Synthesis and biological evaluation of 12 novel (-)-camphene-based 1,3,4-thiadiazoles against Mycobacterium tuberculosis.

Aim: To evaluate the activity, cytotoxicity and efflux pumps inhibition of a series of 12 novels (-)-camphene-based 1,3,4-thiadiazoles (TDZs) against Mycobacterium tuberculosis (Mtb). Materials & methods: The minimum inhibitory concentration (MIC), cytotoxicity for three cell lines, ethidium bromide accumulation and checkerboard methods were carried out. Results: Compounds (6a, 6b, 6c, 6g, 6h and 6j) showed significant anti-Mtb activity (MIC 3.9-7.8 µg/ml) and no antagonism with anti-TB drugs already used in the TB treatment. Selectivity index (SI) was also determined, with values reaching 42.9 for H37Rv strain and 97.1 for clinical isolate. Five compounds also showed bacterial efflux pumps inhibition and one showed modulator effect with three drugs. Conclusion: These six TDZs should be considered as new scaffolds to develop anti-TB drugs.

In vitro genotoxicity of nitroimidazoles as a tool in the search of new trypanocidal agents.

BACKGROUND: Only benznidazole (Bnz) (1) and nifurtimox (Nfx) (2) are licensed for the treatment of Chagas disease although their safety and efficacy profile are far from ideal. Farmanguinhos from Fiocruz has developed seven nitroimidazole compounds (4-10) analogs of megazol (3). OBJECTIVES: To evaluate whether the genotoxic effect of 3 was abolished in the seven nitroimidazoles (4-10) analogs using the in vitro alkaline comet assay (CA) and the in vitro cytokinesis-block micronucleus assay (CBMN) in whole human blood cells (WHBC) and correlate this effect with their trypanocidal activity using bloodstream trypomastigote forms of Trypanosoma cruzi. METHODS: The toxicity of 3-10 to WHBC in the in vitro CA was determined using the fluorescein diacetate/ethidium bromide assay. DNA damage in the in vitro CA was evaluated according to tail size in four classes (0-3) and methyl methane-sulfonate (MMS) was used as a positive control. The cytotoxicity of 3-10 to WHBC in the CBMN was measured using the cytokinesis-block proliferation index and the replication index. The number of the micronucleate cells in 2,000 binucleate cells by experimental group was determined. Mitomycin C and N-deacetyl-N-methylcolchicine were used as positive controls. FINDINGS: Compound 3 showed a significant DNA strand break effect through the in vitro CA and highly significant clastogenic and/or aneugenic effect in the CBMN. Compounds 5, 6, 8, 9 and 10 showed negative results in the CBMN and positive results in the in vitro CA, while the inverse effect was observed for 4 and 7. MAIN CONCLUSIONS: Compound 10 was the most promising to proceed with the development as a drug candidate in the treatment of Chagas disease showing absence of chromosomal cytogenetic damage and high activity against T. cruzi, about two times higher than 3 and the clinical drug 1.

Megazol and its bioisostere 4H-1,2,4-triazole: comparing the trypanocidal, cytotoxic and genotoxic activities and their in vitro and in silico interactions with the Trypanosoma brucei nitroreductase enzyme

Megazol (7) is a 5-nitroimidazole that is highly active against Trypanosoma cruzi and Trypanosoma brucei, as well as drug-resistant forms of trypanosomiasis. Compound 7 is not used clinically due to its mutagenic and genotoxic properties, but has been largely used as a lead compound. Here, we compared the activity of 7 with its 4H-1,2,4-triazole bioisostere (8) in bloodstream forms of T. brucei and T. cruzi and evaluated their activation by T. brucei type I nitroreductase (TbNTR) enzyme. We also analysed the cytotoxic and genotoxic effects of these compounds in whole human blood using Comet and fluorescein diacetate/ethidium bromide assays. Although the only difference between 7 and 8 is the substitution of sulphur (in the thiadiazole in 7) for nitrogen (in the triazole in 8), the results indicated that 8 had poorer antiparasitic activity than 7 and was not genotoxic, whereas 7 presented this effect. The determination of Vmax indicated that although 8 was metabolised more rapidly than 7, it bounds to the TbNTR with better affinity, resulting in equivalent kcat/KM values. Docking assays of 7 and 8 performed within the active site of a homology model of the TbNTR indicating that 8 had greater affinity than 7.

