Inhibition of autophagy may suppress the development of hepatoblastoma

Autophagy and Liver Diseases

Autophagy plays an important role in the physiology and pathology of the liver. It is involved in the development of many liver diseases such as α-1-antitrypsin deficiency, chronic hepatitis virus infection, alcoholic liver disease, nonalcoholic fatty liver disease, and liver cancer. Autophagy has thus become a new target for the treatment of liver diseases. How to treat liver diseases by regulating autophagy has been a hot topic.

Chloroquine Triggers Cell Death and Inhibits PARPs in Cell Models of Aggressive Hepatoblastoma

Background: Hepatoblastoma (HB) is the most common pediatric liver malignancy. Despite advances in chemotherapeutic regimens and surgical techniques, the survival of patients with advanced HB remains poor, underscoring the need for new therapeutic approaches. Chloroquine (CQ), a drug used to treat malaria and rheumatologic diseases, has been shown to inhibit the growth and survival of various cancer types. We examined the antineoplastic activity of CQ in cell models of aggressive HB. Methods: Seven human HB cell models, all derived from chemoresistant tumors, were cultured as spheroids in the presence of relevant concentrations of CQ. Morphology, viability, and induction of apoptosis were assessed after 48 and 96 h of CQ treatment. Metabolomic analysis and RT-qPCR based Death Pathway Finder array were used to elucidate the molecular mechanisms underlying the CQ effect in a 2-dimensional cell culture format. Quantitative western blotting was performed to validate findings at the protein level. Results: CQ had a significant dose and time dependent effect on HB cell viability both in spheroids and in 2-dimensional cell cultures. Following CQ treatment HB spheroids exhibited increased caspase 3/7 activity indicating the induction of apoptotic cell death. Metabolomic profiling demonstrated significant decreases in the concentrations of NAD⁺ and aspartate in CQ treated cells. In further investigations, oxidation of NAD⁺ decreased as consequence of CQ treatment and NAD⁺/NADH balance shifted toward NADH. Aspartate supplementation rescued cells from CQ induced cell death. Additionally, downregulated expression of PARP1 and PARP2 was observed. Conclusions: CQ treatment inhibits cell survival in cell models of aggressive HB, presumably by perturbing NAD⁺ levels, impairing aspartate bioavailability, and inhibiting PARP expression. CQ thus holds potential as a new agent in the management of HB.

PP2A activation alone and in combination with cisplatin decreases cell growth and tumor formation in human HuH6 hepatoblastoma cells

Despite an increase in incidence, treatments for hepatoblastoma remain virtually unchanged for the past 20 years, emphasizing the need for novel therapeutics. FTY720 (fingolimod) is an immunomodulator approved for use in multiple sclerosis in children that has been demonstrated to have anti-cancer properties in multiple cancer types. We have demonstrated that FTY720 activates PP2A in hepatoblastoma, but does not do so via inhibition of the endogenous inhibitors, CIP2A and I2PP2A, as previously observed in other cancers. PP2A activation in hepatoblastoma decreased cell viability, proliferation, and motility and induced apoptosis. In a subcutaneous xenograft model, FTY720 decreased tumor growth. FTY720 in combination with the standard chemotherapeutic, cisplatin, decreased proliferation in a synergistic manner. Finally, animals bearing subcutaneous hepatoblastoma xenografts treated with FTY720 and cisplatin in combination had significantly decreased tumor growth compared to those treated with either drug alone. These findings show that targeting PP2A with FTY70 shows promise in the treatment of hepatoblastoma and that combining FTY720 with cisplatin may be a novel and effective strategy to better treat this devastating pediatric liver tumor.

