Autophagy is a process of cellular self-digestion, whereby the cell degrades subcellular materials in order to generate energy and metabolic precursors in order to prolong survival, classically under conditions of nutrient deprivation. Autophagy can also involve the degradation of damaged or aged organelles, and misfolded or damaged proteins to eliminate these components that might otherwise be deleterious to cellular survival. Consequently, autophagy has generally been considered a prosurvival response. Many, if not most chemotherapeutic drugs and radiation also promote autophagy, which is generally considered a cytoprotective response, in that its inhibition frequently promotes apoptotic cells death. Furthermore, it has been shown that conventional chemotherapeutic drugs and radiation alone rarely induce a form of autophagy that leads to cell death. However, there are multiple examples in the literature where newer chemotherapeutic agents, drug combinations or drugs in combination with radiation promote autophagic cell death. This review will describe autophagic cell death induced in breast tumor cells, lung cancer cells as well as glioblastoma, demonstrating that it cannot be concluded that stress induced autophagy is, of necessity, cytoprotective in function.
autophagy; apoptosis; radiation; chemotherapy
Autophagy and senescence share a number of characteristics, which suggests that both responses could serve to collaterally protect the cell from the toxicity of external stress such as radiation and chemotherapy and internal forms of stress such as telomere shortening and oncogene activation. Studies of oncogene activation in normal fibroblasts as well as exposure of tumor cells to chemotherapy have indicated that autophagy and senescence are closely related but not necessarily interdependent responses; specifically, interference with autophagy delays but does not abrogate senescence. The literature relating to this topic is inconclusive, with some reports appearing to be consistent with a direct relationship between autophagy and senescence and others indicative of an inverse relationship. Before this question can be resolved, additional studies will be necessary where autophagy is clearly inhibited by genetic silencing and where the temporal responses of both autophagy and senescence are monitored, preferably in cells that are intrinsically incapable of apoptosis or where apoptosis is suppressed. Understanding the nature of this relationship may provide needed insights relating to cytoprotective as well as potential cytotoxic functions of both autophagy and senescence.
Light is used to release a drug from a cell impermeable small molecule, uncloaking its cytotoxic effect on cancer cells.
Autophagy is a rapidly expanding field in the sense that our knowledge about the molecular mechanism and its connections to a wide range of physiological processes has increased substantially in the past decade. Similarly, the vocabulary associated with autophagy has grown concomitantly. This fact makes it difficult for readers, even those who work in the field, to keep up with the ever-expanding terminology associated with the various autophagy-related processes. Accordingly, we have developed a comprehensive glossary of autophagy-related terms that is meant to provide a quick reference for researchers who need a brief reminder of the regulatory effects of transcription factors or chemical agents that induce or inhibit autophagy, the function of the autophagy-related proteins, or the role of accessory machinery or structures that are associated with autophagy.
autophagy; definitions; glossary; lexicon; terms
In MCF-7 breast tumor cells, ionizing radiation promoted autophagy that was cytoprotective; pharmacological or genetic interference with autophagy induced by radiation resulted in growth suppression and/or cell killing (primarily by apoptosis). The hormonally active form of vitamin D, 1,25D3, also promoted autophagy in irradiated MCF-7 cells, sensitized the cells to radiation and suppressed the proliferative recovery that occurs after radiation alone. 1,25D3 enhanced radiosensitivity and promoted autophagy in MCF-7 cells that overexpress Her-2/neu as well as in p53 mutant Hs578t breast tumor cells. In contrast, 1,25D3 failed to alter radiosensitivity or promote autophagy in the BT474 breast tumor cell line with low-level expression of the vitamin D receptor. Enhancement of MCF-7 cell sensitivity to radiation by 1,25D3 was not attenuated by a genetic block to autophagy due largely to the promotion of apoptosis via the collateral suppression of protective autophagy. However, MCF-7 cells were protected from the combination of 1,25D3 with radiation using a concentration of chloroquine that produced minimal sensitization to radiation alone. The current studies are consistent with the premise that while autophagy mediates a cytoprotective function in irradiated breast tumor cells, promotion of autophagy can also confer radiosensitivity by vitamin D (1,25D3). As both cytoprotective and cytotoxic autophagy can apparently be expressed in the same experimental system in response to radiation, this type of model could be utilized to distinguish biochemical, molecular and/or functional differences in these dual functions of autophagy.
