Inhibition of Schistosoma mansoni carbonic anhydrase by the antiparasitic drug clorsulon: X-ray crystallographic and in vitro studies

Tetrazole Is a Novel Zinc Binder Chemotype for Carbonic Anhydrase Inhibition

The tetrazole group is here proposed as a zinc-binding warhead for the inhibition of the metalloenzyme carbonic anhydrases. A set of synthesized derivatives incorporating the tetrazole moiety were evaluated as inhibitors against a panel of human isoforms, exhibiting K I values spanning between the submicromolar and low-to-medium micromolar ranges (0.62-19.6 μM). X-ray crystallographic studies were conducted to gain insights into their modes of binding to the target enzyme. These findings mark a significant advancement in the search for inhibitory chemotypes other than classical sulfonamides.

Multi- and polypharmacology of carbonic anhydrase inhibitors

Eight genetically distinct families of the enzyme carbonic anhydrase (CA, EC 4.2.1.1) have been described in organisms overall in the phylogenetic tree. They catalyze the hydration of CO2 to bicarbonate and protons and are involved in pH regulation, chemosensing, and metabolism. The 15 α-CA isoforms present in humans are pharmacological drug targets known for decades, their inhibitors being used as diuretics, antiglaucoma, antiepileptic, or antiobesity drugs, as well as for the management of acute mountain sickness, idiopathic intracranial hypertension, and recently, as antitumor theragnostic agents. Other potential applications include the use of CA inhibitors (CAIs) in inflammatory conditions, cerebral ischemia, neuropathic pain, or Alzheimer/Parkinson disease management. CAs from pathogenic bacteria, fungi, protozoans, and nematodes have started to be considered as drug targets in recent years, with notable advances being registered. CAIs have a complex multipharmacology probably unique to this enzyme, which has been exploited intensely but may lead to other relevant applications in the future due to the emergence of drug design approaches that afforded highly isoform-selective compounds for most α-CAs known to date. They belong to a multitude of chemical classes (sulfonamides and isosteres, [iso]coumarins and related compounds, mono- and dithiocarbamates, selenols, ninhydrines, boronic acids, benzoxaboroles, etc). The polypharmacology of CAIs will also be discussed because drugs originally discovered for the treatment of non-CA related conditions (topiramate, zonisamide, celecoxib, pazopanib, thiazide, and high-ceiling diuretics) show effective inhibition against many CAs, which led to their repurposing for diverse pharmacological applications. SIGNIFICANCE STATEMENT: CAIs have multiple pharmacologic applications, such as diuretics, antiglaucoma, antiepileptic, antiobesity, antiacute mountain sickness, anti-idiopathic intracranial hypertension, and antitumor drugs. Their use in inflammatory conditions, cerebral ischemia, neuropathic pain, or neurodegenerations has started to be investigated recently. Parasite carbonic anhydrases are also drug targets for anti-infectives with novel mechanisms of action that can bypass drug resistance to commonly used agents. Drugs discovered for the management of other conditions that effectively inhibit these enzymes exert interesting polypharmacologic effects.

Identification of major degradation products of Clorsulon drug substance including its degradation pathways by high resolution mass spectrometry and NMR

Clorsulon is an effective anthelmintic drug substance extensively used in the treatment of parasitic infestations in both cattle and sheep. An in-depth investigation of Clorsulon's degradation products (DPs) was carried out through forced degradation study to comprehend its degradation path. A total of eight degradation products were separated under various stress degradation conditions. Structural elucidation of these DPs was conducted using ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS), and their fragmentation patterns were compared to that of the parent compound. Adequate amount of DP-4 was isolated and purified by semi-preparative high-performance liquid chromatography (HPLC) methods. Subsequently, it was examined in detail using both 1D and 2D NMR (nuclear magnetic resonance spectroscopy). Most probable mechanistic pathways for the formation of degradation products under various stress degradation conditions were proposed to better understand the degradation profile. Based on the results of the stress study, Clorsulon drug substance was found to be unstable under photolytic and oxidative conditions. Understanding Clorsulon's degradation pathway is essential for determining shelf-life prediction of the finished product, safety and efficacy assurance, and guiding the development of stable, high-quality formulations.

Anthelmintic potential of sulphonamides and Cucurbita pepo seeds extract on Heterophyes heterophyes experimentally infected mice

Since 1980s, no new drugs were described for treatment of heterophyiasis with many side effects of the currently used drug; praziquantel. This work aimed to study the therapeutic effect of clorsulon (sulphoamide) and aqueous extract of Cucurbita pepo in the treatment of experimental heterophyiasis. Mice were infected with encysted metacercaiae of Heterophyes heterophyes obtained from infected fish flesh. Mice were divided into five groups according to the drug used. The treatment started two weeks post-infection. Our results showed reduction of the recovered worm count with high efficacy of clorsulon and a moderate effect of C. pepo which was increased in the second week with much improvement of the intestinal histopathological changes. Scanning electron microscopy of adult H. heterophyes obtained from the intestine of mice treated with praziquantel appeared contracted with multiple small vesicles over the dorsal surface. Clorsulon produced loss of the spines on the lateral sides of the parasite with few vesicles whereas C. pepo seeds showed complete loss of the spines. In conclusion, clorsulon has high efficacy against H. heterophyes infection. Although the extract of C. pepo showed moderate curative effect against this parasite, it can be used in combination with other agents for a better synergistic effect.

