Structural investigations on coumarins leading to chromeno[4,3-c]pyrazol-4-ones and pyrano[4,3-c]pyrazol-4-ones: New scaffolds for the design of the tumor-associated carbonic anhydrase isoforms IX and XII

Mitigating the resistance of MCF-7 cancer cells to Doxorubicin under hypoxic conditions with novel coumarin based carbonic anhydrase IX and XII inhibitors

In the present study, the design and synthesis of novel coumarin derivatives 8a-h, 11a-d and 16a-c as potential selective inhibitors for the tumor associated human carbonic anhydrase isoforms (hCA IX and XII) was reported. All the newly synthesized derivatives showed potent to mild activity against the targeted CA IX (KI = 0.08-9.57 µM), with selectivity indices over CA I (SI = 2.0-21.9) and over CA II (SI = 1.1-15.7). They showed similar activities against CA XII (KI = 0.06-9.48 µM) with selectivity indices over CA I (SI = 1.4-21.2) and CA II (SI = 0.9-15.5). Compound 16b featuring sulfonamide function possessed promising inhibitory activities against the targeted isoforms CA IX and XII with KI values of 0.08 and 0.06 µM, respectively. Interestingly, it was found that using compound 16b at a nontoxic concentration as an adjuvant with Doxorubicin against MCF-7 cells enhanced the cytotoxicity under hypoxia by almost 3.5 folds; IC50 decreased from 25.74 to 7.43 µM. Therefore, compound 16b restored the cytotoxicity of Doxorubicin against MCF-7 cells under hypoxia, almost as normoxia. Furthermore, flow cytometry analysis of a combination treatment of compound 16b and Doxorubicin to the MCF7 cell line revealed an increase in cell cycle arrest at the G2/M phase and a more efficient apoptotic effect than Doxorubicin alone. Furthermore, compound 16b showed no cytotoxicity against normal breast MCF-10A cell line (IC50 = 296.25 µM).

3,3'-((3,4,5-trifluoropHenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) inhibit lung cancer cell proliferation and migration

Lung cancer is a major public health challenge and, despite therapeutic improvements, is the first leading cause of cancer worldwide. The current cure rate from advanced cancer treatment is excessively low. Therefore, it is of great importance to identify novel, potent and less toxic anticancer agents for the treatment of lung cancer. The aim of our research is to synthesize a new biscoumarin 3,3'-((3,4,5-trifluorop -phenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (C35) as an anticancer agent. C35 was simply prepared by 4-hydroxycoumarin and 3,4,5-trifluorobenzaldehyde under ethanol and its structure was analyzed by spectroscopic analyses. The anti-proliferation effect of C35 was detected using CCK-8 assay. Migration abilities were measured by Transwell assay. The expression of correlated proteins was determined by Western blot. The results showed that C35 displayed strong cytostatic effects on lung cancer cell proliferation. In addition, C35 possessed a significant inhibition of migration by reducing the expression of matrix metalloproteinases-2 (MMP-2) and MMP-9 in lung cancer cells. Furthermore, C35 treatment suppressed the phosphorylation of p38 in lung cancer cells. Moreover, in vivo experiments were carried out, in which we treated Lewis tumor-bearing C57 mice via intraperitoneal injection of C35. Results showed that C35 inhibited tumor growth in vivo. In conclusion, our study demonstrated the anticancer activity of C35 via suppression of lung cancer cell proliferation and migration, which is possibly involved with the inhibition of the p38 pathway.

Anticancer mechanism of coumarin-based derivatives

The structural motif of coumarins is related with various biological activities and pharmacological properties. Both natural coumarin extracted from various plants or a new coumarin derivative synthesized by modification of the basic structure of coumarin, in vitro experiments showed that coumarins are a promising class of anti-tumor agents with high selectivity. Cancer is a complex and multifaceted group of diseases characterized by the uncontrolled and abnormal growth of cells in the body. This review focuses on the anticancer mechanism of various coumarins synthesized and isolated in more than a decade. Isopentenyloxycoumarins inhibit angiogenesis by reducing CCl2 chemokine levels. Ferulin C is a potent colchicine-binding agent that destabilizes microtubules, exhibiting antiproliferative and anti-metastatic effects in breast cancer cells through PAK1 and PAK2-mediated signaling. Trimers of triphenylethylene-coumarin hybrids demonstrated significant proliferation inhibition in HeLa, A549, K562, and MCF-7 cell lines. Platinum(IV) complexes with 4-hydroxycoumarin have the potential for high genotoxicity against tumor cells, inducing apoptosis in SKOV-3 cells by up-regulating caspase 3 and caspase 9 expression. Derivatives of 3-benzyl coumarin seco-B-ring induce apoptosis, mediated through the PI3K/Akt/mTOR signaling pathway. Sesquiterpene coumarins inhibit the efflux pump of multidrug resistance-associated protein. Coumarin imidazolyl derivatives inhibit the aromatase enzyme, a major contributor to estrogen overproduction in estrogen-dependent breast cancer.

pH regulators and their inhibitors in tumor microenvironment

As an important characteristic of tumor, acidic tumor microenvironment (TME) is closely related to immune escape, invasion, migration and drug resistance of tumor. The acidity of the TME mainly comes from the acidic products produced by the high level of tumor metabolism, such as lactic acid and carbon dioxide. pH regulators such as monocarboxylate transporters (MCTs), carbonic anhydrase IX (CA IX), and Na+/H+ exchange 1 (NHE1) expel protons directly or indirectly from the tumor to maintain the pH balance of tumor cells and create an acidic TME. We review the functions of several pH regulators involved in the construction of acidic TME, the structure and structure-activity relationship of pH regulator inhibitors, and provide strategies for the development of small-molecule antitumor inhibitors based on these targets.

