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A group of 5-methylsalicylaldehyde thiosemicarbazone derivatives (HMTs) bearing different lipophilic and steric substituents attached at the 3-position of cresol ring were synthesized and investigated as mushroom tyrosinase (TYR) inhibitors. The ability of HMTs to inhibit the diphenolase activity of TYR was evaluated with L-DOPA as substrate by determining IC50 values in relation to their structure modifications. HMTs displayed distinct inhibitory competencies towards TYR activity with IC50 values in the range of 1.02-143.56 µM. A close correlation between their inhibition potency and both lipophilicity and molecular size was observed. The inhibitory effect of the hydroxyethyl-containing derivatives was much higher than the hydroxyethyl-free ones overall. Among them, HMT-NBO exhibited the most potent effect with IC50 of 5.85 µM, which was nearly 25-fold and 3.8-fold lower than its parent HMT-NBE and the control kojic acid, respectively. The hydroxyethyl clearly benefited the improvement of the inhibitory competences and acted as a regulating group of lipophilicity of the inhibitors. The kinetic analyses showed that HMTs were reversible and mixed type inhibitors against mushroom TYR. The inhibition mechanism was studied by means of fluorescence spectroscopy, FT-IR, ESI-MS and molecular docking analysis. The results indicated that the observed inhibitory effect of HMTs was accomplished by acting on the amino acid residues rather than by chelating the centre copper ions of TYR. Each of HMTs can insert the hydrophobic pocket and interact with the residues of TYR through Van der Waals forces and hydrogen bonds, with additional electrostatic interactions for HMT-NEE and HMT-NEO further strengthening the affinity. Meanwhile, the inhibitors were observed to bind with L-DOPA or/and L-DOPAquinone forming 1:1 stoichiometric complexes, probably exerting indirect inhibition against TYR activity.

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Metal chelation is generally considered as a promising antifungal approach but its specific mechanisms are unclear. Here, we identify 13 thiosemicarbazone derivatives that exert broad-spectrum antifungal activity with potency comparable or superior to that of fluconazole in vitro by screening a small compound library comprising 89 thiosemicarbazone derivatives as iron chelators. Among the hits, 19ak exhibits minimal cytotoxicity and potent activity against either azole-sensitive or azole-resistant fungal pathogens. Mechanism investigations reveal that 19ak inhibits mitochondrial respiration mainly by retarding mitochondrial respiratory chain complex I activity through iron chelation, and further reduces mitochondrial membrane potential and ATP synthesis in Candida albicans. In addition, 19ak inhibits fungal ribosome biogenesis mainly by disrupting intracellular zinc homeostasis. 19ak also stimulates the activities of antioxidant enzymes and decreases reactive oxygen species formation in C. albicans, resulting in an increase in detrimental intracellular reductive stress. However, 19ak has minor effects on mammalian cells in depleting intracellular iron and zinc. Moreover, 19ak exhibits low capacity to induce drug resistance and in vivo efficacy in a Galleria mellonella infection model. These findings uncover retarded fungal mitochondrial respiration and ribosome biogenesis as downstream effects of disruption of iron and zinc homeostasis in C. albicans and provide a basis for the thiosemicarbazone 19ak in antifungal application. IMPORTANCE The increasing incidence of fungal infections and resistance to existing antifungals call for the development of broad-spectrum antifungals with novel mechanisms of action. In this study, we demonstrate that a thiosemicarbazone derivative 19ak selectively inhibits mitochondrial respiration mainly by retarding mitochondrial respiratory chain complex I activity through iron chelation and inhibits ribosome biogenesis mainly by disrupting intracellular zinc homeostasis in C. albicans. In addition, 19ak exhibits low capacity to induce fungal resistance, minimal cytotoxicity, and in vivo antifungal efficacy. This study provides the basis of thiosemicarbazone derivative 19ak as a metal chelator for the treatment of fungal infections.

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Mycobacterium tuberculosis (Mtb) is an infectious disease that affects nearly 9.6 million people every year. Metals are important determinants of growth and pathogenicity of mycobacterium. In the present study, we have analyzed protein-protein interaction networks belonging to the iron, sulfur and molybdenum metabolism of Mycobacterium. Our analysis has identified some of the important target proteins one among them being irtA. Iron taken up by siderophores from the host is transported to irtA through which iron enters Mycobacterium. Thus, irtA plays a major role as an iron transporter in Mycobacterium. As irtA protein structure was not solved experimentally, we have predicted 3D structure of irtA. After successful model evaluation, we have identified thiosemicarbazones as possible drug candidates for irtA. Henceforth, we have designed five analogues of thiosemicarbazones and tested in silico for their efficacy against irtA using molecular docking, among them analogue 1 showed a very good efficacy.Communicated by Ramaswamy H. Sarma.

