Design, synthesis and evaluation of 2-aminothiazole derivatives as sphingosine kinase inhibitors

Anticancer Potential of the S-Heterocyclic Ring Containing Drugs and its Bioactivation to Reactive Metabolites

Sulfur-containing heterocyclic derivatives have been disclosed for binding with a wide range of cancer-specific protein targets. Various interesting derivatives of sulfur-containing heterocyclics such as benzothiazole, thiazole, thiophene, thiazolidinedione, benzothiophene, and phenothiazine, etc have been shown to inhibit diverse signaling pathways implicated in cancer. Significant progress has also been made in molecular targeted therapy against specific enzymes such as kinase receptors due to potential binding interactions inside the ATP pocket. Sulfur-containing heterocyclic ring metal complexes i. e., benzothiazole, thiazole, thiophene, benzothiophene and phenothiazines are among the most promising active anticancer compounds. However, sulfur heteroaromatic rings, particularly thiophene, are of high structural alert due to their metabolism to reactive metabolites. The mere presence of a structural alert itself does not determine compound toxicity therefore, this review focuses on some specific findings that shed light on factors influencing the toxicity. In the current review, synthetic strategies of introducing the sulfur core ring in the synthesized derivatives are discussed with their structure-activity relationships to enhance our understanding of toxicity mechanisms and develop safer therapeutic options. The sulfur-containing marketed anticancer drugs included in this review direct the synthesis of novel compounds and will help in the development of potent, safer sulfur-based anticancer drugs in near future.

Novel meriolin derivatives activate the mitochondrial apoptosis pathway in the presence of antiapoptotic Bcl-2

Meriolin derivatives represent a new class of kinase inhibitors with a pronounced cytotoxic potential. Here, we investigated a newly synthesized meriolin derivative (termed meriolin 16) that displayed a strong apoptotic potential in Jurkat leukemia and Ramos lymphoma cells. Meriolin 16 induced apoptosis in rapid kinetics (within 2-3 h) and more potently (IC50: 50 nM) than the previously described derivatives meriolin 31 and 36 [1]. Exposure of Ramos cells to meriolin 16, 31, or 36 for 5 min was sufficient to trigger severe and irreversible cytotoxicity. Apoptosis induction by all three meriolin derivatives was independent of death receptor signaling but required caspase-9 and Apaf-1 as central mediators of the mitochondrial death pathway. Meriolin-induced mitochondrial toxicity was demonstrated by disruption of the mitochondrial membrane potential (ΔΨm), mitochondrial release of proapoptotic Smac, processing of the dynamin-like GTPase OPA1, and subsequent fragmentation of mitochondria. Remarkably, all meriolin derivatives were able to activate the mitochondrial death pathway in Jurkat cells, even in the presence of the antiapoptotic Bcl-2 protein. In addition, meriolins were capable of inducing cell death in imatinib-resistant K562 and KCL22 chronic myeloid leukemia cells as well as in cisplatin-resistant J82 urothelial carcinoma and 2102EP germ cell tumor cells. Given the frequent inactivation of the mitochondrial apoptosis pathway by tumor cells, such as through overexpression of antiapoptotic Bcl-2, meriolin derivatives emerge as promising therapeutic agents for overcoming treatment resistance.

Visible Light-Prompted Regioselective Synthesis of Novel 5-Aroyl/hetaroyl-2',4-dimethyl-2,4'-bithiazoles as DNA- and BSA-Targeting Agents

Organic transformations mediated by visible light have gained popularity in recent years as they are green, renewable, inexpensive, and clean and yield excellent products. The present study describes cyclo-condensation of 2-methylthiazole-4-carbothioamide with differently substituted α-bromo-1,3-diketones achieved by utilizing a white light-emitting diode (LED) (9W) to accomplish the regioselective synthesis of novel 5-aroyl/hetaroyl-2',4-dimethyl-2,4'-bithiazole derivatives as DNA/bovine serum albumin (BSA)-targeting agents. The structure characterization of the exact regioisomer was achieved unequivocally by heteronuclear two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy [1H-13C] HMBC; [1H-13C] HMQC; and [1H-15N] HMBC. In silico toxicity studies indicated that the synthesized compounds exhibit low toxicity risks and adhere to the rules of oral bioavailability without any exception. Computational molecular modeling of the bithiazole derivatives with the dodecamer sequence of the DNA duplex and BSA identified 5-(4-chlorobenzoyl)-2',4-dimethyl-2,4'-bithiazole 7g as the most suitable derivative that can interact effectively with these biomolecules. Furthermore, theoretical results concurred with the ex vivo binding mode of the 7g with calf thymus DNA (ct-DNA) and BSA through a variety of spectroscopic techniques, viz., ultraviolet-visible (UV-visible), circular dichroism (CD), steady-state fluorescence, and competitive displacement assay, along with viscosity measurements.

