Targeting hypoxic tumor cell viability with carbohydrate-based carbonic anhydrase IX and XII inhibitors

Halo-1,2,3-triazoles: Valuable Compounds to Access Biologically Relevant Molecules

1,2,3-triazole is an important building block in organic chemistry. It is now well known as a bioisostere for various functions, such as the amide or the ester bond, positioning it as a key pharmacophore in medicinal chemistry and it has found applications in various fields including life sciences. Attention was first focused on the synthesis of 1,4-disubstituted 1,2,3-triazole molecules however 1,4,5-trisubstituted 1,2,3-triazoles have now emerged as valuable molecules due to the possibility to expand the structural modularity. In the last decade, methods mainly derived from the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction have been developed to access halo-triazole compounds and have been applied to nucleosides, carbohydrates, peptides and proteins. In addition, late-stage modification of halo-triazole derivatives by metal-mediated cross-coupling or halo-exchange reactions offer the possibility to access highly functionalized molecules that can be used as tools for chemical biology. This review summarizes the synthesis, the functionalization, and the applications of 1,4,5-trisubstituted halo-1,2,3-triazoles in biologically relevant molecules.

Click Pt(IV)-Carbohydrates Pro-Drugs for Treatment of Osteosarcoma

The selectivity vs. cancer cells has always been a major challenge for chemotherapeutic agents and in particular for cisplatin, one of the most important anticancer drugs for the treatment of several types of tumors. One strategy to overtake this challenge is to modify the coordination sphere of the metallic center with specific vectors whose receptors are overexpressed in the tumoral cell membrane, such as monosaccharides. In this paper, we report the synthesis of four novel glyco-modified Pt(IV) pro-drugs, based on cisplatin scaffold, and their biological activity against osteosarcoma (OS), a malignant tumor affecting in particular adolescents and young adults. The sugar moiety and the Pt scaffold are linked exploiting the Copper Azide Alkyne Cycloaddition (CUAAC) reaction, which has become the flagship of click chemistry due to its versatility and mild conditions. Cytotoxicity and drug uptake on three different OS cell lines as well as CSCs (Cancer Stem Cell) are described.

Discovery of novel aminosaccharide-based sulfonamide derivatives as potential carbonic anhydrase II inhibitors

In this paper, a new class of novel sulfonamides incorporating aminosaccharide tails were designed and synthesized based on the sugar-tail approach. Then, all the novel compounds were evaluated for their inhibitory activities against three carbonic anhydrase (CA, EC 4.2.1.1) isoenzymes (hCA I, hCA II and hCA IX). Interestingly, effective inhibition of these three CA isoforms were observed, especially the glaucoma associated isoform hCA II. It is worth noting that these glycoconjugated sulfonamide derivatives also showed better CA inhibitory effects compared to the initial segment carzenide. Among them, compound 8d was the most effective inhibitor with IC₅₀ of 60 nM against hCA II. Subsequent physicochemical properties studies showed that all compounds have good water solubility and neutral pH values in solutions. And these important physicochemical properties make target compounds acquire obvious advantages in the preparation of topical and nonirritating antiglaucoma drugs. Moreover, the target compounds showed lower corneal cytotoxicity than acetazolamide (AAZ) and good metabolic stability in vitro. In addition, molecular docking studies confirmed the interactions between aminosaccharide fragment and hydrophilic subpocket of hCA II active site were crucial for the enhanced CA inhibitory activity. Taken together, these results suggested 8d would be a promising lead compound for the development of topical antiglaucoma CAIs.

Copper-catalyzed in situ oxidative-coupling for one-pot synthesis of 5-aryl-1,4-disubstituted 1,2,3-triazoles under mild conditions

A new reaction system with CuCl as catalyst, TEA as base and O2/chloramine-T as oxidant was developed for one-pot in situ oxidative-coupling to synthesize 5-aryl-1,4-disubstituted 1,2,3-triazoles in this paper. A variety of 5-arylated-1,2,3-triazole compounds could be efficiently prepared directly from the readily accessible organic azides, terminal alkynes and arylboronic acids. Advantages of the method include use of low-cost catalyst, clean oxidant, less-toxic additive, and low reaction temperature. Importantly, due to avoiding harsh strong basic reagents and high temperatures, the presented method can offer mild conditions for multi-component synthesis of 5-aryl-1,2,3-triazoles from the designed structurally complicated alkynyl or azide donors bearing natural product motifs and sensitive functional groups.

Novel triazole-sulfonamide bearing pyrimidine moieties with carbonic anhydrase inhibitory action: Design, synthesis, computational and enzyme inhibition studies

A series of new triazole-sulfonamide bearing pyrimidine derivatives were designed and synthesized via click chemistry. All new compounds (SH-1 to SH-28) were validated by ¹HNMR, ¹³CNMR, HRMS, and SH-3 was further structurally validated by X-Ray single diffraction study. These compounds (SH-1 to SH-28) were tested as inhibitors of human carbonic anhydrase (hCA) isoforms, such as hCA I, II, IX and XII, using a stopped flow CO₂ hydrase assay. Most of the compounds exhibited significant inhibitory activity against hCA II and weak inhibitory activity against hCA I. The target compounds also displayed moderate to excellent inhibitory activity against tumor-related hCAs IX and XII. Some compounds, e.g., SH-20 (K_i = 9.4 nM), SH-26 (K_i = 1.8 nM) and SH-28 (K_i = 0.82 nM) exhibited excellent inhibitory activity and selectivity profile against hCAs XII over IX. SH-23 displayed promising inhibitory activity and selectivity profile against both tumor-related hCAs IX (K_i = 2.9 nM) as well as XII (K_i = 0.82 nM) over hCA I and II. To understand the molecular interactions, molecular docking study of compounds SH-20, SH-23, SH-26 and SH-28 with hCA XII and SH-23 also with hCA IX were performed. The computational study evidenced favorable interaction between the inhibitors and active residues of both proteins. Some of these derivatives are promising leads for the development of selective, anticancer agents based on CA inhibitors.

Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology.

The Carbonic Anhydrase Inhibitor E7070 Sensitizes Glioblastoma Cells to Radio- and Chemotherapy and Reduces Tumor Growth

Glioblastomas (GBMs), the most common and lethal primary brain tumor, show inherent infiltrative nature and high molecular heterogeneity that make complete surgical resection unfeasible and unresponsive to conventional adjuvant therapy. Due to their fast growth rate even under hypoxic and acidic conditions, GBM cells can conserve the intracellular pH at physiological range by overexpressing membrane-bound carbonic anhydrases (CAs). The synthetic sulfonamide E7070 is a potent inhibitor of CAs that harbors putative anticancer properties; however, this drug has still not been tested in GBMs. The present study aimed to evaluate the effects of E7070 on CA9 and CA12 enzymes in GBM cells as well as in the tumor cell growth, migration, invasion, and resistance to radiotherapy and chemotherapy. We found that E7070 treatment significantly reduced tumor cell growth and increased radio- and chemotherapy efficacy against GBM cells under hypoxia. Our data suggests that E7070 has therapeutic potential as a radio-chemo-sensitizing in drug-resistant GBMs, representing an attractive strategy to improve the adjuvant therapy. We showed that CA9 and CA12 represent potentially valuable therapeutic targets that should be further investigated as useful diagnostic and prognostic biomarkers for GBM tailored therapy.

Carbonic Anhydrase IX Promotes Human Cervical Cancer Cell Motility by Regulating PFKFB4 Expression

Simple Summary

Carbonic anhydrase IX (CAIX) is a hypoxia-induced protein that is highly expressed in numerous human cancers. However, the molecular mechanisms involved in CAIX and human cervical cancer metastasis remain poorly understood. Our study found that CAIX overexpression increases PFKFB4 expression and EMT, promoting cervical cancer cell migration. CAIX could contribute to cervical cancer cell metastasis and its inhibition could be a cervical cancer treatment strategy.

Abstract

Carbonic anhydrase IX (CAIX) is a hypoxia-induced protein that is highly expressed in numerous human cancers. However, the molecular mechanisms involved in CAIX and human cervical cancer metastasis remain poorly understood. In this study, CAIX overexpression in SiHa cells increased cell migration and epithelial-to-mesenchymal transition (EMT). Silencing CAIX in the Caski cell line decreased the motility of cells and EMT. Furthermore, the RNA-sequencing analysis identified a target gene, bifunctional 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB4), which is influenced by CAIX overexpression and knockdown. A positive correlation was found between CAIX expression and PFKFB4 levels in the cervical cancer of the TCGA database. Mechanistically, CAIX overexpression activated the phosphorylation of extracellular signal-regulated kinases (ERKs) to induce EMT and promote cell migration. In clinical results, human cervical cancer patients with CAIX^high/PFKFB4^high expression in the late stage had higher rates of lymph node metastasis and the shortest survival time. Our study found that CAIX overexpression increases PFKFB4 expression and EMT, promoting cervical cancer cell migration. CAIX could contribute to cervical cancer cell metastasis and its inhibition could be a cervical cancer treatment strategy.

PEG Linker Length Strongly Affects Tumor Cell Killing by PEGylated Carbonic Anhydrase Inhibitors in Hypoxic Carcinomas Expressing Carbonic Anhydrase IX

Hypoxic tumors overexpress membrane-bound isozymes of carbonic anhydrase (CA) CA IX and CA XII, which play key roles in tumor pH homeostasis under hypoxia. Selective inhibition of these CA isozymes has the potential to generate pH imbalances that can lead to tumor cell death. Since these isozymes are dimeric, we designed a series of bifunctional PEGylated CA inhibitors (CAIs) through the attachment of our preoptimized CAI warhead 1,3,4-thiadiazole-2-sulfonamide to polyethylene glycol (PEG) backbones with lengths ranging from 1 KDa to 20 KDa via a succinyl linker. A detailed structure−thermal properties and structure–biological activity relationship study was conducted via differential scanning calorimetry (DSC) and via viability testing in 2D and 3D (tumor spheroids) cancer cell models, either CA IX positive (HT-29 colon cancer, MDA-MB 231 breast cancer, and SKOV-3 ovarian cancer) or CA IX negative (NCI-H23 lung cancer). We identified PEGylated CAIs DTP1K 28, DTP2K 23, and DTP3.4K 29, bearing short and medium PEG backbones, as the most efficient conjugates under both normoxic and hypoxic conditions, and in the tumor spheroid models. PEGylated CAIs did not affect the cell viability of CA IX-negative NCI-H23 tumor spheroids, thus confirming a CA IX-mediated cell killing for these potential anticancer agents.

