Antimelanoma activity of 1,3,4-thiadiazolium mesoionics: a structure–activity relationship study

The mesoionic compound MI-D changes energy metabolism and induces apoptosis in T98G glioma cells

The mesoionic compound 4-phenyl-5-(4-nitro-cinnamoyl)-1,3,4-thiadiazolium-2-phenylamine chloride (MI-D) impairs mitochondrial oxidative phosphorylation and has a significant antitumour effect against hepatocarcinoma and melanoma. This study evaluated the cytotoxic effect of MI-D on T98G glioblastoma cells and investigated whether the impairment of oxidative phosphorylation promoted by MI-D is relevant to its cytotoxic effect. The effects of MI-D on T98G cells cultured in high glucose Dulbecco's modified Eagle's medium (DMEM) HG (glycolysis-dependent) and galactose plus glutamine-supplemented Dulbecco's modified Eagle's medium (DMEM) GAL (oxidative phosphorylation-dependent) were compared. T98G cells grown in DMEM GAL medium exhibited higher respiration rates and citrate synthase activity and lower lactate levels, confirming the metabolic shift to oxidative phosphorylation in these cells. MI-D significantly decreased the cell viability in a dose-dependent manner in both media; however, T98G cells cultured in DMEM GAL medium were more susceptible. The mesoionic significantly inhibited mitochondrial oxidative phosphorylation of glioma cells in both media. At the same time, lactate levels were not altered, indicating an absence of compensatory glycolysis activation. Additionally, MI-D increased the citrate synthase activity of cells in both media, which in DMEM HG-cultivated cells was followed by citrate accumulation. Apoptosis dependent on caspase-3 mediated the toxicity of MI-D on T98G cells. The higher susceptibility of glioma cells cultured in DMEM GAL medium to MI-D indicates that the impairment of mitochondrial functions is involved in mesoionic cytotoxicity. The results of this study indicate the potential use of MI-D for glioblastoma treatment.

The toxicity of 1,3,4-thiadiazolium mesoionic derivatives on hepatocarcinoma cells (HepG2) is associated with mitochondrial dysfunction

Mesoionic compounds, 4-phenyl-5-(4-X-cinnamoyl)-1,3,4-thiadiazolium-2-phenylamine chloride derivatives (MI-J: X = OH; MI-D: X = NO₂), possess significant antitumor and cytotoxic effects on several cancer cells. In this work, we evaluated the cytotoxicity of MI-J and MI-D on human hepatocellular carcinoma (HepG2 cells) grown in either high glucose (HG) or galactose medium (GAL) to clarify whether the effects of mesoionics on mitochondrial bioenergetics are associated with their cytotoxicity in these cells. MI-J and MI-D (5-50 μM) decreased the viability of HepG2 cells in a dose- and time-dependent manner, as assessed by MTT, LDH release and dye with crystal violet assays. Both compounds at lower (5 μM) and intermediate (25 μM) concentrations were more toxic to cells grown in GAL medium. MI-J inhibited the basal state of respiration in HepG2 cells cultured in HG and GAL media; however, in GAL medium, this effect occurred at the lowest concentration (5 μM). A leak-state stimulus was observed only after incubation with MI-J (5 μM) for GAL medium. MI-D stimulated and inhibited the leak state in cells grown in HG medium at concentrations of 5 μM and 25 μM, respectively. In cells cultured in GAL medium, respiration was strongly inhibited by MI-D at the highest concentration (25 μM). In contrast, at 5 μM, the mesoionic inhibited the basal and uncoupled states at 30% and 50%, respectively. The inhibition of the basal state by MI-J and MI-D was consistent with the increase in lactate levels in both media, which was higher for the GAL medium. Both mesoionics slightly decreased pyruvate levels only in cells cultured in GAL medium. Additionally, MI-J (25 μM) reduced the ATP amount in cells cultured in both media, while MI-D (25 μM) promoted a reduction only in cells grown in GAL medium. Our results show that MI-J and MI-D depress mitochondrial respiration and consequently change metabolism and reduce ATP levels, effects associated with their toxicity in hepatocarcinoma cells.

