Ouabain targets the unfolded protein response for selective killing of HepG2 cells during glucose deprivation

Ouabain-mediated downregulation of ALKBH5 and IGF2BP2 inhibits the malignant progression of DLBCL

m6A modification is a crucial epigenetic regulatory mechanism in diffuse large B-cell lymphoma (DLBCL). Low-dose cardiotonic drugs have been shown to induce apoptosis in DLBCL cells through epigenetic modulation. However, the involvement of the cardiotonic drug ouabain in the malignant progression of DLBCL remains unclear. Our study revealed that ouabain indeed contributes to the malignant progression of DLBCL through m6A modification. Through qPCR analysis, we observed a negative correlation between ouabain concentration and the expression levels of the demethylase ALKBH5 and the m6A-binding protein IGF2BP2 in DLBCL cells. Furthermore, high expression levels of ALKBH5 and IGF2BP2 were identified in both the GEO database and DLBCL patient tissue samples. Notably, elevated ALKBH5 and IGF2BP2 promoted cell proliferation both in vitro and in vivo. Inhibition of their expression rendered DLBCL cells more sensitive to ouabain treatment, resulting in significant suppression of cell proliferation, G1/S phase cell cycle arrest, and increased apoptosis. In summary, our results clarify that the demethylase ALKBH5 and the m6A-binding protein IGF2BP2 are involved in the malignant progression of DLBCL, and that the cardiotonic drug ouabain can inhibit the proliferation of DLBCL cells by inhibiting the expression of ALKBH5 and IGF2BP2, which provides new insights into the targeted treatment of DLBCL.

Integrating cell morphology with gene expression and chemical structure to aid mitochondrial toxicity detection

Mitochondrial toxicity is an important safety endpoint in drug discovery. Models based solely on chemical structure for predicting mitochondrial toxicity are currently limited in accuracy and applicability domain to the chemical space of the training compounds. In this work, we aimed to utilize both -omics and chemical data to push beyond the state-of-the-art. We combined Cell Painting and Gene Expression data with chemical structural information from Morgan fingerprints for 382 chemical perturbants tested in the Tox21 mitochondrial membrane depolarization assay. We observed that mitochondrial toxicants differ from non-toxic compounds in morphological space and identified compound clusters having similar mechanisms of mitochondrial toxicity, thereby indicating that morphological space provides biological insights related to mechanisms of action of this endpoint. We further showed that models combining Cell Painting, Gene Expression features and Morgan fingerprints improved model performance on an external test set of 244 compounds by 60% (in terms of F1 score) and improved extrapolation to new chemical space. The performance of our combined models was comparable with dedicated in vitro assays for mitochondrial toxicity. Our results suggest that combining chemical descriptors with biological readouts enhances the detection of mitochondrial toxicants, with practical implications in drug discovery.

Aglycemic growth enhances carbohydrate metabolism and induces sensitivity to menadione in cultured tumor-derived cells

Background

Hepatocellular carcinoma (HCC) is the most prevalent form of liver malignancy and carries poor prognoses due to late presentation of symptoms. Treatment of late-stage HCC relies heavily on chemotherapeutics, many of which target cellular energy metabolism. A key platform for testing candidate chemotherapeutic compounds is the intrahepatic orthotopic xenograft (IOX) model in rodents. Translational efficacy from the IOX model to clinical use is limited (in part) by variation in the metabolic phenotypes of the tumor-derived cells that can be induced by selective adaptation to subculture conditions.

Methods

In this study, a detailed multilevel systems approach combining microscopy, respirometry, potentiometry, and extracellular flux analysis (EFA) was utilized to examine metabolic adaptations that occur under aglycemic growth media conditions in HCC-derived (HEPG2) cells. We hypothesized that aglycemic growth would result in adaptive “aerobic poise” characterized by enhanced capacity for oxidative phosphorylation over a range of physiological energetic demand states.

Results

Aglycemic growth did not invoke adaptive changes in mitochondrial content, network complexity, or intrinsic functional capacity/efficiency. In intact cells, aglycemic growth markedly enhanced fermentative glycolytic substrate-level phosphorylation during glucose refeeding and enhanced responsiveness of both fermentation and oxidative phosphorylation to stimulated energy demand. Additionally, aglycemic growth induced sensitivity of HEPG2 cells to the provitamin menadione at a 25-fold lower dose compared to control cells.

Conclusions

These findings indicate that growth media conditions have substantial effects on the energy metabolism of subcultured tumor-derived cells, which may have significant implications for chemotherapeutic sensitivity during incorporation in IOX testing panels. Additionally, the metabolic phenotyping approach used in this study provides a practical workflow that can be incorporated with IOX screening practices to aid in deciphering the metabolic underpinnings of chemotherapeutic drug sensitivity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40170-021-00241-0.