Thiazole derivatives as dual inhibitors of deoxyribonuclease I and 5-lipoxygenase: A promising scaffold for the development of neuroprotective drugs

A library of 43 thiazole derivatives, including 31 previously and 12 newly synthesized in the present study, was evaluated in vitro for their inhibitory properties against bovine pancreatic DNase I. Nine compounds (including three newly synthesized) inhibited the enzyme showing improved inhibitory properties compared to that of the reference crystal violet (IC₅₀ = 346.39 μM). Two compounds (5 and 29) stood out as the most potent DNase I inhibitors, with IC₅₀ values below 100 μM. The 5-LO inhibitory properties of the investigated derivatives were also analyzed due to the importance of this enzyme in the development of neurodegenerative diseases. Compounds (12 and 29) proved to be the most prominent new 5-LO inhibitors, with IC₅₀ values of 60 nM and 56 nM, respectively, in cell-free assay. Four compounds, including one previously (41) and three newly (12, 29 and 30) synthesized, have the ability to inhibit DNase I with IC₅₀ values below 200 μM and 5-LO with IC₅₀ values below 150 nM in cell-free assay. Molecular docking and molecular dynamics simulations were used to clarify DNase I and 5-LO inhibitory properties of the most potent representatives at the molecular level. The newly synthesized compound 29 (4-((4-(3-bromo-4-morpholinophenyl)thiazol-2-yl)amino)phenol) represents the most promising dual DNase I and 5-LO inhibitor, as it inhibited 5-LO in the nanomolar and DNase I in the double-digit micromolar concentration ranges. The results obtained in the present study, together with our recently published results for 4-(4-chlorophenyl)thiazol-2-amines, represent a good basis for the development of new neuroprotective therapeutics based on dual inhibition of DNase I and 5-LO.

[1,2,4]Triazolo[3,4-b]benzothiazole Scaffold as Versatile Nicotinamide Mimic Allowing Nanomolar Inhibition of Different PARP Enzymes

We report [1,2,4]triazolo[3,4-b]benzothiazole (TBT) as a new inhibitor scaffold, which competes with nicotinamide in the binding pocket of human poly- and mono-ADP-ribosylating enzymes. The binding mode was studied through analogues and cocrystal structures with TNKS2, PARP2, PARP14, and PARP15. Based on the substitution pattern, we were able to identify 3-amino derivatives 21 (OUL243) and 27 (OUL232) as inhibitors of mono-ARTs PARP7, PARP10, PARP11, PARP12, PARP14, and PARP15 at nM potencies, with 27 being the most potent PARP10 inhibitor described to date (IC₅₀ of 7.8 nM) and the first PARP12 inhibitor ever reported. On the contrary, hydroxy derivative 16 (OUL245) inhibits poly-ARTs with a selectivity toward PARP2. The scaffold does not possess inherent cell toxicity, and the inhibitors can enter cells and engage with the target protein. This, together with favorable ADME properties, demonstrates the potential of TBT scaffold for future drug development efforts toward selective inhibitors against specific enzymes.

An Overview on Synthetic 2-Aminothiazole-Based Compounds Associated with Four Biological Activities

Amongst sulfur- and nitrogen-containing heterocyclic compounds, the 2-aminothiazole scaffold is one of the characteristic structures in drug development as this essential revelation has several biological activities abiding it to act as an anticancer, antioxidant, antimicrobial and anti-inflammatory agent, among other things. Additionally, various 2-aminothiazole-based derivatives as medical drugs have been broadly used to remedy different kinds of diseases with high therapeutic influence, which has led to their wide innovations. Owing to their wide scale of biological activities, their structural variations have produced attention amongst medicinal chemists. The present review highlights the recently synthesized 2-aminothiazole-containing compounds in the last thirteen years (2008-2020). The originality of this proposal is based on the synthetic strategies developed to access the novel 2-aminothiazole derivatives (N-substituted, 3-substituted, 4-substituted, multi-substituted, aryl/alkyl substituents or acyl/other substituents). The literature reports many synthetic pathways of these 2-aminothiazoles associated with four different biological activities (anticancer, antioxidant, antimicrobial and anti-inflammatory activities). It is wished that this review will be accommodating for new views in the expedition for rationalistic designs of 2-aminothiazole-based medical synthetic pathways.

