Twin and triplet drugs in opioid research

Analgesic Peptides: From Natural Diversity to Rational Design

Pain affects one-third of the global population and is a significant public health issue. The use of opioid drugs, which are the strongest painkillers, is associated with several side effects, such as tolerance, addiction, overdose, and even death. An increasing demand for novel, safer analgesic agents is a driving force for exploring natural sources of bioactive peptides with antinociceptive activity. Since the G protein-coupled receptors (GPCRs) play a crucial role in pain modulation, the discovery of new peptide ligands for GPCRs is a significant challenge for novel drug development. The aim of this review is to present peptides of human and animal origin with antinociceptive potential and to show the possibilities of their modification, as well as the design of novel structures. The study presents the current knowledge on structure-activity relationship in the design of peptide-based biomimetic compounds, the modification strategies directed at increasing the antinociceptive activity, and improvement of metabolic stability and pharmacodynamic profile. The procedures employed in prolonged drug delivery of emerging compounds are also discussed. The work summarizes the conditions leading to the development of potential morphine replacements.

Platinum Twin and Triplet Drugs Improve Chemoimmunotherapy

Several chemoimmunotherapy regimens have been approved by the U.S. FDA, verifying the great clinical value and potential of the strategy. However, the immunomodulatory function of chemotherapy was insufficient, which did not provide extra overall survival benefits, especially in a head-to-head comparison of chemoimmunotherapy versus immunotherapy. Here, we engineered twin and triplet drugs derived from an immunogenic chemotherapeutic drug (oxaliplatin) and small-molecule inhibitors of negative immunoregulation pathways (COX2 and IDO) in tumors as an improved chemotherapeutic component within chemoimmunotherapy. The twin and triplet drugs exhibited significantly improved synergy with anti-PD-1 in a CT26 colorectal mouse tumor model. Mechanistic analyses revealed that the drug induced immunogenic cell death and restored tumor immune microenvironment toward tumor clearance in vivo, resulting in a great decrease in tumor-infiltrating Tregs and an increase in the CD8+ T/Treg ratio when combined with anti-PD-1. Our work expands the application of platinum twin drugs in combination with an immune checkpoint blockade.

Multitargeted Opioid Ligand Discovery as a Strategy to Retain Analgesia and Reduce Opioid-Related Adverse Effects

The global "opioid crisis" has placed enormous pressure on the opioid ligand discovery community to produce novel opioid analgesics with superior opioid-related adverse-effect profiles compared with morphine. In this Perspective, the multitargeted opioid ligand strategy for the discovery of opioid analgesics with superior preclinical therapeutic indices relative to morphine is reviewed and discussed. Dual-targeted μ-opioid (MOP)/δ-opioid (DOP) ligands in which the in vitro DOP antagonist potency at least equals that of the MOP agonist activity, and are devoid of DOP or κ-opioid (KOP) agonist activity, are sufficiently promising candidates to warrant further investigation. Dual-targeted MOP/NOP partial agonists have superior preclinical therapeutic indices to morphine and/or fentanyl in nonhuman primates and are also considered promising. Based on the poor preclinical and clinical therapeutic indices of cebranopadol, which is a full agonist at MOP, DOP, and NOP receptors and a partial agonist at the KOP receptor, this pharmacologic template should be avoided.

Chimeric Structures in Mental Illnesses-"Magic" Molecules Specified for Complex Disorders

Mental health problems cover a wide spectrum of diseases, including mild to moderate anxiety, depression, alcohol/drug use disorders, as well as bipolar disorder and schizophrenia. Pharmacological treatment seems to be one of the most effective opportunities to recover function efficiently and satisfactorily. However, such disorders are complex as several target points are involved. This results in a necessity to combine different types of drugs to obtain the necessary therapeutic goals. There is a need to develop safer and more effective drugs. Considering that mental illnesses share multifactorial processes, the paradigm of one treatment with multiple modes of action rather than single-target strategies would be more effective for successful therapies. Therefore, hybrid molecules that combine two pharmacophores in one entity show promise, as they possess the desired therapeutic index with a small off-target risk. This review aims to provide information on chimeric structures designed for mental disorder therapy (i.e., schizophrenia and depression), and new types of drug candidates currently being tested. In addition, a discussion on some benefits and limitations of multifunctional, bivalent drug candidates is also given.

