Larazotide Acetate (AT-1001)

Larazotide acetate (AT-1001) is a synthetic eight-amino acid peptide developed by Alba Therapeutics (acquired by 9 Meters Biopharma) specifically to regulate intestinal tight junction permeability. It represents the most advanced clinical candidate targeting the tight junction system as a therapeutic strategy for intestinal barrier dysfunction - a pathophysiology now recognised as central to coeliac disease, inflammatory bowel disease, and multiple systemic immune and metabolic conditions.

The mechanism centres on zonulin signalling. Zonulin (pre-haptoglobin 2) is an endogenous protein identified by Dr. Alessio Fasano's laboratory that functions as the physiological regulator of intestinal tight junction permeability. When zonulin binds to its receptor on intestinal epithelial cells (CXCR3 receptor), it triggers a signalling cascade that transiently disassembles tight junction proteins (including occludin, claudins, and zonula occludens proteins), increasing paracellular permeability and allowing larger molecules to cross the intestinal barrier.

In coeliac disease, gluten fragments (particularly gliadin) trigger excessive zonulin release, creating a chronically leaky intestinal barrier that allows gluten peptides to access the lamina propria, driving the destructive immune response against enterocytes. Other conditions including type 1 diabetes, multiple sclerosis, and various IBD presentations are associated with dysregulated zonulin-mediated permeability.

Larazotide acetate was designed as a competitive antagonist of the zonulin receptor (CXCR3). By binding CXCR3 without triggering downstream signalling, larazotide blocks zonulin-induced tight junction disassembly. This prevents the pathological permeability increase that allows luminal antigens to access immune cells in the gut mucosa, reducing antigen-driven inflammation.

Phase 2 clinical trials in coeliac disease produced encouraging results. A 12-week Phase 2b study in patients with coeliac disease on a gluten-free diet showed that 0.5 mg three times daily significantly reduced gastrointestinal symptom scores and markers of systemic immune activation compared to placebo - even in patients with inadvertent gluten exposure. The Phase 3 STAND trial (2019-2022) evaluated larazotide as an adjunct to the gluten-free diet, the only currently available management strategy for coeliac disease.

Beyond coeliac disease, preclinical research has investigated larazotide in non-coeliac gluten sensitivity, irritable bowel syndrome, Crohn's disease, and experimental models of sepsis-induced gut barrier failure. The principle that blocking pathological tight junction opening could reduce antigen translocation and downstream systemic inflammation is relevant across many conditions where "leaky gut" has been implicated.

Larazotide's primarily luminal mechanism of action (it is minimally absorbed systemically) means that therapeutic effects are concentrated where they are needed - in the intestinal lumen and epithelial layer - while systemic exposure and associated side effects are minimised. This local action profile is a significant therapeutic advantage for a compound targeting the intestinal epithelium.