Synthesis and antitumor activity evaluation of coumarin Mannich base derivatives

Twenty-one new coumarin Mannich base derivatives (11a-u) were synthesized, which exhibited antiproliferation activities in HepG2 (liver cancer), A549 (lung cancer), MCF-7 (breast cancer), and HT-29 (colon cancer). Most of the target compounds showed the most potent activity against HepG2 cells compared with other cancer cells, compound 11g showed the strongest antiproliferative activity (2.10 μM) against HepG2, even superior to the positive control drug 5-FU(5.49 μM). The nitric oxide (NO) release of all compounds in HepG2 cells was determined, of which compound 11g showed high levels of NO release (10.8 μM). Notably, the solubility of compound 11g increased 13-fold compared with the lead 8. The preliminary cytotoxicity studies suggest that 11g had little effect on LO2 cells(normal liver cells, >50 μM). The effect of compound 11g on the apoptosis of HepG2 cells was also studied, and the results showed that the induction effect of compound 11g on apoptosis is a concentration-dependent manner. Our results indicate that compound 11g might be a promising lead for further studies.

Substituted furan sulfonamides as carbonic anhydrase inhibitors: Synthesis, biological and in silico studies

Carbonic Anhydrases (CAs) are a large family of zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide involved in several of biological processes, such as respiration, calcification, acid-base balance, bone resorption, and the formation of aqueous humor, cerebrospinal fluid, saliva, and gastric acid. They show wide diversity in tissue distribution and in their subcellular localization. Fifteen novel furyl sulfonamides were designed, synthesized and evaluated against four human isoforms: hCA I, hCA II, hCA IV and hCA IX. Compounds appeared to be very active mostly against hCAI (8) and hCA IV (11) isoforms being more potent than reference drug acetazolamide (AAZ). It should be mentioned that four compounds were more active than AAZ against hCA IX isoform, with compound 13d to be selective against hCA I (SI 70), hCA II (SI 13.5) and hCA IV (SI 20). Furthermore, docking was performed for some of these compounds on all isoforms I order to understand the possible interactions with the active site. The most active compounds showed good bioavailability and drug likeness scores.

Tail-Approach-Based Design and Synthesis of Coumarin-Monoterpenes as Carbonic Anhydrase Inhibitors and Anticancer Agents

In this study, sixty novel coumarin-monoterpene compounds were synthesized in two series [thirty-two compounds (12-43) bearing a triazole ring in the first series, and twenty-eight compounds (44-71) bearing an alkyl chain in the second one]. Their inhibitory effects on the human carbonic anhydrase (hCA) isoforms I, II, IX, and XII and anticancer potentials were determined. All synthesized molecules selectively inhibited CA IX and XII. 23 and 42 were found to be the strongest inhibitors, with K _i values of 1.9 nM against hCA IX. Also, 70 showed the highest inhibitory activity with a K _i value of 4.9 nM against hCA XII. Moreover, their cytotoxic effects on colon adenocarcinoma (HT-29), prostate adenocarcinoma (PC-3), and breast adenocarcinoma (MCF-7) cell lines were evaluated. According to the cytotoxicity results, 14 (IC₅₀ = 2.48 μM) and 63 (IC₅₀ = 3.91 μM) exhibited the highest cytotoxicity on the MCF-7 cells, while 23 showed the strongest cytotoxic effect on both PC-3 (IC₅₀ = 9.40 μM) and HT-29 (IC₅₀ = 12.10 μM) cell lines. 14, 23, and 66 decreased CA IX and CA XII protein expression in HT-29 cells, while 23 and 66 showed the strongest reduction of both CA IX and CA XII in MCF-7 cells. All of the selected compounds increased total apoptosis in a concentration-dependent manner in HT-29 and MCF-7 cells. 14 has the strongest apoptotic effect in MCF-7 cells. 23 increased early apoptosis primarily, while 14 and 66 increased total apoptosis in HT-29. In addition, PI/Hoechst staining proves that apoptotic cells are increased in HT-29 with an effect of 14, 23, and 66. As a result of the modeling studies, it has been shown that only the open coumarin form of the compounds can interact directly with the active-site Zn²⁺ ion. It has been shown that coumarin-monoterpene structures with different alkyl and monoterpene groups both specifically inhibit CA IX and XII and exhibit specific cytotoxicity in different cell lines.

Continued Structural Exploration of Sulfocoumarin as Selective Inhibitor of Tumor-Associated Human Carbonic Anhydrases IX and XII

A series of new 3- and 7-substituted sulfocoumarins was obtained by several cyclization reactions and subsequent derivatization for screening as prodrug inhibitors of the human (h) cancer-associated carbonic anhydrases (CAs) IX and XII. All products were ineffective inhibitors against the off-target hCA I and II, whilst hCAs IX and XII were inhibited with inhibition constants (KIs) spanning from low nanomolar to the high micromolar range, according to the sulfocoumarin derivatization pattern. In particular, sulfocoumarin 15 turned out to be the most potent and selective inhibitor herein reported (hCA I and II: KI > 100 µM; hCA IX: KI = 22.9 nM; hCA XII: KI = 19.2 nM). Considering that hCA IX and XII validated anti-tumor targets, such prodrug, isoform-selective inhibitors as the sulfocoumarins reported here may be useful for identifying suitable drug candidates for clinical trials.

