Closantel toxicity.

Closantel is a broad-spectrum antihelminthic agent. It is a veterinary drug used only in animals-usually cattle, sheep and goats. A man in his 60s accidentally ingested approximately 1500 mg closantel. His visual acuity deteriorated. Optical coherence tomography (OCT) showed disruption of the outer retinal layers. Electroretinography identified abnormalities in macula and inner retinal function. He received methylprednisolone 1 g daily intravenously for 3 days. Improvements in both his visual acuity and OCT appearance followed. This case illustrates the profoundly destructive effect of this drug on humans even when consumed in low dose. We provide a concise summary of the small number of cases of closantel toxicity in humans, previously reported, for future reference as needed by others.

Investigating dihydroorotate dehydrogenase inhibitor mediated mitochondrial dysfunction in hepatic in vitro models.

Inhibition of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzymatic step in de novo pyrimidine synthesis, has broad immunosuppressive effects in vivo and shows promise as a therapeutic target for the treatment of malignancies, viral infections and auto-immune diseases. Whilst there are numerous DHODH inhibitors under development, leflunomide and teriflunomide are the only FDA approved compounds on the market, each of which have been issued with black-box warnings for hepatotoxicity. Mitochondrial dysfunction is a putative mechanism by which teriflunomide and leflunomide elicit their hepatotoxic effects, however it is as yet unclear whether this is shared by other nascent DHODH inhibitors. The present study aimed to evaluate the propensity for DHODH inhibitors to mediate mitochondrial dysfunction in two hepatic in vitro models. Initial comparisons of cytotoxicity and ATP content in HepaRG® cells primed for oxidative metabolism, in tandem with mechanistic evaluations by extracellular flux analysis identified multifactorial toxicity and moderate indications of respiratory chain dysfunction or uncoupling. Further investigations using HepG2 cells, a hepatic line with limited capability for phase I xenobiotic metabolism, identified leflunomide and brequinar as positive mitochondrial toxicants. Taken together, biotransformation of some DHODH inhibitor species may play a role in mediating or masking hepatic mitochondrial liabilities.

Molluscicidal activity and mechanism of toxicity of a novel salicylanilide ester derivative against Biomphalaria species.

BACKGROUND: Schistosomiasis mansoni is one of the most important, but often neglected, tropical diseases transmitted by snails of the genus Biomphalaria. Control of the intermediate host snail plays a crucial role in preventing the spread of schistosomiasis. However, there is only one molluscicide, niclosamide, recommended by the World Health Organization. Niclosamide has been used for several decades but is toxic to non-target organisms. Therefore, it is necessary to optimize the scaffold of niclosamide and develop novel molluscicides with enhanced potency and decreased toxicity to non-target organisms. METHODS: In this study, a candidate compound was analyzed by nuclear magnetic resonance and mass spectrometry. The molluscicidal potential against Biomphalaria species and cercaricidal potential against S. mansoni were evaluated using the immersion method. Furthermore, the preliminary mechanism was studied through cellular enzyme tests and electron microscopy. RESULTS: 5-chloro-2-[(2-chloro-4-nitrophenyl)carbamoyl]phenyl-4-methoxybenzoate (salicylanilidate), a novel salicylanilide ester derivative, was derived from niclosamide. The 50% lethal concentration to B. glabrata, B. straminea and B. pfeifferi was 0.261 mg/l, 0.172 mg/l and 0.241 mg/l, respectively. The effective dose required to completely kill S. mansoni cercariae was 0.625 mg/l for salicylanilidate and 0.125 mg/l for niclosamide. However, salicylanilidate was approximately 100-fold less toxic to the fish Danio rerio than niclosamide. Furthermore, salicylanilidate reduced the enzymatic activities of nitric oxide synthase (NOS), lactate dehydrogenase (LDH) and acetylcholinesterase (AChE) in the snail, demonstrating that it could affect neurohypophysis transmission and energy metabolism. Severe swelling in the tentacle and deformation of cilia in the tentacle and mantle were observed through scanning electron microscopy. The results of transmission electron microscopy showed that salicylanilidate could damage critical organelles in hepatopancreas tissues, including degeneration of the endoplasmic reticulum and vacuolization in mitochondria. In addition, transcriptional levels of superoxide dismutase (SOD), acid phosphatase (ACP) and NOS in the hepatopancreas were significantly downregulated as shown by real-time quantitative polymerase chain reaction (RT-PCR). These results indicated that the hepatopancreas is a primary target organ of salicylanilidate. CONCLUSIONS: Salicylanilidate not only had deleterious effects on Biomphalaria species and S. mansoni cercariae but also showed very low toxicity to D. rerio, suggesting that it has broad potential applications.

Synthesis and evaluation of salicylanilide derivatives as potential epidermal growth factor receptor inhibitors.