Investigation of the Reactivity of 1-Azido-3-iodobicyclo[1.1.1]pentane under "Click" Reaction Conditions

The bicyclo[1.1.1]pentane (BCP) unit is under scrutiny as a bioisostere in drug molecules. We employed methodologies for the synthesis of different BCP triazole building blocks from one precursor, 1-azido-3-iodobicyclo[1.1.1]pentane, by "click" reactions and integrated cycloaddition-Sonogashira coupling reactions. Thereby, we accessed 1,4-disubstituted triazoles, 5-iodo-1,4,5-trisubstituted triazoles, and 5-alkynylated 1,4,5-trisubstituted triazoles. This gives entry to the synthesis of multiply substituted BCP triazoles on either a modular or a one-pot basis. These methodologies were further utilized for appending porphyrin moieties onto the BCP core.

Experimental Carbonic Anhydrase Inhibitors for the Treatment of Hypoxic Tumors

Carbonic anhydrase (CA, EC 4.2.1.1) isoforms IX and XII are overexpressed in many hypoxic tumors as a consequence of the hypoxia inducible factor (HIF) activation cascade, being present in limited amounts in normal tissues. These enzymes together with many others are involved in the pH regulation and metabolism of hypoxic cancer cells, and were validated as antitumor targets recently. A multitude of targeting strategies against these enzymes have been proposed and are reviewed in this article. The small molecule inhibitors, small molecule drug conjugates (SMDCs), antibody-drug conjugates (ADACs) or cytokine-drug conjugates but not the monoclonal antibodies against CA IX/XII will be discussed. Relevant synthetic chemistry efforts, coupled with a multitude of preclinical studies, demonstrated that CA IX/XII inhibition leads to the inhibition of growth of primary tumors and metastases and depletes cancer stem cell populations, all factors highly relevant in clinical settings. One small molecule inhibitor, sulfonamide SLC-0111, is the most advanced candidate, having completed Phase I and being now in Phase Ib/II clinical trials for the treatment of advanced hypoxic solid tumors.

Inhibitory Monoclonal Antibodies and Their Recombinant Derivatives Targeting Surface-Exposed Carbonic Anhydrase XII on Cancer Cells

Monoclonal and recombinant antibodies are widely used for the diagnostics and therapy of cancer. They are generated to interact with cell surface proteins which are usually involved in the development and progression of cancer. Carbonic anhydrase XII (CA XII) contributes to the survival of tumors under hypoxic conditions thus is considered a candidate target for antibody-based therapy. In this study, we have generated a novel collection of monoclonal antibodies (MAbs) against the recombinant extracellular domain of CA XII produced in HEK-293 cells. Eighteen out of 24 MAbs were reactive with cellular CA XII on the surface of live kidney and lung cancer cells as determined by flow cytometry. One MAb 14D6 also inhibited the enzymatic activity of recombinant CA XII as measured by the stopped-flow assay. MAb 14D6 showed the migrastatic effect on human lung carcinoma A549 and renal carcinoma A498 cell lines in a ‘wound healing’ assay. It did not reduce the growth of multicellular lung and renal cancer spheroids but reduced the cell viability by the ATP Bioluminescence assay. Epitope mapping revealed the surface-exposed amino acid sequence (35-FGPDGENS-42) close to the catalytic center of CA XII recognized by the MAb 14D6. The variable regions of the heavy and light chains of MAb 14D6 were sequenced and their complementarity-determining regions were defined. The obtained variable sequences were used to generate recombinant antibodies in two formats: single-chain fragment variable (scFv) expressed in E. coli and scFv fused to human IgG1 Fc fragment (scFv-Fc) expressed in Chinese Hamster Ovary (CHO) cells. Both recombinant antibodies maintained the same specificity for CA XII as the parental MAb 14D6. The novel antibodies may represent promising tools for CA XII-related cancer research and immunotherapy.

Structural Basis of Nanomolar Inhibition of Tumor-Associated Carbonic Anhydrase IX: X-Ray Crystallographic and Inhibition Study of Lipophilic Inhibitors with Acetazolamide Backbone

This study provides a structure-activity relationship study of a series of lipophilic carbonic anhydrase (CA) inhibitors with an acetazolamide backbone. The inhibitors were tested against the tumor-expressed CA isozyme IX (CA IX), and the cytosolic CA I, CA II, and membrane-bound CA IV. The study identified several low nanomolar potent inhibitors against CA IX, with lipophilicities spanning two log units. Very potent pan-inhibitors with nanomolar potency against CA IX and sub-nanomolar potency against CA II and CA IV, and with potency against CA I one order of magnitude better than the parent acetazolamide 1 were also identified in this study, together with compounds that displayed selectivity against membrane-bound CA IV. A comprehensive X-ray crystallographic study (12 crystal structures), involving both CA II and a soluble CA IX mimetic (CA IX-mimic), revealed the structural basis of this particular inhibition profile and laid the foundation for further developments toward more potent and selective inhibitors for the tumor-expressed CA IX.

Chemical characteristic and bioactivity of hemicellulose-based polysaccharides isolated from Salvia miltiorrhiza

Salvia miltiorrhiza roots (SMRs), the main component of cell wall from the residual waste extraction, differ depending on the forming ways of monosaccharides. The extraction from 8% sodium hydroxide solution (H-8) was characterized by gel permeation chromatography (GPC), monosaccharide composition, Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) spectroscopy. The structure model of hemicellulose-based polysaccharides (HBPs) was derived by combining one-dimensional and two-dimensional NMR. Monosaccharides difference and correlation were performed by partial least square analysis (PLS). Seven H-8s exhibited optimal inhibitory activities, which varied based on different sources of Danshen. The backbone structure indicated that 4-β-D-Xylp served as the main chain connected by 3-α-L-Araf or 5-α-L-Araf-1, 4-β-D-Galp, and β-D-Glcp branch, as well as α-L-Rhap, α-D-GalpA and α-D-GlcpA fragments. The variation of HBPs in terms of the structure and bioactivity of SMRs correlated with different cultivation sites can be a new approach to optimize and utilize the medical materials by chemical and biological aspects of natural macromolecules.

