STAT3-mediated autophagy dependence identifies subtypes of breast cancer where autophagy inhibition can be efficacious

Tetraarsenic hexoxide enhances generation of mitochondrial ROS to promote pyroptosis by inducing the activation of caspase-3/GSDME in triple-negative breast cancer cells

Although tetraarsenic hexoxide is known to exert an anti-tumor effect by inducing apoptosis in various cancer cells, its effect on other forms of regulated cell death remains unclear. Here, we show that tetraarsenic hexoxide induces the pyroptotic cell death through activation of mitochondrial reactive oxygen species (ROS)-mediated caspase-3/gasdermin E (GSDME) pathway, thereby suppressing tumor growth and metastasis of triple-negative breast cancer (TNBC) cells. Interestingly, tetraarsenic hexoxide-treated TNBC cells exhibited specific pyroptotic characteristics, including cell swelling, balloon-like bubbling, and LDH releases through pore formation in the plasma membrane, eventually suppressing tumor formation and lung metastasis of TNBC cells. Mechanistically, tetraarsenic hexoxide markedly enhanced the production of mitochondrial ROS by inhibiting phosphorylation of mitochondrial STAT3, subsequently inducing caspase-3-dependent cleavage of GSDME, which consequently promoted pyroptotic cell death in TNBC cells. Collectively, our findings highlight tetraarsenic hexoxide-induced pyroptosis as a new therapeutic strategy that may inhibit cancer progression of TNBC cells.

Emerging Autophagy Functions Shape the Tumor Microenvironment and Play a Role in Cancer Progression - Implications for Cancer Therapy

The tumor microenvironment (TME) is a complex environment where cancer cells reside and interact with different types of cells, secreted factors, and the extracellular matrix. Additionally, TME is shaped by several processes, such as autophagy. Autophagy has emerged as a conserved intracellular degradation pathway for clearance of damaged organelles or aberrant proteins. With its central role, autophagy maintains the cellular homeostasis and orchestrates stress responses, playing opposite roles in tumorigenesis. During tumor development, autophagy also mediates autophagy-independent functions associated with several hallmarks of cancer, and therefore exerting several effects on tumor suppression and/or tumor promotion mechanisms. Beyond the concept of degradation, new different forms of autophagy have been described as modulators of cancer progression, such as secretory autophagy enabling intercellular communication in the TME by cargo release. In this context, the synthesis of senescence-associated secretory proteins by autophagy lead to a senescent phenotype. Besides disturbing tumor treatment responses, autophagy also participates in innate and adaptive immune signaling. Furthermore, recent studies have indicated intricate crosstalk between autophagy and the epithelial-mesenchymal transition (EMT), by which cancer cells obtain an invasive phenotype and metastatic potential. Thus, autophagy in the cancer context is far broader and complex than just a cell energy sensing mechanism. In this scenario, we will discuss the key roles of autophagy in the TME and surrounding cells, contributing to cancer development and progression/EMT. Finally, the potential intervention in autophagy processes as a strategy for cancer therapy will be addressed.

Single-cell analysis of autophagy activity in normal and de novo transformed human mammary cells

Assessment of autophagy activity has historically been limited to investigations of fixed tissue or bulk cell populations. To address questions of heterogeneity and relate measurements to functional properties of viable cells isolated from primary tissue, we created a lentiviral (RFP-GFP-MAP1LC3B) vector that allows the autophagosome and autolysosome content of transduced cells to be monitored at the single-cell level. Use of this strategy to analyze purified subsets of normal human mammary cells showed that both the luminal progenitor-containing (LP) subset and the basal cells (BCs) display highly variable but overall similar autophagic flux activity despite differences suggested by measurements of the proteins responsible (i.e., LC3B, ATG7 and BECLIN1) in bulk lysates. Autophagosome content was also highly variable in the clonogenic cells within both the LPs and BCs, but the proliferative response of the BCs was more sensitive to autophagy inhibition. In addition, use of this vector showed cells with the lowest autophagosome content elicited the fastest tumor growth in 2 different models of human mammary tumorigenesis. These results illustrate the utility of this vector to define differences in the autophagy properties of individual cells in primary tissue and couple these with their responses to proliferative and oncogenic stimuli.

Effects of different autophagy inhibitors on sensitizing KG-1 and HL-60 leukemia cells to chemotherapy

A little number of current autophagy inhibitors may have beneficial effects on the acute myeloid leukemia (AML) patients. However, there is a strong need to figure out which settings should be activated or inhibited in autophagy pathway to prevail drug resistance and also to improve current treatment options in leukemia. Therefore, this study aimed to compare the effects of well-known inhibitors of autophagy (as 3-MA, BafA1, and HCQ) in leukemia KG-1 and HL-60 cells exposed to arsenic trioxide (ATO) and/or all-trans retinoic acid (ATRA). Cell proliferation and cytotoxicity of cells were examined by MTT assay. Autophagy was studied by evaluating the development of acidic vesicular organelles, and the autophagosomes formation was investigated by acridine orange staining and transmission electron microscopy. Moreover, the gene and protein expressions levels of autophagy markers (ATGs, p62/SQSTM1, and LC-3B) were also performed by qPCR and western blotting, respectively. The rate of apoptosis and cell cycle were evaluated using flow cytometry. We compared the cytotoxic and apoptotic effects of ATO and/or ATRA in both cell lines and demonstrated that some autophagy markers upregulated in this context. Also, it was shown that autophagy blockers HCQ and/or BafA1 could potentiate the cytotoxic effects of ATO/ATRA, which were more pronounced in KG-1 cells compared to HL-60 cell line. This study showed the involvement of autophagy during the treatment of KG-1 and HL-60 cells by ATO/ATRA. This study proposed that therapy of ATO/ATRA in combination with HCQ can be considered as a more effective strategy for targeting leukemic KG-1 cells.

Design, Synthesis, and Characterization of an Orally Active Dual-Specific ULK1/2 Autophagy Inhibitor that Synergizes with the PARP Inhibitor Olaparib for the Treatment of Triple-Negative Breast Cancer

Inhibition of autophagy, the major cellular recycling pathway in mammalian cells, is a promising strategy for the treatment of triple-negative breast cancer (TNBC). We previously reported SBI-0206965, a small molecule inhibitor of unc-51-like autophagy activating kinase 1 (ULK1), which is a key regulator of autophagy initiation. Herein, we describe the design, synthesis, and characterization of new dual inhibitors of ULK1 and ULK2 (ULK1/2). One inhibitor, SBP-7455 (compound 26), displayed improved binding affinity for ULK1/2 compared with SBI-0206965, potently inhibited ULK1/2 enzymatic activity in vitro and in cells, reduced the viability of TNBC cells and had oral bioavailability in mice. SBP-7455 inhibited starvation-induced autophagic flux in TNBC cells that were dependent on autophagy for survival and displayed synergistic cytotoxicity with the poly (ADP-ribose) polymerase (PARP) inhibitor olaparib against TNBC cells. These data suggest that combining ULK1/2 and PARP inhibition may have clinical utility for the treatment of TNBC.