Cloning, characterization, and inhibition of the novel β-carbonic anhydrase from parasitic blood fluke, Schistosoma mansoni

Schistosoma mansoni is an intestinal parasite with one β-class carbonic anhydrase, SmaBCA. We report the sequence enhancing, production, catalytic activity, and inhibition results of the recombinant SmaBCA. It showed significant catalytic activity on CO₂ hydration in vitro with k_cat 1.38 × 10⁵ s^-1 and k_cat/K_m 2.33 × 10⁷ M^-1 s^-1. Several sulphonamide inhibitors, from which many are clinically used, showed submicromolar or nanomolar inhibitory effects on SmaBCA. The most efficient inhibitor with a K_I of 43.8 nM was 4-(2-amino-pyrimidine-4-yl)-benzenesulfonamide. Other effective inhibitors with K_Is in the range of 79.4-95.9 nM were benzolamide, brinzolamide, topiramate, dorzolamide, saccharin, epacadostat, celecoxib, and famotidine. The other tested compounds showed at least micromolar range inhibition against SmaBCA. Our results introduce SmaBCA as a novel target for drug development against schistosomiasis, a highly prevalent parasitic disease.

A simple yet multifaceted 90 years old, evergreen enzyme: Carbonic anhydrase, its inhibition and activation

Advances in the carbonic anhydrase (CA, EC 4.2.1.1) research over the last three decades are presented, with an emphasis on the deciphering of the activation mechanism, the development of isoform-selective inhibitors/ activators by the tail approach and their applications in the management of obesity, hypoxic tumors, neurological conditions, and as antiinfectives.

Role of the Abcg2 Transporter in Secretion into Milk of the Anthelmintic Clorsulon: Interaction with Ivermectin

Clorsulon is a benzenesulfonamide drug that is effective in treating helminthic zoonoses such as fascioliasis. When used in combination with the macrocyclic lactone ivermectin, it provides high broad-spectrum antiparasitic efficacy. The safety and efficacy of clorsulon should be studied by considering several factors such as drug-drug interactions mediated by ATP-binding cassette (ABC) transporters due to their potential effects on the pharmacokinetics and drug secretion into milk. The aim of this work was to determine the role of ABC transporter G2 (ABCG2) in clorsulon secretion into milk and the effect of ivermectin, a known ABCG2 inhibitor, on this process. Using in vitro transepithelial assays with cells transduced with murine Abcg2 and human ABCG2, we report that clorsulon was transported in vitro by both transporter variants and that ivermectin inhibited its transport mediated by murine Abcg2 and human ABCG2. Wild-type and Abcg2-/- lactating female mice were used to carry out in vivo assays. The milk concentration and the milk-to-plasma ratio were higher in wild-type mice than in Abcg2-/- mice after clorsulon administration, showing that clorsulon is actively secreted into milk by Abcg2. The interaction of ivermectin in this process was shown after the coadministration of clorsulon and ivermectin to wild-type and Abcg2-/- lactating female mice. Treatment with ivermectin had no effect on the plasma concentrations of clorsulon, but the milk concentrations and milk-to-plasma ratios of clorsulon decreased in comparison to those with treatment without ivermectin, only in wild-type animals. Consequently, the coadministration of clorsulon and ivermectin reduces clorsulon secretion into milk due to drug-drug interactions mediated by ABCG2.

Cloning, purification, kinetic and anion inhibition studies of a recombinant β-carbonic anhydrase from the Atlantic salmon parasite platyhelminth Gyrodactylus salaris

A β-class carbonic anhydrase (CA, EC 4.2.1.1) was cloned from the genome of the Monogenean platyhelminth Gyrodactylus salaris, a parasite of Atlantic salmon. The new enzyme, GsaCAβ has a significant catalytic activity for the physiological reaction, CO₂ + H₂O ⇋ HCO₃⁻ + H⁺ with a k_cat of 1.1 × 10⁵ s⁻¹ and a k_cat/K_m of 7.58 × 10⁶ M⁻¹ × s⁻¹. This activity was inhibited by acetazolamide (K_I of 0.46 µM), a sulphonamide in clinical use, as well as by selected inorganic anions and small molecules. Most tested anions inhibited GsaCAβ at millimolar concentrations, but sulfamide (K_I of 81 µM), N,N-diethyldithiocarbamate (K_I of 67 µM) and sulphamic acid (K_I of 6.2 µM) showed a rather efficient inhibitory action. There are currently very few non-toxic agents effective in combating this parasite. GsaCAβ is subsequently proposed as a new drug target for which effective inhibitors can be designed.