Let's talk about flux: the rising potential of autophagy rate measurements in disease.

Macroautophagy/autophagy is increasingly implicated in a variety of diseases, making it an attractive therapeutic target. However, many aspects of autophagy are not fully understood and its impact on many diseases remains debatable and context-specific. The lack of systematic and dynamic measurements in these cases is a key reason for this ambiguity. In recent years, Loos et al. 2014 and Beesabathuni et al. 2022 developed methods to quantitatively measure autophagy holistically. In this commentary, we pose some of the unresolved biological questions regarding autophagy and consider how quantitative measurements may address them. While the applications are ever-expanding, we provide specific use cases in cancer, virus infection, and mechanistic screening. We address how the rate measurements themselves are central to developing cancer therapies and present ways in which these tools can be leveraged to dissect the complexities of virus-autophagy interactions. Screening methods can be combined with rate measurements to mechanistically decipher the labyrinth of autophagy regulation in cancer and virus infection. Taken together, these approaches have the potential to illuminate the underlying mechanisms of various diseases.Abbreviation MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; R1: rate of autophagosome formation; R2: rate of autophagosome-lysosome fusion; R3: rate of autolysosome turnover.

Novel Insights into the Links between N6-Methyladenosine and Regulated Cell Death in Musculoskeletal Diseases.

Musculoskeletal diseases (MSDs), including osteoarthritis (OA), osteosarcoma (OS), multiple myeloma (MM), intervertebral disc degeneration (IDD), osteoporosis (OP), and rheumatoid arthritis (RA), present noteworthy obstacles associated with pain, disability, and impaired quality of life on a global scale. In recent years, it has become increasingly apparent that N6-methyladenosine (m6A) is a key regulator in the expression of genes in a multitude of biological processes. m6A is composed of 0.1-0.4% adenylate residues, especially at the beginning of 3'-UTR near the translation stop codon. The m6A regulator can be classified into three types, namely the "writer", "reader", and "eraser". Studies have shown that the epigenetic modulation of m6A influences mRNA processing, nuclear export, translation, and splicing. Regulated cell death (RCD) is the autonomous and orderly death of cells under genetic control to maintain the stability of the internal environment. Moreover, distorted RCDs are widely used to influence the course of various diseases and receiving increasing attention from researchers. In the past few years, increasing evidence has indicated that m6A can regulate gene expression and thus influence different RCD processes, which has a central role in the etiology and evolution of MSDs. The RCDs currently confirmed to be associated with m6A are autophagy-dependent cell death, apoptosis, necroptosis, pyroptosis, ferroptosis, immunogenic cell death, NETotic cell death and oxeiptosis. The m6A-RCD axis can regulate the inflammatory response in chondrocytes and the invasive and migratory of MM cells to bone remodeling capacity, thereby influencing the development of MSDs. This review gives a complete overview of the regulatory functions on the m6A-RCD axis across muscle, bone, and cartilage. In addition, we also discuss recent advances in the control of RCD by m6A-targeted factors and explore the clinical application prospects of therapies targeting the m6A-RCD in MSD prevention and treatment. These may provide new ideas and directions for understanding the pathophysiological mechanism of MSDs and the clinical prevention and treatment of these diseases.

Discovery of a novel small-molecule activator of SIRT3 that inhibits cell proliferation and migration by apoptosis and autophagy-dependent cell death pathways in colorectal cancer.

Colorectal cancer (CRC) is well known as a prevalent malignancy affecting the digestive tract, yet its precise etiological determinants remain to be elusive. Accordingly, identifying specific molecular targets for colorectal cancer and predicting potential malignant tumor behavior are potential strategies for therapeutic interventions. Of note, apoptosis (type I programmed cell death) has been widely reported to play a pivotal role in tumorigenesis by exerting a suppressive effect on cancer development. Moreover, autophagy-dependent cell death (type II programmed cell death) has been implicated in different types of human cancers. Thus, investigating the molecular mechanisms underlying apoptosis and autophagy-dependent cell death is paramount in treatment modalities of colorectal cancer. In this study, we uncovered that a new small-molecule activator of SIRT3, named MY-13, triggered both autophagy-dependent cell death and apoptosis by modulating the SIRT3/Hsp90/AKT signaling pathway. Consequently, this compound inhibited tumor cell proliferation and migration in RKO and HCT-116 cell lines. Moreover, we further demonstrated that the small-molecule activator significantly suppressed tumor growth in vivo. In conclusion, these findings demonstrate that the novel small-molecule activator of SIRT3 may hold a therapeutic potential as a drug candidate in colorectal cancer.