Aromatic Sulfonamides including a Sulfonic Acid Tail: New Membrane Impermeant Carbonic Anhydrase Inhibitors for Targeting Selectively the Cancer-Associated Isoforms

We report here a new drug design strategy for producing membrane-impermeant carbonic anhydrase (CA; EC 4.2.1.1) inhibitors selectively targeting the tumor-associated, membrane-bound human CAs IX and XII over off-target cytosolic isoforms. To date, this approach has only been pursued by including permanent positively charged pyridinium type or highly hydrophilic glycosidic moieties into the structure of aromatic sulfonamide CA inhibitors (CAIs). Aliphatic (propyl and butyl) sulfonic acid tails, deprotonated at physiological pH, were thus incorporated onto a benzenesulfonamide scaffold by a common 1,2,3-triazole linker and different types of spacers. Twenty such derivatives were synthesized and tested for their inhibition of target (hCAs IV, IX, and XII) and off-target CAs (hCAs I and II). Most sulfonate CAIs induced a potent inhibition of hCAs II, IX, and XII up to a low nanomolar K_I range (0.9–459.4 nM) with a limited target/off-target CA selectivity of action. According to the drug design schedule, a subset of representative derivatives was assessed for their cell membrane permeability using Caco-2 cells and a developed FIA-MS/MS method. The complete membrane impermeability of the sulfonate tailed CAIs (≥98%) validated these negatively charged moieties as being suitable for achieving, in vivo, the selective targeting of the tumor-associated CAs over off-target ones.

Coumarins and Gastrointestinal Cancer: A New Therapeutic Option?

Cancers of the gastrointestinal (GI) tract are often life-threatening malignancies, which can be a severe burden to the health care system. Globally, the mortality rate from gastrointestinal tumors has been increasing due to the lack of adequate diagnostic, prognostic, and therapeutic measures to combat these tumors. Coumarin is a natural product with remarkable antitumor activity, and it is widely found in various natural plant sources. Researchers have explored coumarin and its related derivatives to investigate their antitumor activity, and the potential molecular mechanisms involved. These mechanisms include hormone antagonists, alkylating agents, inhibitors of angiogenesis, inhibitors of topoisomerase, inducers of apoptosis, agents with antimitotic activity, telomerase inhibitors, inhibitors of human carbonic anhydrase, as well as other potential mechanisms. Consequently, drug design and discovery scientists and medicinal chemists have collaborated to identify new coumarin-related agents in order to produce more effective antitumor drugs against GI cancers. Herein, we summarize the therapeutic effects of coumarin and its derivatives against GI cancer.

Cytotoxicity evaluation and DNA interaction of RuII-bipy complexes containing coumarin-based ligands

Although there are various treatment options for cancer, this disease still has caused an increasing number of deaths, demanding more efficient, selective and less harmful drugs. Several classes of ruthenium compounds have been investigated as metallodrugs for cancer, mainly after the entry of imidazolH [trans-RuCl4-(DMSO-S)(imidazole)] (NAMI-A) and indazolH [trans-RuCl4-(Indazol)2] (KP1019) in clinical trials. In this sense, RuII complexes with general formula [Ru(L1-3)(bipy)2]PF6 (1-3) (L1 = ethyl 3-(6-methyl-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L2 = ethyl 3-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L3 = ethyl 3-(8-methoxy-2-oxo-2H-chromen-3-yl)-3-oxopropanoate and bipy = bipyridine) have been synthesized. The crystal structure of 2 revealed that the RuII atom lies on a distorted octahedral geometry with the deprotonated ligand (L2-) coordinated through β-ketoester group oxygen atoms. In vitro cytotoxic activity of the compounds was evaluated against 4T1 (murine mammary carcinoma) and B16-F10 (murine metastatic melanoma) tumor cells, and the non-tumor cell line BHK-21 (baby hamster kidney). Coordination with RuII resulted in expressive enhancement of cytotoxic activity. The precursors were inactive below 100 μM and the final RuII complexes (1-3) showed IC50 ranging from 2.0 to 12.8 μM; 2 being the most potent compound. DNA interaction studies revealed a greater capacity of the complexes to interact with DNA than the ligands, where, 2 exhibited the highest Kb constant of 2.2 × 104 M-1. Fluorescence investigation demonstrated that 1-3 are capable of quenching the fluorescence emission of the EtdBr-DNA complex up to 40%. Molecular docking showed that the interaction of 1-3 between the DNA base pairs from the coumarin portion was with scores of 67.28, 68.62 and 64.88, respectively, and 75.45 for ellipticine, suggesting an intercalative mode of binding. Our findings show that the RuII complexes are eligible for continuing to be investigated as potential antitumor compounds.