Apoptosis; autophagy; breast cancer; ionizing radiation; vitamin D3
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
LC3; autolysosome; autophagosome; flux; lysosome; phagophore; stress; vacuole
The antineoplastic efficacy of anthracyclines is limited by their cardiac toxicity. In this study, we evaluated the toxicity of doxorubicin, non-pegylated liposomal-delivered doxorubicin, and epirubicin in HL-1 adult cardiomyocytes in culture as well as in the mouse in vivo.
The cardiomyocytes were incubated with the three anthracyclines (1 µM) to assess reactive oxygen generation, DNA damage and apoptotic cell death. CF-1 mice (10/group) received doxorubicin, epirubicin or non-pegylated liposomal-doxorubicin (10 mg/kg) and cardiac function was monitored by Doppler echocardiography to measure left ventricular ejection fraction (LVEF), heart rate (HR) and cardiac output (CO) both prior to and 10 days after drug treatment.
In HL-1 cells, non-pegylated liposomal-doxorubicin generated significantly less reactive oxygen species (ROS), as well as less DNA damage and apoptosis activation when compared with doxorubicin and epirubicin. Cultured breast tumor cells showed similar sensitivity to the three anthracyclines. In the healthy mouse, non-pegylated liposomal doxorubicin showed a minimal and non-significant decrease in LVEF with no change in HR or CO, compared to doxorubicin and epirubicin.
This study provides evidence for reduced cardiac toxicity of non-pegylated-liposomal doxorubicin characterized by attenuation of ROS generation, DNA damage and apoptosis in comparison to epirubicin and doxorubicin.
The study of autophagy is rapidly expanding, and our knowledge of the molecular mechanism and its connections to a wide range of physiological processes has increased substantially in the past decade. The vocabulary associated with autophagy has grown concomitantly. In fact, it is difficult for readers—even those who work in the field—to keep up with the ever-expanding terminology associated with the various autophagy-related processes. Accordingly, we have developed a comprehensive glossary of autophagy-related terms that is meant to provide a quick reference for researchers who need a brief reminder of the regulatory effects of transcription factors and chemical agents that induce or inhibit autophagy, the function of the autophagy-related proteins, and the roles of accessory components and structures that are associated with autophagy.
autophagy; lysosome; mitophagy; pexophagy; stress; vacuole
Calcitriol or 1,25 dihydroxy vitamin D3, the hormonally active form of vitamin D, as well as vitamin D analogs, have been shown to increase sensitivity to ionizing radiation in breast tumor cells. The current studies indicate that the combination of 1,25 dihydroxy vitamin D3 with radiation appears to kill p53 wild type, estrogen receptor positive ZR-75-1 breast tumor cells through autophagy. Minimal apoptosis was observed based on cell morphology by DAPI and TUNEL staining, Annexin/PI analysis, Caspase-3 and PARP cleavage as well as cell cycle analysis. Induction of autophagy was indicated by increased acridine orange staining, RFP-LC3 redistribution and detection of autophagic vesicles by electron microscopy, while autophagic flux was monitored based on p62 degradation. The autophagy inhibitors, chloroquine and Bafilomycin A1, as well as genetic suppression of the autophagic signaling proteins Atg5 or Atg 7 attenuated the impact of the combination treatment of 1,25 D3 with radiation. In contrast to autophagy mediating the effects of the combination treatment, the autophagy induced by radiation alone was apparently cytoprotective in that either pharmacological or genetic inhibition increased sensitivity to radiation. These studies support the potential utility of vitamin D for improving the impact of radiation for breast cancer therapy, support the feasibility of combining chloroquine with radiation for the treatment of breast cancer and demonstrate the existence of an “autophagic switch” from cytoprotective autophagy with radiation alone to cytotoxic autophagy with the 1, 25 D3 – radiation combination.
