Linaclotide, Novel Therapy for the Treatment of Chronic Idiopathic Constipation and Constipation-Predominant Irritable Bowel Syndrome

Adv Ther (2013) 30(3):203 11. DOI 10.1007/s12325-013-0012-9 REVIEW Linaclotide, Novel Therapy for the Treatment of Chronic Idiopathic Constipation and Constipation-Predominant Irritable Bowel Syndrome Maria I. Vazquez-Roque Ernest P. Bouras To view enhanced content go to www.advancesintherapy.com Received: November 7, 2012 / Published online: February 20, 2013 Springer Healthcare 2013 ABSTRACT Chronic constipation (CC) and irritable bowel syndrome with constipation (IBS-C) are common gastrointestinal (GI) disorders. Current treatment options, either prescription or nonprescription medications, have limited efficacy in a subset of patients. There is significant demand for more efficacious medications for the treatment of CC and IBS-C. Linaclotide, a secretagogue, has a novel mechanism of action designed to treat patients with CC and IBS-C. It has a low oral bioavailability with negligible systemic side effects, and it acts locally in the intestinal lumen. In several clinical trials, in health and disease, linaclotide has demonstrated durable efficacy and safety in CC and IBS-C. Linaclotide received M. I. Vazquez-Roque E. P. Bouras (*) Division of Gastroenterology and Hepatology, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA e-mail: bouras.ernest@mayo.edu Enhanced content for Advances in Therapy articles is available on the journal web site: www.advancesintherapy.com approval by the Federal Drug Administration in August 2012 to treat chronic idiopathic constipation and IBS-C. Keywords: Constipation; Gastroenterology; Guanylate cyclase C; Guanylin; Irritable bowel syndrome; Linaclotide; Uroguanylin BACKGROUND Chronic constipation (CC) and irritable bowel syndrome with constipation (IBS-C) are common gastrointestinal (GI) disorders. The overall prevalence of CC in the general population is approximately 20% [1]. CC is defined by infrequent bowel movements (less than three bowel movements per week) with associated straining or the sense of incomplete emptying of the bowel. IBS-C is defined by constipation with recurrent abdominal pain that is generally relieved by defecation. Elderly patients, irrespective of gender, have a higher incidence of CC of approximately 20%. Females younger than 50 years of age have a greater incidence compared to men, 18.3% and 9.2% respectively [2, 3]. Overall, female gender, black race, fewer years of education, decreased physical activity, and depression

204 Adv Ther (2013) 30(3):203 11. are independent risk factors for CC [4]. CC has a significant economic burden in the US. Studies have estimated that CC accounts for 5.7 million outpatient doctor visits and 100,000 hospitalizations annually [5, 6]. Patients with CC also have a significantly negative health-related quality of life (HRQOL), significantly decreased work productivity, and increased psychological comorbidities [7 9]. The worldwide prevalence of IBS is approximately 10 15% [10]. IBS is more likely to develop in women compared to men, and it is more likely diagnosed in patients younger than 50 years of age [11]. Additionally, IBS has a significant negative impact on the HRQOL of these patients leading to significant psychological and psychiatric comorbidities [11]. Treatments for CC in the current US market include nonprescription and prescription medications. Nonprescription medications include stool softeners, fiber supplements, osmotic and stimulant laxatives, such as polyethylene glycol and milk of magnesia and bisacodyl, respectively. Lubiprostone is the only prescription medication approved in the US for CC and IBS-C. Tegaserod was a previously approved medication for IBS-C that, although effective, was withdrawn from the US market due to reported adverse effects. Overall, these treatments have variable benefit and efficacy, and there is still great demand for more efficacious and safer treatments for these chronic conditions. Newer therapies for CC and IBS-C have been developed with novel mechanism of actions. Other agents that are either in clinical trials or approved in Europe to treat CC or IBS-C include the uroguanylin (UG) analog plecanatide [12]; prokinetics such as prucalopride [13], velusetrag [12], and naronapride [12]; and the ileal bile acid transporter inhibitor, elobixibat, which increases bile acid concentration in