Stapled truncated orexin peptides as orexin receptor agonists

In vivo photocontrol of orexin receptors with a nanomolar light-regulated analogue of orexin-B

Orexinergic neurons are critically involved in regulating arousal, wakefulness, and appetite. Their dysfunction has been associated with sleeping disorders, and non-peptide drugs are currently being developed to treat insomnia and narcolepsy. Yet, no light-regulated agents are available to reversibly control their activity. To meet this need, a photoswitchable peptide analogue of the endogenous neuroexcitatory peptide orexin-B was designed, synthesized, and tested in vitro and in vivo. This compound - photorexin - is the first photo-reversible ligand reported for orexin receptors. It allows dynamic control of activity in vitro (including almost the same efficacy as orexin-B, high nanomolar potency, and subtype selectivity to human OX2 receptors) and in vivo in zebrafish larvae by direct application in water. Photorexin induces dose- and light-dependent changes in locomotion and a reduction in the successive induction reflex that is associated with sleep behavior. Molecular dynamics calculations indicate that trans and cis photorexin adopt similar bent conformations and that the only discriminant between their structures and activities is the positioning of the N-terminus. This, in the case of the more active trans isomer, points towards the OX2 N-terminus and extra-cellular loop 2, a region of the receptor known to be involved in ligand binding and recognition consistent with a "message-address" system. Thus, our approach could be extended to several important families of endogenous peptides, such as endothelins, nociceptin, and dynorphins among others, that bind to their cognate receptors through a similar mechanism: a "message" domain involved in receptor activation and signal transduction, and an "address" sequence for receptor occupation and improved binding affinity.

Development of a Selective Peptide κ-Opioid Receptor Antagonist by Late-Stage Functionalization with Cysteine Staples

The κ-opioid receptor (KOR) is an attractive target for the development of novel drugs. KOR agonists are potentially safer pain medications, whereas KOR antagonists are promising drug candidates for the treatment of neuropsychiatric disorders. Hitherto, the vast majority of selective drug leads that have been developed for KOR are small molecules. In this study, novel peptide probes were designed by using an endogenous dynorphin A1-13 sequence as a template for peptide stapling via late-stage cysteine functionalization. Leveraging this strategy, we developed a stable and potent KOR antagonist, CSD-CH2(1,8)-NH2, with approximately 1000-fold improved selectivity for KOR over μ- and δ-opioid receptors. Its potent competitive KOR antagonism was verified in KOR-expressing cells, peripheral dorsal root ganglion neurons, and using the tail-flick and rotarod tests in mice. This work highlights the value of cysteine stapling to develop selective peptide probes to modulate central KOR function, as innovative peptide drug candidates for the treatment of KOR-related illnesses.

The Present and Future of Synthetic Orexin Receptor Agonists

The neuropeptide orexin/hypocretin plays a crucial role in various physiological processes, including the regulation of sleep/wakefulness, appetite, emotion and the reward system. Dysregulation of orexin signaling has been implicated in hypersomnia, especially in narcolepsy, which is a chronic neurological disorder characterized by excessive daytime sleepiness (EDS), sudden loss of muscle tone while awake (cataplexy), sleep paralysis, and hallucinations. Small-molecule orexin receptor agonists have emerged as promising therapeutics for these disorders, and significant progress has been made in this field in the past decade. This review summarizes recent advances in the design and synthesis of orexin receptor agonists, with a focus on peptidic and small-molecule OX2R-selective, dual, and OX1R-selective agonists. The review discusses the key structural features and pharmacological properties of these agonists, as well as their potential therapeutic applications. DATA AVAILABILITY: No data was used for the research described in the article.

Advances in therapeutic peptides targeting G protein-coupled receptors

Dysregulation of peptide-activated pathways causes a range of diseases, fostering the discovery and clinical development of peptide drugs. Many endogenous peptides activate G protein-coupled receptors (GPCRs) - nearly 50 GPCR peptide drugs have been approved to date, most of them for metabolic disease or oncology, and more than 10 potentially first-in-class peptide therapeutics are in the pipeline. The majority of existing peptide therapeutics are agonists, which reflects the currently dominant strategy of modifying the endogenous peptide sequence of ligands for peptide-binding GPCRs. Increasingly, novel strategies are being employed to develop both agonists and antagonists, to both introduce chemical novelty and improve drug-like properties. Pharmacodynamic improvements are evolving to allow biasing ligands to activate specific downstream signalling pathways, in order to optimize efficacy and reduce side effects. In pharmacokinetics, modifications that increase plasma half-life have been revolutionary. Here, we discuss the current status of the peptide drugs targeting GPCRs, with a focus on evolving strategies to improve pharmacokinetic and pharmacodynamic properties.

Determinants of Orexin Receptor Binding and Activation-A Molecular Dynamics Study

We assess the stability of two previously suggested binding modes for the neuropeptide orexin-A in the OX₂ receptor through extensive molecular dynamics simulations. As the activation determinants of the receptor remain unknown, we simulated an unliganded receptor and two small-molecular ligands, the antagonist suvorexant and the agonist Nag26 for comparison. Each system was simulated in pure POPC membrane as well as in the 25% cholesterol–POPC membrane. In total, we carried out 36 μs of simulations. Through this set of simulations, we report a stable binding mode for the C-terminus of orexin-A. In addition, we suggest interactions that would promote orexin receptor activation, as well as others that would stabilize the inactive state.

Strengthening peptide-based drug activity with novel glyconanoparticle

The therapeutic application of peptide-based drugs is significantly limited by the rapid proteolytic degradation that occurs when in blood. Encapsulation of these peptide structures within a delivery system, such as liposomes, can greatly improve both stability and target delivery. As part of our work focused on novel ambiphilic mannosylated neoglycolipids as targeted drug delivery systems, we have developed a C14-alkyl-mannopyranoside that forms self-assembled monodisperse liposomes. Herein, these glycoliposomes are investigated as a potential method to improve the plasma stability of peptide-based drugs. Reversed phase high-performance liquid chromatography (RP-HPLC) and mass spectrometry (MS) methods were developed to assess the in vitro plasma stability of two structurally diverse peptides, including the kappa opioid receptor selective antagonist dynantin, and the NOD2 innate immune receptor ligand muramyl dipeptide (MDP). The RP-HPLC methods developed were able to resolve the peptides from background plasma contaminants and provided suitable response levels and linearity over an appropriate concentration range. Both compounds were found to be significantly degraded in rat plasma. Increasing degrees of both entrapment and stabilization were noted when dynantin was combined with the C14-alkyl-mannopyranoside in increasing peptide:glycoside ratios. The combination of MDP with the glycolipid also led to peptide entrapment, which greatly improved the plasma stability of the peptide. Overall, the results clearly indicate that the stability of peptide-based structures, which are subject to degradation in plasma, can be greatly improved via entrapment within C14-alkyl-mannopyranoside-bearing glycoliposomes.