Macroautophagy is dispensable for growth of KRAS mutant tumors and chloroquine efficacy

Autophagy modulation attenuates sorafenib resistance in HCC induced in rats

Hepatocellular carcinoma (HCC) has risen as the villain of cancer-related death globally, with a usual cruel forecasting. Sorafenib was officially approved by the FDA as first-line treatment for advanced HCC. Despite the brilliant promise revealed in research, actual clinical results are limited due to the widespread appearance of drug resistance. The tumor microenvironment (TME) has been correlated to pharmacological resistance, implying that existing cellular level strategies may be insufficient to improve therapy success. The role of autophagy in cancer is a two-edged sword. On one hand, autophagy permits malignant cells to overcome stress, such as hypoxic TME and therapy-induced starvation. Autophagy, on the other hand, plays an important role in damage suppression, which can reduce carcinogenesis. As a result, controlling autophagy is certainly a viable technique in cancer therapy. The goal of this study was to investigate at the impact of autophagy manipulation with sorafenib therapy by analyzing autophagy induction and inhibition to sorafenib monotherapy in rats with HCC. Western blot, ELISA, immunohistochemistry, flow cytometry, and quantitative-PCR were used to investigate autophagy, apoptosis, and the cell cycle. Routine biochemical and pathological testing was performed. Ultracellular features and autophagic entities were observed using a transmission electron microscope (TEM). Both regimens demonstrated significant reductions in chemotherapeutic resistance and hepatoprotective effects. According to the findings, both autophagic inhibitors and inducers are attractive candidates for combating sorafenib-induced resistance in HCC.

Inhibition of autophagy as a novel treatment for neurofibromatosis type 1 tumors

Neurofibromatosis type 1 (NF1) is a genetic disorder caused by mutation of the NF1 gene that is associated with various symptoms, including the formation of benign tumors, called neurofibromas, within nerves. Drug treatments are currently limited. The mitogen-activated protein kinase kinase (MEK) inhibitor selumetinib is used for a subset of plexiform neurofibromas (PNs) but is not always effective and can cause side effects. Therefore, there is a clear need to discover new drugs to target NF1-deficient tumor cells. Using a Drosophila cell model of NF1, we performed synthetic lethal screens to identify novel drug targets. We identified 54 gene candidates, which were validated with variable dose analysis as a secondary screen. Pathways associated with five candidates could be targeted using existing drugs. Among these, chloroquine (CQ) and bafilomycin A1, known to target the autophagy pathway, showed the greatest potential for selectively killing NF1-deficient Drosophila cells. When further investigating autophagy-related genes, we found that 14 out of 30 genes tested had a synthetic lethal interaction with NF1. These 14 genes are involved in multiple aspects of the autophagy pathway and can be targeted with additional drugs that mediate the autophagy pathway, although CQ was the most effective. The lethal effect of autophagy inhibitors was conserved in a panel of human NF1-deficient Schwann cell lines, highlighting their translational potential. The effect of CQ was also conserved in a Drosophila NF1 in vivo model and in a xenografted NF1-deficient tumor cell line grown in mice, with CQ treatment resulting in a more significant reduction in tumor growth than selumetinib treatment. Furthermore, combined treatment with CQ and selumetinib resulted in a further reduction in NF1-deficient cell viability. In conclusion, NF1-deficient cells are vulnerable to disruption of the autophagy pathway. This pathway represents a promising target for the treatment of NF1-associated tumors, and we identified CQ as a candidate drug for the treatment of NF1 tumors.

Emerging dimensions of autophagy in melanoma

Macroautophagy/autophagy has previously been regarded as simply a way for cells to deal with nutrient emergency. But explosive work in the last 15 years has given increasingly new knowledge to our understanding of this process. Many of the functions of autophagy that are unveiled from recent studies, however, cannot be reconciled with this conventional view of cell survival but, instead, point to autophagy being integrally involved at a deeper level of cell biology, playing a critical role in maintaining homeostasis and promoting an integrated stress/immune response. The new appreciation of the role of autophagy in the evolutionary trajectory of cancer and cancer interaction with the immune system provides a mechanistic framework for understanding the clinical benefits of autophagy-based therapies. Here, we examine current knowledge of the mechanisms and functions of autophagy in highly plastic and aggressive melanoma as a model disease of human malignancy, while highlighting emerging dimensions indicating that autophagy is at play beyond its classical face.Abbreviation: AMBRA1: autophagy and beclin 1 regulator 1; AMPK: AMP-activated protein kinase; ATF4: activating transcription factor 4; ATG: autophagy related; BRAF: B-Raf proto-oncogene, serine/threonine kinase; CAFs: cancer-associated fibroblasts; CCL5: C-C motif chemokine ligand 5; CQ: chloroquine; CRISPR: clustered regularly interspaced short palindromic repeats; CTLA4: cytotoxic T-lymphocyte associated protein 4; CTL: cytotoxic T lymphocyte; DAMPs: danger/damage-associated molecular patterns; EGFR: epidermal growth factor receptor; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; FITM2: fat storage inducing transmembrane protein 2; HCQ: hydroxychloroquine; ICB: immune checkpoint blockade; ICD: immunogenic cell death; LDH: lactate dehydrogenase; MAPK: mitogen-activated protein kinase; MTORC1: mechanistic target of rapamycin kinase complex 1; NDP52: nuclear dot protein 52; NFKB/NF-κ B: nuclear factor kappa B; NBR1: the neighbor of BRCA1; NK: natural killer; NRF1: nuclear respiratory factor 1; NSCLC: non-small-cell lung cancer; OPTN: optineurin; PDAC: pancreatic ductal adenocarcinoma; PDCD1/PD-1: programmed cell death 1; PPT1: palmitoyl-protein thioesterase 1; PTEN: phosphatase and tensin homolog; PTK2/FAK1: protein tyrosine kinase 2; RAS: rat sarcoma; SQSTM1/p62: sequestosome 1; STK11/LKB1: serine/threonine kinase 11; TAX1BP1: Tax1 binding protein 1; TFEB: transcription factor EB; TGFB/TGF-β: transforming growth factor beta; TMB: tumor mutational burden; TME: tumor microenvironment; TSC1: TSC complex subunit 1; TSC2: TSC complex subunit 2; ULK1: unc-51 like autophagy activating kinase 1; UVRAG: UV radiation resistance associated.

Risk factors of using late-autophagy inhibitors: Aspects to consider when combined with anticancer therapies

Cancer resistance to therapy is still an unsolved scientific and clinical problem. In 2022, the hallmarks of cancer have been expanded to include four new features, including cellular senescence. Therapy-induced senescence (TIS) is a stressor-based response to conventional treatment methods, e.g. chemo- and radiotherapy, but also to non-conventional targeted therapies. Since TIS reinforces resistance in cancers, new strategies for sensitizing cancer cells to therapy are being adopted. These include macroautophagy as a potential target for inhibition due to its potential cytoprotective role in many cancers. The mechanism of late-stage autophagy inhibitors is based on blockage of autophagolysosome formation or an increase in lysosomal pH, resulting in disrupted cargo degradation. Such inhibitors are relevant candidates for increasing anticancer therapy effectiveness. In particular, 4-aminoquoline derivatives: chloroquine/hydroxychloroquine (CQ/HCQ) have been tested in multiple clinical trials in combination with senescence-inducing anti-cancer drugs. In this review, we summarize the properties of selected late-autophagy inhibitors and their role in the regulation of autophagy and senescent cell phenotype in vitro and in vivo models of cancer as well as treatment response in clinical trials on oncological patients. Additionally, we point out that, although these compounds increase the effectiveness of treatment in some cases, their practical usage might be hindered due to systemic toxicity, hypoxic environment, dose- ant time-dependent inhibitory effects, as well as a possible contribution to escaping from TIS.