DFT Study on the Electronic Properties, Spectroscopic Profile, and Biological Activity of 2-Amino-5-trifluoromethyl-1,3,4-thiadiazole with Anticancer Properties

Extensive investigation on the molecular and electronic structure of 2-amino-5-trifluoromethyl-1,3,4-thiadiazole in the ground state and in the first excited state has been performed. The energy barrier corresponding to the conversion between imino and amino tautomers has been calculated, which indicates the existence of amino tautomer in solid state for the title compound. The FT-Raman and FT-IR spectra were recorded and compared with theoretical vibrational wavenumbers, and a good coherence has been observed. The MESP map, dipole moment, polarizability, and hyperpolarizability have been calculated to comprehend the properties of the title molecule. High polarizability value estimation of the title compound may enhance its bioactivity. Natural bonding orbital analysis has been done on monomer and dimer to investigate the charge delocalization and strength of hydrogen bonding, respectively. Strong hydrogen bonding interaction energies of 17.09/17.49 kcal mol^-1 have been calculated at the B3LYP/M06-2X functional. The UV-vis spectrum was recorded and related to the theoretical spectrum. The title compound was biologically examined for anticancer activity by studying the cytotoxic performance against two human cancer cell lines (A549 and HeLa) along with the molecular docking simulation. Both molecular docking and cytotoxic performance against cancer cell lines show positive outcomes, and the title compound appears to be a promising anticancer agent.

Cytotoxic Activity of the Mesoionic Compound MIH 2.4Bl in Breast Cancer Cell Lines

In this work, we report the synthesis of a new 1,3-thiazolium-5-thiolate derivative of a mesoionic compound (MIH 2.4Bl) and the characterization of its selective cytotoxicity on a panel of breast cancer cells lines. The cytotoxic effect of MIH 2.4Bl on breast cancer cell lines was determined by XTT and crystal violet assays, flow cytometry analysis, electron microscopy characterization, and terminal deoxynucleotidyl transferase (TdT) deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) apoptosis assays. As determined using XTT cell growth and survival assays, MIH 2.4Bl exhibited growth inhibition activity on most breast cancer cell lines tested, compared with normal human mammary epithelial cells. Three breast cancer cell lines (MCF-7, T-47D, and ZR-75-1) showed a more potent sensitivity index to growth inhibition by MIH 2.4Bl than the other breast cancer cell lines. Interestingly, these 3 cell lines were derived from tumors of Luminal A origin and have ER (estrogen receptor), PR (progesterone receptor), and HER2 (human epidermal growth factor receptor 2) positive expression. Additional analysis of cytotoxicity mediated by MIH 2.4Bl was performed using the MCF-7 cell line. MCF-7 cells displayed both time- and dose-dependent decreases in cell growth and survival, with a maximum cytotoxic effect observed at 72 and 96 hours. The MCF-7 cells were also characterized for cell cycle changes upon treatment with MIH 2.4Bl. Using flow cytometry analysis of cell cycle distribution, a treatment-dependent effect was observed; treatment of cells with MIH 2.4Bl increased the G2/M population to 34.2% compared with 0.1% in untreated (control) cells. Ultrastructural analysis of MFC-7 cells treated with MIH 2.4Bl at 2 different concentrations (37.5 and 75 μM) was performed by transmission electron microscopy. Cells treated with 37.5 μM MIH 2.4Bl showed morphologic changes beginning at 6 hours after treatment, while cells treated with 75 μM showed changes beginning at 3 hours after treatment. These changes were characterized by an alteration of nuclear morphology and mitochondrial degeneration consistent with apoptotic cell death. Results of a TUNEL assay performed on cells treated for 96 hours with MIH 2.4Bl supported the observation of apoptosis. Together, these results suggest that MIH 2.4Bl is a promising candidate for treating breast cancer and support further in vitro and in vivo investigation.

Synthetic (E)-3-Phenyl-5-(phenylamino)-2-styryl-1,3,4-thiadiazol-3-ium Chloride Derivatives as Promising Chemotherapy Agents on Cell Lines Infected with HTLV-1