Scd1 and monounsaturated lipids are required for autophagy and survival of adipocytes.

OBJECTIVE: Exposure of adipocytes to 'cool' temperatures often found in the periphery of the body induces expression of Stearoyl-CoA Desaturase-1 (Scd1), an enzyme that converts saturated fatty acids to monounsaturated fatty acids. The goal of this study is to further investigate the roles of Scd in adipocytes. METHOD: In this study, we employed Scd1 knockout cells and mouse models, along with pharmacological Scd1 inhibition to dissect the enzyme's function in adipocyte physiology. RESULTS: Our study reveals that production of monounsaturated lipids by Scd1 is necessary for fusion of autophagosomes to lysosomes and that with a Scd1-deficiency, autophagosomes accumulate. In addition, Scd1-deficiency impairs lysosomal and autolysosomal acidification resulting in vacuole accumulation and eventual cell death. Blocking autophagosome formation or supplementation with monounsaturated fatty acids maintains vitality of Scd1-deficient adipocytes. CONCLUSION: This study demonstrates the indispensable role of Scd1 in adipocyte survival, with its inhibition in vivo triggering autophagy-dependent cell death and its depletion in vivo leading to the loss of bone marrow adipocytes.

Melanoma biology and treatment: a review of novel regulated cell death-based approaches.

The incidence of melanoma, the most lethal form of skin cancer, has increased due to ultraviolet exposure. The treatment of advanced melanoma, particularly metastatic cases, remains challenging with poor outcomes. Targeted therapies involving BRAF/MEK inhibitors and immunotherapy based on anti-PD1/anti-CTLA4 antibodies have achieved long-term survival rates of approximately 50% for patients with advanced melanoma. However, therapy resistance and inadequate treatment response continue to hinder further breakthroughs in treatments that increase survival rates. This review provides an introduction to the molecular-level pathogenesis of melanoma and offers an overview of current treatment options and their limitations. Cells can die by either accidental or regulated cell death (RCD). RCD is an orderly cell death controlled by a variety of macromolecules to maintain the stability of the internal environment. Since the uncontrolled proliferation of tumor cells requires evasion of RCD programs, inducing the RCD of melanoma cells may be a treatment strategy. This review summarizes studies on various types of nonapoptotic RCDs, such as autophagy-dependent cell death, necroptosis, ferroptosis, pyroptosis, and the recently discovered cuproptosis, in the context of melanoma. The relationships between these RCDs and melanoma are examined, and the interplay between these RCDs and immunotherapy or targeted therapy in patients with melanoma is discussed. Given the findings demonstrating melanoma cell death in response to different stimuli associated with these RCDs, the induction of RCD shows promise as an integral component of treatment strategies for melanoma.

Understanding Developmental Cell Death Using Drosophila as a Model System.

Cell death plays an essential function in organismal development, wellbeing, and ageing. Many types of cell deaths have been described in the past 30 years. Among these, apoptosis remains the most conserved type of cell death in metazoans and the most common mechanism for deleting unwanted cells. Other types of cell deaths that often play roles in specific contexts or upon pathological insults can be classed under variant forms of cell death and programmed necrosis. Studies in Drosophila have contributed significantly to the understanding and regulation of apoptosis pathways. In addition to this, Drosophila has also served as an essential model to study the genetic basis of autophagy-dependent cell death (ADCD) and other relatively rare types of context-dependent cell deaths. Here, we summarise what is known about apoptosis, ADCD, and other context-specific variant cell death pathways in Drosophila, with a focus on developmental cell death.

Jiangqi Pingxiao formula regulates dendritic cell apoptosis in an autophagy-dependent manner through the AMPK/mTOR pathway in a murine model of OVA-induced asthma.

