Autophagy Blockade Sensitizes Prostate Cancer Cells towards Src Family Kinase Inhibitors

Protective autophagy is involved in resistance towards MET inhibitors in human gastric adenocarcinoma cells

MET, also known as hepatocyte growth factor receptor (HGFR), is a receptor tyrosine kinase with an important role, both in normal cellular function as well as in oncogenesis. In many cancer types, abnormal activation of MET is related to poor prognosis and various strategies to inhibit its function, including small molecule inhibitors, are currently in preclinical and clinical evaluation. Autophagy, a self-digesting recycling mechanism with cytoprotective functions, is induced by cellular stress. This process is also induced upon cytotoxic drug treatment of cancer cells and partially allows these cells to escape cell death. Thus, since autophagy protects different tumor cells from chemotherapy-induced cell death, current clinical trials aim at combining autophagy inhibitors with different cancer treatments. We found that in a gastric adenocarcinoma cell line GTL-16, where MET activity is deregulated due to receptor overexpression, two different MET inhibitors PHA665752 and EMD1214063 lead to cell death paralleled by the induction of autophagy. A combined treatment of MET inhibitors together with the autophagy inhibitor 3-MA or genetically impairing autophagy by knocking down the key autophagy gene ATG7 further decreased cell viability of gastric cancer cells. In general, we observed the induction of cytoprotective autophagy in MET expressing cells upon MET inhibition and a combination of MET and autophagy inhibition resulted in significantly decreased cell viability in gastric cancer cells.

Autophagic activation potentiates the antiproliferative effects of tyrosine kinase inhibitors in medullary thyroid cancer

BACKGROUND

We hypothesized that autophagy inhibition would enhance the anticancer efficacy of ret protooncogene-targeted therapy in medullary thyroid cancer.

METHODS

Medullary thyroid cancer-1.1 and TT cells were treated with sunitinib or sorafenib in the presence or absence of everolimus, trehalose, or small interfering RNA directed against autophagy protein 5.

RESULTS

Sunitinib and sorafenib each robustly induced light chain 3-II expression, indicating autophagy activation. Autophagy protein 5 silencing diminished the antiproliferative effects of sunitinib and sorafenib by 44% (P < .05) and 41% (P < .05), respectively, in medullary thyroid cancer-1.1 cells and by 43% (P < .01) and 39% (P < .05), respectively, in TT cells. In contrast, everolimus increased the antiproliferative effects of sunitinib and sorafenib by 24% (P < .01) and 27% (P < .01), respectively, in medullary thyroid cancer-1.1 cells and by 20% (P < .05) and 23% (P < .05), respectively, in TT cells. Trehalose increased the antiproliferative effects of sunitinib and sorafenib by 26% (P < .01) and 27% (P < .01), respectively, in medullary thyroid cancer-1.1 cells and by 28% (P < .05) and 29% (P < .05), respectively, in TT cells. Autophagy protein 5 silencing abrogated both everolimus- and trehalose-induced increases in tyrosine kinase inhibitor efficacy.

CONCLUSION

Loss (gain) of autophagy diminishes (improves) the efficacy of sunitinib and sorafenib. Our findings suggest that autophagic activation should be combined with targeted ret protooncogene therapy for patients with advanced medullary thyroid cancer.

Autophagy inhibition for chemosensitization and radiosensitization in cancer: do the preclinical data support this therapeutic strategy?

Recognition of the cytoprotective functions of autophagy that occur in tumor cells exposed to various forms of chemotherapy or radiation has generated intense interest in the possibility that pharmacological interference with autophagy could provide a clinical strategy for overcoming therapeutic resistance. Multiple clinical trials are currently in progress to evaluate the antimalarial agent chloroquine (generally in its clinical formulation as hydroxychloroquine) and its impact on various forms of cancer therapy. In this commentary/review, we focus on the relatively limited number of studies in the literature where chloroquine has been tested in combination with chemotherapy or radiation in experimental tumor-bearing animal models. We also present recent data from our own laboratories, in cell culture experiments as well as in vivo studies, which demonstrate that neither chloroquine nor silencing of an autophagy regulatory gene was effective in conferring radiation sensitivity in an experimental model of breast cancer. The capacity for sensitization by chloroquine appears to be quite wide-ranging, with dramatic effects for some drugs/tumor models and modest or minimal effects in others. One possible caveat is that, with only a few exceptions, experiments have generally been performed in xenograft models, thereby eliminating the involvement of the immune system, which might ultimately be proven to play a central role in determining the effectiveness of autophagy inhibition in chemosensitization or radiosensitization. Nevertheless, a careful review of the current literature suggests that caution is likely to be warranted in translating preclinical findings relating to autophagy inhibition as an adjunctive therapeutic strategy.