Synthesis of four compounds belonging to mesoionic class, (E)-3-phenyl-5-(phenylamino)-2-styryl-1,3,4-thiadiazol-3-ium chloride derivatives (5a–d) and their biological evaluation against MT2 and C92 cell lines infected with human T-cell lymphotropic virus type-1 (HTLV-1), which causes adult T-cell leukemia/lymphoma (ATLL), and non-infected cell lines (Jurkat) are reported. The compounds were obtained by convergent synthesis under microwave irradiation and the cytotoxicity was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Results showed IC₅₀ values of all compounds in the range of 1.51–7.70 μM in HTLV-1-infected and non-infected cells. Furthermore, it was observed that 5b could induce necrosis after 24 h for Jurkat and MT2 cell lines. The experimental (fluorimetric method) and theoretical (molecular docking) results suggested that the mechanism of action for 5b could be related to its capacity to intercalate into DNA. Moreover, the preliminary pharmacokinetic profile of the studied compounds (5a–d) was obtained through human serum albumin (HSA) binding affinity using multiple spectroscopic techniques (circular dichroism, steady-state and time-resolved fluorescence), zeta potential and molecular docking calculations. The interaction HSA:5a–d is spontaneous and moderate (K_a ~ 10⁴ M⁻¹) via a ground-state association, without significantly perturbing both the secondary and surface structures of the albumin in the subdomain IIA (site I), indicating feasible biodistribution in the human bloodstream.

Synthesis and Anticancer Activity of Thiadiazole Containing Thiourea, Benzothiazole and Imidazo[2,1-b][1,3,4]thiadiazole Scaffolds

BACKGROUND

A great array of nitrogen-containing heterocyclic rings were being extensively explored for their functional versatility in the field of medicine, especially in anticancer research. 1,3,4- thiadiazole is one of such heterocyclic rings with promising anticancer activity against several cancer cell lines, inhibiting diverse biological targets.

INTRODUCTION

The 1,3,4-thiadiazole, when equipped with other heterocyclic scaffolds, has displayed enhanced anticancer properties. The thiourea, benzothiazole, imidazo[2,1,b][1,3,4]-thiadiazoles are such potential scaffolds with promising anticancer activity.

METHODS

A new series of 5-substituted-1,3,4-thiadiazoles linked with phenyl thiourea, benzothiazole and 2,6-disubstituted imidazo[2,1-b][1,3,4]thiadiazole derivatives were synthesized and tested for invitro anticancer activity on various cancer cell lines.

RESULTS

The National Cancer Institute's preliminary anticancer screening results showed compounds 4b and 5b having potent antileukemic activity. Compound 4b selectively showed 32 percent lethality on Human Leukemia-60 cell line. The docking studies of the derivatives on aromatase enzyme (Protein Data Bank: 3S7S) have shown reversible interactions at the active site with good docking scores comparable to Letrozole and Exemestane. Furthermore, the selected derivatives were tested for anticancer activity on HeLa cell line based on the molecular docking studies.

CONCLUSION

Compounds 4b and 5b showed effective inhibition equivalent to Letrozole. These preliminary biological screening studies have given positive anticancer activity for these new classes of derivatives. An additional research study like the mechanism of action of the anticancer activity of this new class of compounds is necessary. These groundwork studies illuminate a future pathway for research of this class of compounds enabling the discovery of potent antitumor agents.

Antioxidant effect of 1,3,4-thiadiazolium mesoionic derivatives on isolated mitochondria

Mesoionic compounds have shown antitumor and citotoxic activity against different tumor cells lines, which has been attributed to their physical and chemical characteristics. Among these compounds, the 1,3,4-thiadiazolium-2-phenylamine derivatives have been highlighted due to their important anti-melanoma activity. In this work, the effects of three derivatives that belong this class, MI-J, MI-4F and MI-2,4diF, on the oxidative stress parameters were evaluated using rat liver mitochondria. All the derivatives prevented natural and calcium induced oxidation of pyridine nucleotides at lower concentrations (6.5 and 32.5nmol/mg protein). The calcium uptake was inhibited by all the derivatives at higher concentrations (65 and 130nmol/mg protein), whereas the cation efflux was inhibited only by the MI-J (52%) and MI-4F (50%), possibly by inhibiting the formation of the permeability transition pore (PTP) by 100% and 50%, respectively, as observed in the same experimental conditions. MI-2,4diF did not inhibit the mitochondrial permeability transition or calcium efflux. The enzymatic activity of glutathione reductase, glutathione peroxidase and catalase was not affected by any derivative, but superoxide dismutase was inhibited by all the derivatives. MI-J inhibited enzyme activity significantly (85%) at the highest concentration (130nmol/mg protein); on the other hand, their activity was less affected by fluorine derivatives (MI-4F-20% and MI-2,4diF-32%). These results suggest that these derivatives exert antioxidant effects on isolated mitochondria.