An overview of carbohydrate-based carbonic anhydrase inhibitors

Carbonic anhydrases (CAs) are metalloenzymes responsible for the reversible hydration of carbon dioxide to bicarbonate, a fundamental reaction involved in various physiological and pathological processes. In the last decades, CAs have been considered as important drug targets for different pathologies such as glaucoma, epilepsy and cancer. The design of potent and selective inhibitors has been an outstanding goal leading to the discovery of new drugs. Among the different strategies developed to date, the design of carbohydrate-based CA inhibitors (CAIs) has emerged as a versatile tool in order to selectively target CAs. The insertion of a glycosyl moiety as a hydrophilic tail in sulfonamide, sulfenamide, sulfamate or coumarin scaffolds allowed the discovery of many different series of sugar-based CAIs, with relevant inhibitory results. This review will focus on carbohydrate-based CAIs developed so far, classifying them in glycosidic and glycoconjugated inhibitors based on the conjugation chemistry adopted.

Inhibition of Melanoma Cell Migration and Invasion Targeting the Hypoxic Tumor Associated CAXII

BACKGROUND

Intratumoral hypoxia contributes to cancer progression and poor prognosis. Carbonic anhydrases IX (CAIX) and XII (CAXII) play pivotal roles in tumor cell adaptation and survival, as aberrant Hedgehog (Hh) pathway does. In malignant melanoma both features have been investigated for years, but they have not been correlated before and/or identified as a potential pharmacological target. Here, for the first time, we demonstrated that malignant melanoma cell motility was impaired by targeting CAXII via either CAs inhibitors or through the inhibition of the Hh pathway.

METHODS

We tested cell motility in three melanoma cell lines (WM-35, SK-MEL28, and A375), with different invasiveness capabilities. To this end we performed a scratch assay in the presence of the smoothened (SMO) antagonist cyclopamine (cyclo) or CAs inhibitors under normoxia or hypoxia. Then, we analyzed the invasiveness potential in the cell lines which were more affected by cyclo and CAs inhibitors (SK-MEL28 and A375). Western blot was employed to assess the expression of the hypoxia inducible factor 1α, CAXII, and FAK phosphorylation. Immunofluorescence staining was performed to verify the blockade of CAXII expression.

RESULTS

Hh inhibition reduced melanoma cell migration and CAXII expression under both normoxic and hypoxic conditions. Interestingly, basal CAXII expression was higher in the two more aggressive melanoma cell lines. Finally, a direct CAXII blockade impaired melanoma cell migration and invasion under hypoxia. This was associated with a decrease of FAK phosphorylation and metalloprotease activities.

CONCLUSIONS

CAXII may be used as a target for melanoma treatment not only through its direct inhibition, but also through Hh blockade.

Pyridinium derivatives of 3-aminobenzenesulfonamide are nanomolar-potent inhibitors of tumor-expressed carbonic anhydrase isozymes CA IX and CA XII

Building on the conclusions of previous inhibition studies with pyridinium-benzenesulfonamides from our team and on the X-ray crystal structure of the lead compound identified, a series of 24 pyridinium derivatives of 3-aminobenzenesulfonamide was synthesized and investigated for carbonic anhydrase inhibition. The new pyridinium-sulfonamides were evaluated as inhibitors of four human carbonic anhydrase (CA, EC 4.2.1.1) isoforms, namely CA I, CA II (cytosolic), CA IX and XII (transmembrane, tumor-associated forms). Excellent inhibitory activity in the nanomolar range was observed against CA IX with most of these sulfonamides, and against CA XII (nanomolar/sub-nanomolar) with some of the new compounds. These sulfonamides were generally potent inhibitors of CA II and CA I too. Docking studies revealed a preference of these compounds to bind the P1 hydrophobic site of CAs, supporting the observed inhibition profile. The salt-like nature of these positively charged sulfonamides can further focus the inhibitory ability on membrane-bound CA IX and CA XII and could efficiently decrease the viability of three human carcinomas under hypoxic conditions where these isozymes are over-expressed, thus recommending the new compounds as potential diagnostic tools or therapeutic agents.

In Silico Identification and Biological Evaluation of Antioxidant Food Components Endowed with IX and XII hCA Inhibition

The tumor-associated isoenzymes hCA IX and hCA XII catalyze the hydration of carbon dioxide to bicarbonate and protons. These isoforms are highly overexpressed in many types of cancer, where they contribute to the acidification of the tumor environment, promoting tumor cell invasion and metastasis. In this work, in order to identify novel dual hCA IX and XII inhibitors, virtual screening techniques and biological assays were combined. A structure-based virtual screening towards hCA IX and XII was performed using a database of approximately 26,000 natural compounds. The best shared hits were submitted to a thermodynamic analysis and three promising best hits were identified and evaluated in terms of their hCA IX and XII inhibitor activity. In vitro biological assays were in line with the theoretical studies and revealed that syringin, lithospermic acid, and (-)-dehydrodiconiferyl alcohol behave as good hCA IX and hCA XII dual inhibitors.

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.

