Design and Synthesis of Benzene Congeners of Resolvin E2, a Proresolving Lipid Mediator, as Its Stable Equivalents

Omega-3 polyunsaturated fatty acid derived lipid mediators: a comprehensive update on their application in anti-cancer drug discovery

INTRODUCTION

ω-3 Polyunsaturated fatty acids (PUFAs) have a range of health benefits, including anticancer activity, and are converted to lipid mediators that could be adapted into pharmacological strategies. However, the stability of these mediators must be improved, and they may require formulation to achieve optimal tissue concentrations.

AREAS COVERED

Herein, the author reviews the literature around chemical stabilization and formulation of ω-3 PUFA mediators and their application in anticancer drug discovery.

EXPERT OPINION

Aryl-urea bioisosteres of ω-3 PUFA epoxides that killed cancer cells targeted the mitochondrion by a novel dual mechanism: as protonophoric uncouplers and as inhibitors of electron transport complex III that activated ER-stress and disrupted mitochondrial integrity. In contrast, aryl-ureas that contain electron-donating substituents prevented cancer cell migration. Thus, aryl-ureas represent a novel class of agents with tunable anticancer properties. Stabilized analogues of other ω-3 PUFA-derived mediators could also be adapted into anticancer strategies. Indeed, a cocktail of agents that simultaneously promote cell killing, inhibit metastasis and angiogenesis, and that attenuate the pro-inflammatory microenvironment is a novel future anticancer strategy. Such regimen may enhance anticancer drug efficacy, minimize the development of anticancer drug resistance and enhance outcomes.

Resolvins and cysteinyl-containing pro-resolving mediators activate resolution of infectious inflammation and tissue regeneration

This review is a synopsis of the main points from the opening presentation by the authors in the Resolution of Inflammation session at the 8th European Workshop on Lipid Mediators held at the Karolinska Institute, Stockholm, Sweden, June 29th, 2022. Specialized pro-resolving mediators (SPM) promote tissue regeneration, control infections and resolution of inflammation. These include resolvins, protectins, maresins and the newly identified conjugates in tissue regeneration (CTRs). We reported mechanisms of CTRs in activating primordial regeneration pathways in planaria using RNA-sequencing. Also, the 4S,5S-epoxy-resolvin intermediate in the biosynthesis of resolvin D3 and resolvin D4 was prepared by total organic synthesis. Human neutrophils convert this to resolvin D3 and resolvin D4, while human M2 macrophages transformed this labile epoxide intermediate to resolvin D4 and a novel cysteinyl-resolvin that is a potent isomer of RCTR1. The novel cysteinyl-resolvin significantly accelerates tissue regeneration with planaria and inhibits human granuloma formation.

Major structure-activity relationships of resolvins, protectins, maresins and their analogues

Resolvins, protectins and maresins are a series of polyunsaturated fatty acid-derived molecules which play important roles in the resolution of inflammation. They are termed specialized proresolving mediators and facilitate a return to homeostasis following an inflammatory response. These molecules are currently the focus of intensive investigation, primarily for their ability to suppress inflammation in chronic disease states. Researchers have employed different synthetic approaches to assess whether various structural modifications of these compounds could provide access to future therapeutics. This review summarizes the modifications made thus far and focuses on the key structure-activity relationships which have been uncovered for resolvins, protectins, maresins and their analogues.

Design and Synthesis of Cyclopropane Congeners of Resolvin E3, an Endogenous Pro-Resolving Lipid Mediator, as Its Stable Equivalents

Resolvins are pro-resolving lipid mediators with highly potent anti-inflammatory effects. Because of their polyunsaturated structures, however, they are unstable to oxygen as a drug prototype. To address this issue, we designed and synthesized CP-RvE3 as oxidatively stable congeners of RvE3 by replacing the cis-olefin with a cis-cyclopropane to avoid the unstable bisallylic structure. Although the oxidative stabilities of CP-RvE3 were not improved, β-CP-RvE3 was 3.7 times more metabolically stable than RvE3. Thus, we identified β-CP-RvE3 as a metabolically stable equivalent.

