P-126 PTG-100, An Oral Peptide Antagonist of Integrin α4β7 that Alters Trafficking of Gut Homing T Cells in Preclinical Animal Models

The α4β7 integrin is a clinically validated target in inflammatory bowel disease (IBD). Vedolizumab (Entyvio®), a humanized monoclonal antibody that specifically binds to the α4β7 integrin, is FDA-approved for the treatment of moderate-to-severe ulcerative colitis and Crohn's disease. Vedolizumab binds to α4β7 on circulating memory/effector T cells in the blood and blocks their homing to intestinal tissues expressing the ligand MAdCAM-1. The aim of this study is to characterize PTG-100, a novel oral α4β7 antagonist peptide that is largely restricted to the gut tissues, and is pharmacologically active in murine colitis models and in normal cynomolgus monkeys. Pharmacokinetic (PK) studies of PTG-100 were conducted in mice, rats, and cynomolgus monkeys, with peptide concentrations measured by mass spectrometry. Pharmacodynamic (PD) studies were conducted in murine colitis models and in healthy cynomolgus monkeys. Cell trafficking in blood and gut lymphoid tissues was measured by FACS or immunohistochemistry (IHC). PTG-100 is a potent antagonist of α4β7 (IC50 = 1 nM), but inactive against α4β1, αLβ2 or αEβ7 as measured in a variety of biochemical and cellular assays. Oral dosing of PTG-100 in normal or dextran sodium sulfate (DSS)-treated mice and rats showed dose-dependent exposure in the small intestine, colon, mesenteric lymph nodes (MLN) and Peyer's Patches (PP), but much lower exposure if any in blood and urine. Oral dosing of a fluorescent dye conjugate of PTG-100 and imaging by fluorescence microscopy or IHC showed the peptide accumulates in the lamina propria of tissues from the small intestine. Daily dosing with PTG-100 in murine DSS colitis models showed a dose-dependent reduction of CD4+CD44high CD45RBlow β7+ T cells in the MLN and PP, and a concomitant increase in the spleen and blood as measured by FACS. There was also a strong reduction of β7+ cell infiltration into lamina propria lesions of the distal colon as measured by IHC. PTG-100 also caused a dose-dependent reduction in body weight loss and mucosal injury as assessed by endoscopy. Daily oral dosing of PTG-100 in normal cynomolgus monkeys resulted in high blood receptor occupancy of memory T cells, and a dose-dependent increase in the percentage of α4β7 memory CD4+ T cells in the blood. There were no adverse clinical or microscopic changes with PTG-100 administration in 6-week GLP toxicology studies in rat and monkey up to 90 and 75 mg·kg−1·d−1, respectively. Safety pharmacology and mutagenesis studies demonstrated no adverse findings. PTG-100 is a first-in-class oral α4β7-selective antagonist being developed for the treatment of patients with IBD. PTG-100 reaches high concentrations in gut tissues and alters the trafficking of gut-homing T cells in mice and cynomolgus monkeys. The lack of toxicity in the full battery of safety and toxicology studies to date coupled with low exposure in blood suggest that PTG-100 will be suitable for human trials.