Lysosomal Biogenesis and Implications for Hydroxychloroquine Disposition

Lysosomes act as a cellular drug sink for weakly basic, lipophilic (lysosomotropic) xenobiotics, with many instances of lysosomal trapping associated with multiple drug resistance. Lysosomotropic agents have also been shown to activate master lysosomal biogenesis transcription factor EB (TFEB) and ultimately lysosomal biogenesis. We investigated the role of lysosomal biogenesis in the disposition of hydroxychloroquine (HCQ), a hallmark lysosomotropic agent, and observed that modulating the lysosomal volume of human breast cancer cell lines can account for differences in disposition of HCQ. Through use of an in vitro pharmacokinetic (PK) model, we characterized total cellular uptake of HCQ within the duration of static equilibrium (1 hour), as well as extended exposure to HCQ that is subject to dynamic equilibrium (>1 hour), wherein HCQ increases the size of the lysosomal compartment through swelling and TFEB-induced lysosomal biogenesis. In addition, we observe that pretreatment of cell lines with TFEB-activating agent Torin1 contributed to an increase of whole-cell HCQ concentrations by 1.4- to 1.6-fold, which were also characterized by the in vitro PK model. This investigation into the role of lysosomal volume dynamics in lysosomotropic drug disposition, including the ability of HCQ to modify its own disposition, advances our understanding of how chemically similar agents may distribute on the cellular level and examines a key area of lysosomal-mediated multiple drug resistance and drug-drug interaction. SIGNIFICANCE STATEMENT: Hydroxychloroquine is able to modulate its own cellular pharmacokinetic uptake by increasing the cellular lysosomal volume fraction through activation of lysosomal biogenesis master transcription factor EB and through lysosomal swelling. This concept can be applied to many other lysosomotropic drugs that activate transcription factor EB, such as doxorubicin and other tyrosine kinase inhibitor drugs, as these drugs may actively increase their own sequestration within the lysosome to further exacerbate multiple drug resistance and lead to potential acquired resistance.

Circulating Interleukin-6 (but Not Other Immune Mediators) Associates with Criteria for Fried's Frailty among Very Old Adults

Methods

One hundred and sixty-one very old patients (aged ≥80 years) devoid of cognitive decline were eligible for analyses. Clinical and biochemical data along with physical and cognitive assessments encompassing dual-energy X-ray scans and hand dynamometry were adopted to investigate frailty criteria, while circulating immune mediators (IFNγ, IL-2, IL-4, IL-6, IL-10, and TNFα) were assessed using high-throughput flow cytometry.

Results

Preliminarily, IL-6 correlated positively with waist-to-hip ratio and C-reactive protein and negatively with glycemia. In analyses controlled for these factors, serum levels of IL-6 were comparatively augmented among the very old participants with reduced grip strength (OR = 3.299; 95% CI 1.08–6.09; p=0.032) and among those with slow walk speed (OR = 2.460; 95% CI 1.16–7.05; p=0.022).

Conclusions

Our study shows a strong negative correlation of IL-6 levels with Fried's frailty components of grip strength and walk speed in very old adults, regardless of confounding factors.

Targeting Autophagy in Breast Cancer

Breast cancer is a heterogeneous disease consisting of different biological subtypes, with differences in terms of incidence, response to diverse treatments, risk of disease progression, and sites of metastases. In the last years, several molecular targets have emerged and new drugs, targeting PI3K/Akt/mTOR and cyclinD/CDK/pRb pathways and tumor microenvironment have been integrated into clinical practice. However, it is clear now that breast cancer is able to develop resistance to these drugs and the identification of the underlying molecular mechanisms is paramount to drive further drug development. Autophagy is a highly conserved homeostatic process that can be activated in response to antineoplastic agents as a cytoprotective mechanism. Inhibition of autophagy could enhance tumor cell death by diverse anti-cancer therapies, representing an attractive approach to control mechanisms of drug resistance. In this manuscript, we present a review of autophagy focusing on its interplay with targeted drugs used for breast cancer treatment.

Tumors Responsive to Autophagy-Inhibition: Identification and Biomarkers

Simple Summary

Although the principle of personalized medicine has been the focus of attention, many cancer therapies are still based on a one-size-fits-all approach. The same holds true for targeting cancer cell survival mechanism that allows cancer cells to recycle their constituents (autophagy). In the past several indicators of elevated dependence of cancer cells on autophagy have been described. Addition of autophagy-inhibiting agents could be beneficial in treatment of these tumors. The biomarkers and mechanisms that lead to elevated dependence on autophagy are reviewed in the current manuscript.

Abstract

Recent advances in cancer treatment modalities reveal the limitations of the prevalent “one-size-fits-all” therapies and emphasize the necessity to develop personalized approaches. In this perspective, identification of predictive biomarkers and intrinsic vulnerabilities are an important advancement for further therapeutic strategies. Autophagy is an important lysosomal degradation and recycling pathway that provides energy and macromolecular precursors to maintain cellular homeostasis. Although all cells require autophagy, several genetic and/or cellular changes elevate the dependence of cancer cells on autophagy for their survival and indicates that autophagy inhibition in these tumors could provide a favorable addition to current therapies. In this context, we review the current literature on tumor (sub)types with elevated dependence on autophagy for their survival and highlight an exploitable vulnerability. We provide an inventory of microenvironmental factors, genetic alterations and therapies that may be exploited with autophagy-targeted approaches to improve efficacy of conventional anti-tumor therapies.

Matrine exerts anti‑breast cancer activity by mediating apoptosis and protective autophagy via the AKT/mTOR pathway in MCF‑7 cells

Matrine, a major alkaloid isolated from the traditional Chinese herb Sophora flavescens, has been used clinically to treat breast cancer in China. However, the effects of matrine on apoptosis and autophagy in breast cancer cells remain unclear. In the present study, the anti-breast cancer capacity of matrine was evaluated and its role in regulating apoptosis and autophagy in vitro was investigated. Matrine significantly inhibited the growth of MCF-7 cells. In addition, Hoechst 33342 staining and Annexin V/propidium iodide staining demonstrated that incubation with matrine induced apoptosis in MCF-7 cells. Furthermore, matrine induced autophagy in MCF-7 cells, manifesting as an accumulation of light chain 3 II and downregulation of p62. Additionally, matrine suppressed AKT and mammalian target of rapamycin (mTOR) phosphorylation, indicating that the AKT/mTOR pathway is involved in matrine-induced apoptosis and autophagy. Overall, the results of the present study indicated that matrine possesses anti-breast cancer activity by providing protective autophagy via inhibition of the AKT/mTOR pathway. These findings indicated that matrine may be a promising candidate for drug development targeting breast cancer.

Flavopereirine Inhibits Autophagy via the AKT/p38 MAPK Signaling Pathway in MDA-MB-231 Cells

Autophagy is a potential target for the treatment of triple negative breast cancer (TNBC). Because of a lack of targeted therapies for TNBC, it is vital to find optimal agents that avoid chemoresistance and metastasis. Flavopereirine has anti-proliferation ability in cancer cells, but whether it regulates autophagy in breast cancer cells remains unclear. A Premo™ Tandem Autophagy Sensor Kit was used to image the stage at which flavopereirine affects autophagy by confocal microscopy. A plasmid that constitutively expresses p-AKT and siRNA targeting p38 mitogen-activated protein kinase (MAPK) was used to confirm the related signaling pathways by Western blot. We found that flavopereirine induced microtubule-associated protein 1 light chain 3 (LC3)-II accumulation in a dose- and time-dependent manner in MDA-MB-231 cells. Confocal florescent images showed that flavopereirine blocked autophagosome fusion with lysosomes. Western blotting showed that flavopereirine directly suppressed p-AKT levels and mammalian target of rapamycin (mTOR) translation. Recovery of AKT phosphorylation decreased the level of p-p38 MAPK and LC3-II, but not mTOR. Moreover, flavopereirine-induced LC3-II accumulation was partially reduced in MDA-MB-231 cells that were transfected with p38 MAPK siRNA. Overall, flavopereirine blocked autophagy via LC3-II accumulation in autophagosomes, which was mediated by the AKT/p38 MAPK signaling pathway.