Selective Cytotoxicity of 1,3,4-Thiadiazolium Mesoionic Derivatives on Hepatocarcinoma Cells (HepG2)

In this work, we evaluated the cytotoxicity of mesoionic 4-phenyl-5-(2-Y, 4-X or 4-X-cinnamoyl)-1,3,4-thiadiazolium-2-phenylamine chloride derivatives (MI-J: X=OH, Y=H; MI-D: X=NO2, Y=H; MI-4F: X=F, Y=H; MI-2,4diF: X=Y=F) on human hepatocellular carcinoma (HepG2), and non-tumor cells (rat hepatocytes) for comparison. MI-J, M-4F and MI-2,4diF reduced HepG2 viability by ~ 50% at 25 μM after 24-h treatment, whereas MI-D required a 50 μM concentration, as shown by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. The cytotoxicity was confirmed with lactate dehydrogenase assay, of which activity was increased by 55, 24 and 16% for MI-J, MI-4F and MI-2,4diF respectively (at 25 μM after 24 h). To identify the death pathway related to cytotoxicity, the HepG2 cells treated by mesoionic compounds were labeled with both annexin V and PI, and analyzed by flow cytometry. All compounds increased the number of doubly-stained cells at 25 μM after 24 h: by 76% for MI-J, 25% for MI-4F and MI-2,4diF, and 11% for MI-D. It was also verified that increased DNA fragmentation occurred upon MI-J, MI-4F and MI-2,4diF treatments (by 12%, 9% and 8%, respectively, at 25 μM after 24 h). These compounds were only weakly, or not at all, transported by the main multidrug transporters, P-glycoprotein, ABCG2 and MRP1, and were able to slightly inhibit their drug-transport activity. It may be concluded that 1,3,4-thiadiazolium compounds, especially the hydroxy derivative MI-J, constitute promising candidates for future investigations on in-vivo treatment of hepatocellular carcinoma.

Molecular structure and vibrational spectroscopic studies on 2-furanacetic acid monomer and dimer

In this work, molecular geometries and fundamental vibrational frequencies of 2-furanacetic acid (2FAA) and its hydrogen bonded dimer were investigated using DFT/B3LYP method with 6-311++G(d,p) as basis set. The FT-infrared and FT-Raman spectra of the 2FAA compound were recorded in the region 4000-400 cm(-1). The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. Complete vibrational assignments and analysis of the fundamental modes of monomer and dimer structures were performed on the basis of the potential energy distribution (PED) calculations. A study on the electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. Molecular stability arising from hyperconjugative interactions and charge delocalization has been analyzed using Natural Bond Orbital (NBO) analysis. Topological parameters such an electron density and its Laplacian at bond critical points (BCP) of O-H and O⋯H contact bonds were analyzed in details with the help of the atoms in molecules (AIM) approach in order to study the intermolecular hydrogen bonding. The nonlinear optical properties of the title molecule have been investigated. Moreover, molecular electrostatic potential (MEP) surface was plotted for predicting sites and relative reactivities towards electrophilic and nucleophilic attack. The nonlinear optical properties were reported and compared with that of the urea. The thermodynamic properties like heat capacity, entropy, and enthalpy have been calculated for the molecule at different temperatures.

Synthesis, in vitro anticancer and antioxidant activity of thiadiazole substituted thiazolidin-4-ones

A series of novel 5-alkyl/aryl thiadiazole substituted thiazolidin-4-ones were synthesized by a two-step process. In the first step, 5-alkyl/aryl substituted 2-aminothiadiazoles were synthesized, which on reaction with substituted aromatic aldehydes and thioglycolic acid in the presence of dicyclohexylcarbodiimide afforded thiazolidin- 4-ones. All the compounds were synthesized in fairly good yields and their structures were confirmed by spectral and physical data. The title compounds were screened for in vitro anti-proliferative activity on human breast adenocarcinoma cells (MCF-7) by MTT assay. Most of the derivatives showed an IC₅₀ less than 150 μmol L⁻¹. Among the compounds tested, 2-(2-nitrophenyl)- 3-(5-methyl-1,3,4-thiadiazol-2-yl)-thiazolidin-4-one (3f), 2-(3-fluorophenyl)-3-(5-methyl-1,3,4-thiadiazol-2- -yl)-thiazolidin-4-one (3b), and 2-(4-chlorophenyl)-3- -(5-methyl-1,3,4-thiadiazol-2-yl)-thiazolidin-4-one (3c) were found to be the most active derivatives with IC50 values of 46.34, 66.84, and 60.71 μmol L⁻¹, respectively. Antioxidant studies of all the synthesized compounds were carried out by diphenylpicrylhydrazyl (DPPH) assay. Among the compounds tested, 2-phenyl-3-(5-styryl- -1,3,4-thiadiazol-2-yl)-thiazolidin-4-one (3s) elicited superior antioxidant activity with IC₅₀ of 161.93 μmol L⁻¹.

