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

In Vitro Investigation of Therapy-Induced Senescence and Senescence Escape in Breast Cancer Cells Using Novel Flow Cytometry-Based Methods

Although cellular senescence was originally defined as an irreversible form of cell cycle arrest, in therapy-induced senescence models, the emergence of proliferative senescence-escaped cancer cells has been reported by several groups, challenging the definition of senescence. Indeed, senescence-escaped cancer cells may contribute to resistance to cancer treatment. Here, to study senescence escape and isolate senescence-escaped cells, we developed novel flow cytometry-based methods using the proliferation marker Ki-67 and CellTrace CFSE live-staining. We investigated the role of a novel senescence marker (DPP4/CD26) and a senolytic drug (azithromycin) on the senescence-escaping ability of MCF-7 and MDA-MB-231 breast cancer cells. Our results show that the expression of DPP4/CD26 is significantly increased in both senescent MCF-7 and MDA-MB-231 cells. While not essential for senescence induction, DPP4/CD26 contributed to promoting senescence escape in MCF-7 cells but not in MDA-MB-231 cells. Our results also confirmed the potential senolytic effect of azithromycin in senescent cancer cells. Importantly, the combination of azithromycin and a DPP4 inhibitor (sitagliptin) demonstrated a synergistic effect in senescent MCF-7 cells and reduced the number of senescence-escaped cells. Although further research is needed, our results and novel methods could contribute to the investigation of the mechanisms of senescence escape and the identification of potential therapeutic targets. Indeed, DPP4/CD26 could be a promising marker and a novel target to potentially decrease senescence escape in cancer.

Insights on E1-like enzyme ATG7: functional regulation and relationships with aging-related diseases

Autophagy is a dynamic self-renovation biological process that maintains cell homeostasis and is responsible for the quality control of proteins, organelles, and energy metabolism. The E1-like ubiquitin-activating enzyme autophagy-related gene 7 (ATG7) is a critical factor that initiates classic autophagy reactions by promoting the formation and extension of autophagosome membranes. Recent studies have identified the key functions of ATG7 in regulating the cell cycle, apoptosis, and metabolism associated with the occurrence and development of multiple diseases. This review summarizes how ATG7 is precisely programmed by genetic, transcriptional, and epigenetic modifications in cells and the relationship between ATG7 and aging-related diseases.

Novel exosomal circEGFR facilitates triple negative breast cancer autophagy via promoting TFEB nuclear trafficking and modulating miR-224-5p/ATG13/ULK1 feedback loop

Triple-negative breast cancer (TNBC) cells are in a more hypoxic and starved state than non-TNBC cells, which makes TNBC cells always maintain high autophagy levels. Emerging evidence has demonstrated that circular RNAs (circRNAs) are involved in the progress of tumorigenesis. However, the regulation and functions of autophagy-induced circRNAs in TNBC remain unclear. In our study, autophagy-responsive circRNA candidates in TNBC cells under amino acid starved were identified by RNA sequencing. The results showed that circEGFR expression was significantly upregulated in autophagic cells. Knockdown of circEGFR inhibited autophagy in TNBC cells, and circEGFR derived from exosomes induced autophagy in recipient cells in the tumor microenvironment. In vitro and in vivo functional assays identified circEGFR as an oncogenic circRNA in TNBC. Clinically, circEGFR was significantly upregulated in TNBC and was positively associated with lymph node metastasis. CircEGFR in plasma-derived exosomes was upregulated in breast cancer patients compared with healthy people. Mechanistically, circEGFR facilitated the translocation of Annexin A2 (ANXA2) toward the plasma membrane in TNBC cells, which led to the release of Transcription Factor EB (a transcription factor of autophagy-related proteins, TFEB) from ANXA2-TFEB complex, causing nuclear translocation of TFEB, thereby promoting autophagy in TNBC cells. Meanwhile, circEGFR acted as ceRNA by directly binding to miR-224-5p and inhibited the expression of miR-224-5p, which weakened the suppressive role of miR-224-5p/ATG13/ULK1 axis on autophagy. Overall, our study demonstrates the key role of circEGFR in autophagy, malignant progression, and metastasis of TNBC. These indicate circEGFR is a potential diagnosis biomarker and therapeutic target for TNBC.

Regulation of mitochondrial metabolism by autophagy supports leptin-induced cell migration

Leptin is an adipokine secreted by adipose tissue, which promotes tumor progression by activating canonical signaling pathways such as MAPK/ERK. Recent studies have shown that leptin induces autophagy, and this process is involved in leptin-induced characteristics of malignancy. Autophagy is an intracellular degradation process associated with different hallmarks of cancer, such as cell survival, migration, and metabolic reprogramming. However, its relationship with metabolic reprogramming has not been clearly described. The purpose of this study was to determine the role of leptin-induced autophagy in cancer cell metabolism and its association with cellular proliferation and migration in breast cancer cells. We used ER+/PR+ and triple-negative breast cancer cell lines treated with leptin, autophagy inhibition, or mitochondrial metabolism inhibitors. Our results show that leptin induces autophagy, increases proliferation, mitochondrial ATP production and mitochondrial function in ER+/PR+ cells. Importantly, autophagy was required to maintain metabolic changes and cell proliferation driven by leptin. In triple-negative cells, leptin did not induce autophagy or cell proliferation but increased glycolytic and mitochondrial ATP production, mitochondrial function, and cell migration. In triple negative cells, autophagy was required to support metabolic changes and cell migration, and autophagy inhibition decreased cellular migration similar to mitochondrial inhibitors. In conclusion, leptin-induced autophagy supports mitochondrial metabolism in breast cancer cells as well as glycolysis in triple negative cells. Importantly, leptin-induced mitochondrial metabolism promoted cancer cell migration.

Sensitivity of osteosarcoma cell lines to autophagy inhibition as determined by pharmacologic and genetic manipulation

Pharmacologic inhibition of autophagy can be achieved using lysosomotropic agents such as hydroxychloroquine (HCQ) that interfere with fusion of the autophagosome to the lysosome thus preventing completion of the recycling process. The goal of the present study is to determine the sensitivity of eight canine (cOSA) and four human (hOSA) osteosarcoma tumour cell lines to antiproliferative and cytotoxic effects of lysosomal autophagy inhibitors, and to compare these results to the autophagy-dependence measured using a CRISPR/Cas9 live-cell imaging assay in OSA and other tumour cell lines. Antiproliferative and cytotoxic response to HCQ and Lys05 was determined using live cell imaging and YOYO-1 staining. CRISPR/Cas9 live cell imaging screen was done using species specific guide RNA's and transfection of reagents into cells. Response to autophagy core genes was compared to response to an essential (PCNA) and non-essential (FOXO3A) gene. cOSA and hOSA cell lines showed similar antiproliferative and cytotoxic responses to HCQ and Lys05 with median lethal dose (Dm ) values ranging from 4.6-15.8 μM and 2.1-5.1 μM for measures of anti-proliferative response, respectively. A relationship was observed between antiproliferative responses to HCQ and Lys05 and VPS34 CRISPR score with Dm values correlating with VPS34 response (r = 0.968 and 0.887) in a species independent manner. The results show that a subset of cOSA and hOSA cell lines are autophagy-dependent and sensitive to HCQ at pharmacologically-relevant exposures.

The association and application of sonodynamic therapy and autophagy in diseases

Sonodynamic therapy (SDT) is a new non-invasive treatment method proposed based on photodynamic therapy (PDT). It has advantages such as high precision, strong tissue penetration, minimal side effects, and good patient compliance. With the maturation of nanomedicine, the application of nanosonosensitizers has further propelled the development of SDT. In recent years, people have developed many new types of sonosensitizers and explored the mechanisms of SDT. Among them, the studies about the relationship between autophagy and SDT have attracted increasing attention. After the SDT, cells usually undergo autophagy as a self-protective mechanism to resist external stimuli and reduce cell damage, which is beneficial for the treatment of atherosclerosis (AS), diabetes, and myocardial infarction but counterproductive in cancer treatment. However, under certain treatment conditions, excessive upregulation of autophagy can also promote cell death, which is beneficial for cancer treatment. This article reviews the latest research progress on the relationship between SDT and autophagy in cancers, AS, diabetes, and myocardial infarction. We also discuss and propose the challenges and prospects in enhancing SDT efficacy by regulating autophagy, with the hope of promoting the development of this promising therapeutic approach.

