Anticancer carbonic anhydrase inhibitors: a patent and literature update 2018-2022

Exploring heterocyclic scaffolds in carbonic anhydrase inhibition: a decade of structural and therapeutic insights

Heterocyclic compounds represent a prominent class of molecules with diverse pharmacological activities. Among their therapeutic applications, they have gained significant attention as carbonic anhydrase (CA) inhibitors, owing to their potential in the treatment of various diseases such as epilepsy, cancer and glaucoma. CA is a widely distributed zinc metalloenzyme that facilitates the reversible interconversion of carbon dioxide and bicarbonate. This reaction is essential for numerous physiological and pathological processes. In humans, CA exists in sixteen different isoforms, labeled hCA-I to hCA-XV, each distributed across various tissues and organs and involved in crucial physiological functions. Clinically utilized CA inhibitors, such as brinzolamide, dorzolamide and acetazolamide, exhibit poor selectivity, leading to undesirable side effects. A significant challenge in designing effective CA inhibitors is achieving balanced isoform selectivity, prompting the exploration of new chemotypes. This review compiles recent strategies employed by various researchers in developing CAIs across different structural classes, including pyrazoline, quinoline, imidazole, oxadiazole, pyrimidine, coumarin, chalcone, rhodanine, phthalazine, triazole, isatin, and indole. Additionally, the review summarizes structure-activity relationship (SAR) analyses, isoform selectivity evaluations, along with mechanistic and in silico investigations. Insights derived from SAR studies provide crucial directions for the rational design of next-generation heterocyclic CA inhibitors, with improved therapeutic efficacy and reduced side effects. To the best of our knowledge, for the first time, we have comprehensively summarized all known isoforms of CA in relation to various heterocyclic motifs. This review examines the use of different heterocycles as CA inhibitors, drawing on research published over the past 11 years. It offers a valuable resource for early-career researchers, encouraging further exploration of synthetic heterocycles in the development of CA inhibitors.

Visible-light-promoted selenylation/cyclization of o-(1-alkynyl) benzoates to access seleno-substituted isocoumarins

A simple and efficient method to access 4-selenyl-isocoumarin derivatives through visible-light-promoted selenylation/cyclization of o-(1-alkynyl) benzoates has been developed. This transformation is performed under mild conditions and has the advantages of functional group tolerance and broad substrate scope.

Design, synthesis, and in vitro and in silico studies of morpholine derived thiazoles as bovine carbonic anhydrase-II inhibitors

Carbonic anhydrase CA-II enzyme is essential for maintaining homeostasis in several processes, including respiration, lipogenesis, gluconeogenesis, calcification, bone resorption, and electrolyte balance due to its vital function within cellular processes. Herein, we screened 25 newly synthesized thiazole derivatives and assessed their inhibitory potential against the zinc-containing carbonic anhydrase CA-II enzyme. Intriguingly, derivatives of thiazole exhibited varying degrees of inhibitory action against CA-II. The distinctive attribute of these compounds is that they can attach to the CA-II binding site and block its action. Morpholine based thiazoles can be strategically modified to improve bovine CA-II inhibitor binding affinity, selectivity, and pharmacokinetics. Thiazole and morpholine moieties can boost inhibitory efficacy and selectivity over other calcium-binding proteins by interacting with target bovine CA-II binding sites. The derivatives 23-26 exhibited greater affinity when compared to the standard acetazolamide. Furthermore, kinetic study of the most potent compound 24 was performed, which exhibited concentration dependent inhibition with a K i value of 9.64 ± 0.007 μM. Molecular docking, MD simulation and QSAR analysis was also carried out to elucidate the interactions, orientation, and conformational changes of these compounds within the active site of the enzyme. Moreover, pharmacokinetic assessments showed that most of the compounds possess attributes conducive to potential drug development.

