Autophagy promotes the survival of dormant breast cancer cells and metastatic tumour recurrence

Autophagy in Tumor Immunity and Viral-Based Immunotherapeutic Approaches in Cancer

Autophagy is a fundamental catabolic process essential for the maintenance of cellular and tissue homeostasis, as well as directly contributing to the control of invading pathogens. Unsurprisingly, this process becomes critical in supporting cellular dysregulation that occurs in cancer, particularly the tumor microenvironments and their immune cell infiltration, ultimately playing a role in responses to cancer therapies. Therefore, understanding "cancer autophagy" could help turn this cellular waste-management service into a powerful ally for specific therapeutics. For instance, numerous regulatory mechanisms of the autophagic machinery can contribute to the anti-tumor properties of oncolytic viruses (OVs), which comprise a diverse class of replication-competent viruses with potential as cancer immunotherapeutics. In that context, autophagy can either: promote OV anti-tumor effects by enhancing infectivity and replication, mediating oncolysis, and inducing autophagic and immunogenic cell death; or reduce OV cytotoxicity by providing survival cues to tumor cells. These properties make the catabolic process of autophagy an attractive target for therapeutic combinations looking to enhance the efficacy of OVs. In this article, we review the complicated role of autophagy in cancer initiation and development, its effect on modulating OVs and immunity, and we discuss recent progress and opportunities/challenges in targeting autophagy to enhance oncolytic viral immunotherapy.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Hydroxychloroquine Induces Apoptosis in Cholangiocarcinoma via Reactive Oxygen Species Accumulation Induced by Autophagy Inhibition

Purpose: Despite considerable efforts to improve treatment modalities for cholangiocarcinoma, a common form of malignant tumor, its long-term survival rate remains poor. Hydroxychloroquine (HCQ) is a 4-aminoquinoline derivative antimalarial drug that has antimalarial and autophagy inhibition effects and exhibits comprehensive therapeutic effects on various cancers. In this study, we aimed to explore the anticancer potential and the underlying molecular mechanism of HCQ in cholangiocarcinoma treatment in vitro and in vivo. Methods: Autophagy-related genes (ARGs) were obtained from the Human Autophagy Database and Molecular Signatures Database, and the expression profiles of ARGs were downloaded from the database of The Cancer Genome Atlas. Different expression gene sets were performed using R software. The Gene Ontology and KEGG enrichment analyses were performed to reveal significantly enriched signaling pathways and to identify differentially expressed genes in cholangiocarcinoma tissues. HuCCT-1 and CCLP-1 cells were exposed to different concentrations of HCQ. Cell proliferation was detected by Cell Counting Kit-8 (CCK-8), colony formation, and 5-ethynyl-2'-deoxyuridine (EdU) assays. Cell apoptosis and cycle arrest were detected by the Live/Dead cell assay and flow cytometry (FCM). The inhibition of autophagy was observed using fluorescence microscopy. The reactive oxygen species levels were assessed by fluorescence microscopy and flow cytometry. The protein levels were determined by western blot. A cholangiocarcinoma cell line xenograft model was used to evaluate the antitumor activity of HCQ in vivo. Results: Compared with normal tissues, there were 141 ARGs with an aberrant expression in cholangiocarcinoma tissues which were mainly enriched in autophagy-related processes. Inhibition of autophagy by HCQ effectively suppressed cholangiocarcinoma in vitro and in vivo. HCQ inhibited cell proliferation and induced apoptosis and cycle arrest in vitro by increasing ROS accumulation, which was involved in autophagy inhibition. The ROS scavenger reduced l-glutathione distinctly weakened HCQ-induced cell apoptosis and viability inhibition in cholangiocarcinoma cells. In addition, HCQ inhibited growth of cholangiocarcinoma cell line xenograft tumors. Conclusion: HCQ could inhibit cell proliferation and induce apoptosis in cholangiocarcinoma by triggering ROS accumulation via autophagy inhibition, which makes HCQ a potential antitumor drug candidate for cholangiocarcinoma treatment.

HER2 Signaling and Breast Cancer Stem Cells: The Bridge behind HER2-Positive Breast Cancer Aggressiveness and Therapy Refractoriness

Simple Summary

Breast cancer (BC) is not a single disease, but a group of different tumors, and altered HER2 expression defines a particularly aggressive subtype. Although HER2 pharmacological inhibition has dramatically improved the prognosis of HER2-positive BC patients, there is still an urgent need for improved knowledge of HER2 biology and mechanisms underlying HER2-driven aggressiveness and drug susceptibility. Emerging data suggest that the clinical efficacy of molecularly targeted therapies is related to their ability to target breast cancer stem cells (BCSCs), a population that is not only self-sustaining and able to differentiate into distinct lineages, but also contributes to tumor growth, aggressiveness, metastasis and treatment resistance. The aim of this review is to provide an overview of how the full-length HER2 receptor, the d16HER2 splice variant and the truncated p95HER2 variants are involved in the regulation and maintenance of BCSCs.

Abstract

HER2 overexpression/amplification occurs in 15–20% of breast cancers (BCs) and identifies a highly aggressive BC subtype. Recent clinical progress has increased the cure rates of limited-stage HER2-positive BC and significantly prolonged overall survival in patients with advanced disease; however, drug resistance and tumor recurrence remain major concerns. Therefore, there is an urgent need to increase knowledge regarding HER2 biology and implement available treatments. Cancer stem cells (CSCs) represent a subset of malignant cells capable of unlimited self-renewal and differentiation and are mainly considered to contribute to tumor onset, aggressiveness, metastasis, and treatment resistance. Seminal studies have highlighted the key role of altered HER2 signaling in the maintenance/enrichment of breast CSCs (BCSCs) and elucidated its bidirectional communication with stemness-related pathways, such as the Notch and Wingless/β-catenin cascades. d16HER2, a splice variant of full-length HER2 mRNA, has been identified as one of the most oncogenic HER2 isoform significantly implicated in tumorigenesis, epithelial-mesenchymal transition (EMT)/stemness and the response to targeted therapy. In addition, expression of a heterogeneous collection of HER2 truncated carboxy-terminal fragments (CTFs), collectively known as p95HER2, identifies a peculiar subgroup of HER2-positive BC with poor prognosis, with the p95HER2 variants being able to regulate CSC features. This review provides a comprehensive overview of the current evidence regarding HER2-/d16HER2-/p95HER2-positive BCSCs in the context of the signaling pathways governing their properties and describes the future prospects for targeting these components to achieve long-lasting tumor control.

Hypoxia inducible factor signaling in breast tumors controls spontaneous tumor dissemination in a site-specific manner

Hypoxia is a common feature in tumors and induces signaling that promotes tumor cell survival, invasion, and metastasis, but the impact of hypoxia inducible factor (HIF) signaling in the primary tumor on dissemination to bone in particular remains unclear. To better understand the contributions of hypoxia inducible factor 1 alpha (HIF1α), HIF2α, and general HIF pathway activation in metastasis, we employ a PyMT-driven spontaneous murine mammary carcinoma model with mammary specific deletion of Hif1α, Hif2α, or von Hippel-Lindau factor (Vhl) using the Cre-lox system. Here we show that Hif1α or Hif2α deletion in the primary tumor decreases metastatic tumor burden in the bone marrow, while Vhl deletion increases bone tumor burden, as hypothesized. Unexpectedly, Hif1α deletion increases metastatic tumor burden in the lung, while deletion of Hif2α or Vhl does not affect pulmonary metastasis. Mice with Hif1α deleted tumors also exhibit reduced bone volume as measured by micro computed tomography, suggesting that disruption of the osteogenic niche may be involved in the preference for lung dissemination observed in this group. Thus, we reveal that HIF signaling in breast tumors controls tumor dissemination in a site-specific manner.

Targeting Reactive Oxygen Species Capacity of Tumor Cells with Repurposed Drug as an Anticancer Therapy

Accumulating evidence shows that elevated levels of reactive oxygen species (ROS) are associated with cancer initiation, growth, and response to therapies. As concentrations increase, ROS influence cancer development in a paradoxical way, either triggering tumorigenesis and supporting the proliferation of cancer cells at moderate levels of ROS or causing cancer cell death at high levels of ROS. Thus, ROS can be considered an attractive target for therapy of cancer and two apparently contradictory but virtually complementary therapeutic strategies for the regulation of ROS to treat cancer. Despite tremendous resources being invested in prevention and treatment for cancer, cancer remains a leading cause of human deaths and brings a heavy burden to humans worldwide. Chemotherapy remains the key treatment for cancer therapy, but it produces harmful side effects. Meanwhile, the process of de novo development of new anticancer drugs generally needs increasing cost, long development cycle, and high risk of failure. The use of ROS-based repurposed drugs may be one of the promising ways to overcome current cancer treatment challenges. In this review, we briefly introduce the source and regulation of ROS and then focus on the status of repurposed drugs based on ROS regulation for cancer therapy and propose the challenges and direction of ROS-mediated cancer treatment.

