Drug development and acute gastrointestinal infections

KEYWORDS:

• Antidiarrheal drugs
• diarrhea
• oral rehydration
• treatment

1. Introduction

The mortality rate from diarrhea for children younger than 5 years has decreased from almost five million in the 1980s to over 600,000 in 2015. This remarkable decrease was achieved through the introduction of oral rehydration therapy. Almost 40 years later, equally effective and safe therapy has not been introduced, and oral rehydration therapy with a hypotonic solution remains central to the management of acute diarrhea [1]. For prevention, a success story has been the introduction of rotavirus vaccines. They have had a major effect on rotavirus infection severity and hospitalization rates in all introduced settings [2]. Here, we briefly summarize novel interventions for the management of acute gastrointestinal infections identified through searching PubMed (May 2017) for reports published in the last 3 years and registers for clinical trials (www.clinicaltrials.gov, www.clinicaltrialsregister.eu). The principal search text word terms and MESH headings used were diarrhea/diarrhoea, and gastrointestinal infection. New developments in vaccines and antimicrobial drugs are not reviewed. For examples of early stage randomized controlled trials (RCTs) on acute diarrhea treatment, see Table 1.

Table 1. Examples of early stage randomized controlled trials on acute diarrhea treatment.

Reference/number of trial registry	Population	Intervention	Comparison	Primary outcome	Authors’ conclusions	Proposed mechanism of action
Trials with published results
Alam et al. 2015 [3]	N = 126, malnourished children with acute diarrhea, aged 6–36 mo	ORS with PHGG	ORS	Duration of diarrhea (ORS+PHGG vs. ORS, 57 ± 31 vs. 75 ± 39 h, p = 0.01); Proportion of patient recovered within 72 h (NS), daily stool output (NS) and recovery from severe malnutrition (p = 0.027).	PHGG added to ORS substantially reduced duration of diarrhea and enhanced weight gain.	PHGG to be fermented by colonic bacteria producing SCFAs enhancing colonic mucosa regeneration and water absorption
Zaman et al. 2014 [7]	N = 36, age 7 to 60 mo, acute diarrhea of unknown etiology, mild-to-moderate dehydration.	Antisecretory factor (AF)	Placebo	AF vs. placebo, earlier stool frequency reduction to <3/24 h (7 vs. 18 h, p<0,0001); reduced time to recovery (35 vs. 70h, p = 0.001).	High doses of AF effectively and safely reduce childhood diarrhea	Inhibition of enteric nervous system; decreased epithelial permeability
Macarthur et al. 2013 [8]	N = 376, HIV-seropositive adults with chronic diarrhea	Crofelemer (C)	Placebo (P)	C vs. P higher clinical response (17.6% vs. 8.0%; p = 0.01).	In HIV (+) patients, C provided significant improvement in diarrhea	CFTR and CaCC channel inhibitor; antisecretory
Gnessi et al. 2015 [12]	N = 150, adults with acute diarrhea	Xyloglucan (X)	1. Diosmectite (DS) 2. S. boulardii (SB)	X vs. DS, higher decrease in the mean number of diarrheal stools (p = 0.031); X vs. DS or SB, faster onset of action, more efficient in reducing nausea and abdominal (p values not given)	X was efficacious and safe in the treatment of acute diarrhea	Mucosal protective agent – forms a bio-protective film on the intestinal mucus preventing microorganisms from crossing the mucus barrier.
Çağan et al. 2017 [9]	N = 203, children with acute diarrhea, 3 mo to 12 y	ORS+ gelatin tannate	ORS+ placebo	GT vs. placebo, lower incidence of watery stool at 12 h; (59.2% vs. 77.0%; p = 0.01); lower stool frequency at 12 h; (mean 2 vs. 3 stools; p < 0.01).	GT + ORS was effective for the treatment of acute diarrhea in children	Mucosal protective agent – see above
Sarker et al. 2016 [18]	N = 120, children with E coli diarrhea, 6 to 24 mo,	Intervention group 1: Microgen E. coli phage. Intervention group 2: T4 E. coli phage.	Placebo	Lack of clinical efficacy. Good tolerance.	Phage therapy was safe but had no clinical effect	Phages (virus, that infects and kills E coli cells)
Bruggencate et al. 2016 [17]	N = 58, healthy adults challenged with diarrheagenic E coli	Milk protein concentrate rich in MFGM.	Placebo	MFGM vs. placebo, decreased stool frequency (1.1 ± 0.1 vs. 1.6 ± 0.2 stool/d; p = 0.04) and GI complaints (GSRS score) (1.1 ± 0.5 vs. 2.5 ± 0.6)	MFGM may improve in vivo resistance to diarrheagenic E. coli in healthy adults	Direct antimicrobial activity
Sarker et al. 2015[19]	N = 85 children with acute diarrhea, 6 mo to 5 y	Polyphenols + ORS	ORS	No clinical outcomes studied	Safe for children and infants	Antimicrobial activity related to inhibition of hydrolytic enzymes (proteases and carbohydrolases) or other interactions to inactivate microbial adhesins, cell envelope transport proteins, nonspecific interactions with carbohydrates
Noguera et al. 2014[20]	N = 300, adults and children older than 2 years, with acute gastroenteritis ≤48 h	Polyphenol (P)+ ORS	ORS	P vs. placebo, shorter mean time to last unformed stool (10 h vs. 54 h, p = 0.000)	Significant and sustained improvement of multiple symptoms in polyphenole vs. placebo group
Dover et al. 2015 [21]	N = 61, children with acute diarrhea ≤48 h, 2 to 17 y	Polyphenols + ORS	ORS	The mean time to diarrhea resolution was 3.1 h (study arm) versus 9.2 h (control arm) (p = 0.002).	Significant decreases in bowel movement frequency and rapid normalization of stool consistency
Trials with no published results
NCT01823939	Adult males with acute Vibrio cholerae diarrhea <24 h; severe dehydration.	iOWH032	Placebo	Pharmacokinetic parameters, adverse events, laboratory values, physical examination and vital sign findings, adverse events.		CFTR ion channel inhibition resulting in decreased excretion of chloride anions into the intestinal lumen.
NCT02280759	N = 72, children <5 y with acute diarrhea	Gelatin tannate	Placebo.	Duration of diarrhea, need for intravenous rehydration, need for hospitalization, vomiting, weight gain, diarrhea recurrence, frequency of watery stools, adverse effects, severity of diarrhea.		Mucosal protective agent – see above.
NCT02896465	N = 495 children with acute diarrhea, 6 mo to 2 y	ORS + zinc +  HMO	1: ORS + zinc 2: ORS + zinc + breastfeeding	Stools output, weight gain, adverse events, daily stool frequency, number of vomiting episodes, duration of vomiting, change in Z-score, amount of ORS to correct dehydration.		Stimulation of intestinal beneficial microflora colonization, inhibition of pathogen adherence