the colon leading to accelerated colonic transit [14]. LINACLOTIDE Linaclotide is a guanylin (GN) and UG analog that activates the guanylate cyclase-c (GC-C) receptor. GN and UG are endogenous peptides of the GN peptide family that are produced by the enteroendocrine cells and activate the GC-C receptor, increasing intestinal fluid secretion [15]. The GC-C receptor is expressed in enterocytes from the small intestine to the distal colon and it is the transmembrane receptor for the heat stable enterotoxin (STa) responsible for acute secretory diarrhea [15]. Activation of the GC-C receptor on the lumen of intestinal epithelial cells stimulates the intrinsic GC-C activity that leads to increases in intracellular cyclic guanosine monophosphate (cgmp), which in turn leads to phosphorylation of a cgmp-dependent protein kinase II and phosphorylation of the cystic fibrosis transmembrane conduction regulator (CFTR). Activation of the CFTR channel results in chloride and fluid secretion into the lumen that leads to increased colonic transit [16]. Chemistry Linaclotide is a 14-amino acid peptide with three disulfide bonds [3, 17] with a structure analogous to the endogenous peptides GN and UG. Linaclotide is stabilized by three intramolecular disulfide bonds, similar to the two disulfide bonds in GN and UG [16]. However, the UG sequence has two N-terminal aspartate residues that are not in the amino acid sequence of linaclotide [16]. Mechanism of Action Linaclotide binds to the GC-C receptor and stimulates intestinal secretion by increasing the production of cgmp. Increased intracellular cgmp leads to phosphorylation

Adv Ther (2013) 30(3):203 11. 205 Lumen Linaclotide CI HCO 3 Na + H 2 O GC-C receptor and that this effect is abolished in GC-C null mice. GC-C CFTR Pharmacology Serosa GTP cgmp Afferent pain fibers Fig. 1 Mechanism of action of linaclotide PKGII of a cgmp-dependent protein kinase II and phosphorylation of the CFTR, which results in chloride anion and fluid secretion into the intestinal lumen (Fig. 1). The GC-C receptor is the key receptor for the STa. These enterotoxins are produced by organisms, such as Escherichia coli, and activate the GC-C receptor causing an acute secretory diarrhea. The specific function of this receptor has been confirmed in GC-C null mice, which fail to elicit the STa stimulation of fluid accumulation within the intestines, evidence of the function of this receptor in intestinal fluid secretion [18]. In vitro studies using human carcinoma T84 cells have demonstrated that the binding of linaclotide occurs in the luminal side of the intestine [19]. The selective binding of linaclotide to the GC-C receptor was studied with a competitive radioligand-binding assay using a radiolabeled heat-stable enterotoxin [ 125 I]-STa in GC-C wild-type and null mice. In wild-type mice, linaclotide inhibited binding of [ 125 I]-STa in a concentration-dependent manner. However, in GC-C null mice a low level of residual binding of [ 125 I]-STa to intestinal mucosa was demonstrated, an effect that was inhibited by linaclotide [16]. This is evidence that linaclotide binds to the Human and animal studies have been published demonstrating the pharmacodynamic and pharmacokinetic properties of linaclotide. In vitro studies have shown that linaclotide is stable in an acidic ph and it resists degradation from gastric hydrolases. Linaclotide did not degrade after 3 hours in a gastric ph of 1, and it resisted hydrolysis from pepsin, suggesting that it would be an adequate medication to administer orally [20]. Six hours after intravenous and oral administration of linaclotide minimal absorption was documented with an oral bioavailability of 0.1% [20, 21]. The limited oral bioavailability of linaclotide causes no serious systemic side effects. MM-419447, the active metabolite of linaclotide, has comparable pharmacokinetics and oral bioavailability to the parent compound. Therefore, it is unlikely that the active metabolite of linaclotide will have clinically significant adverse effects [22]. Pharmacodynamics The pharmacodynamic effects of linaclotide in intestinal motility and secretion have been validated in animal studies [20]. In female rats, acceleration in GI motility was demonstrated in gavage studies. Charcoal traveled a greater distanced in a dose-dependent manner with linaclotide. Secretion, determined by the weight and length of excised ligated small intestine (SI) loops from mice, was increased in the lumen of wild-type mice exposed to linaclotide compared to vehicle-treated animals (P < 0.001). There were no differences in secretion in SI loops from GC-C null mice exposed to linaclotide compared to

