Innovations in Oral Therapies for Inflammatory Bowel Disease

Prior to the biologic era, the medical management of patients with inflammatory bowel disease (IBD) was dominated by the use of aminosalicylates, corticosteroids, and immunosuppressants. In the past two decades, the advent of biologic agents that target specific components of the immune response has greatly improved the care of patients with Crohn's disease and ulcerative colitis (UC). However, not all patients respond or maintain response to biologic therapy and some patients develop adverse events that necessitate treatment discontinuation. Furthermore, sensitization with formation of anti-drug antibodies is an inherent limitation to administration of monoclonal antibodies. This circumstance has generated renewed interest in the development of novel oral small-molecule drugs (SMDs) that are effective and well tolerated. Several classes of SMDs are currently progressing through the pipeline and offer the promise of oral delivery and high potency. In this review, we summarize different mechanisms of oral drug delivery to the gastrointestinal tract, highlight key findings from phase II and III randomized trials of novel oral SMDs, and discuss how oral SMDs are likely to be integrated into future IBD treatment paradigms. The most advanced development programs currently involve evaluation of compounds blocking Janus kinase (JAK) receptors or modulating sphingosine-1-phosphate (S1P) receptors. Tofacitinib, an oral JAK inhibitor, was recently approved for the treatment of moderate-to-severe UC. Several more selective JAK-1 inhibitors, including filgotinib and upadacitinib, have also shown positive results in phase II studies and are currently enrolling in phase III development programs. Similarly, ozanimod, an S1P1 and S1P5 receptor agonist, has shown early favorable results and is enrolling in phase III trials. As these and other novel oral SMDs come to market, several questions will need to be answered. The cost effectiveness, comparative treatment efficacy, predictors of response, and relative safety of oral SMDs compared to existing therapies will need to be evaluated. Given the modest efficacy rates observed with both biologic therapies and novel SMDs to date, the potential for combination therapy based on a non-sensitizing oral option is promising and may be facilitated by development of organ-specific therapies with pharmacodynamic activity restricted to the gut to minimize systemic toxicity.