Growth or death? Control of cell destiny by mTOR and autophagy pathways

One of the central regulators of cell growth, proliferation, and metabolism is the mammalian target of rapamycin, mTOR, which exists in two structurally and functionally different complexes: mTORC1 and mTORC2; unlike m TORC2, mTORC1 is activated in response to the sufficiency of nutrients and is inhibited by rapamycin. mTOR complexes have critical roles not only in protein synthesis, gene transcription regulation, proliferation, tumor metabolism, but also in the regulation of the programmed cell death mechanisms such as autophagy and apoptosis. Autophagy is a conserved catabolic mechanism in which damaged molecules are recycled in response to nutrient starvation. Emerging evidence indicates that the mTOR signaling pathway is frequently activated in tumors. In addition, dysregulation of autophagy was associated with the development of a variety of human diseases, such as cancer and aging. Since mTOR can inhibit the induction of the autophagic process from the early stages of autophagosome formation to the late stage of lysosome degradation, the use of mTOR inhibitors to regulate autophagy could be considered a potential therapeutic option. The present review sheds light on the mTOR and autophagy signaling pathways and the mechanisms of regulation of mTOR-autophagy.

The role of autophagy in hypoxia-induced radioresistance

Radiotherapy is a widely used treatment modality against cancer, and although survival rates are increasing, radioresistant properties of tumours remain a significant barrier for curative treatment. Tumour hypoxia is one of the main contributors to radioresistance and is common in most solid tumours. Hypoxia is responsible for many molecular changes within the cell which helps tumours to survive under such challenging conditions. These hypoxia-induced molecular changes are predominantly coordinated by the hypoxia inducible factor (HIF) and have been linked with the ability to confer resistance to radiation-induced cell death. To overcome this obstacle research has been directed towards autophagy, a cellular process involved in self degradation and recycling of macromolecules, as HIF plays a large role in its coordination under hypoxic conditions. The role that autophagy has following radiotherapy treatment is conflicted with evidence of both cytoprotective and cytotoxic effects. This literature review aims to explore the intricate relationship between radiotherapy, hypoxia, and autophagy in the context of cancer treatment. It provides valuable insights into the potential of targeting autophagy as a therapeutic strategy to improve the response of hypoxic tumours to radiotherapy.

The Combined Inhibition of Autophagy and Diacylglycerol Acyltransferase-Mediated Lipid Droplet Biogenesis Induces Cancer Cell Death during Acute Amino Acid Starvation

Lipid droplets (LDs) are dynamic organelles involved in the management of fatty acid trafficking and metabolism. Recent studies suggest that autophagy and LDs serve complementary roles in the protection against nutrient stress, but the autophagy-LD interplay in cancer cells is not well understood. Here, we examined the relationship between autophagy and LDs in starving HeLa cervical cancer- and MDA-MB-231 breast cancer cells. We found that acute amino acid depletion induces autophagy and promotes diacylglycerol acyltransferase 1 (DGAT1)-mediated LD accumulation in HeLa cells. Inhibition of autophagy via late-stage autophagy inhibitors, or by knocking down autophagy-related 5 (ATG5), reduced LD accumulation in amino acid-starved cancer cells, suggesting that autophagy contributes to LD biogenesis. On the contrary, knockdown of adipose triglyceride lipase (ATGL) increased LD accumulation, suggesting that LD breakdown is mediated by lipolysis under these conditions. Concurrent inhibition of autophagy by silencing ATG5 and of LD biogenesis using DGAT inhibitors was effective in killing starving HeLa cells, whereas cell survival was not compromised by suppression of ATGL-mediated lipolysis. Autophagy-dependent LD biogenesis was also observed in the aggressive triple-negative MDA-MB-231 breast cancer cells deprived of amino acids, but these cells were not sensitized to starvation by the combined inhibition of LD biogenesis and autophagy. These findings reveal that while targeting autophagy-driven and DGAT-mediated LD biogenesis reduces the resilience of HeLa cervical cancer cells to amino acid deprivation, this strategy may not be successful in other cancer cell types.

Targeting redox regulation and autophagy systems in cancer stem cells

Cancer is a dysregulated cellular level pathological condition that results in tumor formation followed by metastasis. In the heterogeneous tumor architecture, cancer stem cells (CSCs) are essential to push forward the progression of tumors due to their strong pro-tumor properties such as stemness, self-renewal, plasticity, metastasis, and being poorly responsive to radiotherapy and chemotherapeutic agents. Cancer stem cells have the ability to withstand various stress pressures by modulating transcriptional and translational mechanisms, and adaptable metabolic changes. Owing to CSCs heterogeneity and plasticity, these cells display varied metabolic and redox profiles across different types of cancers. It has been established that there is a disparity in the levels of Reactive Oxygen Species (ROS) generated in CSCs vs Non-CSC and these differential levels are detected across different tumors. CSCs have unique metabolic demands and are known to change plasticity during metastasis by passing through the interchangeable epithelial and mesenchymal-like phenotypes. During the metastatic process, tumor cells undergo epithelial to mesenchymal transition (EMT) thus attaining invasive properties while leaving the primary tumor site, similarly during the course of circulation and extravasation at a distant organ, these cells regain their epithelial characteristics through Mesenchymal to Epithelial Transition (MET) to initiate micrometastasis. It has been evidenced that levels of Reactive Oxygen Species (ROS) and associated metabolic activities vary between the epithelial and mesenchymal states of CSCs. Similarly, the levels of oxidative and metabolic states were observed to get altered in CSCs post-drug treatments. As oxidative and metabolic changes guide the onset of autophagy in cells, its role in self-renewal, quiescence, proliferation and response to drug treatment is well established. This review will highlight the molecular mechanisms useful for expanding therapeutic strategies based on modulating redox regulation and autophagy activation to targets. Specifically, we will account for the mounting data that focus on the role of ROS generated by different metabolic pathways and autophagy regulation in eradicating stem-like cells hereafter referred to as cancer stem cells (CSCs).

Recent Advances in the Role of Autophagy in Endocrine-Dependent Tumors

Autophagy plays a complex role in several cancer types, including endocrine-dependent cancers, by fueling cellular metabolism and clearing damaged substrates. This conserved recycling process has a dual function across tumor types where it can be tumor suppressive at early stages but tumor promotional in established disease. This review highlights the controversial roles of autophagy in endocrine-dependent tumors regarding cancer initiation, tumorigenesis, metastasis, and treatment response. We summarize clinical trial results thus far and highlight the need for additional mechanistic, preclinical, and clinical studies in endocrine-dependent tumors, particularly in breast cancer and prostate cancer.

Autophagy and Breast Cancer: Connected in Growth, Progression, and Therapy

Despite an increase in the incidence of breast cancer worldwide, overall prognosis has been consistently improving owing to the development of multiple targeted therapies and novel combination regimens including endocrine therapies, aromatase inhibitors, Her2-targeted therapies, and cdk4/6 inhibitors. Immunotherapy is also being actively examined for some breast cancer subtypes. This overall positive outlook is marred by the development of resistance or reduced efficacy of the drug combinations, but the underlying mechanisms are somewhat unclear. It is interesting to note that cancer cells quickly adapt and evade most therapies by activating autophagy, a catabolic process designed to recycle damaged cellular components and provide energy. In this review, we discuss the role of autophagy and autophagy-associated proteins in breast cancer growth, drug sensitivity, tumor dormancy, stemness, and recurrence. We further explore how autophagy intersects and reduces the efficacy of endocrine therapies, targeted therapies, radiotherapy, chemotherapies as well as immunotherapy via modulating various intermediate proteins, miRs, and lncRNAs. Lastly, the potential application of autophagy inhibitors and bioactive molecules to improve the anticancer effects of drugs by circumventing the cytoprotective autophagy is discussed.

RANKL Promotes Chemotherapy Resistance in Breast Cancer Cells Through STAT3 Mediated Autophagy Induction

BACKGROUND

This study was to investigate the functional role and mechanism of receptor activator of nuclear factor-kappa B ligand (RANKL) associated autophagy and chemoresistance in breast cancer.