Pharmacological report of recently designed multifunctional coumarin and coumarin-heterocycle derivatives

Coumarin is a naturally available molecule and has been identified as a potent pharmacophore due to its pharmacological activity. Because of this, coumarin has been exploited synthetically to prepare a wide range of derivatives. In fact, most coumarin derivatives have been found to be less toxic, which is the most essential property for a drug molecule. Such molecules are being prepared for therapeutic use as broad-spectrum pharmacological agents. Microbial diseases including viral diseases have become very common and are responsible for many deaths worldwide. In particular, microbial drug resistance is a problem that needs to be tackled in an effective manner. Also, for Alzheimer's disease, which affects most elderly persons, no efficient chemotherapy exists. In addition, although diabetes, a metabolic syndrome, can be treated with many drugs, there is no complete cure. Thus, more potent antidiabetic agents are required for the management of diabetes. Likewise, for the treatment of a wide range of ailments caused by microbes, genetic factors, or lifestyle-related factors, an efficient drug regimen is needed. In view of this, coumarin derivatives are designed and evaluated. Here, coumarin derivatives that have been reported recently are compiled, classified and evaluated critically. This study briefly takes the structure-activity relationship into consideration and suggests the next suitable step. With a focus on the most potent molecules, the pharmacological activity of the evaluated molecules is described.

Synthesis, Crystal Structure, Inhibitory Activity and Molecular Docking of Coumarins/Sulfonamides Containing Triazolyl Pyridine Moiety as Potent Selective Carbonic Anhydrase IX and XII Inhibitors

In this work, two classes of Carbonic Anhydrase (CA) inhibitors, sulfonamide and coumarin derivatives linked to pyta moiety (2a-b) and their corresponding rhenium complexes (3a-b), were designed. These compounds were synthesized and fully characterized by classical analytical methods and X-ray diffraction. All the synthesized compounds were evaluated for their inhibitory activity against the hCA isoforms I, II, IX and XII. They exhibited high inhibitory activities in the range of nanomolar for both hCA IX and hCA XII isoforms. The sulfonamide compound 2a showed the strongest inhibition against the tumour-associated hCA IX isoform with a Ki of 11.7 nM. The tumour-associated isoforms hCA IX and hCA XII were selectively inhibited by all the coumarin derivatives, with inhibition constants ranging from 12.7 nM (2b) to 44.5 nM (3b), while the hCA I and II isoforms were slightly inhibited (in the micromolar range), as expected. In terms of selectivity, compared to previously published rhenium complex-based CA inhibitors, complex 3b showed one of the highest selectivities against hCA IX and hCA XII compared to the off-target isoforms hCA I and hCA II, making it a potential anti-cancer drug candidate. Molecular docking calculations were performed to investigate the inhibition profiles of the investigated compounds at the tumour-associated hCA IX active site and to rationalize our results.

New Sulfanilamide Derivatives Incorporating Heterocyclic Carboxamide Moieties as Carbonic Anhydrase Inhibitors

Carbonic Anhydrases (CAs) are ubiquitous metalloenzymes involved in several disease conditions. There are 15 human CA (hCA) isoforms and their high homology represents a challenge for the discovery of potential drugs devoid of off-target side effects. For this reason, many synthetic and pharmacologic research efforts are underway to achieve the full pharmacological potential of CA modulators of activity. We report here a novel series of sulfanilamide derivatives containing heterocyclic carboxamide moieties which were evaluated as CA inhibitors against the physiological relevant isoforms hCA I, II, IX, and XII. Some of them showed selectivity toward isoform hCA II and hCA XII. Molecular docking was performed for some of these compounds on isoforms hCA II and XII to understand the possible interaction with the active site amino acid residues, which rationalized the reported inhibitory activity.

Design, synthesis and biochemical evaluation of novel carbonic anhydrase inhibitors triggered by structural knowledge on hCA VII

To tackle the challenge of isoform selectivity, we explored the entrance of the cavity for selected druggable human Carbonic Anhydrases (hCAs). Based on X-ray crystallographic studies on the 4-(4-(2-chlorobenzoyl)piperazine-1-carbonyl)benzenesulfonamide in complex with the brain expressed hCA VII (PDB code: 7NC4), a series of 4-(4(hetero)aroylpiperazine-1-carbonyl)benzene-1-sulfonamides has been developed. To evaluate their capability to fit the hCA VII catalytic cavity, the newer benzenesulfonamides were preliminary investigated by means of docking simulations. Then, this series of thirteen benzenesulfonamides was synthesized and tested against selected druggable hCAs. Among them, the 4-(4-(furan-2-carbonyl)piperazine-1-carbonyl)benzenesulfonamide showed remarkable affinity towards hCA VII (Ki: 4.3 nM) and good selectivity over the physiologically widespread hCA I when compared to Topiramate (TPM).

Fragment-type 4-azolylcoumarin derivatives with anticancer properties

Several coumarin derivatives with a directly attached azole substituent at C-4 were synthesized and biologically studied for their anticancer properties. The cell lines used for this investigation (HeLa, K-562, MDA-MB-53, and MCF-7) demonstrated different sensitivities. The best response in the MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) assay was shown by K-562 cells, with compounds displaying activity (3c, IC₅₀ 3.06 μM; 4a, IC₅₀ 5.24 μM; 4c, IC₅₀ 4.7 μM) similar to that of cisplatin (IC₅₀ ~6 μM), which was used as the standard. The studied azole-substituted coumarins demonstrated weaker activity toward other cell lines, except for compound 4c, which was equally potent in the case of MCF-7 cells. Additional biological evaluations supported interference with the cell cycle as a potential mechanism of action and confirmed the absence of toxicity in zebrafish embryos. On the basis of these initial results, 4-azole coumarins should be explored further. Although their activity would need additional optimization, the fact that these compounds are fragment-like structures with MW <300 and clog P <3 offers enough flexibility to fine-tune their drug-like properties.