Combined Inhibition of IGF-1R/IR and Src family kinases enhances antitumor effects in prostate cancer by decreasing activated survival pathways

Background

Treatment of metastatic prostate cancer (PCa) with single agents has shown only modest efficacy. We hypothesized dual inhibition of different pathways in PCa results in improved tumor inhibition. The Src family kinases (SFK) and insulin-like growth factor-1 (IGF-1) signaling axes are aberrantly activated in both primary PCa and bone metastases and regulate distinct and overlapping functions in PCa progression. We examined the antitumor effects of combined inhibition of these pathways.

Materials and Methods

Src andIGF-1 receptor (IGF-1R) inhibition was achieved in vitro by short hairpin (sh)RNA and in vitro and in vivo by small molecule inhibitors (dasatinib and BMS-754807, against SFK and IGF-1R/Insulin Receptor(IR), respectively).

Results

In vitro, inhibition of IGF-1 signaling affected cell survival and proliferation. SFK blockade alone had modest effects on proliferation, but significantly enhanced the IGF-1R blockade. These findings correlated with a robust inhibition of IGF-1-induced Akt1 phophorylation by dasatinib, whereas Akt2 phosphorylation was SFK independent and only inhibited by BMS-754807. Thus, complete inhibition of both Akt genes, not seen by either drug alone, is likely a major mechanism for the decreased survival of PCa cells. Furthermore, dasatinib and BMS-754807 inhibited in vivo growth of the primary human xenograft MDA PCa 133, with corresponding inhibition of Akt in tumors. Also, both orthotopic and intratibial tumor growth of PC-3 cells were more potently inhibited by dual SFK and IGF-1R/IR blockade compared to either pathway alone, with a corresponding decrease in bone turnover markers.

Conclusions

Dual IGF-1R/IR and SFK inhibition may be a rational therapeutic approach in PCa by blocking both independent and complementary processes critical to tumor growth.

Blocked autophagy using lysosomotropic agents sensitizes resistant prostate tumor cells to the novel Akt inhibitor AZD5363

PURPOSE

Prostate cancer development is often associated with deletion or silencing of tumor suppressor phosphatase and tensin homolog (PTEN), a negative regulator of the phosphoinositide 3 kinase (PI3K)-Akt pathway, leading to resistance to various therapies in both the preclinical and clinical setting. Therefore, the PI3K-Akt pathway plays a central role in various cellular processes promoting survival signaling that can contribute to the malignant phenotype, and, consequently, is an attractive pharmacologic target. However, as single agents, the efficacy of AKT inhibitors may be limited by resistance mechanisms that result in minimal cell death in tumor cells.

EXPERIMENTAL DESIGN

We investigated the effects of the Akt inhibitor AZD5363 on cell proliferation, cell cycle, apoptosis, and Akt downstream pathway proteins. Survival mechanisms induced by AZD5363 were investigated. We then examined the impacts of inhibition of autophagy in combination with AZD5363 on cell proliferation and apoptosis. Furthermore, the anticancer activity of combination treatment of the lysosomotropic inhibitor of autophagy (chloroquine) with the Akt inhibitor AZD5363 was evaluated in PC-3 prostate cancer xenografts.

RESULTS

Here, we show that the Akt inhibitor AZD5363 affected the Akt downstream pathway by reducing p-mTOR, p-P70S6K, and p-S6K. While AZD5363 monotherapy induced G(2) growth arrest and autophagy, it failed to induce significant apoptosis in PC-3 and DU145 prostate cancer cell lines. Blocking autophagy using pharmacologic inhibitors (3-methyladenine, chloroquine, and bafilomycin A) or genetic inhibitors (siRNA targeting Atg3 and Atg7) enhanced cell death induced by Akt inhibitor AZD5363 in these tumor prostate cell lines. Importantly, the combination of AZD5363 with chloroquine significantly reduced tumor volume by 84.9% compared with the control group and by 77.5% compared with either drug alone in PC3 xenografts.