E-series resolvin metabolome, biosynthesis and critical role of stereochemistry of specialized pro-resolving mediators (SPMs) in inflammation-resolution: Preparing SPMs for long COVID-19, human clinical trials, and targeted precision nutrition

The COVID-19 pandemic has raised international awareness of the importance of rigorous scientific evidence and the havoc caused by uncontrolled excessive inflammation. Here we consider the evidence on whether the specialized pro-resolving mediators (SPMs) are ready to meet this challenge as well as targeted metabololipidomics of the resolution-inflammation metabolomes. Specific stereochemical mechanisms in the biosynthesis of SPMs from omega-3 essential fatty acids give rise to unique local-acting lipid mediators. SPMs possess stereochemically defined potent bioactive structures that are high-affinity ligands for cognate G protein-coupled surface receptors that evoke the cellular responses required for efficient resolution of acute inflammation. The SPMs biosynthesized from the major omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are coined Resolvins (resolution phase interaction products; E series and D-series), Protectins and Maresins (macrophage mediators in resolving inflammation). Their biosynthesis and stereochemical assignments are established and confirmed (>1,441 resolvin publications in PubMed.gov) as well as their functional roles on innate immune cells and adaptive immune cells (both lymphocyte T-cell subsets and B-cells). The resolution of a protective acute inflammatory response is governed mainly by phagocytes that actively clear apoptotic cells, debris, blood clots and pathogens. These resolution phase functions of the acute inflammatory response are enhanced by SPMs, which together prepare the inflammatory loci for homeostasis and stimulate tissue regeneration via activating stem cells and the biosynthesis of novel cys-SPMs (e.g. MCTRs, PCTRs and RCTRs). These cys-SPMs also activate regeneration, are organ protective and stimulate resolution of local inflammation. Herein, we review the biosynthesis and functions of the E-series resolvins, namely resolvin E1 (the first n-3 resolvin identified), resolvin E2, resolvin E3 and resolvin E4 biosynthesized from their precursor eicosapentaenoic acid (EPA), and the critical role of total organic synthesis in confirming SPM complete stereochemistry, establishing their potent functions in resolution of inflammation, and novel structures. The physical properties of each biologically derived SPM, i.e., ultra-violet (UV) absorbance, chromatographic behavior, and tandem mass spectrometry (MS2) fragmentation, were matched to SPMs biosynthesized and prepared by stereospecific total organic synthesis. We briefly review this approach, also used with the endogenous D-series resolvins, protectins and maresins confirming their potent functions in resolution of inflammation, that paves the way for their rigorous evaluation in human tissues and clinical trials. The assignment of complete stereochemistry for each of the E and D series Resolvins, Protectins and Maresins was a critical and required step that enabled human clinical studies as in SPM profiling in COVID-19 infections and experimental animal disease models that also opened the promise of resolution physiology, resolution pharmacology and targeted precision nutrition as new areas for monitoring health and disease mechanisms.

Resolution of inflammation: An organizing principle in biology and medicine

The resolution of inflammation has emerged as a critical endogenous process that protects host tissues from prolonged or excessive inflammation that can become chronic. Failure of the resolution of inflammation is a key pathological mechanism that drives the progression of numerous inflammation-driven diseases. Essential polyunsaturated fatty acid (PUFA)-derived autacoid mediators termed 'specialized pro-resolving mediators' (SPMs) regulate endogenous resolution programs by limiting further neutrophil tissue infiltration and stimulating local immune cell (e.g., macrophage)-mediated clearance of apoptotic polymorphonuclear neutrophils, cellular debris, and microbes, as well as counter-regulating eicosanoid/cytokine production. The SPM superfamily encompasses lipoxins, resolvins, protectins, and maresins. Our understanding of the resolution phase of acute inflammation has grown exponentially in the past three decades with the discovery of novel pro-resolving lipid mediators, their pro-efferocytosis mechanisms, and their receptors. Technological advancement has further facilitated lipid mediator metabolipidomic based profiling of healthy and diseased human tissues, highlighting the extraordinary therapeutic potential of SPMs across a broad array of inflammatory diseases including cancer. As current front-line cancer therapies such as surgery, chemotherapy, and radiation may induce various unwanted side effects such as robust pro-inflammatory and pro-tumorigenic host responses, characterizing SPMs and their receptors as novel therapeutic targets may have important implications as a new direction for host-targeted cancer therapy. Here, we discuss the origins of inflammation resolution, key discoveries and the failure of resolution mechanisms in diseases with an emphasis on cancer, and future directions focused on novel therapeutic applications for this exciting and rapidly expanding field.

