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Randomised study: effects of the 5‐HT4 receptor agonist felcisetrag vs placebo on gut transit in patients with gastroparesis

Summary Background Gastroparesis is defined by delayed gastric emptying with associated symptoms in the absence of mechanical obstruction. Aim To evaluate pharmacokinetics and pharmacodynamics of felcisetrag, a highly selective 5‐HT4 receptor agonist, on total gut transit in patients with documented delayed gastric emptying of solids. Methods Single‐centre, placebo‐controlled study of 36 participants receiving placebo, 0.1mg, 0.3mg or 1.0mg of felcisetrag I.V. infusion, daily, for 3 days. At baseline, each participant completed a 4h, 99mTc‐egg meal (300 kcal, 30% fat) gastric emptying test. Following infusion (Day 2), gastric, small bowel and colonic transit of solids were measured over 48h (same meal plus 111In‐charcoal delivered in methacrylate‐coated capsule). Samples were collected for pharmacokinetics. The primary endpoint was gastric emptying T1/2. Statistical analysis used baseline parameters as covariates (ANCOVA). Results Patients (22 idiopathic, 14 diabetic gastroparesis) were randomised to felcisetrag (0.1 mg, n = 10; 0.3 mg, n = 9; 1.0 mg, n = 7) or placebo (n = 10). Compared to placebo, felcisetrag significantly accelerated gastric emptying T 1/2, colonic filling at 6h, and 10% small bowel transit time (overall P < 0.01; all three doses individually Bonferroni corrected P < 0.05) for all three measurements. Ascending colon emptying (T 1/2) was significantly accelerated (all doses), and colonic transit at 48 hours was accelerated with 0.1 mg and 0.3 mg felcisetrag compared to placebo. Pharmacokinetic results were dose proportional. Felcisetrag was well tolerated with no clinically significant findings from clinical laboratory, vital signs or ECG. Conclusion I.V. felcisetrag significantly accelerated gastric, small bowel and colonic transit in patients with gastroparesis, and should be further evaluated for short‐term treatment of gastric and intestinal motility disorders. ClinicalTrials.gov #NCT03281577


| INTRODUC TI ON
Gastroparesis is a chronic gastrointestinal disorder affecting stomach motility. 1 It is defined by delayed gastric emptying with associated symptoms in the absence of mechanical obstruction. 1,2 Symptoms of gastroparesis include nausea, vomiting, early satiety, postprandial fullness, upper abdominal pain and bloating, which are known as the cardinal symptoms. 2 interval and sudden cardiac death with domperidone; and tachyphylaxis with erythromycin. 7 There is an unmet need for effective prokinetic agents, particularly for acute exacerbations that preclude oral administration of such agents.
Another class of drugs used in the treatment of motility disorders is the 5-hydroxytryptamine-4 (5-HT 4 ) receptor agonists. 8,9 5-HT 4 agonists vary in chemical structure and selectivity for the 5-HT 4 receptors in the gastrointestinal tract. 9,10 Highly selective and potent 5HT 4 agonists are less likely to cause cardiac conduction abnormalities, for which cisapride, a non-specific 5HT 4 agonist, was withdrawal from the market for all indications. 11 Prucalopride, a highly specific 5HT 4 agonist, significantly enhanced gastric emptying, small bowel transit and colonic transit in patients with chronic constipation. 12 5-HT4a, 4b and 4c receptors are abundantly, but differentially, expressed throughout the gut. Felcisetrag has about 10-to 100-fold greater affinity for human 5-HT 4 receptor splice variants (5-HT4a, 4b and 4c) compared to prucalopride (P. Wade, personal communication, 13 October 2020).
Treatment of gastroparesis can be challenging due to limited availability of approved or efficacious therapeutic options despite the use of dietary changes, vitamin and nutrition supplementation, anti-emetics and prokinetic agents. 2 Although not approved for treatment of gastroparesis, recent data from a small cross-over study suggest that prucalopride significantly enhances gastric emptying and decreases symptoms in patients with idiopathic gastroparesis. 13 Felcisetrag is a highly selective and potent 5-HT 4 receptor agonist with prokinetic activity throughout the gastrointestinal tract in experimental models. 11,14,15 After intravenous administration in healthy volunteers and in treatment of enteral feeding intolerance in critically ill patients, felcisetrag demonstrated prokinetic activity when administered over a short term. 16 As an intravenously administered drug, felcisetrag may be useful in treating acute gastrointestinal motility disorders such as post-operative gastrointestinal dysfunction, acute exacerbations of gastroparesis (which may result in hospitalization) 6,17 and enteral feeding intolerance in critically ill patients.
The aim of this study was to evaluate the pharmacokinetics and pharmacodynamics effects of felcisetrag on gastric, small intestinal and colonic transit in patients with diabetes reporting symptoms of gastroparesis, or in patients with idiopathic gastroparesis; both groups having previously documented delay in gastric emptying of solids. Patients with diabetes and constipation may require prokinetic treatment, as has been demonstrated using the acetylcholinesterase inhibitor, pyridostigmine. 18 It is interesting to note that, in that study, about 37% (11/30) of the patients also had delayed gastric emptying (T 1/2 >150 minutes) measured by the same scintigraphic method used in the current study. Therefore, demonstration of the prokinetic effects of felcisetrag through the different regions of the gastrointestinal tract would be useful to assess its potential for slow transit disorders in the entire gut.