Selective Termination of Autophagy-Dependent Cancers

The goal of cancer research is to identify characteristics of cancer cells that allow them to be selectively eliminated without harming the host. One such characteristic is autophagy dependence. Cancer cells survive, proliferate, and metastasize under conditions where normal cells do not. Thus, the requirement in cancer cells for more energy and macromolecular biosynthesis can evolve into a dependence on autophagy for recycling cellular components. Recent studies have revealed that autophagy, as well as different forms of cellular trafficking, is regulated by five phosphoinositides associated with eukaryotic cellular membranes and that the enzymes that synthesize them are prime targets for cancer therapy. For example, PIKFYVE inhibitors rapidly disrupt lysosome homeostasis and suppress proliferation in all cells. However, these inhibitors selectively terminate PIKFYVE-dependent cancer cells and cancer stem cells with not having adverse effect on normal cells. Here, we describe the biochemical distinctions between PIKFYVE-sensitive and -insensitive cells, categorize PIKFYVE inhibitors into four groups that differ in chemical structure, target specificity and efficacy on cancer cells and normal cells, identify the mechanisms by which they selectively terminate autophagy-dependent cancer cells, note their paradoxical effects in cancer immunotherapy, and describe their therapeutic applications against cancers.

Nanomaterials in crossroad of autophagy control in human cancers: Amplification of cell death mechanisms

Cancer is the result of genetic abnormalities that cause normal cells to grow into neoplastic cells. Cancer is characterized by several distinct features, such as uncontrolled cell growth, extensive spreading to other parts of the body, and the ability to resist treatment. The scientists have stressed the development of nanostructures as novel therapeutic options in suppressing cancer, in response to the emergence of resistance to standard medicines. One of the specific mechanisms with dysregulation during cancer is autophagy. Nanomaterials have the ability to specifically carry medications and genes, and they can also enhance the responsiveness of tumor cells to standard therapy while promoting drug sensitivity. The primary mechanism in this process relies on autophagosomes and their fusion with lysosomes to break down the components of the cytoplasm. While autophagy was initially described as a form of cellular demise, it has been demonstrated to play a crucial role in controlling metastasis, proliferation, and treatment resistance in human malignancies. The pharmacokinetic profile of autophagy modulators is poor, despite their development for use in cancer therapy. Consequently, nanoparticles have been developed for the purpose of delivering medications and autophagy modulators selectively and specifically to the cancer process. Furthermore, several categories of nanoparticles have demonstrated the ability to regulate autophagy, which plays a crucial role in defining the biological characteristics and response to therapy of tumor cells.

Chloroquine-induced DNA damage synergizes with DNA repair inhibitors causing cancer cell death

Background

Cancer is a global health problem accounting for nearly one in six deaths worldwide. Conventional treatments together with new therapies have increased survival to this devastating disease. However, the persistent challenges of treatment resistance and the limited therapeutic arsenal available for specific cancer types still make research in new therapeutic strategies an urgent need.

Methods

Chloroquine was tested in combination with different drugs (Panobinostat, KU-57788 and NU-7026) in 8 human-derived cancer cells lines (colorectal: HCT116 and HT29; breast: MDA-MB-231 and HCC1937; glioblastoma: A-172 and LN-18; head and neck: CAL-33 and 32816). Drug´s effect on proliferation was tested by MTT assays and cell death was assessed by Anexin V-PI apoptosis assays. The presence of DNA double-strand breaks was analyzed by phospho-H2AX fluorescent staining. To measure homologous recombination efficiency the HR-GFP reporter was used, which allows flow cytometry-based detection of HR stimulated by I-SceI endonuclease-induced DSBs.

Results

The combination of chloroquine with any of the drugs employed displayed potent synergistic effects on apoptosis induction, with particularly pronounced efficacy observed in glioblastoma and head and neck cancer cell lines. We found that chloroquine produced DNA double strand breaks that depended on reactive oxygen species formation, whereas Panobinostat inhibited DNA double-strand breaks repair by homologous recombination. Cell death caused by chloroquine/Panobinostat combination were significantly reduced by N-Acetylcysteine, a reactive oxygen species scavenger, underscoring the pivotal role of DSB generation in CQ/LBH-induced lethality. Based on these data, we also explored the combination of CQ with KU-57788 and NU-7026, two inhibitors of the other main DSB repair pathway, nonhomologous end joining (NHEJ), and again synergistic effects on apoptosis induction were observed.

Conclusion

Our data provide a rationale for the clinical investigation of CQ in combination with DSB inhibitors for the treatment of different solid tumors.

The regulatory role of autophagy between TAMs and tumor cells

Cancer has become a global public health problem and its harmful effects have received widespread attention. Conventional treatments such as surgical resection, radiotherapy and other techniques are applicable to clinical practice, but new drugs are constantly being developed and other therapeutic approaches, such as immunotherapy are being applied. In addition to studying the effects on individual tumor cells, it is important to explore the role of tumor microenvironment on tumor cell development since tumor cells do not exist alone but in the tumor microenvironment. In the tumor microenvironment, tumor cells are interconnected with other stromal cells and influence each other, among which tumor-associated macrophages (TAMs) are the most numerous immune cells. At the same time, it was found that cancer cells have different levels of autophagy from normal cells. In cancer therapy, the occurrence of autophagy plays an important role in promoting tumor cell death or inhibiting tumor cell death, and is closely related to the environment. Therefore, elucidating the regulatory role of autophagy between TAMs and tumor cells may be an important breakthrough, providing new perspectives for further research on antitumor immune mechanisms and improving the efficacy of cancer immunotherapy.

Angiogenesis-on-a-chip coupled with single-cell RNA sequencing reveals spatially differential activations of autophagy along angiogenic sprouts

Several functions of autophagy associated with proliferation, differentiation, and migration of endothelial cells have been reported. Due to lack of models recapitulating angiogenic sprouting, functional heterogeneity of autophagy in endothelial cells along angiogenic sprouts remains elusive. Here, we apply an angiogenesis-on-a-chip to reconstruct 3D sprouts with clear endpoints. We perform single-cell RNA sequencing of sprouting endothelial cells from our chip to reveal high activation of autophagy in two endothelial cell populations- proliferating endothelial cells in sprout basements and stalk-like endothelial cells near sprout endpoints- and further the reciprocal expression pattern of autophagy-related genes between stalk- and tip-like endothelial cells near sprout endpoints, implying an association of autophagy with tip-stalk cell specification. Our results suggest a model describing spatially differential roles of autophagy: quality control of proliferating endothelial cells in sprout basements for sprout elongation and tip-stalk cell specification near sprout endpoints, which may change strategies for developing autophagy-based anti-angiogenic therapeutics.

HIV-1 Gag MA domain binds to cardiolipin in a binding mode distinct from virus assemble mediator PI(4,5)P2

The human immunodeficiency virus type 1 (HIV-1) Gag protein is responsible for facilitating HIV-1 virion assembly and budding. Our study demonstrates that cardiolipin (CL), a component found in the inner mitochondrial membrane, exhibits the highest binding affinity to the N-terminal MA domain of the HIV-1 Gag protein within the lipid group of host cells. To assess this binding interaction, we synthesized short acyl chain derivatives of CL and employed surface plasmon resonance (SPR) analysis to determine the dissociation constants (Kd) for CL and the MA domain. Simultaneously, we examined the Kd of D-myo-phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2 ) derivatives, known to play a crucial role in virion formation. Among all the derivatives, Tetra-C7 -CL exhibited the lowest Kd value (Kd = 30.8 ± 6.9 μM) for MA binding on the CL analog-immobilized sensorchip, indicating a higher affinity. Similarly, the Kd value of Di-C7 -PIP2 (Kd = 36.6 ± 4.7 μM) was the lowest on the PI(4,5)P2 analog-immobilized sensorchip. Thus, Tetra-C7 -CL binds to the MA domain using a distinct binding mode while displaying a comparable binding affinity to Di-C7 -PIP2. This discovery holds significant implications for comprehending the virological importance of CL-MA domain binding, such as its subcellular distribution, including mitochondrial translocation, and involvement in viral particle formation in concert with PI(4,5)P2 . Furthermore, this study has the potential to contribute to the development of drugs in the future.