MATERIALS AND METHODS

Cell Counting Kit-8 (CCK-8) assay was used to detect the cell viability. Real-time polymerase chain reaction (PCR) was used for determining the relative mRNA levels of key genes and protein expression was assessed by Western blotting. Immunofluorescence was performed to evaluate the changes in the autophagy flux. Short hairpin (shRNA) was used to knockdown the expression of the target genes in breast cancer cells. Based on The Cancer Genome Atlas (TCGA) database, we explored the expression of receptor activator of nuclear factor-kappa B (RANK), autophagy and signal transducer and activator of transcription 3 (STAT3) signaling associated genes and analyzed their correlation with the prognosis of breast cancer patients.

RESULTS

The findings showed that receptor activator of nuclear factor-kappa B ligand (RANKL), the ligand of RANK, could effectively enhance the chemoresistance potential of breast cancer cells. Our results showed that RANKL induced autophagy and enhanced the expression of autophagy associated genes in breast cancer cells. The knockdown of RANK suppressed RANKL mediated autophagy induction in these cells. Furthermore, the inhibition of autophagy suppressed RANKL mediated chemoresistance in breast cancer cells. We found STAT3 signaling pathway was involved in RANKL-induced autophagy. Analysis of the expression of RANK, and autophagy and STAT3 signaling associated genes in breast cancer tissues showed that the expression of autophagy and STAT3 signaling associated genes was correlated with the prognosis of breast cancer patients.

CONCLUSION

The present study suggests that the RANKL/RANK axis may potentially mediate chemoresistance in breast cancer cells by inducing autophagy through the STAT3 signaling pathway.

Ketoprofen suppresses triple negative breast cancer cell growth by inducing apoptosis and inhibiting autophagy

BACKGROUND

Triple-negative breast cancer (TNBC) is an invasive phenotype with undesirable clinical features, poor prognosis, and therapy resistance. Ketoprofen is a Non-steroidal anti-inflammatory drug (NSAID) with anti-tumor properties.

AIM

To investigate the effects of Ketoprofen on apoptosis and autophagy in TNBC cell line MDA-MB-231.

METHODS

The cytotoxic activity of Ketoprofen was assayed by the MTS method. Flowcytometry was utilized to measure the number of apoptotic MDA-MB-231 cells. The expression levels of apoptosis and autophagy markers, JAK2 and STAT3 were determined using quantitative real time-PCR (qRT-PCR) and western blotting methods.

RESULTS

Ketoprofen significantly decreased the proliferation of MDA-MB-231 cells compared to control cells. It also considerably induced apoptosis and apoptotic markers in these cells in comparison to controls. Treating the MADA-MB-231 cell line with Ketoprofen had an inhibitory effect on autophagy markers in this cell line. The use of FasL, as a death ligand, and ZB4, as an antibody that blocks the extrinsic pathway of apoptosis, revealed the involvement of the extrinsic pathway in the apoptosis-stimulating effect of Ketoprofen in the MADA-MB-231 cell line. Ketoprofen also hindered the phosphorylation and activation of JAK2 and STAT molecules leading to the inhibition of the JAK/STAT pathway in this TNBC cell line.

CONCLUSION

The outcomes of this study uncovered the anti-TNBC activity of Ketoprofen by inducing apoptosis and inhibiting viability and autophagy in MADA-MB-231 cells. Our data also suggested that Ketoprofen impedes apoptosis in TNBC cells by two different mechanisms including the induction of the extrinsic apoptotic pathway and inhibition of the JAK/STAT signaling.

MTX-PEG-modified CG/DMMA polymeric micelles for targeted delivery of doxorubicin to induce synergistic autophagic death against triple-negative breast cancer

The chemotherapy of triple-negative breast cancer based on doxorubicin (DOX) regimens suffers from great challenges on toxicity and autophagy raised off-target. In this study, a conjugate methotrexate-polyethylene glycol (shorten as MTX-PEG)-modified CG/DMMA polymeric micelles were prepared to endue DOX tumor selectivity and synergistic autophagic flux interference to reduce systematic toxicity and to improve anti-tumor capacity. The micelles could effectively promote the accumulation of autophagosomes in tumor cells and interfere with the degradation process of autophagic flux, collectively inducing autophagic death of tumor cells. In vivo and in vitro experiments showed that the micelles could exert improved anti-tumor effect and specificity, as well as reduced accumulation and damage of chemotherapeutic drugs in normal organs. The potential mechanism of synergistic autophagic death exerted by the synthesized micelles in MDA-MB-231 cells has been performed by autophagic flux-related pathway.

Bortezomib abrogates temozolomide-induced autophagic flux through an ATG5 dependent pathway

Introduction: Glioblastoma (GBM) is invariably resistant to temozolomide (TMZ) chemotherapy. Inhibiting the proteasomal pathway is an emerging strategy to accumulate damaged proteins and inhibit their lysosomal degradation. We hypothesized that pre-treatment of glioblastoma with bortezomib (BTZ) might sensitize glioblastoma to temozolomide by abolishing autophagy survival signals to augment DNA damage and apoptosis. Methods: P3 patient-derived glioblastoma cells, as well as the tumour cell lines U87, HF66, A172, and T98G were investigated for clonogenic survival after single or combined treatment with temozolomide and bortezomib in vitro. We investigated the requirement of functional autophagy machinery by utilizing pharmacological inhibitors or CRISPR-Cas9 knockout (KO) of autophagy-related genes -5 and -7 (ATG5 and ATG7) in glioblastoma cells and monitored changes in autophagic flux after temozolomide and/or bortezomib treatments. P3 wild-type and P3 ATG5-/- (ATG5 KO) cells were implanted orthotopically into NOD-SCID mice to assess the efficacy of bortezomib and temozolomide combination therapy with and without functional autophagy machinery. Results: The chemo-resistant glioblastoma cells increased autophagic flux during temozolomide treatment as indicated by increased degradation of long-lived proteins, diminished expression of autophagy markers LC3A/B-II and p62 (SQSTM1), increased co-localisation of LC3A/B-II with STX17, augmented and no induction of apoptosis. In contrast, bortezomib treatment abrogated autophagic flux indicated by the accumulation of LC3A/B-II and p62 (SQSTM1) positive autophagosomes that did not fuse with lysosomes and thus reduced the degradation of long-lived proteins. Bortezomib synergistically enhanced temozolomide efficacy by attenuating cell proliferation, increased DNA double-strand breaks, and apoptosis in an autophagy-dependent manner. Abolishing autophagy in ATG5 KOs reversed the bortezomib-induced toxicity, rescued glioblastoma cell death and reduced animal survival. Discussion: We conclude that bortezomib abrogates temozolomide induced autophagy flux through an ATG5 dependent pathway.

Highly expressed SERCA2 triggers tumor cell autophagy and is a druggable vulnerability in triple-negative breast cancer

Chemoresistance remains a major obstacle to successful treatment of triple negative breast cancer (TNBC). Identification of druggable vulnerabilities is an important aim for TNBC therapy. Here, we report that SERCA2 expression correlates with TNBC progression in human patients, which promotes TNBC cell proliferation, migration and chemoresistance. Mechanistically, SERCA2 interacts with LC3B via LIR motif, facilitating WIPI2-independent autophagosome formation to induce autophagy. Autophagy-mediated SERCA2 degradation induces SERCA2 transactivation through a Ca²⁺/CaMKK/CREB-1 feedback. Moreover, we found that SERCA2-targeting small molecule RL71 enhances SERCA2-LC3B interaction and induces excessive autophagic cell death. The increase in SERCA2 expression predisposes TNBC cells to RL71-induced autophagic cell death in vitro and in vivo. This study elucidates a mechanism by which TNBC cells maintain their high autophagy activity to induce chemoresistance, and suggests increased SERCA2 expression as a druggable vulnerability for TNBC.