CONCLUSION

Taken together, these data show that the Akt inhibitor AZD5363 synergizes with the lysosomotropic inhibitor of autophagy chloroquine to induce apoptosis and delay tumor progression in prostate cancer models that are resistant to monotherapy AZD5363, providing a new therapeutic approach potentially translatable to patients.

Autophagy control by the VEGF-C/NRP-2 axis in cancer and its implication for treatment resistance

A major contributor to cancer mortality is recurrence and subsequent metastatic transformation following therapeutic intervention. Therefore, in order to develop new treatment modalities and improve the efficacy of current ones, it is important to understand the molecular mechanisms that promote resistance to therapy in cancer cells. One pathway contributing to therapy resistance is autophagy, a self-digestive process that can eliminate unnecessary or damaged organelles to protect cancer cells from death. We have found that the VEGF-C/NRP-2 axis is involved in the activation of autophagy, which helps cancer cell survival following treatment. Inhibition of mTOR complex 1 activity by this axis is the underlying mechanism for the activation of autophagy. Furthermore, we identified two VEGF-C/NRP-2-regulated genes, LAMP-2 and WDFY-1, that have previously been suggested to participate in autophagy and vesicular trafficking. Upregulation of WDFY-1 following VEGF-C or NRP-2 depletion contributes to cytotoxic drug-mediated cell death. Together, these data suggest a link between the VEGF-C/NRP-2 axis and cancer cell survival despite the presence of chemotherapy-induced stress. Effective targeting of this pathway may lead to the development of new cancer therapies.

Autophagy is differentially induced in prostate cancer LNCaP, DU145 and PC-3 cells via distinct splicing profiles of ATG5

Autophagic responses to chemotherapeutic agents may vary greatly among different prostate cancer cells and have not been well characterized. In this study, we showed that valproic acid (VPA) induced conversion of LC3-I to LC3-II and formation of LC3 puncta, the typical markers of autophagy, in LNCaP and PC-3 cells. However, these markers were undetectable in DU145 cells upon autophagic stimulation, indicating a defect of autophagy in this cell line. Among several critical autophagy-related proteins, ATG5 and ATG12-ATG5 conjugates, which are essential for autophagy induction, were absent in DU145 cells. No canonical transcripts for full-length ATG5 but only two alternatively spliced ATG5 transcripts were identified in DU145 cells. These alternative transcripts lack one or two exons, leading to premature termination of ATG5 translation. Transfection of the wild-type ATG5 gene into DU145 cells rescued the production of ATG5 and ATG12-ATG5 conjugates, resulting in formation of LC3-II conjugates and LC3 puncta. Moreover, the levels of the SQSTM1 protein, which should be degradable as an autophagy adaptor, were much higher in DU145 than in LNCaP and PC-3 cells, but were significantly decreased after ATG5 restoration in DU145 cells. However, expression of wild-type ATG5 in DU145 or knockdown of ATG5 in LNCaP and PC-3 cells did not change the inhibitory effects of VPA on these cells. Collectively, these results indicated that VPA-induced autophagy in prostate cancer cells depended on ATG5 and more importantly, that the autophagy pathway was genetically impaired in DU145 cells, suggesting caution in interpreting autophagic responses in this cell line.

Autophagic action of new targeting agents in head and neck oncology

The survival rates of patients with squamous cell carcinoma of the head and neck (HNSCC) have not improved significantly despite multi-modality therapy, including surgery, radiation therapy, and chemotherapy. Recently, molecular targeted agents have shown significant improvement in clinical outcomes; for example, in chronic myelogeneous leukemia with imatinib, breast cancer with trastuzumab, colon cancer with bevacizumab and cetuximab, and renal cell cancer with sorafenib and sunitinib. In HNSCC, the epidermal growth factor receptor antibody cetuximab has shown promising results in combination with radiation. Targeted agents including cetuximab induce stresses to activate prosurvival autophagy. Combining autophagy inhibitors with agents that induce autophagy as a prosurvival response may therefore increase their therapeutic efficacy. Whether autophagy contributes to the prosurvival response or to the antitumor effect of chemotherapeutic drugs is largely unknown. This review will discuss the possible role of autophagy as a novel target for anticancer therapy agents in HNSCC.

