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

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.

Leishmanicidal effect of 1,3,4-thiadiazolium mesoionic salts on Leishmania amazonensis in vitro

Leishmaniasis is a neglected broad clinical spectrum disease caused by protozoa of the genus Leishmania, which affect millions of people annually in the world and the treatment has severe side effects and resistant strains have been reported. Mesoionic salts are a subclass of the betaine group with extensive biological activity such as microbicide and anti-inflammatory In this work, we analyze the cytotoxic effects of mesoionic salts, 4-phenyl-5-(X-phenyl)-1,3,4-thiadiazolium-2-phenylamine chloride (X = 4 Cl; 3,4 diCl and 3,4 diF), on Leishmania amazonensis in vitro. Initially, Mesoionic salts toxicity were evaluated by XTT assay on L. amazonensis promastigotes. Our results show that the mesoionic salts MI-3,4 diCl, MI-4 Cl and MI-3,4 diF were toxic to the promastigote parasite with IC₅₀ values of 14.3, 40.1 and 61.8 μM, respectively. The amastigote survival was evaluated in treated infected-macrophages, and the results demonstrate that MI-4 Cl (IC₅₀ = 33 μM) and MI-3,4 diCl (IC₅₀ = 43 μM) have a toxic effect against these forms. None of the mesoionic compounds tested present host cell toxicity up to the tested concentration of 100 μM. The selectivity index for MI-3,4 diCl and MI-4 Cl were 3.94 and 6.97, respectively. Nitric oxide (NO) production assayed by Griess reagent, in LPS-activated macrophages or not, in the presence of the salts showed that only the MI-3,4 diCl compound reduced NO levels. Lipid profile analysis of treated-promastigotes showed no alteration of neutral lipids. Evaluation of mitochondrial membrane potential (∆Ψm) showed that the MI-4Cl compound was able to reduce (∆Ψm) by 50%. Therefore, our results suggest that the chlorinated compounds are promising biomolecules, which cause inhibition of L.amazonensis promastigotes, amastigotes, leading to mitochondrial damage.

C@PA: Computer-Aided Pattern Analysis to Predict Multitarget ABC Transporter Inhibitors

Based on literature reports of the last two decades, a computer-aided pattern analysis (C@PA) was implemented for the discovery of novel multitarget ABCB1 (P-gp), ABCC1 (MRP1), and ABCG2 (BCRP) inhibitors. C@PA included basic scaffold identification, substructure search and statistical distribution, as well as novel scaffold extraction to screen a large virtual compound library. Over 45,000 putative and novel broad-spectrum ABC transporter inhibitors were identified, from which 23 were purchased for biological evaluation. Our investigations revealed five novel lead molecules as triple ABCB1, ABCC1, and ABCG2 inhibitors. C@PA is the very first successful computational approach for the discovery of promiscuous ABC transporter inhibitors.

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.

Impairment of oxidative phosphorylation increases the toxicity of SYD-1 on hepatocarcinoma cells (HepG2)

Toxicity of the SYD-1 mesoionic compound (3-[4-chloro-3-nitrophenyl]-1,2,3-oxadiazolium-5-olate) was evaluated on human liver cancer cells (HepG2) grown in either high glucose (HG) or galactose (GAL) medium, and also on suspended cells kept in HG medium. SYD-1 was able to decrease the viability of cultured HepG2 cells in a dose-dependent manner, as assessed by MTT, LDH release and dye with crystal violet assays, but no effect was observed on suspended cells after 1-40 min of treatment. Respiration analysis was performed after 2 min (suspended cells) or 24 h (cultured cells) of treatment: no change was observed in suspended cells, whereas SYD-1 inhibited as well basal, leak and uncoupled states of the respiration in cultured cells with HG medium. These inhibitions were consistent with the decrease in pyruvate level and increase in lactate level. Even more extended results were obtained with HepG2 cells grown in GAL medium where, additionally, the ATP amount was reduced. Furthermore, SYD-1 appears not to be transported by the main ABC multidrug transporters. These results show that SYD-1 is able to change the metabolism of HepG2 cells, and suggest that its cytotoxicity is related to impairment of mitochondrial metabolism. Therefore, we may propose that SYD-1 is a potential candidate for hepatocarcinoma treatment.

Involvement of PI3K/Akt, ERK and p38 signaling pathways in emodin-mediated extrinsic and intrinsic human hepatoblastoma cell apoptosis

As a natural anthraquinone derivative, 1,3,8-trihydroxy-6-methylanthraquinone, known as emodin, has recently been reported to possess potential chemopreventive capacity, but the underlying molecular mechanism of its hepatocyte toxicity remains poorly clarified. The present research indicated that emodin targeted HepG2 cells without being cytotoxic to primary human hepatocyte cells in comparison with chrysophanol and rhein. The anti-proliferative effect of emodin was ascribed to occurrence of apoptosis, which characterized by higher ethidium bromide signal, brighter DAPI fluorescence, cleavages of procaspase-3 and poly (ADP-ribose) polymerase as well as quantitative result from Annexin V-FITC/PI double staining. Furthermore, emodin improved Bax/Bcl-2 ratio, elicited disruption of mitochondrial membrane potential and promoted efflux of cytochrome c to cytosol, indicative of features of mitochondria-dependent apoptotic signals. Emodin concurrently led to activations of Fas, Fas-L, caspase-8 and tBid, which provoked death receptor apoptotic signals. Notably, activated tBid relayed the Fas apoptotic signal to the mitochondrial pathway. Besides, emodin effectively attenuated phosphorylations of Akt and ERK and promoted phosphorylation of p38. Inhibitions of PI3K/Akt and ERK and activation of p38 mediated emodin-induced apoptosis through modulating the mitochondrial pathway and/or death receptor pathway. Additionally, there was a cross-talk between PI3K/Akt and MAPKs pathways in emodin-induced apoptosis.

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.

The effect of foetal bovine serum supplementation upon the lactate dehydrogenase cytotoxicity assay: Important considerations for in vitro toxicity analysis

The lactate dehydrogenase (LDH) assay is a commonly-used tool for assessing toxicity in vitro. However, anecdotal reports suggest that foetal bovine serum (FBS) may contain LDH at concentrations significant enough to interfere with the assay and thus reduce its sensitivity. A series of experiments were performed to determine whether addition of FBS to culture medium significantly elevated culture media LDH content, and whether replacement of FBS with heat inactivated foetal bovine serum (HI-FBS) reduced LDH content and interfered with cell response to cytotoxic challenge. The addition of FBS at 5, 10 and 15% final concentrations increased culture medium LDH content in a dose-dependent manner. The substitution of HI-FBS for FBS reduced culture medium LDH content and increased the dynamic range of the assay. Cell viability of the SH-SY5Y human neuroblastoma and N27 rat mesencephalic neurone cell lines were significantly reduced as measured using the MTT reduction assay, whilst HI-FBS only affected toxicity response in a cell- and toxin-specific manner, although these effects were small. Hence, for cell lines with a high FBS requirement, the use of HI-FBS or alternative toxicity assays can be considered, or the use of alternative formulations, such as chemically-defined serum-free media, be adopted.