Synthesis and Enzymatic Evaluation of a Small Library of Substituted Phenylsulfonamido-Alkyl Sulfamates towards Carbonic Anhydrase II

A small library of 79 substituted phenylsulfonamidoalkyl sulfamates, 1b-79b, was synthesized starting from arylsulfonyl chlorides and amino alcohols with different numbers of methylene groups between the hydroxyl and amino moieties yielding intermediates 1a-79a, followed by the reaction of the latter with sulfamoyl chloride. All compounds were screened for their inhibitory activity on bovine carbonic anhydrase II. Compounds 1a-79a showed no inhibition of the enzyme, in contrast to sulfamates 1b-79b. Thus, the inhibitory potential of compounds 1b-79b towards this enzyme depends on the substituent and the substitution pattern of the phenyl group as well as the length of the spacer. Bulkier substituents in the para position proved to be better for inhibiting CAII than compounds with the same substituent in the meta or ortho position. For many substitution patterns, compounds with shorter spacer lengths were superior to those with long chain spacers. Compounds with shorter spacer lengths performed better than those with longer chain spacers for a variety of substitution patterns. The most active compound held inhibition constant as low as Ki = 0.67 μM (for 49b) and a tert-butyl substituent in para position and acted as a competitive inhibitor of the enzyme.

An asiatic acid derived trisulfamate acts as a nanomolar inhibitor of human carbonic anhydrase VA

This investigation delves into the inhibitory capabilities of a specific set of triterpenoic acids on diverse isoforms of human carbonic anhydrase (hCA). Oleanolic acid (1), maslinic acid (2), betulinic acid (3), platanic acid (4), and asiatic acid (5) were chosen as representative triterpenoids for evaluation. The synthesis involved acetylation of parent triterpenoic acids 1-5, followed by sequential reactions with oxalyl chloride and benzylamine, de-acetylation of the amides, and subsequent treatment with sodium hydride and sulfamoyl chloride, leading to the formation of final compounds 21-25. Inhibition assays against hCAs I, II, VA, and IX demonstrated noteworthy outcomes. A derivative of betulinic acid, compound 23, exhibited a Ki value of 88.1 nM for hCA VA, and a derivative of asiatic acid, compound 25, displayed an even lower Ki value of 36.2 nM for the same isoform. Notably, the latter compound displayed enhanced inhibitory activity against hCA VA when compared to the benchmark compound acetazolamide (AAZ), which had a Ki value of 63.0 nM. Thus, this compound surpasses the inhibitory potency and isoform selectivity of the standard compound acetazolamide (AAZ). In conclusion, the research offers insights into the inhibitory potential of selected triterpenoic acids across diverse hCA isoforms, emphasizing the pivotal role of structural attributes in determining isoform-specific inhibitory activity. The identification of compound 25 as a robust and selective hCA VA inhibitor prompts further exploration of its therapeutic applications.

Thiosemicarbazone-benzenesulfonamide Derivatives as Human Carbonic Anhydrases Inhibitors: Synthesis, Characterization, and In silico Studies

INTRODUCTION

Carbonic anhydrases (CAs) are widespread metalloenzymes with the core function of catalyzing the interconversion of CO2 and HCO3 -. Targeting these enzymes using selective inhibitors has emerged as a promising approach for the development of novel therapeutic agents against multiple diseases.

METHODS

A series of novel thiosemicarbazone-containing derivatives were synthesized, characterized, and tested for their inhibitory activity against pharmaceutically important human CA I (hCA I), II (hCA II), IX (hCA IX), and XII (hCA XII) using the single tail approach.

RESULTS

The compounds generally inhibited the isoenzymes at low nanomolar concentrations, with compound 6b having Ki values of 7.16, 0.31, 92.5, and 375 nM against hCA I, II, IX and XII, respectively. Compound 6e exhibited Ki values of 27.6, 0.34, 872, and 94.5 nM against hCA I, II, IX and XII, respectively.