Synthesis and antibacterial activities of novel imidazo[2,1-b]-1,3,4-thiadiazoles

2-Amino-5-(2-aryl-2H-1,2,3-triazol-4-yl)-1,3,4-thiadiazoles 2-4 have been synthesized by the reaction of 2-aryl-2H-1,2,3-triazole-4-carboxylic acids 1 with thiosemicarbazide. Their reaction with phenacyl (p-substituted phenacyl) bromides led to formation of the respective 6-aryl-2-(2-aryl-2H-1,2,3-triazol-4-yl)imidazo[2,1-b]-1,3,4-thiadiazoles 5. Reactivity of the latter fused ring towards reaction with different electrophilic reagents afforded the corresponding 5-substituted derivatives 6-8. The structure of the above compounds was confirmed from their spectral characteristics. Some of these compounds were found to possess slight to moderate activity against the microorganisms Staphylococcus aureus, Candida albicans, Pseudomonas aeruginosa, and Escherichia coli.

Effect of sydnone SYD-1, a mesoionic compound, on energy-linked functions of rat liver mitochondria

An important antitumour effect of SYD-1 (3-[4-chloro-3-nitrophenyl]-1,2,3-oxadiazolium-5-olate) has been shown. We now report the effects of this mesoionic compound on mitochondrial metabolism. SYD-1 (1.5 micromol mg(-1) protein) dose-dependently inhibited the respiratory rate by 65% and 40% in state 3 using sodium glutamate and succinate, respectively, as substrates. Phosphorylation efficiency was depressed by SYD-1, as evidenced by stimulation of the state 4 respiratory rate, which was more accentuated with glutamate ( approximately 180%) than with succinate ( approximately 40%), with 1.5 micromol mg(-1) protein of SYD-1. As a consequence of the effects on states 3 and 4, the RCC and ADP/O ratios were lowered by SYD-1 using both substrates, although this effect was stronger with glutamate. The formation of membrane electrical potential was inhibited by approximately 50% (1.5 micromol SYD-1mg(-1) protein). SYD-1 interfered with the permeability of the inner mitochondrial membrane, as demonstrated by assays of mitochondrial swelling in the presence of sodium acetate and valinomycin +K(+). SYD-1 (1.5 micromol mg(-1) protein) inhibited glutamate completely and succinate energized-mitochondrial swelling by 80% in preparations containing sodium acetate. The swelling of de-energized mitochondria induced by K(+) and valinomycin was inhibited by 20% at all concentrations of SYD-1. An analysis of the segments of the respiratory chain suggested that the SYD-1 inhibition site goes beyond the complex I and includes complexes III and IV. Glutamate dehydrogenase was inhibited by 20% with SYD-1 (1.5 micromol mg(-1) protein). The hydrolytic activity of complex F(1)F(o) ATPase in intact mitochondria was greatly increased ( approximately 450%) in the presence of SYD-1. Our results show that SYD-1 depresses the efficiency of electron transport and oxidative phosphorylation, suggesting that these effects may be involved in its antitumoural effect.

Anticancer, neuroprotective activities and computational studies of 2-amino-1,3,4-thiadiazole based compound

Anticancer activity studies of 2-(4-fluorophenylamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole (FABT), as one of the most promising derivatives from the N-substituted 2-amino-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole set, have been continued. The tested compound inhibited proliferation of tumor cells derived from cancers of nervous system (medulloblastoma/rhabdosarcoma, neuroblastoma, and glioma) and peripheral cancers including colon adenocarcinoma and lung carcinoma. The anticancer effect of FABT was attributed to decreased cell division and inhibited cell migration. Furthermore, in anticancer concentrations it exerted a trophic effect in neuronal cell culture and had no influence on viability of normal cells including astrocytes, hepatocytes, and skin fibroblasts. Moreover, a prominent neuroprotective activity of FABT was observed in the neuronal cultures exposed to neurotoxic agents like serum deprivation and glutamate. To determine probability of tautomeric transition and indicate potential sites of interactions of FABT molecule with the receptor, quantum-chemical calculations with the ab initio Hartree-Fock model were made.

