Cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LO) are key enzymes in prostanoid and leukotriene signaling and are overexpressed in various cancers, correlating with malignancy and metastasis. This renders them promising molecular targets for radiotracer development. In this study, isomeric closo-dicarbadodecaborane(12)-based dual COX-2/5-LO inhibitors (1 and 2) served as scaffolds for iodine-123-labeling. Iodinated derivatives 3 and 4 inhibited 5-LO more potently than COX-2 in vitro (IC50 0.62 µM and 41.3 µM (3); 0.54 µM and 67.7 µM (4)). Radioiodination yielded 39%-71% of [123I]3 and [123I]4; and the formulations were stabilized with antioxidants. Cellular uptake of [123I]3 and [123I]4 was evaluated in human cells with distinct COX-2 and 5-LO expression: U87 glioblastoma, HT-29 colorectal carcinoma cells, THP-1 monocytes (MC) and macrophages. Consistent with the observed inhibitory potency, the uptake of the radiotracers proved to be independent of COX-2 expression. In contrast, it was influenced by 5-LO expression in tumor but not inflammatory cells. Single-photon emission computed tomography imaging in tumor xenograft mouse models revealed no tumor retention of [123I]3 and [123I]4 due to rapid metabolism via radiodeiodination. Despite successful radiosynthesis and in vitro evaluation of iodine-123-labeled COX-2/5-LO inhibitors, improved inhibitory activity and stability are required for development of suitable radiotracers.

G2A inhibition has recently been proposed as a novel therapeutic approach to treat oxaliplatin-induced neuropathic pain (OINP) and breast cancer. However, very few G2A antagonists are known to date. In this study, we report the discovery of a novel series of G2A antagonists developed within our research group, along with the first comprehensive structure-activity relationship (SAR) investigation for this class of compounds. Utilizing a rational design approach, we systematically explored the effects of structural modifications on G2A receptor binding and functional activity. The SAR study identified key molecular features critical for potent G2A inhibition. Two of the newly discovered compounds exhibited submicromolar activity and acceptable selectivity profile among GPCRs.

Specialized pro-resolving mediators (SPMs) have been suggested to act as key factors that mediate the resolution of inflammation. With the availability of synthetic standards, pharmacological studies have garnered support for the hypothesis. However, assessment of the catalytic properties of lipoxygenases as well as investigations of the signalling of the proposed SPM receptors raise serious doubt that SPMs are endogenous mediators of the resolution of inflammation. In line with this, careful evaluation of published data on SPM detection revealed a lack of evidence for many reported SPMs in biological samples due to analytical LC-MS/MS methods that do not meet the quality standards of the scientific community, or they rely on ELISAs that lack selectivity and are not suited for the establishment of the presence of SPMs in complex biological samples. Furthermore, artefacts due to autoxidation of PUFAs can be misinterpreted as SPM formation. In this review, we critically assess the published reports on the biosynthesis and the analysis of SPMs and summarize the current status in the field.

The leukotriene B4 receptor 2 (BLT2) is a G-protein coupled receptor, which is endogenously activated by 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid (12-HHT). BLT2 is gaining attention as a potential therapeutic target involved in various pathologies including diabetic wound healing, ophthalmic diseases, and colitis. However, validation of BLT2 as drug target requires chemical probes and pharmacological tools which will allow for application in vivo. In this work, we present the discovery of a novel chemical probe T-10430 for BLT2 agonism following a scaffold-hopping approach. T-10430 exhibits high potency, good selectivity profile, promising physicochemical and PK properties and can potentially serve as orally applicable pharmacological tool for validation of BLT2 as drug target. Using T-10430, we demonstrate the beneficial effect of BLT2 activation in mouse model of psoriasis.

5-Lipoxygenase (5-LO), encoded by the gene ALOX5, is implicated in several pathologies. As key enzyme in leukotriene biosynthesis, 5-LO plays a central role in inflammatory diseases, but the 5-LO pathway has also been linked to development of certain hematological and solid tumor malignancies. Of note, previous studies have shown that the leukemogenic fusion protein MLL-AF4 strongly increases ALOX5 gene promoter activity. Here, we investigate the upregulation of ALOX5 gene expression by MLL-AF4. Using reporter assays, we first identified the tandem GC box within the ALOX5 promotor sequence as the main target of MLL-AF4. Subsequently, we narrowed down the domains within the MLL-AF4 protein responsible for ALOX5 promoter activation. Our findings indicate that MLL-AF4 binds to the ALOX5 promoter via its CXXC domain and that the AF9ID, pSER and CHD domains redundantly activate transcriptional elongation. Knockdown of the MLL-AF4 gene in the human B cell line SEM revealed that MLL-AF4 is an inducer of ALOX5 gene expression in leukemic cells with lymphoid properties. Finally, we found that the MLL-AF4-related protein MLL-AF9, a driver of acute myeloid leukemia, similarly acts on the ALOX5 promoter. Taken together, we show that two prominent MLL fusion proteins are ALOX5 gene inducers in cells with lymphoid features.