ORS: oral rehydration solution; PHGG: partially hydrolyzed guar gum; CaCC: calcium-activated Cl- channel; CFTR: cystic fibrosis transmembrane conductance regulator; S boulardii: Saccharomyces boulardii; MFGM: milk fat globule membranes; GSRS: gastrointestinal symptom rating scale; HMO: human milk oligosaccharides.

2. Oral rehydration solution (ORS)

Efforts are being made to improve the efficacy of ORS. One example is a 2015 RCT performed in malnourished children with acute diarrhea. Compared with ORS, the addition of only partially hydrolyzed guar gum (a soluble fiber, which turns into short-chain fatty acids in the intestine, enhancing colonic mucosa regeneration and water absorption) shortened the duration of diarrhea and enhanced weight gain. However, there was no effect on stool volume [3]. Improved ORS that will reduce stool volume and duration of diarrhea is still desired.

3. Antisecretory drugs

Numerous intestinal ion channels and transporters, regulatory proteins and cell surface receptors, receptors in the enteric nervous system, and enterocytes are known to be involved in the pathogenesis of secretory diarrhea. Each one of them is also a conceivable target for controlling secretory diarrhea (Figure 1). For a summary of potential antidiarrheal interventions discussed in detail elsewhere [4–6], see Table 2.

Table 2. Summary of antisecretory drugs in the preclinical stages of development (based on reference 5).

