Bernard Masereel

An overview of inhibitors of Na+/H+ exchanger

The Na(+)/H(+) exchanger (NHE) is involved in intracellular pH homeostasis of many mammalian cell types. To date seven NHE isoforms (NHE1-NHE7) have been identified. NHE1 is the most predominant isoform expressed in heart where it contributes to cardiomyocyte pH homeostasis. Although the NHE activation is essential for the restoration of physiological pH, hyperactivation of NHE1 during ischemia-reperfusion episodes disrupts the intracellular ion balance, leading to cardiac dysfunction and damage. Beside its ability to inhibit a conductive Na(+) channel and the Na(+)/Ca(++) exchanger, amiloride was the first drug described as NHE inhibitor. Double substitution of the nitrogen of the 5-amino group of amiloride gave DMA, EIPA, MIBA and HMA. Later, several acylguanidines were prepared to selectively inhibit NHE1. The replacement of the pyrazine ring of amiloride by a pyridine ring or by a phenyl increased the potency and the NHE selectivity. The simultaneous replacement of the pyrazine ring by a phenyl, of the 6-chloro by a sulfomethyl led to drugs such as HOE-694, cariporide, eniporide and BIIB-513 which also selectively inhibited NHE1. In the last decade several bicyclic guanidines were prepared: zoniporide, MS-31038, SM-20220, SM-20550, SMP-300, KB-R9032, BMS-284640, T-162559, TY-12533, S-3226 or SL-591227. Extensive pre-clinical studies indicated that NHE inhibitors afford substantial protection in different animal models of myocardial ischemia (MI) and reperfusion, but the results of clinical trials involving eniporide and cariporide were mixed.

Deciphering the Mechanism of Carbonic Anhydrase Inhibition with Coumarins and Thiocoumarins

Coumarin derivatives were recently shown to constitute a totally new class of inhibitors of the zinc metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), being hydrolyzed within the CA active site to 2-hydroxycinnamic acids. We explore here a new series of variously substituted coumarins and a thiocoumarin for their interaction with 13 mammalian CA isoforms, detecting low nanomolar and isoform selective inhibitors. The mechanism of action of this class of inhibitors is delineated in detail by resolving the X-ray crystal structure of CA II in complex with trans-2-hydroxy-cinnamic acid, the in situ hydrolysis product of simple coumarin. Thiocoumarins also act as efficient CAIs, similarly to coumarins. The versatility of the (thio)coumarin chemistry, the cis-trans isomerization evidenced here, and easy derivatization of the (thio)coumarin rings, coupled with the nanomolar inhibition range of several isozymes, afford isoform-selective CAIs with various biomedical applications, which render these classes of compounds superior to the clinically used sulfonamides.

Reversal of tumoral immune resistance by inhibition of tryptophan 2,3-dioxygenase

Tryptophan catabolism mediated by indoleamine 2,3-dioxygenase (IDO1) is an important mechanism of peripheral immune tolerance contributing to tumoral immune resistance, and IDO1 inhibition is an active area of drug development. Tryptophan 2,3-dioxygenase (TDO) is an unrelated hepatic enzyme that also degrades tryptophan along the kynurenine pathway. Here, we show that enzymatically active TDO is expressed in a significant proportion of human tumors. In a preclinical model, TDO expression by tumors prevented their rejection by immunized mice. We developed a TDO inhibitor, which, upon systemic treatment, restored the ability of mice to reject TDO-expressing tumors. Our results describe a mechanism of tumoral immune resistance based on TDO expression and establish proof-of-concept for the use of TDO inhibitors in cancer therapy.

