Does chloroquine, an antimalarial drug, affect autophagy in Tetrahymena pyriformis?

Fangchinoline eliminates intracellular Salmonella by enhancing lysosomal function via the AMPK-mTORC1-TFEB axis

INTRODUCTION

Salmonella, a foodborne zoonotic pathogen, is a significant cause of morbidity and mortality in animals and humans globally. With the prevalence of multidrug-resistant strains, Salmonellosis has become a formidable challenge. Host-directed therapy (HDT) has recently emerged as a promising anti-infective approach for treating intracellular bacterial infections.

OBJECTIVES

Plant-derived natural products, owing to their structural and functional diversity, are increasingly being explored and utilized as encouraging candidates for HDT compounds. This study aims to identify and screen natural compounds with potential as HDT for the treatment of intracellular Salmonella infections.

METHODS

A cell-based screening approach was deployed to identify natural compounds capable of mitigating the intracellular replication of S. enterica. Safety and efficacy of the candidate compounds were evaluated using multiple animal models. RNA sequencing, ELISA, and immunoblotting analyses were conducted to elucidate the underlying mechanisms of action.

RESULTS

Our results reveal that fangchinoline (FAN) effectively reduces S. enterica survival both in vitro and in vivo. Meanwhile, FAN also displays anti-infective activity against other intracellular pathogens, including multidrug-resistant isolates. A 14-day safety evaluation in mice showed no significant toxic or adverse effects from FAN administration. RNA sequencing analysis reveals an upregulation of lysosome pathways in S. enterica-infected cells treated with FAN. Mechanistic studies indicate that FAN increases acid lysosomal quantities and fosters autophagic response in Salmonella-infected cells via the AMPK-mTORC1-TFEB axis. In addition, FAN alleviates the inflammatory response in Salmonella-infected cells by inactivating the NF-κB pathway.

CONCLUSION

Our findings suggest that FAN represents a lead HDT compound for tackling recalcitrant infections caused by intracellular bacterial pathogens.

Structure-activity relationship study of small-molecule inhibitor of Atg12-Atg3 protein-protein interaction

Autophagy is a catabolic process that was described to play a critical role in advanced stages of cancer, wherein it maintains tumor cell homeostasis and growth by supplying nutrients. Autophagy is also described to support alternative cellular trafficking pathways, providing a non-canonical autophagy-dependent inflammatory cytokine secretion mechanism. Therefore, autophagy inhibitors have high potential in the treatment of cancer and acute inflammation. In our study, we identified compound 1 as an inhibitor of the ATG12-ATG3 protein-protein interaction. We focused on the systematic modification of the original hit 1, a casein kinase 2 (CK2) inhibitor, to find potent disruptors of ATG12-ATG3 protein-protein interaction. A systematic modification of the hit structure led us to a wide plethora of compounds that maintain its ATG12-ATG3 inhibitory activity, which could act as a viable starting point to design new compounds with diverse therapeutic applications.

Curcumin induces apoptotic cell death and protective autophagy by inhibiting AKT/mTOR/p70S6K pathway in human ovarian cancer cells

PURPOSE

Curcumin (Cur), a yellow-colored dietary flavor from the plant (Curcuma longa), has been demonstrated to potentially resist diverse diseases, including ovarian cancer, but drug resistance becomes a major limitation of its success clinically. The key molecule or mechanism associated with curcumin resistance in ovarian cancer still remains unclear. The aim of our study was to investigate the effects of curcumin on autophagy in ovarian cancer cells and elucidate the underlying mechanism.

METHODS

In our study, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), EdU proliferation assay and colony-forming assay were used to assess cell viability. Apoptosis was detected by western blot and flow cytometric analysis of apoptosis. Autophagy was defined by both electron microscopy and immunofluorescence staining markers such as microtubule-associated protein 1 light chain 3 (LC3). Plasmid construction and shRNA transfection helped us to confirm the function of curcumin.

RESULTS

Curcumin reduced cell viability and induced apoptotic cell death by MTT assay in human ovarian cancer cell lines SK-OV-3 and A2780 significantly. Electron microscopy, western blot and immunofluorescence staining proved that curcumin could induce protective autophagy. Moreover, treatment with autophagy-specific inhibitors or stable knockdown of LC3B by shRNA could markedly enhance curcumin-induced apoptosis. Finally, the cells transiently transfected with AKT1 overexpression plasmid demonstrated that autophagy had a direct relationship with the AKT/mTOR/p70S6K pathway.