Synergistic killing effect of chloroquine and androgen deprivation in LNCaP cells

Modulation of autophagy is a new paradigm in cancer therapeutics. Recently a novel function of chloroquine (CLQ) in inhibiting degradation of autophagic vesicles has been revealed, which raises the question whether CLQ can be used as an adjuvant in targeting autophagic pro-survival mechanism in prostate cancer (PCa). We previously showed that autophagy played a protective role during hormone ablation therapy, in part, by consuming lipid droplets in PCa cells. In addition, blocking autophagy by genetic and pharmacological means in the presence of androgen deprivation caused cell death in PCa cells. To further investigate the importance of autophagy in PCa survival and dissect the role of CLQ in PCa death, we treated hormone responsive LNCaP cells with CLQ in combination with androgen deprivation. We observed that CLQ synergistically killed LNCaP cells during androgen deprivation in a dose- and time-dependent manner. We further confirmed that CLQ inhibited the maturation of autophagic vesicles and decreased the cytosolic ATP. Moreover, CLQ induced nuclear condensation and DNA fragmentation, a hallmark of apoptosis, in androgen deprived LNCaP cells. Taken together, our finding suggests that CLQ may be an useful adjuvant in hormone ablation therapy to improve the therapeutic efficacy.

Mechanism for the induction of cell death in ONS-76 medulloblastoma cells by Zhangfei/CREB-ZF

Cells from medulloblastoma lines do not contain detectable amounts of the basic leucine-zipper protein Zhangfei. However, we have previously shown that expression of this protein in cells of the ONS-76 and UW228 medulloblastoma lines causes the cells to stop growing and develop processes that resemble neurites. Our objective was to determine the molecular mechanisms by which Zhangfei influences ONS-76 cells. We infected ONS-76 cells with adenovirus vectors expressing either Zhangfei or the control protein LacZ and then compared the following parameters in Zhangfei and LacZ-expressing cells: (a) markers of apoptosis, autophagy and macropinocytosis, (b) transcripts for genes involved in neurogenesis and apoptosis, (c) phosphorylation of peptide targets of selected cellular protein kinases, and (d) activation of transcription factors. Zhangfei-expressing cells appeared to succumb to apoptosis. Increased staining for autophagic vesicles and upregulated expression of autophagy response genes in these cells indicated that they were undergoing autophagy, possibly associated with apoptosis. Within our analysis, patterns of gene expression and phosphorylation-mediated signal transduction activity in Zhangfei-expressing cells indicated that the mitogen-activated protein kinase (MAPK) pathway was active. In addition, we found that the transcription factor Brn3a as well as factors implicated in differentiation were also active in Zhangfei-expressing cells. We tested the hypothesis that Zhangfei enhances the expression of Brn3a, a known inducer of TrkA, the high-affinity receptor for nerve growth factor (NGF). TrkA then engages NGF in an autocrine manner triggering the MAPK pathway and leading to differentiation of ONS-76 cells into neuron and glia-like cells-a process that eventually brings about cell death. We showed that: (a) Zhangfei could enhance transcription from the isolated Brn3a promoter, (b) ONS-76 cells produced NGF and (c) antibodies against NGF and inhibitors of TrkA and selected components of the MAPK pathway could partially restore the growth of Zhangfei-expressing ONS-76 cells.

Autophagy and reactive oxygen species modulate cytotoxicity induced by suppression of ATM kinase activity in head and neck cancer cells

OBJECTIVES

Because Ataxia Telangiectasia Mutated (ATM)-deficient cells are hypersensitive to ionizing irradiation and DNA-damaging agents, ATM kinase inhibition is thought to enhance radiochemotherapy efficacy. In this study, we investigated the roles of autophagy and reactive oxygen species (ROS) in modulating cytotoxicity induced by suppression of ATM kinase in head and neck cancer cells.

MATERIALS AND METHODS

We use KU55933 to inhibit ATM kinase activity. The cell viability was determined by MTT assays. Autophagy was examined by Western blot for LC3-II and microscopy for acidic vesicles and EGFP-LC3 punctate formation. DCF-DA staining and flow cytometry were used for analyzing ROS generation.

