Targeting the prodeath and prosurvival functions of autophagy as novel therapeutic strategies in cancer

Autophagy regulates colistin-induced apoptosis in PC-12 cells

Colistin is a cyclic cationic polypeptide antibiotic with activity against multidrug-resistant Gram-negative bacteria. Our recent study demonstrated that colistin induces apoptosis in primary chick cortex neurons and PC-12 cells. Although apoptosis and autophagy have different impacts on cell fate, there is a complex interaction between them. Autophagy plays an important role as a homeostasis regulator by removing excessive or unnecessary proteins and damaged organelles. The aim of the present study was to investigate the modulation of autophagy and apoptosis regulation in PC-12 cells in response to colistin treatment. PC-12 cells were exposed to colistin (125 to 250 μg/ml), and autophagy was detected by visualization of monodansylcadaverine (MDC)-labeled vacuoles, LC3 (microtubule-associated protein 1 light chain 3) immunofluorescence microscopic examination, and Western blotting. Apoptosis was measured by flow cytometry, Hoechst 33258 staining, and Western blotting. Autophagosomes were observed after treatment with colistin for 12 h, and the levels of LC3-II gene expression were determined; observation and protein levels both indicated that colistin induced a high level of autophagy. Colistin treatment also led to apoptosis in PC-12 cells, and the level of caspase-3 expression increased over the 24-h period. Pretreatment of cells with 3-methyladenine (3-MA) increased colistin toxicity in PC-12 cells remarkably. However, rapamycin treatment significantly increased the expression levels of LC3-II and beclin 1 and decreased the rate of apoptosis of PC-12 cells. Our results demonstrate that colistin induced autophagy and apoptosis in PC-12 cells and that the latter was affected by the regulation of autophagy. It is very likely that autophagy plays a protective role in the reduction of colistin-induced cytotoxicity in neurons.

Arsenic trioxide inhibits growth of human chondrosarcoma cells through G2/M arrest and apoptosis as well as autophagy

It has been demonstrated that Gli1 is expressed in chondrosarcoma but not in the normal articular cartilage tissues. Downregulating Gli1 by small interfering RNA inhibited chondrosarcoma cells growth. Arsenic trioxide (ATO) has been demonstrated to suppress human cancer cell growth by targeting Gli1. The aim of this study was to investigate the effect of ATO on antineoplastic capability of chondrosarcoma cells. We found that ATO inhibited the growth of chondrosarcoma cells in dose-dependent and time-dependent manners via MTT and colony formation assays. In addition, ATO treatment induced apoptosis and promoted G2/M phase arrest in SW1353 cells as analyzed by flow cytometry assays and Western blotting. Furthermore, we observed that ATO also triggered autophagy by regulating mammalian target of rapamycin (mTOR) phosphorylation. Finally, we found that ATO-mediated cell death could be averted by autophagy inhibitor. Taken together, the current study suggested that ATO had therapeutic efficacy in human chondrosarcoma cells through the promotion of G2/M arrest and induction of both apoptosis as well as autophagy. ATO administration could be a novel therapeutic strategy for treating chondrosarcomas.

Defective autophagosome formation in p53-null colorectal cancer reinforces crocin-induced apoptosis

Crocin, a bioactive molecule of saffron, inhibited proliferation of both HCT116 wild-type and HCT116 p53(-/-) cell lines at a concentration of 10 mM. Flow cytometric analysis of cell cycle distribution revealed that there was an accumulation of HCT116 wild-type cells in G1 (55.9%, 56.1%) compared to the control (30.4%) after 24 and 48 h of crocin treatment, respectively. However, crocin induced only mild G2 arrest in HCT116 p53(-/-) after 24 h. Crocin induced inefficient autophagy in HCT116 p53(-/-) cells, where crocin induced the formation of LC3-II, which was combined with a decrease in the protein levels of Beclin 1 and Atg7 and no clear p62 degradation. Autophagosome formation was not detected in HCT116 p53(-/-) after crocin treatment predicting a nonfunctional autophagosome formation. There was a significant increase of p62 after treating the cells with Bafilomycin A1 (Baf) and crocin compared to crocin exposure alone. Annexin V staining showed that Baf-pretreatment enhanced the induction of apoptosis in HCT116 wild-type cells. Baf-exposed HCT116 p53(-/-) cells did not, however, show any enhancement of apoptosis induction despite an increase in the DNA damage-sensor accumulation, γH2AX indicating that crocin induced an autophagy-independent classical programmed cell death.

Development of autophagy inducers in clinical medicine

Defects in autophagy have been linked to a wide range of medical illnesses, including cancer as well as infectious, neurodegenerative, inflammatory, and metabolic diseases. These observations have led to the hypothesis that autophagy inducers may prevent or treat certain clinical conditions. Lifestyle and nutritional factors, such as exercise and caloric restriction, may exert their known health benefits through the autophagy pathway. Several currently available FDA-approved drugs have been shown to enhance autophagy, and this autophagy-enhancing action may be repurposed for use in novel clinical indications. The development of new drugs that are designed to be more selective inducers of autophagy function in target organs is expected to maximize clinical benefits while minimizing toxicity. This Review summarizes the rationale and current approaches for developing autophagy inducers in medicine, the factors to be considered in defining disease targets for such therapy, and the potential benefits of such treatment for human health.

Combination of microRNA therapeutics with small-molecule anticancer drugs: mechanism of action and co-delivery nanocarriers

MicroRNAs (miRNAs) regulate multiple molecular pathways vital for the hallmarks of cancer with a high degree of biochemical specificity and potency. By restoring tumor suppressive miRNAs or ablating oncomiRs, miRNA-based therapies can sensitize cancer cells to conventional cytotoxins and the molecularly targeted drugs by promoting apoptosis and autophagy, reverting epithelial-to-mesenchymal transition, suppressing tumor angiogenesis, and downregulating efflux transporters. The development of miRNA-based therapeutics in combination with small-molecule anticancer drugs provides an unprecedented opportunity to counteract chemoresistance and improve treatment outcome in a broad range of human cancers. This review summarizes the mechanisms and advantages for the combination therapies involving miRNAs and small-molecule drugs, as well as the recent advances in the co-delivery nanocarriers for these agents.

Forkhead box protein O3 transcription factor negatively regulates autophagy in human cancer cells by inhibiting forkhead box protein O1 expression and cytosolic accumulation

FoxO proteins are important regulators in cellular metabolism and are recognized to be nodes in multiple signaling pathways, most notably those involving PI3K/AKT and mTOR. FoxO proteins primarily function as transcription factors, but recent study suggests that cytosolic FoxO1 participates in the regulation of autophagy. In the current study, we find that cytosolic FoxO1 indeed stimulates cellular autophagy in multiple cancer cell lines, and that it regulates not only basal autophagy but also that induced by rapamycin and that in response to nutrient deprivation. These findings illustrate the importance of FoxO1 in cell metabolism regulation independent of its transcription factor function. In contrast to FoxO1, we find the closely related FoxO3a is a negative regulator of autophagy in multiple cancer cell lines, a previously unrecognized function for this protein, different from its function in benign fibroblast and muscle cells. The induction of autophagy by the knockdown of FoxO3a was found not to be mediated through the suppression of mTORC1 signaling; rather, the regulatory role of FoxO3a on autophagy was determined to be through its ability to transcriptionally suppress FoxO1. This complicated interplay of FoxO1 and FoxO3a suggests a complex checks- and balances-relationship between FoxO3a and FoxO1 in regulating autophagy and cell metabolism.