The human 5-lipoxygenase (5-LOX), which is encoded by the arachidonate 5-lipoxygenase (ALOX5) gene, has its canonical function in leukotriene (LT) biosynthesis, which controls inflammatory and allergic responses. Besides oxylipin formation from polyunsaturated fatty acids, 5-LOX has several noncanonical functions. It acts as transcriptional regulator in the nucleus but also interacts with Dicer and modulates microRNA expression and processing. In this study, we employed a tetracycline riboswitch-controlled cassette-exon system to conditionally control ALOX5 expression in the monocytic leukemic cell line MonoMac6. Synthetic riboswitches are gaining increasing interest as a means of controlling transgene expression, with applications in functional genomics and potential therapeutic strategies. We designed an artificial ALOX5 gene that contains two cassette exons with premature termination codons (PTCs), thus only being expressed when both synthetic exons are skipped. The switchable ALOX5 gene was transduced into MonoMac6 5-LOX knock-out (KO) cells, thereby enabling the tetracycline-dependent re-expression of 5-LOX proteins. The newly established cell line was characterized in terms of tetracycline dose dependency and switching kinetics. Induction of ALOX5 exerted the non-canonical 5-LOX effects on prostaglandin-endoperoxide synthase 2 (PTGS2) and L-kynureninase (KYNU) gene expression. This allowed us to demonstrate the outstanding advantages of a riboswitch-controlled system in terms of time dependency and gene function. The novel MonoMac6 cell line now provides a perfect tool for further research into the non-canonical functions of 5-LOX.

Synthetic riboswitches are attracting increasing interest for a diverse range of applications, including synthetic biology, functional genomics, and prospective therapeutic strategies. This study demonstrates that controlling alternative splicing with synthetic riboswitches represents a promising approach to effectively regulating transgene expression in mammalian cells. However, the function of synthetic riboswitches in the eukaryotic system in controlling gene expression is often limited to certain genes or cell types. So far, strategies to increase the dynamic range of regulation have been focused on adapting and modifying the riboswitch sequence itself without taking into account the context in which the riboswitch was inserted. In the present study, the tetracycline riboswitch was chosen to investigate the effects of the context and insertion site of a cassette exon within the gene to control the expression of an artificial arachidonate 5-lipoxygenase gene (ALOX5) in HEK293 cells. We demonstrate here that the use of riboswitch-controlled cassette exons for the control of gene expression via alternative splicing can be easily transferred to another gene through the process of contextual sequence adaptation. This was achieved through the introduction of gene-specific intronic and exonic sequences with different intron lengths and positions being tested. In contrast, the introduction of nonadapted constructs resulted in an unanticipated functionality outcome of the gene switch. Furthermore, we demonstrate that the combination of two cassette exons into a single gene resulted in a notable enhancement in the dynamic range. Finally, we generated a novel riboswitch-controlled splicing concept that enabled us to switch 5-LO wild-type to expression of an ALOX5 isoform that lacks exon 13 (5-LOΔ13). Taken together, this study demonstrates that synthetic riboswitches that control alternative splicing are a powerful tool to regulate gene expression when applied in combination with gene-specific intronic and exonic sequences.

The use of traditional nonsteroidal anti-inflammatory drugs (NSAIDs) and coxibs is effective for the treatment of inflammatory pain and chronic inflammatory conditions. However, their use is associated with enhanced risk of cardiovascular toxicity and thrombotic events, particularly for the latter. The vascular side effects of these drugs could be mitigated by pharmacological inhibition of the thromboxane A2 receptor (TP). Here we describe the development of a new class of dual cyclooxygenase (COX) inhibitors/thromboxane receptor antagonists (COXTRANs) based on the 2-(1,3,4,9-tetrahydropyrano[3,4-b]indol-1-yl)acetic acid scaffold. The in vitro evaluation of 50 newly synthesized compounds resulted in a set of well-balanced compounds exhibiting nanomolar activity on both COX-2 and TP receptor. Further studies in human whole blood and physicochemical profiling allowed the prioritization of 51 (CXT29) as a suitable candidate for in vivo studies. Compound 51, after oral administration, was able to prevent TP receptor-mediated platelet aggregation and to reduce inflammatory pain in mice.