ETHNOPHARMACOLOGICAL RELEVANCE: Allergic asthma is a recurring respiratory condition that typically manifests during childhood or adolescence. It is characterized by a dominant type II immune response triggered by the identification and capturing of inhaled allergens by dendritic cells (DCs). Jiangqi Pingxiao Formula (JQPXF), a prescription medicine used for the treatment of pediatric asthma, has been clinically proven to be both safe and effective. However, its mechanism of action in the treatment of asthma has not been fully been fully elucidated. Recent research suggests that several natural compounds have the potential to target dendritic cells (DCs) and alleviate ovalbumin (OVA)-induced asthma, which may also be found within JQPXF. AIM OF THE STUDY: This study aimed to elucidate the effect of JQPXF on OVA-induced asthma model and its molecular mechanism targeting DCs. MATERIALS AND METHODS: The main constituents of JQPXF were analyzed by ultra performance liquid chromatography (UPLC). An asthma model was established by OVA. Hematoxylin-eosin staining and measurement of respiratory function was used to evaluate the treatment effect of JQPXF on asthmatic mice. Cytokine (IL-5, IL-13 and IgE) concentrations were determined by enzyme-linked immunosorbent assay (ELISA). Flow cytometry was employed to evaluate inflammatory cell infiltration (T helper 2 cells and DCs) in vivo and DC survival in vivo and vitro. Western blot and immunofluorescence were used to verify the molecular mechanisms. RESULTS: The results suggest that JQPXF can ameliorate pathological conditions and improve lung function in asthmatic mice, as well as the Th2 cells. Treatment with JQPXF significantly reduced the number of DCs and increased the number of Propidium iodide+ (PI) DCs. Furthermore, JQPXF upregulated protein levels of the pro-apoptotic factors Cleaved-caspase-3 and Bax, while downregulating the anti-apoptotic factor Bcl-2. Simultaneously, JQPXF increased autophagy levels by facilitating p62 degradation and promoting translation from LC3B I to LC3B II of DCs in vitro, as well as reducing the integrated optical density (IOD) of p62 within the CD11c-positive area in the lung. 3-Methyladenine (3-MA) was used to block autophagic flux and the apoptotic effect of JQPXF on DCs was abolished in vitro, with the number of DCs decreased by JQPXF being reversed in vivo. We further investigated the upstream key regulator of autophagy, the AMPK/mTOR pathway, and found that JQPXF increased AMPK phosphorylation while decreasing mTOR phosphorylation levels. Additionally, we employed Compound C (CC) as an AMPK inhibitor to inhibit this signaling pathway, and our findings revealed that both autophagic flux and apoptotic levels in DCs were abolished in vitro. CONCLUSIONS: In summary, we have demonstrated that JQPXF could alleviate type II inflammation in an asthmatic model by promoting the apoptosis of DCs through an autophagy-dependent mechanism, achieved by regulating the AMPK/mTOR signaling pathway.

Targeting regulated cell death with plant natural compounds for cancer therapy: A revisited review of apoptosis, autophagy-dependent cell death, and necroptosis.

Regulated cell death (RCD) refers to programmed cell death regulated by various protein molecules, such as apoptosis, autophagy-dependent cell death, and necroptosis. Accumulating evidence has recently revealed that RCD subroutines have several links to many types of human cancer; therefore, targeting RCD with pharmacological small-molecule compounds would be a promising therapeutic strategy. Moreover, plant natural compounds, small-molecule compounds synthesized from plant sources, and their derivatives have been widely reported to regulate different RCD subroutines to improve potential cancer therapy. Thus, in this review, we focus on updating the intricate mechanisms of apoptosis, autophagy-dependent cell death, and necroptosis in cancer. Moreover, we further discuss several representative plant natural compounds and their derivatives that regulate the above-mentioned three subroutines of RCD, and their potential as candidate small-molecule drugs for the future cancer treatment.

The role of autophagic cell death in cardiac disease.

Cardiomyocytes undergo various forms of cell death during heart disease such as myocardial infarction and heart failure. Understanding the mechanisms of cell death in cardiomyocytes is one of the most fundamental issues in the treatment of heart failure. Among the several kinds of cell death mechanisms, this review will focus on autophagy-related cardiomyocyte cell death. Although autophagy plays an essential role in mediating cellular quality control mechanisms for cell survival, dysregulation of autophagy can cause cell death, referred to as autophagy-dependent cell death or type II programmed cell death. The recent discovery of autosis as a modality of autophagy-dependent cell death with unique morphological and biochemical features has allowed us to broaden our understanding of the mechanistic role of autophagy in cell death. Here, we discuss autophagy-dependent cardiomyocyte cell death, including autosis, in pathophysiological conditions of the heart.

Targeting regulated cell death (RCD) with small-molecule compounds in triple-negative breast cancer: a revisited perspective from molecular mechanisms to targeted therapies.