CONCLUSIONS

Curcumin can induce protective autophagy of human ovarian cancer cells by inhibiting the AKT/mTOR/p70S6K pathway, indicating the synergistic effects of curcumin and autophagy inhibition as a possible strategy to overcome the limits of current therapies in the eradication of epithelial ovarian cancer.

Inhibition of autophagy attenuated curcumol-induced apoptosis in MG-63 human osteosarcoma cells via Janus kinase signaling pathway

The present study aimed to investigate whether autophagy was triggered by curcumol and to explore the association between autophagy and apoptosis of MG-63 cells and the underlying mechanism. MG-63 cells were cultured in vitro. An MTT assay was performed to evaluate the proliferation inhibition of the MG-63 osteosarcoma cell line by curcumol. Fluorescein isothiocyanate-Annexin V/propidium iodide staining flow cytometry was performed to analyze the apoptotic rate of cells. The morphological alterations of cell nuclei were evaluated by Hoechst 33258 viable cell staining. The effects of autophagy in cells was investigated by green fluorescent protein (GFP)-light chain 3 (LC3) transfection and using a fluorescence microscope. The expression levels of LC3II, LC3I and cleaved caspase-3 and Janus kinase (JNK) signaling pathway activation were determined by western blot analysis. Cell proliferation was inhibited by curcumol in a dose- and time-dependent manner. Curcumol induced apoptosis by the caspase-dependent signaling pathway in MG-63 cells. The present study demonstrated that curcumol could induce autophagy of MG-63 cells, which was evaluated by transmission electron microscopy. Compared with the curcumol treatment alone group, the GFP-LC3-transfected green fluorescence plasmids and the LC3II/LC3I levels in cells of the curcumol and chloroquine (CQ) treatment group were upregulated, and the apoptotic ratio was downregulated following pretreatment with autophagy inhibitor CQ for 1 h. Furthermore, curcumol treatment induced phosphorylation of the JNK signaling pathway. Of note, pretreatment with the JNK inhibitor, SP600125, decreased the rates of autophagy and apoptosis, suggesting a crucial role served by the JNK signaling pathway in the activation of autophagy by curcumol. Taken together, the results of the present study suggested that activation of the JNK signaling pathway was involved in curcumol-induced autophagy. Curcumol is a novel drug for chemotherapeutic combination therapy. Curcumol demonstrated potential antitumor activities in MG-63 cells and may be used as a novel effective reagent in the treatment of osteosarcoma.

Novel mechanisms and approaches to overcome multidrug resistance in the treatment of ovarian cancer

Ovarian cancer remains the leading cause of gynecological cancer-related mortality despite the advances in surgical techniques and chemotherapy drugs over the past three decades. Multidrug resistance (MDR) to chemotherapy is the major cause of treatment failure. Previous research has focused mainly on strategies to reverse MDR by targeting the MDR1 gene encoded P-glycoprotein (Pgp) with small molecular compound inhibitors. However, prior Pgp inhibitors have shown very limited clinical success because these agents have relatively low potency and high toxicity. Therefore, identification of more specific and potent new inhibitors would be useful. In addition, emerging evidence suggests that cancer stem cells (CSCs), deregulated non-coding RNA (ncRNA), autophagy, and tumor heterogeneity also contribute significantly to drug sensitivity/resistance in ovarian cancer. This review summarizes these novel mechanisms of MDR and evaluates several new concepts to overcome MDR in the treatment of ovarian cancer. These new strategies include overcoming MDR with more potent and specific Pgp inhibitors, targeting CSCs and ncRNA, modulating autophagy signaling pathway, and targeting tumor heterogeneity.

Cinobufagin induces autophagy-mediated cell death in human osteosarcoma U2OS cells through the ROS/JNK/p38 signaling pathway