Expression of Autophagy and Mitophagy Markers in Breast Cancer Tissues

Mitochondria play important roles in regulating cell bioenergetics status and reactive oxygen species (ROS) generation. ROS-induced mitochondrial damage is among the main intracellular signal inducers of autophagy. Autophagy is a cellular catabolic process that regulates protein and organelle turnover, while a selective form of autophagy, mitophagy, specifically targets dysfunctional mitochondrial degradation. This study aims to measure the levels of autophagy, mitophagy, oxidative stress, and apoptosis in invasive breast carcinoma tissues using immunohistochemistry (IHC). Tissue microarrays of 76 patients with breast cancer were stained with six IHC markers (MnSOD, Beclin-1, LC3, BNIP3, Parkin, and cleaved caspase 3). The expression intensity was determined for each tumor tissue and the adjacent tumor-matched control tissues. Intermediate and strong staining scores of MnSOD, Beclin-1, LC-3, BNIP-3, and Parkin were significantly higher in tumor tissues compared to the adjacent matched control. The scoring intensity was further classified into tissues with negative staining and positive staining, which showed that positive scores of Beclin-1 and Parkin were significantly high in tumor tissues compared to other markers. Positive association was also noted between BNIP-3 and Beclin-1 as well as LC-3 and cleaved caspase-3 immunostaining. To our knowledge, this is one of the first studies that measure both mitophagy and autophagy in the same breast cancer tissues and the adjacent matched control. The findings from this study will be of great potential in identifying new cancer biomarkers and inspire significant interest in applying anti-autophagy therapies as a possible treatment for breast cancer.

Nanotechnology for Boosting Cancer Immunotherapy and Remodeling Tumor Microenvironment: The Horizons in Cancer Treatment

Immunotherapy that harnesses the human immune system to fight cancer has received widespread attention and become a mainstream strategy for cancer treatment. Cancer immunotherapy not only eliminates primary tumors but also treats metastasis and recurrence, representing a major advantage over traditional cancer treatments. Recently with the development of nanotechnology, there exists much work applying nanomaterials to cancer immunotherapy on the basis of their excellent physiochemical properties, such as efficient tissue-specific delivery function, huge specific surface area, and controllable surface chemistry. Consequently, nanotechnology holds significant potential in improving the efficacy of cancer immunotherapy. Nanotechnology-based immunotherapy mainly manifests its inhibitory effect on tumors via two different approaches: one is to produce an effective anti-tumor immune response during tumorigenesis, and the other is to enhance tumor immune defense ability by modulating the immune suppression mechanism in the tumor microenvironment. With the success of tumor immunotherapy, understanding the interaction between the immune system and smart nanomedicine has provided vigorous vitality for the development of cancer treatment. This review highlights the application, progress, and prospect of nanomedicine in the process of tumor immunoediting and also discusses several engineering methods to improve the efficiency of tumor treatment.

Impairment of Autophagic Flux Participates in the Antitumor Effects of TAT-Cx43266-283 in Glioblastoma Stem Cells

Simple Summary

Autophagy is a process in which the cell recycles components that are not needed at that moment and uses the resulting elements to satisfy more urgent needs. Depending on the specific context, this can be beneficial or detrimental for tumor development. We found that in glioblastoma, the most lethal brain tumor, autophagy is upregulated and contributes to glioblastoma stem cell survival under starvation. Importantly, the antitumor peptide TAT-Cx43_266-283 blocks autophagy flux, contributing to the death of glioblastoma stem cells. This peptide induces glioblastoma stem cell death in nutrient-deprived and complete environments, while the effect of other unsuccessful drugs for glioblastoma depends on nutrient context, supporting the potential of TAT-Cx43_266-283 as a treatment to improve the lives of glioblastoma patients.

Abstract

Autophagy is a physiological process by which various damaged or non-essential cytosolic components are recycled, contributing to cell survival under stress conditions. In cancer, autophagy can have antitumor or protumor effects depending on the developmental stage. Here, we use Western blotting, immunochemistry, and transmission electron microscopy to demonstrate that the antitumor peptide TAT-Cx43_266-283, a c-Src inhibitor, blocks autophagic flux in glioblastoma stem cells (GSCs) under basal and nutrient-deprived conditions. Upon nutrient deprivation, GSCs acquired a dormant-like phenotype that was disrupted by inhibition of autophagy with TAT-Cx43_266-283 or chloroquine (a classic autophagy inhibitor), leading to GSC death. Remarkably, dasatinib, a clinically available c-Src inhibitor, could not replicate TAT-Cx43_266-283 effect on dormant GSCs, revealing for the first time the possible involvement of pathways other than c-Src in TAT-Cx43_266-283 effect. TAT-Cx43_266-283 exerts an antitumor effect both in nutrient-complete and nutrient-deprived environments, which constitutes an advantage over chloroquine and dasatinib, whose effects depend on nutrient environment. Finally, our analysis of the levels of autophagy-related proteins in healthy and glioma donors suggests that autophagy is upregulated in glioblastoma, further supporting the interest in inhibiting this process in the most aggressive brain tumor and the potential use of TAT-Cx43_266-283 as a therapy for this type of cancer.

A multifunctional nanodiamond-based nanoplatform for the enhanced mild-temperature photothermal/chemo combination therapy of triple negative breast cancer via an autophagy regulation strategy

Owing to its aggressive biological behavior, the lack of specific targets, and the strong therapeutic resistance of triple negative breast cancer (TNBC), current therapeutic strategies are still limited. The combination of multiple treatments has been confirmed as a promising strategy for TNBC therapy. However, the efficacy of combination therapy can be restricted due to increasing therapeutic resistance to various treatments. Herein, we constructed a nanodiamond (ND)-based nanoplatform for augmented mild-temperature photothermal/chemo combination therapy against TNBC, weakening the therapeutic resistance via autophagy inhibition enabled by the NDs. A layer-by-layer self-assembly approach was utilized to construct the ND-based nanoplatform. First, the NDs were modified with protamine sulphate (PS). Meanwhile, the photosensitizer indocyanine green (ICG) and the HSP70 small molecule inhibitor apoptozole (APZ) could be synchronously incorporated to form positively charged PS@ND (ICG + APZ). Then negatively charged hyaluronic acid (HA) was assembled onto the outer face of PS@ND (ICG + APZ) to form the NPIAs. Finally, the positively charged small molecule anti-cancer drug doxorubicin (DOX) could be adsorbed onto the surface of the NPIAs through electrostatic interactions (NPIADs). The resulting NPIADs could be triggered by NIR laser irradiation to exhibit enhanced mild-temperature photothermal therapy (PTT) effects via suppressing the expression of HSP70, and PTT combined with chemotherapy could further enhance the anti-tumor efficacy. Subsequently, the sensitivity of MDA-MB-231 cells could be significantly improved through the weakening of the thermal/drug resistance via autophagy inhibition, leading to augmented combination therapy that is efficient both in vitro and in vivo. Furthermore, the NPIADs could be used as a theranostic nanoplatform for fluorescence (FL) and photoacoustic (PA) imaging. Taken together, this study demonstrated a multifunctional ND-based nanoplatform for FL/PA imaging-guided augmented mild-temperature photothermal/chemo combination therapy via an autophagy regulation strategy against TNBC.

Autophagy Regulates Stress Responses, Metabolism, and Anticancer Immunity

Autophagy is a catabolic intracellular nutrient-scavenging pathway triggered by nutrient deprivation and stress that captures and degrades intracellular proteins and organelles in lysosomes. The breakdown products are then recycled into metabolic pathways to sustain survival. Organelle turnover by autophagy contributes to quality control and suppresses inflammation. Autophagy is upregulated in many cancers and supports their growth, survival, and malignancy in a tumor cell-autonomous fashion. Host autophagy also promotes tumor growth by maintaining a supply of essential nutrients and suppressing innate and adaptive antitumor immune responses. Autophagy is also upregulated in response to cancer therapy and confers treatment resistance. Thus, autophagy is a cancer vulnerability and its inhibition is under investigation as a novel therapeutic approach.