Ouabain induces apoptotic cell death in human prostate DU 145 cancer cells through DNA damage and TRAIL pathways

Ouabain, a cardiotonic steroid and specific Na⁺ /K⁺ -ATPase inhibitor, has a potential to induce cancer cell apoptosis but the mechanisms of apoptosis induced by ouabain are not fully understand. The aim of this study was to investigate the cytotoxic effects of ouabain on human prostate cancer DU 145 cells in vitro. Cell morphological changes were examined by phase contrast microscopy. Cell viability, cell cycle distribution, cell apoptosis, DNA damage, the production of ROS and Ca²⁺ , and mitochondrial membrane potential (ΔΨ_m ) were measured by flow cytometry assay. Results indicated that ouabain induced cell morphological changes, decreased total cell viability, induced G0/G1 phase arrest, DNA damage, and cell apoptosis, increased ROS and Ca²⁺ production, but decreased the levels of ΔΨ_m in DU 145 cells. Ouabain also increased the activities of caspase-3, -8, and -9. Western blotting was used for measuring the alterations of apoptosis-associated protein expressions in DU 145 cells and results indicated that ouabain increased the expression of DNA damage associated proteins (pATM^Ser1981 , p-H2A.X^Ser139 , and p-p53^Ser15 ) and ER-stress-associated proteins (Grp78, ATF6β, p-PERK^Thr981 , PERK, eIF2A, GADD153, CaMKIIβ, and caspase-4) in time-dependently. Furthermore, ouabain increased apoptosis-associated proteins (DR4, DR5, Fas, Fas Ligand, and FADD), TRAIL pathway, which related to extrinsic pathway, promoted the pro-apoptotic protein Bax, increased apoptotic-associated proteins, such as cytochrome c, AIF, Endo G, caspase-3, -8, and -9, but reduced anti-apoptotic protein Bcl-2 and Bcl-x in DU 145 cells. In conclusion, we may suggest that ouabain decreased cell viability and induced apoptotic cell death may via caspase-dependent and mitochondria-dependent pathways in human prostate cancer DU 145 cells.

Ouabain potentiates the antimicrobial activity of aminoglycosides against Staphylococcus aureus

Background

Staphylococcus aureus is a notorious pathogen which often causes nosocomial and community attained infections. These infections steadily increased after evolving the resistance due to indecorous practice of antibiotics and now become a serious health issue. Ouabain is a Na⁺/K⁺-ATPase inhibitor that leads to increase the heart contraction in patients with congestive heart failure.

Methods

In the present study, in vitro antimicrobial effect of ouabain together with aminoglycosides was determined against clinical and non-clinical S. aureus strains. Using checkerboard, Gentamycin uptake and biofilm assays, we analysed he interactions of ouabain with aminoglycosides.

Results

Ouabain induced the staphylocidal potency of aminoglycosides by remarkably reducing the MIC of gentamycin (GEN) by 16 (0.25 μg/mL), 8 folds (0.5 μg/mL) amikacin (AMK); and 16 folds (1.0 μg/mL) with kanamycin (KAN), compared to their individual doses. OBN severely reduced cell viability within 60 min with GEN (1 μg/mL), KAN (2 μg/mL) and 90 min with AMK (1 μg/mL). This bactericidal effect was enhanced due to GEN uptake potentiated by 66% which led to increase the cell permeability as revealed by leakage of bacterial ATP and nitrocefin assay. The biofilm adherence disrupted by 80 and 50% at 5 mg/mL and 1.5 mg/mL OBN and 50 and 90% biofilm formation was inhibited at 5 mg/mL (MBIC₅₀) and 10 mg/mL (MBIC₉₀), respectively. Moreover, OBN with GEN further induced biofilm inhibition by 67 ± 5% at pH 7.0.

Conclusions

Taken together, we established that OBN synergizes the antimicrobial activity of aminoglycosides that induces cell killing due to intracellular accumulation of GEN by disturbing cell homeostasis. It may be proven an effective approach for the treatment of staphylococcal infections.

Unveiling new biological relationships using shared hits of chemical screening assay pairs

Motivation: Although the integration and analysis of the activity of small molecules across multiple chemical screens is a common approach to determine the specificity and toxicity of hits, the suitability of these approaches to reveal novel biological information is less explored. Here, we test the hypothesis that assays sharing selective hits are biologically related.

Results: We annotated the biological activities (i.e. biological processes or molecular activities) measured in assays and constructed chemical hit profiles with sets of compounds differing on their selectivity level for 1640 assays of ChemBank repository. We compared the similarity of chemical hit profiles of pairs of assays with their biological relationships and observed that assay pairs sharing non-promiscuous chemical hits tend to be biologically related. A detailed analysis of a network containing assay pairs with the highest hit similarity confirmed biological meaningful relationships. Furthermore, the biological roles of predicted molecular targets of the shared hits reinforced the biological associations between assay pairs.