Identification of non-classical hCA XII inhibitors using combination of computational approaches for drug design and discovery

Human carbonic anhydrase XII (hCA XII) isozyme is of high therapeutic value as a pharmacological target and biomarker for different types of cancer. The hCA XII is one of the crucial effectors that regulates extracellular and intracellular pH and affects cancer cell proliferation, invasion, growth and metastasis. Despite the fact that interaction features of hCAs inhibitors with the catalytic site of the enzyme are well described, lack in the selectivity of the traditional hCA inhibitors based on the sulfonamide group or related motifs is an urgent issue. Moreover, drugs containing sulfanomides can cause sulfa allergies. Thus, identification of novel non-classical inhibitors of hCA XII is of high priority and is currently the subject of a vast field of study. This study was devoted to the identification of novel potential hCA XII inhibitors using comprehensive set of computational approaches for drug design discovery: generation and validation of structure- and ligand-based pharmacophore models, molecular docking, re-scoring of virtual screening results with MMGBSA, molecular dynamics simulations, etc. As the results of the study several compounds with alternative to classical inhibitors chemical scaffolds, in particular one of coumarins derivative, have been identified and are of high interest as potential non-classical hCA XII inhibitors.

Developments of small molecules as inhibitors for carbonic anhydrase isoforms

Carbonic anhydrases are ubiquitous, and their role in the hydration of carbon dioxide is essential for the survival of many tissues and organs. However, their association with many pathological diseases, especially in glaucoma, Alzheimer's, obesity, epilepsy, and tumorigenesis, has prompted the design and synthesis of novel carbonic anhydrase inhibitors (CAIs). Herein we describe (1) approaches used in the design of CAIs and (2) synthesis of small molecules as CAIs within the last five years. Despite the active research in this area, there are still more avenues to explore, especially selective inhibition of CA I, CA IX, and XII. These isoforms would continue to open up a diversity of carbonic anhydrase inhibitors containing 1,2,3-triazoles, imidazolone, pyrrolidone, thiadiazole, isatin, and glycoconjugates as part of their molecular frameworks.

Quinoline-sulfamoyl carbamates/sulfamide derivatives: Synthesis, cytotoxicity, carbonic anhydrase activity, and molecular modelling studies

Carbonic anhydrase (CA) IX, and XII isoforms are known to be highly expressed in various human tissues and malignancies. CA IX is a prominent target for some cancers because it is overexpressed in hypoxic tumors and this overexpression leads to poor prognosis. Novel twenty-seven compounds in two series (sulfamoylcarbamate-based quinoline (2a-2o) and sulfamide-based quinoline (3a-3l)) were synthesized and characterized by means of IR, NMR, and mass spectra. Their inhibitory activities were evaluated against CA I, CA II, CA IX, and CA XII isoforms. 2-Phenylpropyl (N-(quinolin-8-yl)sulfamoyl)carbamate (2m) exhibited the highest hCA IX inhibition with the K_i of 0.5 µM. In addition, cytotoxic effects of the synthesized compounds on human colorectal adenocarcinoma (HT-29; HTB-38), human breast adenocarcinoma (MCF7; HTB-22), human prostate adenocarcinoma (PC3; CRL-1435) and human healthy skin fibroblast (CCD-986Sk; CRL-1947) cell lines were examined. The cytotoxicity results showed that 2j, 3a, 3e, 3f are most active compounds in all cell lines (HT-29, MCF7, PC3, and CCD-986Sk).

4-Chloro-3-formylcoumarin as a multifaceted building block for the development of various bio-active substituted and fused coumarin heterocycles: a brief review

This review presents the diverse synthesis of 3,4-substituted coumarins and 5-, 6- and 7-membered ring fused coumarins using 4-chloro-3-formylcoumarin as the precursor via classical reactions including metal-catalyzed and green reaction protocols.

A Review on Anti-Tumor Mechanisms of Coumarins

Coumarins are a class of compound with benzopyrone as their basic structure. Due to abundant sources, easy synthesis, and various pharmacological activities, coumarins have attracted extensive attention from researchers. In particular, coumarins have very significant anti-tumor abilities and a variety of anti-tumor mechanisms, including inhibition of carbonic anhydrase, targeting PI3K/Akt/mTOR signaling pathways, inducing cell apoptosis protein activation, inhibition of tumor multidrug resistance, inhibition of microtubule polymerization, regulating the reactive oxygen species, and inhibition of tumor angiogenesis, etc. This review focuses on the mechanisms and the research progress of coumarins against cancers in recent years.