RESULTS

we found that KU55933 reduced cell viability in several head and neck cancer cell lines. KU55933-treated cells showed increased cytoplasmic vesicles, LC3-II accumulation, and EGFP-LC3 punctate formation, indicating that autophagy was induced. KU55933 also increased ROS generation, which was required for autophagy induction because the ROS scavenger N-acetyl-L-cysteine could reduce LC3-II accumulation. KU55933-induced autophagy played a cytoprotective role against ROS-mediated cytotoxicity because autophagy inhibition by chloroquine augmented KU55933's cytotoxicity. In addition, KU55933 reduced cisplatin-resistant head and neck cancer cell viabilities, and induced LC3-II accumulation in these cells.

CONCLUSION

Together, these results shed light on KU55933's therapeutic values as well as autophagy inhibitors in treating primary and cisplatin-resistant head and neck cancers.

Autophagy and cancer

Basal autophagy plays a critical role in maintaining cellular homeostasis and genomic integrity by degrading aged or malfunctioning organelles and damaged or misfolded proteins. However, autophagy also plays a complicated role in tumorigenesis and treatment responsiveness. It can be tumor-suppressing during the early stages of tumorigenesis (i.e., it is an anti-tumor mechanism), as reduced autophagy is found in tumor cells and may be associated with malignant transformation. In this case, induction of autophagy would seem to be beneficial for cancer prevention. In established tumors, however, autophagy can be tumor- promoting (i.e., it is a pro-tumor mechanism), and cancer cells can use enhanced autophagy to survive under metabolic and therapeutic stress. The pharmacological and/or genetic inhibition of autophagy was recently shown to sensitize cancer cells to the lethal effects of various cancer therapies, including chemotherapy, radiotherapy and targeted therapies, suggesting that suppression of the autophagic pathway may represent a valuable sensitizing strategy for cancer treatments. In contrast, excessive stimulation of autophagy may also provide a therapeutic strategy for treating resistant cancer cells having high apoptotic thresholds. In order for us to develop successful autophagy- modulating strategies against cancer, we need to better understand how the roles of autophagy differ depending on the tumor stage, cell type and/or genetic factors, and we need to determine how specific pathways of autophagy are activated or inhibited by the various anti-cancer therapies.

Hirsutanol A induces apoptosis and autophagy via reactive oxygen species accumulation in breast cancer MCF-7 cells

Hirsutanol A is a novel sesquiterpene compound purified from the marine fungus Chondrostereum sp in the coral Sarcophyton tortuosum. Our previous studies had demonstrated that hirsutanol A exerted potent cytotoxic effect in many kinds of cancer cell lines. Here, the anticancer molecular mechanisms of hirsutanol A were investigated in breast cancer MCF-7 cells. The results showed that hirsutanol A could inhibit cell proliferation, elevate reactive oxygen species (ROS) level, and induce apoptosis and autophagy. Co-treatment with the potent antioxidant agent N-acetyl-L-cysteine could effectively reverse the effect of enhanced ROS production, which in turn, reduces growth inhibition, apoptosis, and autophagy mediated by hirsutanol A. In addition, blocking autophagy by bafilomycin A1 or Atg7-siRNA could synergistically enhance the antiproliferative effect and apoptosis induced by hirsutanol A. These data suggested that hirsutanol A could induce apoptosis and autophagy via accumulation of ROS and co-treatment with an autophagy inhibitor could sensitize MCF-7 cells to hirsutanol A.

Cotargeting stress-activated Hsp27 and autophagy as a combinatorial strategy to amplify endoplasmic reticular stress in prostate cancer

Hsp27 is a stress-activated multifunctional chaperone that inhibits treatment-induced apoptosis and causes treatment resistance in prostate and other cancers. We previously showed that targeted suppression of Hsp27 sensitizes cancer cells to hormone and chemotherapy. However, mechanisms by which Hsp27 confers cell treatment resistance are incompletely defined. Here, we report that Hsp27 protects human prostate cancer cells against proteotoxic stress induced by proteasome inhibition, and that Hsp27 silencing using siRNA or antisense (OGX-427) induced both apoptosis and autophagy through mechanisms involving reduced proteasome activity and induction of endoplasmic reticulum (ER) stress. We found that autophagy activation protected against ER stress-induced cell death, whereas inhibition of autophagy activation following Hsp27 silencing using either pharmacologic inhibitors or atg3 silencing enhanced cell death. Importantly, cotargeting Hsp27 and autophagy by combining OGX-427 with the autophagy inhibitor, chloroquine, significantly delayed PC-3 prostate tumor growth in vivo. These findings identify autophagy as a cytoprotective, stress-induced adaptive pathway, activated following disruption of protein homeostasis and ER stress induced by Hsp27 silencing. Combinatorial cotargeting cytoprotective Hsp27 and autophagy illustrates potential benefits of blocking activation of adaptive pathways to improve treatment outcomes in cancer.