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

A number of N-substituted 2-amino-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles were synthesized and evaluated for their antiproliferative activities. The panel substitution included alkyl, aryl, and morpholinoalkyl derivatives. The structures of compounds were identified from elemental, IR, (1)H NMR, (13)C NMR and MS spectra analyses. The cytotoxicity in vitro against the four human cell lines: SW707 (rectal), HCV29T (bladder), A549 (lung), and T47D (breast) was determined. Alkyl and morpholinoalkyl derivatives exhibited significantly lower effect than phenyl ones. The highest antiproliferative activity was found for 2-(2,4-dichlorophenylamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole, with ID(50) two times lower (SW707, T47D) than for cisplatin studied comparatively as the control compound.

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.

Evaluation of Antiproliferative Effect in Vitro of Some 2-Amino-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole Derivatives

New compounds of N-substituted 2-amino-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole set were synthesized and tested for their antiproliferative activity as part of our research in the antitumour field. Title compounds were obtained by reaction of sulfinylbis(2,4-dihydroxythiobenzoyl) (STB) with 4-substituted 3-thiosemicarbazides. The structures of compounds were identified from elemental, IR, 1H-, 13C-NMR and MS spectra analyses. The cytotoxicity in vitro against human bladder cancer HCV29T cells was determined. The most active compounds were also tested against human cancer cell lines: SW707 (rectal), A549 (lung) and T47D (breast). The antiproliferative effect of some compounds was higher than cisplatin studied comparatively.

Hispidulin: antioxidant properties and effect on mitochondrial energy metabolism

Hispidulin (6-methoxy-5,7,4'-trihydroxyflavone) and eupafolin (6-methoxy-5,7,3',4'-tetrahydroxyflavone), are flavonoids found in the leaves of Eupatorium litoralle. They have recognized antioxidant and antineoplastic properties, although their action mechanisms have not been previously described. We now report the effects of hispidulin on the oxidative metabolism of isolated rat liver mitochondria (Mit) and have also investigated the prooxidant and antioxidant capacity of both flavonoids. Hispidulin (0.05-0.2 mM) decreased the respiratory rate in state III and stimulated it in state IV, when glutamate or succinate was used as oxidizable substrate. Hispidulin inhibited enzymatic activities between complexes I and III of the respiratory chain. In broken Mit hispidulin (0.2 mM) slightly inhibited ATPase activity (25%). However, when intact Mit were used, the flavonoid stimulated this activity by 100%. Substrate energized mitochondrial swelling was markedly inhibited by hispidulin. Both hispidulin and eupafolin were able to promote iron release from ferritin, this effect being more accentuated with eupafolin with the suggestion of a possible involvement of H2O2 in the process. Hispidulin was incapable of donating electrons to the stable free radical DPPH, while eupafolin reacted with it in a similar way to ascorbic acid. The results indicate that hispidulin as an uncoupler of oxidative phosphorylation, is able to release iron from ferritin, but has distinct prooxidant and antioxidant properties when compared to eupafolin.

Cytotoxic effect of a new 1,3,4-thiadiazolium mesoionic compound (MI-D) on cell lines of human melanoma

The structural characteristics of mesoionic compounds, which contain distinct regions of positive and negative charges associated with a poly-heteroatomic system, enable them to cross cellular membranes and interact strongly with biomolecules. Potential biological applications have been described for mesoionic compounds. 1,3,4-Thiadiazolium mesoionic compound (MI-D), a new mesoionic compound, has been demonstrated to be extremely cytotoxic to B16-F10 murine melanoma cells when compared to fotemustine and dacarbazine, drugs of reference in melanoma treatment protocols, describing inhibition of tumours grown in vitro and in vivo. We now evaluate the effects of mesoionic compound MI-D on different human melanoma cell lines. The drug decreased the viability and proliferation of MEL-85, SK-MEL, A2058 and MEWO cell lines in vitro, showing a considerable cytotoxic activity on these human cells. Adhesion of MEL-85 cells was evaluated in the presence of the drug using different extracellular matrix (ECM) constituents. MI-D decreased MEL-85 adhesion to laminin, fibronectin and matrigel. The morphology and actin cytoskeleton organisation of MEL-85 cells were also modified on MI-D treatment. These results on human melanoma cell lines indicate that MI-D is a very encouraging drug against melanoma, a tumour that is extremely resistant to chemotherapy.