No abstract

Oxytocin (OT) is an exciting potential therapeutic agent, but it is highly sensitive to modification and suffers extensive degradation at elevated temperature and in vivo. Here we report studies towards OT analogs with favorable selectivity, affinity and potency towards the oxytocin receptor (OTR), in addition to improving stability of the peptide by bridging the disulfide region with substituted dibromo-xylene analogs. We found a sensitive structure-activity relationship in which meta-cyclized analogs (dOT) gave highest affinity (50 nM K), selectivity (34-fold), and agonist potency (34 nM EC, 87-fold selectivity) towards OTR. Surprisingly, ortho-cyclized analogs demonstrated OTR and vasopressin V receptor subtype affinity (220 nM and 69 nM, respectively) and pharmacological activity (294 nM and 35 nM, respectively). V binding and selectivity for ortho-cyclized peptides could be improved 6-fold by substituting a neutral residue at position 8 with a basic amino acid, providing potent antagonists (14 nM IC) that displayed no activation of the OTR. Furthermore, xylene-bridged analogs demonstrated increased stability compared to OT at elevated temperature, demonstrating promising therapeutic potential for these analogs which warrants further study.

3 Inverse agonism of MPEP at hmGlu5a receptors was partially reduced by mutation C57S, significantly reduced by C99S and C57/99S mutations and totally abolished in the tetramutant. 4 We confirmed the surface expression of all the mutated receptors using [ 3 H]MPEP binding analysis on whole cells. However, B max values were increased for mutant C57S, C99S, and C57/99S but decreased in the C57/93/99/129S receptor. 5 The 24 h preincubation of cells expressing hmGlu5a receptors with 1 mM MPEP followed by extensive washing dramatically increased the wild-type receptor efficacy to quisqualate, to the same levels seen with C57/99S receptors. MPEP preincubation did not affect C57/99S function. 6 We conclude that cysteines 57 and 99 are key residues necessary for modulating hmGlu5a receptor function.