Canonical and Noncanonical ER Stress-Mediated Autophagy Is a Bite the Bullet in View of Cancer Therapy

Cancer cells adapt multiple mechanisms to counter intense stress on their way to growth. Tumor microenvironment stress leads to canonical and noncanonical endoplasmic stress (ER) responses, which mediate autophagy and are engaged during proteotoxic challenges to clear unfolded or misfolded proteins and damaged organelles to mitigate stress. In these conditions, autophagy functions as a cytoprotective mechanism in which malignant tumor cells reuse degraded materials to generate energy under adverse growing conditions. However, cellular protection by autophagy is thought to be complicated, contentious, and context-dependent; the stress response to autophagy is suggested to support tumorigenesis and drug resistance, which must be adequately addressed. This review describes significant findings that suggest accelerated autophagy in cancer, a novel obstacle for anticancer therapy, and discusses the UPR components that have been suggested to be untreatable. Thus, addressing the UPR or noncanonical ER stress components is the most effective approach to suppressing cytoprotective autophagy for better and more effective cancer treatment.

Targeting Both Autophagy and Immunotherapy in Breast Cancer Treatment

As clinical efforts towards breast-conserving therapy and prolonging survival of those with metastatic breast cancer increase, innovative approaches with the use of biologics are on the rise. Two areas of current focus are cancer immunotherapy and autophagy, both of which have been well-studied independently but have recently been shown to have intertwining roles in cancer. An increased understanding of their interactions could provide new insights that result in novel diagnostic, prognostic, and therapeutic strategies. In this breast cancer-focused review, we explore the interactions between autophagy and two clinically relevant immune checkpoint pathways; the programmed cell death-1 receptor with its ligand (PD-L1)/PD-1 and the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4)/CD80 and CD86 (B7-1 and B7-2). Furthermore, we discuss emerging preclinical and clinical data supporting targeting both immunotherapy and autophagy pathway manipulation as a promising approach in the treatment of breast cancer.

Recent advances in glioblastoma multiforme therapy: A focus on autophagy regulation

Despite conventional treatment options including chemoradiation, patients with the most aggressive primary brain tumor, glioblastoma multiforme (GBM), experience an average survival time of less than 15 months. Regarding the malignant nature of GBM, extensive research and discovery of novel treatments are urgently required to improve the patients' prognosis. Autophagy, a crucial physiological pathway for the degradation and recycling of cell components, is one of the exciting targets of GBM studies. Interventions aimed at autophagy activation or inhibition have been explored as potential GBM therapeutics. This review, which delves into therapeutic techniques to block or activate autophagy in preclinical and clinical research, aims to expand our understanding of available therapies battling GBM.

β-Caryophyllene Counteracts Chemoresistance Induced by Cigarette Smoke in Triple-Negative Breast Cancer MDA-MB-468 Cells

Exposure to cigarette smoke (CS) has been associated with an increased risk of fatal breast cancers and recurrence, along with chemoresistance and chemotherapy impairment. This strengthens the interest in chemopreventive agents to be exploited both in healthy and oncological subjects to prevent or repair CS damage. In the present study, we evaluated the chemopreventive properties of the natural sesquiterpene β-caryophyllene towards the damage induced by cigarette smoke condensate (CSC) in triple negative breast cancer MDA-MB-468 cells. Particularly, we assessed the ability of the sesquiterpene to interfere with the mechanisms exploited by CSC to promote cell survival and chemoresistance, including genomic instability, cell cycle progress, autophagy/apoptosis, cell migration and related pathways. β-Caryophyllene was found to be able to increase the CSC-induced death of MDA-MB-468 cells, likely triggering oxidative stress, cell cycle arrest and apoptosis; moreover, it hindered cell recovery, autophagy activation and cell migration; at last, a marked inhibition of the signal transducer and activator of transcription 3 (STAT3) activation was highlighted: this could represent a key mechanism of the chemoprevention by β-caryophyllene. Although further studies are required to confirm the in vivo efficacy of β-caryophyllene, the present results suggest a novel strategy to reduce the harmful effect of smoke in cancer patients and to improve the survival expectations in breast cancer women.

STAT3 and PD-L1 are negatively correlated with ATM and have impact on the prognosis of triple-negative breast cancer patients with low ATM expression

INTRODUCTION

Triple-negative breast cancer (TNBC) is known for its aggressive behaviors and lacking of effective treatment. Programmed cell death ligand-1 (PD-L1) inhibitor has just been approved for using in the management of advanced TNBC. To accurately screen TNBC sensitive to anti-PD-L1 treatment and to explore the feasibility of the ataxia-telangiectasia mutation protein (ATM) inhibitor combined with PD-L1 inhibitor, radiotherapy and chemotherapy, we focus on whether ATM participates in the regulation of PD-L1 and affects the prognosis of patients through c-Src, signal transducer and activator of transcription 1&3 (STAT1 and STAT3).

MATERIALS AND METHODS

We used immunohistochemical staining to explore the relationship of ATM with c-Src, STAT1, STAT3, PD-1/PD-L1, Tumor-infiltrating lymphocytes (TILs), as well as other clinicopathologic features in 86 pathological stage III TNBCs. Their impact on prognosis was also explored.

RESULTS

We found ATM expression was negatively correlated with STAT1, STAT3, PD-L1, TILs and CD8 + cells in TNBC. STAT1 positively correlated the expression of PD-L1. In TNBC with ATM low expression, STAT3 was an independent factor for improved prognosis, while PD-L1 was an independent negative prognostic factor. Furthermore, in low ATM group, the phosphorylation of tyrosine at position 419 of c-Src (p-c-src Y419) was correlated with the overexpression of STAT3.

CONCLUSION

Locally advanced TNBC with low ATM expression may be more likely to benefit from anti-PD-L1 inhibitors. The feasibility of ATM functional inhibitor combined with immune checkpoint blockade therapies in the treatment of TNBC is also worthy of further exploration. Our study suggests that STAT3 has different impacts on tumor progression in different tumors.

Decreased expression of GRIM-19 induces autophagy through the AMPK/ULK1 signaling pathway during adenomyosis

The processes underlying adenomyosis are similar to those of tumor metastasis, and it is defined as progressive invasion by the endometrium and the subsequent creation of ectopic lesions. GRIM-19 regulates cell death via the mitochondrial respiratory chain. Stress following oxygen deprivation can induce tumor cell autophagy, leading to cell invasion and migration. Here, we revealed that GRIM-19 negatively regulates autophagy, and, at least in adenomyosis, decreased expression of GRIM-19 is accompanied by an increased level of autophagy and 5'-adenosine monophosphate-activated protein kinase-Unc-51 like autophagy activating kinase 1 (AMPK-ULK1) activation. Upregulation of GRIM-19 expression in human primary endometrial cells and ISHIKAWA cells inhibits autophagy via the AMPK-ULK1 pathway and helps control cell invasion and migration. In addition, we also identified increased expression of AMPK and ULK1, and higher levels of autophagy in the uterine tissues of GRIM-19+/- mice. Importantly, the function of the GRIM-19-AMPK-ULK1 axis in regulating autophagy in adenomyosis is similar to that of tumor tissues, which may help elucidate the regulation of adenomyosis tumor-like behavior, and is expected to help identify novel targets for the diagnosis and treatment of adenomyosis.

Re-evaluation of the role of autophagy in thyroid cancer treatment

Numerous studies have examined the role of autophagy in thyroid cancer treatment; however there are discrepancies among the reported data, with some showing the pro-survival and others the anti-survival effects of autophagy. These discrepant results appear to be at least in part due to insufficient analyses or data misinterpretation as well as improper assessments of autophagic activity. Therefore, the present study re-evaluated the regulation of autophagic activity by various anticancer modalities and examined the role of autophagy in thyroid cancer treatment in three thyroid cancer cell lines (TPC1, ACT1 and KTC1). The immunofluorescence and DalGreen findings demonstrated that cisplatin, irradiation and sorafenib were all autophagy inducers as previously reported, but, unlike previous studies using thyroid cancer cells, doxorubicin acted as an inhibitor. KTC1 cells are unique because they only responded to cisplatin. The efficacy of anticancer therapeutics was significantly higher in chloroquine or 3-methyladenine-treated autophagy-defective cells than in autophagy-competent cells, thereby indicating the pro-survival effect of autophagy induced by anticancer therapeutics, which is partly due to inhibition of apoptosis. Thus, the present findings relating to several anticancer therapeutics and three thyroid cancer cell lines demonstrate the pro-survival effect of autophagy in thyroid cancer treatment. Although the present study only involved cell lines, it provides evidence for the beneficial combination of the anticancer therapeutic modalities with autophagy inhibitors, and proposes that autophagy inhibitors may serve as a possible adjunctive therapy for thyroid cancer.

