Ruthenium complex containing 1,3-thiazolidine-2-thione inhibits hepatic cancer stem cells by suppressing Akt/mTOR signalling and leading to apoptotic and autophagic cell death.

Hepatic cancer is one of the main causes of cancer-related death worldwide. Cancer stem cells (CSCs) are a unique subset of cancer cells that promote tumour growth, maintenance, and therapeutic resistance, leading to recurrence. In the present work, the ability of a ruthenium complex containing 1,3-thiazolidine-2-thione (RCT), with the chemical formula [Ru(tzdt)(bipy)(dppb)]PF6, to inhibit hepatic CSCs was explored in human hepatocellular carcinoma HepG2 cells. RCT exhibited potent cytotoxicity to solid and haematological cancer cell lines and reduced the clonogenic potential, CD133+ and CD44high cell percentages and tumour spheroid growth of HepG2 cells. RCT also inhibited cell motility, as observed in the wound healing assay and transwell cell migration assay. RCT reduced the levels of Akt1, phospho-Akt (Ser473), phospho-Akt (Thr308), phospho-mTOR (Ser2448), and phospho-S6 (Ser235/Ser236) in HepG2 cells, indicating that interfering with Akt/mTOR signalling is a mechanism of action of RCT. The levels of active caspase-3 and cleaved PARP (Asp214) were increased in RCT-treated HepG2 cells, indicating the induction of apoptotic cell death. In addition, RCT modulated the autophagy markers LC3B and p62/SQSTM1 in HepG2 cells and increased mitophagy in a mt-Keima-transfected mouse embryonic fibroblast (MEF) cell model, and RCT-induced cytotoxicity was partially prevented by autophagy inhibitors. Furthermore, mutant Atg5-/- MEFs and PentaKO HeLa cells (human cervical adenocarcinoma with five autophagy receptor knockouts) were less sensitive to RCT cytotoxicity than their parental cell lines, indicating that RCT induces autophagy-mediated cell death. Taken together, these data indicate that RCT is a novel potential anti-liver cancer drug with a suppressive effect on CSCs.

Improving the Therapeutic Efficacy of Sorafenib for Hepatocellular Carcinoma by Repurposing Disulfiram.

Background: Sorafenib, a kinase inhibitor, is a standard treatment for advanced hepatocellular carcinoma (HCC) but provides only a limited survival benefit. Disulfiram (DSF), a drug for treating alcoholism and a chelator of copper (Cu), forms a complex with Cu (DSF/Cu). DSF/Cu is a potent inducer of autophagic apoptosis of cancer stem cells, which can demonstrate drug resistance. Thus, we hypothesized that DSF/Cu could increase the sensitivity of HCC cells to sorafenib by targeting hepatic cancer stem cells. Methods: The synergistic effect of DSF/Cu and sorafenib on human HCC cell lines was assessed by cell viability MTT assay. Changes in stemness gene expression in HCC cells were investigated by assessing the presence of hepatic cancer stem cells (HCSCs) (defined as ALDH+ cells) using flow cytometry, sphere formation ability as an index of in vitro tumorigenicity, and expression of stemness gene-encoded proteins by western blot. Autophagic apoptosis and the ERK signaling pathway were also assessed by western blot. Most importantly, the in vivo anti-tumor efficacy of DSF/Cu and sorafenib was tested using orthotopic HCC xenografts in mice. Results: Compared with sorafenib alone, DSF/Cu + sorafenib synergistically inhibited proliferation of all HCC cell lines, decreased the stemness of HCC cells, and increased the autophagy and apoptosis of HCC cells. The mechanism by which DSF/Cu mediated these phenomena with sorafenib was sustained activation of the ERK pathway. The combination of DSF/Cu (formed with endogenous Cu2+) and sorafenib was significantly more effective than sorafenib alone in inhibiting the growth of orthotopic HCC xenografts in mice. This in vivo anti-tumor efficacy was associated with decreased stemness in treated HCC tumors. Conclusions: DSF/Cu and sorafenib can synergistically and effectively treat HCC by targeting HCSCs in vitro and in vivo. Our data provide a foundation for clinical translation.

Targeting Liver Cancer Stem Cells: An Alternative Therapeutic Approach for Liver Cancer.

The first report of cancer stem cell (CSC) from Bruce et al. has demonstrated the relatively rare population of stem-like cells in acute myeloid leukemia (AML). The discovery of leukemic CSCs prompted further identification of CSCs in multiple types of solid tumor. Recently, extensive research has attempted to identity CSCs in multiple types of solid tumors in the brain, colon, head and neck, liver, and lung. Based on these studies, we hypothesize that the initiation and progression of most malignant tumors rely largely on the CSC population. Recent studies indicated that stem cell-related markers or signaling pathways, such as aldehyde dehydrogenase (ALDH), CD133, epithelial cell adhesion molecule (EpCAM), Wnt/ß-catenin signaling, and Notch signaling, contribute to the initiation and progression of various liver cancer types. Importantly, CSCs are markedly resistant to conventional therapeutic approaches and current targeted therapeutics. Therefore, it is believed that selectively targeting specific markers and/or signaling pathways of hepatic CSCs is an effective therapeutic strategy for treating chemotherapy-resistant liver cancer. Here, we provide an overview of the current knowledge on the hepatic CSC hypothesis and discuss the specific surface markers and critical signaling pathways involved in the development and maintenance of hepatic CSC subpopulations.

Hepatitis B Virus-Associated Hepatocellular Carcinoma and Hepatic Cancer Stem Cells.