Targeting the RAS/RAF/MAPK pathway for cancer therapy: from mechanism to clinical studies

Metastatic dissemination of solid tumors, a leading cause of cancer-related mortality, underscores the urgent need for enhanced insights into the molecular and cellular mechanisms underlying metastasis, chemoresistance, and the mechanistic backgrounds of individuals whose cancers are prone to migration. The most prevalent signaling cascade governed by multi-kinase inhibitors is the mitogen-activated protein kinase (MAPK) pathway, encompassing the RAS-RAF-MAPK kinase (MEK)-extracellular signal-related kinase (ERK) pathway. RAF kinase is a primary mediator of the MAPK pathway, responsible for the sequential activation of downstream targets, such as MEK and the transcription factor ERK, which control numerous cellular and physiological processes, including organism development, cell cycle control, cell proliferation and differentiation, cell survival, and death. Defects in this signaling cascade are associated with diseases such as cancer. RAF inhibitors (RAFi) combined with MEK blockers represent an FDA-approved therapeutic strategy for numerous RAF-mutant cancers, including melanoma, non-small cell lung carcinoma, and thyroid cancer. However, the development of therapy resistance by cancer cells remains an important barrier. Autophagy, an intracellular lysosome-dependent catabolic recycling process, plays a critical role in the development of RAFi resistance in cancer. Thus, targeting RAF and autophagy could be novel treatment strategies for RAF-mutant cancers. In this review, we delve deeper into the mechanistic insights surrounding RAF kinase signaling in tumorigenesis and RAFi-resistance. Furthermore, we explore and discuss the ongoing development of next-generation RAF inhibitors with enhanced therapeutic profiles. Additionally, this review sheds light on the functional interplay between RAF-targeted therapies and autophagy in cancer.

Hydroquinone-selected chronic myelogenous leukemia cells are sensitive to chloroquine-induced cytotoxicity via MCL1 suppression and glycolysis inhibition

Previous studies have provided evidence that repeated exposure to the benzene metabolite hydroquinone (HQ) induces malignant transformation and increases basal autophagy in the chronic myeloid leukemia (CML) cell line K562. This study explored the cytotoxicity of the autophagy inhibitor chloroquine (CQ) on parental and HQ-selected K562 (K562/HQ) cells. CQ triggered apoptosis in these cells independently of inhibiting autophagic flux; however, in K562/HQ cells, CQ-induced cytotoxicity was higher than in K562 cells. Mechanistically, CQ-induced NOXA upregulation led to MCL1 downregulation and mitochondrial depolarization in K562/HQ cells. MCL1 overexpression or NOXA silencing attenuated CQ-mediated cytotoxicity in K562/HQ cells. CQ triggered ERK inactivation to increase Sp1, NFκB, and p300 expression, and co-assembly of Sp1, NFκB, and p300 in the miR-29a promoter region coordinately upregulated miR-29a transcription. CQ-induced miR-29a expression destabilized tristetraprolin (TTP) mRNA, which in turn reduced TTP-mediated NOXA mRNA decay, thereby increasing NOXA protein expression. A similar mechanism explained the CQ-induced downregulation of MCL1 in K562 cells. K562/HQ cells relied more on glycolysis for ATP production than K562 cells, whereas inhibition of glycolysis by CQ was greater in K562/HQ cells than in K562 cells. Likewise, CQ-induced MCL1 suppression and glycolysis inhibition resulted in higher cytotoxicity in CML KU812/HQ cells than in KU812 cells. Taken together, our data confirm that CQ inhibits MCL1 expression through the ERK/miR-29a/TTP/NOXA pathway, and that inhibition of glycolysis is positively correlated to higher cytotoxicity of CQ on HQ-selected CML cells.

Unraveling the interplay between RAS/RAF/MEK/ERK signaling pathway and autophagy in cancer: From molecular mechanisms to targeted therapy

RAS/RAF/MEK/ERK signaling pathway is one of the most important pathways of Mitogen-activated protein kinases (MAPK), which widely participate in regulating cell proliferation, differentiation, apoptosis and signaling transduction. Autophagy is an essential mechanism that maintains cellular homeostasis by degrading aged and damaged organelles. Recently, some studies revealed RAS/RAF/MEK/ERK signaling pathway is closely related to autophagy regulation and has a dual effect in tumor cells. However, the specific mechanism by which RAS/RAF/MEK/ERK signaling pathway participates in autophagy regulation is not fully understood. This article provides a comprehensive review of the research progress with regard to the RAS/RAF/MEK/ERK signaling pathway and autophagy, as well as their interplay in cancer therapy. The impact of small molecule inhibitors that target the RAS/RAF/MEK/ERK signaling pathway on autophagy is discussed in this study. The advantages and limitations of the clinical combination of these small molecule inhibitors with autophagy inhibitors are also explored. The findings from this study may provide additional perspectives for future cancer treatment strategies.

Autophagy: Regulator of cell death

Autophagy is the process by which cells degrade and recycle proteins and organelles to maintain intracellular homeostasis. Generally, autophagy plays a protective role in cells, but disruption of autophagy mechanisms or excessive autophagic flux usually leads to cell death. Despite recent progress in the study of the regulation and underlying molecular mechanisms of autophagy, numerous questions remain to be answered. How does autophagy regulate cell death? What are the fine-tuned regulatory mechanisms underlying autophagy-dependent cell death (ADCD) and autophagy-mediated cell death (AMCD)? In this article, we highlight the different roles of autophagy in cell death and discuss six of the main autophagy-related cell death modalities, with a focus on the metabolic changes caused by excessive endoplasmic reticulum-phagy (ER-phagy)-induced cell death and the role of mitophagy in autophagy-mediated ferroptosis. Finally, we discuss autophagy enhancement in the treatment of diseases and offer a new perspective based on the use of autophagy for different functional conversions (including the conversion of autophagy and that of different autophagy-mediated cell death modalities) for the clinical treatment of tumors.

The role of epithelial-mesenchymal transition and autophagy in pancreatic ductal adenocarcinoma invasion

Of all pancreatic cancer (PC) cases, approximately 90% are pancreatic ductal adenocarcinoma (PDAC), which progress rapidly due to its high degree of invasiveness and high metastatic potential. Epithelial-mesenchymal transition (EMT) is a prerequisite for cancer cell invasion and spread, and it is mediated by the specific cellular behaviors and the tumor microenvironment. Autophagy has long been a target of cancer therapy, and it has been considered to play a dual and contradictory role, particularly regarding EMT-mediated PDAC invasion. This review discusses the characteristics and the biological role of EMT and autophagy from a cellular perspective, explaining invasion as a survival behavior of PDAC, with the aim of providing novel insights into targeting EMT and autophagy to overcome PDAC invasion.

Autophagy and autophagy-related pathways in cancer

Maintenance of protein homeostasis and organelle integrity and function is critical for cellular homeostasis and cell viability. Autophagy is the principal mechanism that mediates the delivery of various cellular cargoes to lysosomes for degradation and recycling. A myriad of studies demonstrate important protective roles for autophagy against disease. However, in cancer, seemingly opposing roles of autophagy are observed in the prevention of early tumour development versus the maintenance and metabolic adaptation of established and metastasizing tumours. Recent studies have addressed not only the tumour cell intrinsic functions of autophagy, but also the roles of autophagy in the tumour microenvironment and associated immune cells. In addition, various autophagy-related pathways have been described, which are distinct from classical autophagy, that utilize parts of the autophagic machinery and can potentially contribute to malignant disease. Growing evidence on how autophagy and related processes affect cancer development and progression has helped guide efforts to design anticancer treatments based on inhibition or promotion of autophagy. In this Review, we discuss and dissect these different functions of autophagy and autophagy-related processes during tumour development, maintenance and progression. We outline recent findings regarding the role of these processes in both the tumour cells and the tumour microenvironment and describe advances in therapy aimed at autophagy processes in cancer.