A Novel Series of N-aryltriazole and N-acridinyltriazole Hybrids as Potential Anticancer Agents

BACKGROUND

Triazoles are a class of aza-heterocycles with broad spectrum of biological importance. The synthetic tunability of the triazole moiety allows for the development of new pharmacophores with applications as drugs to contend with the burden of cancer.

OBJECTIVE

In this study, we aimed to develop a series of N-aryltriazole and N-acridinyltriazole molecular hybrids and evaluate their potential as anticancer agents.

METHODS

The triazole derivatives (1-10) were synthesized via a tandem nucleophilic substitution of aryl chlorides with sodium azide followed by 1,3-dipolar cycloaddition of the resulting organic azides with terminal/internal alkynes. From terminal alkynes, the well established copper(I) catalyzed azide-alkynes 1,3- dipolar cycloaddition, a premier example of click chemistry, was employed to access the 1,4-regioisomers of N-benzyl-1H-1,2,3-triazoles and N-acridynyl-1H-1,2,3-triazoles. All the compounds thus synthesized were characterized by 1D and 2D NMR spectroscopy and high resolution mass spectrometry.

RESULTS

Thermally controlled 1,3-dipolar cycloaddition was used to deliver N-aryl-1H-1,2,3-triazoles with 1,4,5-substitution on the triazole framework. The unprecedented high regioselectivity promoted by the sterically-strained silylated 1,4,5-trisubstituted moiety 4a offers a useful synthetic precursor with the silyl group being a synthetic handle for further structural elaboration to the desired 1,(4),5-di(tri)substituted 1,2,3- triazoles. Notably, anticancer evaluation revealed good cytotoxic activities of the novel acridinyltriazole hybrids (6-10) at micromolar concentrations in the range of 12.5 µM-100 µM against cervical cancer HeLa, kidney cancer HEK293, lung cancer A549 and leukemic MT4 cancer cell lines (p < 0.05).

CONCLUSION

A series of novel triazole-based acridine hybrids have been developed as potential leads for the development of multifaceted anticancer agents.

A Route to Triazole-Fused Sultams via Metal-Free Base-Mediated Cyclization of Sulfonamide-Tethered 5-Iodotriazoles

An efficient direct approach to triazole-fused sultams has been developed. The key step of the proposed strategy is base-mediated cyclization of sulfonamide-tethered 5-iodo-1,2,3-triazoles which are readily available via an improved protocol for Cu-catalyzed 1,3-dipolar cycloaddition. The annulation of the sultam fragment to the triazole ring proceeds smoothly under transition-metal-free conditions in the presence of Cs₂CO₃ in dioxane at 100 °C and affords fused heterocycles in high yields up to 99%. The favorability of an S_NAr-like mechanism for the cyclization was supported by DFT calculations. The applicability of the developed procedure to modification of natural compounds was demonstrated by preparation of a deoxycholic acid derivative.

Carbohydrates: Potential Sweet Tools Against Cancer

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Cancer, one of the most devastating degenerative diseases nowadays, is one of the main targets in Medicinal Chemistry and Pharmaceutical industry. Due to the significant increase in the incidence of cancer within world population, together with the complexity of such disease, featured with a multifactorial nature, access to new drugs targeting different biological targets connected to cancer is highly necessary.

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Among the vast arsenal of compounds exhibiting antitumor activities, this review will cover the use of carbohydrate derivatives as privileged scaffolds. Their hydrophilic nature, together with their capacity of establishing selective interactions with biological receptors located on cell surface, involved in cell-to-cell communication processes, has allowed the development of an ample number of new templates useful in cancer treatment.

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Their intrinsic water solubility has allowed their use as of pro-drug carriers for accessing more efficiently the pharmaceutical targets. The preparation of glycoconjugates in which the carbohydrate is tethered to a pharmacophore has also allowed a better permeation of the drug through cellular membranes, in which selective interactions with the carbohydrate motifs are involved. In this context, the design of multivalent structures (e.g. gold nanoparticles) has been demonstrated to enhance crucial interactions with biological receptors like lectins, glycoproteins that can be involved in cancer progression.

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Moreover, the modification of the carbohydrate structural motif, by incorporation of metal complexes, or by replacing their endocyclic oxygen, or carbon atoms with heteroatoms has led to new antitumor agents.

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Such diversity of sugar-based templates with relevant antitumor activity will be covered in this review.

1-Iodobuta-1,3-diynes in Copper-Catalyzed Azide-Alkyne Cycloaddition: A One-Step Route to 4-Ethynyl-5-iodo-1,2,3-triazoles

Cu-catalyzed 1,3-dipolar cycloaddition of iododiacetylenes with organic azides using iodotris(triphenylphosphine)copper(I) as a catalyst was found to be an efficient one-step synthetic route to 5-iodo-4-ethynyltriazoles. The reaction is tolerant to various functional groups in both butadiyne and azide moieties. The synthetic application of 5-iodo-4-ethynyl triazoles obtained was also evaluated: the Sonogashira coupling with alkynes resulted in unsymmetrically substituted triazole-fused enediyne systems, while the Suzuki reaction yielded the corresponding 5-aryl-4-ethynyl triazoles.