Development and therapeutic potential of 2-aminothiazole derivatives in anticancer drug discovery

Currently, the development of anticancer drug resistance is significantly restricted the clinical efficacy of the most commonly prescribed anticancer drug. Malignant disease is widely prevalent and considered to be the major challenges of this century, which concerns the medical community all over the world. Consequently, investigating small molecule antitumor agents, which could decrease drug resistance and reduce unpleasant side effect is more desirable. 2-aminothiazole scaffold has emerged as a promising scaffold in medicinal chemistry and drug discovery research. This nucleus is a fundamental part of some clinically applied anticancer drugs such as dasatinib and alpelisib. Literature survey documented that different 2-aminothiazole analogs exhibited their potent and selective nanomolar inhibitory activity against a wide range of human cancerous cell lines such as breast, leukemia, lung, colon, CNS, melanoma, ovarian, renal, and prostate. In this paper, we have reviewed the progresses and structural modification of 2-aminothiazole to pursuit potent anticancers and also highlighted in vitro activities and in silico studies. The information will useful for future innovation. Representatives of 2-aminothiazole-containing compounds classification.

2-Aminothiazole: A privileged scaffold for the discovery of anti-cancer agents

Cancer has been the second heath killer being next only to cardiovascular diseases in human society. Although many efforts have been taken for cancer therapy and many achievements have been yielded in the diagnosis and treatment of cancer, the current first-line anti-cancer agents are insufficient owing to the emergence of multi-drug resistance and side effects. Therefore, it is urgent to develop new anti-cancer agents with high activity and low toxicity. 2-Aminothiazole is a class of important scaffold which widely distributes in many natural and synthetic compounds with many pharmacological effects including the potential anti-cancer activity. In this review, we summarized the recent progress of 2-aminothiazole as a privileged scaffold for the discovery of anti-cancer agents based on biological targets, such as tubulin protein, histone acetylase/histone deacetylase (HAT/HDAC), phosphatidylinositol 3-kinases (PI3Ks), Src/Abl kinase, BRAF kinase, epidermal growth factor receptor (EGFR) kinase and sphingosine kinase (SphK), and also investigated the structure-activity relationships (SARs) of most compounds. It is believed that this review could be helpful for medicinal chemists in the discovery of more anti-cancer agents bearing 2-aminothiazole scaffold with excellent activity and high therapeutic index.

Targeting the SphK-S1P-SIPR Pathway as a Potential Therapeutic Approach for COVID-19

The world is currently experiencing the worst health pandemic since the Spanish flu in 1918-the COVID-19 pandemic-caused by the coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This pandemic is the world's third wake-up call this century. In 2003 and 2012, the world experienced two major coronavirus outbreaks, SARS-CoV-1 and Middle East Respiratory syndrome coronavirus (MERS-CoV), causing major respiratory tract infections. At present, there is neither a vaccine nor a cure for COVID-19. The severe COVID-19 symptoms of hyperinflammation, catastrophic damage to the vascular endothelium, thrombotic complications, septic shock, brain damage, acute disseminated encephalomyelitis (ADEM), and acute neurological and psychiatric complications are unprecedented. Many COVID-19 deaths result from the aftermath of hyperinflammatory complications, also referred to as the "cytokine storm syndrome", endotheliitus and blood clotting, all with the potential to cause multiorgan dysfunction. The sphingolipid rheostat plays integral roles in viral replication, activation/modulation of the immune response, and importantly in maintaining vasculature integrity, with sphingosine 1 phosphate (S1P) and its cognate receptors (SIPRs: G-protein-coupled receptors) being key factors in vascular protection against endotheliitus. Hence, modulation of sphingosine kinase (SphK), S1P, and the S1P receptor pathway may provide significant beneficial effects towards counteracting the life-threatening, acute, and chronic complications associated with SARS-CoV-2 infection. This review provides a comprehensive overview of SARS-CoV-2 infection and disease, prospective vaccines, and current treatments. We then discuss the evidence supporting the targeting of SphK/S1P and S1P receptors in the repertoire of COVID-19 therapies to control viral replication and alleviate the known and emerging acute and chronic symptoms of COVID-19. Three clinical trials using FDA-approved sphingolipid-based drugs being repurposed and evaluated to help in alleviating COVID-19 symptoms are discussed.

