Phosphorothioate analogues of alkyl lysophosphatidic acid as LPA ₃ receptor-selective agonists

The metabolically stabilized LPA analogue 1-oleoyl-2-O-methyl-rac- glycerophosphorothioate (OMPT) was recently shown to be a potent subtype-selective agonist for LPA₃, a G-protein-coupled receptor (GPCR) in the endothelial differentiation gene (EDG) family. Further stabilization was achieved by replacing the sn-1 O-acyl group with an O-alkyl ether. A new synthetic route for the enantiospecific synthesis of the resulting alkyl LPA phosphorothioate analogues is described. The pharmacological properties of the alkyl OMPT analogues were characterized for subtype-specific agonist activity using Ca²⁺-mobilization assays in RH7777 cells expressing the individual EDG family LPA receptors. Alkyl OMPT analogues induced cell migration in cancer cells mediated through LPA₁. Alkyl OMPT analogues also activated Ca²⁺ release through LPA₂ activation but with less potency than sn-1-oleoyl LPA. In contrast, alkyl OMPT analogues were potent LPA₃ agonists. The alkyl OMPTs 1 and 3 induced cell proliferation at submicromolar concentrations in 10T1/2 fibroblasts. Interestingly, the absolute configuration of the sn-2 methoxy group of the alkyl OMPT analogues was not recognized by any of the LPA receptors in the EDG family. By using a reporter gene assay for the LPA-activated nuclear transcription factor PPARγ, we demonstrated that phosphorothioate diesters have agonist activity that is independent of their ligand properties at the LPA-activated GPCRs. The availability of new alkyl LPA analogues expands the scope of structure-activity studies and will further refine the molecular nature of ligand-receptor interactions for this class of GPCRs.