Antibody-functionalized polymer-coated gold nanoparticles targeting cancer cells: an in vitro and in vivo study

Gold nanoparticles (∼5 nm) coated with plasma-polymerized allylamine were produced through plasma vapor deposition and bioconjugated with a monoclonal antibody targeting the epidermal growth factor receptor. The resulting nanoconjugates displayed an antibody loading of about 1.7 nmol mg−1 and efficiently target epidermal growth factor receptor overexpressing cell lines, as ascertained by ELISA and Western blot assays. The in vitro targeting properties were also confirmed in vivo, where a similar biodistribution profile of what was experienced for the unconjugated antibody was observed. Thanks to the possibility of doping the gold nanoparticles with radionuclides during plasma vapor deposition, the proposed functionalization strategy represents a very suitable platform for the in vivo cancer targeting with nanosized multifunctional particles.

Carbonic Anhydrase Inhibitors as Anticonvulsant Agents

Seizures are one of the most common neurological disorders in clinical medicine. Triggering mechanisms by which seizures form remain unclear, but are related to a rapid change in ionic composition, including an increase of intracellular potassium concentration and pH shifts within the brain. pH buffering of extra- and intracellular spaces is mainly carried out by the CO(2)/ HCO(3)(-) buffer, the equilibration of the two species being assured by the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). Some carbonic anhydrase inhibitors (CAIs) are used as anticonvulsants in the treatment of epilepsy. In this review, we will describe the link between CA and seizures on the basis of several putative mechanisms. Several CA isozymes have been pointed out for their contribution to epileptiform activity. An overview of the CA isozyme expression in the brain and of their specifics roles is also discussed. This article reviews the research achievements published on CA inhibitors, clinically used as anticonvulsant and those under development.

Specific inhibition of carbonic anhydrase IX activity enhances the in vivo therapeutic effect of tumor irradiation

BACKGROUND AND PURPOSE Carbonic anhydrase (CA) IX expression is increased upon hypoxia and has been proposed as a therapeutic target since it has been associated with poor prognosis, tumor progression and pH regulation. The aim of this study was to evaluate the antitumor activity of a high CAIX-affinity indanesulfonamide (11c) combined with irradiation, compared with the general CA inhibitor acetazolamide (AZA). MATERIAL AND METHODS HT-29 carcinoma cells with or without (genetic knockdown, KD) CAIX expression were incubated with 11c/AZA under different oxygen levels and proliferation, apoptosis and radiosensitivity were evaluated. 11c/AZA was administered intravenously (1×/day; 5 days) to tumor-bearing mice and tumor irradiation (10 Gy) was performed at day 3 of the injection period. Tumor growth and potential treatment toxicity were monitored (3×/week). RESULTS Treatment with 11c/AZA alone resulted in tumor regression, which was further increased in CAIX expressing cells by combining 11c with irradiation. AZA demonstrated also an additional effect in the KD tumors when combined with irradiation. CAIX inhibition in vitro significantly reduced proliferation and increased apoptosis upon hypoxia exposure without affecting intrinsic radiosensitivity. CONCLUSIONS Specific inhibition of CAIX activity enhanced the effect of tumor irradiation and might, therefore, be an attractive strategy to improve overall cancer treatment.

Tryptophan 2,3-Dioxygenase (TDO) Inhibitors. 3-(2-(Pyridyl)ethenyl)indoles as Potential Anticancer Immunomodulators

Tryptophan catabolism mediated by indoleamine 2,3-dioxygenase (IDO) is an important mechanism of peripheral immune tolerance contributing to tumoral immune resistance. IDO inhibition is thus an active area of research in drug development. Recently, our group has shown that tryptophan 2,3-dioxygenase (TDO), an unrelated hepatic enzyme also catalyzing the first step of tryptophan degradation, is also expressed in many tumors and that this expression prevents tumor rejection by locally depleting tryptophan. Herein, we report a structure-activity study on a series of 3-(2-(pyridyl)ethenyl)indoles. More than 70 novel derivatives were synthesized, and their TDO inhibitory potency was evaluated. The rationalization of the structure-activity relationships (SARs) revealed essential features to attain high TDO inhibition and notably a dense H-bond network mainly involving His(55) and Thr(254) residues. Our study led to the identification of a very promising compound (58) displaying good TDO inhibition (K(i) = 5.5 μM), high selectivity, and good oral bioavailability. Indeed, 58 was chosen for preclinical evaluation.