Breast cancer; vitamin D; radiation; autophagy; chloroquine
Accumulating evidence indicates that the chemokine receptor CCR5 and the chemokine CCL5 may be involved in the proliferation and metastasis of prostate cancer. Consequently, chemokine receptor CCR5 antagonists could potentially act as anti prostate cancer agents. As the first natural product CCR5 antagonist, anibamine provides a novel chemical structural skeleton compared with other known antagonists identified through high-throughput screening. Our studies demonstrate that anibamine produces significant inhibition of prostate cancer cell proliferation at micromolar to submicromolar concentrations as well as suppressing adhesion and invasion of the highly metastatic M12 prostate cancer cell line. Preliminary in vivo studies indicate that anibamine also inhibits prostate tumor growth in mice. These findings indicate that anibamine may prove to be a novel lead compound for the development of prostate cancer therapeutic agents.
chemokine receptor CCR5; antagonist; anibamine; prostate cancer
JG-03-14, a novel tetrasubstituted pyrrole with microtubule-depolymerizing and anti-proliferative activities, was tested for its effect on endothelial cell (EC) functions in vitro. JG-03-14 was a potent inhibitor of EC vessel-like tube formation on extracellular matrix (IC50 of 40 nM) and caused the involution of established vessels, potential anti-angiogenic and vascular-disrupting activities, respectively. These actions were not due to the inhibition of EC proliferation or to the induction of apoptosis by JG-03-14. While similar effects were observed with the microtubule-depolymerizing and vascular-disrupting drug combretastatin-A4 (CoA4), JG-03-14 had a more selective effect on tube formation, relative to its cytotoxic actions, than did CoA4. Potential molecular mechanisms for JG-03-14’s anti-vascular actions were explored. In contrast to the taxanes, which also have anti-vascular actions, JG-03-14 did not disrupt focal adhesion formation or block VEGF-induced phosphorylation of focal adhesion kinase. It did, however, inhibit VEGF-induced phosphorylation of VE-cadherin and reduce the association of β-catenin with VE-cadherin. It caused cell retraction, intercellular gaps, and abnormally elongated adherens junctions at low concentrations, and prominent, but reversible, plasma membrane blebbing at higher concentrations. These results suggest that JG-03-14 may affect vascular morphogenesis by disrupting the interaction of adjacent endothelial cells, possibly as a consequence of effects on VE-cadherin, β-catenin, and/or actin. They also provide the first report of anti-vascular activity for this class of compounds.
JG-03-14; Microtubule-binding drugs; Angiogenesis inhibitors; Vascular-disrupting drugs; VE-cadherin
Cisplatin is one of the primary drugs utilized in the treatment of ovarian cancer. However, despite the initial effectiveness of chemotherapy in suppressing this disease, drug resistance almost invariably develops and cures are relatively rare. While it is generally thought that only compounds of the cis geometry express antitumor activity, a number of transplatinum derivates have shown preclinical promise. The current work investigates the influence of transplanaramine (TPA) compounds of structure trans-[Pt (O2CR)2 (L) (L′)], (L=NH3, L′= pyridine, quinoline, isoquinoline; L = L′ = pyridine; R = H, CH3, CH2OH etc.) (with a focus on the contribution of the carboxylate leaving group to drug action) on growth and viability of A2780 human ovarian carcinoma cells as well as their putative mechanism(s) of cytotoxicity. The compounds, as a class, induce cell death through caspase-dependent apoptosis, with activation of both caspase 3 and caspase 9 and concomitant PARP cleavage. The trans-platinum compounds tested show induction of p53 as well as time dependent γH2AX induction, consistent with the promotion of DNA lesions. trans-[Pt(O2CH)2(NH3)(pyr)] can be shown to promote significant DNA strand breaks and DNA interstrand cross linking. The enhanced cytotoxicity of trans-[Pt(O2CH)2(NH3)(pyr)] compared to its isostructural -O2CCH3 and -O2CCH2OH analogs may be a consequence of its accelerated cellular accumulation. increased hydrolytic activation, interstrand crosslinking and abortive efforts by the cell to repair the cross linked DNA.