Modulation of induced cytotoxicity of doxorubicin by using apoferritin and liposomal cages

Doxorubicin is an effective chemotherapeutic drug, however, its toxicity is a significant limitation in therapy. Encapsulation of doxorubicin inside liposomes or ferritin cages decreases cardiotoxicity while maintaining anticancer potency. We synthesized novel apoferritin- and liposome-encapsulated forms of doxorubicin (“Apodox” and “lip-8-dox”) and compared its toxicity with doxorubicin and Myocet on prostate cell lines. Three different prostatic cell lines PNT1A, 22Rv1, and LNCaP were chosen. The toxicity of the modified doxorubicin forms was compared to conventional doxorubicin using the MTT assay, real-time cell impedance-based cell growth method (RTCA), and flow cytometry. The efficiency of doxorubicin entrapment was 56% in apoferritin cages and 42% in the liposome carrier. The accuracy of the RTCA system was verified by flow-cytometric analysis of cell viability. The doxorubicin half maximal inhibition concentrations (IC₅₀) were determined as 170.5, 234.0, and 169.0 nM for PNT1A, 22Rv1, and LNCaP, respectively by RTCA. Lip8-dox is less toxic on the non-tumor cell line PNT1A compared to doxorubicin, while still maintaining the toxicity to tumorous cell lines similar to doxorubicin or epirubicin (IC₅₀ = 2076.7 nM for PNT1A vs. 935.3 and 729.0 nM for 22Rv1 and LNCaP). Apodox IC₅₀ was determined as follows: 603.1, 1344.2, and 931.2 nM for PNT1A, 22Rv1, and LNCaP.

Immunotherapy targeting folate receptor induces cell death associated with autophagy in ovarian cancer

PURPOSE

Cancer cells are highly dependent on folate metabolism, making them susceptible to drugs that inhibit folate receptor activities. Targeting overexpressed folate receptor alpha (FRα) in cancer cells offers a therapeutic opportunity. We investigated the functional mechanisms of MORAB-003 (farletuzumab), a humanized mAb against FRα, in ovarian cancer models.

EXPERIMENTAL DESIGN

We first examined FRα expression in an array of human ovarian cancer cell lines and then assessed the in vivo effect of MORAB-003 on tumor growth and progression in several orthotopic mouse models of ovarian cancer derived from these cell lines. Molecular mechanisms of tumor cell death induced by MORAB-003 were investigated by cDNA and protein expression profiling analysis. Mechanistic studies were performed to determine the role of autophagy in MORAB-003-induced cell death.

RESULTS

MORAB-003 significantly decreased tumor growth in the high-FRα IGROV1 and SKOV3ip1 models but not in the low-FRα A2780 model. MORAB-003 reduced proliferation, but had no significant effect on apoptosis. Protein expression and cDNA microarray analyses showed that MORAB-003 regulated an array of autophagy-related genes. It also significantly increased expression of LC3 isoform II and enriched autophagic vacuolization. Blocking autophagy with hydroxychloroquine or bafilomycin A1 reversed the growth inhibition induced by MORAB-003. In addition, alteration of FOLR1 gene copy number significantly correlated with shorter disease-free survival in patients with ovarian serous cancer.

CONCLUSIONS

MORAB-003 displays prominent antitumor activity in ovarian cancer models expressing FRα at high levels. Blockade of folate receptor by MORAB-003 induced sustained autophagy and suppressed cell proliferation.

Bortezomib enhances cancer cell death by blocking the autophagic flux through stimulating ERK phosphorylation

The antitumor activity of an inhibitor of 26S proteasome bortezomib (Velcade) has been observed in various malignancies, including colon cancer, prostate cancer, breast cancer, and ovarian cancer. Bortezomib has been proposed to stimulate autophagy, but scientific observations did not always support this. Interactions between ERK activity and autophagy are complex and not completely clear. Autophagy proteins have recently been shown to regulate the functions of ERK, and ERK activation has been found to induce autophagy. On the other hand, sustained activation of ERK has also been shown to inhibit the maturation step of the autophagy process. In this study, we sought to identify the mechanism of autophagy regulation in cancer cells treated with bortezomib. Our results indicate that bortezomib blocked the autophagic flux without inhibiting the fusion of the autophagosome and lysosome. In ovarian cancer, as well as endometrial cancer and hepatocellular carcinoma cells, bortezomib inhibited protein degradation in lysosomes by suppressing cathepsins, which requires the participation of ERK phosphorylation, but not JNK or p38. Our findings that ERK phosphorylation reduced cathepsins further explain how ERK phosphorylation inhibits the autophagic flux. In conclusion, bortezomib may induce ERK phosphorylation to suppress cathepsin B and inhibit the catalytic process of autophagy in ovarian cancer and other solid tumors. The inhibition of cisplatin-induced autophagy by bortezomib can enhance chemotherapy efficacy in ovarian cancer. As we also found that bortezomib blocks the autophagic flux in other cancers, the synergistic cytotoxic effect of bortezomib by abolishing chemotherapy-related autophagy may help us develop strategies of combination therapies for multiple cancers.

Regulation of autophagy by polyphenolic compounds as a potential therapeutic strategy for cancer

Autophagy, a lysosomal degradation pathway for cellular constituents and organelles, is an adaptive and essential process required for cellular homeostasis. Although autophagy functions as a survival mechanism in response to cellular stressors such as nutrient or growth factor deprivation, it can also lead to a non-apoptotic form of programmed cell death (PCD) called autophagy-induced cell death or autophagy-associated cell death (type II PCD). Current evidence suggests that cell death through autophagy can be induced as an alternative to apoptosis (type I PCD), with therapeutic purpose in cancer cells that are resistant to apoptosis. Thus, modulating autophagy is of great interest in cancer research and therapy. Natural polyphenolic compounds that are present in our diet, such as rottlerin, genistein, quercetin, curcumin, and resveratrol, can trigger type II PCD via various mechanisms through the canonical (Beclin-1 dependent) and non-canonical (Beclin-1 independent) routes of autophagy. The capacity of these compounds to provide a means of cancer cell death that enhances the effects of standard therapies should be taken into consideration for designing novel therapeutic strategies. This review focuses on the autophagy- and cell death-inducing effects of these polyphenolic compounds in cancer.

Autophagy in acute leukemias: a double-edged sword with important therapeutic implications

Macroautophagy, usually referred to as autophagy, is a degradative pathway wherein cytoplasmatic components such as aggregated/misfolded proteins and organelles are engulfed within double-membrane vesicles (autophagosomes) and then delivered to lysosomes for degradation. Autophagy plays an important role in the regulation of numerous physiological functions, including hematopoiesis, through elimination of aggregated/misfolded proteins, and damaged/superfluous organelles. The catabolic products of autophagy (amino acids, fatty acids, nucleotides) are released into the cytosol from autophagolysosomes and recycled into bio-energetic pathways. Therefore, autophagy allows cells to survive starvation and other unfavorable conditions, including hypoxia, heat shock, and microbial pathogens. Nevertheless, depending upon the cell context and functional status, autophagy can also serve as a death mechanism. The cohort of proteins that constitute the autophagy machinery function in a complex, multistep biochemical pathway which has been partially identified over the past decade. Dysregulation of autophagy may contribute to the development of several disorders, including acute leukemias. In this kind of hematologic malignancies, autophagy can either act as a chemo-resistance mechanism or have tumor suppressive functions, depending on the context. Therefore, strategies exploiting autophagy, either for activating or inhibiting it, could find a broad application for innovative treatment of acute leukemias and could significantly contribute to improved clinical outcomes. These aspects are discussed here after a brief introduction to the autophagic molecular machinery and its roles in hematopoiesis.