ARL-17477 is a dual inhibitor of NOS1 and the autophagic-lysosomal system that prevents tumor growth in vitro and in vivo

ARL-17477 is a selective neuronal nitric oxide synthase (NOS1) inhibitor that has been used in many preclinical studies since its initial discovery in the 1990s. In the present study, we demonstrate that ARL-17477 exhibits a NOS1-independent pharmacological activity that involves inhibition of the autophagy-lysosomal system and prevents cancer growth in vitro and in vivo. Initially, we screened a chemical compound library for potential anticancer agents, and identified ARL-17477 with micromolar anticancer activity against a wide spectrum of cancers, preferentially affecting cancer stem-like cells and KRAS-mutant cancer cells. Interestingly, ARL-17477 also affected NOS1-knockout cells, suggesting the existence of a NOS1-independent anticancer mechanism. Analysis of cell signals and death markers revealed that LC3B-II, p62, and GABARAP-II protein levels were significantly increased by ARL-17477. Furthermore, ARL-17477 had a chemical structure similar to that of chloroquine, suggesting the inhibition of autophagic flux at the level of lysosomal fusion as an underlying anticancer mechanism. Consistently, ARL-17477 induced lysosomal membrane permeabilization, impaired protein aggregate clearance, and activated transcription factor EB and lysosomal biogenesis. Furthermore, in vivo ARL-17477 inhibited the tumor growth of KRAS-mutant cancer. Thus, ARL-17477 is a dual inhibitor of NOS1 and the autophagy-lysosomal system that could potentially be used as a cancer therapeutic.

Specific inhibitory effects of guanosine on breast cancer cell proliferation

Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer-related death. Drug therapy for breast cancer is currently selected based on the subtype classification; however, many anticancer drugs are highly cytotoxic. Since intracellular levels of GTP are elevated in many cancer cells that undergo a specific cell proliferation cycle, GTP has potential as a target for cancer therapy. The present study focused on nucleosides and nucleotides and examined intracellular GTP-dependent changes in cell proliferation rates in normal (MCF-12A) and cancer (MCF-7) breast cell lines. Decreased cell proliferation due to a reduction in intracellular GTP levels by mycophenolic acid (MPA), an inosine monophosphate dehydrogenase inhibitor, was observed in both cell lines. The inhibitory effects of MPA on cell proliferation were suppressed when it was applied in combination with Guanosine (Guo), a substrate for GTP salvage synthesis, while the single exposure to Guo suppressed the proliferation of MCF-7 cells only. Although the underlying mechanisms remain unclear, since the inhibitory effects of Guo on cell proliferation did not correlate with GTP or ATP intracellular levels or the GTP/ATP ratio, there may be another cause besides GTP metabolism. Guo inhibited the proliferation of MCF-7, a human breast cancer cell line, but not MCF-12A, a human normal breast cell line. Further studies are needed to investigate the potential of applying Guo as a target for the development of a novel cancer treatment system.

Concurrent Activation of Both Survival-Promoting and Death-Inducing Signaling by Chloroquine in Glioblastoma Stem Cells: Implications for Potential Risks and Benefits of Using Chloroquine as Radiosensitizer

Lysosomotropic agent chloroquine was shown to sensitize non-stem glioblastoma cells to radiation in vitro with p53-dependent apoptosis implicated as one of the underlying mechanisms. The in vivo outcomes of chloroquine or its effects on glioblastoma stem cells have not been previously addressed. This study undertakes a combinatorial approach encompassing in vitro, in vivo and in silico investigations to address the relationship between chloroquine-mediated radiosensitization and p53 status in glioblastoma stem cells. Our findings reveal that chloroquine elicits antagonistic impacts on signaling pathways involved in the regulation of cell fate via both transcription-dependent and transcription-independent mechanisms. Evidence is provided that transcriptional impacts of chloroquine are primarily determined by p53 with chloroquine-mediated activation of pro-survival mevalonate and p21-DREAM pathways being the dominant response in the background of wild type p53. Non-transcriptional effects of chloroquine are conserved and converge on key cell fate regulators ATM, HIPK2 and AKT in glioblastoma stem cells irrespective of their p53 status. Our findings indicate that pro-survival responses elicited by chloroquine predominate in the context of wild type p53 and are diminished in cells with transcriptionally impaired p53. We conclude that p53 is an important determinant of the balance between pro-survival and pro-death impacts of chloroquine and propose that p53 functional status should be taken into consideration when evaluating the efficacy of glioblastoma radiosensitization by chloroquine.

Autophagy-Dependent Ferroptosis in Cancer

Significance: Autophagy is a self-degrading process that determines cell fate in response to various environmental stresses. In contrast to autophagy-mediated cell survival, the signals, mechanisms, and effects of autophagy-dependent cell death remain obscure. The discovery of autophagy-dependent ferroptosis provides a paradigm for understanding the relationship between aberrant degradation pathways and excessive lipid peroxidation in driving regulated cell death. Recent Advances: Ferroptosis was originally described as an autophagy-independent and iron-mediated nonapoptotic cell death. Current studies reveal that the level of intracellular autophagy is positively correlated with ferroptosis sensitivity. Selective autophagic degradation of proteins (e.g., ferritin, SLC40A1, ARNTL, GPX4, and CDH2) or organelles (e.g., lipid droplets or mitochondria) promotes ferroptosis by inducing iron overload and/or lipid peroxidation. Several upstream autophagosome regulators (e.g., TMEM164), downstream autophagy receptors (e.g., HPCAL1), or danger signals (e.g., DCN) are selectively required for ferroptosis-related autophagy, but not for starvation-induced autophagy. The induction of autophagy-dependent ferroptosis is an effective approach to eliminate drug-resistant cancer cells. Critical Issues: How different organelles selectively activate autophagy to modulate ferroptosis sensitivity is not fully understood. Identifying direct protein effectors of ferroptotic cell death remains a challenge. Future Directions: Further understanding of the molecular mechanics and immune consequences of autophagy-dependent ferroptosis is critical for the development of precision antitumor therapies.

Blocking the Hormone Receptors Modulates NLRP3 in LPS-Primed Breast Cancer Cells

NOD-like receptor protein 3 (NLRP3) may contribute to the growth and propagation of breast cancer (BC). The effect of estrogen receptor-α (ER-α), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) on NLRP3 activation in BC remains unknown. Additionally, our knowledge of the effect of blocking these receptors on NLRP3 expression is limited. We used GEPIA, UALCAN, and the Human Protein Atlas for transcriptomic profiling of NLRP3 in BC. Lipopolysaccharide (LPS) and adenosine 5'-triphosphate (ATP) were used to activate NLRP3 in luminal A MCF-7 and in TNBC MDA-MB-231 and HCC1806 cells. Tamoxifen (Tx), mifepristone (mife), and trastuzumab (Tmab) were used to block ER-α, PR, and HER2, respectively, on inflammasome activation in LPS-primed MCF7 cells. The transcript level of NLRP3 was correlated with ER-ɑ encoding gene ESR1 in luminal A (ER-α⁺, PR⁺) and TNBC tumors. NLRP3 protein expression was higher in untreated and LPS/ATP-treated MDA-MB-231 cells than in MCF7 cells. LPS/ATP-mediated NLRP3 activation reduced cell proliferation and recovery of wound healing in both BC cell lines. LPS/ATP treatment prevented spheroid formation in MDA-MB-231 cells but did not affect MCF7. HGF, IL-3, IL-8, M-CSF, MCP-1, and SCGF-b cytokines were secreted in both MDA-MB-231 and MCF7 cells in response to LPS/ATP treatment. Tx (ER-α inhibition) promoted NLRP3 activation and increased migration and sphere formation after LPS treatment of MCF7 cells. Tx-mediated activation of NLRP3 was associated with increased secretion of IL-8 and SCGF-b compared to LPS-only-treated MCF7 cells. In contrast, Tmab (Her2 inhibition) had a limited effect on NLRP3 activation in LPS-treated MCF7 cells. Mife (PR inhibition) opposed NLRP3 activation in LPS-primed MCF7 cells. We have found that Tx increased the expression of NLRP3 in LPS-primed MCF7. These data suggest a link between blocking ER-α and activation of NLRP3, which was associated with increased aggressiveness of the ER-α⁺ BC cells.

Crosstalk between autophagy and immune cell infiltration in the tumor microenvironment

Autophagy is a conserved process for self-degradation and provides cells with a rescue mechanism to respond to circumstances such as stress and starvation. The role of autophagy in cancer is extremely complex and often paradoxical. Most of the related published studies on tumors are always focused on cancer cells. However, present studies gradually noticed the significance of autophagy in the tumor microenvironment. These studies demonstrate that autophagy and immunity work synergistically to affect tumor progression, indicating that autophagy could become a potential target for cancer immunotherapy. Therefore, it is crucial to clarify the correlation between autophagy and various tumor-infiltrating immune cells in the tumor microenvironment. The context-dependent role of autophagy is critical in the design of therapeutic strategies for cancer.