| Study design and ethical approval
This was a phase IIa dose-ranging, randomised, parallel-group, double-blind, placebo-controlled study conducted at a single medical centre. The study was approved by Mayo Clinic Institutional Review Board (IRB #17-006648). Participants were randomised (based on computer-generated schema) to felcisetrag 0.1, 0.3 or 1.0 mg, or placebo, given as a 60-minute i.v. infusion once a day for 3 days. The random allocation sequence was retained in the Mayo Clinic Research Pharmacy, and all study personnel and participants were blinded to treatment allocation. Interventions were assigned according to randomisation by study pharmacist. Both interventions appeared identical.

| Patient and public involvement
Patients were first invited to participate in the research process by electronic or phone invitation or by public advertisement on the Mayo Clinic campus in Rochester, MN. The research question(s) and outcome measures were developed based on previously validated measurements of the transit of radiolabeled solids, as well as the use of validated instruments to appraise symptoms and bowel function as well as evidence that a significant change in the primary endpoint had been shown to be associated with clinical benefit. 21 The public was not involved in the design of this study; participants consented to be included, but they did not provide any feedback regarding the conduct of the study, or the burden of the intervention, or time required to participate in the research. When the study is published in peer-reviewed literature, the study results will be disseminated to participants and to relevant wider patient communities.

| Study protocol
The study was registered at ClinicalTrials.gov #NCT03281577. An overview of the study design is shown in Figure 1. The study consisted of three periods: screening, baseline and treatment, and a follow-up phone call 10 to 14 days later; further details of the protocol are included in the Supplemental Materials.

| Gastric emptying of solids, small bowel and colonic transit by scintigraphy
Gastric emptying of solids was measured at baseline by scintigraphy.

| Pharmacokinetics measurements
Pharmacokinetics measurements were done on collected plasma samples obtained in the opposite arm from where the infusion was delivered. This was done at previously set intervals relative to the i.v.

| Endpoints
The primary endpoint was gastric emptying T 1/2 . The secondary endpoints were small bowel transit (colonic filling at 6 hours and SBTT10%), colonic transit (ascending colon emptying T 1/2 and colonic geometric centre at 24 and 48 hours) and felcisetrag pharmacokinetics (T max , C max , AUC and clearance half-time), safety and tolerability.

| Pharmacokinetics
Plasma samples were analysed for felcisetrag using validated liquid chromatography with tandem mass spectrometry methods. The lower limit of quantification for felcisetrag is 5.00 pg/mL

| Pharmacokinetics
Pharmacokinetic parameters were determined from the concentration-time data for all evaluable subjects using noncompartmental analysis. Actual sampling times, rather than scheduled sampling times, were used in all pharmacokinetic computations involving sampling times for plasma pharmacokinetic parameters.
The plasma concentrations of felcisetrag were summarized by treatment group over each scheduled sampling time point using descriptive statistics. In addition, the mean plasma concentrations of felcisetrag vs time were generated by treatment group.