Resolvins as potential candidates for the treatment of major depressive disorder

In contrast with the delayed onset of therapeutic responses and relatively low efficacy of currently available monoamine-based antidepressants, a single subanesthetic dose of ketamine, an N-methyl-D-aspartate receptor antagonist, produces rapid and sustained antidepressant actions even in patients with treatment-resistant depression. However, since the clinical use of ketamine as an antidepressant is limited owing to its adverse effects, such as psychotomimetic/dissociative effects and abuse potential, there is an unmet need for novel rapid-acting antidepressants with fewer side effects. Preclinical studies have revealed that the antidepressant actions of ketamine are mediated via the release of brain-derived neurotrophic factor and vascular endothelial growth factor, with the subsequent activation of mechanistic target of rapamycin complex 1 (mTORC1) in the medial prefrontal cortex. Recently, we demonstrated that resolvins (RvD1, RvD2, RvE1, RvE2 and RvE3), endogenous lipid mediators generated from n-3 polyunsaturated fatty acids (docosahexaenoic and eicosapentaenoic acids), exert antidepressant effects in a rodent model of depression, and that the antidepressant effects of RvD1, RvD2, and RvE1 necessitate mTORC1 activation. In this review, we first provide an overview of the mechanisms underlying the antidepressant effects of ketamine and other rapid-acting agents. We then discuss the possibility of using resolvins as novel therapeutic candidates for depression.

Stereoselective Synthesis and Structural Confirmation of the Specialized Pro-Resolving Mediator Resolvin E4

Herein, we report the stereoselective and convergent synthesis of resolvin E4, a newly identified specialized pro-resolving mediator. This synthesis proves the absolute configuration and exact olefin geometry. Key elements of the successful strategy include a highly stereoselective MacMillan organocatalytic oxyamination, a Midland Alpine borane reduction, and the use of a 1,4-pentadiyne unit as a linchpin building block. The application of reaction telescoping in several of the synthetic transformations enabled the preparation of the resolvin E4 methyl ester in 10% yield over 10 steps (longest linear sequence). The physical property (UV–Vis and LC–MS/MS) data of synthetic resolvin E4 matched those obtained from biologically produced material.

Synthesis of Resolvin E1 and Its Conformationally Restricted Cyclopropane Congeners with Potent Anti-Inflammatory Effect

RvE1 (1) is an endogenous lipid mediator with very potent anti-inflammatory activity, which is due to the inhibition of neutrophil chemotaxis and inflammatory cytokine production and the promotion of macrophage phagocytosis. On the basis of the conformational analysis of RvE1, we designed its four cyclopropane congeners (2a-d), in which the conformationally flexible terminal C1-C4 moiety of RvE1 was rigidified by introducing stereoisomeric cyclopropanes. The four congeners and also RvE1 were efficiently synthesized via a common synthetic route. The evaluation of the anti-inflammatory effects of the compounds in mice resulted in the identification of trans-β-CP-RvE1 (2d), which was significantly more active than RvE1, as a potential lead for anti-inflammatory drugs of a novel mechanism of action.

A New E-Series Resolvin: RvE4 Stereochemistry and Function in Efferocytosis of Inflammation-Resolution

The resolution of the acute inflammatory response is governed by phagocytes actively clearing apoptotic cells and pathogens. Biosynthesis of the specialized pro-resolving mediators (SPMs) is pivotal in the resolution of inflammation via their roles in innate immune cells. Resolvin E4 (RvE4: 5S,15S-dihydroxy-eicosapentaenoic acid) is a newly uncovered member of the E-series resolvins biosynthesized from eicosapentaenoic acid (EPA) recently elucidated in physiologic hypoxia. This new resolvin was termed RvE4 given its ability to increase efferocytosis of apoptotic cells by macrophages. Herein, we report on the total organic synthesis of RvE4 confirming its unique structure, complete stereochemistry assignment and function. This synthetic RvE4 matched the physical properties of biogenic RvE4 material, i.e. ultra-violet (UV) absorbance, chromatographic behavior, and tandem mass spectrometry (MS²) fragmentation, as well as bioactivity. We confirmed RvE4 potent responses with human M2 macrophage efferocytosis of human apoptotic neutrophils and senescent red blood cells. Together, these results provide direct evidence for the assignment of the complete stereochemistry of RvE4 as 5S,15S-dihydroxy-6E,8Z,11Z,13E,17Z-eicosapentaenoic acid and its bioactions in human phagocyte response.