Several oxylipins including hydroxy-PUFAs act as lipid mediators. In biological samples, the major part occurs esterified in glycero-phospholipids (PLs) or other lipids. In this work, the incorporation into glycero-PLs of 15-hydroxyeicosatetraenoic acid (15(S)-HETE), 15(S)-hydroxyeicosapentaenoic acid (15(S)-HEPE), 17(S)-hydroxydocosahexaenoic acid (17(S)-HDHA), and 13-(S)-hydroxyoctadecadienoic acid (13(S)-HODE) was investigated in oxylipin-supplemented human embryonic kidney 293T cells and cells overexpressing 15-lipoxgenase-2 (15-LOX-2, ALOX15B). Indirect quantification of esterified oxylipins in lipid fractions showed that >97% of each supplemented 15-LOX-2 product is esterified and that <25% are bound to neutral lipids, whereas >75% are bound to distinct glycero-PL classes, depending on the hydroxy-PUFA. 15-HETE and 15-HEPE were found in phosphatidylinositol (PI)/phosphatidylserine, whereas 17-HDHA was in phosphatidylethanolamine (PE) and 13-HODE in phosphatidylcholine (PC). The same pattern was found for oxylipins endogenously formed by overexpression of 15-LOX-2. A new targeted method for the analysis of oxidized glycero-PLs enabled to pinpoint the specific molecular species of the oxylipins. 15-HETE (20:4;15OH) and 15-HEPE (20:5;15OH) are dominantly found as PI 18:0/20:4;15OH (70%) and PI 18:0/20:5;15OH (80%), respectively. This preferential incorporation of 20:4;15OH and 20:5;15OH into PI may be biologically relevant for PI signaling pathways. In contrast, >50% of 17-HDHA (22:6;17OH) was found in PE P-16:0/22:6;17OH, PE P-18:0/22:6;17OH, and PE P-18:1/22:6;17OH. At least 40% of 13-HODE (18:2;13OH) was incorporated into PC 16:0/18:2;13OH, and relevant amounts were found in PI 18:0/18;13OH, PC 18:1/18;13OH, and PC-O (ether PC) 16:0/18;13OH. These results indicate that hydroxy-PUFAs are bound to glycero-PLs in a specific manner. The distinct incorporation of 15-LOX-2 products from different PUFAs into glycero-PLs might contribute to the biological effect of these oxylipins and their precursor FAs.

Several oxylipins are potent lipid mediators that regulate diverse aspects of health and disease and whose quantitative analysis by liquid chromatography-mass spectrometry (LC-MS) presents substantial technical challenges. As members of the lipidomics community, we developed technical recommendations to ensure best practices when quantifying oxylipins by LC-MS.

IntroductionCritically ill patients suffer from a wide variety of clinical events, most of them leading to pro-inflammatory states such as sepsis or simply as consequence of major surgery. Many of these patients develop forms of acute kidney injury, heart or acute liver failure during intensive care. Lipid signaling is critically involved in triggering systemic inflammation processes, pain and vascular tone. We therefore hypothesized that fatty-acid-derived lipid mediators might be regulated during inflammatory stages and other clinical events in critically ill patients and might serve as potential biomarker candidates.Methods and study designUsing liquid chromatography-tandem mass spectrometry (LC-MS/MS), we determined the levels of 53 lipid mediators in plasma from nine patients. These patients were hospitalized at Frankfurt University Hospital’s intensive care unit (ICU) after cardiac surgery. Inflammatory stages were illustrated over time using clinically established biomarkers such as interleukin-6 (IL-6) and leukocyte count. Normal range values of the lipids were obtained from healthy volunteers.ResultsPlasma levels clearly outside the normal range were observed for 22 of 53 lipid mediators, of which 13 were increased (including ceramides Cer (d18:0/18:0), Cer (d18:1/16:0), Cer (d18:1/18:1), glucosyl-ceramide GluCer (d18:1/24:1), lactosylceramide LacCer (d18:1/18:0), and LacCer (d18:1/24:1), 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha), 11,12- and 14,15-DHET and 1- and 2-arachidonoyl glycerol (1-AG and 2-AG), Sphingosine SPH (d18:1) and 20-HETE. Furthermore, nine lipids were decreased (Cer (d18:1/24:0), LacCer (d18:1/16:0), LacCer (d18:1/24:0), sphingosine-1-phosphate S1P (d18:1), S1P (d18:0), the lysophosphatidic acids LPA (16:0), LPA (18:0), LPA (18:1) and 9-HODE. Among increased lipids, the remarkable changes in 1-AG, 2-AG, and to a lower extent of 6-keto-PGF1-alpha plasma levels showed a certain agreement with inflammatory phases. Furthermore, 6-keto-PGF1alpha had its peak shortly before initiation of continuous veno-venous hemodialysis (at least in 5 of the observed patients), 2-AG was elevated in all our nine patients during (right) heart failure in the context of either re-opening patient’s chest, implementation of veno-arterial ECMO or at least while significantly increasing the amount of catecholamines.DiscussionIn this pilot trial we identified several evaluated lipids in critically ill patients representing either potentially (patho-) physiologically relevant mediators of the pro-inflammatory processes and during heart failure or possible markers preceding veno-venous hemodialysis.