Histone lysine demethylase 3B (KDM3B) regulates the propagation of autophagy via transcriptional activation of autophagy-related genes

Autophagy, a self-degradative physiological process, is critical for homeostasis maintenance and energy source balancing in response to various stresses, including nutrient deprivation. It is a highly conserved catabolic process in eukaryotes and is indispensable for cell survival as it involves degradation of unessential or excessive components and their subsequent recycling as building blocks for the synthesis of necessary molecules. Although the dysregulation of autophagy has been reported to broadly contribute to various diseases, including cancers and neurodegenerative diseases, the molecular mechanisms underlying the epigenetic regulation of autophagy are poorly elucidated. Here, we report that the level of lysine demethylase 3B (KDM3B) increases in nutrient-deprived HCT116 cells, a colorectal carcinoma cell line, resulting in transcriptional activation of the autophagy-inducing genes. KDM3B was found to enhance the transcription by demethylating H3K9me2 on the promoter of these genes. Furthermore, we observed that the depletion of KDM3B inhibited the autophagic flux in HCT116 cells. Collectively, these data suggested the critical role of KDM3B in the regulation of autophagy-related genes via H3K9me2 demethylation and induction of autophagy in nutrient-starved HCT116 cells.

Autophagy and cancer: Modulation of cell death pathways and cancer cell adaptations

Autophagy is intricately linked with many intracellular signaling pathways, particularly nutrient-sensing mechanisms and cell death signaling cascades. In cancer, the roles of autophagy are context dependent. Tumor cell-intrinsic effects of autophagy can be both tumor suppressive and tumor promotional. Autophagy can therefore not only activate and inhibit cell death, but also facilitate the switch between cell death mechanisms. Moreover, autophagy can play opposing roles in the tumor microenvironment via non-cell-autonomous mechanisms. Preclinical data support a tumor-promotional role of autophagy in established tumors and during cancer therapy; this has led to the launch of dozens of clinical trials targeting autophagy in multiple cancer types. However, many questions remain: which tumors and genetic backgrounds are the most sensitive to autophagy inhibition, and which therapies should be combined with autophagy inhibitors? Additionally, since cancer cells are under selective pressure and are prone to adaptation, particularly after treatment, it is unclear if and how cells adapt to autophagy inhibition. Here we review recent literature addressing these issues.

Differential expression and prognostic relevance of autophagy-related markers ATG4B, GABARAP, and LC3B in breast cancer

PURPOSE

Previous studies indicate that breast cancer molecular subtypes differ with respect to their dependency on autophagy, but our knowledge of the differential expression and prognostic significance of autophagy-related biomarkers in breast cancer is limited.

METHODS

Immunohistochemistry (IHC) was performed on tissue microarrays from a large population of 3992 breast cancer patients divided into training and validation cohorts. Consensus staining scores were used to evaluate the expression levels of autophagy proteins LC3B, ATG4B, and GABARAP and determine the associations with clinicopathological variables and molecular biomarkers. Survival analyses were performed using the Kaplan-Meier function and Cox proportional hazards regression models.

RESULTS

We found subtype-specific expression differences for ATG4B, with its expression lowest in basal-like breast cancer and highest in Luminal A, but there were no significant associations with patient prognosis. LC3B and GABARAP levels were highest in basal-like breast cancers, and high levels were associated with worse outcomes across all subtypes (DSS; GABARAP: HR 1.43, LC3B puncta: HR 1.43). High ATG4B levels were associated with ER, PR, and BCL2 positivity, while high LC3B and GABARAP levels were associated with ER, PR, and BCL2 negativity, as well as EGFR, HER2, HER3, CA-IX, PD-L1 positivity, and high Ki67 index (p < 0.05 for all associations). Exploratory multi-marker analysis indicated that the combination of ATG4B and GABARAP with LC3B could be useful for further stratifying patient outcomes.

CONCLUSIONS

ATG4B levels varied across breast cancer subtypes but did not show prognostic significance. High LC3B expression and high GABARAP expression were both associated with poor prognosis and with clinicopathological characteristics of aggressive disease phenotypes in all breast cancer subtypes.

Subtype-specific risk models for accurately predicting the prognosis of breast cancer using differentially expressed autophagy-related genes

Emerging evidence suggests that the dysregulation of autophagy-related genes (ARGs) is coupled with the carcinogenesis and progression of breast cancer (BRCA). We constructed three subtype-specific risk models using differentially expressed ARGs. In Luminal, Her-2, and Basal-like BRCA, four- (BIRC5, PARP1, ATG9B, and TP63), three- (ITPR1, CCL2, and GAPDH), and five-gene (PRKN, FOS, BAX, IFNG, and EIF4EBP1) risk models were identified, which all have a receiver operating characteristic > 0.65 in the training and testing dataset. Multivariable Cox analysis showed that those risk models can accurately and independently predict the overall survival of BRCA patients. Comprehensive analysis showed that the 12 identified ARGs were correlated with the overall survival of BRCA patients; six of the ARGs (PARP1, TP63, CCL2, GAPDH, FOS, and EIF4EBP1) were differentially expressed between BRCA and normal breast tissue at the protein level. In addition, the 12 identified ARGs were highly interconnected and displayed high frequency of copy number variation in BRCA samples. Gene set enrichment analysis suggested that the deactivation of the immune system was the important driving force for the progression of Basal-like BRCA. This study demonstrated that the 12 ARG signatures were potential multi-dimensional biomarkers for the diagnosis, prognosis, and treatment of BRCA.

The Autophagy Machinery Contributes to E-cadherin Turnover in Breast Cancer

Autophagy is an intracellular catabolic process that is increasingly being recognized as a crucial factor in several human diseases including cancers. Mounting evidence suggests that autophagy allows tumor cells to overcome otherwise fatal stresses and to increase dissemination. Nevertheless, how autophagy controls these processes and in particular how it impinges on cell-cell adhesion is still poorly understood. Here, we investigate the role of autophagy in the turnover of the epithelial adhesion molecule E-cadherin in the context of breast cancer. We demonstrated in breast cancer cell lines that autophagy impinges on E-cadherin expression and in the configuration of adherens junctions. Besides, we showed that E-cadherin colocalizes with LC3B and SQSTM1/p62, two components of the autophagosome machinery. Pull down and immunoprecipitation analyses provided evidence that E-cadherin and SQSTM1/p62 physically interact. Moreover, the physical closeness of E-cadherin and SQSTM1/p62 was demonstrated by proximity ligation assays in breast cancer cell lines and primary tumors. Finally, we proved that the silencing of SQSTM1/p62 diminished the E-cadherin/LC3B colocalization, further supporting the role of SQSTM1/p62 in E-cadherin delivery to autophagosomes. These findings suggest that the activation of autophagy, reported in breast cancers with poor prognosis and in dormant breast cancer cells, may contribute to the control of tumor progression via downmodulation of E-cadherin protein levels.

Molecular modulation of autophagy: New venture to target resistant cancer stem cells

Autophagy is a highly regulated catabolic process in which superfluous, damaged organelles and other cytoplasmic constituents are delivered to the lysosome for clearance and the generation of macromolecule substrates during basal or stressed conditions. Autophagy is a bimodal process with a context dependent role in the initiation and the development of cancers. For instance, autophagy provides an adaptive response to cancer stem cells to survive metabolic stresses, by influencing disease propagation via modulation of essential signaling pathways or by promoting resistance to chemotherapeutics. Autophagy has been implicated in a cross talk with apoptosis. Understanding the complex interactions provides an opportunity to improve cancer therapy and the clinical outcome for the cancer patients. In this review, we provide a comprehensive view on the current knowledge on autophagy and its role in cancer cells with a particular focus on cancer stem cell homeostasis.