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Seven isatin-thiosemicarbazone analogues bearing different substituents (R) attached at C-5 of the indoline ring, TSC-ISA-R (R = -H, -CH3, -OCH3, -OCF3, -F, -Cl and -NO2), were synthesized and evaluated as inhibitors of mushroom tyrosinase (TYR). The inhibitory behaviour and performance of TSC-ISA-R were investigated spectroscopically in relation to the substituent modifications through examining their inhibition against the diphenolase activity of TYR using L-DOPA as a substrate. The IC50 values of TSC-ISA-R were determined to be in the range of 81-209 µM. The kinetic analysis showed that TSC-ISA-R were reversible and mixed type inhibitors. Three potential non-covalent interactions rather than complexation including the binding of TSC-ISA-R with free TYR, TYR-L-DOPA complex, and with substrate L-DOPA were found to be involved in the inhibition. The substituent modifications affected these interactions by varying the characters of the resulting TSC-ISA-R in different degrees. The thiosemicarbazido moiety of each TSC-ISA-R contributed predominantly to the inhibition, and the isatin moiety seemed to play a regulatory role in the binding of TSC-ISA-R to the target molecules. The results of theoretical calculations using density functional theory method indicated a different effect of -R on the electron distribution in HOMO of TSC-ISA-R. The LUMO-HOMO energy gap of TSC-ISA-R almost accords with the trend of their experimental inhibition potency.

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New Delhi metallo-ß-lactamase-1 (NDM-1) is capable of hydrolyzing nearly all ß-lactam antibiotics, posing an emerging threat to public health. There are currently less effective treatment options for treating NDM-1 positive "superbug", and no promising NDM-1 inhibitors were used in clinical practice. In this study, structure-activity relationship based on thiosemicarbazone derivatives was systematically characterized and their potential activities combined with meropenem (MEM) were evaluated. Compounds 19bg and 19bh exhibited excellent activity against 10 NDM-positive isolate clinical isolates in reversing MEM resistance. Further studies demonstrated compounds 19bg and 19bh were uncompetitive NDM-1 inhibitors with Ki = 0.63 and 0.44 µmol/L, respectively. Molecular docking speculated that compounds 19bg and 19bh were most likely to bind in the allosteric pocket which would affect the catalytic effect of NDM-1 on the substrate meropenem. Toxicity evaluation experiment showed that no hemolysis activities even at concentrations of 1000 mg/mL against red blood cells. In vivo experimental results showed combination of MEM and compound 19bh was markedly effective in treating infections caused by NDM-1 positive strain and prolonging the survival time of sepsis mice. Our finding showed that compound 19bh might be a promising lead in developing new inhibitor to treat NDM-1 producing superbug.

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BACKGROUND: Breast cancer, the most commonly diagnosed malignancy in women, accounts for the highest cancer-related deaths worldwide. Triple negative breast cancer (TNBC), lacking the expression of estrogen, progesterone and HER2 receptors, has an aggressive clinical phenotype and is susceptible to chemotherapy but not to hormonal or targeted immunotherapy. In an attempt to identify potent and selective anti-TNBC agents, a set of thiosemicarbazone derivatives were screened for their cytotoxic activity against MDA-MB 231 breast cancer cell line. METHODS: MTT assay was used to examine cell viability. P53 phosphorylation status, poly (ADP-ribose) polymerase (PARP) cleavage as well as Bcl2 and Bax protein levels were assessed by Western blot. Quantitative Real Time-PCR was carried out to characterize miRNAs expression levels. RESULTS: Combining Cisplatin + thiosemicarbazone compound 4 showed potent anti-TNBC potential. Cisplatin + compound 4 significantly enhanced p53 phosphorylation, induced Bax amount, reduced Bcl2 protein levels, enhanced PARP cleavage and modulated miRNAs expression profile in TNBCs, with a particular overexpression of miR-125a-5p and miR-181a-5p. Intriguingly, miR-125a-5p and miR-181a-5p could significantly downregulate BCL2 expression by binding to their target sites in the 3'UTR. CONCLUSIONS: Collectively, our results demonstrate an anti-TNBC activity of Cisplatin + thiosemicarbazone compound 4 combination mediated via induction of apoptosis.