| Pharmacodynamics
The statistical analysis by intention-to-treat population used baseline parameters (where available) as covariates (ANCOVA). ANCOVA was used to assess the effect of treatment on the T 1/2 of gastric emptying of solids, including the following as covariates: gastroparesis type (diabetic or idiopathic), age, gender, BMI and the baseline measurement of gastric emptying T 1/2 . Multiplicity adjusted and unadjusted 95% two-sided confidence intervals were presented. Normality was tested using the Shapiro-Wilk W test with criteria <0.01.
The effects of treatment on the secondary endpoints were also assessed using an ANCOVA model. The covariates considered for inclusion in the analyses were gastroparesis type (diabetic or idiopathic), age, gender, BMI and the baseline measurement of the respective endpoint. Dunnett's test, multiplicity adjusted and unadjusted 95% two-sided confidence intervals, and Kruskal-Wallis test were used as outlined for primary endpoint.

| Pharmacokinetics-pharmacodynamics relationship
Felcisetrag gastric half-emptying time models were estimated using the NLME Library (version 3.1-140) in R (version 3.6.1). The best model was selected by Akaike's Information Criterion (AIC). Colonic geometric centre models were estimated using the BRMS Library (version 2.10.0) in R (version 3.6.1). The best model was selected by widely accepted information criterion (WAIC). Final models were evaluated by visual predictive check.

| Safety
Safety analyses included adverse events, clinical laboratory evaluations, vital sign results and 12-lead ECG results. All summaries of safety data were based on patients in the safety set.

| Patient reported outcomes
Information on the global score using the Gastroparesis Cardinal Symptom Index (GCSI), as well as bowel movement frequency per day and average stool consistency on the Bristol Stool Form Scale were tabulated and analysed.
2.9.6 | Sample size considerations Table S1 summarises data for the primary and secondary PD response measures and uses the (relative) per cent coefficient of variation (% CV) to estimate the effect size detectable with 80% power, based on a two-sample z-test (i.e. assuming the variation values were known) at a two-sided alpha level of 0.05. The effect size is the difference in group means as a percentage of the overall mean for each response and assumes 12 subjects per group. The ANCOVA provided 80% power to detect similar (pairwise) differences using a pooled estimate of variation across all three groups and potentially even smaller effect sizes by adjusting for important covariates. An effect size of at least 30% for the primary endpoint is considered to be clinically important.  Table S1 shows the a priori power statement based on the variance used to plan the study with 12 patients per treatment arm, and the final power statement as a result of the interim analysis. Based on the results of the pre-planned interim analysis, one of the felcisetrag doses stopped enrolling. The specific dose that stopped enrolling was not specified in order to maintain the blind of the study team.

| Role of the funding source
This was a single-centre study at Mayo Clinic in Rochester, MN. The trial was sponsored by Takeda Pharmaceuticals International Co., Cambridge, MA, USA. Felcisetrag was supplied by Takeda. The investigative team at one site in the United States was responsible for recruitment, enrolment and follow-up of patients.
All authors had access to the study data and reviewed and approved the final manuscript.

| Conduct of the study
Twenty-six patients were randomised using a computer-generated list to receive felcisetrag intravenously (n = 10 to 0.1 mg, n = 9 to 0.3 mg and n = 7 to 1.0 mg doses) from Days 1 to 3. Ten patients were randomised to receive placebo intravenously from Days 1 to 3.
Baseline characteristics according to the treatment allocation group are summarised in Table 1   The abdominal pain was not consistent with typical clinical features of pancreatitis (e.g. radiation to the back) and there was no evidence of pancreatitis on abdominal imaging in association with the pain experienced during the study. We have follow-up information up to 1 year after the increase in serum lipase which occurred during the trial. He has undergone endoscopic ultrasound which did not reveal any structural abnormalities in the pancreas, and he has had further episodes of pain similar to that observed prior to, as well as during the trial. Therefore, it was deemed that this SAE was unrelated to felcisetrag. All other patients participated in the full study protocol as planned. Figure 2 shows the CONSORT flow chart.