Crosstalk between autophagy and apoptosis: Mechanisms and therapeutic implications

The cellular recycling process of macroautophagy, which is the mechanism by which cellular material is delivered to lysosomes via double membraned vesicles called autophagosomes, is intimately connected to programmed cell death pathways, especially apoptosis. In this article, I discuss some underlying mechanisms and their implications for improving cancer therapy and propose that the approaches that have been taken to understand the autophagy-apoptosis connection to enhance cancer drug action can serve as a model for the kinds of information that should be developed to understand how autophagy controls other biological processes as well.

The autophagy-independent role of BECN1 in colorectal cancer metastasis through regulating STAT3 signaling pathway activation

BECN1 is a critical regulator of autophagy, which plays important roles in tumor formation and metastasis. However, the autophagy-independent role of BECN1 and the clinical prediction value of BECN1 still need to be explored. Here, we observed significantly lower expression of BECN1 in colorectal cancers (CRCs) compared with adjacent normal colon tissue, and downregulation of BECN1 was positively related to poor prognosis in CRC patients. In addition, we found that knockdown of BECN1 markedly promoted CRC cell motility and invasion. Bioinformatics gene set enrichment analysis (GSEA) revealed that low levels of BECN1 were significantly correlated with the STAT3 signaling pathway in CRC. Consistently, knockdown of BECN1 increased the phosphorylation of STAT3 and activated the STAT3 signaling pathway in CRC cells. Furthermore, we demonstrated that STAT3 was involved in the CRC metastasis mediated by knockdown of BECN1 in vitro and in vivo. Mechanistically, knockdown of BECN1 promoted the phosphorylation of STAT3 via regulation of the interaction between STAT and JAK2 but did not inhibit autophagy. Our study revealed that BECN1 served as a negative regulator of CRC metastasis by regulating STAT3 signaling pathway activation in an autophagy-independent manner. The BECN1/JAK2/STAT3 signaling pathway can be used as a potential therapeutic target for metastatic CRC.

Ethanol Extract of Brucea javanica Seed Inhibit Triple-Negative Breast Cancer by Restraining Autophagy via PI3K/Akt/mTOR Pathway

Triple-negative breast cancer (TNBC) is an aggressive disease with worst prognosis than other subtypes of breast cancer. Owing to the lack of hormone receptors and HER2 expression on TNBC cells, patients do not have targeted therapy options available with other breast cancer subtypes. Extensive efforts have been made to identify novel therapeutics against TNBC. Interestingly, recent studies had shown that plant-derived natural products could modulate the autophagy and induce the breast cancer cells death. Seed of Brucea javanica has been used as an important traditional Chinese medicine against cancers. In the present study, the anti-breast cancer potential of ethanol crude extracts from B. javanica seed (BJE) was explored. Data demonstrated that BJE could inhibit the TNBC cell line MDA-MB-231 proliferation and induced apoptosis. In the cells exposed to BJE, protein expressions of UNC-51-like kinase-1 (ULK1) and Beclin-1 and the ratio of light chain 3 II/I (LC3 II/I) were reduced, while the expression of p62 was increased, indicating an inhibition on autophagy. Moreover, BJE promoted the phosphorylation of mammalian target of rapamycin (mTOR), phosphatidylinositol 3-kinase (PI3K), and Akt in MDA-MB-231. BJE also suppressed the MDA-MB-231 tumor growth in vivo. Coincide with the results in vitro, autophagy in the tumor tissue was weakened as indicated by decreased ratio of LC 3 II/I and Beclin-1 accompanied by enhanced phosphorylation of mTOR, which confirmed that autophagy restraint via the PI3K/Akt/mTOR signaling pathway contributes to the suppression by BJE. Notably, no noticeable toxicity in non-targeted organs was found, including small intestine, liver, and kidney. Taken together, this study revealed anti-breast cancer activity of BJE based on autophagy restraint, highlighting its clinical importance as a novel natural agent against TNBC.

A STAT3 of Addiction: Adipose Tissue, Adipocytokine Signalling and STAT3 as Mediators of Metabolic Remodelling in the Tumour Microenvironment

Metabolic remodelling of the tumour microenvironment is a major mechanism by which cancer cells survive and resist treatment. The pro-oncogenic inflammatory cascade released by adipose tissue promotes oncogenic transformation, proliferation, angiogenesis, metastasis and evasion of apoptosis. STAT3 has emerged as an important mediator of metabolic remodelling. As a downstream effector of adipocytokines and cytokines, its canonical and non-canonical activities affect mitochondrial functioning and cancer metabolism. In this review, we examine the central role played by the crosstalk between the transcriptional and mitochondrial roles of STAT3 to promote survival and further oncogenesis within the tumour microenvironment with a particular focus on adipose-breast cancer interactions.

Autophagy-dependent cancer cells circumvent loss of the upstream regulator RB1CC1/FIP200 and loss of LC3 conjugation by similar mechanisms

Macroautophagy/autophagy degrades proteins and organelles to generate macromolecular building blocks. As such, some cancer cells are particularly dependent on autophagy. In a previous paper, we found that even highly autophagy-dependent cancer cells can adapt to circumvent autophagy inhibition. However, it remains unclear if autophagy-dependent cancer cells could survive the complete elimination of autophagosome formation. We extended our previous findings to show that knockout (KO) of both the upstream autophagy regulator RB1CC1/FIP200 and the downstream regulator and mediator of LC3 conjugation, ATG7, strongly inhibits growth in highly autophagy-dependent cells within one week of editing. However, rare clones survived the loss of ATG7 or RB1CC1 and maintained growth even under autophagy-inducing conditions. Autophagy-dependent cells circumvent the complete loss of autophagy that is mediated by RB1CC1 KO, similar to the loss of ATG7, by upregulating NFE2L2/NRF2 signaling. These results indicate that cancer cell lines could adapt to the complete loss of autophagy by changing their biology to adopt alternative ways of dealing with autophagy-mediated cellular functions.

ABBREVIATIONS

CGS: CRISPR growth score; CQ: chloroquine; CRISPR: clustered regularly interspaced short palindromic repeats; EBSS: Earl's balanced salt solution; EEF2: eukaryotic translation elongation factor 2; FOXO3/FOXO3a: forkhead box O3; GFP: green fluorescent protein; KEAP1: kelch Like ECH associated protein 1; KO: knockout; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MEFs: mouse embryonic fibroblasts; NFE2L2/NRF2: nuclear factor, erythroid 2 like 2; NLS: nuclear localization signal; PCNA: proliferating cell nuclear antigen; PE: phosphatidylethanolamine; POLR2A: RNA polymerase II subunit A; PTEN: phosphatase and tensin homolog; ROS: reactive oxygen species; SNARE: soluble NSF attachment protein receptor; SQSTM1: sequestosome 1; STX17: syntaxin 17; TBHP: tert-butyl hydroperoxide; ULK1: unc-51 like autophagy activating kinase 1; ULK2: unc-51 like autophagy activating kinase 2; WT: wild type.

