Etrasimod (formerly known as APD334) is Arena Pharmaceuticals’ therapeutic candidate to treat autoimmune diseases like multiple sclerosis (MS) and ulcerative colitis. The drug is an oral formulation agonist (a substance which exerts its effect after binding to a particular receptor) that targets the S1P receptor. This receptor is involved in the regulation of the body’s immune response and is an important target of treatments for autoimmune disorders.
How etrasimod works
S1P receptors are heavily involved in immune modulation, immune cell (lymphocyte) regulation and development, and in suppressing the innate immune response of T-cells (a type of lymphocyte).
S1P receptors are found on the outside of lymphocytes. The activation of these receptors triggers the lymphocytes to leave lymph nodes and enter the bloodstream, ultimately making their way into target tissue. In MS patients, lymphocytes enter and accumulate in the brain and spinal cord, causing damage to nerve cells through inflammation.
S1P receptor modulators are immunosuppressive and anti-inflammatory in nature as they block S1P signaling and prevent the lymphocytes from entering tissues. This is how etrasimod works.
Research has shown that the drug successfully reduced the rate of inflammation in preclinical mouse models of MS.
Etrasimod in clinical trials
With positive results from preclinical studies, a Phase 1b randomized, double-blind and placebo-controlled trial was undertaken to evaluate the safety, tolerability, pharmacodynamics, and pharmacokinetics of multiple-ascending doses of etrasimod. Results from this study, in 50 healthy volunteers given etrasimod and 10 others given a placebo, demonstrated that the treatment can reduce the lymphocyte count in the blood, with mean decreases of up to 69% over a 21-day period from baseline. No serious adverse effects were recorded, and those reported were mild to moderate cases of dizziness, headache, constipation, or diarrhea.
Arena is currently running Phase 2 clinical trials, assessing the safety and efficacy of estrasimod in patients with a number of autoimmune diseases, including inflammatory bowel disease (NCT03139032), ulcerative colitis (NCT02447302 and NCT02536404), primary biliary cholangitis (NCT03155932), and pyoderma gangrenosum (NCT03072953). Currently, no clinical studies are being prepared to assess estrasimod as an MS treatment.
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