Megazol and its bioisostere 4H-1,2,4-triazole: comparing the trypanocidal, cytotoxic and genotoxic activities and their in vitro and in silico interactions with the Trypanosoma brucei nitroreductase enzyme.

Megazol (7) is a 5-nitroimidazole that is highly active against Trypanosoma cruzi and Trypanosoma brucei, as well as drug-resistant forms of trypanosomiasis. Compound 7 is not used clinically due to its mutagenic and genotoxic properties, but has been largely used as a lead compound. Here, we compared the activity of 7 with its 4H-1,2,4-triazole bioisostere (8) in bloodstream forms of T. brucei and T. cruzi and evaluated their activation by T. brucei type I nitroreductase (TbNTR) enzyme. We also analysed the cytotoxic and genotoxic effects of these compounds in whole human blood using Comet and fluorescein diacetate/ethidium bromide assays. Although the only difference between 7 and 8 is the substitution of sulphur (in the thiadiazole in 7) for nitrogen (in the triazole in 8), the results indicated that 8 had poorer antiparasitic activity than 7 and was not genotoxic, whereas 7 presented this effect. The determination of Vmax indicated that although 8 was metabolised more rapidly than 7, it bounds to the TbNTR with better affinity, resulting in equivalent kcat/KM values. Docking assays of 7 and 8 performed within the active site of a homology model of the TbNTR indicating that 8 had greater affinity than 7.

Identification of thioredoxin glutathione reductase inhibitors that kill cestode and trematode parasites.

Parasitic flatworms are responsible for serious infectious diseases that affect humans as well as livestock animals in vast regions of the world. Yet, the drug armamentarium available for treatment of these infections is limited: praziquantel is the single drug currently available for 200 million people infected with Schistosoma spp. and there is justified concern about emergence of drug resistance. Thioredoxin glutathione reductase (TGR) is an essential core enzyme for redox homeostasis in flatworm parasites. In this work, we searched for flatworm TGR inhibitors testing compounds belonging to various families known to inhibit thioredoxin reductase or TGR and also additional electrophilic compounds. Several furoxans and one thiadiazole potently inhibited TGRs from both classes of parasitic flatworms: cestoda (tapeworms) and trematoda (flukes), while several benzofuroxans and a quinoxaline moderately inhibited TGRs. Remarkably, five active compounds from diverse families possessed a phenylsulfonyl group, strongly suggesting that this moiety is a new pharmacophore. The most active inhibitors were further characterized and displayed slow and nearly irreversible binding to TGR. These compounds efficiently killed Echinococcus granulosus larval worms and Fasciola hepatica newly excysted juveniles in vitro at a 20 µM concentration. Our results support the concept that the redox metabolism of flatworm parasites is precarious and particularly susceptible to destabilization, show that furoxans can be used to target both flukes and tapeworms, and identified phenylsulfonyl as a new drug-hit moiety for both classes of flatworm parasites.

Metabolism of the mesoionic compound (MI-D) by mouse liver microsome, detection of its metabolite in vivo, and acute toxicity in mice.

The mesoionic derivative 4-phenyl-5-[4-nitrocinnamoyl]-1,3,4-thiadiazolyl-2-phenylamine chloride (MI-D) has antitumoral and anti-inflammatory effects. In this study, we present aspects of its metabolism and toxicity in mice. MI-D was metabolized in vitro by liver microsome, generating a main product with a much shorter retention time than MI-D in high-performance liquid chromatography (HPLC) analysis but with a spectrum similar to that of the original molecule. Mass spectrometry with electrospray ionization in positive mode analysis of the purified compound by HPLC indicated that the product of metabolism has four additional hydroxyl groups (m/z = 465) compared with MI-D (m/z = 401). The HPLC analyses of plasma and urine samples from mice treated with MI-D showed the presence of the metabolite product. The kinetic parameters K(m) (19.5 +/- 4.5 microM) and V(max) [1.5 +/- 0.4 units of fluorescence/(100 microg of microsomal protein/mL/s)] were estimated, confirming the metabolism of MI-D and indicating that the reaction follows Michaelis-Menten kinetics. Acute toxicity was established on the basis of an estimation of mean lethal dose (LD-50; 181.2 mg/kg) and histopathological analysis of animals that survived the LD-50 test. Abdominal adhesions, inflammatory foci, and formation of granulomas were observed. Altogether, the results contribute to the advancement of research in support of MI-D as a future chemotherapeutic drug.