206 Adv Ther (2013) 30(3):203 11. the vehicle. Linaclotide increased the secretion of cgmp in wild-type mice but this effect was abolished in GC-C null mice. This confirms the mechanism of action of linaclotide on the GC-C receptor, resulting in increasing fluid secretion. Animal studies have suggested that linaclotide may have a hyperalgesic effect [21, 23]. Using the trinitrobenzene sulfonic acid (TNBS) colitis rodent model, Eutamene and colleagues evaluated the antinociceptive effects of linaclotide [23]. They used colorectal distention (CRD) as a visceromotor response of pain in mice [23]. They demonstrated a significant reduction in the observed TNBS-induced abdominal wall contractions in response to CRD (P < 0.05) with escalating doses of orally administered linaclotide (0.01, 0.03, 0.3 µg/kg) [23]. A similar effect was not observed with the higher dose of linaclotide arguing against a dose-dependent effect and the strength of its visceral analgesic effects. Using GC-C wild-type and GC-C null mice, linaclotide reversed the hypersensitivity response induced by TNBS in the GC-C wild-type mice, but not in the GC-C null mice. These data suggest that the GC-C receptor may mediate the antinociceptive effects of linaclotide. An acute restraint stress-induced visceral hyperalgesia (PRS) model was also used to evaluate the antinociceptive effects of linaclotide. Linaclotide at doses of 0.3, 3.0, and 30.0 µg/kg were administered; however, a significant effect in reducing hyperalgesia to CRD was seen in the 3.0 µg/kg dose (P < 0.05). In another model of stress, acute water avoidance (WAS) delayed stress-induced visceral hyperalgesia in male Wistar rats [23]; visceral hyperalgesia was determined by performing CRD as a painful stimulus to evoke EMG responses from electrodes placed in the abdominal wall. The EMG response after CRD was completely abolished after oral linaclotide at doses 0.3 and 3.0 µg/kg. A recent animal study, using C57/BL6 mice, which were mechanically hypersensitive 28 days after TNBS exposure, sought to elucidate the mechanism of action of pain relief with linaclotide [24]. Linaclotide reduced nociceptor mechanosensitivity in viscerally sensitive mice at 100, 300, and 1,000 nm doses, in a dose-dependent response with the greatest effect seen in the 1,000 nm dose. These effects in nociception are similar to those seen in exogenously applied cgmp; however, it seems the GC-C agonists are more potent. Overall, the analgesic effects of linaclotide are seen in colonic sensitivity animal models and recent data show a dose-dependent effect in mechanosensitivity. However, additional studies are necessary to elucidate the analgesic mechanisms by which linaclotide reduces pain in humans. METHODS A search of the published literature using the PubMed database was performed. Search dates were from 2005 until November 2012. Separate searches using the key terms linaclotide, MD-1100, irritable bowel syndrome, and chronic constipation (English language) were combined (using the AND operator) with adults, followed by additional search terms as text terms. Results were limited to human trials, animal studies, English language, adults, and full manuscripts. For this review paper, all available data were reviewed and no studies were excluded. Press releases from Ironwood Pharmaceuticals were also reviewed. Clinical Trials The clinical efficacy of linaclotide has been demonstrated in phase 1, 2, and 3 trials of patients with CC and IBS-C. Linaclotide

Adv Ther (2013) 30(3):203 11. 