Triple-negative breast cancer (TNBC) is a subtype of human breast cancer with one of the worst prognoses, with no targeted therapeutic strategies currently available. Regulated cell death (RCD), also known as programmed cell death (PCD), has been widely reported to have numerous links to the progression and therapy of many types of human cancer. Of note, RCD can be divided into numerous different subroutines, including autophagy-dependent cell death, apoptosis, mitotic catastrophe, necroptosis, ferroptosis, pyroptosis and anoikis. More recently, targeting the subroutines of RCD with small-molecule compounds has been emerging as a promising therapeutic strategy, which has rapidly progressed in the treatment of TNBC. Therefore, in this review, we focus on summarizing the molecular mechanisms of the above-mentioned seven major RCD subroutines related to TNBC and the latest progress of small-molecule compounds targeting different RCD subroutines. Moreover, we further discuss the combined strategies of one drug (e.g., narciclasine) or more drugs (e.g., torin-1 combined with chloroquine) to achieve the therapeutic potential on TNBC by regulating RCD subroutines. More importantly, we demonstrate several small-molecule compounds (e.g., ONC201 and NCT03733119) by targeting the subroutines of RCD in TNBC clinical trials. Taken together, these findings will provide a clue on illuminating more actionable low-hanging-fruit druggable targets and candidate small-molecule drugs for potential RCD-related TNBC therapies.

STAT3 Enhances Sensitivity of Glioblastoma to Drug-Induced Autophagy-Dependent Cell Death.

Glioblastoma (GBM) is a devastating disease and the most common primary brain malignancy of adults with a median survival barely exceeding one year. Recent findings suggest that the antipsychotic drug pimozide triggers an autophagy-dependent, lysosomal type of cell death in GBM cells with possible implications for GBM therapy. One oncoprotein that is often overactivated in these tumors and associated with a particularly dismal prognosis is Signal Transducer and Activator of Transcription 3 (STAT3). Here, we used isogenic human and murine GBM knockout cell lines, advanced fluorescence microscopy, transcriptomic analysis and FACS-based assessment of cell viability to show that STAT3 has an underappreciated, context-dependent role in drug-induced cell death. Specifically, we demonstrate that depletion of STAT3 significantly enhances cell survival after treatment with Pimozide, suggesting that STAT3 confers a particular vulnerability to GBM. Furthermore, we show that active STAT3 has no major influence on the early steps of the autophagy pathway, but exacerbates drug-induced lysosomal membrane permeabilization (LMP) and release of cathepsins into the cytosol. Collectively, our findings support the concept of exploiting the pro-death functions of autophagy and LMP for GBM therapy and to further determine whether STAT3 can be employed as a treatment predictor for highly apoptosis-resistant, but autophagy-proficient cancers.

A Balance Between Autophagy and Other Cell Death Modalities in Cancer.

Autophagy is an intracellular self-digestive process involved in catabolic degradation of damaged proteins, and organelles, and the elimination of cellular pathogens. Initially, autophagy was considered as a prosurvival mechanism, but the following insights shed light on its prodeath function. Nowadays, autophagy is established as a crucial player in the development of various diseases through interaction with other molecular pathways within a cell. Additionally, disturbance in autophagy is one of the main pathological alterations that lead to resistance of cancer cells to treatment. These autophagy-related pathologies gave rise to the development of new therapeutic drugs. Here, we summarize the current knowledge on the autophagic role in disease pathogenesis, particularly in cancer, and the interplay between autophagy and other cell death modalities in order to combat cancer.

Targeting regulated cell death (RCD) with small-molecule compounds in cancer therapy: A revisited review of apoptosis, autophagy-dependent cell death and necroptosis.

Evasion of regulated cell death (RCD), mainly referring to apoptosis, autophagy-dependent cell death, necroptosis, and other subroutines, is one of the well-established hallmarks of cancer cells. Accumulating evidence has revealed several small-molecule compounds that target different subroutines of RCD in cancer therapy. In this review, we summarize key pathways of apoptosis, autophagy-dependent cell death and necroptosis in cancer, and describe small-molecule compounds that target these pathways and have potential as therapeutics. These inspiring findings light the way towards the discovery of more 'magic bullets' that could work individually or cooperatively to target precisely the three RCD subroutines and so improve cancer treatment.

Regulated cell death: discovery, features and implications for neurodegenerative diseases.