Perturbation of Autophagy by a Beclin 1-Targeting Stapled Peptide Induces Mitochondria Stress and Inhibits Proliferation of Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, with a dismal five-year survival rate of less than 10%. PDAC possesses prominent genetic alterations in the oncogene KRAS and tumor suppressors p53, SMAD4 and CDKN2A. However, efforts to develop targeted drugs against these molecules have not been successful, and novel therapeutic modalities for PDAC treatment are urgently needed. Autophagy is an evolutionarily conserved self-degradative process that turns over intracellular components in a lysosome-dependent manner. The role of autophagy in PDAC is complicated and context-dependent. Elevated basal autophagy activity has been detected in multiple human PDAC cell lines and primary tumors resected from patients. However, clinical trials using chloroquine (CQ) to inhibit autophagy failed to show therapeutic efficacy. Here we show that a Beclin 1-targeting stapled peptide (Tat-SP4) developed in our lab further enhanced autophagy in multiple PDAC cell lines possessing high basal autophagy activity. Tat-SP4 also triggered faster endolysosomal degradation of EGFR and induced significant mitochondria stress as evidenced by partial loss of Δψ, increased level of ROS and reduced OXPHOS activity. Tat-SP4 exerted a potent anti-proliferative effect in PDAC cell lines in vitro and prohibited xenograft tumor growth in vivo. Intriguingly, excessive autophagy has been reported to trigger a unique form of cell death termed autosis. Tat-SP4 does induce autosis-like features in PDAC cells, including mitochondria stress and non-apoptotic cell death. Overall, our study suggests that autophagy perturbation by a Beclin 1-targeting peptide and the resulting autosis may offer a new strategy for PDAC drug discovery.

Autophagy Paradox: Strategizing Treatment Modality in Melanoma

OPINION STATEMENT

The primordial autophagy process, originally identified as a starvation response in baker's yeast, has since been shown to have a wide spectrum of functions other than survival. In many cases, it is accepted that autophagy operates as a key tumor suppressor mechanism that protects cells from adverse environmental cues by enforcing homeostasis and maintaining the functional and structural integrity of organelles. Paradoxically, heightened states of autophagy are also seen in some cancers, leading to the prevailing view that the pro-survival aspect of autophagy might be hijacked by some tumors to promote their fitness and pathogenesis. Notably, recent studies have revealed a broad range of cell-autonomous autophagy in reshaping tumor microenvironment and maintaining lineage integrity and immune homeostasis, calling for a renewed understanding of autophagy beyond its classical roles in cell survival. Here, we evaluate the increasing body of literature that argues the "double-edged" consequences of autophagy manipulation in cancer therapy, with a particular focus on highly plastic and mutagenic melanoma. We also discuss the caveats that must be considered when evaluating whether autophagy blockade is the effector mechanism of some anti-cancer therapy particularly associated with lysosomotropic agents. If autophagy proteins are to be properly exploited as targets for anticancer drugs, their diverse and complex roles should also be considered.

The participation of non-canonical autophagic proteins in the autophagy process and their potential as therapeutic targets

INTRODUCTION

Autophagy is a conserved catabolic process that helps recycle intracellular components to maintain homeostasis. The completion of autophagy requires the synergistic effect of multiple canonical autophagic proteins. Defects in autophagy machinery have been reported to promote diseases, rendering autophagy a bone fide health-modifying agent. However, the clinical implication of canonical pan-autophagic activators or inhibitors has often led to undesirable side effects, making it urgent to find a safer autophagy-related therapeutic target. The discovery of non-canonical autophagic proteins has been found to specifically affect the development of diseases without causing a universal impact on autophagy and has shed light on finding a safer way to utilize autophagy in the therapeutic context.

AREAS COVERED

This review summarizes recently discovered non-canonical autophagic proteins, how these proteins influence autophagy, and their potential therapeutic role in the disease due to their interaction with autophagy.

EXPERT OPINION

Several therapies have been studied thus far and continued research is needed to identify the potential that non-canonical autophagic proteins have for treating certain diseases. In the meantime, continue to uncover new non-canonical autophagic proteins and examine which are likely to have therapeutic implications.

The role of autophagy in acute myeloid leukemia development

INTRODUCTION

Autophagy is a highly conservative self-degradative process. It aims at elimination-impaired proteins and cellular organelles. Previous research confirmed the autophagy role in cancer pathogenesis.

AREAS COVERED

This article discusses the role of autophagy in the development of AML. Autophagy seems to be a 'double-sword' mechanism, hence, either its suppression or induction could promote neoplasm growth. This mechanism could also be the aim of the 'molecular targeted therapy.' Chemo- and radiotherapy induce cellular stress in neoplasm cells with subsequent autophagy suppression. Simultaneously, it is claimed that the autophagy suppression increases chemosensitivity 'in neoplastic cells. Some agents, like bortezomib, in turn could promote autophagy process, e.g. in AML (acute myeloid leukemia). However, currently there are not many studies focusing on the role of autophagy in patients suffering for AML. In this review, we summarize the research done so far on the role of autophagy in the development of AML.

EXPERT OPINION

The analysis of autophagy genes expression profiling in AML could be a relevant factor in the diagnostic process and treatment 'individualization.' Autophagy modulation seems to be a relevant target in the oncological therapy - it could limit disease progression and increase the effectiveness of treatment.

Autophagy and tumorigenesis

Autophagy is a catabolic process that captures cellular waste and degrades them in the lysosome. The main functions of autophagy are quality control of cytosolic proteins and organelles, and intracellular recycling of nutrients in order to maintain cellular homeostasis. Autophagy is upregulated in many cancers to promote cell survival, proliferation, and metastasis. Both cell-autonomous autophagy (also known as tumor autophagy) and non-cell-autonomous autophagy (also known as host autophagy) support tumorigenesis through different mechanisms, including inhibition of p53 activation, sustaining redox homeostasis, maintenance of essential amino acids levels in order to support energy production and biosynthesis, and inhibition of antitumor immune responses. Therefore, autophagy may serve as a tumor-specific vulnerability and targeting autophagy could be a novel strategy in cancer treatment.

The role of autophagy in colorectal cancer: Impact on pathogenesis and implications in therapy

Colorectal cancer (CRC) is considered as a global major cause of cancer death. Surgical resection is the main line of treatment; however, chemo-, radiotherapy and other adjuvant agents are crucial to achieve good outcomes. The tumor microenvironment (TME) is a well-recognized key player in CRC progression, yet the processes linking the cancer cells to its TME are not fully delineated. Autophagy is one of such processes, with a controversial role in the pathogenesis of CRC, with its intricate links to many pathological factors and processes. Autophagy may apparently play conflicting roles in carcinogenesis, but the precise mechanisms determining the overall direction of the process seem to depend on the context. Additionally, it has been established that autophagy has a remarkable effect on the endothelial cells in the TME, the key substrate for angiogenesis that supports tumor metastasis. Favorable response to immunotherapy occurs only in a specific subpopulation of CRC patients, namely the microsatellite instability-high (MSI-H). In view of such limitations of immunotherapy in CRC, modulation of autophagy represents a potential adjuvant strategy to enhance the effect of those relatively safe agents on wider CRC molecular subtypes. In this review, we discussed the molecular control of autophagy in CRC and how autophagy affects different processes and mechanisms that shape the TME. We explored how autophagy contributes to CRC initiation and progression, and how it interacts with tumor immunity, hypoxia, and oxidative stress. The crosstalk between autophagy and the TME in CRC was extensively dissected. Finally, we reported the clinical efforts and challenges in combining autophagy modulators with various cancer-targeted agents to improve CRC patients’ survival and restrain cancer growth.

The cell-line-derived subcutaneous tumor model in preclinical cancer research

Tumor-bearing experimental animals are essential for preclinical cancer drug development. A broad range of tumor models is available, with the simplest and most widely used involving a tumor of mouse or human origin growing beneath the skin of a mouse: the subcutaneous tumor model. Here, we outline the different types of in vivo tumor model, including some of their advantages and disadvantages and how they fit into the drug-development process. We then describe in more detail the subcutaneous tumor model and key steps needed to establish it in the laboratory, namely: choosing the mouse strain and tumor cells; cell culture, preparation and injection of tumor cells; determining tumor volume; mouse welfare; and an appropriate experimental end point. The protocol leads to subcutaneous tumor growth usually within 1-3 weeks of cell injection and is suitable for those with experience in tissue culture and mouse experimentation.