CONCLUSION

To rationalize the inhibition data, molecular docking studies were conducted, providing insight into the binding mechanisms, molecular interactions, and selectivity of the compounds towards the isoenzymes.

pH-Dependent Structure and Dynamics of the Catalytic Domains of Human Carbonic Anhydrase II and IX

Extensive computer simulation studies have been carried out to probe the pH-dependent structure and dynamics of the two most efficient isoenzymes II and IX of human carbonic anhydrase (HCA) that control the pH in the human body. The equilibrium structure and hydration of their catalytic domains are found to be largely unaffected by the variation of pH in the range studied, in close agreement with the known experimental results. In contrast, a significant effect of the change in pH is observed for the first time on the local electrostatic potential of the active site walls and the dynamics of active site water molecules. We also report for the first time the free energy and kinetics of coupled fluctuations of orientation and protonation states of the well-known His-mediated proton shuttle (His-64) in both isozymes at pH 7 and 8. The transitions between different tautomers of in or out conformations of His-64 side chain range between 109 and 106 s-1 depending on pH. Possible implications of these results on conformation-dependent pKa of His-64 side chain and its role in driving the catalysis toward hydration of CO2 or dehydration of HCO3- with varying pH are discussed.

Targeting carbonic anhydrases for the management of hypoxic metastatic tumors

INTRODUCTION

Several isoforms of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) are connected with tumorigenesis. Hypoxic tumors overexpress CA IX and XII as a consequence of HIF activation cascade, being involved in pH regulation, metabolism, and metastases formation. Other isoforms (CA I, II, III, IV) were also reported to be present in some tumors.

AREAS COVERED

Some CA isoforms are biomarkers for disease progression or response to therapy. Inhibitors, antibodies, and other procedures for targeting these enzymes for the treatment of tumors/metastases are discussed. Sulfonamides and coumarins represent the most investigated classes of inhibitors, but carboxylates, selenium, and tellurium-containing inhibitors were also investigated. Hybrid drugs of CA inhibitors with other antitumor agents for multitargeted therapy were reported.

EXPERT OPINION

Targeting CAs present in solid or hematological tumors with selective, targeted inhibitors is a validated approach, which has been consolidated in the last years. A host of new preclinical data and several clinical trials of antibodies and small-molecule inhibitors are ongoing, which connected with the large number of new chemotypes/procedures discovered to be effective, may lead to a breakthrough in this therapeutic area. The scientific/patent literature has been searched for on PubMed, ScienceDirect, Espacenet, and PatentGuru, from 2018 to 2023.

Biology of childhood hepatoblastoma and the search for novel treatments

Our research laboratory has a longstanding interest in developmental disorders and embryonic tumors, and recent efforts have focused on the pathogenesis of pediatric liver tumors. This review focuses on hepatoblastoma (HB), the most common pediatric liver malignancy. Despite advances in treatment, patients with metastatic HB have a poor prognosis, and survivors often have permanent side effects attributable to chemotherapy. In an effort to improve survival and lessen long-term complications of HB, we have searched for novel molecular vulnerabilities using a combination of patient derived cell lines, metabolomics, and RNA sequencing of human samples at diagnosis and follow-up. These studies have shed light on pathogenesis and identified putative targets for future therapies in children with advanced HB.

The critical role of mode of action studies in kinetoplastid drug discovery

Understanding the target and mode of action of compounds identified by phenotypic screening can greatly facilitate the process of drug discovery and development. Here, we outline the tools currently available for target identification against the neglected tropical diseases, human African trypanosomiasis, visceral leishmaniasis and Chagas' disease. We provide examples how these tools can be used to identify and triage undesirable mechanisms, to identify potential toxic liabilities in patients and to manage a balanced portfolio of target-based campaigns. We review the primary targets of drugs that are currently in clinical development that were initially identified via phenotypic screening, and whose modes of action affect protein turnover, RNA trans-splicing or signalling in these protozoan parasites.