Design and Development of Novel Urea, Sulfonyltriurea, and Sulfonamide Derivatives as Potential Inhibitors of phingosine Kinase 1

Sphingosine kinase 1 (SphK1) is one of the well-studied drug targets for cancer and inflammatory diseases. Recently discovered small-molecule inhibitors of SphK1 have been recommended in cancer therapeutics; however, selectivity and potency of first-generation inhibitors are great challenge. In search of effective SphK1 inhibitors, a set of small molecules have been designed and synthesized bearing urea, sulfonylurea, sulfonamide, and sulfonyltriurea groups. The binding affinity of these inhibitors was measured by fluorescence-binding assay and isothermal titration calorimetry. Compounds 1, 5, 6, and 7 showed an admirable binding affinity to the SphK1 in the sub-micromolar range and significantly inhibited SphK1 activity with admirable IC50 values. Molecular docking studies revealed that these compounds fit well into the sphingosine binding pocket of SphK1 and formed significant number of hydrogen bonds and van der Waals interactions. These molecules may be exploited as potent and selective inhibitors of SphK1 that could be implicated in cancer therapeutics after the required in vivo validation.

Design, synthesis, and biological evaluation of novel arylcarboxamide derivatives as anti-tubercular agents

Our group has previously reported several indolecarboxamides exhibiting potent antitubercular activity. Herein, we rationally designed several arylcarboxamides based on our previously reported homology model and the recently published crystal structure of the mycobacterial membrane protein large 3 (MmpL3). Many analogues showed considerable anti-TB activity against drug-sensitive (DS) Mycobacterium tuberculosis (M. tb) strain. Naphthamide derivatives 13c and 13d were the most active compounds in our study (MIC: 6.55, 7.11 μM, respectively), showing comparable potency to the first line anti-tuberculosis (anti-TB) drug ethambutol (MIC: 4.89 μM). In addition to the naphthamide derivatives, we also identified the quinolone-2-carboxamides and 4-arylthiazole-2-carboxamides as potential MmpL3 inhibitors in which compounds 8i and 18b had MIC values of 9.97 and 9.82 μM, respectively. All four compounds retained their high activity against multidrug-resistant (MDR) and extensively drug-resistant (XDR) M. tb strains. It is worth noting that the two most active compounds 13c and 13d also exhibited the highest selective activity towards DS, MDR and XDR M. tb strains over mammalian cells [IC₅₀ (Vero cells) ≥ 227 μM], indicating their potential lack of cytotoxicity. The four compounds were docked into the MmpL3 active site and were studied for their drug-likeness using Lipinski's rule of five.

Synthesis and pharmacological evaluation of arylcarboxamide derivatives based on an antimycobacterial indole-2-carboxamide scaffold. The most active compounds demonstrated activities against MDR and XDR M. tb strains.

Thiazole-containing compounds as therapeutic targets for cancer therapy

In the last few decades, considerable progress has been made in anticancer agents development, and several new anticancer agents of natural and synthetic origin have been produced. Among heterocyclic compounds, thiazole, a 5-membered unique heterocyclic motif containing sulphur and nitrogen atoms, serves as an essential core scaffold in several medicinally important compounds. Thiazole nucleus is a fundamental part of some clinically applied anticancer drugs, such as dasatinib, dabrafenib, ixabepilone, patellamide A, and epothilone. Recently, thiazole-containing compounds have been successfully developed as possible inhibitors of several biological targets, including enzyme-linked receptor(s) located on the cell membrane, (i.e., polymerase inhibitors) and the cell cycle (i.e., microtubular inhibitors). Moreover, these compounds have been proven to exhibit high effectiveness, potent anticancer activity, and less toxicity. This review presents current research on thiazoles and elucidates their biological importance in anticancer drug discovery. The findings may aid researchers in the rational design of more potent and bio-target specific anticancer drug molecules.

