Antifungal effects of a 1,3,4-thiadiazole derivative determined by cytochemical and vibrational spectroscopic studies

Compounds belonging to the group of 5-substituted 4-(1,3,4-thiadiazol-2-yl) benzene-1,3-diols exhibit a broad spectrum of biological activity, including antibacterial, antifungal, and anticancer properties. The mechanism of the antifungal activity of compounds from this group has not been described to date. Among the large group of 5-substituted 4-(1,3,4-thiadiazol-2-yl) benzene-1,3-diol derivatives, the compound 4-(5-methyl-1,3,4-thiadiazole-2-yl) benzene-1,3-diol, abbreviated as C1, was revealed to be one of the most active agents against pathogenic fungi, simultaneously with the lowest toxicity to human cells. The C1 compound is a potent antifungal agent against different Candida species, including isolates resistant to azoles, and molds, with MIC100 values ranging from 8 to 96 μg/ml. The antifungal activity of the C1 compound involves disruption of the cell wall biogenesis, as evidenced by the inability of cells treated with C1 to maintain their characteristic cell shape, increase in size, form giant cells and flocculate. C1-treated cells were also unable to withstand internal turgor pressure causing protoplast material to leak out, exhibited reduced osmotic resistance and formed buds that were not covered with chitin. Disturbances in the chitin septum in the neck region of budding cells was observed, as well as an uneven distribution of chitin and β(1→3) glucan, and increased sensitivity to substances interacting with wall polymerization. The ATR-FTIR spectral shifts in cell walls extracted from C. albicans cells treated with the C1 compound suggested weakened interactions between the molecules of β(1→3) glucans and β(1→6) glucans, which may be the cause of impaired cell wall integrity. Significant spectral changes in the C1-treated cells were also observed in bands characteristic for chitin. The C1 compound did not affect the ergosterol content in Candida cells. Given the low cytotoxicity of the C1 compound to normal human dermal fibroblasts (NHDF), it is possible to use this compound as a therapeutic agent in the treatment of surface and gastrointestinal tract mycoses.

Synergistic antifungal interactions of amphotericin B with 4-(5-methyl-1,3,4-thiadiazole-2-yl) benzene-1,3-diol

Amphotericin B (AmB) is a very potent antifungal drug with very rare resistance among clinical isolates. Treatment with the AmB formulations available currently is associated with severe side effects. A promising strategy to minimize the toxicity of AmB is reducing its dose by combination therapy with other antifungals, showing synergistic interactions. Therefore, substances that display synergistic interactions with AmB are still being searched for. Screening tests carried out on several dozen of synthetic 1,3,4-thiadiazole derivatives allowed selection of a compound called 4-(5-methyl-1,3,4-thiadiazole-2-yl) benzene-1,3-diol (abbreviated as C1), which shows strong synergistic interaction with AmB and low toxicity towards human cells. The aim of the present study was to investigate the type of in vitro antifungal interactions of the C1 compound with AmB against fungal clinical isolates differing in susceptibility. The results presented in the present paper indicate that the C1 derivative shows strong synergistic interaction with AmB, which allows the use of a dozen to several dozen times lower AmB concentration necessary for 100% inhibition of the growth of pathogenic fungi in vitro. Synergistic interactions were noted for all tested strains, including strains with reduced sensitivity to AmB and azole-resistant isolates. These observations give hope for the possibility of application of the AmB - C1 combinatory therapy in the treatment of fungal infections.

[2-(2,4-Dihydroxyphenyl)-1,3,4-thiadiazole analogues: antifungal activity in vitro against Candida species]

The antifungal activity in vitro of the newly synthesized and previously reported compounds of 5-substituted 2-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole series was evaluated. Their structures were confirmed by elemental analyses and IR, 1H and 13C NMR and mass spectra. The azole-resistant clinical isolates of C. albicans and nonalbicans Candida spp. were used in the antifungal tests. Some compounds exhibit higher activities than the comparatively studied antifungal drugs. 2-Amino-1,3,4-thiadiazole derivatives exhibited higher (than other analogues) antifungal effects against Candida nonalbicans spp. than against C. alhicans. Derivatives with strong antifungal activity have a narrow range of lipophilicity values determined by the Villar approach.

Evaluation of electronic, lipophilic and membrane affinity effects on antiproliferative activity of 5-substituted-2-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles against various human cancer cells

The QSAR studies of 5-substituted-2-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles set of antiproliferative activity against human cancer cell lines have been performed. Electronic properties of compounds were estimated by the Hartree-Fock method at 6-31G** level. Lipophilicity and membrane affinity parameters were determined by the chromatographic methods RP-8 OPLC and IAM HPLC, respectively. Mono- and multivariable regression analyses were performed. The principle factor for determination of activity of compounds is partial charge of nitrogen (q(N3), q(N4)) and carbon (q(C5)) atoms of the 1,3,4-thiadiazole ring. Biological effect is also connected with molar refractivity (CMR) and lipophilicity of derivatives obtained by RP-8 chromatography. The analysis of the QSAR equations for individual cell lines indicates both similarities and differences of electron, steric factors and hydrophobic-hydrophilic character of the analogues of the tested set affecting the antiproliferative activity.

Synthesis and antiproliferative activity of some 5-substituted 2-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles

A series of new 5-substituted 2-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles has been synthesised and evaluated for their antiproliferative activity. The compounds were prepared by the reaction of the sulphinylbis(2,4-dihydroxythiobenzoyl) (STB) wit hydrazides or carbazates. The panel substitution included alkyl, alkoxy, aryl and heteroaryl derivatives. The structures of compounds were identified from the elemental, IR, (1)H NMR and MS spectra analysis. The highest antiproliferative activity against the cells of human cancer lines for 2-(2,4-dihydroxyphenyl)-5-(4-methoxybenzyloxy)-1,3,4-thiadiazole was found with ID(50) values comparable (HCV29T and SW707) or significantly lower (T47D) than for cisplatin applied as the reference compound. The influence of 5-substiution type of 2-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles on antiproliferative activity is discussed.