Autophagy in cancer: moving from understanding mechanism to improving therapy responses in patients

Autophagy allows for cellular material to be delivered to lysosomes for degradation resulting in basal or stress-induced turnover of cell components that provide energy and macromolecular precursors. These activities are thought to be particularly important in cancer where both tumor-promoting and tumor-inhibiting functions of autophagy have been described. Autophagy has also been intricately linked to apoptosis and programmed cell death, and understanding these interactions is becoming increasingly important in improving cancer therapy and patient outcomes. In this review, we consider how recent discoveries about how autophagy manipulation elicits its effects on cancer cell behavior can be leveraged to improve therapeutic responses.

Human omental adipose-derived mesenchymal stem cells enhance autophagy in ovarian carcinoma cells through the STAT3 signalling pathway

BACKGROUND

Our previous study showed that human omental adipose-derived stem cells (ADSCs) promote ovarian cancer growth and metastasis. In this study, the role of autophagy in the ovarian cancer-promoting effects of omental ADSCs was further determined.

METHODS

The growth and invasion of ovarian cancer cells were detected by CCK-8 and Transwell assays, respectively. The autophagy of ovarian cancer cells transfected with MRFP-GFP-LC3 adenoviral vectors was evaluated by confocal microscopy and western blot assay. Transfection of STAT3 siRNA was used to inhibit the expression of STAT3.

RESULTS

Our results show that autophagy plays a vital role in ovarian cancer and is promoted by ADSCs. Specifically, we show that proliferation and invasion are correlated with autophagy induction by ADSCs in two ovarian cancer cell lines under hypoxic conditions. Mechanistically, ADSCs activate the STAT3 signalling pathway, thereby promoting autophagy. Knockdown of STAT3 expression using siRNA decreased hypoxia-induced autophagy and decreased the proliferation and metastasis of ovarian cancer cells.

CONCLUSION

Taken together, our data indicate that STAT3-mediated autophagy induced by ADSCs promotes ovarian cancer growth and metastasis.

Autophagy Inhibition Induces the Secretion of Macrophage Migration Inhibitory Factor (MIF) with Autocrine and Paracrine Effects on the Promotion of Malignancy in Breast Cancer

Breast cancer is the main cause of cancer-related death in women in the world. Because autophagy is a known survival pathway for cancer cells, its inhibition is currently being explored in clinical trials for treating several types of malignancies. In breast cancer, autophagy has been shown to be necessary for the survival of cancer cells from the triple negative subtype (TNBC), which has the worst prognosis among breast cancers and currently has limited therapeutic options. Autophagy has also been involved in the regulation of protein secretion and, of importance for this work, the inhibition of autophagy is known to promote the secretion of proinflammatory cytokines from distinct cell types. We found that the inhibition of autophagy in TNBC cell lines induced the secretion of the macrophage migration inhibitory factor (MIF), a pro-tumorigenic cytokine involved in breast cancer invasion and immunomodulation. MIF secretion was dependent on an increase in reactive oxygen species (ROS) induced by the inhibition of autophagy. Importantly, MIF secreted from autophagy-deficient cells increased the migration of cells not treated with autophagy inhibitors, indicating that autophagy inhibition in cancer cells promoted malignancy in neighboring cells through the release of secreted factors, and that a combinatorial approach should be evaluated for cancer therapy.

Circumventing autophagy inhibition

Autophagy is cellular recycling process that plays a complex role in cancer. Pre-clinical studies indicating a pro-tumorigenic role of autophagy have led to the launch of dozens of clinical trials combining autophagy inhibition with other standard of care therapies in different tumor types. A recent publication utilized a novel, acute, CRISPR/Cas9 assay to identify cancer cell lines that are exquisitely sensitive to loss of core autophagy genes within the first 7 days. However, weeks later, rare populations of originally autophagy dependent cells were found that could circumvent autophagy inhibition. Analysis of these rare clones revealed that in the process of circumventing loss of autophagy, the cells upregulated NRF2 signaling to maintain protein homeostasis and consequently become more sensitive to proteasome inhibition as well as knock down of NRF2. This review highlights recent publications regarding the role of autophagy in cancer and potential mechanisms cancer cells may be able to commandeer to circumvent autophagy inhibition. We hope to make significant clinical advances by understanding if and when cancer cells will become resistant to autophagy inhibition, and pre-clinical studies may be able to provide insight into the best combinatorial therapies to prevent tumor relapse while on autophagy inhibitors.

Autophagy and Its Relationship to Epithelial to Mesenchymal Transition: When Autophagy Inhibition for Cancer Therapy Turns Counterproductive

The manipulation of autophagy for cancer therapy has gained recent interest in clinical settings. Although inhibition of autophagy is currently being used in clinical trials for the treatment of several malignancies, autophagy has been shown to have diverse implications for normal cell homeostasis, cancer cell survival, and signaling to cells in the tumor microenvironment. Among these implications and of relevance for cancer therapy, the autophagic process is known to be involved in the regulation of protein secretion, in tumor cell immunogenicity, and in the regulation of epithelial-to-mesenchymal transition (EMT), a critical step in the process of cancer cell invasion. In this work, we have reviewed recent evidence linking autophagy to the regulation of EMT in cancer and normal epithelial cells, and have discussed important implications for the manipulation of autophagy during cancer therapy.

Pulsed-wave Ultrasound Hyperthermia Enhanced Nanodrug Delivery Combined with Chloroquine Exerts Effective Antitumor Response and Postpones Recurrence

Autophagy is found to serve as a surviving mechanism for cancer cells. Inhibiting autophagy has been considered as an adjuvant anti-cancer strategy. In this study, we investigated the anti-tumor effect of combining pulsed-wave ultrasound hyperthermia (pUH) enhanced PEGylated liposomal doxorubicin (PLD) delivery with an autophagy inhibitor chloroquine (CQ). BALB/c mice bearing subcutaneous 4T1 tumor received intravenous injection of PLD (10 mg/kg) plus 15-minute on-tumor pUH on Day 5 after tumor implantation and were then fed with CQ (50 mg/kg daily) thereafter. Prolonged suppression of tumor growth was attained with PLD + pUH + CQ treatment, whereas in PLD + pUH group tumors quickly recurred after an initial inhibition. Treatment with CQ monotherapy had no benefit compared to the control group. Immunohistochemical staining and Western blotting showed that autophagy of cancer cells was blocked for the mice receiving CQ. It indicates that PLD + pUH + CQ is a promising strategy to treat cancer for a long-term inhibition.

Colorectal cancer cells respond differentially to autophagy inhibition in vivo

Autophagy has both tumor-promoting and -suppressing effects in cancer, including colorectal cancer (CRC), with transformed cells often exhibiting high autophagic flux. In established tumors, autophagy inhibition can lead to opposite responses resulting in either tumor cell death or hyperproliferation. The functional mechanisms underlying these differences are poorly understood. The present study aimed to investigate the relationship between the autophagic capacities of CRC cells and their sensitivities to autophagy inhibition. All studied CRC cell lines showed high basal autophagic flux. However, only HCT116 and Caco-2/15 cells displayed regulated autophagic flux upon starvation. Knockdown of ATG5 (which disrupts autophagosome elongation) or RAB21 (which decreases autophagosome/lysosome fusion) had little effect on CRC cell proliferation in vitro. Nonetheless, inhibition of autophagy in vivo had a substantial cell line-dependent impact on tumor growth, with some cells displaying decreased (HCT116 and Caco-2/15) or increased (SW480 and LoVo) proliferation. RNA sequencing and Western blot analyses in hyperproliferative SW480 tumors revealed that the mTORC2 and AKT pathways were hyperactivated following autophagy impairment. Inhibition of either mTOR or AKT activities rescued the observed hyperproliferation in autophagy-inhibited SW480 and reduced tumor growth. These results highlight that autophagy inhibition can lead, in specific cellular contexts, to compensatory mechanisms promoting tumor growth.