Synthesis and Evaluation of 4-Hydroxycoumarin Imines as Inhibitors of Class II Myosins

Inhibitors of muscle myosin ATPases are needed to treat conditions that could be improved by promoting muscle relaxation. The lead compound for this study ((3-(N-butylethanimidoyl)ethyl)-4-hydroxy-2H-chromen-2-one; BHC) was previously discovered to inhibit skeletal myosin II. BHC and 34 analogues were synthesized to explore structure-activity relationships. The properties of analogues, including solubility, stability, and toxicity, suggest that the BHC scaffold may be useful for developing therapeutics. Inhibition of actin-activated ATPase activity of fast skeletal and cardiac muscle myosin II, inhibition of skeletal muscle contractility ex vivo, and slowing of in vitro actin-sliding velocity were measured. Several analogues with aromatic side arms showed improved potency (half-maximal inhibitory concentration (IC50) <1 μM) and selectivity (≥12-fold) for skeletal myosin versus cardiac myosin compared to BHC. Several analogues blocked neurotransmission, suggesting that they are selective for nonmuscle myosin II over skeletal myosin. Competition and molecular docking studies suggest that BHC and blebbistatin bind to the same site on myosin.

Discovery of first-in-class multi-target adenosine A2A receptor antagonists-carbonic anhydrase IX and XII inhibitors. 8-Amino-6-aryl-2-phenyl-1,2,4-triazolo [4,3-a]pyrazin-3-one derivatives as new potential antitumor agents

This paper describes identification of the first-in-class multi-target adenosine A_2A receptor antagonists-carbonic anhydrase (CA) IX and XII inhibitors, as new potential antitumor agents. To obtain the multi-acting ligands, the 8-amino-2,6-diphenyltriazolo[4,3-a]pyrazin-3-one, a potent adenosine hA_2A receptor (AR) antagonist, was taken as lead compound. To address activity against the tumor-associated CA isoforms, it was modified by introduction of different substituents (OH, COOH, CONHOH, SO₂NH₂) on the 6-phenyl ring or on a phenyl pendant connected to the former through different spacers. Among the new triazolopyrazines 1-23, the most active were those featuring the sulfonamide residue. Derivative 20, featuring a 4-sulfonamidophenyl residue attached through a CONH(CH₂)₂CONH spacer at the para-position of the 6-phenyl ring, showed the best combination of activity at the three targets. In fact, it inhibited both the tumor-associated hCA IX and XII isozymes at nanomolar concentration (K_i = 5.0 and 27.0 nM), and also displayed a quite good affinity for the hA_2A AR (K_i = 108 nM). Compound 14, bearing the 4-sulfonamidophenyl residue linked at the para-position of the 6-phenyl ring by a CONH spacer, was remarkable because both its hA_2A AR affinity and hCA XII inhibitory potency were in the low nanomolar range (K_i = 6.4 and 6.2 nM, respectively). Molecular docking studies highlighted the interaction mode of selected triazolopyrazines in the hA_2A AR recognition pocket and in the active site of hCA II, IX and XII isoforms.

Development of oxathiino[6,5-b]pyridine 2,2-dioxide derivatives as selective inhibitors of tumor-related carbonic anhydrases IX and XII

Oxathiino[6,5-b]pyridine 2,2-dioxides are identified as a new class of isoform-selective nanomolar inhibitors of tumor associated human carbonic anhydrases (hCA) IX and XII. At the same time they do not inhibit or poorly inhibit cytosolic isoforms hCA I and II. Oxathiino[6,5-b]pyridine 2,2-dioxides exhibited good antiproliferative properties on tumor cell lines MCF-7 (Human breast adenocarcinoma), A549 (human lung (alveolar) adenocarcinoma) and HeLa (epithelioid cervix carcinoma).

Access to 4-Alkenylated Coumarins via Ruthenium-Catalyzed Olefinic C-H Alkenylation of Coumarins with Modifiable and Removable Directing Groups

The ruthenium-catalyzed activation of the C4 position of coumarins for coupling with acrylates was described using modifiable ketone as a directing group. The alkenylation reaction provided a direct approach to prepare previously inaccessible 4-alkenylated coumarins with operational simplicity and high atom-economy. This protocol also worked well with coumarin-3-carboxylic acids to unveil a rare instance of a tandem alkenylation/decarboxylation reaction. The potential value of this approach was further highlighted by the efficient synthesis of several heterocyclic fused coumarin derivatives.

Progress in the development of human carbonic anhydrase inhibitors and their pharmacological applications: Where are we today?

Carbonic anhydrases (CAs, EC 4.2.1.1) are widely distributed metalloenzymes in both prokaryotes and eukaryotes. They efficiently catalyze the reversible hydration of carbon dioxide to bicarbonate and H⁺  ions and play a crucial role in regulating many physiological processes. CAs are well-studied drug target for various disorders such as glaucoma, epilepsy, sleep apnea, and high altitude sickness. In the past decades, a large category of diverse families of CA inhibitors (CAIs) have been developed and many of them showed effective inhibition toward specific isoforms, and effectiveness in pathological conditions in preclinical and clinical settings. The discovery of isoform-selective CAIs in the last decade led to diminished side effects associated with off-target isoforms inhibition. The many new classes of such compounds will be discussed in the review, together with strategies for their development. Pharmacological advances of the newly emerged CAIs in diseases not usually associated with CA inhibition (neuropathic pain, arthritis, cerebral ischemia, and cancer) will also be discussed.