Diverse Functions of Autophagy in Liver Physiology and Liver Diseases

Autophagy is a catabolic process by which eukaryotic cells eliminate cytosolic materials through vacuole-mediated sequestration and subsequent delivery to lysosomes for degradation, thus maintaining cellular homeostasis and the integrity of organelles. Autophagy has emerged as playing a critical role in the regulation of liver physiology and the balancing of liver metabolism. Conversely, numerous recent studies have indicated that autophagy may disease-dependently participate in the pathogenesis of liver diseases, such as liver hepatitis, steatosis, fibrosis, cirrhosis, and hepatocellular carcinoma. This review summarizes the current knowledge on the functions of autophagy in hepatic metabolism and the contribution of autophagy to the pathophysiology of liver-related diseases. Moreover, the impacts of autophagy modulation on the amelioration of the development and progression of liver diseases are also discussed.

Down-regulation of dishevelled-2 inhibits cell proliferation and invasion in hepatoblastoma

BACKGROUND

Hepatoblastoma (HB) is the most common liver cancer found in early childhood. These patients suffer poor outcomes and need novel therapies. An abnormal activation of Wnt signaling is the hallmark of HB tumorigenesis, and its pathway is a potential candidate for a pharmacological intervention.

PROCEDURE

Tissue samples of patients with HB were collected for RNA-seq, quantitative real-time PCR, and immunohistochemistry to identify if disheveled-2 (Dvl-2) was a target gene. The correlation between Dvl-2 expression and different clinicopathological features was analyzed using statistical methods. Proliferation and invasion assays were applied after knocking down Dvl-2 by shRNA in HepG2 and Huh6 HB cell lines. The antitumor effect of niclosamide on HB was ascertained in vitro and in vivo.

RESULTS

Dvl-2 was overexpressed in 90% of patients with HB, and Dvl-2 expression was positively correlated with the age of patients with HB. Knockdown of Dvl-2 could inhibit proliferation and invasion of HB cell lines. Also, niclosamide, a Food and Drug Administration approved antihelminth compound, could effectively inhibit HB cell growth in vitro and in vivo via downregulation of Dvl-2 and β-catenin expression.

CONCLUSIONS

Our results implicate that Dvl-2 is a potential therapeutic target in HB, and niclosamide could have clinical potential to treat patients with HB.

B-cell lymphoma 2 inhibitor ABT-737 induces Beclin1- and reactive oxygen species-dependent autophagy in Adriamycin-resistant human hepatocellular carcinoma cells

ABT-737, a B-cell lymphoma 2 homology 3 mimetic, not only induces cell apoptosis by inhibiting the interaction of B-cell lymphoma 2 and Bax but also induces cell autophagy by interrupting the interaction of B-cell lymphoma 2 and Beclin1. Several recent studies have reported that ABT-737 has antitumor efficacy in diverse cancers. However, another study showed that hepatocellular carcinoma cells with high B-cell lymphoma 2 expression were resistant to ABT-737 compared to hepatocellular carcinoma cells with low B-cell lymphoma 2 expression. It was also found that ABT-737-induced autophagy is crucial for drug resistance. Here, we observed that of B-cell lymphoma 2 expression in Adriamycin-resistant human hepatocellular carcinoma HepG2/ADM cells is higher than that in human hepatocellular carcinoma HepG2 cells. Therefore, we further confirmed the mechanism and effect of autophagy induced by ABT-737 on apoptosis in HepG2/ADM cells with high B-cell lymphoma 2 expression. Our results showed that ABT-737 induced apoptosis and autophagy in time- and dose-dependent manner in HepG2/ADM cells, and this ABT-737-induced autophagy was Beclin1-dependent. In addition, we demonstrated that ABT-737 induced reactive oxygen species-mediated autophagy, and the reactive oxygen species-inhibitor N-acetyl-l-cysteine suppressed the reactive oxygen species-induced autophagy and ABT-737-induced increase in HepG2/ADM cell apoptosis. Furthermore, autophagy inhibitors increased HepG2/ADM cell apoptosis. In conclusion, our study further confirms that Beclin1- and reactive oxygen species-dependent autophagy induced by ABT-737 also plays a protective function in HepG2/ADM cells, which show B-cell lymphoma 2 expression higher than that in HepG2 cells.