A vaginal nanoformulation of a SphK inhibitor attenuates lipopolysaccharide-induced preterm birth in mice

Aim: Previously, we have shown that inhibition of SphK by the SphK inhibitor-II (SKI II) prevents lipopolysaccharide-induced preterm birth in mice. The aim of this study was to develop a vaginal self-nanoemulsifying drug-delivery system (SNEDDS) for SKI II. Materials & methods: A SKI II-loaded SNEDDS was characterized and tested in a murine preterm birth model. Results: The SNEDDS immediately formed a gel and then slowly emulsified to nanoglobules with over 500-fold enhancement of SKI II solubility at vaginal pH. Intravaginal administration of the SKI II SNEDDS significantly decreased lipopolysaccharide-induced preterm birth in mice. Conclusion: A vaginal nanoformulation of SKI II represents a novel, noninvasive approach to prevent preterm birth.

Novel meriolin derivatives as rapid apoptosis inducers

3-(Hetero)aryl substituted 7-azaindoles possessing multikinase inhibitor activity are readily accessed in a one-pot Masuda borylation-Suzuki coupling sequence. Several promising derivatives were identified as apoptosis inducers and, emphasizing the multikinase inhibition potential, as sphingosine kinase 2 inhibitors. Our measurements provide additional insights into the structure-activity relationship of meriolin derivatives, suggesting derivatives bearing a pyridine moiety with amino groups in 2-position as most active anticancer compounds and thus as highly promising candidates for future in vivo studies.

The sphingosine kinase-1/sphingosine-1-phosphate axis in cancer: Potential target for anticancer therapy

Sphingolipid metabolites, such as ceramide, sphingosine and sphingosine-1-phosphate (S1P), play many important roles in cellular activities. Ceramide and sphingosine inhibit cell proliferation and induce cell apoptosis while S1P has the opposite effect. Maintaining a metabolic balance of sphingolipids is essential for growth and development of cells. Sphingosine kinase (SPHK) is an important regulator for keeping this balance. It controls the level of S1P and plays important roles in proliferation, migration, and invasion of cancer cells and tumor angiogenesis. There are two isoenzymes of sphingosine kinase, SPHK1 and SPHK2. SPHK1 is ubiquitously expressed in most cancers where it promotes survival and proliferation, while SPHK2 is restricted to only certain tissues and its functions are not well characterized. SPHK1 is currently considered as a novel target for the treatment of cancers. Targeting SPHK1 would provide new strategies for cancer treatment and improve the prognosis of cancer patients. Here we review and summarize the current research findings on the SPHK1-S1P axis in cancer from many aspects including structure, expression, regulation, mechanism, and potential inhibitors.

Mammalian sphingosine kinase (SphK) isoenzymes and isoform expression: challenges for SphK as an oncotarget

The various sphingosine kinase (SphK) isoenzymes (isozymes) and isoforms, key players in normal cellular physiology, are strongly implicated in cancer and other diseases. Mutations in SphKs, that may justify abnormal physiological function, have not been recorded. Nonetheless, there is a large and growing body of evidence demonstrating the contribution of gain or loss of function and the imbalance in the SphK/S1P rheostat to a plethora of pathological conditions including cancer, diabetes and inflammatory diseases. SphK is expressed as two isozymes SphK1 and SphK2, transcribed from genes located on different chromosomes and both isozymes catalyze the phosphorylation of sphingosine to S1P. Expression of each SphK isozyme produces alternately spliced isoforms. In recent years the importance of the contribution of SpK1 expression to treatment resistance in cancer has been highlighted and, additionally, differences in treatment outcome appear to also be dependent upon SphK isoform expression. This review focuses on an exciting emerging area of research involving SphKs functions, expression and subcellular localization, highlighting the complexity of targeting SphK in cancer and also comorbid diseases. This review also covers the SphK isoenzymes and isoforms from a historical perspective, from their first discovery in murine species and then in humans, their role(s) in normal cellular function and in disease processes, to advancement of SphK as an oncotarget.