Looking toward the Rim of the Active Site Cavity of Druggable Human Carbonic Anhydrase Isoforms

We report the synthesis and biochemical evaluation of a series of substituted 4-(4-aroylpiperazine-1-carbonyl)benzenesulfonamides (5a-s) developed as inhibitors of druggable carbonic anhydrase (CA) isoforms, as tools for the identification of new therapeutics. X-ray crystallography confirmed that this class of benzenesulfonamides binds CAs through the canonical anchoring of the benzenesulfonamide moiety to the metal ion and a tail-mediated recognition of the middle/top area of the active site cavity. Compound 5e (R = 2-Cl) demonstrated relevant selectivity toward brain-expressed hCA VII. The best balancing in binding affinity and selectivity toward tumor-expressed hCA IX/hCA XII over ubiquitous hCA I/hCA II was found for inhibitor 5o (R = 3-NO₂). Notably 5b (R = 2-F) proved to be the most efficacious inhibitor of hCA XII for which computational studies elucidated the CA recognition process.

Synthesis, computational study and cytotoxicity of 4-hydroxycoumarin-derived imines/enamines

In this study, we applied a direct condensation between 3-acetyl-4-hydroxy-2H-chromen-2-one and different amines (anilines and benzyl amines) in order to synthesize some coumarin-based imines/enamines (3a-o) as cytotoxic agents. All the compounds were characterized by means of FT-IR, NMR, mass spectroscopy and elemental analyses. Since the title compounds can exist as different forms including (s-cis)-imine and (s-trans)-imine or (E and Z)-enamines, their conformational and geometrical aspects were investigated computationally by DFT method. The optimized geometry parameters, ΔE, ΔG, ΔH, Mulliken atomic charge, HOMO and LUMO energy, and NBO analysis suggested that these compounds can exist predominantly in (E)-enamine form. All the synthesized compounds (3a-o) were evaluated in vitro for their cytotoxic activities against cancer cell lines (MCF-7 and A549) and normal cell line (BEAS-2B) using the MTT assay. The 4-hydroxybenzyl derivative 3k was found to be the most potent cytotoxic agent with no selectivity, similar to doxorubicin. However, the 4-chlorobenzyl analog 3o could be considered as an equipotent compound respect to doxorubicin with higher selectivity.

Benzoxepinones: A new isoform-selective class of tumor associated carbonic anhydrase inhibitors

Benzoxepinones ("homocoumarins") are identified as a new class of selective inhibitors for tumor associated human carbonic anhydrases (hCA, EC 4.2.1.1) isoforms IX and XII. Similar to coumarins, they do not inhibit or poorly inhibit cytosolic human (h) isoforms hCA I and II, but act as nanomolar inhibitors of the trans-membrane, tumor associated isoforms hCA IX and XII.

Multicomponent Cascade Reaction by Metal-Free Aerobic Oxidation for Synthesis of Highly Functionalized 2-Amino-4-coumarinyl-5-arylpyrroles

A novel approach has been constructed for the synthesis of two types of 2-amino-4-coumarinyl-5-arylpyrroles (ACAPs, 5 and 6) through a cascade reaction and a metal-free catalyzed aerobic oxidation reaction of arylglyoxal monohydrates 1, 1,1-enediamines (EDAMs) 2 and 3, and 4-hydroxy-2H-chromen-2-ones 4 via multicomponent reactions to produce the target compounds with good to excellent yields. Specifically, hydroxyl-substituted 2-amino-4-coumarinyl-5-arylpyrroles, that is, 2-amino-4-coumarinyl-5-aryl-6-hydroxylpyrroles (ACAHPs) 6, were obtained by metal-free aerobic oxidation in 1,4-dioxane at simple reflux for approximately 10 h. As a result, ACAHPs 6 have been produced without metal catalysts or traditional oxidizing agents. This method represents a route to obtain the novel ACAPs in an environmentally friendly, concise, rapid, and practical manner with potential biological activity of the product.

Synthesis of coumarin-sulfonamide derivatives and determination of their cytotoxicity, carbonic anhydrase inhibitory and molecular docking studies

Carbonic anhydrases isoforms CA IX, and XII are known to be highly expressed in various human tissues and malignancies. CA IX is a prominent target for especially colorectal cancers, because it is overexpressed in colorectal cancer and this overexpression leads poor prognosis. Inhibition of CA IX activity by small molecule CA inhibitors like sulfonamides, sulfonamide derivative or coumarins leads to inhibition of tumorigenesis. Novel twenty-seven compounds in three series (sulfonamide-based imines (6a-6i), coumarin-based aldehydes (7a-7i), and coumarin-sulfonamide-based target molecules (8a-8i)) were synthesized and characterized by means of IR, NMR, and mass spectra. All compounds were tested for their ability to inhibit CA I, CA II, CA IX, and CA XII isoforms. 4-((((2-((1-(3-((2-oxo-2H-chromen-7-yl)oxy)propyl)-1H-1,2,3-triazol-4-yl)methoxy)naphthalen-1-yl)-methylene)amino)methyl)benzenesulfonamide (8i) exhibited the highest hCA IX inhibition with the Ki of 45.5 nM. In addition, 8i was found to be potent in inhibiting cancer cell proliferation as selective (IC₅₀ = 17.01 ± 1.35 μM for HT-29, IC₅₀ = 118.73 ± 1.19 μM for HEK293T). This novel compound inhibited the CA IX and CA XII protein expression in HT-29 cells. These findings indicate that 8i can inhibit cellular proliferation in human colon cancer cells by specifically targeting the CA IX and CA XII expression.