RANK Ligand Modulation of Autophagy in Oral Squamous Cell Carcinoma Tumor Cells

Autophagy is a cellular process to recycle nutrients and has been implicated in cancer treatment. Oral squamous cell carcinoma (OSCC) is the most common oral cancer which ranks 3% of cancers in men and 2% in women. In this study, immunohistochemical staining of OSCC tumor specimens from human subjects and an athymic mouse model demonstrated high levels of autophagy markers LC3-II and ATG5 expression. Further, we identified high levels LC3-II expression in OSCC tumor cell lines (SCC-1, SCC-12, and SCC-14a) compared to normal human epithelial (RWPE-1) cells. OSCC cells express high levels of RANK ligand (RANKL); however, a functional role in autophagy is unknown. Interestingly, RANKL stimulation significantly increased autophagosome-related gene expressions such as LC3, ATG5, BECN1, and PI3KC3 mRNA expression in OSCC cells. Further, Western blot analysis of total cell lysates demonstrated a dose-dependent increase in LC3-II and ATG5 expression in RANKL-stimulated cells. In addition, RANKL increased expression of LC3-I and LC3-II, essential for autophagosome formation. Confocal microscopy analysis of LC3-II and localization with lysosome further confirms autophagosome formation in response to RANKL treatment in OSCC cells. Collectively, our results indicate a novel function of RANKL to induce autophagosome formation, and could be a potential therapeutic target to control OSCC tumor progression.

Increased ATG5-ATG12 in hepatitis B virus-associated hepatocellular carcinoma and their role in apoptosis

AIM

To investigate autophagy-related genes, particularly ATG12, in apoptosis and cell cycle in hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC) and non-HBV-HCC cell lines.

METHODS

The expression of autophagy-related genes in HBV-associated hepatocellular carcinoma and non-HBV-HCC cell lines and human liver tissues was examined by quantitative real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) and western blotting. The silencing of target genes was used to examine the function of various genes in apoptosis and cell cycle progression.

RESULTS

The expression of autophagy related genes ATG5, ATG12, ATG9A and ATG4B expression was analyzed in HepG2.2.15 cells and compared with HepG2 and THLE cells. We found that ATG5 and ATG12 mRNA expression was significantly increased in HepG2.2.15 cells compared to HepG2 cells (P < 0.005). Moreover, ATG5-ATG12 protein levels were increased in tumor liver tissues compared to adjacent non-tumor tissues mainly from HCC patients with HBV infection. We also analyzed the function of ATG12 in cell apoptosis and cell cycle progression. The percentage of apoptotic cells increased by 11.4% in ATG12-silenced HepG2.2.15 cells (P < 0.005) but did not change in ATG12-silenced HepG2 cells under starvation with Earle’s balanced salt solution. However, the combination blockade of Notch signaling and ATG12 decreased the apoptotic rate of HepG2.2.15 cells from 55.6% to 50.4% (P < 0.05).

CONCLUSION

ATG12 is important for HBV-associated apoptosis and a potential drug target for HBV-HCC. Combination inhibition of ATG12/Notch signaling had no additional effect on HepG2.2.15 apoptosis.

The role of mTOR during cisplatin treatment in an in vitro and ex vivo model of cervical cancer

Cisplatin is used as a cytotoxic agent for the management of cervical cancer. However, the severity of the side-effects limits the use of this drug, particularly at high doses. Resistance to cisplatin is often attributed to a disruption in the normal apoptotic response via aberrant activation of pathways such as the mTOR pathway. Here we assess the role of mTOR and its effect on cell death sensitization and autophagy in response to a low concentration of cisplatin in cervical cancer cells. Additionally we measured the expression profile of mTOR in normal, low- and high-grade squamous intraepithelial (LSIL and HSIL) lesions and cancerous tissue. An in vitro model of cervical cancer was established using HeLa and CaSki cells. mTOR protein expression as well as autophagy-related proteins were evaluated through Western blotting. Inhibition of mTOR was achieved with the use of rapamycin and RNA silencing. A low concentration of cisplatin administered as a single agent induces autophagy, but not apoptosis. Cisplatin cytotoxicity was greatly enhanced in cancer cells when mTOR had been inhibited prior to cisplatin treatment which was likely due to autophagy being increased above cisplatin-induced levels, thereby inducing apoptosis. Cervical tissue samples revealed an increase in mTOR protein expression in LSIL and carcinoma tissue which suggests a change in autophagy control. Our data suggest that utilising a lower dose of cisplatin combined with mTOR inhibition is a viable treatment option and addresses the challenge of cisplatin dose-dependent toxicity, however future studies are required to confirm this in a clinical setting.

