- Building bridges for highly selective, potent and stable oxytocin and vasopressin analogs
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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 (dOTmeta) gave highest affinity (50 nM Ki), selectivity (34-fold), and agonist potency (34 nM EC50, 87-fold selectivity) towards OTR. Surprisingly, ortho-cyclized analogs demonstrated OTR and vasopressin V1a receptor subtype affinity (220 nM and 69 nM, respectively) and pharmacological activity (294 nM and 35 nM, respectively). V1a 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 IC50) 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.
- Beard, Rhiannon,Stucki, Andy,Schmitt, Muriel,Py, Gabrielle,Grundschober, Christophe,Gee, Antony D.,Tate, Edward W.
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- Systematic N-methylation of oxytocin: Impact on pharmacology and intramolecular hydrogen bonding network
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Oxytocin (OT) is a peptide hormone agonist of the OT receptor (OTR) that plays an important role in social behaviors such as pair bonding, maternal bonding and trust. The pharmaceutical development of OT as an oral peptide therapeutic has been hindered historically by its unfavorable physicochemical properties, including molecular weight, polarity and number of hydrogen bond donors, which determines poor cell permeability. Here we describe the first systematic study of single and multiple N-methylations of OT and their effect on physicochemical properties as well as potency at the OT receptor. The agonist EC50and percent effect for OTR are reported and show that most N-methylations are tolerated but with some loss in potency compared to OT. The effect of N-methylation on exposed polarity is assessed through the EPSA chromatographic method and the results validated against NMR temperature coefficient experiments and the determination of NMR solution structures. We found that backbone methylation of residues not involved in IMHB and removal of the N-terminal amine can significantly reduce the exposed polarity of peptides, and yet retain a significant OTR agonist activity. The results of this study also expose the potential challenge of using the N-methylation strategy for the OT system; while exposed polarity is reduced, in some cases backbone methylation produces a significant conformational change that compromises agonist activity. The data presented provides useful insights on the SAR of OT and suggests future design strategies that can be used to develop more permeable OTR agonists based on the OT framework.
- Sciabola, Simone,Goetz, Gilles H.,Bai, Guoyun,Rogers, Bruce N.,Gray, David L.,Duplantier, Allen,Fonseca, Kari R.,Vanase-Frawley, Michelle A.,Kablaoui, Natasha M.
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- A study of the relationship between biological activity and prolyl amide isomer geometry in oxytocin using 5-tert-butylproline to augment the Cys6- Pro7 amide cis-isomer population
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Three [5-t-BuPro7]oxytocin analogues were synthesized by substituting (2S,5R)-5-tert-butyl-proline for proline in oxytocin, [Mpa1]oxytocin, and [dPen1]oxytocin. Relative to oxytocin, [5-t-BuPro7]oxytocin and [Mpa1,5-t- BuPro7]oxytocin exhibited strongly reduced binding affinity to the receptor; however, both peptides maintained the pharmacophore characteristics responsible for signal transfer evoking the same maximal response as oxytocin in the single-dose procedure and exhibiting partial agonistic activity in the cumulative dose-response procedure. Although [dPen1]oxytocin exhibited inhibitory as well as partial agonistic activity, [dPen1,5-t- BuPro7]oxytocin exhibited only inhibitory potency with a similar in vitro pA2 value of 7.50 in the absence of magnesium. In the presence of magnesium, [dPen1,5-t-BuPro7]oxytocin exhibited stronger inhibitory potency than [dPen1]oxytocin and no partial agonism. Assignment of the proton signals for the 5-tert-butylprolyl amide cis- and trans-isomers by two-dimensional NMR experiments in water indicated that the Cys6-Pro7 peptide bond cis-isomer population was augmented relative to the prolyl peptides and measured respectively at 35%, 33%, and 20% in the 5-tert-butylproline7 analogues of oxytocin, [Mpa1]oxytocin and [Dpen1]oxytocin. Although caution must be taken when relating the increase in cis-isomer population with an influence on biological activity in [5-t-BuPro7]oxytocin analogues, the synthesis and evaluation of analogues 1-3 have provided additional evidence that can be used to support the hypothesis that the prolyl amide cis-isomer may favor antagonism and the trans-isomer is necessary for agonist activity.
- Bélec, Laurent,Slaninova, Jirina,Lubell, William D.
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p. 1448 - 1455
(2007/10/03)
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