207 from 30 to 300 µg per day was given to 30 healthy volunteers in a phase 1 clinical trial and was the first study to confirm that it was safe and had no significant adverse events [17, 25]. A trial using a single oral ascending dose of linaclotide in 30 healthy participants demonstrated looser stool consistency using the Bristol stool form scale [26]. In a doseranging study of 48 healthy volunteers, linaclotide at 30, 100, 300, or 1,000 µg dose or placebo was given orally once daily for 7 days. There was a dose response and significant difference in stool consistency and in ease of passage of stool with the 1,000 µg dose. [27]. Pharmacodynamic effects of linaclotide were evaluated in a double-blind, placebo-controlled, randomized, multiple repeat-dose study of linaclotide 100 µg, 1,000 µg, and placebo orally once daily for 5 days in 36 females with IBS-C [28]. In this trial, linaclotide at a dose of 1,000 µg accelerated ascending colonic transit and colonic transit at 48 hours. Linaclotide also improved bowel function and was well tolerated with no adverse or safety concerns. A randomized, double-blind, placebocontrolled efficacy trial of linaclotide was conducted to evaluate its safety in 42 patients with CC [29]. Patients were randomized to receive 100, 300, or 1,000 µg of linaclotide or placebo once daily for 14 days. Rebound constipation was assessed in an 8-day posttreatment period. Efficacy parameters were daily bowel movements using weekly rates of spontaneous bowel movements (SBM), complete SBM (CSBM), stool consistency, straining, and complete evacuation. At all doses studied, linaclotide produced an increase in SBM and CSBM compared to the placebo [29]. A phase 2b clinical trial in patients with CC was performed to evaluate the primary endpoint of SBM and secondary endpoints of CSBM, stool consistency, abdominal discomfort, and bloating. This trial randomized 310 patients with CC to four doses of linaclotide or placebo once daily for 4 weeks [30]. There was a dose response for linaclotide at the studied doses of 75, 150, 300, or 600 µg with an increase mean weekly SBM compared to the placebo [30]. There was an overall improvement in the other secondary endpoints and global measures of constipation and HRQOL in patients on linaclotide compared to the placebo. A study of IBS-C patients was conducted to evaluate the efficacy and safety of linaclotide doses of 75, 150, 300, or 600 µg or placebo for 12 weeks [31]. The primary endpoint was the difference from baseline in the number of CSBM per week. Secondary endpoints were the change from baseline in abdominal pain, bloating, and bowel function. All endpoints, primary and secondary, improved at all linaclotide doses (P 0.01 for each dose). Patients treated with linaclotide had significant improvement in abdominal pain, discomfort, bloating, and global measures of IBS symptoms. There were no significant adverse events, and the most common reported side effect was diarrhea at all doses. Table 1 summarizes the phase 3 trials that have been conducted to date of linaclotide in CC and IBS-C patients [32 34]. Two randomized, multicenter, double-blind, placebo-controlled, dual-dose trials, denoted 303 and 01, in 1,276 patients with CC were conducted [32]. Only 1,272 patients were included in the intention-totreat analysis because four patients who received at least one dose of the study medication did not report CSBM and were not included in the analysis. Trials 303 and 01 were identical with the only difference that trial 303 had a 4-week period of randomized withdrawal after the treatment period. Trial 303 included 642 patients and trial 01 included 630 patients (intent-to-treat population). The patients were randomized to

208 Adv Ther (2013) 30(3):203 11. Table 1 Phase 3 trials of linaclotide in chronic constipation and irritable bowel syndrome with constipation Author Trial n Linaclotide dose (µg/d) Duration Primary endpoints Results (% patients) Ref Chronic constipation Lembo, et al. Lembo, et al. 303 642 145 or 290 12 weeks and 4-week randomized withdrawal a) 3 CSBM and increase 1 from baseline for 9 of 12 weeks 01 630 145 or 290 12 weeks a) 3 CSBM and increase 1 from baseline for 9 of 12 weeks Irritable bowel syndrome with constipation Rao, et al. Chey, et al. - 800 290 12 weeks and 4-week randomized withdrawal a) Composite responder: abdominal pain and CSBM ( 30% reduction in pain and increase 1 from baseline for 6 of 12 weeks) b) 3 CSBM from baseline for 9 of 12 weeks c) Abdominal pain responder ( 30% reduction in pain at least 9 of 12 weeks) d) CSBM increase 1 from baseline for 9 of 12 weeks - 805 266 26 weeks a) Composite responder: abdominal pain and CSBM ( 30% reduction in pain and 3 CSBM and 1 from baseline for 9 of 12 weeks) b) CSBM responder ( 3 CSBM and 1 from baseline for 9 of 12 weeks) c) Abdominal pain responder ( 30% reduction in pain at least 9 of 12 weeks) d) Composite responder #2: abdominal pain and CSBM ( 30% reduction in pain and 3 CSBM and 1 from baseline for 6 of 12 weeks) CSBM complete spontaneous bowel movement a) 21.2% in 145 µg/d, 19.4% in 290 µg/d versus 3.3% placebo (P < 0.0001, all groups vs. placebo) a) 16.0% in 145 µg/d (P < 0.01), 21.3% in 290 µg/d (P < 0.0001) versus 6.0% placebo a) 55% linaclotide group versus 42% placebo group (P = 0.0002) b) 37% linaclotide group versus 18% placebo group (P < 0.0001) a) Composite responder: 12.7% linaclotide versus 3.0% placebo (P < 0.0001) b) CSBM responder: 18% linaclotide group versus 5% placebo group (P <0.0001) c) Abdominal pain responder: 38.9% linaclotide group versus 19.6% placebo group (P < 0.0001) d) Composite responder #2: 33.7% linaclotide group versus 13.9% placebo group (P < 0.0001) [32] [32] [33] [34]

