Abstract
S1P1 (sphingosine-1-phosphate receptor 1) agonists prevent lymphocyte egress from secondary lymphoid organs and cause a reduction of the number of circulating blood lymphocytes. We hypothesized that S1P1 receptor modulators with pathway-selective signaling properties could help to further elucidate molecular mechanisms involved in lymphocyte trapping. A proprietary S1P1 receptor modulator library was screened for compounds with clear potency differences in β-arrestin recruitment and Gαi protein-mediated signaling. We describe here structure-activity relationships of highly potent S1P1 modulators with apparent pathway selectivity for β-arrestin recruitment. The most differentiated compound (D3-2) displayed a 180-fold higher potency in the β-arrestin recruitment assay (EC50 0.9 ±1 nM) as compared with the Gαi-activation assay (167 ± 1.4 nM), whereas ponesimod, a S1P1 modulator that is currently in advanced clinical development in multiple sclerosis, was equipotent in both assays (EC50 1.5 ±1.3 nM and EC50 1.1 ±1.5 nM, respectively). Using these novel compounds as pharmacological tools, we showed that although a high potency in β-arrestin recruitment is required to fully internalize the S1P1 receptors, the potency in inducing Gαi signaling determines the rate of receptor internalization in vitro. In contrast to ponesimod, the compound D3-2 did not reduce the number or circulating lymphocytes in rats despite high plasma exposures. Thus, for rapid and maximal S1P1 receptor internalization a high potency in both Gαi signaling and β-arrestin recruitment is mandatory and this translates into efficient reduction of the number of circulating lymphocytes in vivo.
- The American Society for Pharmacology and Experimental Therapeutics