Regulated cell death (RCD) is a ubiquitous process in living organisms that is essential for tissue homeostasis or to restore biological balance under stress. Over the decades, various forms of RCD have been reported and are increasingly being found to involve in human pathologies and clinical outcomes. We focus on five high-profile forms of RCD, including apoptosis, pyroptosis, autophagy-dependent cell death, necroptosis and ferroptosis. Cumulative evidence supports that not only they have different features and various pathways, but also there are extensive cross-talks between modes of cell death. As the understanding of RCD pathway in evolution, development, physiology and disease continues to improve. Here we review an updated classification of RCD on the discovery and features of processes. The prominent focus will be placed on key mechanisms of RCD and its critical role in neurodegenerative disease. Video abstract.

Autophagy activation, lipotoxicity and lysosomal membrane permeabilization synergize to promote pimozide- and loperamide-induced glioma cell death.

Increasing evidence suggests that induction of lethal macroautophagy/autophagy carries potential significance for the treatment of glioblastoma (GBM). In continuation of previous work, we demonstrate that pimozide and loperamide trigger an ATG5- and ATG7 (autophagy related 5 and 7)-dependent type of cell death that is significantly reduced with cathepsin inhibitors and the lipid reactive oxygen species (ROS) scavenger α-tocopherol in MZ-54 GBM cells. Global proteomic analysis after treatment with both drugs also revealed an increase of proteins related to lipid and cholesterol metabolic processes. These changes were accompanied by a massive accumulation of cholesterol and other lipids in the lysosomal compartment, indicative of impaired lipid transport/degradation. In line with these observations, pimozide and loperamide treatment were associated with a pronounced increase of bioactive sphingolipids including ceramides, glucosylceramides and sphingoid bases measured by targeted lipidomic analysis. Furthermore, pimozide and loperamide inhibited the activity of SMPD1/ASM (sphingomyelin phosphodiesterase 1) and promoted induction of lysosomal membrane permeabilization (LMP), as well as release of CTSB (cathepsin B) into the cytosol in MZ-54 wild-type (WT) cells. Whereas LMP and cell death were significantly attenuated in ATG5 and ATG7 knockout (KO) cells, both events were enhanced by depletion of the lysophagy receptor VCP (valosin containing protein), supporting a pro-survival function of lysophagy under these conditions. Collectively, our data suggest that pimozide and loperamide-driven autophagy and lipotoxicity synergize to induce LMP and cell death. The results also support the notion that simultaneous overactivation of autophagy and induction of LMP represents a promising approach for the treatment of GBM.Abbreviations: ACD: autophagic cell death; AKT1: AKT serine/threonine kinase 1; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG14: autophagy related 14; CERS1: ceramide synthase 1; CTSB: cathepsin B; CYBB/NOX2: cytochrome b-245 beta chain; ER: endoplasmatic reticulum; FBS: fetal bovine serum; GBM: glioblastoma; GO: gene ontology; HTR7/5-HT7: 5-hydroxytryptamine receptor 7; KD: knockdown; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LAP: LC3-associated phagocytosis; LMP: lysosomal membrane permeabilization; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; RB1CC1: RB1 inducible coiled-coil 1; ROS: reactive oxygen species; RPS6: ribosomal protein S6; SMPD1/ASM: sphingomyelin phosphodiesterase 1; VCP/p97: valosin containing protein; WT: wild-type.

Organelle-specific mechanisms of drug-induced autophagy-dependent cell death.

The conserved catabolic process of autophagy is an important control mechanism that degrades cellular organelles, debris and pathogens in autolysosomes. Although autophagy primarily protects against cellular insults, nutrient starvation or oxidative stress, hyper-activation of autophagy is also believed to cause autophagy-dependent cell death (ADCD). ADCD is a caspase-independent form of programmed cell death (PCD), characterized by an over-activation of autophagy, leading to prominent self-digestion of cellular material in autolysosomes beyond the point of cell survival. ADCD plays important roles in the development of lower organisms, but also in the response of cancer cells upon exposure of specific drugs or natural compounds. Importantly, the induction of ADCD as an alternative cell death pathway is of special interest in apoptosis-resistant cancer types and serves as an attractive and potential therapeutic option. Although the mechanisms of ADCD are diverse and not yet fully understood, both non-selective (bulk) autophagy and organelle-specific types of autophagy are believed to be involved in this type of cell death. Accordingly, several ADCD-inducing drugs are known to trigger severe mitochondrial damage and endoplasmic reticulum (ER) stress, whereas the contribution of other cell organelles, like ribosomes or peroxisomes, to the control of ADCD is not well understood. In this review, we highlight the general mechanisms of ADCD and discuss the current evidence for mitochondria- and ER-specific killing mechanisms of ADCD-inducing drugs.