Adv Ther (2013) 30(3):203 11. 209 linaclotide 145 or 290 µg, or placebo once daily for 12 weeks after a 14-day pretreatment period. The combined primary efficacy endpoints were three or more CSBMs per week and an increase of at least one CSBM per week from baseline for 9 or more weeks during the 12-week treatment period. In trial 303, the primary endpoint was achieved in 21.2% of patients in the 145 µg linaclotide group, 19.4% in the 290 µg group, compared to 3.3% in the placebo group [32]. In trial 01, the primary endpoint was achieved in 16.0% of patients in the 145 µg linaclotide group, 21.3% in the 290 µg group, compared to 6.0% in the placebo group [32]. All secondary endpoints (bloating, abdominal discomfort, stool consistency, straining, and constipation severity) were significantly different for the linaclotide groups compared to the placebo. There was no rebound constipation in patients that were taking linaclotide, who were randomized to receive the placebo during the 4-week randomized withdrawal period. The most common adverse events across these two phase 3 trials were diarrhea (linaclotide 14 16%, placebo 4.7%), flatulence, and abdominal pain. The overall rate of discontinuation during the 12-week trial was higher in the linaclotide group, approximately 7.5% of patients treated with linaclotide compared to 4.2% in the placebo group. This was a result of increased diarrhea in the linaclotide group compared to the placebo group. Two phase 2 trials in IBS-C patients have been conducted and recently published [33]. A multicenter, randomized, double-blind, placebo-controlled 12-week treatment trial of 800 IBS-C patients was conducted. Patients were randomized to either linaclotide 290 µg once daily or placebo followed by a 4-week randomized withdrawal period [33]. There were four primary endpoints in this study. The composite responder endpoint for abdominal pain (improvement of at least 30% from baseline on an 11-point numerical scale) and on a CSBM (an increase of at least 1 from baseline) had to be met at least 6 weeks of the 12 weeks of the treatment period to be considered a responder for this composite endpoint, this meets the US Food and Drug Administration s (FDA s) primary endpoint for IBS-C. The other three primary endpoints had to be met for at least 9 of the 12 weeks of the treatment period. These endpoints were improvement of at least 30% in abdominal pain, three or more CSBMs, and an increase of one or more CSBM from baseline. The linaclotide treatment group had a greater proportion of responders compared to the placebo, 33.6% versus 21.0%, respectively [33]. A 26-week phase 3 clinical trial was conducted assessing the efficacy and safety of linaclotide in patients with IBS-C [34]. After a 2-week pretreatment period, 804 IBS-C patients were randomized to linaclotide 290 µg once daily or placebo for the trial duration. The four primary endpoints are summarized in Table 1. Secondary endpoints included difference from baseline of abdominal pain and discomfort, bloating, percent pain-free days, CSBM weekly frequency, SBM weekly frequency, stool consistency, and straining. Linaclotide-treated patients had a greater proportion of responders for the primary composite endpoint compared to the placebo group [34]. Linaclotide-treated patients had a statistically significant difference in the other primary and secondary endpoints compared to the placebo group. Diarrhea was the most common adverse event, seen in 19.7% of patients in the linaclotide treated group and in 2.5% in the placebo group. The discontinuation rate due to diarrhea was approximately 4.5% in the linaclotide-treated patients compared to 0.2% in the placebo group. Overall, at all doses, linaclotide has been well tolerated with an adequate safety profile [26].

