Definition

The fumarate salt form of siponimod, an orally bioavailable sphingosine 1-phosphate (S1P) receptor modulator, with potential anti-inflammatory and immunomodulating activities. Upon oral administration, siponimod targets and binds to S1P receptors 1 and 5 on lymphocytes. This prevents the egress of lymphocytes from lymph nodes, thereby reducing both the number of circulating peripheral lymphocytes and the infiltration of lymphocytes into target tissues, such as the central nervous system (CNS). This prevents lymphocyte-mediated immune response and may reduce inflammation. S1P plays a key role in lymphocyte migration from lymphoid tissues. Siponimod does not target S1P receptor 3, the activation of which may be responsible for adverse effects such as bradycardia associated with other S1P receptor modulators.