Our RDX009 program is aimed at discovering and evaluating small molecule, orally-administered drug candidates that stimulate TGR5. We are initially focused on the treatment of inflammatory bowel disease or IBD, for proof-of-concept, but believe the stimulation of TGR5 may have utility in several other conditions, including short bowel syndrome.
TGR5 is a receptor present on the membrane of certain cells within the GI tract that responds to bile acids secreted in response to food. In the normal physiological response, binding of bile acids to TGR5 stimulates the production of hormones such as glucagon-like peptides 1 and 2 (GLP-1 and GLP-2). GLP-2 is involved in maintenance of the structural integrity of the gut as well as its growth. GLP-2 also communicates with immune cells including macrophages and is believed to serve a role in the reduction of the inflammation response.
We believe that endogenous and local secretion of GLP-2 triggered by the stimulation of TGR5 receptors may have significant therapeutic potential for the treatment of IBD. An injectable, stabilized form of GLP-2, called teduglutide (Gattex®), is marketed for short bowel syndrome and has been studied in Crohn’s disease.
GLP-2 is hypothesized to work in IBD such as Crohn’s disease and ulcerative colitis, or UC, by stimulating the repair of the gut and improving the structural integrity of gut wall that is damaged in patients with IBD. Additionally, the anti-inflammatory effects of GLP-2 may help reduce the inflammation present in IBD. Together these properties would represent a unique approach to treating IBD. We are therefore working to identify and optimize TGR5 agonists that can stimulate GLP-2 in rodent models of IBD.
Historically one of the limitations for the development of TGR5 agonists has been the observation with systemic compounds that stimulation of TGR5 in the gallbladder results in excess gallbladder filling, potentially increasing the risk of gallstones. Utilizing our approach to design small molecules, we have created novel TGR5 agonist candidates that have extremely low systemic exposure and we have shown that these agents do not result in excess gallbladder filling in preclinical animal models.
Recently, we have demonstrated that our TGR5 agonists are significantly more active in animal models of IBD if they are combined with an inhibitor of DPP4. This effect may be due to the mechanisms of DPP4 inhibitors, which prevent the degradation of GLP-2 in the body. Without a DPP4 inhibitor present, GLP-2 would rapidly degrade and disappear from the blood. DPP4 inhibitors lengthen the half-life of GLP-2. In animal models of colonic inflammation, the combination of our TGR5 agonists and a DPP4 inhibitor, both orally administered, have been able to significantly reduce various measures of disease severity. We continue to test our TGR5 agonists to determine a lead product that would be appropriate for beginning IND-enabling studies.