Chronic Hepatitis B Virus (HBV) infection is linked to hepatocellular carcinoma (HCC) pathogenesis. Despite the availability of a HBV vaccine, current treatments for HCC are inadequate. Globally, 257 million people are chronic HBV carriers, and children born from HBV-infected mothers become chronic carriers, destined to develop liver cancer. Thus, new therapeutic approaches are needed to target essential pathways involved in HCC pathogenesis. Accumulating evidence supports existence of hepatic cancer stem cells (hCSCs), which contribute to chemotherapy resistance and cancer recurrence after treatment or surgery. Understanding how hCSCs form will enable development of therapeutic strategies to prevent their formation. Recent studies have identified an epigenetic mechanism involving the downregulation of the chromatin modifying Polycomb Repressive Complex 2 (PRC2) during HBV infection, which results in re-expression of hCSC marker genes in infected hepatocytes and HBV-associated liver tumors. However, the genesis of hCSCs requires, in addition to the expression of hCSC markers cellular changes, rewiring of metabolism, cell survival, escape from programmed cell death, and immune evasion. How these changes occur in chronically HBV-infected hepatocytes is not yet understood. In this review, we will present the basics about HBV infection and hepatocarcinogenesis. Next, we will discuss studies describing the mutational landscape of liver cancers and how epigenetic mechanisms likely orchestrate cellular reprograming of hepatocytes to enable formation of hCSCs.

Research progress on regulatory mechanism and therapeutic targets of hepatic cancer stem cells / 医学研究生学报

HCC is the 5th most common malignant cancer worldwide. The high rate of tumor recurrence and widespread metastasis are closely associated with low survival rates in cancer patients . Several studies have demonstrated hepatic cancer stem cells (HCSCs), also called tumor-initiating cells, are involved in regulation of HCC initiation, progression, metastasis, and drug resistance. Therefore ,in this review we integrated the latest research progress on HCSC, explained the main mechanism of signaling pathways such as TGF/β，Hippo-YAP/TAZ,Wnt/β protein,Hedgehog(Hh),etc. In the mwantime, we analyzed the potential therapeutic targets in signaling pathways to provid a new promising treatment strategies for chemotherapy drug resistance of liver tumor.

Mitophagy Controls the Activities of Tumor Suppressor p53 to Regulate Hepatic Cancer Stem Cells.

Autophagy is required for benign hepatic tumors to progress into malignant hepatocellular carcinoma. However, the mechanism is unclear. Here, we report that mitophagy, the selective removal of mitochondria by autophagy, positively regulates hepatic cancer stem cells (CSCs) by suppressing the tumor suppressor p53. When mitophagy is enhanced, p53 co-localizes with mitochondria and is removed by a mitophagy-dependent manner. However, when mitophagy is inhibited, p53 is phosphorylated at serine-392 by PINK1, a kinase associated with mitophagy, on mitochondria and translocated into the nucleus, where it binds to the NANOG promoter to prevent OCT4 and SOX2 transcription factors from activating the expression of NANOG, a transcription factor critical for maintaining the stemness and the self-renewal ability of CSCs, resulting in the reduction of hepatic CSC populations. These results demonstrate that mitophagy controls the activities of p53 to maintain hepatic CSCs and provide an explanation as to why autophagy is required to promote hepatocarcinogenesis.

New insight into the role of autophagy in tumorigenesis.

Autophagy plays an important role in maintaining cellular homeostasis. Its dysfunction can cause many diseases, including neurodegenerative diseases, metabolic diseases and cancer. The role of autophagy in carcinogenesis is complex, as it was shown to have pro-tumorigenic functions in some reports, but anti-tumorigenic functions in others. By using mice with hepatocyte-specific knockout of Atg5, a gene essential for autophagy, we had previously demonstrated that impairing autophagy in hepatocytes would induce oxidative stress and DNA damage, followed by the initiation of hepatocarcinogenesis. Interestingly, these mice developed only benign tumors with no hepatocellular carcinoma (HCC), even after they were treated with the carcinogen diethylnitrosamine (DEN), which induced HCC in wild-type mice. Our recent studies indicated that the inability of mice to develop HCC when autophagy was impaired was at least partially due to the activation of the tumor suppressor TP53, which suppressed the expression of NANOG, a transcription factor critical for the self-renewal and the maintenance of cancer stem cells (CSCs).

Establishment of a novel system for the culture and expansion of hepatic stem-like cancer cells.

Hepatocellular carcinoma (HCC) is a major primary liver malignancy in adults. Despite the progress made, the outcome of the treatment to this disease is less than satisfactory as the post therapy tumor recurrence is almost inevitable. Accumulating pieces of evidence have suggested that the recurrence is due to the existence of a subpopulation of the HCC cells that possess the properties of stem cells and are resistant to radiation and chemotherapy. It is therefore important to understand the characteristics of this subpopulation of HCC cells, and which requires the establishment of an in vitro system to study these stem-like cancer cells. However, despite extensive efforts, the progress in establishing such an in vitro system has been slow largely due to the lack of definitive biomarkers in the isolation and expansion of these cells. In order to successfully maintain and expand HCC CSCs, we first optimized the culture system. We establish a novel medium system that allows the culture and enrichment of these hepatic stem-like cancer cells from both hepatoma cells and human primary HCC cells. These cells exhibited typical stem cell properties, such as enhanced stem cell markers, gain of EMT properties and drug resistance, and more importantly, stronger tumor-initiating capabilities. The medium may help to establish an in vitro model for hepatic cancer stem cell (HCSC) studies, which may contribute to the development of novel cell therapies and new drugs for the treatment of HCC.