N3-substituted temozolomide analogs overcome methylguanine-DNA methyltransferase and mismatch repair precipitating apoptotic and autophagic cancer cell death

Glioblastoma multiforme (GBM) treatment includes temozolomide (TMZ) chemotherapy. O6-Methylguanine lesions are repaired by methylguanine-DNA methyltransferase (MGMT). Response to TMZ requires low MGMT and functional mismatch repair (MMR); resistance, conferred by MGMT or MMR deficiency, represents a barrier to successful treatment. TMZ analogs were synthesized, substituting N3-methyl with propargyl (1) or sulfoxide (2). MTT assays were conducted in SNB19 and U373 isogenic glioma cell lines (V = vector control; M = MGMT-transfected). TMZ potency was reduced >5-fold in SNB19M and U373M cells; in contrast, MGMT-expressing cells were equisensitive as vector controls to analogs 1 and 2 . GI50 values <50 μM of analogs 1 or 2 were detected in V cells possessing acquired TMZ resistance: SNB19VR (hMSH6 loss) and U373VR (MGMT upregulation). Analogs 1 and 2 inhibited MMR-deficient colorectal carcinoma cell growth (irrespective of p53); G2/M cell cycle arrest preceded apoptosis. γH2AX foci inferred the generation of DNA double-strand breaks by analogs 1 and 2 . Acridine orange-stained vesicles, intracellular punctate GFP-LC3 protein and double-membraned autophagosomes indicate that TMZ, 1 and 2 induce autophagy in apoptotis-resistant GBM cells. Analogs 1 and 2 elicit in vitro antitumor activity irrespective of MGMT, MMR and p53. Such imidazotetrazines may treat MGMT+ GBM and possess broader spectrum activity causing apoptosis and autophagy in malignancies which evade apoptosis.

Autophagy is modulated in human neuroblastoma cells through direct exposition to low frequency electromagnetic fields

In neurogenerative diseases, comprising Alzheimer's (AD), functional alteration in autophagy is considered one of the pathological hallmarks and a promising therapeutic target. Epidemiological investigations on the possible causes undergoing these diseases have suggested that electromagnetic fields (EMF) exposition can contribute to their etiology. On the other hand, EMF have therapeutic implications in reactivating neuronal functionality. To partly clarify this dualism, the effect of low-frequency EMF (LF-EMF) on the modulation of autophagy was investigated in human neuroblastoma SH-SY5Y cells, which were also subsequently exposed to Aβ peptides, key players in AD. The results primarily point that LF-EMF induce a significant reduction of microRNA 30a (miR-30a) expression with a concomitant increase of Beclin1 transcript (BECN1) and its corresponding protein. Furthermore, LF-EMF counteract the induced miR-30a up-regulation in the same cells transfected with miR-30a mimic precursor molecules and, on the other side, rescue Beclin1 expression after BECN1 siRNA treatment. The expression of autophagy-related markers (ATG7 and LC3B-II) as well as the dynamics of autophagosome formation were also visualized after LF-EMF exposition. Finally, different protocols of repeated LF-EMF treatments were assayed to contrast the effects of Aβ peptides in vitro administration. Overall, this research demonstrates, for the first time, that specific LF-EMF treatments can modulate in vitro the expression of a microRNA sequence, which in turn affects autophagy via Beclin1 expression. Taking into account the pivotal role of autophagy in the clearance of protein aggregates within the cells, our results indicate a potential cytoprotective effect exerted by LF-EMF in neurodegenerative diseases such as AD. J. Cell. Physiol. 229: 1776-1786, 2014. © 2014 Wiley Periodicals, Inc.

Transient overexpression of Werner protein rescues starvation induced autophagy in Werner syndrome cells

Reduced autophagy may be associated with normal and pathological aging. Here we report a link between autophagy and Werner protein (WRNp), mutated in Werner syndrome, the human premature aging Werner syndrome (WS). WRN mutant fibroblast AG11395 and AG05229 respond weakly to starvation induced autophagy compared to normal cells. While the fusion of phagosomes with lysosome is normal, WS cells contain fewer autophagy vacuoles. Cellular starvation autophagy in WS cells is restored after transfection with full length WRN. Further, siRNA mediated silencing of WRN in the normal fibroblast cell line WI-38 results in decreased autophagy and altered expression of autophagy related proteins. Thus, our observations suggest that WRN may have a role in controlling autophagy and hereby cellular maintenance.

The importance of autophagy regulation in breast cancer development and treatment

Breast cancer (BC) is a potentially life-threatening malignant tumor that still causes high mortality among women. One of the mechanisms through which cancer development could be controlled is autophagy. This process exerts different effects during the stages of cancer initiation and progression due to the occurring superimposition of signaling pathways of autophagy and carcinogenesis. Chronic inhibition of autophagy or autophagy deficiency promotes cancer, due to instability of the genome and defective cell growth and as a result of cell stress. However, increased induction of autophagy can become a mechanism which allows tumor cells to survive the conditions of hypoxia, acidosis, or chemotherapy. Therefore, in the development of cancer, autophagy is regarded as a double-edged sword. Determination of the molecular mechanisms underlying autophagy regulation and its role in tumorigenesis is an essential component of modern anticancer strategies. Results of scientific studies show that inhibition of autophagy may enhance the effectiveness of currently used anticancer drugs and other therapies (like radiotherapy). However, in some cases, the promotion of autophagy can induce death and, hence, elimination of the cancer cells and reduction of tumor size. This review summarizes the current knowledge on autophagy regulation in BC and up-to-date anticancer strategies correlated with autophagy.

A novel functional interplay between Progesterone Receptor-B and PTEN, via AKT, modulates autophagy in breast cancer cells

The tumour suppressor activity of the phosphatase and tensin homologue on chromosome 10 (PTEN) is subject of intense investigative efforts, although limited information on its regulation in breast cancer is available. Herein, we report that, in breast cancer cells, progesterone (OHPg), through its cognate receptor PR-B, positively modulates PTEN expression by inducing its mRNA and protein levels, and increasing PTEN-promoter activity. The OHPg-dependent up-regulation of PTEN gene activity requires binding of the PR-B to an Sp1-rich region within the PTEN gene promoter. Indeed, ChIP and EMSA analyses showed that OHPg treatment induced the occupancy of PTEN promoter by PR and Sp1 together with transcriptional coactivators such as SRC1 and CBP. PR-B isoform knockdown abolished the complex formation indicating its specific involvement. The OHPg/PR-B dependent induction of PTEN causes the down-regulation of PI3K/AKT signal, switching on the autophagy process through an enhanced expression of UVRAG and leading to a reduced cell survival. Altogether these findings highlight a novel functional connection between OHPg/PR-B and tumour suppressor pathways in breast cancer.