HEIH Promotes Malignant Progression of Gastric Cancer by Regulating STAT3-Mediated Autophagy and Glycolysis

To study the clinical value of HEIH hyperexpression in gastric cancer and the molecular mechanism of promoting malignant proliferation of gastric cancer cells, qRT-PCR was used to detect the expression of HEIH in gastric cancer and nontumor gastric tissues. HEIH interference sequence was constructed to downregulate HEIH expression in MGC-803 and BGC-823 cell lines. CCK8, clonogenesis, and Transwell assay were used to detect the effects of HEIH on proliferation and invasion of tumor cells. The protein levels of STAT3, p-STAT3, P62, and LC3 were detected by Western blotting. The results showed that HEIH was highly expressed in gastric cancer (P < 0.01). Interference of HEIH expression in MGC-803 and BGC-823 cells reduced the proliferation and invasion of gastric cancer cells, and the results were statistically significant (P < 0.05). HEIH acts as a miRNA sponge for miR-4500. HEIH promotes gastric cancer development by inhibiting miR-4500. STAT3 is a downstream target of miR-4500. HEIH inhibits autophagy and promotes glycolysis. In conclusion, HEIH is highly expressed in gastric cancers. HEIH promotes malignant proliferation and development of gastric cancer cells. HEIH may be a new candidate site for pathological diagnosis and molecular drug therapy for future clinical treatment of gastric cancer.

Inhibition of autophagy by chloroquine prevents resistance to PI3K/AKT inhibitors and potentiates their antitumor effect in combination with paclitaxel in triple negative breast cancer models

Background

Triple negative breast cancer (TNBC) is an aggressive disease characterized by high risk of relapse and development of resistance to different chemotherapy agents. Several targeted therapies have been investigated in TNBC with modest results in clinical trials. Among these, PI3K/AKT inhibitors have been evaluated in addition to standard therapies, yielding conflicting results and making attempts on elucidating inherent mechanisms of resistance of great interest. Increasing evidences suggest that PI3K/AKT inhibitors can induce autophagy in different cancers. Autophagy represents a supposed mechanism of drug-resistance in aggressive tumors, like TNBC. We, therefore, investigated if two PI3K/AKT inhibitors, ipatasertib and taselisib, could induce autophagy in breast cancer models, and whether chloroquine (CQ), a well known autophagy inhibitor, could potentiate ipatasertib and taselisib anti-cancer effect in combination with conventional chemotherapy.

Methods

The induction of autophagy after ipatasertib and taselisib treatment was evaluated in MDAMB231, MDAM468, MCF7, SKBR3 and MDAB361 breast cancer cell lines by assaying LC3-I conversion to LC3-II through immunoblotting and immunofluorescence. Other autophagy-markers as p62/SQSTM1 and ATG5 were evaluated by immunoblotting. Synergistic antiproliferative effect of double and triple combinations of ipatasertib/taselisib plus CQ and/or paclitaxel were evaluated by SRB assay and clonogenic assay. Anti-apoptotic effect of double combination of ipatasertib/taselisib plus CQ was evaluated by increased cleaved-PARP by immunoblot and by Annexin V- flow cytometric analysis. In vivo experiments were performed on xenograft model of MDAMB231 in NOD/SCID mice.

Results

Our results suggested that ipatasertib and taselisib induce increased autophagy signaling in different breast cancer models. This effect was particularly evident in PI3K/AKT resistant TNBC cells, where the inhibition of autophagy by CQ potentiates the therapeutic effect of PI3K/AKT inhibitors in vitro and in vivo TNBC models, synergizing with taxane-based chemotherapy.

Conclusion

These data suggest that inhibition of authophagy with CQ could overcome mechanism of drug resistance to PI3K/AKT inhibitors plus paclitaxel in TNBC making the evaluation of such combinations in clinical trials warranted.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03462-z.

Porcupine Inhibition Disrupts Mitochondrial Function and Homeostasis in WNT Ligand-Addicted Pancreatic Cancer

WNT signaling promotes pancreatic ductal adenocarcinoma (PDAC) through diverse effects on proliferation, differentiation, survival, and stemness. A subset of PDAC with inactivating mutations in ring finger protein 43 (RNF43) show growth dependency on autocrine WNT ligand signaling and are susceptible to agents that block WNT ligand acylation by Porcupine O-acyltransferase, which is required for proper WNT ligand processing and secretion. For this study, global transcriptomic, proteomic, and metabolomic analyses were performed to explore the therapeutic response of RNF43-mutant PDAC to the Porcupine inhibitor (PORCNi) LGK974. LGK974 disrupted cellular bioenergetics and mitochondrial function through actions that included rapid mitochondrial depolarization, reduced mitochondrial content, and inhibition of oxidative phosphorylation and tricarboxylic acid cycle. LGK974 also broadly altered transcriptional activity, downregulating genes involved in cell cycle, nucleotide metabolism, and ribosomal biogenesis and upregulating genes involved in epithelial-mesenchymal transition, hypoxia, endocytosis, and lysosomes. Autophagy and lysosomal activity were augmented in response to LGK974, which synergistically inhibited tumor cell viability in combination with chloroquine. Autocrine WNT ligand signaling dictates metabolic dependencies in RNF43-mutant PDAC through a combination of transcription dependent and independent effects linked to mitochondrial health and function. Metabolic adaptations to mitochondrial damage and bioenergetic stress represent potential targetable liabilities in combination with PORCNi for the treatment of WNT ligand-addicted PDAC.

The Interaction Between Autophagy and JAK/STAT3 Signaling Pathway in Tumors

Tumor is one of the important factors affecting human life and health in today’s world, and scientists have studied it extensively and deeply, among which autophagy and JAK/STAT3 signaling pathway are two important research directions. The JAK/STAT3 axis is a classical intracellular signaling pathway that assumes a key role in the regulation of cell proliferation, apoptosis, and vascular neogenesis, and its abnormal cell signaling and regulation are closely related to the occurrence and development of tumors. Therefore, the JAK/STAT3 pathway in tumor cells and various stromal cells in their microenvironment is often considered as an effective target for tumor therapy. Autophagy is a process that degrades cytoplasmic proteins and organelles through the lysosomal pathway. It is a fundamental metabolic mechanism for intracellular degradation. The mechanism of action of autophagy is complex and may play different roles at various stages of tumor development. Altered STAT3 expression has been found to be accompanied by the abnormal autophagy activity in many oncological studies, and the two may play a synergistic or antagonistic role in promoting or inhibiting the occurrence and development of tumors. This article reviews the recent advances in autophagy and its interaction with JAK/STAT3 signaling pathway in the pathogenesis, prevention, diagnosis, and treatment of tumors.

A racemosin B derivative, C25, suppresses breast cancer growth via lysosomal membrane permeabilization and inhibition of autophagic flux

Breast cancer is the most common malignancy among women worldwide. As conventional therapies are only partially successful in eradicating breast cancer, the development of novel strategies is a top priority. We previously showed that C25, a new racemosin B derivative, exerts its anti-cancer activity through inhibition of autophagy, but the underlying mechanism remained unknown. Here we show that C25 inhibits the growth of diverse breast cancer cell subtypes and effectively suppresses tumor progression in a xenotransplantation model of triple negative breast cancer. C25 acts as a lysosomotropic agent to induce lysosomal membrane permeabilization and inhibit autophagic flux, resulting in cathepsin release and cell death. In accordance, RNA sequencing and gene set enrichment analysis revealed that C25 induces pathways consistent with autophagy inhibition, cell cycle arrest and senescence. Interestingly, knockdown of TFEB or SQSTM1 reduced cell death induced by C25 treatment. Finally, we show that C25 synergizes with the chemo-therapeutics etoposide and paclitaxel to further limit breast cancer cell growth. Thus, C25 alone or in combination with other anti-neoplastic agents offers a novel therapeutic strategy for aggressive forms of breast cancer and possibly other malignancies.