Diastereoselective [3 + 1] Cyclization Reaction of Oxindolyl Azaoxyallyl Cations with Sulfur Ylides: Assembly of 3,3'-Spiro[β-lactam]-oxindoles

Oxindoles and β-lactams are attractive structural motifs because of their unique biological importance. However, the fusion of the two moieties featuring 3,3'-spirocyclic scaffolds is a challenging task in organic synthesis. Herein we designed a novel type of oxindole-based azaoxyallyl cation synthons, which could readily participate in the [3 + 1] cyclization with sulfur ylides. With this protocol, a collection of 3,3-spiro[β-lactam]-oxindoles were facilely produced in up to 94% yield with perfect diastereoselectivity.

The search for opioid analgesics with limited tolerance liability

Reducing the well-known side effects of opioids prescribed to treat chronic pain remains unresolved, despite extensive research in this field. Among several options to tackle this problem the synthesis of multifunctional compounds containing hybridized structures gained a lot of interest. Recently, extensively investigated are combinations of opioid agonist and antagonist pharmacophores embodied in a single molecule. To this end, agonism at the μ opioid receptor (MOR) with simultaneous antagonism at the δ opioid receptor (DOR) emerged as a promising avenue to obtaining novel analogs devoid of serious adverse effects associated with morphine-based analgesics. In this review we covered up-to-date research on the synthesis of peptide-based ligands with MOR agonist/DOR antagonist profile.

Synthesis and Pharmacological Evaluation of Hybrids Targeting Opioid and Neurokinin Receptors

Morphine, which acts through opioid receptors, is one of the most efficient analgesics for the alleviation of severe pain. However, its usefulness is limited by serious side effects, including analgesic tolerance, constipation, and dependence liability. The growing awareness that multifunctional ligands which simultaneously activate two or more targets may produce a more desirable drug profile than selectively targeted compounds has created an opportunity for a new approach to developing more effective medications. Here, in order to better understand the role of the neurokinin system in opioid-induced antinociception, we report the synthesis, structure–activity relationship, and pharmacological characterization of a series of hybrids combining opioid pharmacophores with either substance P (SP) fragments or neurokinin receptor (NK1) antagonist fragments. On the bases of the in vitro biological activities of the hybrids, two analogs, opioid agonist/NK1 antagonist Tyr-[d-Lys-Phe-Phe-Asp]-Asn-d-Trp-Phe-d-Trp-Leu-Nle-NH₂ (2) and opioid agonist/NK1 agonist Tyr-[d-Lys-Phe-Phe-Asp]-Gln-Phe-Phe-Gly-Leu-Met-NH₂ (4), were selected for in vivo tests. In the writhing test, both hybrids showed significant an antinociceptive effect in mice, while neither of them triggered the development of tolerance, nor did they produce constipation. No statistically significant differences in in vivo activity profiles were observed between opioid/NK1 agonist and opioid/NK1 antagonist hybrids.

Asymmetric Michael addition between kojic acid derivatives and unsaturated ketoesters promoted by C2-symmetric organocatalysts

An efficient sterically hindered C2-symmetric bifunctional tertiary amine-squaramide organocatalyst for the asymmetric Michael addition/hemiketalization domino reaction of kojic acid derivatives with β,γ-unsaturated α-ketoesters has been designed. Pharmacology-relevant functionalized 2,3,4,8-tetrahydropyrano[3,2-b]pyran derivatives were produced over the catalyst in as low as 1 mol% with up to 99% yield and 99% ee. The procedure is at least 30-fold scalable and the catalyst is readily reusable in the catalytic reaction via acid-base extraction. Acylation of the products with (S)- or rac-ibuprofen and with undec-10-enoic acid afforded the corresponding chiral esters containing two privileged pharmacophoric motifs.

Asymmetric synthesis of warfarin and its analogs catalyzed by C2-symmetric squaramide-based primary diamines

Novel C2-symmetric N,N'-bis(2-amino-1,2-diphenylethyl)squaramides with 1,2-di(pyridin-2-yl)ethane and 1,2-diphenylethane spacer groups were designed and applied as organocatalysts in asymmetric additions of 4-hydroxycoumarin and 4-hydroxy-6-methyl-2H-pyran-2-one to α,β-unsaturated ketones. Both enantiomers of the anticoagulant warfarin and its analogs were prepared in up to 96% yield and with 96% ee. Recyclability of the developed catalysts and synthetic utility of the prepared Michael adducts for asymmetric synthesis of potential chiral medications via acylation reactions were demonstrated.