Cancer Cells Upregulate NRF2 Signaling to Adapt to Autophagy Inhibition

While autophagy is thought to be an essential process in some cancer cells, it is unknown if or how such cancer cells can circumvent autophagy inhibition. To address this, we developed a CRISPR/Cas9 assay with dynamic live-cell imaging to measure acute effects of knockout (KO) of autophagy genes compared to known essential and non-essential genes. In some cancer cells, autophagy is as essential for cancer cell growth as mRNA transcription or translation or DNA replication. However, even these highly autophagy-dependent cancer cells evolve to circumvent loss of autophagy by upregulating NRF2, which is necessary and sufficient for autophagy-dependent cells to circumvent ATG7 KO and maintain protein homeostasis. Importantly, however, this adaptation increases susceptibly to proteasome inhibitors. These studies identify a common mechanism of acquired resistance to autophagy inhibition and show that selection to avoid tumor cell dependency on autophagy creates new, potentially actionable cancer cell susceptibilities.

Proliferation of rheumatoid arthritis fibroblast-like synoviocytes is enhanced by IL-17-mediated autophagy through STAT3 activation

Fibroblast-like synoviocytes (FLSs), with their tumor-like proliferation, play an important role in rheumatoid arthritis (RA), and interleukin-17 (IL-17) participates in RA pathology by affecting FLSs. The aims of this study were to investigate the effects of IL-17 on the proliferation and autophagy of FLSs and the role of signal transducer and activator of transcription-3 (STAT3) in RA. FLSs were treated with IL-17 at different concentrations (0, 1, 10, and 20 ng/mL); then, autophagy was assayed with western blotting, immunofluorescence, and transmission electron microscopy. The effects of IL-17 on FLSs proliferation were measured with the Cell Counting Kit-8 assay and flow cytometry to analyze cell cycle distribution, and proliferating cell nuclear antigen (PCNA) was detected by western blotting. The autophagy inhibitors, 3-methyladenine (3-MA) and chloroquine (CQ), were used to determine the effect of autophagy on proliferation in IL-17-treated FLSs. Finally, the STAT3 inhibitor STA21 was used to examine the relationship between STAT3 and autophagy in IL-17-treated FLSs. Our results showed that IL-17 positively affected autophagy and proliferation in FLSs. Inhibition of autophagy suppressed the IL-17-mediated proliferation of FLSs. Additionally, suppression of STAT3 activation decreased autophagy in IL-17-treated FLSs. Our findings showed that IL-17 promoted the tumor-like proliferation of FLSs by upregulating autophagy via STAT3 activation.

STAT3 as a potential therapeutic target in triple negative breast cancer: a systematic review

Triple negative breast cancer (TNBC), which is typically lack of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), represents the most aggressive and mortal subtype of breast cancer. Currently, only a few treatment options are available for TNBC due to the absence of molecular targets, which underscores the need for developing novel therapeutic and preventive approaches for this disease. Recent evidence from clinical trials and preclinical studies has demonstrated a pivotal role of signal transducer and activator of transcription 3 (STAT3) in the initiation, progression, metastasis, and immune evasion of TNBC. STAT3 is overexpressed and constitutively activated in TNBC cells and contributes to cell survival, proliferation, cell cycle progression, anti-apoptosis, migration, invasion, angiogenesis, chemoresistance, immunosuppression, and stem cells self-renewal and differentiation by regulating the expression of its downstream target genes. STAT3 small molecule inhibitors have been developed and shown excellent anticancer activities in in vitro and in vivo models of TNBC. This review discusses the recent advances in the understanding of STAT3, with a focus on STAT3’s oncogenic role in TNBC. The current targeting strategies and representative small molecule inhibitors of STAT3 are highlighted. We also propose potential strategies that can be further examined for developing more specific and effective inhibitors for TNBC prevention and therapy.

Placenta-conditioned extracellular matrix (ECM) activates breast cancer cell survival mechanisms: A key for future distant metastases

The extracellular matrix (ECM) affects cancer cell characteristics. Inability of normal epithelial cells to attach to the ECM induces apoptosis (anoikis). Cancer cells are often anoikis resistant, a prerequisite for their metastatic spread. Previously we demonstrated that the placenta manipulates its surrounding ECM in a way that prevents breast cancer cells (BCCL) attachment and induces their motility and aggregation. This fits with the fact that although breast cancer during pregnancy is often advanced, metastasis to the placenta is rarely observed. Placental intervillous space provides suitable conditions for cancer cell arrival. Yet, the outcome of the short communication between the placental ECM to the BCCL and its effect on BCCL malignant potential are unknown, and are the focus of our study. In the current study we analyzed the effect of placental ECM on BCCL survival pathways and drug resistance. Microarray analysis suggested activation of the NF-κB and stress response pathways. Indeed, the placenta-conditioned ECM induced autophagy in ERα + BCCL, inactivated the NF-κB inhibitor (IκB) and increased integrin α5 in the BCCL. The autophagy mediated MCF-7 and T47D migration and the placental ECM-BCCL interactions reduced the BCCL sensitivity to Taxol. We also demonstrated by using siRNA that integrin α5 was responsible for the MCF-7 autophagy and suggest this molecule as a suitable target for therapy.

PLCε promotes urinary bladder cancer cells proliferation through STAT3/LDHA pathway‑mediated glycolysis

Phospholipase Cε (PLCε) and anaerobic glycolysis were determined to be involved in the development of human urinary bladder cancer (UBC), but the mechanisms remain unclear. In the present study, 64 bladder cancer specimens and 42 adjacent tissue specimens were obtained from 64 patients, and immunochemistry indicated that PLCε and lactate dehydrogenase (LDHA) are overexpressed in UBC. PLCε and LDHA were demonstrated to be positively correlated at transcription levels, indicating that one of these two genes may be regulated by another. To elucidate the mechanisms, PLCε was knocked down in T24 cells by short hairpin RNA, and then signal transducer and activator of transcription 3 (STAT3) phosphorylation and LDHA were determined to be downregulated, which indicated that PLCε may serve roles upstream of LDHA through STAT3 to regulate glycolysis in UBC. Furthermore, chromatin immunoprecipitation and luciferase reporter assays were performed to confirm that STAT3 could bind to the promoter of the LDHA gene to enhance its expression. A xenograft tumor mouse model also demonstrated similar results as the in vitro experiments, further confirming the role of PLCε in regulating bladder cell growth in vivo. Collectively, the present study demonstrated that PLCε may regulate glycolysis through the STAT3/LDHA pathway to take part in the development of human UBC.