The main objective of this study was to explore whether autophagy could be triggered by cinobufagin, and to clarify the role of autophagy in the antitumor effects of cinobufagin on U2OS cells and the underlying mechanisms. U2OS cells were exposed to 15, 30, 60 and 120 mg/l cinobufagin for 0, 12, 24 and 48 h. An MTT assay was used to measure cell viability. FITC-Annexin Ⅴ/PI staining and flow cytometry were used to analyze the apoptotic ratio, while apoptotic morphological changes were assessed by PI and Hoechst 33258 viable cell staining. The effects of autophagy on the cells were investigated with GFP-LC3b green fluorescence plasmid transfection and transmission electron microscopy. The levels of caspase-3, -8, - 9, cleaved PARP, LC3-II/LC3-I, p62 and the activation of JNK/p-38 were detected by western blot analysis. Reactive oxygen species (ROS) fluorescence intensity was examined under fluorescence microscopy with an analysis software system. Cell proliferation was obviously inhibited by cinobufagin in a dose- and time-dependent manner. The apoptosis ratio was gradually increased with treatment time as evidenced by flow cytometric analysis and Hoechst 33258 staining. Exposure to cinobufagin resulted in the activation of caspase-3, -8, -9, as well as cleaved PARP which indicated that cinobufagin induced caspase-dependent apoptosis. Autophagy was confirmed in the cinobufagin-treated cells as evidenced by formation of autophagosomes, accumulation of GFP-LC3 fluorescence particles as well as the upregulation of LC3-II/LC3-I levels. Inhibition of autophagy diminished apoptosis as detected by the MTT assays. Moreover the percentage of apoptotic cells decreased following pretreatment with 3-MA, CQ and si-beclin-1. Cinobufagin also induced phosphorylation of the JNK and p38 signaling pathway as well as ROS generation. The JNK and p38 inhibitors significantly attenuated coexistence of apoptosis and autophagy-related proteins. The ROS scavenger also prevented phosphorylation of the JNK and p38 signaling pathway. Our research proved that cinobufagin triggered apoptosis and autophagic cell death via activation of the ROS/JNK/p-38 axis.

Induction of cytosine arabinoside-resistant human myeloid leukemia cell death through autophagy regulation by hydroxychloroquine

We investigated the effects of the autophagy inhibitor hydroxychloroquine (HCQ) on cell death of cytosine arabinoside (Ara-C)-resistant human acute myeloid leukemia (AML) cells. Ara-C-sensitive (U937, AML-2) and Ara-C-resistant (U937/AR, AML-2/AR) human AML cell lines were used to evaluate HCQ-regulated cytotoxicity, autophagy, and apoptosis as well as effects on cell death-related signaling pathways. We found that HCQ-induced dose- and time-dependent cell death in Ara-C-resistant cells compared to Ara-C-sensitive cell lines. The extent of cell death and features of HCQ-induced autophagic markers including increase in microtubule-associated protein light chain 3 (LC3) I conversion to LC3-II, beclin-1, ATG5, as well as green fluorescent protein-LC3 positive puncta and autophagosome were remarkably greater in U937/AR cells. Also, p62/SQSTM1 was increased in response to HCQ. p62/SQSTM1 protein interacts with both LC3-II and ubiquitin protein and is degraded in autophagosomes. Therefore, a reduction of p62/SQSTM1 indicates increased autophagic degradation, whereas an increase of p62/SQSTM1 by HCQ indicates inhibited autophagic degradation. Knock down of p62/SQSTM1 using siRNA were prevented the HCQ-induced LC3-II protein level as well as significantly reduced the HCQ-induced cell death in U937/AR cells. Also, apoptotic cell death and caspase activation in U937/AR cells were increased by HCQ, provided evidence that HCQ-induced autophagy blockade. Taken together, our data show that HCQ-induced apoptotic cell death in Ara-C-resistant AML cells through autophagy regulation.

JNK confers 5-fluorouracil resistance in p53-deficient and mutant p53-expressing colon cancer cells by inducing survival autophagy

Deficiency or mutation in the p53 tumor suppressor gene commonly occurs in human cancer and can contribute to disease progression and chemotherapy resistance. Currently, although the pro-survival or pro-death effect of autophagy remains a controversial issue, increasing data seem to support the idea that autophagy facilitates cancer cell resistance to chemotherapy treatment. Here we report that 5-FU treatment causes aberrant autophagosome accumulation in HCT116 p53^−/− and HT-29 cancer cells. Specific inhibition of autophagy by 3-MA, CQ or small interfering RNA treatment targeting Atg5 or Beclin 1 can potentiate the re-sensitization of these resistant cancer cells to 5-FU. In further analysis, we show that JNK activation and phosphorylation of Bcl-2 are key determinants in 5-FU-induced autophagy. Inhibition of JNK by the compound SP600125 or JNK siRNA suppressed autophagy and phosphorylation of c-Jun and Bcl-2 but increased 5-FU-induced apoptosis in both HCT116 p53^−/− and HT29 cells. Taken together, our results suggest that JNK activation confers 5-FU resistance in HCT116 p53^−/− and HT29 cells by promoting autophagy as a pro-survival effect, likely via inducing Bcl-2 phosphorylation. These results provide a promising strategy to improve the efficacy of 5-FU-based chemotherapy for colorectal cancer patients harboring a p53 gene mutation.