Chloroquine-Induced DNA Damage Synergizes with Nonhomologous End Joining Inhibition to Cause Ovarian Cancer Cell Cytotoxicity

Ovarian cancer (OC) is the most lethal gynecological malignancy; therefore, more effective treatments are urgently needed. We recently reported that chloroquine (CQ) increased reactive oxygen species (ROS) in OC cell lines (OCCLs), causing DNA double-strand breaks (DSBs). Here, we analyzed whether these lesions are repaired by nonhomologous end joining (NHEJ), one of the main pathways involved in DSB repair, and if the combination of CQ with NHEJ inhibitors (NHEJi) could be effective against OC. We found that NHEJ inhibition increased the persistence of γH2AX foci after CQ-induced DNA damage, revealing an essential role of this pathway in the repair of the lesions. NHEJi decreased the proliferation of OCCLs and a strong in vitro synergistic effect on apoptosis induction was observed when combined with CQ. This effect was largely abolished by the antioxidant N-Acetyl-L-cysteine, revealing the critical role of ROS and DSB generation in CQ/NHEJi-induced lethality. We also found that the NHEJ efficiency in OCCLs was not affected by treatment with Panobinostat, a pan-histone deacetylase inhibitor that also synergizes with CQ in OCCLs by impairing homologous recombination. Accordingly, the triple combination of CQ-NHEJi-Panobinostat exerted a stronger in vitro synergistic effect. Altogether, our data suggest that the combination of these drugs could represent new therapeutic strategies against OC.

SEMA3C Supports Pancreatic Cancer Progression by Regulating the Autophagy Process and Tumor Immune Microenvironment

To date, driver genes for pancreatic cancer treatment are difficult to pursue therapeutically. Targeting mutated KRAS, the most renowned driver gene in pancreatic cancer, is an active area of study. We discovered a gene named SEMA3C was highly expressed in pancreatic cancer cell lines and patients with a G12D mutation in KRAS. High expression of SEMA3C in patients was significantly associated with the decreased survival of pancreatic cancer patients based on the TCGA database. In pancreatic cancer cells, SEMA3C knockdown or inhibition exhibited growth/colony inhibition and cell cycle arrest. In addition, SEMA3C inhibition sensitized KRAS or MEK1/2 inhibition in pancreatic cancer cells. Overexpression of SEMA3C resulted in the induction of autophagy, whereas depletion of SEMA3C compromised induction of autophagy. SEMA3C modified the PD-L1 expression in tumor and immune cells and is correlated with the M2-like macrophage marker ARG1/CD163 expression, which could reshape the tumor microenvironment. Inhibition of SEMA3C decreased tumor formation in the xenograft model in vivo. Taken together, our data suggest that SEMA3C plays a substantial role in promoting cancer cell survival by regulating the autophagy process and impacting the tumor environment immune response. SEMA3C can be used as a novel target or marker with therapeutic or diagnostic potential in pancreatic cancer especially in tumors harboring the specific KRAS G12D mutation.

The multifaceted role of autophagy in cancer

Autophagy is a cellular degradative pathway that plays diverse roles in maintaining cellular homeostasis. Cellular stress caused by starvation, organelle damage, or proteotoxic aggregates can increase autophagy, which uses the degradative capacity of lysosomal enzymes to mitigate intracellular stresses. Early studies have shown a role for autophagy in the suppression of tumorigenesis. However, work in genetically engineered mouse models and in vitro cell studies have now shown that autophagy can be either cancer-promoting or inhibiting. Here, we summarize the effects of autophagy on cancer initiation, progression, immune infiltration, and metabolism. We also discuss the efforts to pharmacologically target autophagy in the clinic and highlight future areas for exploration.

Autophagy, Oxidative Stress and Cancer Development

Simple Summary

Autophagy, as an important cellular repair mechanism, is important for the prevention of several diseases, including metabolic and neurologic disorders, and cancer. Hence, dysfunctional autophagy has been linked to these diseases, and in recent years researchers have tried to outline therapeutic targets in autophagy-related pathways as a treatment. With this review of the literature, we want to give an overview about the connection between oxidative stress, autophagy and cancer.

Abstract

Autophagy is an important cellular repair mechanism, aiming at sequestering misfolded and dysfunctional proteins and damaged cell organelles. Dysfunctions in the autophagy process have been linked to several diseases, like infectious and neurodegenerative diseases, type II diabetes mellitus and cancer. Living organisms are constantly subjected to some degree of oxidative stress, mainly induced by reactive oxygen and nitrogen species. It has been shown that autophagy is readily induced by reactive oxygen species (ROS) upon nutrient deprivation. In recent years, research has increasingly focused on outlining novel therapeutic targets related to the autophagy process. With this review of the literature, we want to give an overview about the link between autophagy, oxidative stress and carcinogenesis.

Discovery and Structure-Based Optimization of Novel Atg4B Inhibitors for the Treatment of Castration-Resistant Prostate Cancer

Autophagy inhibition is an attractive target for cancer therapy. In this study, we discovered inhibitors of Atg4B essential for autophagosome formation and evaluated their potential as therapeutics for prostate cancer. Seventeen compounds were identified as candidates after in silico screening and a thermal shift assay. Among them, compound 17 showed the most potent Atg4B inhibitory activity, inhibited autophagy induced by anti-castration-resistant prostate cancer (CRPC) drugs, and significantly enhanced apoptosis. Although 17 has been known as a phospholipase A₂ (PLA₂) inhibitor, other PLA₂ inhibitors had no effect on Atg4B and autophagy. We then performed structural optimization based on molecular modeling and succeeded in developing 21f (by shortening the alkyl chain of 17), which was a potent competitive inhibitor for Atg4B (K_i = 3.1 μM) with declining PLA₂ inhibitory potency. Compound 21f enhanced the anticancer activity of anti-CRPC drugs via autophagy inhibition. These findings suggest that 21f can be used as an adjuvant drug for therapy with anti-CRPC drugs.

Autophagy Contributes to Metabolic Reprogramming and Therapeutic Resistance in Pancreatic Tumors

Metabolic reprogramming is a feature of cancers for which recent research has been particularly active, providing numerous insights into the mechanisms involved. It occurs across the entire cancer process, from development to resistance to therapies. Established tumors exhibit dependencies for metabolic pathways, constituting vulnerabilities that can be targeted in the clinic. This knowledge is of particular importance for cancers that are refractory to any therapeutic approach, such as Pancreatic Ductal Adenocarcinoma (PDAC). One of the metabolic pathways dysregulated in PDAC is autophagy, a survival process that feeds the tumor with recycled intracellular components, through both cell-autonomous (in tumor cells) and nonautonomous (from the local and distant environment) mechanisms. Autophagy is elevated in established PDAC tumors, contributing to aberrant proliferation and growth even in a nutrient-poor context. Critical elements link autophagy to PDAC including genetic alterations, mitochondrial metabolism, the tumor microenvironment (TME), and the immune system. Moreover, high autophagic activity in PDAC is markedly related to resistance to current therapies. In this context, combining autophagy inhibition with standard chemotherapy, and/or drugs targeting other vulnerabilities such as metabolic pathways or the immune response, is an ongoing clinical strategy for which there is still much to do through translational and multidisciplinary research.

Sequestsome-1/p62-targeted small molecules for pancreatic cancer therapy

Pancreatic ductal adenocarcinoma (PDAC) is characterized by heightened autophagy and systemic immune dysfunction. Modest improvements in clinical outcomes have been demonstrated in completed clinical trials targeting autophagy with combination hydroxychloroquine (HCQ) and chemotherapy. Recent mechanistic insights into the role of autophagy-dependent immune evasion have prompted the need for more precise and druggable targets of autophagy inhibition. Sequestosome-1 (SQSTM-1) is a multidomain scaffold protein with well-established roles in autophagy, tumor necrosis factor alpha (TNFα)- and NF-κB-related signaling pathways. SQSTM1 overexpression is frequently observed in PDAC, correlating with clinical stage and outcome. Given the unique molecular structure of SQSTM-1 and its diverse activity, identifying means of limiting SQSTM-1-dependent autophagy to promote an effective immune response in PDAC could be a promising treatment strategy.