Autophagy, cancer stem cells and drug resistance

Autophagy is a cellular survival mechanism that is induced by cancer therapy, among other stresses, and frequently contributes to cancer cell survival during long periods of dormancy and the eventual outgrowth of metastatic disease. Autophagy degrades large cellular structures that, once broken down, contribute to cellular survival through the recycling of their constituent metabolites. However, the extent to which this fuel function of autophagy is key to its role in promoting stemness, dormancy and drug resistance remains to be determined. Other roles for autophagy in determining cell fate more directly through targeted degradation of key transcription factors, such as p53 and FoxO3A, or by enforcing a reversible quiescent growth arrest, are discussed in this review. This review also highlights the need to parse out the roles of different forms of selective autophagy in stemness, CD44 expression and dormancy that, for example, are increasingly being attributed explicitly to mitophagy. The clinical relevance of this work and how an increased understanding of functions of autophagy in stemness, dormancy and drug resistance could be manipulated for increased therapeutic benefit, including eliminating minimal residual disease and preventing metastasis, are discussed. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Beclin1 inhibition enhances paclitaxel‑mediated cytotoxicity in breast cancer in vitro and in vivo

Beclin1, a key regulator of autophagy, has been demonstrated to be associated with cancer cell resistance to chemotherapy. Paclitaxel is a conventional chemotherapeutic drug used in the clinical treatment of breast cancer. However, the function and mechanism of Beclin1 in paclitaxel‑mediated cytotoxicity in breast cancer are not well defined. The present study demonstrated that paclitaxel suppressed cell viability and Beclin1 expression levels in BT‑474 breast cancer cells in a dose‑ and time‑dependent fashion. Compared with the control, the knockdown of Beclin1 significantly enhanced breast cancer cell death via the induction of caspase‑dependent apoptosis following paclitaxel treatment in vitro (P<0.05). In a BT‑474 xenograft model, paclitaxel achieved substantial inhibition of tumor growth in the Beclin1 knockdown group compared with the control group. Furthermore, analysis of the publicly available Gene Expression Omnibus datasets revealed a clinical correlation between Beclin1 levels and the response to paclitaxel therapy in patients with breast cancer. Collectively, the present results suggest that Beclin1 protects breast cancer cells from apoptotic death. Thus, the inhibition of Beclin1 may be a novel way to improve the effect of paclitaxel. Additionally, Beclin1 may function as a favorable prognostic biomarker for paclitaxel treatment in patients with breast cancer.

LT-IIc, A Bacterial Type II Heat-Labile Enterotoxin, Induces Specific Lethality in Triple Negative Breast Cancer Cells by Modulation of Autophagy and Induction of Apoptosis and Necroptosis

Triple negative breast cancer (TNBC) remains a serious health problem with poor prognosis and limited therapeutic options. To discover novel approaches to treat TNBC, we screened cholera toxin (CT) and the members of the bacterial type II heat-labile enterotoxin family (LT-IIa, LT-IIb, and LT-IIc) for cytotoxicity in TNBC cells. Only LT-IIc significantly reduced viability of the TNBC cell lines BT549 and MDA-MB-231 (IC₅₀ = 82.32 nM). LT-IIc had no significant cytotoxic effect on MCF10A (IC₅₀ = 2600 nM), a non-tumorigenic breast epithelial cell line, and minimal effects on MCF7 and T47D, ER⁺ cells, or SKBR-3 cells, HER2⁺ cells. LT-IIc stimulated autophagy through inhibition of the mTOR pathway, while simultaneously inhibiting autophagic progression, as seen by accumulation of LC3B-II and p62. Morphologically, LT-IIc induced the formation of enlarged LAMP2+ autolysosomes, which was blocked by co-treatment with bafilomycin A1. LT-IIc induced apoptosis as demonstrated by the increase in caspase 3/7 activity and Annexin V staining. Co-treatment with necrostatin-1, however, demonstrated that the lethal response of LT-IIc is elicited, in part, by concomitant induction of necroptosis. Knockdown of ATG-5 failed to rescue LT-IIc-induced cytotoxicity, suggesting LT-IIc can exert its cytotoxic effects downstream or independently of autophagophore initiation. Collectively, these experiments demonstrate that LT-IIc acts bifunctionally, inducing autophagy, while simultaneously blocking autolysosomal progression in TNBC cells, inducing a specific cytotoxicity in this breast cancer subtype.

Autophagy and Its Role in Protein Secretion: Implications for Cancer Therapy

Autophagy is a protein and organelle degradation pathway important for the maintenance of cytoplasmic homeostasis and for providing nutrients for survival in response to stress conditions. Recently, autophagy has been shown to be important for the secretion of diverse proteins involved in inflammation, intercellular signaling, and cancer progression. The role of autophagy in cancer depends on the stage of tumorigenesis, serving a tumor-suppressor role before transformation and a tumor-survival function once a tumor is established. We review recent evidence demonstrating the complexity of autophagy regulation during cancer, considering the interaction of autophagy with protein secretion pathways. Autophagy manipulation during cancer treatment is likely to affect protein secretion andinter-cellular signaling either to the neighboring cancer cells or to the antitumoral immune response. This will be an important consideration during cancer therapy since several clinical trials are trying to manipulate autophagy in combination with chemotherapy for the treatment of diverse types of cancers.

Metastatic cells are preferentially vulnerable to lysosomal inhibition

Molecular alterations that confer phenotypic advantages to tumors can also expose specific therapeutic vulnerabilities. To search for potential treatments that would selectively affect metastatic cells, we examined the sensitivity of lineage-related human bladder cancer cell lines with different lung colonization abilities to chloroquine (CQ) or bafilomycin A1, which are inhibitors of lysosome function and autophagy. Both CQ and bafilomycin A1 were more cytotoxic in vitro to highly metastatic cells compared with their less metastatic counterparts. Genetic inactivation of macroautophagy regulators and lysosomal proteins indicated that this was due to greater reliance on the lysosome but not upon macroautophagy. To identify the mechanism underlying these effects, we generated cells resistant to CQ in vitro. Surprisingly, selection for in vitro CQ resistance was sufficient to alter gene expression patterns such that unsupervised cluster analysis of whole-transcriptome data indicated that selection for CQ resistance alone created tumor cells that were more similar to the poorly metastatic parental cells from which the metastatic cells were derived; importantly, these tumor cells also had diminished metastatic ability in vivo. These effects were mediated in part by differential expression of the transcriptional regulator ID4 (inhibitor of DNA binding 4); depletion of ID4 both promoted in vitro CQ sensitivity and restored lung colonization and metastasis of CQ-resistant cells. These data demonstrate that selection for metastasis ability confers selective vulnerability to lysosomal inhibitors and identify ID4 as a potential biomarker for the use of lysosomal inhibitors to reduce metastasis in patients.

BECN1-knockout impairs tumor growth, migration and invasion by suppressing the cell cycle and partially suppressing the epithelial-mesenchymal transition of human triple-negative breast cancer cells

Beclin1 (BECN1), which directly interacts with B‑cell lymphoma 2, serves an important role in autophagy and is involved in the tumorigenesis of various types of cancer. However, the definite role of BECN1 in breast cancer remains controversial. Bi-allelic knockout of Becn1 in a mouse model leads to an embryonic lethal phenotype, which hampers further investigation. To generate cell lines with knockout of BECN1, the CRISPR/Cas9 technique was used to disrupt BECN1 in human triple-negative breast cancer (TNBC) MDA‑MB‑231 cells. To the best of our knowledge, the present study was the first to successfully disrupt BECN1 in MDA‑MB‑231 cells and to screen three stable monoclonal BECN1‑knockout cell lines, suggesting that BECN1‑knockout is not lethal in TNBC cells. Functional analysis revealed that complete loss of BECN1 suppressed MDA‑MB‑231 proliferation and colony formation via inducing G0/G1 cell cycle arrest, not apoptosis, in vitro. On the other hand, BECN1‑knockout inhibited the migratory and invasive ability of MDA‑MB‑231 cells by partially reversing signals of epithelial-mesenchymal transition. Finally, analysis of publicly available gene expression datasets revealed increased expression of BECN1 in TNBC samples. Taken together, the results of the present study identified BECN1 as an oncogene, providing a novel potential target for the treatment of TNBC.

