resulting intracellular production of its downstream effector cyclic GMP, occurs in a pH-dependent manner and modulates key physiological functions. These include fluid and electrolyte homeostasis, maintenance of the intestinal barrier, anti-inflammatory activity and regulation of epithelial regeneration. Studies of the GC-C paracrine signalling axis have revealed the therapeutic potential of these receptors in treating GI disorders, including chronic idiopathic constipation and irritable bowel syndrome-constipation. This review focuses on the evolving understanding of GC-C function in health and disease, and strategies for translating these principles into new treatments for FGIDs and IBDs.

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.