Small Structural Differences Govern the Carbonic Anhydrase II Inhibition Activity of Cytotoxic Triterpene Acetazolamide Conjugates

Acetylated triterpenoids betulin, oleanolic acid, ursolic acid, and glycyrrhetinic acid were converted into their succinyl-spacered acetazolamide conjugates. These conjugates were screened for their inhibitory activity onto carbonic anhydrase II and their cytotoxicity employing several human tumor cell lines and non-malignant fibroblasts. As a result, the best inhibitors were derived from betulin and glycyrrhetinic acid while those derived from ursolic or oleanolic acid were significantly weaker inhibitors but also of diminished cytotoxicity. A betulin-derived conjugate held a K_i = 0.129 μM and an EC₅₀ = 8.5 μM for human A375 melanoma cells.

Coumaryl-sulfonamide moiety: Unraveling their synthetic strategy and specificity toward hCA IX/XII, facilitating anticancer drug development

Currently, cancer is the most grieving threat to society. The cancer-related death rate has had an ascending trend, despite the implementation of numerous treatment strategies or the discovery of an array of potent molecules against several pathways of cancer growth. The need of the hour is to prevent the multidrug resistance toll, and the current efforts have been bestowed upon a versatile small molecule scaffold, coumarin (benz[α]pyrone), a natural compound possessing interesting affinity toward the cancer target human carbonic anhydrase (hCA), focusing on hCA I, II, IX, and XII. Along with coumarin, the age-old known antibacterial drug sulfonamide, when conjugated at positions 3, 7, and 8 of coumarin either with a linker group or as a single entity, has been reported to enhance the affinity of coumarin toward the overexpressed enzymes in tumor cell lines. The sulfonamides have been listed as obsolete drugs due to the severe side effects caused by them; however, their affinity toward the hCA-zinc-binding core has attracted the attention of researchers. Hence, in the process of drug development, coumarin and sulfonamides have remained the choice of last resort. To unveil the synthetic strategy of coumarin-sulfonamide conjugation, their rationale for inhibiting cancer cells/enzymes, and their affinity toward various types of carcinoma have been the sole goal of the researchers. This review specifically focuses on the mechanism of action and the structure-activity relationship through synthetic strategies and the binding affinity of coumaryl-sulfonamide conjugates with the anticancer targets possessing the highest enzyme affinity, since 2008.

Enaminone-based carboxylic acids as novel non-classical carbonic anhydrases inhibitors: design, synthesis and in vitro biological assessment

In searching for new molecular drug targets, Carbonic Anhydrases (CAs) have emerged as valuable targets in diverse diseases. CAs play critical functions in maintaining pH and CO₂ homeostasis, metabolic pathways, and much more. So, it is becoming attractive for medicinal chemists to design novel inhibitors for this class of enzymes with improved potency and selectivity towards the different isoforms. In the present study, three sets of carboxylic acid derivatives 5a-q, 7a-b and 12a-c were designed, developed and evaluated for the hCA inhibitory effects against hCA I, II, IX and XII. Compounds 5l, 5m, and 5q elicited the highest inhibitory activities against hCA II, IX and XII. In summary, structural rigidification, regioisomerism and structural extension, all played obvious roles in the degree of hCA inhibition. This present work could be a good starting point for the design of more non-classical selective hCA inhibitors as potential targets for several diseases.

Design and synthesis of benzothiazole-based SLC-0111 analogues as new inhibitors for the cancer-associated carbonic anhydrase isoforms IX and XII

In this work, different series of benzothiazole-based sulphonamides 8a-c, 10, 12, 16a-b and carboxylic acids 14a-c were developed as novel SLC-0111 analogues with the goal of generating potent carbonic anhydrase (CA) inhibitors. The adopted strategy involved replacing the 4-fluorophenyl tail in SLC-0111 with a benzothiazole motif that attached to the ureido linker to produce compounds 8c and its regioisomers 8a-b. In addition, the ureido spacer was elongated by methylene or ethylene groups to afford the counterparts 10 and 12. In turn, the primary sulfamoyl zinc binding group (ZBG) was either substituted or replaced by carboxylic acid functionality in order to provide the secondary sulphonamide-based SLC-0111 analogues 16a-b, and the carboxylic acid derivatives 14a-c, respectively. All compounds (8a-c, 10, 12, 14a-c and 16a-b) were tested for their ability to inhibit CA isoforms CA I, II, IX and XII. Additionally, the in vitro anticancer properties of the developed CAIs were evaluated.

