Bortezomib inhibits mammalian carbonic anhydrases

Boron-containing carbonic anhydrases inhibitors

Over the last decades, the medicinal chemistry of boron-based compounds has been extensively explored, designing valuable small molecule drugs to tackle diseases and conditions, such as cancer, infections, inflammatory and neurological disorders. Notably, boron has proven to also be a valuable element for the development of inhibitors of the metalloenzymes carbonic anhydrases (CAs), a class of drug targets with significant potential in medicinal chemistry. Incorporating boron into carbonic anhydrase inhibitors (CAIs) can modulate the ligand ability to recognize the target and/or influence selectivity towards different CA isoforms, using the tail approach and boron-based tails. The electron-deficient nature of boron and its associated properties have also led to the discovery of novel zinc-binding CAIs, such as boronic acids and the benzoxaboroles, capable of inhibiting the CAs upon a Lewis acid-base mechanism of action. The present manuscript reviews the state-of-the-art of boron-based CAIs. As research in the applications of boron compounds in medicinal chemistry continues, it is anticipated that new boron-based CAIs will soon expand the current array of such compounds. However, further research is imperative to fully unlock the potential of boron-based CAIs and to advance them towards clinical applications.

Targeting Metalloenzymes by Boron-Containing Metal-Binding Pharmacophores

Metalloenzymes have critical roles in a wide range of biological processes and are directly involved in many human diseases; hence, they are considered as important targets for therapeutic intervention. The specific characteristics of metal ion(s)-containing active sites make exploitation of metal-binding pharmacophores (MBPs) critical to inhibitor development targeting metalloenzymes. This Perspective focuses on boron-containing MBPs, which display unique binding modes with metalloenzyme active sites, particularly via mimicking native substrates or tetrahedral transition states. The design concepts regarding boron-containing MBPs are highlighted through the case analyses on five distinct classes of clinically relevant nucleophilic metalloenzymes from medicinal chemistry perspectives. The challenges (e.g., selectivity) faced by some boron-containing MBPs and possible strategies (e.g., bioisosteres) for metalloenzyme inhibitor transformation are also discussed.

An anion and small molecule inhibition study of the β-carbonic anhydrase from Staphylococcus aureus

Pathogenic bacteria resistant to most antibiotics, including the methicillin-resistant Staphylococcus aureus (MRSA) represent a serious medical problem. The search for new antiinfectives, possessing a diverse mechanism of action compared to the clinically used antibiotics, has become an attractive research field. S. aureus DNA encodes a β-class carbonic anhydrase, SauBCA. It is a druggable target that can be inhibited by certain aromatic and heterocyclic sulphonamides. Here we investigated inorganic anions and some other small molecules for their inhibition of SauBCA. The halides, nitrite, nitrate, bicarbonate, carbonate, bisulphite, sulphate, stannate, and N,N-diethyldithiocarbamate were submillimolar SauBCA inhibitors with K_Is in the range of 0.26 − 0.91 mM. The most effective inhibitors were sulfamide, sulfamate, phenylboronic acid, and phenylarsonic acid with K_Is of 7 − 43 µM. Several interesting inhibitors detected here may be considered lead compounds for the development of even more effective derivatives, which should be investigated for their bacteriostatic effects.

Anion inhibition studies of the α-carbonic anhydrases from Neisseria gonorrhoeae

The bacterial pathogen Neisseria gonorrhoeae encodes for an α-class carbonic anhydrase (CA, EC 4.2.1.1), NgCA, which was investigated for its inhibition with a series of inorganic and organic anions. Perchlorate and hexafluorophosphate did not significantly inhibit NgCA CO₂ hydrase activity, whereas the halides, azide, bicarbonate, carbonate, stannate, perosmate, diphosphate, divanadate, perruthenate, and trifluoromethanesulfonate showed inhibition constants in the range of 1.3–9.6 mM. Anions/small molecules such as cyanate, thiocyanate, nitrite, nitrate, bisulphite, sulphate, hydrogensulfide, phenylboronic acid, phenylarsonic acid, selenate, tellurate, tetraborate, perrhenate, peroxydisulfate, selenocyanate, iminodisulfonate, and fluorosulfonate showed K_Is in the range of 0.15–1.0 mM. The most effective inhibitors detected in this study were sulfamide, sulfamate, trithiocarbonate and N,N-diethyldithiocarbamate, which had K_Is in the range of 5.1–88 µM. These last compounds incorporating the CS₂^- zinc-binding group may be used as leads for developing even more effective NgCA inhibitors in addition to the aromatic/heterocyclic sulphonamides, as this enzyme was recently validated as an antibacterial drug target for obtaining novel antigonococcal agents

Benzimidazole derivatives as potent and isoform selective tumor-associated carbonic anhydrase IX/XII inhibitors