Molecular Consortia-Various Structural and Synthetic Concepts for More Effective Therapeutics Synthesis

The design and discovery of novel drug candidates are the initial and most probably the crucial steps in the drug development process. One of the tasks of medicinal chemistry is to produce new molecules that have a desired biological effect. However, even today the search for new pharmaceuticals is a very complicated process that is hard to rationalize. Literature provides many scientific reports on future prospects of design of potentially useful drugs. Many trends have been proposed for the design of new drugs containing different structures (dimers, heterodimers, heteromers, adducts, associates, complexes, biooligomers, dendrimers, dual-, bivalent-, multifunction drugs and codrugs, identical or non-identical twin drugs, mixed or combo drugs, supramolecular particles and various nanoindividuals. Recently much attention has been paid to different strategies of molecular hybridization. In this paper, various molecular combinations were described e.g., drug–drug or drug-non-drug combinations which are expressed in a schematic multi-factor form called a molecular matrix, consisting of four factors: association mode, connection method, and the number of elements and linkers. One of the most popular trends is to create small–small molecule combinations such as different hybrids, codrugs, drug–drug conjugates (DDCs) and small-large molecule combinations such as antibody-drug conjugates (ADCs), polymer-drug conjugates (PDCs) or different prodrugs and macromolecular therapeutics. A review of the structural possibilities of active framework combinations indicates that a wide range of potentially effective novel-type compounds can be formed. What is particularly important is that new therapeutics can be obtained in fast, efficient, and selective methods using current trends in chemical synthesis and the design of drugs such as the “Lego” concept or rational green approach.

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

Herein, the synthesis and biological evaluation of dual opioid agonists-neurokinin 1 receptor (NK1R) antagonists is described. In these multitarget ligands, the two pharmacophores do not overlap, and this allowed maintaining high NK1R affinity and antagonist potency in compounds 12 and 13. Although the fusion of the two ligands resulted in slightly diminished opioid agonism at the μ- and δ-opioid receptors (MOR and DOR, respectively), as compared to the opioid parent peptide, balanced MOR/DOR activities were obtained. Compared to morphine, compounds 12 and 13 produced more potent antinociceptive effects in both acute (tail-flick) and neuropathic pain models (von Frey and cold plate). Similarly to morphine, analgesic tolerance developed after repetitive administration of these compounds. To our delight, compound 12 did not produce cross-tolerance with morphine and high antihyperalgesic and antiallodynic effects could be reinstated after chronic administration of each of the two compounds.

Multitarget opioid ligands in pain relief: New players in an old game

Still nowadays pain is one of the most common disabling conditions and yet it remains too often unsolved. Analgesic opioid drugs, and mainly MOR agonists such as morphine, are broadly employed for pain management. MOR activation, however, has been seen to cause not only analgesia but also undesired side effects. A potential pain treatment option is represented by the simultaneous targeting of different opioid receptors. In fact, ligands possessing multitarget capabilities led to an improved pharmacological fingerprint. This review focuses on the examination of multitarget opioid ligands which have been distinguished in peptide and non-peptide and further listed as bivalent and bifunctional ligands. Moreover, the potential of these compounds, both as analgesic drugs and pharmacological tools to explore heteromer receptors, has been stressed.

Effects of the Hybridization of Opioid and Neurotensin Pharmacophores on Cell Survival in Rat Organotypic Hippocampal Slice Cultures

Several neurotransmitter and neuromodulatory systems can control physiological glutamatergic activity. For example, opioid receptor ligands were shown to partially inhibit N-methyl-D-aspartic acid (NMDA) receptor-dependent glutamatergic excitotoxicity. Also, the endogenous tridecapeptide neurotensin (NT) was found to modulate excessive glutamate release and glutamate receptor activity in neurons. Alternatively to the one target-one drug approach, it has been well documented that hybrid compounds encompassing two pharmacophores in one molecular scaffold can represent more potent drugs. Moreover, such structures with dual activity can potentially enable a reduction of undesirable side effects and/or improved bioavailability. Herein, we describe the neuroprotective potential of an opioid-NT hybrid peptide (PK20), which was recently designed and synthesized within our group. The protective properties of PK20, assessed in an in vitro model of excitotoxic injury in organotypic hippocampal slice cultures subjected to NMDA, were compared to the effects caused by NT. Our results indicate that PK20 is a potent anti-neurodegenerative agent. Moreover, co-administered with NMDA, PK20 (25-100 ng/ml) dose-dependently reduced hippocampal cell death, determined by a decrease in the propidium iodide signal. We also report for the first time the significant NT-induced neuroprotective effect, as its application (50-100 ng/ml) to hippocampal slice cultures protected CA1 damage against neurotoxicity caused by NMDA.