FBXL16 modulates the proliferation and autophagy in breast cancer cells via activating SRC-3-AKT signaling pathway

Breast cancer (BC) is the major reason of cancer deaths in females. However, the underlying mechanism remains to be elucidated. F-box and leucine-rich repeat protein 16 (FBXL16) is known to be an important protein in regulating cancer growth. Nonetheless, little is known about FBXL16 in BC. Herein, FBXL16 protein expression was found to be elevated in the tumor tissues of BC patients and BC cell lines (MDA-MB-231, MCF-7, MDA-MB-361, and T47D). FBXL16 silencing inhibited cell growth and increased cell apoptosis as well as cell autophagy in MDA-MB-231 and MCF-7 cells, indicating that FBXL16 could aggravate malignant behaviors in BC. Moreover, FBXL16 deficiency was demonstrated to reduce the level of steroid receptor coactivator 3 (SRC-3) in MDA-MB-231 and MCF-7 cells. FBXL16 silencing also suppressed the level of p-AKT and p-mTOR. Whereas SCR-3 overexpression reversed FBXL16 knockdown-mediated p-AKT and p-mTOR reduction. Rescue assays uncovered that SRC-3 overexpression offset FBXL16 silencing-mediated decrease in cell proliferation and increase in cell apoptosis and autography in MDA-MB-231 and MCF-7 cells. In conclusion, our study found that FBXL16 modulates cell proliferation and autophagy in BC cells via activating the SRC-3-AKT signaling pathway, which shed a light on potential novel biomarkers for the treatment of BC.

Cisplatin-induced hydroxyl radicals mediate pro-survival autophagy in human lung cancer H460 cells

Background

Accumulated evidence demonstrates cisplatin, a recommended chemotherapy, modulating pro-survival autophagic response that contributes to treatment failure in lung cancer patients. However, distinct mechanisms involved in cisplatin-induced autophagy in human lung cancer cells are still unclear.

Results

Herein, role of autophagy in cisplatin resistance was indicated by a decreased cell viability and increased apoptosis in lung cancer H460 cells pre-incubated with wortmannin, an autophagy inhibitor, prior to treatment with 50 µM cisplatin for 24 h. The elevated level of hydroxyl radicals detected via flow-cytometry corresponded to autophagic response, as evidenced by the formation of autophagosomes and autolysosomes in cisplatin-treated cells. Interestingly, apoptosis resistance, autophagosome formation, and the alteration of the autophagic markers, LC3-II/LC3-I and p62, as well as autophagy-regulating proteins Atg7 and Atg3, induced by cisplatin was abrogated by pretreatment of H460 cells with deferoxamine, a specific hydroxyl radical scavenger. The modulations in autophagic response were also indicated in the cells treated with hydroxyl radicals generated via Fenton reaction, and likewise inhibited by pretreatment with deferoxamine.

Conclusions

In summary, the possible role of hydroxyl radicals as a key mediator in the autophagic response to cisplatin treatment, which was firstly revealed in this study would benefit for the further development of novel therapies for lung cancer.

Autophagy inhibition reinforces stemness together with exit from dormancy of polydisperse glioblastoma stem cells

Therapeutic resistance and infiltrative capacities justify the aggressiveness of glioblastoma. This is due to cellular heterogeneity, especially the presence of stemness-related cells, i.e. Cancer Stem Cells (CSC). Previous studies focused on autophagy and its role in CSCs maintenance; these studies gave conflicting results as they reported either sustaining or disruptive effects. In the present work, we silenced two autophagy related genes -either Beclin1 or ATG5- by shRNA and we explored the ensuing consequences on CSCs markers’ expression and functionalities. Our results showed that the down regulation of autophagy led to enhancement in expression of CSCs markers, while proliferation and clonogenicity were boosted. Temozolomide (TMZ) treatment failed to induce apoptotic death in shBeclin1-transfected cells, contrary to control. We optimized the cellular subset analysis with the use of Sedimentation Field Flow Fractionation, a biological event monitoring- and cell sorting-dedicated technique. Fractograms of both shBeclin1 and shATG5 cells exhibited a shift of elution peak as compared with control cells, showing cellular dispersion and intrinsic sub-fraction modifications. The classical stemness fraction (i.e. F3) highlighted data obtained with the overall cellular population, exhibiting enhancement of stemness markers and escape from dormancy. Our results contributed to illustrate CSCs polydispersity and to show how these cells develop capacity to bypass autophagy inhibition, thanks to their acute adaptability and plasticity.

Triple negative breast cancer and non-small cell lung cancer: Clinical challenges and nano-formulation approaches

Triple negative breast cancer (TNBC) and non-small cell lung cancer (NSCLC) are amongst the most aggressive forms of solid tumors. TNBC is highlighted by absence of genetic components of progesterone receptor, HER2/neu and estrogen receptor in breast cancer. NSCLC is characterized by integration of malignant carcinoma into respiratory system. Both cancers are associated with poor median and overall survival rates with low progression free survival with high incidences of relapse. These cancers are characterized by tumor heterogeneity, genetic mutations, generation of cancer-stem cells, immune-resistance and chemoresistance. Further, these neoplasms have been reported for tumor cross-talk into second primary cancers for each other. Current chemotherapeutic regimens include usage of multiple agents in tandem to affect tumor cells through multiple mechanisms with various such combinations being clinically tested. However, lack of controlled delivery and effective temporospatial presence of chemotherapeutics has resulted in suboptimal therapeutic response. Consequently, passive targeted albumin bound paclitaxel and PEGylated liposomal doxorubicin have been clinically used and tested with newer drugs for improved therapeutic efficacy in these cancers. Active targeting of nanocarriers against surface overexpressed proteins in both neoplasms have been explored. However, use of single agent nanoparticulate formulations against both cancers have failed to elicit desired outcomes. This review aims to identify clinical unmet need in these cancers while establishing a correlation with tested nano-formulation approaches and issues with preclinical to clinical translation. Lipid and polymer-based drug-drug and drug-gene combinatorial nanocarriers delivering multiple chemotherapeutics simultaneously to desired site of action have been detailed. Finally, emerging opportunities such as pharmacological targets (immune check point and epigentic modulators) as well as gene-based modulation (siRNA/CRISPR/Cas9) and the nano-formulation challenges for effective treatment of both cancers have been explored.

Protein Aggregation Patterns Inform about Breast Cancer Response to Antiestrogens and Reveal the RNA Ligase RTCB as Mediator of Acquired Tamoxifen Resistance

Simple Summary

Acquired resistance to antiestrogenic therapy remains the major obstacle to curing luminal subtype breast cancer. While current treatment in acquired endocrine-resistant settings includes combined therapy with receptor tyrosine kinase or cyclin-dependent kinase inhibitors, progression to incurable disease remains possible. In recent years, the antioxidant system and the protein quality control network have been associated with the enhanced resistance of breast cancer cells to hormonal therapy. In this work, we raise the hypothesis that antiestrogen treatment induces the accumulation of protein aggregates in sensitive cells, which in turn could hinder the activation of survival pathways. We present evidence concerning a novel way to identify antiestrogen response and disclose a novel protein, RTBC, that controls acquired antiestrogen resistance. This work opens a new avenue for research towards finding breast cancer prognostic markers and therapeutic targets, where the identification of proteins prone to aggregate could help to identify antiestrogen response and understand mechanisms of disease.

Abstract

The protein quality control network, including autophagy, the proteasome and the unfolded protein response (UPR), is triggered by stress and is overactive in acquired antiestrogen therapy resistance. We show for the first time that the aggresome load correlates with apoptosis and is increased in antiestrogen-sensitive cells compared to endocrine-resistant variants. LC-MS/MS analysis of the aggregated proteins obtained after 4OH-tamoxifen and Fulvestrant treatment identified proteins with essential function in protein quality control in antiestrogen-sensitive cells, but not in resistant variants. These include the UPR modulators RTCB and PDIA6, as well as many proteasome proteins such as PSMC2 and PSMD11. RTCB is a tRNA and XBP1 ligase and its aggregation induced by antiestrogens correlated with impaired XBP1s expression in sensitive cells. Knock down of RTCB was sufficient to restore sensitivity to tamoxifen in endocrine-resistant cells and increased the formation of aggresomes, leading to apoptotic cell death. Analysis of primary human breast cancer samples and their metastases appearing after endocrine treatment showed that RTCB is only localized to aggresomes in the primary tumors, while total aggresomes, including aggregated RTCB, were significantly reduced in the metastases. Therefore, different protein aggregation patterns may indicate loss of function of essential proteins resulting in enhanced protein aggregation that can be used to identify antiestrogen-resistant breast cancer cells and improve the response to antiestrogenic therapy.