Research in autophagy continues to accelerate,1 and as a result many new scientists are entering the field. Accordingly, it is important to establish a standard set of criteria for monitoring macroautophagy in different organisms. Recent reviews have described the range of assays that have been used for this purpose.2,3 There are many useful and convenient methods that can be used to monitor macroautophagy in yeast, but relatively few in other model systems, and there is much confusion regarding acceptable methods to measure macroautophagy in higher eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers of autophagosomes versus those that measure flux through the autophagy pathway; thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from fully functional autophagy that includes delivery to, and degradation within, lysosomes (in most higher eukaryotes) or the vacuole (in plants and fungi). Here, we present a set of guidelines for the selection and interpretation of the methods that can be used by investigators who are attempting to examine macroautophagy and related processes, as well as by reviewers who need to provide realistic and reasonable critiques of papers that investigate these processes. This set of guidelines is not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to verify an autophagic response.
autolysosome; autophagosome; flux; lysosome; phagophore; stress; vacuole
Compounds that bind at the colchicine site of tubulin have drawn considerable attention with studies indicating that these agents suppress microtubule dynamics and inhibit tubulin polymerization. Data for eighteen polysubstituted pyrrole compounds are reported, including antiproliferative activity against human MDA-MB-435 cells and calculated free energies of binding following docking the compounds into models of αβ-tubulin. These docking calculations coupled with HINT interaction analyses are able to represent the complex structures and the binding modes of inhibitors such that calculated and measured free energies of binding correlate with an r2 of 0.76. Structural analysis of the binding pocket identifies important intermolecular contacts that mediate binding. As seen experimentally, the complex with JG-03-14 (3,5-dibromo-4-(3,4-dimethoxyphenyl)-1H-pyrrole-2- carboxylic acid ethyl ester) is the most stable. These results illuminate the binding process and should be valuable in the design of new pyrrole-based colchicine site inhibitors as these compounds have very accessible syntheses.
Anti-tubulin; cytotoxicity; HINT; molecular docking; pyrroles
JG-03-14, a substituted pyrrole that inhibits microtubule polymerization, was screened against MCF-7 (p53 wild type), MDA-MB 231 (p53 mutant), MCF-7/caspase 3 and MCF-7/ADR (multidrug resistant) breast tumor cell lines. Cell viability and growth inhibition were assessed by the crystal violet dye assay. Apoptosis was evaluated by the TUNEL assay, cell cycle distribution by flow cytometry, autophagy by acridine orange staining of vesicle formation, and senescence based on β-galactosidase staining and cell morphology. Our studies indicate that exposure to JG-03-14, at a concentration of 500 nM, induces time dependent cell death in the MCF-7 and MDA-MB 231 cell lines. In MCF-7 cells, a residual surviving cell population was found to be senescent; in contrast, there was no surviving senescent population in treated MDA-MB 231 cells. No proliferative recovery was detected over a period of 15 days post-treatment in either cell line. Both the TUNEL assay and FLOW cytometry indicated a relatively limited degree of apoptosis (< 10%) in response to drug treatment in MCF-7 cells with more extensive apoptosis (but < 20%) in MDA-MB231 cells; acidic vacuole formation indicative of autophagic cell death was relatively extensive in both MCF-7 and MDA-MB231 cells. In addition, JG-03-14 induced the formation of a large hyperdiploid cell population in MDA-MB231 cells. JG-03-14 also demonstrated pronounced anti-proliferative activity in MCF-7/caspase 3 cells and in the MCF-7/ADR cell line. The observation that JG-03-14 promotes autophagic cell death and also retains activity in tumor cells expressing the multidrug resistance pump indicates that novel microtubule poisons of the substituted pyrroles class may hold promise in the treatment of breast cancer.