210 Adv Ther (2013) 30(3):203 11. As expected the most common reported adverse event is diarrhea in 8.3 21.0% [28 31, 34]. The diarrhea seems to be dose-dependent and it is not severe. Other reported GI adverse events that were experienced in less than 5% of the linaclotide-treated patients were abdominal pain, flatulence, and nausea, but these were not different than placebo. Linaclotide received approval by the FDA on August 30, 2012 for the treatment of chronic idiopathic constipation and IBS-C in adults. Although not fully approved by the European Commission, it has received a recommendation for approval by the Committee for Medicinal Products for Human Use (CHMP) for the treatment of moderate to severe IBS-C. CONCLUSION Linaclotide is a drug with minimal bioavailability that induces intestinal secretion and improves stool consistency in patients with CC and IBS-C. Animal studies have suggested that linaclotide may have an effect in improving pain, and, in human studies, pain scores do improve but the exact mechanism is not well understood. Clinical trials have demonstrated the efficacy and safety of linaclotide for up to 26 weeks. Linaclotide was recently approved by the FDA in the USA. The efficacy of linaclotide in patients with other etiologies of constipation, such as pelvic floor dysfunction, needs to be further elucidated. ACKNOWLEDGMENTS Dr. Bouras is the guarantor for this article and takes responsibility for the integrity of the work as a whole. Conflict of interest. Dr. Vazquez declares she has no conflict of interest. Dr. Bouras declares he has no conflict of interest. REFERENCES 1. Higgins PD, Johanson JF. Epidemiology of constipation in North America: a systematic review. Am J Gastroenterol. 2004;99:750 9. 2. Choung RS, Locke GR, 3rd, Schleck CD, et al. Cumulative incidence of chronic constipation: a population-based study 1988 2003. Aliment Pharmacol Ther. 2007;26:1521 8. 3. Vazquez Roque M, Camilleri M. Linaclotide, a synthetic guanylate cyclase C agonist, for the treatment of functional gastrointestinal disorders associated with constipation. Expert Rev Gastroenterol Hepatol. 2011;5:301 10. 4. Everhart JE, Go VL, Johannes RS, et al. A longitudinal survey of self-reported bowel habits in the United States. Dig Dis Sci. 1989;34:1153 62. 5. Sonnenberg A, Koch TR. Physician visits in the United States for constipation: 1958 to 1986. Dig Dis Sci. 1989;34:606 11. 6. Martin BC, Barghout V, Cerulli A. Direct medical costs of constipation in the United States. Manag Care Interface. 2006;19:43 9. 7. Bongers ME, Benninga MA, Maurice-Stam H, et al. Health-related quality of life in young adults with symptoms of constipation continuing from childhood into adulthood. Health Qual Life Outcomes. 2009;7:20. 8. Wang JP, Duan LP, Ye HJ, et al. [Assessment of psychological status and quality of life in patients with functional constipation]. Zhonghua Nei Ke Za Zhi. 2008;47:460 3. In Chinese. 9. Sun SX, Dibonaventura M, Purayidathil FW, et al. Impact of chronic constipation on health-related quality of life, work productivity, and healthcare resource use: an analysis of the National Health and Wellness Survey. Dig Dis Sci. 2011;56:2688 95. 10. Drossman DA, Camilleri M, Mayer EA, et al. AGA technical review on irritable bowel syndrome. Gastroenterology. 2002;123:2108 31. 11. Spiegel BM. The burden of IBS: looking at metrics. Curr Gastroenterol Rep. 2009;11:265 9. 12. Vazquez Roque M, Camilleri M. Velusetrag. Drugs Future. 2011;36:447 54. 13. Camilleri M, Kerstens R, Rykx A, et al. A placebocontrolled trial of prucalopride for severe chronic constipation. N Engl J Med. 2008;358:2344 54.

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