KSI-6666 is a potent and selective competitive antagonist of sphingosine 1-phosphate receptor 1 (S1PR1, S1P1 receptor) with IC50 of 6.4 nM in GTP binding assay, and IC50 of 2.64 nM in in Ca2+ mobilization assays.
KSI-6666 competitively inhibits the agonist-dependent Ca2+ mobilization of S1PR1, but not for other S1PRs. KSI-6666 inhibited mouse and rat S1PR1 with similar inhibitory activity as human S1PR1, demonstrating its cross-species efficacy.
KSI-6666 functions as a potent competitive inhibitor of S1PR1 with less effect on cardiac and pulmonary functions.
KSI-6666 is a potent anti-inflammatory agent in the mouse EAE model.
KSI-6666 is an insurmountable antagonist with pseudoirreversible inhibitory activity, which is consistent with the hindered dissociation of KSI-6666 predicted by MetaD simulation, shows persistent efficacy.
Residue Met124 of S1PR1 is critical for the pseudoirreversible inhibition by KSI-6666.