Apelin/APJ signaling activates autophagy to promote human lung adenocarcinoma cell migration

AIMS

Beclin1(BECN1) is known as an autophagy-related protein and the expression is promoted by apelin in lung adenocarcinoma cells, suggesting that apelin activates autophagy in lung adenocarcinoma. However, the functions of apelin-induced autophagy in lung adenocarcinoma tumorigenesis and deterioration are still unknown. Thus, this study aims to investigate the effects of apelin-induced autophagy on lung adenocarcinoma tumorigenesis and deterioration.

MAIN METHODS

Protein expression of exogenous genes were detected by Western blotting analysis. Lung adenocarcinoma cell migration was assessed with cell migration assays. Autophagy was measured with quantification of GFP-LC3 or RFP-GFP-LC3 puncta using fluorescence microscopy in cells by an observed blinded to experimental condition and by western blot analysis of LC3 and p62 in cell lysates as well as autophagy flux. Immunofluorescence staining was performed in human lung adenocarcinoma A549 cells with p-cofilin antibody. The proteins expression in cancer specimens were examined with immunohistochemistry.

KEY FINDINGS

Here, we reveal that apelin induces autophagy activation in lung adenocarcinoma. Apelin/APJ regulates BECN1 transcription via HIF1A. Apelin/APJ-activated autophagy promotes lung adenocarcinoma cell migration. Moreover, treatment with autophagy inhibitors significantly decreases apelin/APJ-induced lung adenocarcinoma cell migration. Evaluation of patient samples of lung adenocarcinoma reveals an association between APJ with BECN1 expression and a poor prognosis.

SIGNIFICANCE

Our studies demonstrate that apelin-induced autophagy promotes lung adenocarcinoma cell migration which suggests a potential therapeutic target for lung adenocarcinoma.

Azithromycin enhances the cytotoxicity of DNA-damaging drugs via lysosomal membrane permeabilization in lung cancer cells

Cancer cells use autophagy for growth, survival, and cytoprotection from chemotherapy. Therefore, autophagy inhibitors appear to be good candidates for cancer treatment. Our group previously reported that macrolide antibiotics, especially azithromycin (AZM), have potent autophagy inhibitory effects, and combination treatment with tyrosine kinase inhibitors or proteasome inhibitors enhances their anti-cancer activity. In this study, we evaluated the effect of combination therapy with DNA-damaging drugs and AZM in non-small-cell lung cancer (NSCLC) cells. We found that the cytotoxic activities of DNA-damaging drugs, such as doxorubicin (DOX), etoposide, and carboplatin, were enhanced in the presence of AZM in NSCLC cell lines, whereas AZM alone exhibited almost no cytotoxicity. This enhanced cell death was dependent on wild-type-p53 status and autophagosome-forming ability because TP53 knockout (KO) and ATG5-KO cells attenuated AZM-enhanced cytotoxicity. DOX treatment upregulated lysosomal biogenesis by activating TFEB and led to lysosomal membrane damage as assessed by galectin 3 puncta assay and cytoplasmic leakage of lysosomal enzymes. In contrast, AZM treatment blocked autophagy, which resulted in the accumulation of lysosomes/autolysosomes. Thus, the effects of DOX and AZM were integrated into the marked increase in damaged lysosomes/autolysosomes, leading to prominent lysosomal membrane permeabilization (LMP) for apoptosis induction. Our data suggest that concomitant treatment with DNA-damaging drugs and AZM is a promising strategy for NSCLC treatment via pronounced LMP induction.

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.

Patient-derived scaffolds influence secretion profiles in cancer cells mirroring clinical features and breast cancer subtypes

BACKGROUND

Breast cancer is a common malignancy with varying clinical behaviors and for the more aggressive subtypes, novel and more efficient therapeutic approaches are needed. Qualities of the tumor microenvironment as well as cancer cell secretion have independently been associated with malignant clinical behaviors and a better understanding of the interplay between these two features could potentially reveal novel targetable key events linked to cancer progression.

METHODS

A newly developed human derived in vivo-like growth system, consisting of decellularized patient-derived scaffolds (PDSs) recellularized with standardized breast cancer cell lines (MCF7 and MDA-MB-231), were used to analyze how 63 individual patient specific microenvironments influenced secretion determined by proximity extension assays including 184 proteins and how these relate to clinical outcome.

RESULTS

The secretome from cancer cells in PDS cultures varied distinctly from cells grown as standard monolayers and besides a general increase in secretion from PDS cultures, several secreted proteins were only detectable in PDSs. Monolayer cells treated with conditioned media from PDS cultures, further showed increased mammosphere formation demonstrating a cancer stem cell activating function of the PDS culture induced secretion. The detailed secretomic profiles from MCF7s growing on 57 individual PDSs differed markedly but unsupervised clustering generated three separate groups having similar secretion profiles that significantly correlated to different clinical behaviors. The secretomic profile that associated with cancer relapse and high grade breast cancer showed induced secretion of the proteins IL-6, CCL2 and PAI-1, all linked to cancer stem cell activation, metastasis and priming of the pre-metastatic niche. Cancer promoting pathways such as "Suppress tumor immunity" and "Vascular and tissue remodeling" was also linked to this more malignant secretion cluster.

CONCLUSION

PDSs repopulated with cancer cells can be used to assess how cancer secretion is effected by specific and varying microenvironments. More malignant secretion patterns induced by specific patient based cancer microenvironments could further be identified pinpointing novel therapeutic opportunities targeting micro environmentally induced cancer progression via secretion of potent cytokines. Video abstract.

The P2X7 Receptor in the Maintenance of Cancer Stem Cells, Chemoresistance and Metastasis

Metastasis is the worst prognosis predictor in the clinical course of cancer development. Features of metastatic cancer cells include migratory ability, low degree of differentiation, self-renewal and proliferation potentials, as well as resistance to therapies. Metastatic cells do not present all of the necessary characteristics at once. Indeed, they have a unique phenotypic plasticity, allowing the acquisition of features that make them successful in all steps of metastasis. Cancer stem cells (CSC), the most undifferentiated cells in the tumor mass, display highest metastatic potential and resistance to radio- and chemotherapy. Growing tumors exhibit marked upregulation of P2X7 receptor expression and secrete ATP. Since the P2X7 receptor plays an important role in the maintenance of undifferentiated state of pluripotent cells, its importance on cell fate regulation in the tumor mass is suggested. Considering the extensive crosstalk between CSCs, epithelial-mesenchymal transition, drug resistance and metastasis, current knowledge implicating P2X7 receptor function in these phenomena and new avenues for therapeutic strategies to control metastasis are reviewed.

Autophagy suppresses the formation of hepatocyte-derived cancer-initiating ductular progenitor cells in the liver

Hepatocellular carcinoma (HCC) is driven by repeated rounds of inflammation, leading to fibrosis, cirrhosis, and, ultimately, cancer. A critical step in HCC formation is the transition from fibrosis to cirrhosis, which is associated with a change in the liver parenchyma called ductular reaction. Here, we report a genetically engineered mouse model of HCC driven by loss of macroautophagy and hemizygosity of phosphatase and tensin homolog, which develops HCC involving ductular reaction. We show through lineage tracing that, following loss of autophagy, mature hepatocytes dedifferentiate into biliary-like liver progenitor cells (ductular reaction), giving rise to HCC. Furthermore, this change is associated with deregulation of yes-associated protein and transcriptional coactivator with PDZ-binding motif transcription factors, and the combined, but not individual, deletion of these factors completely reverses the dedifferentiation capacity and tumorigenesis. These findings therefore increase our understanding of the cell of origin of HCC development and highlight new potential points for therapeutic intervention.

A novel autophagy-related genes prognostic risk model and validation of autophagy-related oncogene VPS35 in breast cancer

BACKGROUND

Accumulating evidence implies that autophagy plays a critical role in breast cancer development and progression. It is crucial to screen out autophagy-related encoding genes (ARGs) with prognostic value in breast cancer and reveal their biological properties in the aggressiveness of breast cancer.

METHODS

Univariate and multivariate Cox proportional hazards analyses were used to identify a prognostic risk model of ARGs from The Cancer Genome Atlas (TCGA). Kaplan-Meier analysis, univariate and multivariate Cox regression analyses and receiver operating characteristic (ROC) curve analysis were performed to validate the risk model. Western blot and immunohistochemistry (IHC) were conducted to assess the expression of VPS35 (one of ARGs in risk model). CCK8, Colony formation assay, Transwell migration/invasion assays and autophagy flux assay were used to confirm biological function of VPS35 in breast cancer.