Temsirolimus, the mTOR inhibitor, induces autophagy in adenoid cystic carcinoma: in vitro and in vivo

Temsirolimus acts as a mammalian target of rapamycin (mTOR)-dependent autophagic inhibitor. In order to clarify its effects and mechanisms on human salivary adenoid cystic carcinoma (ACC), we examined whether temsirolimus induced autophagy as the mTOR inhibitor in ACC, both in vitro and in vivo. In this study, MTT assay showed that the inhibition effect of temsirolimus assumed an obvious dose-response relationship on ACC-M cells, and the 50% inhibitory concentration (IC(50)) approached 20 μmol/l; numerous autophagosomes were observed by the transmission electron microscopy (TEM) in temsirolimus treatment groups; notably, expression of LC3 and Beclin1 was significantly up-regulated by temsirolimus. More importantly, the xenograft model provided further evidence of temsirolimus-induced autophagy in vivo by inhibiting mTOR activation as well as up-regulation the expression of Beclin1. These results suggest that temsirolimus could act as an mTOR inhibitor to induce autophagy in adenoid cystic carcinoma both in vitro and in vivo.

Integration of autophagy and anoikis resistance in solid tumors

Macroautophagy or autophagy is a lysosome-dependent process in which enzymatic degradation and recycling of cytosolic components occurred due to stressful conditions. This cellular arrangement imparts anoikis resistance in solid tumors. Anoikis, a special form of apoptosis occurring when cells detach from the extracellular matrix, is a critical mechanism in maintaining tissue homeostasis and development. Anoikis resistance facilitates tumorigenesis and metastasis. However, the complexity of the role of autophagy in tumor is underscored by evidence that autophagy can function as both a pro-survival or pro-death depending on the context and the stimuli, which are likely exploitable for tumor therapy. This review focuses on recent progress in understanding anoikis resistance and autophagy signaling, paying particular attention to its relevance in solid tumor metastasis.

The role of autophagy in liver cancer: molecular mechanisms and potential therapeutic targets

Autophagy is an evolutionarily conserved pathway for degradation of cytoplasmic proteins and organelles via lysosome. Proteins coded by the autophagy-related genes (Atgs) are the core molecular machinery in control of autophagy. Among the various biological functions of autophagy identified so far, the link between autophagy and cancer is probably among the most extensively studied and is often viewed as controversial. Autophagy might exert a dual role in cancer development: autophagy can serve as an anti-tumor mechanism, as defective autophagy (e.g., heterozygous knockdown Beclin 1 and Atg7 in mice) promotes the malignant transformation and spontaneous tumors. On the other hand, autophagy functions as a protective or survival mechanism in cancer cells against cellular stress (e.g., nutrient deprivation, hypoxia and DNA damage) and hence promotes tumorigenesis and causes resistance to therapeutic agents. Liver cancer is one of the common cancers with well-established etiological factors including hepatitis virus infection and environmental carcinogens such as aflatoxin and alcohol exposure. In recent years, the involvement of autophagy in liver cancer has been increasingly studied. Here, we aim to provide a systematic review on the close cross-talks between autophagy and liver cancer, and summarize the current status in development of novel liver cancer therapeutic approaches by targeting autophagy. It is believed that understanding the molecular mechanisms underlying the autophagy modulation and liver cancer development may provoke the translational studies that ultimately lead to new therapeutic strategies for liver cancer.