Structure-Based Design of Glycosylated Oxytocin Analogues with Improved Selectivity and Antinociceptive Activity

Acute and chronic pain is often treated with opioids despite the negative side effects of constipation, physical dependence, respiratory depression, and overdose. The misuse of opioid analgesics has given rise to the opioid crisis/epidemic, and alternate nonaddictive analgesics are urgently needed. Oxytocin, a pituitary hormone, is an alternative to the small molecule treatments available and has been used as an analgesic as well as for the treatment and prevention of opioid use disorder (OUD). Clinical implementation is limited by its poor pharmacokinetic profile, a result of the labile disulfide bond between two cysteine residues in the native sequence. Stable brain penetrant oxytocin analogues have been synthesized by replacement of the disulfide bond with a stable lactam and glycosidation of the C-terminus. These analogues show exquisite selectivity for the oxytocin receptor and potent in vivo antinociception in mice following peripheral (i.v.) administration, supporting further study of their clinical potential.

Design of Analgesic Trivalent Peptides with Low Withdrawal Symptoms: Probing the Antinociceptive Profile of Novel Linear and Cyclic Peptides as Opioid Pan Ligands

The discovery of efficacious and safe analgesics with reduced side effects is the foremost challenge in the pain field. In this work, we report the in vitro and in vivo evaluation of linear and cyclic analogues of biphalin with the aim to complete the series of structural modifications previously applied in the development of opioid peptides incorporating a xylene bridge. Replacement of Tyr^1,1' by Dmt (2,5-dimethyltyrosine) in the linear biphalin analogue AM94 and cyclic analogue MACE4 resulted in two new compounds (namely, MJ2 and MJ5) endowed with improved KOR/MOR/DOR binding affinity. Both compounds showed a strong antinociceptive profile in in vivo models of nociception, allodynia, and hyperalgesia via the tail flick, hot plate, and formalin tests after intracerebroventricular and subcutaneous administration. One of these ligands, MJ2, was also tested in tolerance and dependence studies, exhibiting very little withdrawal symptoms.

The role of opioid receptors in modulating Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurological disorder characterized by accumulation of amyloid plaques and neurofibrillary tangles. Long term investigation of AD pathogenesis suggests that β-site amyloid precursor protein [APP] cleaving enzyme 1 (BACE1) and γ-secretase enzymes promote the amyloidogenic pathway and produce toxic Aβ peptides that are predisposed to aggregate in the brain. Hence, the targeted inhibition of BACE1/γ-secretase expression and function is a promising approach for AD therapy. Several reports have suggested that the opioid family of G-protein coupled receptors modulate the etiology of AD progression. It has also been found that changes in the signaling pathways of opioid receptors increased the expression of BACE1 and γ-secretase, and is strongly correlated with abnormal production of Aβ and pathogenesis of AD. Thus, the opioid receptor family is a promising candidate for targeted drug development to treat AD. In this review, we outline the involvement and mechanisms of opioid receptor signaling modulation in Alzheimer's Disease progression.

Discovery of κ Opioid Receptor (KOR)-Selective d-Tetrapeptides with Improved In Vivo Antinociceptive Effect after Peripheral Administration

Peripherally active tetrapeptides as selective κ opioid receptor (KOR) agonists have been prepared in good overall yields and high purity following solid-phase peptide synthesis via Fmoc protection strategy. Structural modifications at the first and second position of the lead compound FF(d-Nle)R-NH2 (FE200041) were contemplated with aromatic side chains containing d-amino acids, such as (d)-pF-Phe, (d)-mF-Phe, (d)-oF-Phe, which led to highly selective and efficacious KOR agonists endowed with strong antinociceptive activity in vivo following intravenous (i.v.) and subcutaneous (s.c.) administration in the tail flick and formalin tests. These results suggest potential clinical applications in the treatment of neuropathic and inflammatory pain.

Design and Synthesis of Brain Penetrant Glycopeptide Analogues of PACAP With Neuroprotective Potential for Traumatic Brain Injury and Parkinsonism

There is an unmet clinical need for curative therapies to treat neurodegenerative disorders. Most mainstay treatments currently on the market only alleviate specific symptoms and do not reverse disease progression. The Pituitary adenylate cyclase-activating polypeptide (PACAP), an endogenous neuropeptide hormone, has been extensively studied as a potential regenerative therapeutic. PACAP is widely distributed in the central nervous system (CNS) and exerts its neuroprotective and neurotrophic effects via the related Class B GPCRs PAC1, VPAC1, and VPAC2, at which the hormone shows roughly equal activity. Vasoactive intestinal peptide (VIP) also activates these receptors, and this close analogue of PACAP has also shown to promote neuronal survival in various animal models of acute and progressive neurodegenerative diseases. However, PACAP's poor pharmacokinetic profile (non-linear PK/PD), and more importantly its limited blood-brain barrier (BBB) permeability has hampered development of this peptide as a therapeutic. We have demonstrated that glycosylation of PACAP and related peptides promotes penetration of the BBB and improves PK properties while retaining efficacy and potency in the low nanomolar range at its target receptors. Furthermore, judicious structure-activity relationship (SAR) studies revealed key motifs that can be modulated to afford compounds with diverse selectivity profiles. Most importantly, we have demonstrated that select PACAP glycopeptide analogues (2LS80Mel and 2LS98Lac) exert potent neuroprotective effects and anti-inflammatory activity in animal models of traumatic brain injury and in a mild-toxin lesion model of Parkinson's disease, highlighting glycosylation as a viable strategy for converting endogenous peptides into robust and efficacious drug candidates.

Synthesis and In Vitro Characterization of Glycopeptide Drug Candidates Related to PACAP1-23

The search for efficacious treatment of neurodegenerative and progressive neuroinflammatory diseases continues, as current therapies are unable to halt or reverse disease progression. PACAP represents one potential therapeutic that provides neuroprotection effects on neurons, and also modulates inflammatory responses and circulation within the brain. However, PACAP is a relatively long peptide hormone that is not trivial to synthesize. Based on previous observations that the shortened isoform PACAP1-23 is capable of inducing neuroprotection in vitro, we were inspired to synthesize shortened glycopeptide analogues of PACAP1-23. Herein, we report the synthesis and in vitro characterization of glycosylated PACAP1-23 analogues that interact strongly with the PAC1 and VPAC1 receptors, while showing reduced activity at the VPAC2 receptor.