BML‐241 fails to display selective antagonism at the sphingosine‐1‐phosphate receptor, S1P 3

Background and purpose: The thiazolidine carboxylic acid, BML‐241, has been proposed as a lead compound in development of selective antagonists at the sphingosine‐1‐phosphate receptor (S1P 3 ), based on its inhibition of the rise in intracellular calcium concentrations ([Ca 2+ ] i ) in HeLa cells overexpressing S1P receptors. We have studied the antagonistic properties of BML‐241 for the S1P 3 receptor in more detail. Experimental approach: Chinese hamster ovary (CHO) cells stably transfected with the S1P 3 , S1P 2 or α 1A ‐adrenoceptors were used to investigate the effect of BML‐241 on increases in [Ca 2+ ] i mediated via different receptors. CHO‐K1 cells were used to study ATP‐induced [Ca 2+ ] i elevations. Effects on S1P 3 ‐mediated inhibition of forskolin‐induced cAMP accumulation and on binding to α 1A ‐adrenoceptors were also investigated. In addition, the effect of BML‐241 on contractions of rat mesenteric artery induced by phenylephrine was studied in an organ bath. Key results: High concentrations of BML‐241 (10 μM) inhibited the rise in [Ca 2+ ] i induced by S1P 3 and S1P 2 receptor stimulation; lower concentrations were ineffective. This high concentration of BML‐241 also inhibited [Ca 2+ ] i increases via P2 (nucleotide) receptor or α 1A ‐adrenoceptor stimulation. Moreover, BML‐241 (10 μM) inhibited α 1 ‐adrenoceptor‐mediated contraction of rat mesenteric artery but did not displace [ 3 H]‐prazosin from α 1A ‐adrenoceptors in concentrations up to 100 μM. BML‐241 (10 μM) did not affect the S1P 3 ‐mediated decrease of forskolin‐induced cAMP accumulation. Conclusions and Implications: We conclude that BML‐241 is a low potency, non‐selective inhibitor of increases in [Ca 2+ ] i , rather than a specific antagonist at the S1P 3 receptor. British Journal of Pharmacology (2006) 149 , 277–282. doi: 10.1038/sj.bjp.0706872