Syntheses and anti-cancer activity of CO-releasing molecules with targeting galactose receptors

CO-releasing molecules (CORMs) containing cobalt have many bioactivities, but most of them do not dissolve in water and have no selectivity to tissue and organs. On the basis of the specific recognition of galactose or sialic acid by a receptor, a series of CORMs based on carbohydrates were synthesized and evaluated. The test results show that all the complexes displayed anticancer activity. Among them, the effects of the complexes of galactose (1), GalNAc (8) and sialic acid (10) were very distinct. Complex 1 displayed higher activity against HeLa, HePG2, MCF-7 and HT-29 cell proliferation than cis-platin (DDP), and its selectivity was far much better than DDP compared with normal cell W138. Furthermore, the uptakes of complexes 1, 8 and 10 by HePG2, HT-29, A549 and RAW264.7 cell lines were studied. The uptake ratio of each cell line for complex 1 was different, and the order of uptake ratio in the four cell lines was HePG2 > HT-29 > RAW264.7 > A549. The HePG2 cells absorbed complex 1 beyond 60% after incubation for 8 h, while A549 absorbed only 27.8%. For complex 8, the uptake trend was similar to that of complex 1 with it being absorbed by all the four cancer cells, but the uptake rate was lower. However, differently, complex 10 was absorbed heavily by macrophage RAW264.7, followed by HePG2; after 8 h incubation, the uptake ratio of RAW264.7 was over 50%. In addition, the mechanism of action was explored, and the results showed that the complexes inhibited cell cycle arrest at the G2/M phase; complex 1 up-regulated the expression levels of caspase-3 and Bax, and down-regulated the Bcl-2 expression, giving rise to HePG2 cell apoptosis.

Medium Rings Bearing Bitriazolyls: Easily Accessible Structures with Superior Performance as Cu Catalyst Ligands

Benefiting from their unique properties, the development of structurally novel and easily accessible medium rings is of significant interest in the pharmaceutical industry and academic research. However, synthetic access to medium-ring scaffolds is very difficult due to their rigid skeleton and large-angle strains. In this paper, a new class of medium rings bearing bitriazolyls (MRBTs) was designed, synthesized, identified as a promising new skeleton ligand for the Cu(I)-catalyzed click reaction, and used in site-special modification of protein. One of the MRBTs, 3aa, exhibited a turnover number (TON) as high as 55 000 and dramatic accelerating effects ( k_obs = 1.95 M^-1 s^-1) and ranked among the most efficient ligands for copper-catalyzed alkyne and azide cycloaddition. Unlike the difficult access to other known medium rings, these 7-12-membered MRBTs can be prepared in straightforward, one-step manner from structurally diverse linear terminal diynes and azides. The unique accessibility and intriguing properties therefore imply their broad application perspectives.

Carbonic Anhydrase XII Inhibitors Overcome P-Glycoprotein-Mediated Resistance to Temozolomide in Glioblastoma

The role of carbonic anhydrase XII (CAXII) in the chemoresistance of glioblastoma is unexplored. We found CAXII and P-glycoprotein (Pgp) coexpressed in neurospheres derived from 3 of 3 patients with different genetic backgrounds and low response to temozolomide (time to recurrence: 6-9 months). CAXII was necessary for the Pgp efflux of temozolomide and second-line chemotherapeutic drugs, determining chemoresistance in neurospheres. Psammaplin C, a potent inhibitor of CAXII, resensitized primary neurospheres to temozolomide by reducing temozolomide efflux via Pgp. This effect was independent of other known temozolomide resistance factors present in the patients. The overall survival in orthotopic patient-derived xenografts of temozolomide-resistant neurospheres, codosed with Psammaplin C and temozolomide, was significantly increased over temozolomide-treated (P < 0.05) and untreated animals (P < 0.02), without detectable signs of systemic toxicity. We propose that a CAXII inhibitor in combination with temozolomide may provide a new and effective approach to reverse chemoresistance in glioblastoma stem cells. This novel mechanism of action, via the interaction of CAXII and Pgp, ultimately blocks the efflux function of Pgp to improve glioblastoma patient outcomes.

An inhibitory antibody targeting carbonic anhydrase XII abrogates chemoresistance and significantly reduces lung metastases in an orthotopic breast cancer model in vivo

Carbonic anhydrase XII (CAXII) is a membrane-tethered ectoenzyme involved in intracellular pH regulation and overexpressed across various types of human cancer. Because CAXII inhibition shows antitumor activity in vitro, it is thought that the enzyme is mandatory for maximum tumor growth, above all under hypoxic conditions. Recently, it has been shown that CAXII is co-expressed along with the P-glycoprotein (P-GP) on many tumor cells and that both proteins physically interact. Of interest, blocking CAXII activity also decreases P-GP activity in cancer cells both in vitro and in vivo. Previously, we have reported on the development of a monoclonal antibody, termed 6A10, which specifically and efficiently blocks human CAXII activity. Here, we demonstrate that 6A10 also indirectly reduces P-GP activity in CAXII/P-GP double-positive chemoresistant cancer cells, resulting in enhanced chemosensitivity as revealed by enhanced accumulation of anthracyclines and increased cell death in vitro. Even more important, we show that mice carrying human triple-negative breast cancer xenografts co-treated with doxorubicin (DOX) and 6A10 show a significantly reduced number of metastases. Collectively, our data provide evidence that the inhibition of CAXII with 6A10 is an attractive way to reduce chemoresistance of cancer cells and to interfere with the metastatic process in a clinical setting.