RESULTS

In this study, the prognostic risk model consisting of six ARGs (VPS35, TRIM21, PRKAB2, RUFY4, MAP1LC3A and LARP1) in breast cancer were identified. The risk model was further verified as a novel independent prognostic factor for breast cancer patients. We also clarified that vacuolar protein sorting-associated protein 35 (VPS35), one of ARGs in the risk model, was upregulated in breast cancer samples and cell lines. VPS35 overexpression was correlated with more aggressive phenotype of breast cancer and indicated worse prognosis in both progression-free survival and overall survival analyses. Meanwhile, VPS35 knockdown inhibited breast cancer cell proliferation, migration and invasion, suggesting that VPS35 promoted the progression of breast cancer. VPS35 silence also influenced autophagy process, indicating that VPS35 was essential for autophagy completion.

CONCLUSION

Taken together, the six ARGs risk model has a remarkably prognostic value for breast cancer. Among them, VPS35 might exert as a significant oncogenic and prognostic factor for breast cancer and could be a promising autophagy-related therapeutic target in clinical practice.

An Updated Review on Implications of Autophagy and Apoptosis in Tumorigenesis: Possible Alterations in Autophagy through Engineered Nanomaterials and Their Importance in Cancer Therapy

Most commonly recognized as a catabolic pathway, autophagy is a perplexing mechanism through which a living cell can free itself of excess cytoplasmic components, i.e., organelles, by means of certain membranous vesicles or lysosomes filled with degrading enzymes. Upon exposure to external insult or internal stimuli, the cell might opt to activate such a pathway, through which it can gain control over the maintenance of intracellular components and thus sustain homeostasis by intercepting the formation of unnecessary structures or eliminating the already present dysfunctional or inutile organelles. Despite such appropriateness, autophagy might also be considered a frailty for the cell, as it has been said to have a rather complicated role in tumorigenesis. A merit in the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. In fact, several investigations on tumorigenesis have reported diminished levels of autophagic activity in tumor cells, which might result in transition to malignancy. On the contrary, autophagy has been suggested to be a seemingly favorable mechanism to progressed malignancies, as it contributes to survival of such cells. Based on the recent literature, this mechanism might also be activated upon the entry of engineered nanomaterials inside a cell, supposedly protecting the host from foreign materials. Accordingly, there is a good chance that therapeutic interventions for modulating autophagy in malignant cells using nanoparticles may sensitize cancerous cells to certain treatment modalities, e.g., radiotherapy. In this review, we will discuss the signaling pathways involved in autophagy and the significance of the mechanism itself in apoptosis and tumorigenesis while shedding light on possible alterations in autophagy through engineered nanomaterials and their potential therapeutic applications in cancer. SIGNIFICANCE STATEMENT: Autophagy has been said to have a complicated role in tumorigenesis. In the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. On the contrary, autophagy has been suggested to be a favorable mechanism to progressed malignancies. This mechanism might be affected upon the entry of nanomaterials inside a cell. Accordingly, therapeutic interventions for modulating autophagy using nanoparticles may sensitize cancerous cells to certain therapies.

Tumor Dormancy: Implications for Invasion and Metastasis

Tumor dormancy refers to a critical stage of cancer development when tumor cells are present, but cancer does not progress. It includes both the concept of cellular dormancy, indicating the reversible switch of a cancer cell to a quiescent state, and that of tumor mass dormancy, indicating the presence of neoplastic masses that have reached cell population equilibrium via balanced growth/apoptosis rates. Tumor dormancy provides the conceptual framework, potentially explaining a major challenge in clinical oncology, tumor recurrence, which may occur years after cancer diagnosis. The mechanisms by which tumors are kept dormant, and what triggers their reawakening, are fundamental questions in cancer biology. It seems that a plethora of intracellular pathways and extracellular factors are involved in this process, rewiring the cells to plastically alter their metabolic and proliferative status. This phenomenon is highly dynamic in space and time. Mechanistic insights into both cellular and tumor dormancy have provided the rationale for targeting this otherwise stable period of cancer development, in order to prevent recurrence and maximize therapeutic benefit.

Innovative Approaches in the Battle Against Cancer Recurrence: Novel Strategies to Combat Dormant Disseminated Tumor Cells

Cancer recurrence remains a great fear for many cancer survivors following their initial, apparently successful, therapy. Despite significant improvement in the overall survival of many types of cancer, metastasis accounts for ~90% of all cancer mortality. There is a growing understanding that future therapeutic practices must accommodate this unmet medical need in preventing metastatic recurrence. Accumulating evidence supports dormant disseminated tumor cells (DTCs) as a source of cancer recurrence and recognizes the need for novel strategies to target these tumor cells. This review presents strategies to target dormant quiescent DTCs that reside at secondary sites. These strategies aim to prevent recurrence by maintaining dormant DTCs at bay, or eradicating them. Various approaches are presented, including: reinforcing the niche where dormant DTCs reside in order to keep dormant DTCs at bay; promoting cell intrinsic mechanisms to induce dormancy; preventing the engagement of dormant DTCs with their supportive niche in order to prevent their reactivation; targeting cell-intrinsic mechanisms mediating long-term survival of dormant DTCs; sensitizing dormant DTCs to chemotherapy treatments; and, inhibiting the immune evasion of dormant DTCs, leading to their demise. Various therapeutic approaches, some of which utilize drugs that are already approved, or have been tested in clinical trials and may be considered for repurposing, will be discussed. In addition, clinical evidence for the presence of dormant DTCs will be reviewed, along with potential prognostic biomarkers to enable the identification and stratification of patients who are at high risk of recurrence, and who could benefit from novel dormant DTCs targeting therapies. Finally, we will address the shortcomings of current trial designs for determining activity against dormant DTCs and provide novel approaches.

GRP94 promotes brain metastasis by engaging pro-survival autophagy

BACKGROUND

GRP94 is a glucose-regulated protein critical for survival in endoplasmic reticulum stress. Expression of GRP94 is associated with cellular transformation and increased tumorigenicity in breast cancer. Specifically, overexpression of GRP94 predicts brain metastasis (BM) in breast carcinoma patients with either triple negative or ErbB2 positive tumors. The aim of this study was to understand if microenvironmental regulation of GRP94 expression might be a hinge orchestrating BM progression.

METHODS

GRP94 ablation was performed in a BM model BR-eGFP-CMV/Luc-V5CA1 (BRV5CA1) of breast cancer. In vitro results were validated in a dataset of 29 metastases in diverse organs from human breast carcinomas and in BM tissue from tumors of different primary origin. BM patient-derived xenografts (PDXs) were used to test sensitivity to the therapeutic approach.

RESULTS

BMs that overexpress GRP94 as well as tumor necrosis factor receptor-associated factor 2 are more resistant to glucose deprivation by induction of anti-apoptotic proteins (B-cell lymphoma 2 and inhibitors of apoptosis proteins) and engagement of pro-survival autophagy. GRP94 ablation downregulated autophagy in tumor cells, resulting in increased BM survival in vivo. These results were validated in a metastasis dataset from human patients, suggesting that targeting autophagy might be strategic for BM prevention. Indeed, hydroxychloroquine treatment of preclinical models of BM from PDX exerts preventive inhibition of tumor growth (P < 0.001).

CONCLUSIONS

We show that GRP94 is directly implicated in BM establishment by activating pro-survival autophagy. Disruption of this compensatory fueling route might prevent metastatic growth.

The role of ATG-7 contributes to pulmonary hypertension by impacting vascular remodeling

AIM

Pulmonary hypertension (PH) is a pathophysiological syndrome with functional abnormalities of the pulmonary artery and heart, eventually becoming life threatening to the patients. Autophagy-related gene 7 (ATG)-7 is involved in many cardiovascular diseases, but little is known about the specific role of ATG-7 in the development of PH. We aimed to examine the expression of ATG-7 in PH patients and PH mice, specifically investigate pulmonary physiological responses in a mouse model with conditional deletion of ATG-7 in smooth muscle cells (SMCs) and further clarify the mechanism of PH caused by ATG-7 deficiency.

METHODS AND RESULTS

SMC-ATG-7^-/- mice underwent echocardiography and subsequent pulmonary arterial pressure (PAP) checks. The PAP was lower in wild-type (WT) mice (22.6 ± 2.0 mmHg) than knockout (KO) mice (34.0 ± 2.5 mmHg; p < 0.001). Pulmonary artery resistance was increased in KO (17.61 ± 2.03 mm²·s^-1) versus WT mice (8.91 ± 1.62 mm²·s^-1; p < 0.005). Combined with these statistics, SMC-ATG7^-/- mice were diagnosed with PH. The increase of ATG-7 expression in vessels from PH patients and PH mice were assessed and the effects of ATG-7 on vascular remodeling were investigated in SMCs using relevant methods. We also identified silencing ATG-7 in SMCs induced the increased level of Ca²⁺ and abnormal proliferation through PP2A/ 4EBP-1/ elf-4E pathway.