Drug	Target	Mechanism of action
CaCCinh-A01	CaCC channel	Inhibits transport of chloride anions to the intestinal lumen, and, as a result, affects one of the main mechanisms of intestinal fluid secretion.
Gallotannins
CFTRinh-172	CFTR channel
PPQ/BPO
Lysophosphatidic acid	Lysophosphatidic acid receptor 2	Formation of a complex that modulates CFTR channel activity (see above).
R-568	Calcium-sensing receptor	Modulation of intracellular signaling pathways responsible for electrolyte transport.

BPO: benzopyrimido-pyrrolo-oxazinedione; CaCC: calcium-activated chloride channels; CaCCinh: selective inhibitors of calcium-activated chloride channels; CFTR: cystic fibrosis transmembrane conductance regulator; CFTRinh: selective inhibitors of cystic fibrosis transmembrane conductance regulator; PPQ: pyrimido-pyrrolo-quinoxalinedione; R-568: type II calcium-sensing receptor agonist.

Figure 1. lnvestigational antisecretory therapeutics for acute diarrhea and their targets. Abbreviations: BPO, benzopyrimidopyrrolo- oxazinedione; CaCC, calcium-activated chloride channel; CaSR, calcium-sensing receptor; CFTR, cystic fibrosis transmembrane conductance regulator; LPAR2, lysophosphatidic acid receptor 2; NHE, sodium/ hydrogen exchanger; PPQ, pyrimido-pyrrolo-quinoxalinedione.

In children with acute diarrhea with mild-to-moderate dehydration, compared with placebo, the administration of high doses of a modified egg yolk containing antisecretory factor (an endogenous 43kD protein) resulted in a reduced recovery time [7].

One of the novel antisecretory drugs is crofelemer. It prevents chloride (Cl-) and fluid secretion into the lumen by inhibiting the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel and the calcium-activated Cl- channel (CaCC). Currently, crofelemer is only approved for the management of noninfectious diarrhea in HIV/AIDS patients receiving antiretroviral therapy [8].

iOWH032 is a synthetic CFTR inhibitor. Pharmacokinetic studies of iOWH032 in adult healthy volunteers and adult males with cholera have been completed, but the results are not yet available (clinicaltrials.gov, NCT01823939). However, it has been suggested that iOWH032 is unlikely to be effective, as it is a weak CFTR inhibitor and nonresistant to washout in the gut.

4. Mucosal protective agents

Clarifying the role of intestinal mucus in reducing inflammation and infection has led to the development of ‘mucosal protectors’. These agents form a bioprotective film in the gastrointestinal tract and potentially may prevent microorganisms from crossing the mucus barrier [9]. To date, the best-studied substances include xyloglucan (a hemicellulose polysaccharide found in all land plants) and gelatin tannate (a complex of tannic acid, which possesses astringent, antibacterial, and anti-inflammatory properties, and is a protective gelatin). However, data on the efficacy of these two agents are very preliminary [10–13].

5. Bacteriophages

Bacteriophages (phages) are viruses that infect and kill solely bacterial cells [14]. A 2016 phase II, placebo-controlled RCT in 120 Bangladeshi children hospitalized with Escherichia coli diarrhea showed similar effects of two different phage preparations and standard treatment with ORS and zinc in terms of stool output, stool frequency, or need for ORS [15].

6. Human milk oligosaccharides (HMO)

These are a structurally diverse group of unconjugated glycans that are present in human milk. Their mechanism of action remains unclear. However, there is evidence suggesting that HMO contribute to the defense against enteric pathogens by serving as soluble decoy receptors, thus, preventing pathogen attachment to infant mucosal surfaces and lowering the risk for viral, bacterial, and protozoan parasite infections [16]. We identified one ongoing (registered at clinicaltrials.gov NCT02896465) double-blind RCT in children aged 6 months to 2 years with acute diarrhea comparing the use of ORS plus zinc with the additional intervention of HMO. The primary outcome measures include improvement (change) of clinical symptoms of diarrhea and passage of the last abnormal stool prior to formed/soft stools during two consecutive 8-h periods.