Two series of novel salicylanilide were synthesized as potential epidermal growth factor receptor (EGFR) inhibitors. The enzyme inhibitory activity against EGFR of all compounds was carried out, and their antiproliferative activities against the A549 and A431 cell lines were also evaluated. Of the compounds studied, majority of them exhibited high antiproliferative activities compared with gefitinib; especially, 12a and 12b exhibited stronger inhibitory activity against EGFR with IC50 values of 10.4 ± 2.25 and 15.4 ± 2.33 nm, respectively, which were comparable to the positive control of gefitinib (IC50 = 12.1 ± 2.21 nm). Compound 12b also showed outstanding inhibitory activity against A431 and A549 cell lines with the IC50 values of 0.42 ± 0.43 µm and 0.57 ± 0.43 µm, which was better than the positive controls. In the molecular modeling study, compound 12b was bound into the active pocket of EGFR with two hydrogen bond and with minimum binding free energy ▵Gb = -25.1125 kcal/mol. The result also suggested that compound 12b could bind the EGFR kinase well.

Structure-activity relationships of antitubercular salicylanilides consistent with disruption of the proton gradient via proton shuttling.

A series of salicylanilides was synthesized based on a high-throughput screening hit against Mycobacterium tuberculosis. A free phenolic hydroxyl on the salicylic acid moeity is required for activity, and the structure-activity relationship of the aniline ring is largely driven by the presence of electron withdrawing groups. We synthesized 94 analogs exploring substitutions of both rings and the linker region in this series and we have identified multiple compounds with low micromolar potency. Unfortunately, cytotoxicity in a murine macrophage cell line trends with antimicrobial activity, suggesting a similar mechanism of action. We propose that salicylanilides function as proton shuttles that kill cells by destroying the cellular proton gradient, limiting their utility as potential therapeutics.

Antimycobacterial assessment of Salicylanilide benzoates including multidrug-resistant tuberculosis strains.

The increasing emergence especially of drug-resistant tuberculosis has led to a strong demand for new anti-tuberculosis drugs. Eighteen salicylanilide benzoates were evaluated for their inhibition potential against Mycobacterium tuberculosis, Mycobacterium avium and two strains of Mycobacterium kansasii; minimum inhibitory concentration values ranged from 0.5 to 16 μmol/L. The most active esters underwent additional biological assays. Four benzoates inhibited effectively the growth of five multidrug-resistant strains and one extensively drug-resistant strain of M. tuberculosis at low concentrations (0.25–2 μmol/L) regardless of the resistance patterns. The highest rate of multidrug-resistant mycobacteria inhibition expressed 4-chloro-2-[4-(trifluoromethyl)-phenylcarbamoyl]phenyl benzoate (0.25–1 μmol/L). Unfortunately, the most potent esters were still considerably cytotoxic, although mostly less than their parent salicylanilides.

Photomicronucleus assay of phototoxic and pseudophotoclastogenic chemicals in human keratinocyte NCTC2544 cells.

Photochemical genotoxicity was evaluated in human keratinocyte NCTC2544 cells. The cells were pre-treated with photogenotoxic or pseudophotoclastogenic chemicals and irradiated with a solar-simulator for 50min at a total UV dose of 5J/cm(2) or placed in the dark for the same period. After washing, the cells were cultured for 1.5-2 cell cycles with fresh culture medium. At the end of culturing, slide specimens were prepared and examined for micronucleus formation. 8-Methoxypsoralen, a photogenotoxic chemical, strongly induced micronucleated cells with UV irradiation but not under non-irradiation conditions. Therefore, NCTC2544 cells were subjected to further investigation to evaluate the possible photogenotoxicity of other chemicals. 6-Methylcoumarin, 3,3',4',5-tetrachlorosalicylanilide and protoporphyrin IX disodium salt, which are all known phototoxic substances, induced micronucleated cells with irradiation but not in the non-irradiation state. These phototoxic substances were confirmed to be photogenotoxic. Tetrabenzoporphine and 5-aminolevulinic acid, which are used for photodynamic therapy, showed phototoxicity. However, these chemicals did not induce micronucleated cells in the irradiated or non-irradiated state, suggesting a lack of photogenotoxicity. Among 3 pseudophotoclastogenic chemicals having no light absorbance at 290-700nm, neither cycloheximide nor disulfoton induced micronucleated cells with or without irradiation; zinc oxide induced micronucleated cells with irradiation and, to a lesser extent, without irradiation. Based on the results of the photogenotoxicity assays of these 9 chemicals, NCTC2544 cells are considered to be a suitable test system to evaluate the photogenotoxic potential of chemicals.

New antituberculotics originated from salicylanilides with promising in vitro activity against atypical mycobacterial strains.