CONCLUSIONS

ATG-7 affects vascular remodeling and exerts a protective function during the pathogenesis of PH. Our study revealed a novel mechanism ATG-7 deficiency promotes cell proliferation via the interaction between PP2A, 4EBP-1 and elf-4E.

Metastasis-Initiating Cells and Ecosystems

Metastasis is initiated and sustained through therapy by cancer cells with stem-like and immune-evasive properties, termed metastasis-initiating cells (MIC). Recent progress suggests that MICs result from the adoption of a normal regenerative progenitor phenotype by malignant cells, a phenotype with intrinsic programs to survive the stresses of the metastatic process, undergo epithelial-mesenchymal transitions, enter slow-cycling states for dormancy, evade immune surveillance, establish supportive interactions with organ-specific niches, and co-opt systemic factors for growth and recurrence after therapy. Mechanistic understanding of the molecular mediators of MIC phenotypes and host tissue ecosystems could yield cancer therapeutics to improve patient outcomes. SIGNIFICANCE: Understanding the origins, traits, and vulnerabilities of progenitor cancer cells with the capacity to initiate metastasis in distant organs, and the host microenvironments that support the ability of these cells to evade immune surveillance and regenerate the tumor, is critical for developing strategies to improve the prevention and treatment of advanced cancer. Leveraging recent progress in our understanding of the metastatic process, here we review the nature of MICs and their ecosystems and offer a perspective on how this knowledge is informing innovative treatments of metastatic cancers.

Mitoflash generated at the Qo site of mitochondrial Complex III

The previous research has shown that mitochondrial flash (mitoflash) genesis are functionally and mechanistically integrated with mitochondrial electron transport chain (ETC) energy metabolism. However, the response of mitoflash to superoxide is not entirely consistent with the response of MitoSOX Red. The generation mechanism of mitoflash is still unclear. Here, we investigated mitoflash activities, using the different combinations of ETC substrates and inhibitors, in permeabilized cardiomyocytes or hearts. We found that blocking the complete electron flow, from Complex I to IV, with any one of ETC inhibitors including rotenone (Rot), antimycin A (AntA), myxothiazol (Myxo), stigmatellin, and sodium cyanide, will lead to the abolishment of mitoflashes triggered by substrates in adult permeabilized cardiomyocytes. However, Myxo boosted mitoflashes triggered by the reverse electron of N,N,N',N'-tetramethyl-p-phenylenediamine/ascorbate. Moreover, Rot and AntA furtherly enhanced mitoflash activity rather than depressed it, suggesting that mitoflashes generated at the Complex III Qo site. Meanwhile, the inhibition of Complex III protein expression resulted in the activity of Complex III decrease, which decreased mitoflash frequency. The function defect (no change of protein level) of the Qo site of Complex III in aging hearts augmented mitoflash generation confirmed the Qo site function was critical to mitoflash genesis. Thus, our results indicate that mitoflash detected by circularly permuted yellow fluorescent protein is generated at the Qo site of Complex III.

Autophagy and Cancer Dormancy

Metastasis and relapse account for the great majority of cancer-related deaths. Most metastatic lesions are micro metastases that have the capacity to remain in a non-dividing state called “dormancy” for months or even years. Commonly used anticancer drugs generally target actively dividing cancer cells. Therefore, cancer cells that remain in a dormant state evade conventional therapies and contribute to cancer recurrence. Cellular and molecular mechanisms of cancer dormancy are not fully understood. Recent studies indicate that a major cellular stress response mechanism, autophagy, plays an important role in the adaptation, survival and reactivation of dormant cells. In this review article, we will summarize accumulating knowledge about cellular and molecular mechanisms of cancer dormancy, and discuss the role and importance of autophagy in this context.

A Signature of Autophagy-Related Long Non-coding RNA to Predict the Prognosis of Breast Cancer

Background: A surge in newly diagnosed breast cancer has overwhelmed the public health system worldwide. Joint effort had beed made to discover the genetic mechanism of these disease globally. Accumulated research has revealed autophagy may act as a vital part in the pathogenesis of breast cancer.

Objective: Aim to construct a prognostic model based on autophagy-related lncRNAs and investigate their potential mechanisms in breast cancer.

Methods: The transcriptome data and clinical information of patients with breast cancer were obtained from The Cancer Genome Atlas (TCGA) database. Autophagy-related genes were obtained from the Human Autophagy Database (HADb). Long non-coding RNAs (lncRNAs) related to autophagy were acquired through the Pearson correlation analysis. Univariate Cox regression analysis as well as the least absolute shrinkage and selection operator (LASSO) regression analysis were used to identify autophagy-related lncRNAs with prognostic value. We constructed a risk scoring model to assess the prognostic significance of the autophagy-related lncRNAs signatures. The nomogram was then established based on the risk score and clinical indicators. Through the calibration curve, the concordance index (C-index) and receiver operating characteristic (ROC) curve analysis were evaluated to obtain the model's predictive performance. Subgroup analysis was performed to evaluate the differential ability of the model. Subsequently, gene set enrichment analysis was conducted to investigate the potential functions of these lncRNAs.

Results: We attained 1,164 breast cancer samples from the TCGA database and 231 autophagy-related genes from the HAD database. Through correlation analysis, 179 autophagy-related lncRNAs were finally identified. Univariate Cox regression analysis and LASSO regression analysis further screened 18 prognosis-associated lncRNAs. The risk scoring model was constructed to divide patients into high-risk and low-risk groups. It was found that the low-risk group had better overall survival (OS) than those of the high-risk group. Then, the nomogram model including age, tumor stage, TNM stage and risk score was established. The evaluation index (C-index: 0.78, 3-year OS AUC: 0.813 and 5-year OS AUC: 0.785) showed that the nomogram had excellent predictive power. Subgroup analysis showed there were difference in OS between high-risk and low-risk patients in different subgroups (stage I-II, ER positive, Her-2 negative and non-TNBC subgroups; all P < 0.05). According to the results of gene set enrichment analysis, these lncRNAs were involved in the regulation of multicellular organismal macromolecule metabolic process in multicellular organisms, nucleotide excision repair, oxidative phosphorylation, and TGF-β signaling pathway.

Conclusions: We identified 18 autophagy-related lncRNAs with prognostic value in breast cancer, which may regulate tumor growth and progression in multiple ways.

Autophagy and senescence in cancer therapy

Tumor cells can undergo diverse responses to cancer therapy. While apoptosis represents the most desirable outcome, tumor cells can alternatively undergo autophagy and senescence. Both autophagy and senescence have the potential to make complex contributions to tumor cell survival via both cell autonomous and cell non-autonomous pathways. The induction of autophagy and senescence in tumor cells, preclinically and clinically, either individually or concomitantly, has generated interest in the utilization of autophagy modulating and senolytic therapies to target autophagy and senescence, respectively. This chapter summarizes the current evidence for the promotion of autophagy and senescence as fundamental responses to cancer therapy and discusses the complexity of their functional contributions to cell survival and disease outcomes. We also highlight current modalities designed to exploit autophagy and senescence in efforts to improve the efficacy of cancer therapy.

Towards a Framework for Better Understanding of Quiescent Cancer Cells

Quiescent cancer cells (QCCs) are cancer cells that are reversibly suspended in G₀ phase with the ability to re-enter the cell cycle and initiate tumor growth, and, ultimately, cancer recurrence and metastasis. QCCs are also therapeutically challenging due to their resistance to most conventional cancer treatments that selectively act on proliferating cells. Considering the significant impact of QCCs on cancer progression and treatment, better understanding of appropriate experimental models, and the evaluation of QCCs are key questions in the field that have direct influence on potential pharmacological interventions. Here, this review focuses on existing and emerging preclinical models and detection methods for QCCs and discusses their respective features and scope for application. By providing a framework for selecting appropriate experimental models and investigative methods, the identification of the key players that regulate the survival and activation of QCCs and the development of more effective QCC-targeting therapeutic agents may mitigate the consequences of QCCs.