| Gastric emptying of solids (GE T 1/2 ) and small intestinal transit
At baseline, GE T 1/2 was similar across the four groups and was delayed in all groups (Table 1), consistent with a diagnosis of gastroparesis. After two i.v. doses of felcisetrag, GE T 1/2 was accelerated with all three doses of felcisetrag compared to placebo ( Table 1).
The absolute change (Table S2) and percent change in GE T 1/2 were significantly more rapid than baseline across all doses compared to placebo (P < 0.001 for all dose groups compared to placebo (Table 1;   Figure 5; P < 0.05).

| Colonic transit
The ascending colon emptying T 1/2 was significantly accelerated with all three doses of felcisetrag compared to placebo (Table 1; P < 0.05). Table 1 shows the numerical differences in colonic transit at 48 hours (GC, geometric center; GC48) in all four groups, with placebo having the lowest GC at all time points (Figure 6). We noted an effect on colonic transit starting at 30 minutes after i.v. infusion of felcisetrag in all three dose groups (Figure 4). Colonic transit at 24 hours (GC24) and GC48 was numerically greater than placebo at all three doses (

| Adverse events
Felcisetrag was well tolerated. There were no patient deaths. One patient withdrew due to poor i.v. access and one was withdrawn due to a serious adverse event (mild elevated pancreatic enzymes without evidence of pancreatitis; not drug related). Adverse events were mostly mild or moderate and frequency was generally comparable between felcisetrag doses and placebo (Tables   S3 and S4).
A few patients had >30 milliseconds change in QTcF from baseline; however, none of those receiving felcisetrag had QTcF >500 milliseconds. There were no significant ECG changes in all treatment groups. One asymptomatic participant had a recorded QTcF >500 milliseconds, and this patient was eventually discovered to have been in the placebo group. The most common adverse events were diarrhoea and nausea, possibly secondary to enhanced pharmacologic effect in individual patients.
No clinically significant findings were identified from clinical laboratory results, vital signs or ECG.

| Pharmacokinetics
The maximum plasma concentration (C max ) of felcisetrag and the area under the curve (AUC τ ) were similar from Day 1 to Day 3 at each dose level as seen in Figure 5. Both C max and AUC τ were approximately dose proportional at 0.1 mg, 0.3 mg, and 1 mg dose levels ( Figure S1).

| Pharmacokinetics and pharmacodynamics relationship
The felcisetrag/gastric half-emptying model ( Figure S2)  Furthermore, felcisetrag is a highly selective 5-HT 4 receptor ago- nist. As such it would be expected to have a preferable safety profile.
In this study, felcisetrag was well tolerated as a short-term administration in patients with idiopathic or diabetic gastroparesis. Most of the adverse events reported were gastrointestinal symptoms such as nausea and diarrhoea, which are typically seen in patients using prokinetics like 5-HT 4 agonists. Most importantly, in this small study, there were no clinically significant cardiac effects of felcisetrag. This is an important point, since in developing a 5-HT 4 receptor agonist, the risk of cardiovascular adverse events is of serious concern. In the current study, while a few patients had >30 milliseconds change in Future formulations of felcisetrag should focus on a more accessible route of administration such as the oral route.
In conclusion, felcisetrag, an i.v. administered, highly selective 5-HT 4 receptor agonist, significantly accelerated gastric emptying, orocecal as well as small bowel transit, and colonic transit compared to placebo in patients with gastroparesis with previously confirmed delayed gastric emptying. The pharmacokinetic/pharmacodynamic modelling supports the findings of this study and indicates that all doses investigated were sufficient to enhance gastric, small bowel and colonic transit. Felcisetrag was well tolerated, and its efficacy and safety should be further assessed in phase 2B and 3 trials. These results support further evaluation of felcisetrag for the treatment of gastric and intestinal motility disorders.

ACK N OWLED G EM ENTS
The authors thank Mrs. Cindy Stanislav for excellent secretarial assistance. All authors approved the final version of the article, including the authorship list.

DATA AVA I L A B I L I T Y S TAT E M E N T
All data are reported in the paper.