In vivo antinociception of potent mu opioid agonist tetrapeptide analogues and comparison with a compact opioid agonist - neurokinin 1 receptor antagonist chimera

Abstract

BackgroundAn important limiting factor in the development of centrally acting pharmaceuticals is the blood-brain barrier (BBB). Transport of therapeutic peptides through this highly protective physiological barrier remains a challenge for peptide drug delivery into the central nervous system (CNS). Because the most common strategy to treat moderate to severe pain consists of the activation of opioid receptors in the brain, the development of active opioid peptide analogues as potential analgesics requires compounds with a high resistance to enzymatic degradation and an ability to cross the BBB.ResultsHerein we report that tetrapeptide analogues of the type H-Dmt1-Xxx2-Yyy3-Gly4-NH2 are transported into the brain after intravenous and subcutaneous administration and are able to activate the μ- and δ opioid receptors more efficiently and over longer periods of time than morphine. Using the hot water tail flick test as the animal model for antinociception, a comparison in potency is presented between a side chain conformationally constrained analogue containing the benzazepine ring (BVD03, Yyy3: Aba), and a "ring opened" analogue (BVD02, Yyy3: Phe). The results show that in addition to the increased lipophilicity through amide bond N-methylation, the conformational constraint introduced at the level of the Phe3 side chain causes a prolonged antinociception. Further replacement of NMe-D-Ala2 by D-Arg2 in the tetrapeptide sequence led to an improved potency as demonstrated by a higher and maintained antinociception for AN81 (Xxx2: D-Arg) vs. BVD03 (Xxx2: NMe-D-Ala). A daily injection of the studied opioid ligands over a time period of 5 days did however result in a substantial decrease in antinociception on the fifth day of the experiment. The compact opioid agonist - NK1 antagonist hybrid SBCHM01 could not circumvent opioid induced tolerance.ConclusionsWe demonstrated that the introduction of a conformational constraint has an important impact on opioid receptor activation and subsequent antinociception in vivo. Further amino acid substitution allowed to identify AN81 as an opioid ligand able to access the CNS and induce antinociception at very low doses (0.1 mg/kg) over a time period up to 7 hours. However, tolerance became apparent after repetitive i.v. administration of the investigated tetrapeptides. This side effect was also observed with the dual opioid agonist-NK1 receptor antagonist SBCHM01.

Endomorphin-1 analogues (MELs) penetrate the blood–brain barrier and exhibit good analgesic effects with minimal side effects

“…We propose that the improved BBB permeability of our peptides was achieved by incorporation of the conformational constrained residue Map into the 4th position of EM-1. Compared with the Phe 4 in the parent peptide, both the aromatic group and the backbone structure of Map were highly constrained, and this limitation of the conformational flexibility could be regarded as an efficient strategy for BBB permeability (Keresztes et al, 2010;Guillemyn et al, 2012). In addition, the improved CNS penetrating efficacy of EM-1 has previously been achieved by second-site or multiple-site modifications (Keresztes et al, 2010;Liu and Wang, 2012), and our study indicated that the C-terminus is another potential site to regulate the BBB permeability of EM-1.…”

“…injections of morphine and examined compounds once daily for five days, between 10 and 12 am (Matsumoto et al, 2008;Guillemyn et al, 2012). The development of tolerance was established by assessing the antinociception effect.…”

Investigational peptide and peptidomimetic μ and δ opioid receptor agonists in the relief of pain

“…Guillemyn et al has reported [38] that tetrapeptide analogs of the type H-Dmt 1 -Xxx 2 -Yyy 3 -Gly 4 -NH 2 are able to cross the BBB after intravenous and subcutaneous administration and successfully activate the MOR and DOR more efficiently and over longer periods of time compared to morphine. The authors have shown a comparison in potency of antinociception (using the hot water tail flick test as the animal model) between a side chain conformationally constrained analogue containing the benzazepine ring (BVD03: H-Dmt-NMe-D-Ala-Aba-Gly-NH 2 , where Xxx 2 = NMe-D-Ala and Yyy 3 = Aba), and a ‘ring opened’ analog (BVD02: H-Dmt-NMe-D-Ala-Aba-Gly-NH 2 , where Xxx 2 = NMe-D-Ala and Yyy 3 = Phe).…”

Dual Alleviation of Acute and Neuropathic Pain by Fused Opioid Agonist-Neurokinin 1 Antagonist Peptidomimetics

“…19,20,26 Moreover, the in vivo studies showed activity in acute pain 26 as well as in neuropathic pain models. 20 The potent analgesic responses after intravenous (i.v.)…”

“…administration indicated that these hybrid compounds were capable of crossing the blood−brain barrier (BBB), but unfortunately they still produced analgesic tolerance and cross-tolerance with morphine. 20,26 The activity profile of DMLs, such as the opioid agonist-NK1 antagonist hybrids, is often dependent on the relative potency at the two target receptors, the modulation of which is a very challenging aspect of DML design.…”