Identification of Annexin A2 as a key mTOR target to induce roller coaster pattern of autophagy fluctuation in stress.

Autophagy can either be cytoprotective or promote cell death in a context-dependent manner in response to stress. How autophagy leads to autophagy dependent cell death requires further clarification. In this study, we document a nonlinear roller coaster form of autophagy oscillation when cells are subjected to different stress conditions. Serum starvation induces an initial primary autophagic peak at 6 h, that helps to replenish cells with de novo fluxed nutrients, but protracted stress lead to a secondary autophagic peak around 48 h. Time kinetic studies indicate that the primary autophagic peak is reversible, whereas the secondary autophagic peak is irreversible and leads to cell death. Key players involved in different stages of autophagy including initiation, elongation and degradation during this oscillatory sequence were identified. A similar molecular pattern was intensified under apoptosis-deficient conditions. mTOR was the central molecule regulating this autophagic activity, and upon knockdown a steady increase of autophagy without any non-linear fluctuation was evident. An unbiased proteome screening approach was employed to identify the autophagy molecules potentially regulating these autophagic peaks. Our proteomics analysis has identified Annexin A2 as a stress-induced protein to implicate in autophagy fluctuation and its deficiency reduced autophagy. Moreover, we report that mTOR in its phosphorylated condition interacts with Annexin A2 to induce autophagy fluctuation by altering its cellular localization. The work highlights the molecular mechanism of a mTOR-dependent roller coaster fluctuation of autophagy and autophagy dependent cell death during prolong stress.

Parkin Promotes Mitophagic Cell Death in Adult Hippocampal Neural Stem Cells Following Insulin Withdrawal.

Regulated cell death (RCD) plays a fundamental role in human health and disease. Apoptosis is the best-studied mode of RCD, but the importance of other modes has recently been gaining attention. We have previously demonstrated that adult rat hippocampal neural stem (HCN) cells undergo autophagy-dependent cell death (ADCD) following insulin withdrawal. Here, we show that Parkin mediates mitophagy and ADCD in insulin-deprived HCN cells. Insulin withdrawal increased the amount of depolarized mitochondria and their colocalization with autophagosomes. Insulin withdrawal also upregulated both mRNA and protein levels of Parkin, gene knockout of which prevented mitophagy and ADCD. c-Jun is a transcriptional repressor of Parkin and is degraded by the proteasome following insulin withdrawal. In insulin-deprived HCN cells, Parkin is required for Ca2+ accumulation and depolarization of mitochondria at the early stages of mitophagy as well as for recognition and removal of depolarized mitochondria at later stages. In contrast to the pro-death role of Parkin during mitophagy, Parkin deletion rendered HCN cells susceptible to apoptosis, revealing distinct roles of Parkin depending on different modes of RCD. Taken together, these results indicate that Parkin is required for the induction of ADCD accompanying mitochondrial dysfunction in HCN cells following insulin withdrawal. Since impaired insulin signaling is implicated in hippocampal deficits in various neurodegenerative diseases and psychological disorders, these findings may help to understand the mechanisms underlying death of neural stem cells and develop novel therapeutic strategies aiming to improve neurogenesis and survival of neural stem cells.

Association between radiation-induced cell death and clinically relevant radioresistance.

Radiotherapy (RT) is one of the major modalities for the treatment of human cancer and has been established as an excellent local treatment for malignant tumors. However, the existence of radioresistant cells remains one of the most critical obstacles in RT. To know the characteristics of radioresistant cells, clinically relevant radioresistant (CRR) cell lines were established. CRR cells can continue to proliferate in vitro and in vivo after exposure to 2 Gy/day of X-rays for more than 30 days. Daily microscopic observation of the irradiated CRR cells has indicated that the increase in cell death is not observed within 7 days of irradiation with 10 Gy of X-rays, suggesting that cell death is involved in cellular radioresistance. Radiation-induced regulated cell death (RCD) can be classified into three categories: apoptosis, autophagy-dependent cell death and necrosis (necroptosis). This review focuses on an aspect of radiation-induced RCD that has often been neglected: the manner in which the cells are destroyed. In many studies, apoptosis is considered the primary mode of RCD in irradiated cancer cells; however, it is necessary to consider necrosis or necroptosis as one of the modes of radiation-induced RCD.