Leishmanicidal activity of new megazol derivatives.

A series of thirteen new megazol derivatives, designed exploring the molecular hybridization approach between megazol (3) and heterocombretastatins (2), was synthesized. These new compounds were tested for in vitro antiparasitic activity upon axenic amastigotes of Leishmania donovani. Biological results led us to identify a new potent megazol derivative (4g), which presents an IC(50) = 0.081microg/mL, more active tham the reference drug miltefosine (IC(50) = 0.131microg/mL).

Assessment of cytotoxic and cytogenetic effects of a 1,2,5-thiadiazole derivative on CHO-K1 cells. Its application as corrosion inhibitor.

This work focuses on the possible use of phenanthro[9,10-c]-1,2,5-thiadiazole 1,1-dioxide (TDZ) as a harmless corrosion inhibitor. TDZ range-dose providing minimum adverse effects to the environment and human health, with satisfactory corrosion-inhibiting properties was evaluated. Cytotoxicity and genotoxicity of TDZ at 0.57-12.50 microM concentration range were tested by neutral red, chromosomal aberrations, mitotic index, and colony formation assays. Results showed a significant increase of chromatid-type aberrations for the highest concentration of TDZ assayed (12.50 microM). Additionally, a reduction in the proliferative rate for lower concentrations was detected by the MI assay. We concluded that TDZ should be used at concentrations lower than 1.16 microM. Corrosion assays performed showed good inhibition effect (ca. 50%) at low (0.65 microM) TDZ concentration. Consequently, our results indicated that TDZ induced a time- and dose-dependent genotoxic and cytotoxic response on CHO-K1 cells. Short assays should be complemented with long exposure tests to simulate chronic contact with TDZ since lower threshold levels may be found for shorter exposures and a wrong safety range could be determined.

Antileishmanial activity of 1,3,4-thiadiazolium-2-aminide in mice infected with Leishmania amazonensis.

The efficacy of two mesoionic derivatives (MI-H-H and MI-4-OCH(3)) was evaluated in CBA/J mice infected with Leishmania amazonensis. Treatment with these compounds demonstrated that the MI-4-OCH(3) derivative and the reference drug meglumine antimoniate (Glucantime) presented significant activity relative to an untreated control. No apparent hepatic or renal toxicity due to these mesoionic compounds was found.

Advanced treatment of benzothiazole contaminated waters: comparison of O3, AC, and O3/AC processes.

Benzothiazole (BT) is a toxic and poorly biodegradable contaminant, usually found in wastewater from rubber related applications. This compound could be effectively eliminated using advanced treatment processes. This paper compares experimental results on detoxification systems based on ozone oxidation, activated carbon adsorption, and simultaneous adsorption-oxidation using ozone in the presence of activated carbon. The effect of pH (2-11), and the presence of radical scavengers (tert-butyl alcohol and sodium carbonate) on process rates and removal efficiencies are assessed at laboratory scale. The experimental system consisted of a 1 L differential circular flow reactor and an ozone generator rated at 5 g O3/h. Results show that ozone oxidation combined with activated carbon adsorption increases the overall BT oxidation rate with respect to the ozonation process and activated carbon adsorption. In the presence of free radical scavenger, only a 44% reduction in BT removal rate is observed in the simultaneous treatment, as compared with 72% when ozonation treatment is used, suggesting that BT oxidation reactions mainly take place on the activated carbon surface.

CL 64,855, a potent anti-Trypanosoma cruzi drug, is also mutagenic in the Salmonella/microsome assay.

The nitroimidazole-tiadiazole derivative CL 64,855 (2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazole, a potent anti-trypanosomal drug, was assayed in a short-term bacterial mutagenicity test with Salmonella typhimurium strains TA 98, TA 100 and TA 102. Results indicate that CL 64,855 is a potent frameshift mutagen detected by strains TA 98 and TA 102. CL 64,855 was able to revert the indicators strains at concentrations as low as 0.1 micrograms/plate. Metabolic activation experiments with rat liver microsomal fractions did not increase the mutagenic action of CL 64,855.