Synthesis of novel triplets with a 1,3,5-trioxazatriquinane skeleton and their pharmacologies for opioid receptors

We designed and synthesized novel triplet molecules with 1,3,5-trioxazatriquinane skeletons. One class comprises double-capped triplets with a morphinan skeleton; the other class comprises simple phenol derivatives with phenethylamine moieties. One compound with m-phenolic hydroxyl group, called SYK-146, is a highly selective, potent agonist for the κ receptor, with activity nearly equivalent to that of U-50488H. The o-phenolic isomer of SYK-146, called SYK-524, showed potent but non-selective agonistic activity for the opioid receptors. We also added several simple phenol derivatives to a library of compounds that target opioid receptors, and they showed high hit rates for the receptor. This library might also be expected to show high hit rates for other receptors.

Synthesis and Pharmacology of a Novel κ Opioid Receptor (KOR) Agonist with a 1,3,5-Trioxazatriquinane Skeleton

We designed and synthesized the 1,3,5-trioxazatriquinane derivatives with m-hydroxyphenyl groups. These compounds include the phenethylamine structure within them, which is a common structure observed in morphinan derivatives like morphine. Among the synthesized compounds, (-)-8c with two m-hydroxyphenyl groups selectively bound and exerted full agonist activity toward the κ opioid receptor (KOR). Subcutaneously administered (-)-8c exhibited significant antinociceptive effects via the KOR in a dose-dependent manner. These results suggest the emergence of a novel class of KOR agonist.

3,5-Dimethoxy-4-(3-(2-carbonyl-ethyldisulfanyl)-propionyl)-benzoic acid 4-guanidino-butyl ester: a novel twin drug that prevents primary cardiac myocytes from hypoxia-induced apoptosis

Leonurine possesses cardioprotective effects in myocardial ischemia due to its anti-apoptotic properties. However, the process to isolate and purify leonurine is difficult, because of its low content in the Herb Leonuri and its impurity. Moreover, the high dosage used indicates low potency of leonurine. To overcome these defects, we had synthesized a novel twin drug of leonurine, 3,5-dimethoxy-4-(3-(2-carbonyl-ethyldisulfanyl)-propionyl)-benzoic acid 4-guanidino-butyl ester (compound 2). In this paper, we focused on investigating the cardioprotective effect and underlying mechanisms of compound 2. Our data showed that cell viability was significantly increased in a dose-dependent manner and the levels of lactate dehydrogenase (LDH) and creatine kinase (CK) were also significantly attenuated in the compound 2-treated group. In addition, we observed the cardioprotective effects by Hoechst 33258 nucleus staining, JC-1 staining, Annexin V-FITC/PI staining and transmission electron microscopy. Compound 2 inhibited apoptosis by reducing the ratio of Bcl-2/Bax, decreasing cleaved-caspase-3 expression and enhancing the phosphorylation of Akt. Furthermore, the phosphorylation effect of compound 2 was reversed by LY294002 the phosphatidylinositol-3-kinase (PI3K) inhibitor from happening. We concluded that compound 2 played a cardioprotective role in hypoxia-induced primary cardiac myocytes apoptosis partly via modulating the PI3K/Akt pathway at a 10-fold lower concentration than leonurine.

Synthesis of novel triplet drugs with 1,3,5-trioxazatriquinane skeletons and their pharmacologies. 3: synthesis of novel triplet drugs with the bis(epoxymethano) or bis(dimethylepoxymethano) structure (double-capped triplet)

Novel double-capped triplet drugs, which have one pharmacophore unit and two epoxymethano or dimethylepoxymethano structures (termed cap or diMe-cap structures, respectively) were synthesized. Key intermediate oxazoline 16 derived from acetone enabled the effective synthesis of double-capped triplets. SYK-134 (7a) and SYK-135 (8a) with N-cyclopropylmethyl substituent and cap structures showed selectivities for the κ opioid receptor. On the other hand, the N-Me series exhibited selectivities for the μ opioid receptor. The double-capped triplet drugs with diMe-cap structures preferred the μ receptor independently of their N-substituents. SYK-385 (19b), one of the μ-selective double-capped triplet drugs, showed the highest selectivity for the μ receptor among the reported μ-selective nonpeptide ligands.