Exploiting oxidized lipids and the lipid-binding GPCRs against cardiometabolic diseases

Lipids govern vital cellular processes and drive physiological changes in response to different pathological or environmental cues. Lipid species can be roughly divided into structural and signalling lipids. The former is essential for membrane composition, while the latter are usually oxidized lipids. These mediators provide beneficial effects against cardiometabolic diseases (CMDs), including fatty-liver diseases, atherosclerosis, thrombosis, obesity, and Type 2 diabetes. For instance, several oxylipins were recently found to improve glucose homeostasis, increase insulin secretion, and inhibit platelet aggregation, while specialized pro-resolving mediators (SPMs) are able to ameliorate CMD by shaping the immune system. These lipids act mainly by stimulating GPCRs. In this review, we provide an updated and comprehensive overview of the current state of the literature on signalling lipids in the context of CMD. We also highlight the network encompassing the lipid-modifying enzymes and the lipid-binding GPCRs, as well as their interactions in health and disease.

[Resolvins as novel targets for rapid-acting antidepressants]

Conventional monoaminergic antidepressants have significant limitations, including delayed onset of therapeutic response and relatively low efficacy. Recent studies reveal that the NMDA receptor antagonist ketamine produces rapid and sustained antidepressant effects in treatment-resistant depressed patients. Despite the unique antidepressant efficacy, clinical use of ketamine as an antidepressant is limited due to its serious drawbacks, such as abuse potential and psychotomimetic/dissociative effects. The molecular and neuronal mechanisms underlying the antidepressant actions of ketamine have been intensively studied to pave the way for the development of novel, rapid and more efficacious antidepressants with fewer side effects than ketamine. Preclinical studies demonstrate that ketamine produces antidepressant effects through rapid release and/or expression of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), and stimulation of mechanistic target of rapamycin complex 1 (mTORC1) signaling in the medial prefrontal cortex and hippocampus. We have recently found that resolvins (RvD1, RvD2, RvE1, RvE2 and RvE3), bioactive metabolites derived from docosahexaenoic acid and eicosapentaenoic acid, produce antidepressant effects, and that the antidepressant effects of RvD1, RvD2 and RvE1 require mTORC1 activation. These findings suggest that resolvins could be promising targets for the development of novel rapid antidepressants with fewer side effects than ketamine because they are endogenous lipid mediators that play an important role in homeostasis.

Enantioselective Synthesis of 7(S)-Hydroxydocosahexaenoic Acid, a Possible Endogenous Ligand for PPARα

We report the first total synthesis of the polyunsaturated fatty acid 7-hydroxydocosahexaenoic acid (7-HDHA) in racemic form and the enantioselective synthesis of 7-(S)-HDHA. Both syntheses follow a convergent approach that unites the C1-C9 and C10-C22 fragments using Sonogashira coupling and Boland reduction as key steps. These syntheses enabled the unambiguous characterization of this natural product for the first time and helped establish 7(S)-HDHA as a possible endogenous ligand for peroxisome proliferator-activated receptor alpha.

Specialized pro-resolving mediator network: an update on production and actions

Today, persistent and uncontrolled inflammation is appreciated to play a pivotal role in many diseases, such as cardiovascular diseases, neurodegenerative diseases, metabolic syndrome and many other diseases of public health concern (e.g. Coronavirus Disease 2019 (COVID-19) and periodontal disease). The ideal response to initial challenge in humans is a self-limited inflammatory response leading to complete resolution. The resolution phase is now widely recognized as a biosynthetically active process, governed by a superfamily of endogenous chemical mediators that stimulate resolution of inflammatory responses, namely specialized proresolving mediators (SPMs). Because resolution is the natural ideal response, the SPMs have gained attention. SPMs are mediators that include ω-6 arachidonic acid-derived lipoxins, ω-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)-derived resolvins, protectins and maresins, cysteinyl-SPMs, as well as n-3 docosapentaenoic acid (DPA)-derived SPMs. These novel immunoresolvents, their biosynthetic pathways and receptors have proven to promote resolution of inflammation, clearance of microbes, reduce pain and promote tissue regeneration via specific cellular and molecular mechanisms. As of 17 August, 2020, PubMed.gov reported >1170 publications for resolvins, confirming their potent protective actions from many laboratories worldwide. Since this field is rapidly expanding, we provide a short update of advances within 2-3 years from human and preclinical animal studies, together with the structural-functional elucidation of SPMs and identification of novel SPM receptors. These new discoveries indicate that SPMs, their pathways and receptors could provide a basis for new approaches for treating inflammation-associated diseases and for stimulating tissue regeneration via resolution pharmacology and precision nutrition.