Contact:monica.campillos@helmholtz-muenchen.de

Supplementary information:Supplementary data are available at Bioinformatics online.

Involvement of general control nonderepressible kinase 2 in cancer cell apoptosis by posttranslational mechanisms

GCN2 exerts its proapoptotic function in cancer cell death by posttranslational mechanisms. Modulation of GCN2 expression can be used for molecular targeted cancer therapy and drug development. Na⁺,K⁺-ATPase ligands are the first identified small-molecule drugs that can trigger cancer cell death by modulating GCN2 signaling.

General control nonderepressible kinase 2 (GCN2) is a promising target for cancer therapy. However, the role of GCN2 in cancer cell survival or death is elusive; further, small molecules targeting GCN2 signaling are not available. By using a GCN2 level-based drug screening assay, we found that GCN2 protein level critically determined the sensitivity of the cancer cells toward Na⁺,K⁺-ATPase ligand–induced apoptosis both in vitro and in vivo, and this effect was largely dependent on C/EBP homologous protein (CHOP) induction. Further analysis revealed that GCN2 is a short-lived protein. In A549 lung carcinoma cells, cellular β-arrestin1/2 associated with GCN2 and maintained the GCN2 protein level at a low level by recruiting the E3 ligase NEDD4L and facilitating consequent proteasomal degradation. However, Na⁺,K⁺-ATPase ligand treatment triggered the phosphorylation of GCN2 at threonine 899, which increased the GCN2 protein level by disrupting the formation of GCN2–β-arrestin–NEDD4L ternary complex. The enhanced GCN2 level, in turn, aggravated Na⁺,K⁺-ATPase ligand–induced cancer cell apoptosis. Our findings reveal that GCN2 can exert its proapoptotic function in cancer cell death by posttranslational mechanisms. Moreover, Na⁺,K⁺-ATPase ligands emerge as the first identified small-molecule drugs that can trigger cancer cell death by modulating GCN2 signaling.

Ouabain downregulates Mcl-1 and sensitizes lung cancer cells to TRAIL-induced apoptosis

Resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a prerequisite for cancer progression, and TRAIL resistance is prevalent in lung cancer. Ouabain, a recently identified human hormone, has shown therapeutic promise by potentiating the apoptotic response of metastatic lung cancer cells to TRAIL. Nontoxic concentrations of ouabain are shown to increase caspase-3 activation, poly(ADP-ribose) polymerase (PARP) cleavage, and apoptosis of H292 cells in response to TRAIL. While ouabain had a minimal effect on c-FLIP, Bcl-2, and Bax levels, we show that it possesses an ability to downregulate the antiapoptotic Mcl-1 protein. The present study also reveals that the sensitizing effect of ouabain is associated with its ability to generate reactive oxygen species (ROS), and hydrogen peroxide is identified as the principle ROS triggering proteasomal Mcl-1 degradation. In summary, our results indicate a novel function for ouabain in TRAIL-mediated cancer cell death through Mcl-1 downregulation, thereby providing new insight into a potential lung cancer treatment as well as a better understanding of the physiological activity of ouabain.

The effect of ouabain on mitochondrial DNA damage in HepG2 cell lines

Our purpose in this study is to analyze mitochondrial DNA (mtDNA) lesion frequencies and mtDNA(4977) deletion in HepG2 cells to examine the effects of ouabain on mtDNA. HepG2 cells were treated with 0.75, 7.5, 75, and 750 nM of ouabain for 24 h in the presence and absence of 10 mM 2-deoxyglucose (2-DG). The frequency of mtDNA(4977) deletions and mitochondrial lesions were determined by real-time polymerase chain reaction. A ≥ 1.2-fold change or greater was considered significant. Ouabain doses of 750, 75, and 7.5 nM alone increased the frequency of mtDNA(4977) deletions 1.39, 1.92, and 1.44 times, respectively. The 750 and 75 nM ouabain doses combined with 2-DG increased the mtDNA(4977) deletion frequency 4.94 and 1.57 times, respectively. The 750 and 75 nM ouabain doses alone increased the mtDNA lesion frequency 2.5 and 1.5 times, respectively. The 750 nM ouabain dose combined with 2-DG increased the mtDNA lesion frequency 2.28 times. The 7.5 nM ouabain dose alone and combined with 2-DG decreased the mtDNA lesion frequency 0.67 and 0.45 times, respectively. Ouabain alone and when combined with 2-DG increases mtDNA lesion and mtDNA(4977) deletion frequencies. This supports the thesis that ouabain creates oxidative stress and induces DNA damage and apoptosis.