A perspective on the role of autophagy in cancer

Autophagy refers to a ubiquitous set of catabolic pathways required to achieve proper cellular homeostasis. Aberrant autophagy has been implicated in a multitude of diseases including cancer. In this review, we highlight pioneering and groundbreaking research that centers on delineating the role of autophagy in cancer initiation, proliferation and metastasis. First, we discuss the autophagy-related (ATG) proteins and their respective roles in the de novo formation of autophagosomes and the subsequent delivery of cargo to the lysosome for recycling. Next, we touch upon the history of cancer research that centers upon ATG proteins and regulatory mechanisms that control an appropriate autophagic response and how these are altered in the diseased state. Then, we discuss the various discoveries that led to the idea of autophagy as a double-edged sword when it comes to cancer therapy. This review also briefly narrates how different types of autophagy-selective macroautophagy and chaperone-mediated autophagy, have been linked to different cancers. Overall, these studies build upon a steadfast trajectory that aims to solve the monumentally daunting challenge of finding a cure for many types of cancer by modulating autophagy either through inhibition or induction.

Hydroxychloroquine synergizes with the PI3K inhibitor BKM120 to exhibit antitumor efficacy independent of autophagy

BACKGROUND

The critical role of phosphoinositide 3-kinase (PI3K) activation in tumor cell biology has prompted massive efforts to develop PI3K inhibitors (PI3Kis) for cancer therapy. However, recent results from clinical trials have shown only a modest therapeutic efficacy of single-agent PI3Kis in solid tumors. Targeting autophagy has controversial context-dependent effects in cancer treatment. As a FDA-approved lysosomotropic agent, hydroxychloroquine (HCQ) has been well tested as an autophagy inhibitor in preclinical models. Here, we elucidated the novel mechanism of HCQ alone or in combination with PI3Ki BKM120 in the treatment of cancer.

METHODS

The antitumor effects of HCQ and BKM120 on three different types of tumor cells were assessed by in vitro PrestoBlue assay, colony formation assay and in vivo zebrafish and nude mouse xenograft models. The involved molecular mechanisms were investigated by MDC staining, LC3 puncta formation assay, immunofluorescent assay, flow cytometric analysis of apoptosis and ROS, qRT-PCR, Western blot, comet assay, homologous recombination (HR) assay and immunohistochemical staining.

RESULTS

HCQ significantly sensitized cancer cells to BKM120 in vitro and in vivo. Interestingly, the sensitization mediated by HCQ could not be phenocopied by treatment with other autophagy inhibitors (Spautin-1, 3-MA and bafilomycin A1) or knockdown of the essential autophagy genes Atg5/Atg7, suggesting that the sensitizing effect might be mediated independent of autophagy status. Mechanistically, HCQ induced ROS production and activated the transcription factor NRF2. In contrast, BKM120 prevented the elimination of ROS by inactivation of NRF2, leading to accumulation of DNA damage. In addition, HCQ activated ATM to enhance HR repair, a high-fidelity repair for DNA double-strand breaks (DSBs) in cells, while BKM120 inhibited HR repair by blocking the phosphorylation of ATM and the expression of BRCA1/2 and Rad51.

CONCLUSIONS

Our study revealed that HCQ and BKM120 synergistically increased DSBs in tumor cells and therefore augmented apoptosis, resulting in enhanced antitumor efficacy. Our findings provide a new insight into how HCQ exhibits antitumor efficacy and synergizes with PI3Ki BKM120, and warn that one should consider the "off target" effects of HCQ when used as autophagy inhibitor in the clinical treatment of cancer.

Redox sensitive nano-capsules self-assembled from hyaluronic acid-hydroxychloroquine conjugates for CD44-targeted delivery of hydroxychloroquine to combat breast cancer metastasis in vitro and in vivo

Identifying an efficient tumor-targeted drug delivery system is an urgent task for the treatment of metastatic breast cancer. Herein, we report for the first time that a pH and redox dual-responsive polymer prodrug displays prominent inhibition of breast cancer metastasis to the lung. The polymer molecule was synthesized from hyaluronic acid (HA) and hydroxychloroquine (HCQ) through disulfide bonds as redox-sensitive linkers that self-assemble into nanocapsules (HA-ss-HCQ nanocapsules) at pH 7.4. Due to the pKa value of HCQ and built-in disulfide bonds, the nanocapsules were endowed with pH and redox dual-responsive properties. The in vitro drug release curve revealed that HA-ss-HCQ nanocapsules release drugs more quickly under low pH and high redox conditions. Moreover, the nanocapsules displayed active targeting and selectivity to metastatic breast cancer cells. Cellular uptake of Nile red-loaded nanocapsules observed by fluorescence microscopy showed that the nanocapsules exerted significantly enhanced cellular internalization capacity, which was greatly diminished by free HA. The IC₅₀ of HA-ss-HCQ nanocapsules in 4T1 cells was 2.23-fold lower than that of free HCQ. Importantly, wound healing assays and Transwell experiments demonstrated that HA-ss-HCQ nanocapsules greatly inhibited the migration and invasion of 4T1 cells. In particular, the metastasis of 4T1 cells to the lung was also remarkably suppressed by HA-ss-HCQ nanocapsules with minimal toxicity in an in vitro lung metastasis model, which was verified by the detection of macroscopic metastatic nodules and histological examination. In summary, this study provides a promising strategy for active-targeting therapy in metastatic breast cancer.

Autophagy and cancer metabolism-The two-way interplay

Autophagy is an intracellular catabolic process that degrades cytoplasmic components for recycling in response to stressed conditions, such as nutrient deprivation. Dysregulation of autophagy is associated with various diseases, including cancer. Although autophagy plays dichotomous and context-dependent roles in cancer, evidence has emerged that cancer cells exploit autophagy for metabolic adaptation. Autophagy is upregulated in many cancer types through tumor cell-intrinsic proliferation demands and the hypoxic and nutrient-limited tumor microenvironment (TME). Autophagy-induced breakdown products then fuel into various metabolic pathways to supply tumor cells with energy and building blocks for biosynthesis and survival. This bidirectional regulation between autophagy and tumor constitutes a vicious cycle to potentiate tumor growth and therapy resistance. In addition, the pro-tumor functions of autophagy are expanded to host, including cells in TME and distant organs. Thus, inhibition of autophagy or autophagy-mediated metabolic reprogramming may be a promising strategy for anticancer therapy. Better understanding the metabolic rewiring mechanisms of autophagy for its pro-tumor effects will provide insights into patient treatment.

Autophagy inhibition is the next step in the treatment of glioblastoma patients following the Stupp era

It has now been nearly 15 years since the last major advance in the treatment of patients with glioma. "The addition of temozolomide to radiotherapy for newly diagnosed glioblastoma resulted in a clinically meaningful and statistically significant survival benefit with minimal additional toxicity". Autophagy is primarily a survival pathway, literally self-eating, that is utilized in response to stress (such as radiation and chemotherapy), enabling clearance of effete protein aggregates and multimolecular assemblies. Promising results have been observed in patients with glioma for over a decade now when autophagy inhibition with chloroquine derivatives coupled with conventional therapy. The application of autophagy inhibitors, the role of immune cell-induced autophagy, and the potential role of novel cellular and gene therapies, should now be considered for development as part of this well-established regimen.

Redox modulation of vitagenes via plant polyphenols and vitamin D: Novel insights for chemoprevention and therapeutic interventions based on organoid technology

Polyphenols are chemopreventive through the induction of nuclear factor erythroid 2 related factor 2 (Nrf2)-mediated proteins and anti-inflammatory pathways. These pathways, encoding cytoprotective vitagenes, include heat shock proteins, such as heat shock protein 70 (Hsp70) and heme oxygenase-1 (HO-1), as well as glutathione redox system to protect against cancer initiation and progression. Phytochemicals exhibit biphasic dose responses on cancer cells, activating at low dose, signaling pathways resulting in upregulation of vitagenes, as in the case of the Nrf2 pathway upregulated by hydroxytyrosol (HT) or curcumin and NAD/NADH-sirtuin-1 activated by resveratrol. Here, the importance of vitagenes in redox stress response and autophagy mechanisms, as well as the potential use of dietary antioxidants in the prevention and treatment of multiple types of cancer are discussed. We also discuss the possible relationship between SARS-CoV-2, inflammation and cancer, exploiting innovative therapeutic approaches with HT-rich aqueous olive pulp extract (Hidrox®), a natural polyphenolic formulation, as well as the rationale of Vitamin D supplementation. Finally, we describe innovative approaches with organoids technology to study human carcinogenesis in preclinical models from basic cancer research to clinical practice, suggesting patient-derived organoids as an innovative tool to test drug toxicity and drive personalized therapy.