7. Milk-fat globule membranes (MFGM)

MFGM are a natural component of human milk, known to possess antimicrobial activities [17]. The addition of bovine MFGM is now technically feasible. A 2016 double-blind RCT assessed 58 healthy adults challenged with a diarrheagenic Escherichia coli (E. coli), which transiently induced mild symptoms of a food-borne infection. MFGM significantly decreased the diarrheagenic E. coli-induced changes in reported stool frequency and gastrointestinal complaints at day 2 after the challenge. However, compared with the placebo, the administration of milk protein concentrate rich in MFGM did not significantly affect fecal wet weight and fecal diarrheagenic E. coli excretion (the primary outcomes) [18].

8. Polyphenols

Plant-derived products that are an integral part of the human diet have been shown to positively affect intestinal function, as confirmed in some recent human studies that investigated the effect of the administration of polyphenol extracts [19–21].

9. Passive therapy

The routine use of immunoglobulins is not recommended. However, there is new evidence that immunoglobulins such as chicken egg yolk antibodies may reduce the severity of clinical manifestation of gastroenteritis, especially diarrhea induced by rotavirus [22].

10. Microbiota modulators

With the growing recognition that the gut microbiota has both short- and long-term effects on health, the gut microbiota is a target for improving outcomes in subjects affected or at risk for certain diseases. To date, modification of gut microbiota via the provision of probiotics and/or prebiotics is the most extensively studied strategy [23].

11. Expert opinion

The development of antidiarrheal drugs poses a challenge, as simple, inexpensive treatment for diarrhea is available. Any novel drug should be as effective and as safe as ORS, and preferably, if to be widely used, inexpensive. No major breakthrough has been made since the introduction of ORS into everyday practice. However, the scarcity of new therapies does not indicate a lack of new concepts. There is an extensive body of data on the role of intestinal ion channels and transporters, regulatory proteins, and cell surface receptors in the pathogenesis of secretory diarrhea. Even if none of the identified novel strategies to treat secretory diarrhea have entered the market recently, some of these interventions show some benefit. It is unclear, however, whether this benefit is robust. Previously, the effects of some antisecretory drugs (also other antidiarrheal therapies) were often small, and in some cases, associated with adverse effects. Conversely, there are unmet needs. For example, in low-income countries, acute gastrointestinal infections, particularly recurrent infections, may lead to acute or chronic malnutrition, resulting in more severe and/or frequent episodes of diarrhea. This, in turn, may lead to stunting and deficits in cognition. Therapies that will reduce the risk of such complications are needed.

The first study failed to show a benefit of bacteriophage therapy. However, there is a scientific rationale for using phages in the management of bacterial diarrheal diseases. One limitation of this approach is that acute gastrointestinal infections are predominantly of viral origin, thus, the use of phages may be limited.

Biotechnology allows the production of a synthesized HMO. However, structural equivalence does not mean functional equivalence that needs to be documented. The same applies to MGFM. Whereas both interventions are likely to be safe needs to be documented.

Microbiota modulating therapies are likely to develop due to improved understanding of the host–microbiota interaction. Interest is in the next-generation probiotics/prebiotics that are likely to include microorganisms or compounds beyond those currently used. Nowadays, probiotics and/or prebiotics are found mainly in food and dietary supplements. However, if they are intended to be used for treating diseases, they will need to be registered as pharmaceutical products, which, among other advantages, ensures better product quality.

Taken together, despite the burden of gastrointestinal infections, other than ORS, very few antidiarrheal therapies have been recently successfully introduced. This is despite the fact that there are more than 900 pipeline therapeutics in the field of gastroenterology in active development [24]. Many reasons contribute to the current situation. First, the development process is lengthy. The time between preclinical testing and final approval on average is about 8.5 years. Second, it is costly. The cost of developing a prescription drug that gains market approval is estimated at over $2.6 billion. Third, there is a very high attrition rate. It has been estimated that only one of every 10,000 chemicals will make it to the market [25]. Even if the above may not directly apply to antidiarrheal drugs, the valid question is who is willing to take the risk and pay for drug development if, as stated earlier, simple, inexpensive treatment is available. Moreover, progress in novel drug development for gastrointestinal infections will likely depend on the progress in vaccine development, along with the availability of efficacious, well-tolerated, and affordable vaccines, as most acute gastrointestinal infections are potentially preventable. In summary, progress is likely and much needed, but the standard treatment for gastrointestinal infections holds its place for the time being.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Additional information

Funding

This paper was not funded.