Synthesis, biological activity and multiscale molecular modeling studies of bis-coumarins as selective carbonic anhydrase IX and XII inhibitors with effective cytotoxicity against hepatocellular carcinoma

A series of novel bis-coumarin derivatives containing triazole moiety as a linker between the alkyl chains was synthesized and their inhibitory activity against the human carbonic anhydrase (hCA) isoforms I, II, IX and XII were evaluated. In addition, cytotoxic effects of the synthesized compounds on renal adenocarcinoma (769P), hepatocellular carcinoma (HepG2) and breast adeno carcinoma (MDA-MB-231) cell lines were examined. While the hCA I and II isoforms were inhibited in the micromolar range, the tumor-associated isoform hCA IX and XII were inhibited in the high nanomolar range. 4-methyl-7-((1-(12-((2-oxo-2H-chromen-7-yl)oxy)dodecyl)-1H-1,2,3-triazol-4-yl)methoxy)-2H-chromen-2-one (5p) showed the strongest inhibitory activity against hCA IX with the K_i of 144.6 nM and 4-methyl-7-((1-(10-((2-oxo-2H-chromen-7-yl)oxy)decyl)-1H-1,2,3-triazol-4-yl)methoxy)-2H-chromen-2-one (5n) exhibited the highest hCA XII inhibition with the K_i of 71.5 nM. In order to better understand the inhibitory profiles of studied molecules, multiscale molecular modelling approaches were applied. Low energy docking poses of studied molecules at the binding sites of targets have been predicted. In addition, electrostatic potential surfaces (ESP) for binding sites were also generated to understand interactions between proteins and active ligands.

4-Hydroxy-3-nitro-5-ureido-benzenesulfonamides Selectively Target the Tumor-Associated Carbonic Anhydrase Isoforms IX and XII Showing Hypoxia-Enhanced Antiproliferative Profiles

Human carbonic anhydrases (CA, EC, 4.2.1.1) IX and XII are overexpressed in cancer cells as adaptive response to hypoxia and acidic conditions characteristic of many tumors. In addition, hypoxia facilitates the activity of specific oxido-reductases that may be exploited to selectively activate bioreductive prodrugs. Here, new selective CA IX/XII inhibitors, as analogues of the antitumor phase II drug SLC-0111 are described, namely ureido-substituted benzenesulfonamides appended with a nitro-aromatic moiety to yield an antiproliferative action increased by hypoxia. These compounds were screened for the inhibition of the ubiquitous hCA I/II and the target hCA IX/XII. Six X-ray crystallographies with CA II and IX/mimic allowed for the rationalization of the compounds inhibitory activity. The effects of some such compounds on the viability of HT-29, MDA-MB-231, and PC-3 human cancer cell lines in both normoxic and hypoxic conditions were examined, providing the initiation toward the development of hypoxia-activated antitumor CAIs.

Novel coumarin-6-sulfonamides as apoptotic anti-proliferative agents: synthesis, in vitro biological evaluation, and QSAR studies

Herein, we report the synthesis of different novel sets of coumarin-6-sulfonamide derivatives bearing different functionalities (4a, b, 8a-d, 11a-d, 13a, b, and 15a-c), and in vitro evaluation of their growth inhibitory activity towards the proliferation of three cancer cell lines; HepG2 (hepatocellular carcinoma), MCF-7 (breast cancer), and Caco-2 (colon cancer). HepG2 cells were the most sensitive cells to the influence of the target coumarins. Compounds 13a and 15a emerged as the most active members against HepG2 cells (IC50 = 3.48 ± 0.28 and 5.03 ± 0.39 µM, respectively). Compounds 13a and 15a were able to induce apoptosis in HepG2 cells, as assured by the upregulation of the Bax and downregulation of the Bcl-2, besides boosting caspase-3 levels. Besides, compound 13a induced a significant increase in the percentage of cells at Pre-G1 by 6.4-folds, with concurrent significant arrest in the G2-M phase by 5.4-folds compared to control. Also, 13a displayed significant increase in the percentage of annexin V-FITC positive apoptotic cells from 1.75-13.76%. Moreover, QSAR models were established to explore the structural requirements controlling the anti-proliferative activities.

Heterocoumarins Are Selective Carbonic Anhydrase IX and XII Inhibitors with Cytotoxic Effects against Cancer Cells Lines

We have synthesized a new series of coumarin-based compounds demonstrating high selectivity and potent effects with low nanomolar affinity against the tumor associated carbonic anhydrase (CA, EC 4.2.1.1) isoforms hCA IX and XII. A number of these compounds were evaluated ex vivo against human prostate (PC3) and breast (MDA-MB-231) cancer cell lines. Compounds 4b and 15 revealed effective cytotoxic effects after 48 h of incubation in both normoxic and hypoxic conditions with PC3 cancer cell line. However, compound 3 showed selective cytotoxic effects against MDA-MB-231 in hypoxic condition. These results may be of particular importance for the choice of future drug candidates targeting hypoxic tumors and metastases, considering the fact that a selective carbonic anhydrase CA IX inhibitor (SLC-0111) is presently in phase II clinical trials.