Inhibition of carbonic anhydrase IX targets primary tumors, metastases, and cancer stem cells: Three for the price of one

Human carbonic anhydrase (CA) IX is a tumor-associated protein, since it is scarcely present in normal tissues, but highly overexpressed in a large number of solid tumors, where it actively contributes to survival and metastatic spread of tumor cells. Due to these features, the characterization of its biochemical, structural, and functional features for drug design purposes has been extensively carried out, with consequent development of several highly selective small molecule inhibitors and monoclonal antibodies to be used for different purposes. Aim of this review is to provide a comprehensive state-of-the-art of studies performed on this enzyme, regarding structural, functional, and biomedical aspects, as well as the development of molecules with diagnostic and therapeutic applications for cancer treatment. A brief description of additional pharmacologic applications for CA IX inhibition in other diseases, such as arthritis and ischemia, is also provided.

Inhibition of pH regulation as a therapeutic strategy in hypoxic human breast cancer cells

Hypoxic cancer cells exhibit resistance to many therapies. This study compared the therapeutic effect of targeting the pH regulatory proteins (CAIX, NHE1 and V-ATPase) that permit cancer cells to adapt to hypoxic conditions, using both 2D and 3D culture models. Drugs targeting CAIX, NHE1 and V-ATPase exhibited anti-proliferative effects in MCF-7, MDA-MB-231 and HBL-100 breast cancer cell lines in 2D. Protein and gene expression analysis in 2D showed that CAIX was the most hypoxia-inducible protein of the 3 targets. However, the expression of CAIX differed between the 3 cell lines. This difference in CAIX expression in hypoxia was consistent with a varying activity of FIH-1 between the cell lines. 3D expression analysis demonstrated that both CAIX and NHE1 were up-regulated in the hypoxic areas of multicellular tumor spheroids. However, the induction of CAIX expression in hypoxia was again cell line dependent. 3D invasion assays conducted with spheroids showed that CAIX inhibition significantly reduced the invasion of cells. Finally, the capability of both NHE1 and CAIX inhibitors to combine effectively with irradiation was exhibited in clonogenic assays. Proteomic-mass-spectrometric analysis indicated that CAIX inhibition might be combining with irradiation through stimulating apoptotic cell death. Of the three proteins, CAIX represents the target with the most promise for the treatment of breast cancer.

Thiazole-substituted benzenesulfonamides as inhibitors of 12 human carbonic anhydrases

Four series of para or meta - substituted thiazolylbenzenesulfonamides bearing Cl substituents were designed, synthesized, and evaluated as inhibitors of all 12 catalytically active recombinant human carbonic anhydrase (CA) isoforms. Observed affinities were determined by the fluorescent thermal shift assay and the intrinsic affinities were calculated based on the fractions of binding-ready deprotonated sulfonamide and CA bearing protonated hydroxide bound to the catalytic Zn(II) in the active site. Several compounds exhibited selectivity towards CA IX, an anticancer target. Intrinsic affinities reached 30 pM, while the observed affinities - 70 nM. The structure-intrinsic affinity relationship map of the compounds showed the energetic contributions of the thiazole ring and its substituents.

P-glycoprotein-mediated chemoresistance is reversed by carbonic anhydrase XII inhibitors

Carbonic anhydrase XII (CAXII) is a membrane enzyme that maintains pH homeostasis and sustains optimum P-glycoprotein (Pgp) efflux activity in cancer cells. Here, we investigated a panel of eight CAXII inhibitors (compounds 1–8), for their potential to reverse Pgp mediated tumor cell chemoresistance. Inhibitors (5 nM) were screened in human and murine cancer cells (colon, lung, breast, bone) with different expression levels of CAXII and Pgp. We identified three CAXII inhibitors (compounds 1, 2 and 4) that significantly (≥ 2 fold) increased the intracellular retention of the Pgp-substrate and chemotherapeutic doxorubicin, and restored its cytotoxic activity. The inhibitors lowered intracellular pH to indirectly impair Pgp activity. Ca12-knockout assays confirmed that the chemosensitizing property of the compounds was dependent on active CAXII. Furthermore, in a preclinical model of drug-resistant breast tumors compound 1 (1900 ng/kg) restored the efficacy of doxorubicin to the same extent as the direct Pgp inhibitor tariquidar. The expression of carbonic anhydrase IX had no effect on the intracellular doxorubicin accumulation. Our work provides strong evidence that CAXII inhibitors are effective chemosensitizer agents in CAXII-positive and Pgp-positive cancer cells. The use of CAXII inhibitors may represent a turning point in combinatorial chemotherapeutic schemes to treat multidrug-resistant tumors.

Genetic disruption of the pHi-regulating proteins Na+/H+ exchanger 1 (SLC9A1) and carbonic anhydrase 9 severely reduces growth of colon cancer cells

Hypoxia and extracellular acidosis are pathophysiological hallmarks of aggressive solid tumors. Regulation of intracellular pH (pH_i) is essential for the maintenance of tumor cell metabolism and proliferation in this microenvironment and key proteins involved in pH_i regulation are of interest for therapeutic development. Carbonic anhydrase 9 (CA9) is one of the most robustly regulated proteins by the hypoxia inducible factor (HIF) and contributes to pH_i regulation. Here, we have investigated for the first time, the role of CA9 via complete genomic knockout (ko) and compared its impact on tumor cell physiology with the essential pH_i regulator Na⁺/H⁺ exchanger 1 (NHE1). Initially, we established NHE1-ko LS174 cells with inducible CA9 knockdown. While increased sensitivity to acidosis for cell survival in 2-dimensions was not observed, clonogenic proliferation and 3-dimensional spheroid growth in particular were greatly reduced. To avoid potential confounding variables with use of tetracycline-inducible CA9 knockdown, we established CA9-ko and NHE1/CA9-dko cells. NHE1-ko abolished recovery from NH₄Cl pre-pulse cellular acid loading while both NHE1 and CA9 knockout reduced resting pH_i. NHE1-ko significantly reduced tumor cell proliferation both in normoxia and hypoxia while CA9-ko dramatically reduced growth in hypoxic conditions. Tumor xenografts revealed substantial reductions in tumor growth for both NHE1-ko and CA9-ko. A notable induction of CA12 occurred in NHE1/CA9-dko tumors indicating a potential means to compensate for loss of pH regulating proteins to maintain growth. Overall, these genomic knockout results strengthen the pursuit of targeting tumor cell pH regulation as an effective anti-cancer strategy.