Monepantel induces autophagy in human ovarian cancer cells through disruption of the mTOR/p70S6K signalling pathway

We have recently shown that the novel anthelmintic drug monepantel (MPL) inhibits growth, proliferation and colony formation, arrests the cell cycle and induces cleavage of PARP-1 in ovarian cancer cell lines. Here we report on the mechanism behind the anticancer properties of MPL. The cytotoxic effect of MPL on ovarian cancer cells (OVCAR-3 and A2780) was investigated employing a panel of tests used for the detection of apoptosis and autophagy. Apoptosis and autophagy were defined by caspase activity, DNA-laddering, Annexin-V and acridine orange (AO) staining. Autophagy markers such as LC3B, SQSTM1/p62 and mammalian target of rapamycin (mTOR) pathway related proteins were assessed by western blotting and ELISA techniques. MPL did not activate caspases 3 or 8, nor did it alter the percentage of Annexin V positive stained cells. Failure to cause DNA laddering and the inability of z-VAD-fmk to block the MPL antiproliferative effects led to the ruling out of apoptosis as the mechanism behind MPL-induced cell death. On the other hand, accumulation of acidic vacuoles with distinct chromatin morphology and an increase in punctuate localization of green fluorescent protein-LC3B, and MPL-induced changes in the expression of SQSTM1/p62 were all indicative of MPL-induced autophagy. Consistent with this, we found inhibition of mTOR phosphorylation leading to suppression of the mTOR/p70S6K signalling pathway. Our findings provide the first evidence to show that MPL triggers autophagy through the deactivation of mTOR/p70S6K signalling pathway.

BIX-01294 induces autophagy-associated cell death via EHMT2/G9a dysfunction and intracellular reactive oxygen species production

We screened a chemical library in MCF-7 cells stably expressing green fluorescent protein (GFP)-conjugated microtubule-associated protein 1 light chain 3 (LC3) (GFP-LC3-MCF-7) using cell-based assay, and identified BIX-01294 (BIX), a selective inhibitor of euchromatic histone-lysine N-methyltransferase 2 (EHMT2), as a strong autophagy inducer. BIX enhanced formation of GFP-LC3 puncta, LC3-II, and free GFP, signifying autophagic activation. Inhibition of these phenomena with chloroquine and increasement in punctate dKeima ratio (550/438) signal indicated that BIX activated autophagic flux. BIX-induced cell death was suppressed by the autophagy inhibitor, 3-methyladenine, or siRNA against BECN1 (VPS30/ATG6), ATG5, and ATG7, but not by caspase inhibitors. Moreover, EHMT2 siRNA augmented GFP-LC3 puncta, LC3-II, free GFP, and cell death, implying that inhibition of EHMT2 caused autophagy-mediated cell death. Treatment with EHMT2 siRNA and BIX accumulated intracellular reactive oxygen species (ROS). BIX augmented mitochondrial superoxide via NADPH oxidase activation. In addition, BIX increased hydrogen peroxide and glutathione redox potential in both cytosol and mitochondria. Treatment with N-acetyl-L-cysteine (NAC) or diphenyleneiodonium chloride (DPI) decreased BIX-induced LC3-II, GFP-LC3 puncta, and cell death, indicating that ROS instigated autophagy-dependent cell death triggered by BIX. We observed that BIX potentiated autophagy-dependent and caspase-independent cell death in estrogen receptor (ESR)-negative SKBr3 and ESR-positive MCF-7 breast cancer cells, HCT116 colon cancer cells, and importantly, in primary human breast and colon cancer cells. Together, the results suggest that BIX induces autophagy-dependent cell death via EHMT2 dysfunction and intracellular ROS accumulation in breast and colon cancer cells, therefore EHMT2 inhibition can be an effective therapeutic strategy for cancer treatment.

Graphene oxide triggers toll-like receptors/autophagy responses in vitro and inhibits tumor growth in vivo

Graphene oxide (GO) is a nanomaterial with burgeoning bioapplications, while autophagy is implicated in cancer therapy. Although induction of autophagy by nanomaterials is reported, the underlying signaling mechanism in cancer cells and how this implicates the potential of GO in cancer therapy remain obscure. Here, it is shown that GO itself can induce the toll-like receptors (TLRs) responses and autophagy in cancer cells and confer antitumor effects in mice. GO can be phagocytosed by CT26 colon cancer cells, simultaneously triggering autophagy as well as TLR-4 and TLR-9 signaling cascades. By dissecting the crosstalk between the TLRs and autophagy pathways, it is uncovered that the GO-activated autophagy is regulated through the myeloid differentiation primary response gene 88 (MyD88)- and TNF receptor-associated factor 6 (TRAF6)-associated TLR-4/9 signaling pathways. Injection of GO alone into immunocompetent mice bearing the CT26 colon tumors not only suppresses the tumor progression but also enhances cell death, autophagy, and immune responses within the tumor bed. These data altogether implicate the potential of GO as an effective nanomaterial for autophagy induction and cancer therapy.

Biological activities of novel pyrazolyl hydroxamic acid derivatives against human lung cancer cell line A549

We synthesized a series of novel pyrazolyl hydroxamic acid derivatives (4a-4l) and investigated their biological activities against human lung cancer cell line A549 in vitro to determine their mechanism of action. The results showed that the majority of derivatives had inhibitory effects on the growth of A549 cancer cells in dose and time-dependent manners, in which the compounds 4b, 4f, 4h and 4j (10 μM) exerted more effective anti-proliferation activity. However, it should be noted that 4j may result in necrosis at 10 μM. Furthermore, the three compounds 4b, 4f and 4h induced cell cycle arrest at G1 phase and triggered autophagy, but could not obviously induce apoptosis and necrosis under the stimulatory condition. Therefore, the pyrazolyl hydroxamic acid derivatives 4b, 4f and 4h can be used to investigate the regulatory mechanism of autophagy and offer new approaches to the prevention of lung cancer.

Inhibition of mTOR affects protein stability of OGT

Autophagy regulates cellular homeostasis through degradation of aged or damaged subcellular organelles and components. Interestingly, autophagy-deficient beta cells, for example Atg7-mutant mice, exhibited hypoinsulinemia and hyperglycemia. Also, autophagy response is diminished in heart of diabetic mice. These results implied that autophagy and diabetes are closely connected and affect each other. Although protein O-GlcNAcylation is up-regulated in hyperglycemia and diabetes, and O-GlcNAcylated proteins play an important role in metabolism and nutrient sensing, little is known whether autophagy affects O-GlcNAc modification and vice versa. In this study, we suppressed the action of mTOR by treatment of mTOR catalytic inhibitors (PP242 and Torin1) to induce autophagic flux. Results showed a decrease in global O-GlcNAcylation, which is due to decreased OGT protein and increased OGA protein. Interestingly, knockdown of ATG genes or blocking of lysosomal degradation enhanced protein stability of OGT. In addition, when proteasomal inhibitor was treated together with mTOR inhibitor, protein level of OGT almost recovered to control level. These data suggest that mTOR inhibition is a more efficient way to reduce protein level of OGT rather than that of CHX treatment. We also showed that not only proteasomal degradation regulated OGT stability but autophagic degradation also affected OGT stability in part. We concluded that mTOR signaling regulates protein O-GlcNAc modification through adjustment of OGT stability.

Potent antitumor activity of oncolytic adenovirus expressing Beclin-1 via induction of autophagic cell death in leukemia

An attractive strategy among adenovirus-based oncolytic systems is to design adenoviral vectors to express pro-apoptotic genes, in which this gene-virotherapy approach significantly enhances tumor cell death by activating apoptotic pathways. However, the existence of cancer cells with apoptotic defects is one of the major obstacles in gene-virotherapy. Here, we investigated whether a strategy that combines the oncolytic effects of an adenoviral vector with simultaneous expression of Beclin-1, an autophagy gene, offers a therapeutic advantage for leukemia. A Beclin-1 cDNA was cloned in an oncolytic adenovirus with chimeric Ad5/11 fiber (SG511-BECN). SG511-BECN treatment induced significant autophagic cell death, and resulted in enhanced cell killing in a variety of leukemic cell lines and primary leukemic blasts. SG511-BECN effects were seen in chronic myeloid leukemia and acute myeloid leukemia with resistance to imatinib or chemotherapy, but exhibited much less cytotoxicity on normal cells. The SG511-BECN-induced autophagic cell death could be partially reversed by RNA interference knockdown of UVRAG, ATG5, and ATG7. We also showed that SG511-BECN strongly inhibited the growth of leukemic progenitors in vitro. In murine leukemia models, SG511-BECN prolonged the survival and decreased the xenograft tumor size by inducing autophagic cell death. Our results suggest that infection of leukemia cells with an oncolytic adenovirus overexpressing Beclin-1 can induce significant autophagic cell death and provide a new strategy for the elimination of leukemic cells via a unique mechanism of action distinct from apoptosis.