Simultaneous proteasome and autophagy inhibition synergistically enhances cytotoxicity of doxorubicin in breast cancer cells

Ubiquitin-proteasome system (UPS) and autophagy are interconnected proteolysis pathways implicated in doxorubicin resistance of breast cancer cells. Following anticancer treatments, autophagy either plays a cytoprotective role or augments treatment-induced cytotoxicity. However, the role of autophagy in breast cancer cells cotreated with doxorubicin and ixazomib remains unclear. The expression of autophagy proteins (LC3A/B and Beclin-1) and UPS protein (ubiquitin) in MDA-MB-231 and MCF-7 cells following doxorubicin, ixazomib, and/or hydroxychloroquine were determined by western blot. The combinatorial effects and combination index (CI) of triple-combination were determined by cell viability assay and CompuSyn software, respectively. Doxorubicin and ixazomib cotreatment increased Beclin-1 (3.8- and 3.5-fold) and LC3-II expression (13.5- and 1.9-fold) in MDA-MB-231 and MCF-7 cells, respectively. Adding lysosomal inhibitor hydroxychloroquine to doxorubicin and ixazomib further increased LC3-II expression to 45.0- and 16.5-fold in MDA-MB-231 and MCF-7 cells, respectively, confirming autophagy induction. The triple-combination synergistically inhibited cell growth, achieving CI 0.672 and 0.157 in MDA-MB-231 and MCF-7 cells, respectively. The triple-combination also induced ubiquitinated proteins accumulation (2.5-fold and 3.0-fold) in MDA-MB-231 and MCF-7 cells, respectively. These results suggest that the autophagy induced by doxorubicin and ixazomib cotreatment serves cytoprotective role in breast cancer cells. Simultaneous UPS and autophagy inhibition synergistically enhanced doxorubicin-mediated cytotoxicity.

Lucanthone Targets Lysosomes to Perturb Glioma Proliferation, Chemoresistance and Stemness, and Slows Tumor Growth In Vivo

Glioblastoma is the most common and aggressive primary brain tumor in adults. Median survival time remains at 16-20 months despite multimodal treatment with surgical resection, radiation, temozolomide and tumor-treating fields therapy. After genotoxic stress glioma cells initiate cytoprotective autophagy, which contributes to treatment resistance, limiting the efficacy of these therapies and providing an avenue for glioma recurrence. Antagonism of autophagy steps has recently gained attention as it may enhance the efficacy of classical chemotherapies and newer immune-stimulating therapies. The modulation of autophagy in the clinic is limited by the low potency of common autophagy inhibitors and the inability of newer ones to cross the blood-brain barrier. Herein, we leverage lucanthone, an anti-schistosomal agent which crosses the blood-brain barrier and was recently reported to act as an autophagy inhibitor in breast cancer cells. Our studies show that lucanthone was toxic to glioma cells by inhibiting autophagy. It enhanced anti-glioma temozolomide (TMZ) efficacy at sub-cytotoxic concentrations, and suppressed the growth of stem-like glioma cells and temozolomide-resistant glioma stem cells. In vivo lucanthone slowed tumor growth: reduced numbers of Olig2+ glioma cells, normalized tumor vasculature, and reduced tumor hypoxia. We propose that lucanthone may serve to perturb a mechanism of temozolomide resistance and allow for successful treatment of TMZ-resistant glioblastoma.

Autophagy in cancer: The cornerstone during glutamine deprivation

Over the past two decades, researchers have revealed the crucial functions of glutamine in supporting the hyperproliferation state of cancer cells. Glutamine acts on maintaining high energy production, supporting redox status and amino acid homeostasis. Therefore, cancer cells exhibit excessive uptake of the extracellular glutamine, synthesize it in some cases, and recycle intracellular and extracellular proteins to provide an additional source of glutamine to satisfy the increasing glutamine demand. On the other hand, autophagy's role is still debated regarding tumor initiation and progression. However, most cancer cells urgently need autophagy to overcome the existential threats during glutamine restriction stress. Downstream to various stress pathways induced during such a condition, autophagy is considered an indispensable cytoprotective tool to maintain cell integrity and survival. However, the overactivation of the autophagy process is related to lethal consequences. This review summarized glutamine pathways to control autophagy and highlighted autophagy's primary activation pathways, and discussed the roles during glutamine deprivation.

Construction and Validation of a Prognostic Risk Model for Triple-Negative Breast Cancer Based on Autophagy-Related Genes

Background

Autophagy plays an important role in triple-negative breast cancer (TNBC). However, the prognostic value of autophagy-related genes (ARGs) in TNBC remains unknown. In this study, we established a survival model to evaluate the prognosis of TNBC patients using ARGs signature.

Methods

A total of 222 autophagy-related genes were downloaded from The Human Autophagy Database. The RNA-sequencing data and corresponding clinical data of TNBC were obtained from The Cancer Genome Atlas (TCGA) database. Differentially expressed autophagy-related genes (DE-ARGs) between normal samples and TNBC samples were determined by the DESeq2 package. Then, univariate Cox, least absolute shrinkage and selection operator (LASSO), and multivariate Cox regression analyses were performed. According to the LASSO regression results based on univariate Cox, we identified a prognostic signature for overall survival (OS), which was further validated by using the Gene Expression Omnibus (GEO) cohort. We also found an independent prognostic marker that can predict the clinicopathological features of TNBC. Furthermore, a nomogram was drawn to predict the survival probability of TNBC patients, which could help in clinical decision for TNBC treatment. Finally, we validated the requirement of an ARG in our model for TNBC cell survival and metastasis.

Results

There are 43 DE-ARGs identified between normal and tumor samples. A risk model for OS using CDKN1A, CTSD, CTSL, EIF4EBP1, TMEM74, and VAMP3 was established based on univariate Cox regression and LASSO regression analysis. Overall survival of TNBC patients was significantly shorter in the high-risk group than in the low-risk group for both the training and validation cohorts. Using the Kaplan–Meier curves and receiver operating characteristic (ROC) curves, we demonstrated the accuracy of the prognostic model. Multivariate Cox regression analysis was used to verify risk score as an independent predictor. Subsequently, a nomogram was proposed to predict 1-, 3-, and 5-year survival for TNBC patients. The calibration curves showed great accuracy of the model for survival prediction. Finally, we found that depletion of EIF4EBP1, one of the ARGs in our model, significantly reduced cell proliferation and metastasis of TNBC cells.

Conclusion

Based on six ARGs (CDKN1A, CTSD, CTSL, EIF4EBP1, TMEM74, and VAMP3), we developed a risk prediction model that can help clinical doctors effectively predict the survival status of TNBC patients. Our data suggested that EIF4EBP1 might promote the proliferation and migration in TNBC cell lines. These findings provided a novel insight into the vital role of the autophagy-related genes in TNBC and may provide new therapeutic targets for TNBC.

The complex interplay between autophagy and cell death pathways

Autophagy is a universal cellular homeostatic process, required for the clearance of dysfunctional macromolecules or organelles. This self-digestion mechanism modulates cell survival, either directly by targeting cell death players, or indirectly by maintaining cellular balance and bioenergetics. Nevertheless, under acute or accumulated stress, autophagy can also contribute to promote different modes of cell death, either through highly regulated signalling events, or in a more uncontrolled inflammatory manner. Conversely, apoptotic or necroptotic factors have also been implicated in the regulation of autophagy, while specific factors regulate both processes. Here, we survey both earlier and recent findings, highlighting the intricate interaction of autophagic and cell death pathways. We, Furthermore, discuss paradigms, where this cross-talk is disrupted, in the context of disease.

Pharmacokinetic and Pharmacodynamic Assessment of Hydroxychloroquine in Breast Cancer

Hydroxychloroquine (HCQ) is being tested in a number of human clinical trials to determine the role of autophagy in response to standard anticancer therapies. However, HCQ pharmacodynamic (PD) responses are difficult to assess in patients, and preclinical studies in mouse models are equivocal with regard to HCQ exposure and inhibition of autophagy. Here, pharmacokinetic (PK) assessment of HCQ in non-tumor-bearing mice after intraperitoneal dosing established 60 mg/kg as the human equivalent dose of HCQ in mice. Autophagy inhibition, cell proliferation, and cell death were assessed in two-dimensional (2D) cell culture and three-dimensional tumor organoids in breast cancer. Mice challenged with breast cancer xenografts were then treated with 60 mg/kg HCQ via intraperitoneal dosing, and subsequent PK and PD responses were assessed. Although autophagic flux was significantly inhibited in cells irrespective of autophagy-dependence status, autophagy-dependent tumors had decreased cell proliferation and increased cell death at earlier time points compared with autophagy-independent tumors. Overall, this study shows that 2D cell culture, three-dimensional tumor organoids, and in vivo studies produce similar results, and in vitro studies can be used as surrogates to recapitulate in vivo antitumor responses of HCQ. SIGNIFICANCE STATEMENT: Autophagy-dependent tumors but not autophagy-independent tumors have decreased cell proliferation and increased cell death after single-agent hydroxychloroquine treatment. However, hydroxychloroquine causes decreased autophagic flux regardless of autophagy status, suggesting its clinical efficacy in the context of autophagy inhibition.