Autophagy, Cell Viability, and Chemoresistance Are Regulated By miR-489 in Breast Cancer

It is postulated that the complexity and heterogeneity in cancer may hinder most efforts that target a single pathway. Thus, discovery of novel therapeutic agents targeting multiple pathways, such as miRNAs, holds promise for future cancer therapy. One such miRNA, miR-489, is downregulated in a majority of breast cancer cells and several drug-resistant breast cancer cell lines, but its role and underlying mechanism for tumor suppression and drug resistance needs further investigation. The current study identifies autophagy as a novel pathway targeted by miR-489 and reports Unc-51 like autophagy activating kinase 1 (ULK1) and lysosomal protein transmembrane 4 beta (LAPTM4B) to be direct targets of miR-489. Furthermore, the data demonstrate autophagy inhibition and LAPTM4B downregulation as a major mechanism responsible for miR-489-mediated doxorubicin sensitization. Finally, miR-489 and LAPTM4B levels were inversely correlated in human tumor clinical specimens, and more importantly, miR-489 expression levels predict overall survival in patients with 8q22 amplification (the region in which LAPTM4B resides).Implications: These findings expand the understanding of miR-489-mediated tumor suppression and chemosensitization in and suggest a strategy for using miR-489 as a therapeutic sensitizer in a defined subgroup of resistant breast cancer patients. Mol Cancer Res; 16(9); 1348-60. ©2018 AACR.

Role of autophagy in breast cancer and breast cancer stem cells (Review)

Autophagy is a key catabolic process, in which cytosolic cargo is engulfed by the formation of a double membrane and then degraded through the fusing of autophagosomes with lysosomes. Autophagy is a constitutively active, evolutionarily conserved, catabolic process important for the maintenance of homeostasis in cellular stress responses and cell survival. Although the mechanisms of autophagy have not yet been fully elucidated, emerging evidence suggests that it plays a dual role in breast cancer and in maintaining the activity of breast cancer stem cells (CSCs). However, it may play a complex role in breast CSC therapy. Breast CSCs, a population of cells with the ability to self-renew, differentiate, and initiate and sustain tumor growth, play an essential role in cancer recurrence, anticancer resistance and metastasis. In addition, the elucidation of the association between autophagy and apoptosis in the tumor context is crucial in order to better address appropriate therapy strategies. In the present review, a summary of the mechanisms and roles of autophagy in breast cancer and CSCs is presented. The potential value of such autophagy modulators in the development of novel breast cancer therapies is discussed.

Game-changing restraint of Ros-damaged phenylalanine, upon tumor metastasis

An abrupt increase in metastatic growth as a consequence of the removal of primary tumors suggests that the concomitant resistance (CR) phenomenon might occur in human cancer. CR occurs in murine tumors and ROS-damaged phenylalanine, meta-tyrosine (m-Tyr), was proposed as the serum anti-tumor factor primarily responsible for CR. Herein, we demonstrate for the first time that CR happens in different experimental human solid tumors (prostate, lung anaplastic, and nasopharyngeal carcinoma). Moreover, m-Tyr was detected in the serum of mice bearing prostate cancer (PCa) xenografts. Primary tumor growth was inhibited in animals injected with m-Tyr. Further, the CR phenomenon was reversed when secondary implants were injected into mice with phenylalanine (Phe), a protective amino acid highly present in primary tumors. PCa cells exposed to m-Tyr in vitro showed reduced cell viability, downregulated NFκB/STAT3/Notch axis, and induced autophagy; effects reversed by Phe. Strikingly, m-Tyr administration also impaired both, spontaneous metastasis derived from murine mammary carcinomas (4T1, C7HI, and LMM3) and PCa experimental metastases. Altogether, our findings propose m-Tyr delivery as a novel approach to boost the therapeutic efficacy of the current treatment for metastasis preventing the escape from tumor dormancy.

Stat3-Atg5 signal axis inducing autophagy to alleviate hepatic ischemia-reperfusion injury

In performing our experiment, impaired autophagy increased hepatocellular damage during the reperfusion period. It was demonstrated by the effect of blocking autophagy using bafilomycin A1 or knocking Atg5 gene out reduces the anti-apoptotic effect of Stat3. Here we focus on the role of signal transducer and activator of transcription 3 (Stat3) in regulating autophagy to alleviate hepatic IRI. We found that Stat3 was up-regulated during hepatic IRI and was associated with an activation of the autophagic signaling pathway. This increased Stat3 expression, which was allied with high autophagic activity, alleviated liver damage to IR, an effect which was abrogated by Stat3 epletion as demonstrated in both in vivo and in vitro methods. The levels of Atg5 protein were decreased when Stat3 was inhibited by HO 3867 or siStat3. We conclude that Stat3 appeared to exert a pivotal role in hepatic IRI, by activating autophagy to alleviate hepatic IRI, and Atg5 was required for this process. The identification of this novel pathway, that links expression levels of Stat3 with Atg5-mediated autophagy, may provide new insights for the generation of novel protective therapies directed against hepatic IRI.

Nutritional shortage augments cisplatin-effects on murine melanoma cells

Melanoma incidence increases every year worldwide and is responsible for 80% of skin cancer deaths. Due to its metastatic potential and resistance to almost any treatments such as chemo, radio, immune and targeted-therapy, the patients still have a poor prognosis, especially at metastatic stage. Considering that, it is crucial to find new therapeutic approaches to overcome melanoma resistance. Here we investigated the effect of cisplatin (CDDP), one of the chemotherapeutic agents used for melanoma treatment, in association with nutritional deprivation in murine melanoma cell lines. Cell death and autophagy were evaluated after the treatment with cisplatin, nutritional deprivation and its association using an in vitro model of murine melanocytes malignant transformation to metastatic melanoma. Our results showed that nutritional deprivation augmented cell death induced by cisplatin in melanoma cells, especially at the metastatic subtype, with slight effects on melanocytes. Mechanistic studies revealed that although autophagy was present at high levels in basal conditions in melanoma cells, was not essential for cell death process that involved mitochondrial damage, reactive oxygen species production and possible glycolysis inhibition. In conclusion, nutritional shortage in combination with chemotherapeutic drugs as cisplatin can be a valuable new therapeutic strategy to overcome melanoma resistance.

Repurposing Drugs in Oncology (ReDO)-chloroquine and hydroxychloroquine as anti-cancer agents

Chloroquine (CQ) and hydroxychloroquine (HCQ) are well-known 4-aminoquinoline antimalarial agents. Scientific evidence also supports the use of CQ and HCQ in the treatment of cancer. Overall, preclinical studies support CQ and HCQ use in anti-cancer therapy, especially in combination with conventional anti-cancer treatments since they are able to sensitise tumour cells to a variety of drugs, potentiating the therapeutic activity. Thus far, clinical results are mostly in favour of the repurposing of CQ. However, over 30 clinical studies are still evaluating the activity of both CQ and HCQ in different cancer types and in combination with various standard treatments. Interestingly, CQ and HCQ exert effects both on cancer cells and on the tumour microenvironment. In addition to inhibition of the autophagic flux, which is the most studied anti-cancer effect of CQ and HCQ, these drugs affect the Toll-like receptor 9, p53 and CXCR4-CXCL12 pathway in cancer cells. In the tumour stroma, CQ was shown to affect the tumour vasculature, cancer-associated fibroblasts and the immune system. The evidence reviewed in this paper indicates that both CQ and HCQ deserve further clinical investigations in several cancer types. Special attention about the drug (CQ versus HCQ), the dose and the schedule of administration should be taken in the design of new trials.