A4250 is a highly potent and selective inhibitor of the ileal bile acid transporter (IBAT, sometimes also referred to as the apical sodium dependent bile acid transporter (ASBT)) that has minimal systemic exposure and acts locally in the gut. In an open label Phase 2 study in children with cholestatic liver disease and pruritus, A4250 showed reductions in serum bile acids and pruritus in most patients and exhibited a favorable overall tolerability profile.

Albireo is developing A4250 initially to treat patients with PFIC, a rare genetic liver disease, and plans to consider additional development in other pediatric cholestatic liver diseases and disorders in the future. Albireo expects to initiate a planned Phase 3 study of A4250 in patients with PFIC in the second half of 2017.

A4250 has been granted orphan drug designation for PFIC in the United States and the European Union and has been granted access to the PRIority MEdicines (PRIME) program of the European Medicines Agency (EMA) for the treatment of PFIC.

How it works:

When the flow of bile from the liver stops or is disrupted, known as cholestasis, bile acids accumulate in the liver. Elevated bile acid levels in the liver and serum are primary characteristics of cholestatic liver diseases and have been linked to severe pruritus in these patients. The IBAT is primarily responsible for mediating the uptake of bile acids from the small intestine to the liver as part of a process known as enterohepatic circulation. Typically, approximately 95 percent of bile acids are recirculated via the IBAT to the liver. Accordingly, a product capable of inhibiting the IBAT would lead to less bile acids returning to the liver and represent a promising approach for treating cholestatic liver diseases.

In addition to the effects on liver and serum bile acids, IBAT inhibition has also been shown in the clinic to decrease LDL cholesterol and increase GLP1 secretion (which is linked to decreased insulin resistance) and, preclinically, to decrease pro-inflammatory markers (such as tumor necrosis factor alpha, or Tnf-α), and profibrotic markers (such as collagen, type 1, alpha 1 and 2) in the liver, as well as NAFLD (nonalcoholic fatty liver disease) Activity Score. High cholesterol, insulin resistance, increased liver inflammation and fibrosis are all key hallmarks of NASH, making IBAT inhibition likewise a promising approach for treating NASH.

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