Structure and Dynamics of the Isozymes II and IX of Human Carbonic Anhydrase

Human carbonic anhydrases (HCAs) are responsible for the pH control and sensing in our body and constitute key components in the central pH paradigm connected to cancer therapeutics. However, little or no molecular level studies are available on the pH-dependent stability and functional dynamics of the known isozymes of HCA. The main objective of this Article is to report the first bench-marking study on the structure and dynamics of the two most efficient isozymes, HCA II and IX, at neutral pH using classical molecular dynamics (MD) and constant pH MD (CpHMD) simulations combined with umbrella sampling, transition path sampling, and Markov state models. Starting from the known crystal structures of HCA II and the monomeric catalytic domain of HCA IX (labeled as HCA IX-c), we have generated classical MD and CpHMD trajectories (of length 1 μs each). In all cases, the overall stability, RMSD, and secondary structure segments of the two isozymes are found to be quite similar. Functionally important dynamics of these two enzymes have been probed in terms of active site hydration, coordination of the Zn(II) ion to a transient excess water, and the formation of putative proton transfer paths. The most important difference between the two isozymes is observed for the side-chain fluctuations of His-64 that is expected to shuttle an excess proton out of the active site as a part of the rate-determining intramolecular proton transfer reaction. The relative stability of the stable inward and outward conformations of the His-64 side-chain and the underlying free energy surfaces are found to depend strongly on the isozyme. In each case, a lower free energy barrier is detected between predominantly inward conformations from predominantly outward ones when simulated under constant pH conditions. The kinetic rate constants of interconversion between different free energy basins are found to span 10⁷-10⁸ s^-1 with faster conformational transitions predicted at constant pH condition. The estimated rate constants and free energies are expected to validate if the fluctuation of the His-64 side-chain in HCA IX may have a significance similar to that known in the multistep catalytic cycle of HCA II.

Novel 2-substituted thioquinazoline-benzenesulfonamide derivatives as carbonic anhydrase inhibitors with potential anticancer activity

A novel series of 2-thioquinazoline-benzenesulfonamide hybrids were designed as carbonic anhydrase (CA) inhibitors. The design approach relies on molecular hybridization between the benzenesulfonamide scaffold as a Zn²⁺ binding group and 2-substituted thioquinazolines as a tail. Assaying the thioquinazoline-benzenesulfonamide conjugates against four different CA isoforms revealed that compounds 12f and 12p are the most potent derivatives. They exhibit K_i  = 0.09 and 0.05 µM on CA II, 0.32 and 0.47 µM on CA IX, and 0.58 and 0.46 µM on CA XII, respectively. In addition, 12p demonstrated high selectivity for CA II over CA I with selectivity index (SI) = 92, and slightly higher specificity for CA II over CA IX and CA XII with SI = 9.40 and 9.20, respectively. The synthesized compounds were screened for their cytotoxic activity at 10 µM concentration and derivatives 12o, 12n, and 12f turned out to be the most potent ones from the synthesized series; they exhibit mean growth inhibition % values of 89.38%, 58.75%, and 54.71%, respectively, while 12p demonstrated moderate activity against the NCI cancer cell lines, with mean growth inhibition % = 29.62%. The analysis of the MCF-7 cell cycle after treatment with 5.0 µM of 12f displayed that it arrests the cell cycle at the G2/M phase. Molecular docking simulation of the thioquinazoline-benzenesulfonamide hybrids in the CA II active site rationalized the potent activity to the settlement of the sulfonamide moiety at the depth of the CA II active site and its stabilization by performing the important interactions with the Zn²⁺ ion as well as with the key amino acids Thr199 and/or Thr200, while the thioquinazoline moiety with different (un)substituted phenyl tails is stabilized by the formation of various hydrogen bonding and hydrophobic interactions with the surrounding amino acids in the binding site.

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.