Activity of 2-substituted lysophosphatidic acid (LPA) analogs at LPA receptors: Discovery of a LPA₁/LPA₃ receptor antagonist

The physiological implications of lysophosphatidic acid occupancy of individual receptors are largely unknown because selective agonists/antagonists are unavailable currently. The molecular cloning of three high-affinity lysophosphatidic acid receptors, LPA₁, LPA₂, and LPA₃, provides a platform for developing receptor type-selective ligands. Starting with an N-acyl ethanolamide phosphate LPA analog, we made a series of substitutions at the second carbon to generate compounds with varying spatial, stereochemical, and electronic characteristics. Analysis of this series at each recombinant LPA receptor using a guanosine 5′-O-(3-[³⁵S]thio)triphosphate (GTP[-γ³⁵S]) binding assay revealed sharp differences in activity. Our results suggest that these receptors have one spatially restrictive binding pocket that interacts with the 2-substituted moieties and prefers small hydrophobic groups and hydrogen bonding functionalities. The agonist activity predicted by the GTP[γ³⁵S] binding assay was reflected in the activity of a subset of compounds in increasing arterial pressure in anesthetized rats. One compound with a bulky hydrophobic group (VPC12249) was a dual LPA₁/LPA₃ competitive antagonist. Several compounds that had smaller side chains were found to be LPA₁-selective agonists.