Hypoxia Induces autophagic cell death through hypoxia-inducible factor 1α in microglia

As phagocytic cells of central nervous system, excessive activation or cell death of microglia is involved in a lot of nervous system injury and degenerative disease, such as stroke, epilepsy, Parkinson's disease, Alzheimer's disease. Accumulating evidence indicates that hypoxia upregulates HIF-1α expression leading to cell death of microglia. However, the exact mechanism of cell death induced by hypoxia in microglia is not clear. In the current study, we showed that hypoxia induced cell death and autophagy in microglia. The suppression of autophagy using either pharmacologic inhibitors (3-methyladenine, bafilomycin A1) or RNA interference in essential autophagy genes (BECN1 and ATG5) decreased the cell death induced by hypoxia in microglia cells. Moreover, the suppression of HIF-1α using either pharmacologic inhibitors (3-MA, Baf A1) or RNA interference decreased the microglia death and autophagy in vitro. Taken together, these data indicate that hypoxia contributes to autophagic cell death of microglia through HIF-1α, and provide novel therapeutic interventions for cerebral hypoxic diseases associated with microglia activation.

Autophagy promotes resistance to photodynamic therapy-induced apoptosis selectively in colorectal cancer stem-like cells

Recent studies have indicated that cancer stem-like cells (CSCs) exhibit a high resistance to current therapeutic strategies, including photodynamic therapy (PDT), leading to the recurrence and progression of colorectal cancer (CRC). In cancer, autophagy acts as both a tumor suppressor and a tumor promoter. However, the role of autophagy in the resistance of CSCs to PDT has not been reported. In this study, CSCs were isolated from colorectal cancer cells using PROM1/CD133 (prominin 1) expression, which is a surface marker commonly found on stem cells of various tissues. We demonstrated that PpIX-mediated PDT induced the formation of autophagosomes in PROM1/CD133⁺ cells, accompanied by the upregulation of autophagy-related proteins ATG3, ATG5, ATG7, and ATG12. The inhibition of PDT-induced autophagy by pharmacological inhibitors and silencing of the ATG5 gene substantially triggered apoptosis of PROM1/CD133⁺ cells and decreased the ability of colonosphere formation in vitro and tumorigenicity in vivo. In conclusion, our results revealed a protective role played by autophagy against PDT in CSCs and indicated that targeting autophagy could be used to elevate the PDT sensitivity of CSCs. These findings would aid in the development of novel therapeutic approaches for CSC treatment.

Antagonism of tumoral prolactin receptor promotes autophagy-related cell death

Therapeutic upregulation of macroautophagy in cancer cells provides an alternative mechanism for cell death. Prolactin (PRL) and its receptor (PRLR) are considered attractive therapeutic targets because of their roles as growth factors in tumor growth and progression. We utilized G129R, an antagonist peptide of PRL, to block activity of the tumoral PRL/PRLR axis, which resulted in inhibition of tumor growth in orthotopic models of human ovarian cancer. Prolonged treatment with G129R induced the accumulation of redundant autolysosomes in 3D cancer spheroids, leading to a type II programmed cell death. This inducible autophagy was a noncanonical beclin-1-independent pathway and was sustained by an astrocytic phosphoprotein (PEA-15) and protein kinase C zeta interactome. Lower levels of tumoral PRL/PRLR in clinical samples were associated with longer patient survival. Our findings provide an understanding of the mechanisms of tumor growth inhibition through targeting PRL/PRLR and may have clinical implications.

Absence of autophagy-related proteins expression is associated with poor prognosis in patients with colorectal adenocarcinoma

Background/Aim. Autophagy, a cellular degradation process, has paradoxical roles in tumorigenesis and the progression of human cancers. The aim of this study was to investigate the expression levels of autophagy-related proteins in colorectal cancer (CRC) and to evaluate their prognostic significance. Methods. This study is a retrospective review of immunohistochemical and clinicopathological data. All specimens evaluated were obtained from 263 patients with colorectal cancer who had undergone surgery between November 1996 and August 2007. The primary outcomes measured were the expression levels of three autophagy-related proteins (ATG5, BECN1/Beclin 1, and Microtubule-associated protein 1 light chain 3B (LC3B)) by immunohistochemistry and its association in clinicopathological parameters and patient survival. Results. The autophagy-related protein expression frequencies were 65.1% (151/232) for ATG5, 71.3% (174/244) for BECN1, and 74.7% (186/249) for LC3B for the 263 patients. Correlation between the expression of autophagy-related proteins was significant for all protein pairs. Multivariate analysis showed that negative LC3B expression and absence of autophagy-related proteins expression were independently associated with poor prognosis. Conclusion. Absence of autophagy-related proteins expression is associated with poor clinical outcome in CRC, suggesting that these proteins have potential uses as novel prognostic markers.

Stratification of clear cell renal cell carcinoma by signaling pathway analysis

Investigation of cell signaling pathways in 16 clear cell renal cell carcinomas to identify groups based on commonly shared phosphorylation-driven signaling networks. Using laser capture microdissection and reverse-phase protein arrays, we profiled 75 key nodes spanning signaling pathways important in tumorigenesis. Analysis revealed significantly different (P < 0.05) signaling levels for 27 nodes between two groups of samples, designated A (4 samples; high EGFR, RET, and RASGFR1 levels, converging to activate AKT/mTOR) and B (12 samples; high ERK1/2 and STAT phosphorylation). Group B was further partitioned into groups C (7 samples; elevated expression of LC3B) and D (5 samples; activation of Src and STAT). Network analysis indicated that group A was characterized by signaling pathways related to cell cycle and proliferation, and group B by pathways related to cell death and survival. Homogeneous clear cell renal cell carcinomas could be stratified into at least two major functional groups.

