A Promising New Anti-Cancer Strategy: Iron Chelators Targeting CSCs

Iron is a trace but vital element in the human body and is necessary for a multitude of crucial processes in life. However, iron overload is known to induce carcinogenesis via oxidative stress. Cancer cells require large amounts of iron for their rapid division and cell growth. Iron was recently found to play a role in cancer stem cells (CSCs); it maintains stemness during development. Iron also plays an important role in stemness by moderating reactive oxygen species. Thus, iron metabolism in CSCs is a promising therapeutic target. In this review, we summarize the roles of iron in cancer cells and CSCs. We also summarize anti-cancer therapeutic studies with iron chelators and describe our expectation of a new therapeutic strategy for CSCs on the basis of our findings

The Deubiquitinase ZRANB1 Is an E3 Ubiquitin Ligase for SLC7A11 and Regulates Ferroptotic Resistance

The dependency of cancer cells on iron increases their susceptibility to ferroptosis, thus providing new opportunities for patients with treatment-resistant tumors. However, we show that lipid peroxidation, a hallmark of ferroptosis, was found in various areas of patient samples, indicating the potential resistance of ferroptosis. Using whole deubiquitinases (DUBs) sgRNA screening, we found that loss of ZRANB1 confers cancer cell resistance to ferroptosis. Intriguingly, functional studies revealed that ZRANB1 ubiquitinates and represses SLC7A11 expression as an E3 ubiquitin ligase and that ZRANB1 inhibits glutathione (GSH) synthesis through SLC7A11 degradation, leading to elevated lipid peroxidation and ferroptosis. Deletion of the region (residues 463–584) abolishes the E3 activity of ZRANB1. Moreover, we show that ZRANB1 has lower expression in tumors, which is positively correlated with lipid peroxidation. Collectively, our results demonstrate the role of ZRANB1 in ferroptosis resistance and unveil mechanisms involving modulation of E3 ligase activity through an unconventional catalytic domain

Polyamine-Mediated Ferroptosis Amplification Acts as a Targetable Vulnerability in Cancer

Targeting ferroptosis, an iron-dependent form of regulated cell death triggered by the lethal overload of lipid peroxides, in cancer therapy is impeded by our limited understanding of the intersection of tumour’s metabolic feature and ferroptosis vulnerability. In the present study, arginine is identified as a ferroptotic promoter using a metabolites library. This effect is mainly achieved through arginine’s conversion to polyamines, which exerts their potent ferroptosis-promoting property in an H2O2-dependent manner. Notably, the expression of ornithine decarboxylase 1 (ODC1), the critical enzyme catalysing polyamine synthesis, is significantly activated by the ferroptosis signal——iron overload——through WNT/MYC signalling, as well as the subsequent elevated polyamine synthesis, thus forming a ferroptosis-iron overload-WNT/MYC-ODC1-polyamine-H2O2 positive feedback loop that amplifies ferroptosis. Meanwhile, we notice that ferroptotic cells release enhanced polyamine-containing extracellular vesicles into the microenvironment, thereby further sensitizing neighbouring cells to ferroptosis and accelerating the “spread” of ferroptosis in the tumour region. Besides, polyamine supplementation also sensitizes cancer cells or xenograft tumours to radiotherapy or chemotherapy through inducing ferroptosis. Considering that cancer cells are often characterized by elevated intracellular polyamine pools, our results indicate that polyamine metabolism exposes a targetable vulnerability to ferroptosis and represents an exciting opportunity for therapeutic strategies for cancer

A Novel Combination Cancer Therapy with Iron Chelator Targeting Cancer Stem Cells via Suppressing Stemness

Excess iron causes cancer and is thought to be related to carcinogenesis and cancer progression including stemness, but the details remain unclear. Here, we hypothesized that stemness in cancer is related to iron metabolism and that regulating iron metabolism in cancer stem cells (CSCs) may be a novel therapy. In this study, we used murine induced pluripotent stem cells that expressed specific stem cell genes such as Nanog, Oct3/4, Sox2, Klf4, and c-Myc, and two human cancer cell lines with similar stem cell gene expression. Deferasirox, an orally available iron chelator, suppressed expression of stemness markers and spherogenesis of cells with high stemness status in vitro. Combination therapy had a marked antitumor effect compared with deferasirox or cisplatin alone. Iron metabolism appears important for maintenance of stemness in CSCs. An iron chelator combined with chemotherapy may be a novel approach via suppressing stemness for CSC targeted therapy

High co-expression of the SDF1/CXCR4 axis in hepatocarcinoma cells is regulated by AnnexinA7 in vitro and in vivo

Abstract Background SDF1/CXCR4 and AnnexinA7 play important roles in many physiological and pathological conditions, but the molecular association between them in cancer cells has not been studied thus far. Methods The expression changes of SDF1/CXCR4 were detected by gene transcriptome sequencing, qRT-PCR, Western blotting, cytoimmunofluorescence and immunohistochemistry in mouse hepatocarcinoma F/P cells, AnnexinA7 downregulated expression F (FA7DOWN) cells, AnnexinA7 overexpression P (PA7UP) cells, AnnexinA7 unrelated sequence F (FSHUS) cells, empty vector P (PNCEV) cells and normal liver cells in vitro and in vivo. Results SDF1 and CXCR4 were co-expressed in hepatocarcinoma cells. SDF1 was localized mainly in the cytoplasm of cells, while CXCR4 was mainly localized in the cell membrane. Both in vitro and in vivo, expression levels of SDF1/CXCR4 in F and P cells were higher than in normal liver cells, and expression levels of SDF1/CXCR4 in F cells with high lymphatic metastatic potential were higher than those in P cells with low lymphatic metastatic potential. Expression of SDF1 was higher than that of CXCR4 in P cells and normal liver cells, while expression of CXCR4 was higher than that of SDF1 in F cells. Expression levels of SDF1/CXCR4 were completely consistent with AnnexinA7 regulation. After the AnnexinA7 gene was downregulated or upregulated, expression levels of SDF1/CXCR4 in FA7DOWN/PA7UP cells were lower or higher than those in FSHUS/PNCEV cells. Furthermore, CXCR4 was more sensitively modulated by AnnexinA7 regulation than SDF1. Conclusions High co-expression of SDF1/CXCR4 is a molecular characteristic of hepatocarcinoma cells, especially those with high lymphatic metastatic potential. AnnexinA7 positively regulates expression levels of SDF1/CXCR4, in particular CXCR4, and AnnexinA7 is a functional regulator of SDF1/CXCR4

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field