Targeting Chronic Inflammation of the Digestive System in Cancer Prevention: Modulators of the Bioactive Sphingolipid Sphingosine-1-Phosphate Pathway

SIMPLE SUMMARY: Obesity, an ongoing global pandemic, is a major contributor to inflammation and cancers of the digestive system. High saturated fat diets and being overweight are associated with chronic inflammation and increased cancer risk. Signalling molecules made from saturated fats known as bioactive sphingolipids play essential roles in healthy gastrointestinal immunity. In excess, these sphingolipid molecules can compromise our immune system leading to chronic, low-grade inflammation within the digestive system preceding many metabolic diseases including cancer. Sphingosine-1-phosphate is a bioactive sphingolipid and, in excess, contributes to chronic inflammation. Drugs that block sphingosine-1-phosphate activity have the potential to prevent chronic inflammation and reduce gastrointestinal cancer risk. We review how disruption of the sphingosine-1-phosphate pathway contributes to gastrointestinal inflammation and cancer. We also discuss the use of modulators of the sphingospine-1-phosphate pathway in clinical trials and in the clinic as therapeutics for inflammatory gastrointestinal diseases with the benefit of reducing cancer risk. ABSTRACT: Incidence of gastrointestinal (GI) cancers is increasing, and late-stage diagnosis makes these cancers difficult to treat. Chronic and low-grade inflammation are recognized risks for most GI cancers. The GI mucosal immune system maintains healthy homeostasis and signalling molecules made from saturated fats, bioactive sphingolipids, play essential roles in healthy GI immunity. Sphingosine-1-phosphate (S1P), a bioactive sphingolipid, is a key mediator in a balanced GI immune response. Disruption in the S1P pathway underlies systemic chronic metabolic inflammatory disorders, including diabetes and GI cancers, providing a strong rationale for using modulators of the S1P pathway to treat pathological inflammation. Here, we discuss the effects of bioactive sphingolipids in immune homeostasis with a focus on S1P in chronic low-grade inflammation associated with increased risk of GI carcinogenesis. Contemporary information on S1P signalling involvement in cancers of the digestive system, from top to bottom, is reviewed. Further, we discuss the use of novel S1P receptor modulators currently in clinical trials and their potential as first-line drugs in the clinic for chronic inflammatory diseases. Recently, ozanimod (Zeposia(TM)) and etrasimod have been approved for clinical use to treat ulcerative colitis and eosinophilic oesophagitis, respectively, which may have longer term benefits in reducing risk of GI cancers.