Autophagy pathway is required for IL-6 induced neuroendocrine differentiation and chemoresistance of prostate cancer LNCaP cells

Prostate cancer (PCa) cells undergoing neuroendocrine differentiation (NED) are clinically relevant to the development of relapsed castration-resistant PCa. Increasing evidences show that autophagy involves in the development of neuroendocrine (NE) tumors, including PCa. To clarify the effect of autophagy on NED, androgen-sensitive PCa LNCaP cells were examined. Treatment of LNCaP cells with IL-6 resulted in an induction of autophagy. In the absence of androgen, IL-6 caused an even stronger activation of autophagy. Similar result was identified in NED induction. Inhibition of autophagy with chloroquine (CQ) markedly decreased NED. This observation was confirmed by beclin1 and Atg5 silencing experiments. Further supporting the role of autophagy in NED, we found that LC3 was up-regulated in PCa tissue that had relapsed after androgen-deprivation therapy when compared with their primary tumor counterpart. LC3 staining in relapsed PCa tissue showed punctate pattern similar to the staining of chromogranin A (CgA), a marker for NED cells. Moreover, autophagy inhibition induced the apoptosis of IL-6 induced NE differentiated PCa cells. Consistently, inhibition of autophagy by knockdown of beclin1 or Atg5 sensitized NE differentiated LNCaP cells to etoposide, a chemotherapy drug. To identify the mechanisms, phosphorylation of IL-6 downstream targets was analyzed. An increase in phospho-AMPK and a decrease in phospho-mTOR were found, which implies that IL-6 regulates autophagy through the AMPK/mTOR pathway. Most important to this study is the discovery of REST, a neuronal gene-specific transcriptional repressor that is involved in autophagy activation. REST was down-regulated in IL-6 treatment. Knockdown experiments suggest that REST is critical to NED and autophagy activation by IL-6. Together, our studies imply that autophagy is involved in PCa progression and plays a cytoprotective role when NED is induced in PCa cells by IL-6 treatment. These results reveal the potential of targeting autophagy as part of a combined therapeutic regime for NE tumors.

Autophagy suppresses tumorigenesis of hepatitis B virus-associated hepatocellular carcinoma through degradation of microRNA-224

In hepatocellular carcinoma (HCC), dysregulated expression of microRNA-224 (miR-224) and impaired autophagy have been reported separately. However, the relationship between them has not been explored. In this study we determined that autophagy is down-regulated and inversely correlated with miR-224 expression in hepatitis B virus (HBV)-associated HCC patient specimens. These results were confirmed in liver tumors of HBV X gene transgenic mice. Furthermore, miR-224 was preferentially recruited and degraded during autophagic progression demonstrated by real-time polymerase chain reaction and miRNA in situ hybridization electron microscopy after extraction of autophagosomes. Our in vitro study demonstrated that miR-224 played an oncogenic role in hepatoma cell migration and tumor formation through silencing its target gene Smad4. In HCC patients, the expression of low-Atg5, high-miR-224, and low-Smad4 showed significant correlation with HBV infection and a poor overall survival rate. Autophagy-mediated miR-224 degradation and liver tumor suppression were further confirmed by the autophagy inducer amiodarone and miR-224 antagonist using an orthotopic SD rat model.

CONCLUSION

A noncanonical pathway links autophagy, miR-224, Smad4, and HBV-associated HCC. These findings open a new avenue for the treatment of HCC.

QSOX1 inhibits autophagic flux in breast cancer cells

The QSOX1 protein (Quiescin Sulfhydryl oxidase 1) catalyzes the formation of disulfide bonds and is involved in the folding and stability of proteins. More recently, QSOX1 has been associated with tumorigenesis and protection against cellular stress. It has been demonstrated in our laboratory that QSOX1 reduces proliferation, migration and invasion of breast cancer cells in vitro and reduces tumor growth in vivo. In addition, QSOX1 expression has been shown to be induced by oxidative or ER stress and to prevent cell death linked to these stressors. Given the function of QSOX1 in these two processes, which have been previously linked to autophagy, we wondered whether QSOX1 might be regulated by autophagy inducers and play a role in this catabolic process. To answer this question, we used in vitro models of breast cancer cells in which QSOX1 was overexpressed (MCF-7) or extinguished (MDA-MB-231). We first showed that QSOX1 expression is induced following amino acid starvation and maintains cellular homeostasis. Our results also indicated that QSOX1 inhibits autophagy through the inhibition of autophagosome/lysosome fusion. Moreover, we demonstrated that inhibitors of autophagy mimic the effect of QSOX1 on cell invasion, suggesting that its role in this process is linked to the autophagy pathway. Previously published data demonstrated that extinction of QSOX1 promotes tumor growth in NOG mice. In this study, we further demonstrated that QSOX1 null tumors present lower levels of the p62 protein. Altogether, our results demonstrate for the first time a role of QSOX1 in autophagy in breast cancer cells and tumors.

Novel analogue of colchicine induces selective pro-death autophagy and necrosis in human cancer cells

Colchicine, a natural product of Colchicum autumnae currently used for gout treatment, is a tubulin targeting compound which inhibits microtubule formation by targeting fast dividing cells. This tubulin-targeting property has lead researchers to investigate the potential of colchicine and analogs as possible cancer therapies. One major study conducted on an analogue of allocolchicine, ZD 6126, was halted in phase 2 clinical trials due to severe cardio-toxicity associated with treatment. This study involves the development and testing of novel allocolchicine analogues that hold non-toxic anti-cancer properties. Currently we have synthesized and evaluated the anti-cancer activities of two analogues; N-acetyl-O-methylcolchinol (NSC 51046 or NCME), which is structurally similar to ZD 6126, and (S)-3,8,9,10-tetramethoxyallocolchicine (Green 1), which is a novel derivative of allocolchicine that is isomeric in the A ring. NSC 51046 was found to be non-selective as it induced apoptosis in both BxPC-3 and PANC-1 pancreatic cancer cells and in normal human fibroblasts. Interestingly, we found that Green 1 was able to modestly induce pro-death autophagy in these pancreatic cancer cells and E6-1 leukemia cells but not in normal human fibroblasts. Unlike colchicine and NSC 51046, Green 1 does not appear to affect tubulin polymerization indicating that it has a different molecular target. Green 1 also caused increased reactive oxygen species (ROS) production in mitochondria isolated from pancreatic cancer cells. Furthermore, in vivo studies revealed that Green 1 was well tolerated in mice. Our findings suggest that a small change in the structure of colchicine has apparently changed the mechanism of action and lead to improved selectivity. This may lead to better selective treatments in cancer therapy.

Apelin inhibits the proliferation and migration of rat PASMCs via the activation of PI3K/Akt/mTOR signal and the inhibition of autophagy under hypoxia

Apelin is highly expressed in the lungs, especially in the pulmonary vasculature, but the functional role of apelin under pathological conditions is still undefined. Hypoxic pulmonary hypertension is the most common cause of acute right heart failure, which may involve the remodeling of artery and regulation of autophagy. In this study, we determined whether treatment with apelin regulated the proliferation and migration of rat pulmonary arterial smooth muscle cells (SMCs) under hypoxia, and investigated the underlying mechanism and the relationship with autophagy. Our data showed that hypoxia activated autophagy significantly at 24 hrs. The addition of exogenous apelin decreased the level of autophagy and further inhibited pulmonary arterial SMC (PASMC) proliferation via activating downstream phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/the mammalian target of Rapamycin (mTOR) signal pathways. The inhibition of the apelin receptor (APJ) system by siRNA abolished the inhibitory effect of apelin in PASMCs under hypoxia. This study provides the evidence that exogenous apelin treatment contributes to inhibit the proliferation and migration of PASMCs by regulating the level of autophagy.

Inhibition of grade dependent autophagy in urothelial carcinoma increases cell death under nutritional limiting condition and potentiates the cytotoxicity of chemotherapeutic agent

PURPOSE

We evaluated the status of autophagy in different grades of urothelial carcinoma and explored autophagy modulators as a potential adjunctive therapeutic agent for urothelial carcinoma.

MATERIALS AND METHODS

The study was performed in tumor tissue from patients with low and high grade urothelial carcinoma, in normal urothelial tissue and in the T24 cell line. Autophagic vesicles and the expression of various autophagic proteins were studied in tissue samples by transmission electron microscopy and Western blot, respectively. The effect of autophagy induction and inhibition was evaluated by measuring AMPK and mTOR expression, cell viability and mitochondrial membrane potential. The therapeutic implication of autophagy was studied using cisplatin alone or combined with an autophagy inhibitor.

