Targeting the Prostaglandin F2α Receptor for Preventing Preterm Labor with Azapeptide Tocolytics

The prostaglandin-F2 alpha (PGF2 alpha) receptor (FP) was targeted to develop tocolytic agents for inhibiting preterm labor. Azabicycloalkane and azapeptide mimics 2-10 were synthesized based on the (3S,6S,9S)-indolizidin-2-one amino acid analogue PDC113.824 (1), which was shown to modulate FP by a biased allosteric mechanism, involving both G alpha q- and G alpha 12-mediated signaling pathways, and exhibited significant tocolytic activity delaying preterm labor in a mouse model (Goupil; J. Biol. Chem. 2010, 285,25624-25636), Although changes in azabicycloalkane stereochemistry and ring size caused loss of activity, replacement of the indolizidin-2-one amino acid with azaGly-Pro and azaPhe-Pro gave azapeptides 6 and 8, which reduced PGF2 alpha-induced myometrial contractions, potentiated the effect of PGF2 alpha on G alpha q-mediated ERK1/2 activation, and inhibited FP modulation of cell ruffling, a response dependent on the G alpha 12/RhoA/ROCK signaling pathway. Revealing complementarities of azabicycloalkane and azapeptide mimics, novel probes, and efficient tocolytic agents were made to study allosteric modulation of the FP receptor.