Anticonvulsant Sulfonamides/Sulfamates/Sulfamides with Carbonic Anhydrase Inhibitory Activity : Drug Design and Mechanism of Action

The marketed antiepileptic drugs can not solve entirely the problem of seizure in patients suffering from refractory epilepsies. Therefore, new anticonvulsant compounds structurally and pharmacologically different of the currently prescribed drugs are needed. Carbonic anhydrase (CA) inhibitors are known to act as anticonvulsant since several decades while the link between CA and seizure is not straightforward. However, the recent discovery that several CA isozymes are expressed in brain and the better knowledge of their physiological/pathological role, lead to the emergence of new CA inhibitors with anticonvulsant effect including: analogues of acetazolamide, analogues of topiramate, aromatic or heterocyclic sulfonamides incorporating valproyl or adamantyl moieties. Different strategies are developed for the design of new more selective CA inhibitors with anticonvulsant properties.

New Developments on Thromboxane and Prostacyclin Modulators Part II: Prostacyclin Modulators

Prostacyclin (PGI(2)) is a potent endogenous inhibitor of platelet function and possesses a strong vasodilator effect. Furthermore, prostacyclin is currently presented as the physiologic antagonist of thromboxane A(2)(TXA(2)), which exhibits pro-aggregatory and vasoconstrictor properties. So, the balance between PGI(2) and TXA(2) production is crucial for the cardiovascular system. Indeed, an imbalance in the production or effect of these products is deleterious for the circulatory system and can lead to characterized vascular diseases such as hypertension, stroke, atherosclerosis or myocardial infarction. Although the biological effects of PGI(2) are considered to be clinically useful, its use as therapeutic agent is largely limited by both its chemical and metabolic instability. Actually, several prostacyclin agonists have been synthesized and pharmacologically evaluated. Among these, some have been clinically evaluated as therapeutic agents in several vascular diseases. This review focuses on the latest chemical and pharmacological developments in the field of the prostacyclin agonists.

Effects of endotoxic shock on right ventricular systolic function and mechanical efficiency

OBJECTIVE To investigate the effects of endotoxin infusion on right ventricular (RV) systolic function and mechanical efficiency. METHODS Six anesthetized pigs (Endo group) received a 0.5 mg/kg endotoxin infusion over 30 min and were compared with six other anesthetized pigs (Control group) receiving placebo for 5 h. RV pressure-volume (PV) loops were obtained by the conductance catheter technique and pulmonary artery flow and pressure were measured with high-fidelity transducers. RESULTS RV adaptation to increased afterload during the early phase of endotoxin-induced pulmonary hypertension (T30) was obtained by both homeometric and hetereometric regulations: the slope of the end-systolic PV relationship of the right ventricle increased from 1.4+/-0.2 mmHg/ml to 2.9+/-0.4 mmHg/ml (P<0.05) and RV end-diastolic volume increased from 56+/-6 ml to 64+/-11 ml (P<0.05). Consequently, right ventricular-vascular coupling was maintained at a maximum efficiency. Ninety minutes later (T120), facing the same increased afterload, the right ventricle failed to maintain its contractility to such an elevated level and, as a consequence, right ventricular-vascular uncoupling occurred. PV loop area, which is known to be highly correlated with oxygen myocardial consumption, increased from 1154+/-127 mmHg/ml (T0) to 1798+/-122 mmHg/ml (T180) (P<0.05) while RV mechanical efficiency decreased from 63+/-2% (T0) to 45+/-5% (T270) (P<0.05). CONCLUSIONS In the very early phase of endotoxinic shock, right ventricular-vascular coupling is preserved by an increase in RV contractility. Later, myocardial oxygen consumption and energetic cost of RV contractility are increased, as evidenced by the decrease in RV efficiency, and right ventricular-vascular uncoupling occurs. Therefore, therapies aiming at restoring right ventricular-vascular coupling in endotoxic shock should attempt to increase RV contractility and to decrease RV afterload but also to preserve RV mechanical efficiency.