Understanding the Role of Autophagy in Cancer Formation and Progression Is a Real Opportunity to Treat and Cure Human Cancers

Simple Summary

The modulation of autophagy represents a potential therapeutic strategy for cancer. More than one hundred clinical trials have been conducted or are ongoing to explore the efficacy of autophagy modulators to reduce the tumor growth and potentiate the anti-cancer effects of conventional therapy. Despite this, the effective role of autophagy during tumor initiation, growth, and metastasis remains not well understood. Depending on the cancer type and stage of cancer, autophagy may have tumor suppressor properties as well as help cancer cells to proliferate and evade cancer therapy. The current review aims to summarize the current knowledge about the autophagy implications in cancer and report the therapeutic opportunities based on the modulation of the autophagy process.

Abstract

The malignant transformation of a cell produces the accumulation of several cellular adaptions. These changes determine variations in biological processes that are necessary for a cancerous cell to survive during stressful conditions. Autophagy is the main nutrient recycling and metabolic adaptor mechanism in eukaryotic cells, represents a continuous source of energy and biomolecules, and is fundamental to preserve the correct cellular homeostasis during unfavorable conditions. In recent decades, several findings demonstrate a close relationship between autophagy, malignant transformation, and cancer progression. The evidence suggests that autophagy in the cancer context has a bipolar role (it may act as a tumor suppressor and as a mechanism of cell survival for established tumors) and demonstrates that the targeting of autophagy may represent novel therapeutic opportunities. Accordingly, the modulation of autophagy has important clinical benefits in patients affected by diverse cancer types. Currently, about 30 clinical trials are actively investigating the efficacy of autophagy modulators to enhance the efficacy of cytotoxic chemotherapy treatments. A deeper understanding of the molecular pathways regulating autophagy in the cancer context will provide new ways to target autophagy for improving the therapeutic benefits. Herein, we describe how autophagy participates during malignant transformation and cancer progression, and we report the ultimate efforts to translate this knowledge into specific therapeutic approaches to treat and cure human cancers.

The Emerging Roles of Autophagy in Human Diseases

Autophagy, a process of cellular self-digestion, delivers intracellular components including superfluous and dysfunctional proteins and organelles to the lysosome for degradation and recycling and is important to maintain cellular homeostasis. In recent decades, autophagy has been found to help fight against a variety of human diseases, but, at the same time, autophagy can also promote the procession of certain pathologies, which makes the connection between autophagy and diseases complex but interesting. In this review, we summarize the advances in understanding the roles of autophagy in human diseases and the therapeutic methods targeting autophagy and discuss some of the remaining questions in this field, focusing on cancer, neurodegenerative diseases, infectious diseases and metabolic disorders.

Bruceae Fructus Oil Inhibits Triple-Negative Breast Cancer by Restraining Autophagy: Dependence on the Gut Microbiota-Mediated Amino Acid Regulation

Triple-negative breast cancer (TNBC) has been acknowledged as an aggressive disease with worst prognosis, which requires endeavor to develop novel therapeutic agents. Bruceae fructus oil (BO), a vegetable oil derived from the fruit of Brucea javanica (L.) Merr., is an approved marketable drug for the treatment of cancer in China for several decades. Despite that the anti–breast cancer activity of several quassinoids derived from B. javanica has been found, it was the first time that the potential of BO against TNBC was revealed. Although BO had no cytotoxicity on TNBC cell lines in vitro, the oral administration of BO exhibited a gut microbiota–dependent tumor suppression without toxicity on the non-targeted organs in vivo. By metagenomics and untargeted metabolomics, it was found that BO not only altered the composition and amino acid metabolism function of gut microbiota but also regulated the host’s amino acid profile, which was in accordance with the metabolism alternation in gut microbiota. Moreover, the activity of mTOR in tumor was promoted by BO treatment as indicated by the phosphorylation of 4E-binding protein 1 (4E-BP1) and ribosomal protein S6, and hyper-autophagy was consequently restrained. By contrast, the failure of tumor suppression by BO under pseudo germ-free (PGF) condition came with indistinctive changes in autophagy and mTOR activity, implying the critical role of the gut microbiota in BO’s anticancer activity. The present study highlighted a promising application of BO against breast cancer with novel efficacy and safety.

Flubendazole Elicits Antitumor Effects by Inhibiting STAT3 and Activating Autophagy in Non-small Cell Lung Cancer

Non-small cell lung carcinoma (NSCLC) is a major neoplastic disease with a high mortality worldwide; however, effective treatment of this disease remains a challenge. Flubendazole, a traditional anthelmintic drug, possesses potent antitumor properties; however, the detailed molecular mechanism of flubendazole activity in NSCLC needs to be further explored. In the present study, flubendazole was found to exhibit valid antitumor activity in vitro as well as in vivo. Flubendazole blocked phosphorylation of STAT3 in a dose- and time-dependent manner and regulated the transcription of STAT3 target genes encoding apoptotic proteins. Further, flubendazole inhibited STAT3 activation by inhibiting its phosphorylation and nuclear localization induced by interleukin-6 (IL-6). Notably, the autophagic flux of NSCLC cell lines was increased after flubendazole treatment. Furthermore, flubendazole downregulated the expression of BCL2, P62, and phosphorylated-mTOR, but it upregulated LC3-I/II and Beclin-1 expression, which are the main genes associated with autophagy. Collectively, these data contribute to elucidating the efficacy of flubendazole as an anticancer drug, demonstrating its potential as a therapeutic agent via its suppression of STAT3 activity and the activation of autophagy in NSCLC.

Autophagy inhibition in breast cancer cells induces ROS-mediated MIF expression and M1 macrophage polarization

Autophagy can function as a survival mechanism for cancer cells and therefore, its inhibition is currently being explored as a therapy for different cancer types. For breast cancer, triple negative breast cancer (TNBC) is the subtype most sensitive to the inhibition of autophagy; but its inhibition has also been shown to promote ROS-dependent secretion of macrophage migration inhibitory factor (MIF), a pro-tumorigenic cytokine. In this work, we explore the role of MIF in breast cancer, the mechanism by which autophagy inhibition promotes MIF secretion and its effects on neighboring cancer cell signaling and macrophage polarization. We analyzed MIF mRNA expression levels in tumors from breast cancer patients from different subtypes and found that Luminal B, HER2 and Basal subtypes, which are associated to high proliferation, displayed high MIF levels. However, MIF expression had no prognostic relevance in any breast cancer subtype. In addition, we found that autophagy inhibition in 66cl4 TNBC cells increased intracellular Reactive Oxygen Species (ROS) levels, which increased MIF expression and secretion. MIF secreted from 66cl4 TNBC cells induced the activation of MIF-regulated pathways in syngeneic cell lines, increasing Akt phosphorylation in 4T1 cells and ERK phosphorylation in 67NR cells. Regarding MIF/ chemokine receptors, higher levels of CD74 and CXCR2 were found in TNBC tumor cell lines when compared to non-tumorigenic cells and CXCR7 was elevated in the highly metastatic 4T1 cell line. Finally, secreted MIF from autophagy deficient 66cl4 cells induced macrophage polarization towards the M1 subtype. Together, our results indicate an important role for the inhibition of autophagy in the regulation of ROS-mediated MIF gene expression and secretion, with paracrine effects on cancer cell signaling and pro-inflammatory repercussions in macrophage M1 polarization. This data should be considered when considering the inhibition of autophagy as a therapy for different types of cancer.