We describe the synthesis of a series of 2-arylbenzimidazole derivatives bearing sulfonamide functionality (4a-d, 7a-c and 10) as well as hydroxamic acid (15a-b), carboxylic acid (16a-b), carboxamide (17a-b) and boronic acid (22a-b and 26) functionalities, which act as human carbonic anhydrase (hCA, EC 4.2.1.1) inhibitors. The newly synthesized benzimidazole derivatives were evaluated against 4 physiologically relevant CA isoforms (hCA I, II, IX, and XII), and especially the sulfonamide-containing benzimidazoles demonstrated intriguing inhibitory activity against tumor associated CA IX and XII with K_I values in the range of 5.2-29.3 nM and 9.9-41.7 nM, respectively. Notably, compound 4c was the most potent and selective CA IX (K_I = 6.6 nM) and XII (K_I = 9.9 nM) inhibitor with a significant selectivity ratio over cytosolic CA I and II isoforms in the range of 3.4-25.2. In addition, compounds having hydroxamic acid (15a-b) or carboxylic acid (16a-b) functionalities resulted in greater selectivity ratios for CA IX/XII over CAI/II in the range of 4.1-121.5 although with K_I values in lower micromolar potency (K_Is = 0.36-0.85 μM for CA IX/XII).

Phaeodactylum tricornutum as a model organism for testing the membrane penetrability of sulphonamide carbonic anhydrase inhibitors

Carbonic anhydrases (CAs) are ubiquitous metalloenzymes, which started to be investigated in detail in pathogenic, as well as non-pathogenic species since their pivotal role is to accelerate the physiological CO₂ hydration/dehydration reaction significantly. Here, we propose the marine unicellular diatom Phaeodactylum tricornutum as a model organism for testing the membrane penetrability of CA inhibitors (CAIs). Seven inhibitors belonging to the sulphonamide type and possessing a diverse scaffold have been explored for their in vitro inhibition of the whole diatom CAs and the in vivo inhibitory effect on the growth of P. tricornutum. Interesting, inhibition of growth was observed, in vivo, demonstrating that this diatom is a good model for testing the cell wall penetrability of this class of pharmacological agents. Considering that many pathogens are difficult and dangerous to grow in the laboratory, the growth inhibition of P. tricornutum with different such CAIs may be subsequently used to design inhibition studies of CAs from pathogenic organisms.

Design, synthesis, in vitro and in vivo evaluation, and structure-activity relationship (SAR) discussion of novel dipeptidyl boronic acid proteasome inhibitors as orally available anti-cancer agents for the treatment of multiple myeloma and mechanism studies

A series of novel dipeptidyl boronic acid inhibitors of 20S proteasome were designed and synthesized. Aliphatic groups at R¹ position were designed for the first time to fully understand the SAR (structure-activity relationship). Among the screened compounds, novel inhibitor 5c inhibited the CT-L (chymotrypsin-like) activity with IC₅₀ of 8.21 nM and the MM (multiple myeloma) cells RPMI8226, U266B and ARH77 proliferations with the IC₅₀ of 8.99, 6.75 and 9.10 nM, respectively, which showed similar in vitro activities compared with the compound MLN2238 (biologically active form of marketed MLN9708). To investigate the oral availability, compound 5c was esterified to its prodrug 6a with the enzymatic IC₅₀ of 6.74 nM and RPMI8226, U266B and ARH77 cell proliferations IC₅₀ of 2.59, 4.32 and 3.68 nM, respectively. Furthermore, prodrug 6a exhibited good pharmacokinetic properties with oral bioavailability of 24.9%, similar with MLN9708 (27.8%). Moreover, compound 6a showed good microsomal stabilities and displayed stronger in vivo anticancer efficacy than MLN9708 in the human ARH77 xenograft mouse model. Finally, cell cycle results showed that compound 6a had a significant inhibitory effect on CT-L and inhibited cell cycle progression at the G2M stage.

Benzoxaboroles as Efficient Inhibitors of the β-Carbonic Anhydrases from Pathogenic Fungi: Activity and Modeling Study

A series of 6-substituted benzoxaboroles were investigated as inhibitors of the β-class carbonic anhydrase from three pathogenic fungi (Cryptococcus neoformans, Candida glabrata, and Malassezia globosa). Independently from the nature of the substituents on the phenyl of the urea/thiourea group, all reported derivatives showed nanomolar inhibitory activities against Can2 and CgNce103 vs micromolar inhibition against MgCA. Selectivity over human CA I and CA II was noticed. The observed structure-activity relationship trends have been rationalized by modeling study of selected compounds into the active site of Can2 and MgCA. The present letter demonstrates that benzoxaborole chemotype may offer interesting opportunities for the inhibition of β-CA from pathogenic fungi and for the development of antifungal agents with a new mechanism of action.