Autophagy and chemotherapy resistance: a promising therapeutic target for cancer treatment

Induction of cell death and inhibition of cell survival are the main principles of cancer therapy. Resistance to chemotherapeutic agents is a major problem in oncology, which limits the effectiveness of anticancer drugs. A variety of factors contribute to drug resistance, including host factors, specific genetic or epigenetic alterations in the cancer cells and so on. Although various mechanisms by which cancer cells become resistant to anticancer drugs in the microenvironment have been well elucidated, how to circumvent this resistance to improve anticancer efficacy remains to be defined. Autophagy, an important homeostatic cellular recycling mechanism, is now emerging as a crucial player in response to metabolic and therapeutic stresses, which attempts to maintain/restore metabolic homeostasis through the catabolic lysis of excessive or unnecessary proteins and injured or aged organelles. Recently, several studies have shown that autophagy constitutes a potential target for cancer therapy and the induction of autophagy in response to therapeutics can be viewed as having a prodeath or a prosurvival role, which contributes to the anticancer efficacy of these drugs as well as drug resistance. Thus, understanding the novel function of autophagy may allow us to develop a promising therapeutic strategy to enhance the effects of chemotherapy and improve clinical outcomes in the treatment of cancer patients.

Cotargeting EGFR and autophagy signaling: A novel therapeutic strategy for non-small-cell lung cancer

Epidermal growth factor receptor (EGFR) somatic mutations are found in the majority of non-small-cell lung cancers (NSCLCs) and patients with NSCLC who harbor EGFR mutations have been shown to exhibit increased sensitivity to the small-molecule EGFR-tyrosine kinase inhibitors (TKIs) gefitinib and erlotinib. However, the majority of tumors develop acquired resistance to EGFR-TKIs after a median of 10-16 months, which limits the clinical efficacy of these drugs. Autophagy, an important homeostatic cellular recycling mechanism, has emerged as a potential target for the acquired resistance phenotype. Recently, several studies demonstrated that autophagy may be induced in a dose-dependent manner by treatment of multiple cancer cell lines with EGFR-TKIs in vitro. Furthermore, it was recently reported that autophagy, as a cytoprotective response, may be activated by EGFR-TKIs in lung cancer cells and that the inhibition of autophagy enhanced the cytotoxic effect of EGFR-TKIs. In this review, we aimed to focus on the association between resistance to EGFR-TKIs and autophagy, and assess whether autophagy inhibition represents a promising approach to improve the efficacy of EGFR-TKIs in the treatment of NSCLC patients.

Tetrahymena pyriformis: a tool for toxicological studies. A review

Among protozoa, Tetrahymena pyriformis is the most commonly ciliated model used for laboratory research. After a brief description of the morphology and biology of Tetrahymena pyriformis, this article focuses on the most important and recent investigations performed with this species in toxicology and ecotoxicology. The methodological features of its culture, and main tests, based on cell growth rate, biochemical markers, behavioral changes and motility, are discussed. Examples of xenobiotics (organic and inorganic substances, pharmaceutical drugs, water pollutants) tested with Tetrahymena pyriformis are also given.

Alterations induced by the antifungal compounds ketoconazole and terbinafine in Leishmania

The antiproliferative effects and ultrastructural alterations induced in vitro by two antifungal compounds, the azole ketoconazole and the allylamine terbinafine on Leishmania amazonensis are reported. Promastigotes treatment with ketoconazole and terbinafine induced growth arrest and cell lysis in 72 hours. Combination of the two agents produced additive effects on promastigote axenic growth and synergistic effects on intracellular amastigote proliferation. The amastigotes, either axenically grown or infecting murine macrophages, were about 100-fold more sensitive to the drugs. These compounds induced the appearance of large multivesicular bodies, especially after ketoconazole treatment, increased amount of lipid inclusions as well as numerous, polymorphic volutin granules, particularly in terbinafine-treated cells. Multivesicular bodies were observed in close apposition with organelles such as mitochondria, which also showed alterations in the distribution and appearance of cristae, and the formation of paracrystalline arrays within the matrix. Some cells presented large portions of cytoplasm wrapped by endoplasmic reticulum and many parasites also presented myelin-like endoplasmic reticulum profiles. Such alterations together with the strong acid phosphatase activity observed in the multivesicular bodies and volutin granules may indicate the existence of an unusual autophagic process in cells treated with ergosterol biosynthesis inhibitors.