This invention relates to the identification of LPA as a ligand for the G-protein coupled receptors OSGPR114 and OSGPR78. The invention is directed to new methods for screening candidate drugs for their ability to modulate the activity of OSGPR114 or OSGPR78, and new pharmaceutical agents identified by these methods. It is also directed to the use of such agents in the manufacture of medicaments for the treatment of OSGPR114 or OSGPR78 mediated diseases, and methods of treating diseases such as cancers by administering to an individual a therapeutic amount of a modulator of OSGPR114 or OSGPR78 identified by these methods.