Fighting Drug Resistance through the Targeting of Drug-Tolerant Persister Cells

Designing specific therapies for drug-resistant cancers is arguably the ultimate challenge in cancer therapy. While much emphasis has been put on the study of genetic alterations that give rise to drug resistance, much less is known about the non-genetic adaptation mechanisms that operate during the early stages of drug resistance development. Drug-tolerant persister cells have been suggested to be key players in this process. These cells are thought to have undergone non-genetic adaptations that enable survival in the presence of a drug, from which full-blown resistant cells may emerge. Such initial adaptations often involve engagement of stress response programs to maintain cancer cell viability. In this review, we discuss the nature of drug-tolerant cancer phenotypes, as well as the non-genetic adaptations involved. We also discuss how malignant cells employ homeostatic stress response pathways to mitigate the intrinsic costs of such adaptations. Lastly, we discuss which vulnerabilities are introduced by these adaptations and how these might be exploited therapeutically.

EphB6 Regulates TFEB-Lysosomal Pathway and Survival of Disseminated Indolent Breast Cancer Cells

Late relapse of disseminated cancer cells is a common feature of breast and prostate tumors. Several intrinsic and extrinsic factors have been shown to affect quiescence and reawakening of disseminated dormant cancer cells (DDCCs); however, the signals and processes sustaining the survival of DDCCs in a foreign environment are still poorly understood. We have recently shown that crosstalk with lung epithelial cells promotes survival of DDCCs of estrogen receptor-positive (ER+) breast tumors. By using a lung organotypic system and in vivo dissemination assays, here we show that the TFEB-lysosomal axis is activated in DDCCs and that it is modulated by the pro-survival ephrin receptor EphB6. TFEB lysosomal direct targets are enriched in DDCCs in vivo and correlate with relapse in ER+ breast cancer patients. Direct coculture of DDCCs with alveolar type I-like lung epithelial cells and dissemination in the lung drive lysosomal accumulation and EphB6 induction. EphB6 contributes to survival, TFEB transcriptional activity, and lysosome formation in DDCCs in vitro and in vivo. Furthermore, signaling from EphB6 promotes the proliferation of surrounding lung parenchymal cells in vivo. Our data provide evidence that EphB6 is a key factor in the crosstalk between disseminated dormant cancer cells and the lung parenchyma and that the TFEB-lysosomal pathway plays an important role in the persistence of DDCCs.

A Lung Organotypic Coculture Reveals a Role for TFEB-Lysosomal Axis in the Survival of Disseminated Dormant Cancer Cells

(1) Background: metastatic relapse following a prolonged period of disease-free survival is a common cause of mortality for many cancer patients. Disseminated dormant cancer cells (DDCCs) lie below the radar before waking up years, or even decades, after the removal of the primary tumor. This implies that they are able to survive in a latent state in a foreign environment for an extended period of time supported by intrinsic and extrinsic factors still to be elucidated. (2) Methods: we employed a coculture of DDCCs with lung epithelial cells together with RNA sequencing analysis to understand the overlap in gene transcription between in vivo and cocultured DDCCs. (3) Results: we found a significant overlap between the processes activated in DDCCs from lungs and in the coculture, as well as in alveolar type I cells in vivo and in coculture. We identified the transcription factor EB (TFEB)-lysosomal axis as a relevant process activated in DDCCs upon dissemination to the lung and confirmed the results in our lung coculture. Interestingly, breast cancer patients with a higher expression of TFEB targets show increased likelihood of developing relapses. (4) Conclusions: we propose that lysosomal accumulation following TFEB activation is an important feature of breast cancer DDCCs that might be exploited for future therapeutic interventions.

Mechanisms of Pharmaceutical Therapy and Drug Resistance in Esophageal Cancer

Pharmaceutical therapies are essential for esophageal cancer (EC). For the advanced EC, the neoadjuvant therapy regimen, including chemotherapy plus radiotherapy and/or immunotherapy, is effective to achieve clinical benefit, even pathological complete response. For the unresectable, recurrent, and metastatic EC, the pharmaceutical therapy is the limited effective regimen to alleviate the disease and prolong the progression-free survival and overall survival. In this review, we focus on the pharmaceutical applications in EC treatment including cytotoxic agents, molecular targeted antibodies, and immune checkpoint inhibitors (ICIs). The chemotherapy regimen is based on cytotoxic agents such as platinum-based complexes, fluorinated pyrimidines and taxenes. Although the cytotoxic agents have been developed in past decades, the standard chemotherapy regimen is still the cisplatin and 5-FU or paclitaxel because the derived drugs have no significant advantages of overcoming the shortcomings of side effects and drug resistance. The targeted molecular therapy is an essential supplement for chemotherapy; however, there are only a few targeted therapies available in clinical practice. Trastuzumab and ramucirumab are the only two molecular therapy drugs which are approved by the US Food and Drug Administration to treat advanced and/or metastatic EC. Although the targeted therapy usually achieves effective benefits in the early stage therapy of EC, the patients will always develop drug resistance during treatment. ICIs have had a significant impact on routine clinical practice in cancer treatment. The anti-programmed cell death-1 monoclonal antibodies pembrolizumab and nivolumab, as the ICIs, are recommended for advanced EC by several clinical trials. However, the significant issues of pharmaceutical treatment are still the dose-limiting side effects and primary or secondary drug resistance. These defects of pharmaceutical therapy restrain the clinical application and diminish the effectiveness of treatment.

Mitochondria autophagy: a potential target for cancer therapy

Mitophagy is a selective form of macroautophagy in which dysfunctional and damaged mitochondria can be efficiently degraded, removed and recycled through autophagy. Selective removal of damaged or fragmented mitochondria is critical to the functional integrity of the entire mitochondrial network and cells. In past decades, numerous studies have shown that mitophagy is involved in various diseases; however, since the dual role of mitophagy in tumour development, mitophagy role in tumour is controversial, and further elucidation is needed. That is, although mitophagy has been demonstrated to contribute to carcinogenesis, cell migration, ferroptosis inhibition, cancer stemness maintenance, tumour immune escape, drug resistance, etc. during cancer progression, many research also shows that to promote cancer cell death, mitophagy can be induced physiologically or pharmacologically to maintain normal cellular metabolism and prevent cell stress responses and genome damage by diminishing mitochondrial damage, thus suppressing tumour development accompanying these changes. Signalling pathway-specific molecular mechanisms are currently of great biological significance in the identification of potential therapeutic targets. Here, we review recent progress of molecular pathways mediating mitophagy including both canonical pathways (Parkin/PINK1- and FUNDC1-mediated mitophagy) and noncanonical pathways (FKBP8-, Nrf2-, and DRP1-mediated mitophagy); and the regulation of these pathways, and abovementioned pro-cancer and pro-death roles of mitophagy. Finally, we summarise the role of mitophagy in cancer therapy. Mitophagy can potentially be acted as the target for cancer therapy by promotion or inhibition.

TFEB Biology and Agonists at a Glance

Autophagy is a critical regulator of cellular survival, differentiation, development, and homeostasis, dysregulation of which is associated with diverse diseases including cancer and neurodegenerative diseases. Transcription factor EB (TFEB), a master transcriptional regulator of autophagy and lysosome, can enhance autophagic and lysosomal biogenesis and function. TFEB has attracted a lot of attention owing to its ability to induce the intracellular clearance of pathogenic factors in a variety of disease models, suggesting that novel therapeutic strategies could be based on the modulation of TFEB activity. Therefore, TFEB agonists are a promising strategy to ameliorate diseases implicated with autophagy dysfunction. Recently, several TFEB agonists have been identified and preclinical or clinical trials are applied. In this review, we present an overview of the latest research on TFEB biology and TFEB agonists.

The Breast Cancer Stem Cells Traits and Drug Resistance

Drug resistance is a major challenge in breast cancer (BC) treatment at present. Accumulating studies indicate that breast cancer stem cells (BCSCs) are responsible for the BC drugs resistance, causing relapse and metastasis in BC patients. Thus, BCSCs elimination could reverse drug resistance and improve drug efficacy to benefit BC patients. Consequently, mastering the knowledge on the proliferation, resistance mechanisms, and separation of BCSCs in BC therapy is extremely helpful for BCSCs-targeted therapeutic strategies. Herein, we summarize the principal BCSCs surface markers and signaling pathways, and list the BCSCs-related drug resistance mechanisms in chemotherapy (CT), endocrine therapy (ET), and targeted therapy (TT), and display therapeutic strategies for targeting BCSCs to reverse drug resistance in BC. Even more importantly, more attention should be paid to studies on BCSC-targeted strategies to overcome the drug resistant dilemma of clinical therapies in the future.