Targeting autophagy in disease: established and new strategies

Macroautophagy/autophagy is an evolutionarily conserved pathway responsible for clearing cytosolic aggregated proteins, damaged organelles or invading microorganisms. Dysfunctional autophagy leads to pathological accumulation of the cargo, which has been linked to a range of human diseases, including neurodegenerative diseases, infectious and autoimmune diseases and various forms of cancer. Cumulative work in animal models, application of genetic tools and pharmacologically active compounds, has suggested the potential therapeutic value of autophagy modulation in disease, as diverse as Huntington, Salmonella infection, or pancreatic cancer. Autophagy activation versus inhibition strategies are being explored, while the role of autophagy in pathophysiology is being studied in parallel. However, the progress of preclinical and clinical development of autophagy modulators has been greatly hampered by the paucity of selective pharmacological agents and biomarkers to dissect their precise impact on various forms of autophagy and cellular responses. Here, we summarize established and new strategies in autophagy-related drug discovery and indicate a path toward establishing a more efficient discovery of autophagy-selective pharmacological agents. With this knowledge at hand, modern concepts for therapeutic exploitation of autophagy might become more plausible.

Abbreviations: ALS: amyotrophic lateral sclerosis; AMPK: AMP-activated protein kinase; ATG: autophagy-related gene; AUTAC: autophagy-targeting chimera; CNS: central nervous system; CQ: chloroquine; GABARAP: gamma-aminobutyric acid type A receptor-associated protein; HCQ: hydroxychloroquine; LYTAC: lysosome targeting chimera; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NDD: neurodegenerative disease; PDAC: pancreatic ductal adenocarcinoma; PE: phosphatidylethanolamine; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol 3-phosphate; PROTAC: proteolysis-targeting chimera; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1.

Autophagy-targeted therapy to modulate age-related diseases: Success, pitfalls, and new directions

Autophagy is a critical metabolic process that supports homeostasis at a basal level and is dynamically regulated in response to various physiological and pathological processes. Autophagy has some etiologic implications that support certain pathological processes due to alterations in the lysosomal-degradative pathway. Some of the conditions related to autophagy play key roles in highly relevant human diseases, e.g., cardiovascular diseases (15.5%), malignant and other neoplasms (9.4%), and neurodegenerative conditions (3.7%). Despite advances in the discovery of new strategies to treat these age-related diseases, autophagy has emerged as a therapeutic option after preclinical and clinical studies. Here, we discuss the pitfalls and success in regulating autophagy initiation and its lysosome-dependent pathway to restore its homeostatic role and mediate therapeutic effects for cancer, neurodegenerative, and cardiac diseases. The main challenge for the development of autophagy regulators for clinical application is the lack of specificity of the repurposed drugs, due to the low pharmacological uniqueness of their target, including those that target the PI3K/AKT/mTOR and AMPK pathway. Then, future efforts must be conducted to deal with this scenery, including the disclosure of key components in the autophagy machinery that may intervene in its therapeutic regulation. Among all efforts, those focusing on the development of novel allosteric inhibitors against autophagy inducers, as well as those targeting autolysosomal function, and their integration into therapeutic regimens should remain a priority for the field.

Novel therapeutic strategies and perspectives for pancreatic cancer: Autophagy and apoptosis are key mechanisms to fight pancreatic cancer

Pancreatic cancer (PC) is the most lethal malignancy of the gastrointestinal tract. The poor prognosis of patients with PC is primarily due to lack of effective treatments against its progressive and metastatic behavior. Hence, figuring out the mechanisms underlying PC development and putting up with effective targeted therapies are of great significance to improve the prognosis of patients with PC. Apoptosis and autophagy serve to maintain tissue homoeostasis. Escaping from apoptosis or autophagy is one of the features of malignancy. PC is seriously resistant to autophagy and apoptosis, which explains its invasiveness and resistance to conventional treatment. Recently, several biological activities and pharmacological functions found in natural product extracts have been reported to inhibit PC progression. The current review focuses on understanding natural product extracts and their derivatives as one kind of novel treatments through affecting the apoptosis or autophagy in PC.

Synergistic effect of Chloroquine and Panobinostat in ovarian cancer through induction of DNA damage and inhibition of DNA repair

Ovarian cancer (OC) is the deadliest gynecologic malignancy, which is mainly due to late-stage diagnosis and chemotherapy resistance. Therefore, new and more effective treatments are urgently needed. The in vitro effects of Panobinostat (LBH), a histone deacetylase inhibitor that exerts pleiotropic antitumor effects but induces autophagy, in combination with Chloroquine (CQ), an autophagy inhibitor that avoid this cell survival mechanism, were evaluated in 4 OC cell lines. LBH and CQ inhibited ovarian cancer cell proliferation and induced apoptosis, and a strong synergistic effect was observed when combined. Deeping into their mechanisms of action we show that, in addition to autophagy modulation, treatment with CQ increased reactive oxygen species (ROS) causing DNA double strand breaks (DSBs), whereas LBH inhibited their repair by avoiding the correct recruitment of the recombinase Rad51 to DSBs. Interestingly, CQ-induced DSBs and cell death caused by CQ/LBH combination were largely abolished by the ROS scavenger N-Acetylcysteine, revealing the critical role of DSB generation in CQ/LBH-induced lethality. This role was also manifested by the synergy found when we combined CQ with Mirin, a well-known homologous recombination repair inhibitor. Altogether, our results provide a rationale for the clinical investigation of CQ/LBH combination in ovarian cancer.

Autophagy in tumour immunity and therapy

Autophagy is a regulated mechanism that removes unnecessary or dysfunctional cellular components and recycles metabolic substrates. In response to stress signals in the tumour microenvironment, the autophagy pathway is altered in tumour cells and immune cells - thereby differentially affecting tumour progression, immunity and therapy. In this Review, we summarize our current understanding of the immunologically associated roles and modes of action of the autophagy pathway in cancer progression and therapy, and discuss potential approaches targeting autophagy to enhance antitumour immunity and improve the efficacy of current cancer therapy.

Repurposing Chloroquine Against Multiple Diseases With Special Attention to SARS-CoV-2 and Associated Toxicity

Chloroquine and its derivatives have been used since ages to treat malaria and have also been approved by the FDA to treat autoimmune diseases. The drug employs pH-dependent inhibition of functioning and signalling of the endosome, lysosome and trans-Golgi network, immunomodulatory actions, inhibition of autophagy and interference with receptor binding to treat cancer and many viral diseases. The ongoing pandemic of COVID-19 has brought the whole world on the knees, seeking an urgent hunt for an anti-SARS-CoV-2 drug. Chloroquine has shown to inhibit receptor binding of the viral particles, interferes with their replication and inhibits "cytokine storm". Though multiple modes of actions have been employed by chloroquine against multiple diseases, viral diseases can provide an added advantage to establish the anti-SARS-CoV-2 mechanism, the in vitro and in vivo trials against SARS-CoV-2 have yielded mixed results. The toxicological effects and dosage optimization of chloroquine have been studied for many diseases, though it needs a proper evaluation again as chloroquine is also associated with several toxicities. Moreover, the drug is inexpensive and is readily available in many countries. Though much of the hope has been created by chloroquine and its derivatives against multiple diseases, repurposing it against SARS-CoV-2 requires large scale, collaborative, randomized and unbiased clinical trials to avoid false promises. This review summarizes the use and the mechanism of chloroquine against multiple diseases, its side-effects, mechanisms and the different clinical trials ongoing against "COVID-19".

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.