Carbonic Anhydrase IX (CAIX), Cancer, and Radiation Responsiveness

Carbonic anhydrase IX has been under intensive investigation as a therapeutic target in cancer. Studies demonstrate that this enzyme has a key role in pH regulation in cancer cells, allowing these cells to adapt to the adverse conditions of the tumour microenviroment. Novel CAIX inhibitors have shown efficacy in both in vitro and in vivo pre-clinical cancer models, adversely affecting cell viability, tumour formation, migration, invasion, and metastatic growth when used alone. In co-treatments, CAIX inhibitors may enhance the effects of anti-angiogenic drugs or chemotherapy agents. Research suggests that these inhibitors may also increase the response of tumours to radiotherapy. Although many of the anti-tumour effects of CAIX inhibition may be dependent on its role in pH regulation, recent work has shown that CAIX interacts with several of the signalling pathways involved in the cellular response to radiation, suggesting that pH-independent mechanisms may also be an important basis of its role in tumour progression. Here, we discuss these pH-independent interactions in the context of the ability of CAIX to modulate the responsiveness of cancer to radiation.

One-pot three component synthesis of 5-allyl-1,2,3-triazoles using copper(i) acetylides

One-pot three-component reactions using copper(i) acetylide, azide, allyl iodide, and NaOH have been developed. The reactions proceed smoothly at room temperature to afford 5-allyl-1,2,3-triazoles, which can be further transformed into a variety of 1,2,3-triazole-fused bi-/tricyclic scaffolds. This method offers the most efficient, convenient, and practical route towards useful polycyclic scaffolds in moderate to excellent yields.

"Seriously Sweet": Acesulfame K Exhibits Selective Inhibition Using Alternative Binding Modes in Carbonic Anhydrase Isoforms

Human carbonic anhydrase IX (CA IX) is upregulated in neoplastic tissues; as such, it is studied as a drug target for anticancer chemotherapy. Inhibition of CA IX has been shown to be therapeutically favorable in terms of reducing tumor growth. Previously, saccharin, a commonly used artificial sweetener, has been observed to selectively inhibit CA IX over other CA isoforms. In this study, X-ray crystallography showed acesulfame potassium (Ace K) binding directly to the catalytic zinc in CA IX (mimic) and through a bridging water in CA II. This modulation in binding is reflected in the binding constants, with Ace K inhibiting CA IX but not other CA isoforms. Hence, this study establishes the potential of Ace K (an FDA approved food additive) as a lead compound in the design and development of CA IX specific inhibitors.

1,4-Substituted Triazoles as Nonsteroidal Anti-Androgens for Prostate Cancer Treatment

Prostate cancer (PC) is the fifth leading cause of cancer death in men, and the androgen receptor (AR) represents the primary target for PC treatment, even though the disease frequently progresses toward androgen-independent forms. Most of the commercially available nonsteroidal antiandrogens show a common scaffold consisting of two aromatic rings connected by a linear or a cyclic spacer. By taking advantage of a facile, one-pot click chemistry reaction, we report herein the preparation of a small library of novel 1,4-substituted triazoles with AR antagonistic activity. Biological and theoretical evaluation demonstrated that the introduction of the triazole core in the scaffold of nonsteroidal antiandrogens allowed the development of small molecules with improved overall AR-antagonist activity. In fact, compound 14d displayed promising in vitro antitumor activity toward three different prostate cancer cell lines and was able to induce 60% tumor growth inhibition of the CW22Rv1 in vivo xenograft model. These results represent a step toward the development of novel and improved AR antagonists.

Dual-tail approach to discovery of novel carbonic anhydrase IX inhibitors by simultaneously matching the hydrophobic and hydrophilic halves of the active site

Dual-tail approach was employed to design novel Carbonic Anhydrase (CA) IX inhibitors by simultaneously matching the hydrophobic and hydrophilic halves of the active site, which also contains a zinc ion as part of the catalytic center. The classic sulfanilamide moiety was used as the zinc binding group. An amino glucosamine fragment was chosen as the hydrophilic part and a cinnamamide fragment as the hydrophobic part in order to draw favorable interactions with the corresponding halves of the active site. In comparison with sulfanilamide which is largely devoid of the hydrophilic and hydrophobic interactions with the two halves of the active site, the compounds so designed and synthesized in this study showed 1000-fold improvement in binding affinity. Most of the compounds inhibited the CA effectively with IC₅₀ values in the range of 7-152 nM. Compound 14e (IC₅₀: 7 nM) was more effective than the reference drug acetazolamide (IC₅₀: 30 nM). The results proved that the dual-tail approach to simultaneously matching the hydrophobic and hydrophilic halves of the active site by linking hydrophobic and hydrophilic fragments was useful for designing novel CA inhibitors. The effectiveness of those compounds was elucidated by both the experimental data and molecular docking simulations. This work laid a solid foundation for further development of novel CA IX inhibitors for cancer treatment.