The pleiotropic functions of autophagy in metastasis

Autophagy is deregulated in many cancers and represents an attractive target for therapeutic intervention. However, the precise contributions of autophagy to metastatic progression, the principle cause of cancer-related mortality, is only now being uncovered. While autophagy promotes primary tumor growth, metabolic adaptation and resistance to therapy, recent studies have unexpectedly revealed that autophagy suppresses the proliferative outgrowth of disseminated tumor cells into overt and lethal macrometastases. These studies suggest autophagy plays unexpected and complex roles in the initiation and progression of metastases, which will undoubtedly impact therapeutic approaches for cancer treatment. Here, we discuss the intricacies of autophagy in metastatic progression, highlighting and integrating the pleiotropic roles of autophagy on diverse cell biological processes involved in metastasis.

Minimal Residual Disease, Metastasis and Immunity

Progression from localized to metastatic disease requires cancer cells spreading to distant organs through the bloodstream. Only a small proportion of these circulating tumor cells (CTCs) survives dissemination due to anoikis, shear forces and elimination by the immune system. However, all metastases originate from CTCs capable of surviving and extravasating into distant tissue to re-initiate a tumor. Metastasis initiation is not always immediate as disseminated tumor cells (DTCs) may enter a non-dividing state of cell dormancy. Cancer dormancy is a reversible condition that can be maintained for many years without being clinically detectable. Subsequently, late disease relapses are thought to be due to cancer cells ultimately escaping from dormant state. Cancer dormancy is usually associated with minimal residual disease (MRD), where DTCs persist after intended curative therapy. Thus, MRD is commonly regarded as an indicator of poor prognosis in all cancers. In this review, we examine the current understanding of MRD and immunity during cancer progression to metastasis and discuss clinical perspectives for oncology.

Cadmium promotes breast cancer cell proliferation, migration and invasion by inhibiting ACSS2/ATG5-mediated autophagy

Cadmium (Cd), which is considered a carcinogenic metal, promotes breast cancer (BC) progression, but the precise mechanism remains unclear. Herein, MCF-7 and T47-D cells were treated with 0.1, 1, and 10 μM cadmium chloride (CdCl2) for 24, 48 and 72 h. In our study, Cd exposure significantly accelerated the proliferation, migration and invasion of MCF-7 and T47-D cells. Notably, Cd inhibited autophagic flux by suppressing ATG5-dependent autophagosome formation but had no significant effect on autophagosome-lysosome fusion and lysosomal function. The genetic enhancement of autophagy through ATG5 overexpression suppressed the Cd-mediated increases in proliferation, migration and invasion, which indicated a carcinogenic role of autophagy impairment in Cd-exposed BC cells. GSEA and GeneMANIA were utilized to demonstrate that the Cd-induced decrease in ACSS2 expression mechanistically inhibited ATG5-dependent autophagy in BC cells. Importantly, ACSS2 overexpression increased the level of H3K27 acetylation in the promoter region of ATG5, and this result maintained autophagic flux and abolished the Cd-induced increases in proliferation, migration and invasion. We also verified that the expression of ACSS2 in BC tissues was low and positively related to ATG5 expression. These findings indicated that the promoting effect of Cd on BC cell proliferation, migration and invasion through the impairment of ACSS2/ATG5-dependent autophagic flux suggests a new mechanism for BC cell proliferation and metastasis stimulated by Cd.

Progression-Mediated Changes in Mitochondrial Morphology Promotes Adaptation to Hypoxic Peritoneal Conditions in Serous Ovarian Cancer

Ovarian cancer is the deadliest gynecological cancer in women, with a survival rate of less than 30% when the cancer has spread throughout the peritoneal cavity. Aggregation of cancer cells increases their viability and metastatic potential; however, there are limited studies that correlate these functional changes to specific phenotypic alterations. In this study, we investigated changes in mitochondrial morphology and dynamics during malignant transition using our MOSE cell model for progressive serous ovarian cancer. Mitochondrial morphology was changed with increasing malignancy from a filamentous network to single, enlarged organelles due to an imbalance of mitochondrial dynamic proteins (fusion: MFN1/OPA1, fission: DRP1/FIS1). These phenotypic alterations aided the adaptation to hypoxia through the promotion of autophagy and were accompanied by changes in the mitochondrial ultrastructure, mitochondrial membrane potential, and the regulation of reactive oxygen species (ROS) levels. The tumor-initiating cells increased mitochondrial fragmentation after aggregation and exposure to hypoxia that correlated well with our previously observed reduced growth and respiration in spheroids, suggesting that these alterations promote viability in non-permissive conditions. Our identification of such mitochondrial phenotypic changes in malignancy provides a model in which to identify targets for interventions aimed at suppressing metastases.

Colorectal Cancer Cells Enter a Diapause-like DTP State to Survive Chemotherapy

Cancer cells enter a reversible drug-tolerant persister (DTP) state to evade death from chemotherapy and targeted agents. It is increasingly appreciated that DTPs are important drivers of therapy failure and tumor relapse. We combined cellular barcoding and mathematical modeling in patient-derived colorectal cancer models to identify and characterize DTPs in response to chemotherapy. Barcode analysis revealed no loss of clonal complexity of tumors that entered the DTP state and recurred following treatment cessation. Our data fit a mathematical model where all cancer cells, and not a small subpopulation, possess an equipotent capacity to become DTPs. Mechanistically, we determined that DTPs display remarkable transcriptional and functional similarities to diapause, a reversible state of suspended embryonic development triggered by unfavorable environmental conditions. Our study provides insight into how cancer cells use a developmentally conserved mechanism to drive the DTP state, pointing to novel therapeutic opportunities to target DTPs.

Endolysosomal TRPMLs in Cancer

Lysosomes, the degradative endpoints and sophisticated cellular signaling hubs, are emerging as intracellular Ca²⁺ stores that govern multiple cellular processes. Dys-homeostasis of lysosomal Ca²⁺ is intimately associated with a variety of human diseases including cancer. Recent studies have suggested that the Ca²⁺-permeable channels Transient Receptor Potential (TRP) Mucolipins (TRPMLs, TRPML1-3) integrate multiple processes of cell growth, division and metabolism. Dysregulation of TRPMLs activity has been implicated in cancer development. In this review, we provide a summary of the latest development of TRPMLs in cancer. The expression of TRPMLs in cancer, TRPMLs in cancer cell nutrient sensing, TRPMLs-mediated lysosomal exocytosis in cancer development, TRPMLs in TFEB-mediated gene transcription of cancer cells, TRPMLs in bacteria-related cancer development and TRPMLs-regulated antitumor immunity are discussed. We hope to guide readers toward a more in-depth discussion of the importance of lysosomal TRPMLs in cancer progression and other human diseases.

Lysosomotropic agents including azithromycin, chloroquine and hydroxychloroquine activate the integrated stress response

The integrated stress response manifests with the phosphorylation of eukaryotic initiation factor 2α (eIF2α) on serine residue 51 and plays a major role in the adaptation of cells to endoplasmic reticulum stress in the initiation of autophagy and in the ignition of immune responses. Here, we report that lysosomotropic agents, including azithromycin, chloroquine, and hydroxychloroquine, can trigger eIF2α phosphorylation in vitro (in cultured human cells) and, as validated for hydroxychloroquine, in vivo (in mice). Cells bearing a non-phosphorylatable eIF2α mutant (S51A) failed to accumulate autophagic puncta in response to azithromycin, chloroquine, and hydroxychloroquine. Conversely, two inhibitors of eIF2α dephosphorylation, nelfinavir and salubrinal, enhanced the induction of such autophagic puncta. Altogether, these results point to the unexpected capacity of azithromycin, chloroquine, and hydroxychloroquine to elicit the integrated stress response.

Role of hydrogen sulfide donors in cancer development and progression

In recent years, a vast number of potential cancer therapeutic targets have emerged. However, developing efficient and effective drugs for the targets is of major concern. Hydrogen sulfide (H2S), one of the three known gasotransmitters, is involved in the regulation of various cellular activities such as autophagy, apoptosis, migration, and proliferation. Low production of H2S has been identified in numerous cancer types. Treating cancer cells with H2S donors is the common experimental technique used to improve H2S levels; however, the outcome depends on the concentration/dose, time, cell type, and sometimes the drug used. Both natural and synthesized donors are available for this purpose, although their effects vary independently ranging from strong cancer suppressors to promoters. Nonetheless, numerous signaling pathways have been reported to be altered following the treatments with H2S donors which suggest their potential in cancer treatment. This review will analyze the potential of H2S donors in cancer therapy by summarizing key cellular processes and mechanisms involved.