– RO-3 is a potent, CNS-penetrant, and orally active P2X3 and P2X2/3 antagonist with pIC50s of 5.9 and 7.0 for human homomultimeric P2X3 and heteromultimeric P2X2/3 receptors, respectively. RO-3 shows selectivity for P2X3 and P2X2/3 over all other functional homomultimeric P2X receptors (IC50 >10??M at P2X1,2,4,5,7)[1].