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The present work aimed to carry out in vitro biological assays of indol-3-yl derivatives thiosemicarbazones (2a-e) and 4-thiazolidinones (3a-d) against juvenile and adult worms of S. mansoni, as well as the in silico determination of pharmacokinetic parameters for the prediction of the oral bioavailability of these derivatives. All compounds were initially screened at a concentration of 200 µM against S. mansoni adult worms and the results evidenced the good activity of compounds 2b, 2d and 3b, which caused 100% mortality after 24, 48 and 72 h, respectively. Subsequent studies with these same compounds revealed that compound 2b was able to reduce the viability of the parasites by 85% and 83% at concentrations of 200 and 100 µM, respectively. In relation to the juvenile worms, all compounds (2b, 2d and 3b) were able to cause mortality, but compound 2b demonstrated better activity causing 100% mortality in 48 h. Additionally, it was possible to observe reduction in the viability of juvenile worms of 85%, 81% and 64% at concentrations of 200, 100 and 50 µM, respectively. Several ultrastructural damages were observed when adult and juvenile S. mansoni worms were exposed to compound 2b (200 µM) that was characterized by extensive destruction by the integument, which may justify the mortality rate of cultured parasites. In the DNA interaction assay, fragmentation of the genetic material of adult worms when treated with compound 2b (200 µM) was evidenced, indicating the apoptosis process as mechanism of parasite death. Regarding pharmacokinetic properties, all derivatives are according to the required parameters, predicting good oral bioavailability for the studied compounds. The results presented in this study reveal the good activity of compound 2b in both adult and juvenile worms of S. mansoni, pointing this compound as promising in the development of further studies on schistosomicidal activity.

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A series of novel 2-isocamphanyl thiosemicarbazone derivatives were synthesized and characterized by 1 H NMR, 13 C NMR, and HRMS. In in vitro anticancer activity, most derivatives showed considerable cytotoxic activity against four cancer cell lines (RPMI-8226, A549, MDA-MB-231, and HepG2 cancer cells) and showed low toxicity against human gastric mucosal cells (GES-1). Among them, compound 4h exhibited excellent antitumor activity against the tested cancer cells with IC50 values of 0.4, 1.1, 1.6, and 1.7 µM for MDA-MB-231, RPMI-8226, A549, and HepG2, respectively. Further, mechanism studies indicated that compound 4h induced apoptosis in MDA-MB-231 cells through enhancing reactive oxygen species levels, inducing mitochondrial membrane potential decrease, and influencing the expression of Bax, Bcl-2, caspase-3, and caspase-9.

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Isatin, thiosemicarbazone and their derivatives have been widely used in biological applications such as antimicrobial, antiviral and anticancer therapies. Herein, eight isatin and thiosemicarbazone derivative compounds were re-synthesized and evaluated for DNA binding analysis including DNA protection studies using plasmid DNA (pUC19) and DNA interaction experiments using calf thymus DNA (CT-DNA). All compounds were also utilized in vitro assay to assess the antimicrobial activity of compounds against different pathogenic bacterial strains. All isatin and thiosemicarbazone derivative compounds exhibited DNA protection activity which ranged from 23.5 to 59.5%. Among them, I3-(N-2-MP)-TSC had the greatest DNA protective activity. For DNA binding analysis, all compounds had the same constant concentration (40 µM), which interacts with CT-DNA. It was also observed that DNA interactions gave a high intrinsic binding constant (Kb = 1.72 × 104 M-1-9.73 × 105 M-1). Besides, several derivatives of isatin thiosemicarbazone exhibited significant and selective antibacterial activity with low concentration. These compounds primarily affected Gram-positive bacteria, but were not effective against P. vulgaris and E. coli. The Gram-positive methicillin-resistant S. aureus ATCC 43300 (MRSA) was the most influenced strain by these compounds. It was found that methyphenyl group at isatin was essential for its antibacterial activity for MRSA.

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Three structurally similar aromatic heterocyclic compounds 2-thiophenecarboxaldehyde (a), 2-furaldehyde (b), 2-pyrrolecarboxaldehyde (c) were chosen and a series of their thiosemicarbazone derivatives(1a-3a, 1b-3b and 1c-3c) were synthesized to evaluate their biological activities as mushroom tyrosinase inhibitors. The inhibitory effects of these compounds on tyrosinase were investigated by using spectrofluorimetry, (1)H NMR titration and molecular docking techniques. From the results of fluorescence spectrum and (1)H NMR titration, it was found that forming complexes between the sulfur atom from thiourea and copper ion of enzyme center may play a key role for inhibition activity. Moreover, investigation of (1)H NMR spectra further revealed that formation of hydrogen bond between inhibitor and enzyme may be helpful to above complexes formation. The results were well coincident with the suggestion of molecular docking and obviously showed that 2-thiophone N(4)-thiosemicarbazone (1a), 2-furfuran N(4)-thiosemicarbazone (1b) and 2-pyrrole N(4)-thiosemicarbazone (1c) are potential inhibitors which deserves further investigation.

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