A new series of 30 N-protected amino acid esters were prepared as a part of ongoing search for new anti-tuberculosis active salicylanilides. The esters possess high in vitro activity against Mycobacterium tuberculosis, Mycobacterium avium, and two strains of Mycobacterium kansasii, where one is an isolate from the patient, with MIC in the range 1-32 micromol/L for all tested strains. The prepared esters can be considered as prodrugs with better bio-availability and as more efficient transport forms through the mycobacterial cell membranes due to the higher lipophilicity. The experimental and calculated lipophilicity, stability, antituberculotic activity, cytotoxicity as well as the quantitative structure-activity relationships (QSARs) explored by the Intelligent Problem Solver (IPS) in Trajan Neural Network Simulator 6.0 are presented.

Synthesis of furo-salicylanilides and their heterocyclic derivatives with anticipated molluscicidal activity.

The synthesis of new furo-salicylanilides and their heterocyclic derivatives is described. Twenty-three compounds were screened for their molluscicidal activity against Biomphalaria alexandrina snails, the intermediate host of Schistosoma mansoni. Five of the tested compounds showed no activity, while eighteen compounds showed strong to moderate activity using bayluscide as a reference.

[Relation between chemical structure and antimycobacterial activity against atypical strains. XIII. Thiosalicylanilides]. / Vztahy mezi chemickou strukturou látek a jejich antimykobakteriální aktivitou vuci atypickým kmenum XIII. Thiosalicylanilidy.

On the basis of a preliminary study of antimycobacterial activity of thiobenzanilides a series of eight thiosalicylanilides have been prepared. Synthetized compounds have been examined in vitro against Mycobacterium tuberculosis, Mycobacterium kansasii, Mycobacterium avium and Mycobacterium fortuitum. All compounds have been found very active. The values of minimal inhibitory concentrations are summarized in Table 1. 3',4'-Salicylanilide was selected for the following research. The compound have been found inactive in vivo (on experimental murine tuberculosis).

In vitro culture of Oestrus ovis (Linné 1761) first instar larvae: its application to antiparasitic drug screening.

A culture medium in which 1st instar larvae of Oestrus ovis can survive for up to 2 months has been developed with Dulbecco's Modified Eagle's Medium (DMEM) pH 7.7, penicillin 100 U/ml, streptomycin 100 micrograms ml-1, gentamicin 10 micrograms ml-1 and foetal calf serum (50%) added. Larvae were incubated in flat plastic tissue culture bottles (3 ml of medium) in a 5% CO2 atmosphere at 37 degrees C in darkness. Subsequently an antiparasitic in vitro screening test was developed with moxidectin and closantel. These drugs were not as effective in vitro as in vivo. This might be due to the fact that they cause damage to parasites and host immune responses, then contribute to their death.

[The synthesis and study of the acute toxicity and anthelmintic activity of salicylanilides containing a quinoline residue]. / Sintez, izuchenie ostroi toksichnosti i protivogel'mintnoi aktivnosti salitsilanilinov, soderzhashchikh ostatok khinolina.

Salicylanilides containing quinoline moiety were synthesized and examined for acute toxicity and antinematodal activity. All the compounds were shown to possess a low toxicity. In the trials on a nematodal model (Aspiculuris tetraptera, white mice), 2 compounds--G-1570 and G-1575--were shown to be highly effective.

Inhibitory effect of melanin pigment on sensitization and elicitation of murine contact photosensitivity: mechanism of low responsiveness in C57BL/10 background mice.

We have shown that murine contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) is genetically controlled mainly by the major histocompatibility complex. The H-2b,d haplotypes are closely associated with high responders, whereas mice with the H-2k are non-responders. Irrespective of their H-2 haplotypes, the C57BL/10 (B10) background strains, including B10, B10.D2, B10.A, and B10.BR, possessing black fur color, were low or nonresponders in CPS to TCSA. In B10 mice, however, high-sensitivity responses were induced when subcutaneous inoculation of epidermal cells (ECs) photomodified in vitro with TCSA was used for both immunization and challenge, suggesting that the epicutaneous route for induction and elicitation is defective in B10 background mice. F1 mice obtained by crossing high-responder BALB/c and low-responder B10 mice, possessing agouti fur color, were non-responders of CPS. The magnitude of CPS in the F2 mice derived from F1 (BALB/c X B10) siblings varied from low to high. When these F2 mice were divided into five groups with regard to fur color, the magnitude of reaction was correlated with the fur color and there was inverse relationship between the magnitude of CPS and the amount of melanin pigment in earlobe ECs. Furthermore, the in vivo formation of TCSA-EC photoadducts was negatively correlated to the melanin amount in earlobes. These observations suggested that the failure in CPS of the B10 background mice stems from inability of in vivo photocoupling of TCSA to ECs, presumably due to absorption of ultraviolet radiation by melanin pigment.