Transforming Sphingosine Kinase 1 Inhibitors into Dual and Sphingosine Kinase 2 Selective Inhibitors: Design, Synthesis, and in Vivo Activity

Sphingosine 1-phosphate (S1P) is a pleiotropic signaling molecule that interacts with its five G-protein coupled receptors (S1P1-5) to regulate cell growth and survival and has been implicated in a variety of diseases including cancer and sickle cell disease. As the key mediators in the synthesis of S1P, sphingosine kinase (SphK) isoforms 1 and 2 have attracted attention as viable targets for pharmaceutical inhibition. In this article, we describe the design, synthesis, and biological evaluation of aminothiazole-based guanidine inhibitors of SphK. Surprisingly, combining features of reported SphK1 inhibitors generated SphK1/2 dual inhibitor 20l (SLC4011540) (hSphK1 Ki = 120 nM, hSphK2 Ki = 90 nM) and SphK2 inhibitor 20dd (SLC4101431) (Ki = 90 nM, 100-fold SphK2 selectivity). These compounds effectively decrease S1P levels in vitro. In vivo administration of 20dd validated that inhibition of SphK2 increases blood S1P levels.

Classification of sphingosine kinase inhibitors using counter propagation artificial neural networks: A systematic route for designing selective SphK inhibitors

Accurate and robust classification models for describing and predicting the activity of 330 chemicals that are sphingosine kinase 1 (SphK1) and/or sphingosine kinase 2 (SphK2) inhibitors were derived. The classification models developed in this work assist in finding selective subspaces in chemical space occupied by particular groups of SphK inhibitors. A combination of a genetic algorithm (GA) and a counter propagation artificial neural network (CPANN) was utilized to select the most efficient subsets of the molecular descriptors. The optimized models in this work reasonably separate active inhibitors of SphK1 from active SphK2 inhibitors. Generally, the CPANN models in this work were used to classify the compounds according to their therapeutic targets and activities. The simplicity of the chosen descriptors and their relative importance sheds some light on the structural features necessary to induce selective inhibitory activity to the studied molecules. The areas under the receiver operating characteristic (ROC) curves for the GA-CPANN models in this work were 0.934 and 0.922 for active SphK1 and SphK2 inhibitors, respectively. Generally, the results in this work suggest some important molecular features and pharmacophores that could help medicinal chemists develop selective and potent SphK inhibitors.

Substituted (E)-2-(2-benzylidenehydrazinyl)-4-methylthiazole-5-carboxylates as dual inhibitors of 15-lipoxygenase & carbonic anhydrase II: synthesis, biochemical evaluation and docking studies

15-Lipoxygenase (15-LOX) plays a major role in many inflammatory lung diseases including chronic obstructive pulmonary disease (COPD), asthma and chronic bronchitis. Over-expression of 15-LOX is related with some specific carcinomas including pancreatic, gastric and brain tumor. Similarly among different isozymes of carbonic anhydrase (CA), CA II is expressed in pancreatic, gastric carcinomas as well as in brain tumors. Therefore, novel potent inhibitors of both 15-LOX and CA II are required to explore the role of these enzymes further and to enable the drug discovery efforts. For this purpose, a series of benzyledinyl-hydrazinyl substituted thiazole derivatives were designed, synthesized and characterized by FTIR, ¹H, &¹³C NMR spectroscopy. The derivatives were then evaluated for their potential to inhibit 15-LOX and bovine carbonic anhydrase II (bCA II). Most of these compounds showed excellent inhibitory potential for 15-LOX with an IC₅₀ of 0.12 ± 0.002 to 0.69 ± 0.5 μM and showed moderate inhibition potency for bCA II with compound 5h (IC₅₀ = 1.26 ± 0.24 μM) being the most active. The most potent compound 5a that emerged as a dual inhibitor of both enzymes, exhibiting 24 times greater selectivity for 15-LOX over bCA II. Compound 5a exhibited dual potent inhibitory activity against both 15-LOX and bCA II enzymes having IC₅₀ values of 0.12 ± 0.002 and 2.93 ± 0.22 μM, respectively. Molecular docking studies of potent as well as dual inhibitors were also carried out to provide an insight into the binding site interactions.