RESULTS

High grade urothelial carcinoma showed a higher number of autophagic vesicles and significantly higher expression of autophagic proteins. Upon starvation cells cultured from high and low grade urothelial carcinoma demonstrated significant autophagy induction associated with AMPK activation and mTOR inhibition. AMPK inhibition decreased the autophagic response and increased cell death. Autophagy inhibition by wortmannin, 3-methyladenine and chloroquine increased mitochondrial hypopolarization as well as caspase-9 and 3 dependent cell death. Combined treatment with cisplatin and an autophagy inhibitor resulted in greater cell death than cisplatin treatment alone.

CONCLUSIONS

Autophagy is related to urothelial carcinoma grade and regulated via the AMPK pathway for tumor cell survival. Autophagy inhibition leads to cancer cell death through an intrinsic apoptotic pathway. The potential application of autophagy inhibitors as an adjunct to chemotherapy for urothelial carcinoma must be explored.

Inhibition of autophagy enhances apoptosis induced by proteasome inhibitor bortezomib in human glioblastoma U87 and U251 cells

Glioblastoma is the most aggressive cerebral gliomas. Despite advances in therapies, the prognosis is still very poor. Therefore, novel therapeutic strategies are required. As a proteasome inhibitor, bortezomib has shown its efficacy as an active antitumor agent against a variety of tumors. However, inhibition of proteasome activity leads to cell death and also induces cell autophagy, and due to the dual roles of autophagy in the survival and death of tumor cells, the effect of inhibition of autophagy on glioblastoma cells remains to be explored. We therefore assessed whether bortezomib is capable of inducing autophagy, and investigated the antitumor effect of bortezomib combined with autophagy inhibitors on human glioblastoma U251 and U87 cells. Cell viability was measured by MTT assay. The expressions of autophagy and apoptosis-related proteins were determined by Western blot analysis. U251 and U87 cells proliferation was inhibited in a dose-dependent manner. Both apoptosis and autophagy induced by bortezomib were observed in human glioblastoma U87 and U251 cells. However, when U251 and U87 cells were co-treated with bortezomib and autophagy inhibitors 3-MA or Atg7 siRNA, the autophagy inhibitors blocked the autophagy in the cells and resulted in a further inhibition of cell proliferation and a further increase in cell apoptosis as compared with that treated with bortezomib alone. These findings indicated that combination of bortezomib and autophagy inhibitors may shed new light on glioblastoma treatment.

Manipulation of autophagy in cancer cells: an innovative strategy to fight drug resistance

Autophagy is a catabolic process activated by stress conditions and nutrient deprivation, to which it reacts by promoting the degradation of damaged organelles and misfolded/aggregated proteins, as well as generating new energetic pools. Paradoxically, in cancer cells, which signal the dangerous microenvironment occurring during clinical therapies, autophagy could promote their proliferation and sustain drug resistance. Special attention is given to autophagy manipulation in order to counteract drug resistance of cancer cells. This article describes the basic properties of autophagy and focuses on the strategies of manipulating it.

Transglutaminse 2 and EGGL, the protein cross-link formed by transglutaminse 2, as therapeutic targets for disabilities of old age

Aging of the extracellular matrix (ECM), the protein matrix that surrounds and penetrates the tissues and binds the body together, contributes significantly to functional aging of tissues. ECM proteins become increasingly cross-linked with age, and this cross-linking is probably important in the decline of the ECM's function. This article reviews the role of ε-(γ-glutamyl)-lysine (EGGL), a cross-link formed by transglutaminase enzymes, and particularly the widely expressed isozyme transglutaminase 2 (TG2), in the aging ECM. There is little direct data on EGGL accumulation with age, and no direct evidence of a role of EGGL in the aging of the ECM with pathology. However, several lines of circumstantial evidence suggest that EGGL accumulates with age, and its association with pathology suggests that this might reflect degradation of ECM function. TG activity increases with age in many circumstances. ECM protein turnover is such that some EGGL made by TG is likely to remain in place for years, if not decades, in healthy tissue, and both EGGL and TG levels are enhanced by age-related diseases. If further research shows EGGL does accumulate with age, removing it could be of therapeutic benefit. Also reviewed is the blockade of TG and active removal of EGGL as therapeutic strategies, with the conclusion that both have promise. EGGL removal may have benefit for acute fibrotic diseases, such as tendinopathy, and for treating generalized decline in ECM function with old age. Extracellular TG2 and EGGL are therefore therapeutic targets both for specific and more generalized diseases of aging.

Deconvoluting the role of reactive oxygen species and autophagy in human diseases

Reactive oxygen species (ROS), chemically reactive molecules containing oxygen, can form as a natural byproduct of the normal metabolism of oxygen and also have their crucial roles in cell homeostasis. Of note, the major intracellular sources including mitochondria, endoplasmic reticulum (ER), peroxisomes and the NADPH oxidase (NOX) complex have been identified in cell membranes to produce ROS. Interestingly, autophagy, an evolutionarily conserved lysosomal degradation process in which a cell degrades long-lived proteins and damaged organelles, has recently been well-characterized to be regulated by different types of ROS. Accumulating evidence has demonstrated that ROS-modulated autophagy has numerous links to a number of pathological processes, including cancer, ageing, neurodegenerative diseases, type-II diabetes, cardiovascular diseases, muscular disorders, hepatic encephalopathy and immunity diseases. In this review, we focus on summarizing the molecular mechanisms of ROS-regulated autophagy and their relevance to diverse diseases, which would shed new light on more ROS modulators as potential therapeutic drugs for fighting human diseases.

The Effect of Selective Estrogen Receptor Modulators (SERMs) on the Tamoxifen Resistant Breast Cancer Cells

Selective estrogen receptor modulators (SERMs) are synthetic molecules which bind to estrogen receptors (ER) and can modulate its transcriptional capabilities in different ways in diverse estrogen target tissues. Tamoxifen, the prototypical SERM, is extensively used for targeted therapy of ER positive breast cancers. Unfortunately, the use of tamoxifen is associated with acquired resistance and some undesirable side effects. This study investigated the availability of the conventional SERMs on the TAM-resistance breast cancer cells. SERMs showed more effectiveness in MCF-7 cells than tamoxifen resistant cells, except toremifene and ospemifene. Especially, toremifene was more efficacious in tamoxifen resistant cells than MCF-7. Ospemifene had similar cytotoxic activity on the two types of breast cancers. The other SERMs used in this experiment didn’t inhibit efficiently the proliferation of tamoxifen resistant cells. These results support the possibility to usage of toremifene on tamoxifen resistant cancer. The effectiveness by toremifene on tamoxifen resistant cells might be different pathways from the apoptosis and the autophagy. Further study should be needed to elucidate the underlying mechanism of effect of toremifene on tamoxifen resistant cancer.