G protein-coupled receptor G2A was postulated to be a promising target for the development of new therapeutics in neuropathic pain, acute myeloid leukemia, and inflammation. However, there is still a lack of potent, selective, and drug-like G2A agonists to be used as a chemical tool or as the starting matter for the development of drugs. In this work, we present the discovery and structure-activity relationship elucidation of a new potent and selective G2A agonist scaffold. Systematic optimization resulted in (3-(pyridin-3-ylmethoxy)benzoyl)-d-phenylalanine (T-10418) exhibiting higher potency than the reference and natural ligand 9-HODE and high selectivity among G protein-coupled receptors. With its favorable activity, a clean selectivity profile, excellent solubility, and high metabolic stability, T-10418 qualifies as a pharmacological tool to investigate the effects of G2A activation.

Many drugs can act on multiple targets or disease pathways, regardless of their original purpose. Drug repurposing involves reevaluating existing compounds for new medical uses. This can include repositioning approved drugs, redeveloping unapproved drugs, or repurposing any chemical, nutraceutical, or biotherapeutic product for new applications. Traditional drug development is slow, expensive, and has high failure rates. Drug repurposing can speed up the process, costing less and saving time. This approach can save 6–7 years of early-stage research time. Drug repurposing benefits from existing compounds with optimized structures and approved for clinical use with associated structure-activity relationship publications, supporting the development of new effective compounds. Drug repurposes can now utilize advanced in silico screening enabled by artificial intelligence (AI) and sophisticated tissue and organ-level in vitro models. These models more accurately replicate human physiology and improve the selection of existing drugs for further pre-clinical testing and, eventually, clinical trials for new indications. This mini-review discusses some examples of drug repurposing and novel strategies for further development of compounds for targets of the arachidonic acid cascade. In particular, we will delve into the prospect of repurposing antiplatelet agents for cancer prevention and addressing the emerging noncanonical functionalities of 5-lipoxygenase, potentially for leukemia therapy.

Human 5-lipoxygenase (5-LO) is the key enzyme in the biosynthesis of leukotrienes, mediators of the innate immune system that also play an important role in inflammatory diseases and cancer. In this study, we present compounds, containing a Michael-reactive cyanoacrylate moiety as potent inhibitors of 5-LO. Representatives of the tyrosine kinase inhibitor family called tyrphostins, structurally related to known 5-LO inhibitors, were screened for their 5-LO inhibitory properties using recombinant human 5-LO, intact human PMNL (polymorphonuclear leukocytes), and PMNL homogenates. Their mode of action was characterized by the addition of glutathione, using a fourfold cysteine 5-LO mutant and mass spectrometry analysis. SAR studies revealed several members of the tyrphostin family containing a Michael-reactive cyanoacrylate to efficiently inhibit 5-LO. We identified degrasyn (IC50 0.11 µM), tyrphostin A9 (IC50 0.8 µM), AG879 (IC50 78 nM), and AG556 (IC50 64 nM) as potent 5-LO inhibitors. Mass spectrometry analysis revealed that degrasyn and AG556 covalently bound to up to four cysteines, including C416 and/or C418 which surround the substrate entry site. Furthermore, the 5-LO inhibitory effect of degrasyn was remarkably impaired by the addition of glutathione or by the mutation of cysteines to serines at the surface of 5-LO. We successfully identified several tyrphostins as potent inhibitors of human 5-LO. Degrasyn and AG556 were able to covalently bind to 5-LO via their cyanoacrylate moiety. This provides a promising mechanism for targeting 5-LO by Michael acceptors, leading to new therapeutic opportunities in the field of inflammation and cancer.