Therapeutic Strategies and Pharmacological Tools Influencing S1P Signaling and Metabolism

During the last two decades the study of the sphingolipid anabolic, catabolic, and signaling pathways has attracted enormous interest. Especially the introduction of fingolimod into market as first p.o. therapeutic for the treatment of multiple sclerosis has boosted this effect. Although the complex regulation of sphingosine-1-phosphate (S1P) and other catabolic and anabolic sphingosine-related compounds is not fully understood, the influence on different (patho)physiological states from inflammation to cytotoxicity as well as the availability of versatile pharmacological tools that represent new approaches to study these states are described. Here, we have summarized various aspects concerning the many faces of sphingolipid function modulation by different pharmacological tools up to clinical candidates. Due to the immense heterogeneity of physiological or pharmacological actions and complex cross regulations, it is difficult to predict their role in upcoming therapeutic approaches. Currently, inflammatory, immunological, and/or antitumor aspects are discussed.

Identification of KPNB1 as a Cellular Target of Aminothiazole Derivatives with Anticancer Activity

We found that aminothiazole derivative (E)-N-(5-benzylthiazol-2-yl)-3-(furan-2-yl)acrylamide (1) has strong anticancer activity, and undertook proteomics approaches to identify the target protein of compound 1, importin β1 (KPNB1). A competitive binding assay using fluorescein-labeled 1 showed that 1 has strong binding affinity for KPNB1 (Kd : ∼20 nm). Furthermore, through western blotting assays for KPNB1, KPNA2, EGFR, ErbB2, and STAT3, we confirmed that 1 has inhibitory effects on the importin pathway. KPBN1 appears to be overexpressed in several cancer cells, and siRNA-induced inhibition of KPNB1 shows significant inhibition of cancer cell proliferation, while leaving non-cancerous cells unaffected. Therefore, compound 1 is a promising new lead for the development of KPNB1-targeted anticancer agents. Fluorescein-labeled 1 could be a useful quantitative probe for the development of novel KPNB1 inhibitors.

Synthesis and evaluation of sulfonamide-bearing thiazole as carbonic anhydrase isoforms hCA I and hCA II

Sulfonamide-bearing thiazole compounds were synthesized and their inhibitory effects on the activity of purified human carbonic anhydrase I and II were evaluated. Human carbonic anhydrase isoenzymes (hCA-I and hCA-II) were purified from erythrocyte cells by affinity chromatography. The inhibitory effects of the 12 synthesized sulfonamide (5a-l) on the hydratase and esterase activities of these isoenzymes (hCA-I and hCA-II) were studied in vitro. In relation to these activities, the inhibition equilibrium constants (Ki) were determined. The results showed that all the synthesized compounds inhibited the CA isoenzyme activity. Among them 5b was found to be the most active (IC50 = 0.35 μM; Ki: 0.33 μM) for hCA I and hCA II.

Sphingosine Kinase 2 and Ceramide Transport as Key Targets of the Natural Flavonoid Luteolin to Induce Apoptosis in Colon Cancer Cells

The plant flavonoid luteolin exhibits different biological effects, including anticancer properties. Little is known on the molecular mechanisms underlying its actions in colorectal cancer (CRC). Here we investigated the effects of luteolin on colon cancer cells, focusing on the balance between ceramide and sphingosine-1-phosphate (S1P), two sphingoid mediators with opposite roles on cell fate. Using cultured cells, we found that physiological concentrations of luteolin induce the elevation of ceramide, followed by apoptotic death of colon cancer cells, but not of differentiated enterocytes. Pulse studies revealed that luteolin inhibits ceramide anabolism to complex sphingolipids. Further experiments led us to demonstrate that luteolin induces an alteration of the endoplasmic reticulum (ER)-Golgi flow of ceramide, pivotal to its metabolic processing to complex sphingolipids. We report that luteolin exerts its action by inhibiting both Akt activation, and sphingosine kinase (SphK) 2, with the consequent reduction of S1P, an Akt stimulator. S1P administration protected colon cancer cells from luteolin-induced apoptosis, most likely by an intracellular, receptor-independent mechanism. Overall this study reveals for the first time that the dietary flavonoid luteolin exerts toxic effects on colon cancer cells by inhibiting both S1P biosynthesis and ceramide traffic, suggesting its dietary introduction/supplementation as a potential strategy to improve existing treatments in CRC.