Role of the EphB2 receptor in autophagy, apoptosis and invasion in human breast cancer cells

The Eph and Ephrin proteins, which constitute the largest family of receptor tyrosine kinases, are involved in normal tissue development and cancer progression. Here, we examined the expression and role of the B-type Eph receptor EphB2 in breast cancers. By immunohistochemistry using a progression tissue microarray of human clinical samples, we found EphB2 to be expressed in benign tissues, but strongly increased in cancers particularly in invasive and metastatic carcinomas. Subsequently, we found evidence that EphB2, whose expression varies in established cell breast lines, possesses multiple functions. First, the use of a DOX-inducible system to restore EphB2 function to low expressers resulted in decreased tumor growth in vitro and in vivo, while its siRNA-mediated silencing in high expressers increased growth. This function involves the onset of apoptotic death paralleled by caspases 3 and 9 activation. Second, EphB2 was also found to induce autophagy, as assessed by immunofluorescence and/or immunoblotting examination of the LC3, ATG5 and ATG12 markers. Third, EphB2 also has a pro-invasive function in breast cancer cells that involves the regulation of MMP2 and MMP9 metalloproteases and can be blocked by treatment with respective neutralizing antibodies. Furthermore, EphB2-induced invasion is kinase-dependent and is impeded in cells expressing a kinase-dead mutant EphB2. In summary, we identified a mechanism involving a triple role for EphB2 in breast cancer progression, whereby it regulates apoptosis, autophagy, and invasion.

Bozepinib, a novel small antitumor agent, induces PKR-mediated apoptosis and synergizes with IFNα triggering apoptosis, autophagy and senescence

Bozepinib [(RS)-2,6-dichloro-9-[1-(p-nitrobenzenesulfonyl)-1,2,3,5-tetrahydro-4,1-benzoxazepin-3-yl]-9H-purine] is a potent antitumor compound that is able to induce apoptosis in breast cancer cells. In the present study, we show that bozepinib also has antitumor activity in colon cancer cells, showing 50% inhibitory concentration (IC₅₀) values lower than those described for breast cancer cells and suggesting great potential of this synthetic drug in the treatment of cancer. We identified that the double-stranded RNA-dependent protein kinase (PKR) is a target of bozepinib, being upregulated and activated by the drug. However, p53 was not affected by bozepinib, and was not necessary for induction of apoptosis in either breast or colon cancer cells. In addition, the efficacy of bozepinib was improved when combined with the interferon-alpha (IFNα) cytokine, which enhanced bozepinib-induced apoptosis with involvement of protein kinase PKR. Moreover, we report here, for the first time, that in combined therapy, IFNα induces a clear process of autophagosome formation, and prior treatment with chloroquine, an autophagy inhibitor, is able to significantly reduce IFNα/bozepinib-induced cell death. Finally, we observed that a minor population of caspase 3-deficient MCF-7 cells persisted during long-term treatment with lower doses of bozepinib and the bozepinib/IFNα combination. Curiously, this population showed β-galactosidase activity and a percentage of cells arrested in S phase, that was more evident in cells treated with the bozepinib/IFNα combination than in cells treated with bozepinib or IFNα alone. Considering the resistance of some cancer cells to conventional chemotherapy, combinations enhancing the diversity of the cell death outcome might succeed in delivering more effective and less toxic chemotherapy.

Tumour hypoxia determines the potential of combining mTOR and autophagy inhibitors to treat mammary tumours

BACKGROUND

Hypoxia can activate autophagy, a self-digest adaptive process that maintains cell turnover. Mammalian target of rapamycin (mTOR) inhibitors are used to treat cancer but also stimulate autophagy.

METHODS

Human mammary cancer cells and derived xenografts were used to examine whether hypoxia could exacerbate autophagy-mediated resistance to the mTOR inhibitor rapamycin.

RESULTS

Rapamycin exerted potent antitumour effects in MCF-7 and MDA-MB-231 mammary tumours through a marked inhibition of angiogenesis, but the autophagy inhibitor chloroquine (CQ) failed to further sensitise tumours to mTOR inhibition. Rapamycin treatment actually led to tumour reoxygenation, thereby preventing the development of autophagy. Chloroquine alone, however, blocked the growth of MCF-7 tumours and in vitro blunted the hypoxia-induced component of autophagy in these cells. Finally, when initiating CQ treatment in large, hypoxic tumours, a robust antitumour effect could be observed, which also further increased the antiproliferative effects of rapamycin.

CONCLUSION

The mTOR inhibitor rapamycin significantly contributes to tumour growth inhibition and normalisation of the tumour vasculature through potent antiangiogenic effects. The resulting reduction in hypoxia accounts for a lack of sensitisation by the autophagy inhibitor CQ, except if the tumours are already at an advanced stage, and thus largely hypoxic at the initiation of the combination of rapamycin and CQ treatment.

IBP-mediated suppression of autophagy promotes growth and metastasis of breast cancer cells via activating mTORC2/Akt/FOXO3a signaling pathway

Interferon regulatory factor-4 binding protein (IBP) is a novel upstream activator of Rho GTPases. Our previous studies have shown that ectopic expression of IBP was correlated with malignant behaviors of human breast cancer cells, and invasive human breast cancer had high expression of IBP that promoted the proliferation of these cells. However, it remains unknown whether autophagy inhibition contributes to IBP-mediated tumorigenesis. In this study, we for the first time, reported that upregulation of IBP expression significantly suppressed the autophagy of breast cancer cells, and downregulation of IBP expression markedly induced autophagy of these cells. Further investigation revealed that IBP effectively counteracted autophagy by directly activating mammalian target of rapamycin complex 2 (mTORC2) and upregulating phosphorylation of Akt on ser473 and FOXO3a on Thr32. Moreover, IBP-mediated suppression of autophagy was dependent on mTORC2/Akt/FOXO3a signaling pathway. Finally, our results demonstrated that IBP-mediated breast cancer cell growth in vitro and in vivo was strongly correlated with suppression of mTORC2-dependent autophagy. These findings suggest that the anti-autophagic property of IBP has an important role in IBP-mediated tumorigenesis, and IBP may serve as an attractive target for treatment of breast cancer.

Quinacrine synergistically enhances the antivascular and antitumor efficacy of cediranib in intracranial mouse glioma

BACKGROUND

Despite malignant glioma vascularity, anti-angiogenic therapy is largely ineffective. We hypothesize that efficacy of the antiangiogenic agent cediranib is synergistically enhanced in intracranial glioma via combination with the late-stage autophagy inhibitor quinacrine.

METHODS

Relative cerebral blood flow and volume (rCBF, rCBV), vascular permeability (K(trans)), and tumor volume were assessed in intracranial 4C8 mouse glioma using a dual-bolus perfusion MRI approach. Tumor necrosis and tumor mean vessel density (MVD) were assessed immunohistologically. Autophagic vacuole accumulation and apoptosis were assessed via Western blot in 4C8 glioma in vitro.

RESULTS

Cediranib or quinacrine treatment alone did not alter tumor growth. Survival was only marginally improved by cediranib and unchanged by quinacrine. In contrast, combined cediranib/quinacrine reduced tumor growth by >2-fold (P < .05) and increased median survival by >2-fold, compared with untreated controls (P < .05). Cediranib or quinacrine treatment alone did not significantly alter mean tumor rCBF or K(trans) compared with untreated controls, while combined cediranib/quinacrine substantially reduced both (P < .05), indicating potent tumor devascularization. MVD and necrosis were unchanged by cediranib or quinacrine treatment. In contrast, MVD was reduced by nearly 2-fold (P < .01), and necrosis increased by 3-fold (P < .05, one-tailed), in cediranib + quinacrine treated vs untreated groups. Autophagic vacuole accumulation was induced by cediranib and quinacrine in vitro. Combined cediranib/quinacrine treatment under hypoxic conditions induced further accumulation and apoptosis.

CONCLUSION

Combined cediranib/quinacrine treatment synergistically increased antivascular/antitumor efficacy in intracranial 4C8 mouse glioma, suggesting a promising and facile treatment strategy for malignant glioma. Modulations in the autophagic pathway may play a role in the increased efficacy.