Actions of a series of PPADS analogs at P2X(1) and P2X(3) receptors

Seven PPADS (Pyridoxal-5'- Phosphate 6-Azophenyl 2',4'-DiSulfonate) analogs were investigated at Group 1 P2X receptors expressed in Xenopus oocytes. A ll seven analogs potently inhibited P2X, (IC50 range, 5-32 nM) and P2X(3) ( IC50 range, 22-345 nM), the two Group I P2X receptor subtypes. Analogs show ed greater inhibitory activity where the pyridoxal moiety of PPADS containe d a 5'-phosphonate group, rather than a 5'-phosphate group. Analogs also sh owed greater potency where disulfonate groups were removed from, or substit uted at, the azophenyl moiety. The most active analog was MRS 2257 (pyridox al-5'-phosphonate 6-azophenyl 3',5'-bismethylenephosphonate) at P2X(1) (IC5 0, 5 nM) and P2X(3) (IC50, 22 nM) receptors, being 14-fold and 10-fold more potent than PPADS itself. MRS 2257 produced a nonsurmountable inhibition w hen tested against a range of ATP concentrations, although blockade was rev ersed by about 85% after 20 minutes of washout. TNP-ATP and Ip(5)I were equ ipotent with MRS 2257 at P2X1 receptors, whereas TNP-ATP was 64-fold more p otent than MRS 2257 at P2X3 receptors. In conclusion, the PPADS template ca n be altered at the pyridoxal and phenyl moieties to produce P2X1 and P2X3 receptor antagonists showing higher potency and greater degree of reversibi lity than the parent compound at these Group I P2X receptors. (C) 2001 Wile y-Liss, Inc.