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, LPA(1), LPA(2), and LPA(3), 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-[S-35]thio)triphosphate (GTP[gamma S-35]) 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[gamma S-35] 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 LPA(1)/LPA(3) competitive antagonist. Several compounds that had smaller side chains were found to be LPA(1)-selective agonists.