Oxidative Stress Activated by Sorafenib Alters the Temozolomide Sensitivity of Human Glioma Cells Through Autophagy and JAK2/STAT3-AIF Axis

The development of temozolomide (TMZ) resistance in glioma leads to poor patient prognosis. Sorafenib, a novel diaryl urea compound and multikinase inhibitor, has the ability to effectively cross the blood-brain barrier. However, the effect of sorafenib on glioma cells and the molecular mechanism underlying the ability of sorafenib to enhance the antitumor effects of TMZ remain elusive. Here, we found that sorafenib could enhance the cytotoxic effects of TMZ in glioma cells in vitro and in vivo. Mechanistically, the combination of sorafenib and TMZ induced mitochondrial depolarization and apoptosis inducing factor (AIF) translocation from mitochondria to nuclei, and this process was dependent on STAT3 inhibition. Moreover, the combination of sorafenib and TMZ inhibited JAK2/STAT3 phosphorylation and STAT3 translocation to mitochondria. Inhibition of STAT3 activation promoted the autophagy-associated apoptosis induced by the combination of sorafenib and TMZ. Furthermore, the combined sorafenib and TMZ treatment induced oxidative stress while reactive oxygen species (ROS) clearance reversed the treatment-induced inhibition of JAK2/STAT3. The results indicate that sorafenib enhanced the temozolomide sensitivity of human glioma cells by inducing oxidative stress-mediated autophagy and JAK2/STAT3-AIF axis.

The Multifaceted Functions of Autophagy in Breast Cancer Development and Treatment

Macroautophagy (herein referred to as autophagy) is a complex catabolic process characterized by the formation of double-membrane vesicles called autophagosomes. During this process, autophagosomes engulf and deliver their intracellular content to lysosomes, where they are degraded by hydrolytic enzymes. Thereby, autophagy provides energy and building blocks to maintain cellular homeostasis and represents a dynamic recycling mechanism. Importantly, the clearance of damaged organelles and aggregated molecules by autophagy in normal cells contributes to cancer prevention. Therefore, the dysfunction of autophagy has a major impact on the cell fate and can contribute to tumorigenesis. Breast cancer is the most common cancer in women and has the highest mortality rate among all cancers in women worldwide. Breast cancer patients often have a good short-term prognosis, but long-term survivors often experience aggressive recurrence. This phenomenon might be explained by the high heterogeneity of breast cancer tumors rendering mammary tumors difficult to target. This review focuses on the mechanisms of autophagy during breast carcinogenesis and sheds light on the role of autophagy in the traits of aggressive breast cancer cells such as migration, invasion, and therapeutic resistance.

IFN-λ Modulates the Migratory Capacity of Canine Mammary Tumor Cells via Regulation of the Expression of Matrix Metalloproteinases and Their Inhibitors

Interactions between neoplastic and immune cells taking place in tumors drive cancer regulatory mechanisms both in humans and animals. IFN-λ, a potent antiviral factor, is also secreted in the tumor; however, its role in tumor development is still unclear. In our study, we investigate the influence of IFN-λ on the canine mammary tumor (CMT) cell survival and their metastatic potential in vitro. First, we examined, by Western blot, the expression of the IFN-λ receptor complex in three CMT cell lines (P114, CMT-U27 and CMT-U309). We showed that only two cell lines (P114 and CMT-U27) express both (IL-28RA and IL-10Rb) receptor subunits and respond to IFN-λ treatment by STAT phosphorylation and the expression of interferon-stimulated genes. Using MTT, crystal violet and annexin-V assays, we showed a minimal role of IFN-λ in CMT viability. However, IFN-λ administration had a contradictory effect on cell migration in the scratch test, namely, it increased P114 and decreased CMT-U27 motility. Moreover, we demonstrated that this process is related to the expression of extracellular matrix metalloproteinases and their inhibitors; furthermore, it is independent of Akt and ERK signaling pathways. To conclude, we showed that IFN-λ activity is reliant on the expression of two receptor subunits and tumor type, but further investigations are needed.

Autophagy and senescence: Insights from normal and cancer stem cells

Autophagy is a fundamental cellular process, which allows cells to adapt to metabolic stress through the degradation and recycling of intracellular components to generate macromolecular precursors and produce energy. Autophagy is also critical in maintaining cellular/tissue homeostasis, as well preserving immunity and preventing human disease. Deregulation of autophagic processes is associated with cancer, neurodegeneration, muscle and heart disease, infectious diseases and aging. Research on a variety of stem cell types establish that autophagy plays critical roles in normal and cancer stem cell quiescence, activation, differentiation, and self-renewal. Considering its critical function in regulating the metabolic state of stem cells, autophagy plays a dual role in the regulation of normal and cancer stem cell senescence, and cellular responses to various therapeutic strategies. The relationships between autophagy, senescence, dormancy and apoptosis frequently focus on responses to various forms of stress. These are interrelated processes that profoundly affect normal and abnormal human physiology that require further elucidation in cancer stem cells. This review provides a current perspective on autophagy and senescence in both normal and cancer stem cells.

Two Faces of Autophagy in the Struggle against Cancer

Autophagy can play a double role in cancerogenesis: it can either inhibit further development of the disease or protect cells, causing stimulation of tumour growth. This phenomenon is called "autophagy paradox", and is characterised by the features that the autophagy process provides the necessary substrates for biosynthesis to meet the cell's energy needs, and that the over-programmed activity of this process can lead to cell death through apoptosis. The fight against cancer is a difficult process due to high levels of resistance to chemotherapy and radiotherapy. More and more research is indicating that autophagy may play a very important role in the development of resistance by protecting cancer cells, which is why autophagy in cancer therapy can act as a "double-edged sword". This paper attempts to analyse the influence of autophagy and cancer stem cells on tumour development, and to compare new therapeutic strategies based on the modulation of these processes.

Autophagy Mediates Leptin-Induced Migration and ERK Activation in Breast Cancer Cells

Autophagy is an intracellular recycling process active in eukaryotic cells that involves the formation of an autophagosome which delivers cytoplasmic components to the lysosome for degradation. This process occurs at low rates under basal conditions, but it can be induced by diverse types of stress such as starvation, hypoxia, metabolic disorders or in response to hormones, including leptin. Leptin is considered a pro-tumorigenic protein whose circulating levels have been related to bad prognosis in obese breast cancer patients. It has been recently demonstrated that leptin can induce autophagy in cancer cell lines from different tissues, suggesting that autophagy could modulate the pro-tumorigenic effects associated with leptin. In this study, the role of autophagy in leptin-induced proliferation, migration, apoptosis and ERK phosphorylation in breast cancer cell lines was evaluated. Although leptin differentially induced autophagy in the breast cancer cell lines tested, autophagy inhibition reduced leptin-induced cell proliferation in MCF7 cells and decreased cell migration, ERK activation, and impaired morphological changes in both cell lines. Our data demonstrates an important role for basal autophagy or leptin-induced autophagy in leptin-induced migration and ERK phosphorylation in breast cancer cell lines, suggesting a potential use for the inhibition of autophagy in breast cancer associated with obesity.

Targeting ubiquitin conjugating enzyme UbcH5b by a triterpenoid PC3-15 from Schisandra plants sensitizes triple-negative breast cancer cells to lapatinib

Increasing evidence suggested that a number of ubiquitin enzymes, including ubiquitin-activating enzymes, ubiquitin-conjugating enzymes, E3 ubiquitin ligases and deubiquitination enzymes contribute to therapeutic resistance in triple-negative breast cancer (TNBC) cells. Inhibition of these enzymes with small molecule inhibitors may restore therapeutic sensitivity. Here, we demonstrated ubiquitin conjugating enzyme UbcH5b strongly supports HECTD3 auto-ubiquitination in vitro. Based on this, we developed a Fluorescence Resonance Energy Transfer (FRET) assay and identified three Schisandraceae triterpenoids, including PC3-15, to block HECTD3/UbcH5b auto-ubiquitination. Furthermore, we revealed that PC3-15 directly binds to UbcH5b and also inhibits UbcH5b-mediated p62 ubiquitination. We found that the UbcH5b-p62 axis confers TNBC cells resistance to lapatinib by promoting autophagy. Consistently, PC3-15 inhibits lapatinib-induced autophagy and increases lapatinib sensitivity in TNBC in vitro and in mouse xenografts. These findings suggest that the UbcH5b-p62 axis provides potential therapeutic targets and that Schisandraceae triterpenoids may be used for TNBC treatment in combination with lapatinib.

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.