Autophagy and cancer--issues we need to digest

Autophagy is an evolutionarily conserved catabolic pathway that has multiple roles in carcinogenesis and cancer therapy. It can inhibit the initiation of tumorigenesis through limiting cytoplasmic damage, genomic instability and inflammation, and the loss of certain autophagy genes can lead to cancer. Conversely, autophagy can also assist cells in dealing with stressful metabolic environments, thereby promoting cancer cell survival. In fact, some cancers rely on autophagy to survive and progress. Furthermore, tumour cells can exploit autophagy to cope with the cytotoxicity of certain anticancer drugs. By contrast, it appears that certain therapeutics require autophagy for the effective killing of cancer cells. Despite these dichotomies, it is clear that autophagy has an important, if complex, role in cancer. This is further exemplified by the fact that autophagy is connected with major cancer networks, including those driven by p53, mammalian target of rapamycin (mTOR), RAS and glutamine metabolism. In this Commentary, we highlight recent advances in our understanding of the role that autophagy has in cancer and discuss current strategies for targeting autophagy for therapeutic gain.

Deconvoluting the context-dependent role for autophagy in cancer

Autophagy (also known as macroautophagy) captures intracellular components in autophagosomes and delivers them to lysosomes, where they are degraded and recycled. Autophagy can have two functions in cancer. It can be tumour suppressive through the elimination of oncogenic protein substrates, toxic unfolded proteins and damaged organelles. Alternatively, it can be tumour promoting in established cancers through autophagy-mediated intracellular recycling that provides substrates for metabolism and that maintains the functional pool of mitochondria. Therefore, defining the context-specific role for autophagy in cancer and the mechanisms involved will be important to guide autophagy-based therapeutic intervention.

Autophagy in tumorigenesis and cancer therapy: Dr. Jekyll or Mr. Hyde?

Autophagy is an evolutionarily conserved mechanism for intracellular substance degradation, responsible for the recycling of metabolic substances and the maintenance of intracellular stability. It has early been demonstrated to play a significant role in tumorigenesis, but whether it acts as a promoter or a suppressor during tumorigenesis seems to be context-specific. Moreover, autophagy is also implicated in promoting chemoresistance of cancer cells so as to attenuate therapeutic efficacy of chemotherapy. On the contrary, other reports highlight a tumor-killing role of autophagy during cancer treatment. Herein, this review aims to revisit the key features of autophagy, summarize the seemingly contradictory roles of autophagy during both tumorigenesis and cancer chemotherapy, and evaluate the feasibility of altering the level of cellular autophagy as part of cancer adjuvant treatment.

Autophagy inhibition synergistically enhances anticancer efficacy of RAMBA, VN/12-1 in SKBR-3 cells, and tumor xenografts

VN/12-1 is a novel retinoic acid metabolism blocking agent discovered in our laboratory. The purpose of the study was to elucidate the molecular mechanism of anticancer activity of VN/12-1 in breast cancer cell lines and in tumor xenografts. We investigated the effects of VN/12-1 on induction of autophagy and apoptosis in SKBR-3 cells. Furthermore, we also examined the impact of pharmacologic and genomic inhibition of autophagy on anticancer activity of VN/12-1. Finally, the antitumor activity of VN/12-1 was evaluated as a single agent and in combination with autophagy inhibitor chloroquine in an SKBR-3 mouse xenograft model. Short exposure of low dose (<10 μmol/L) of VN/12-1 induced endoplasmic reticulum stress, autophagy, and inhibited G(1)-S phase transition and caused a protective response. However, a higher dose of VN/12-1 initiated apoptosis in vitro. Inhibition of autophagy using either pharmacologic inhibitors or RNA interference of Beclin-1 enhanced anticancer activity induced by VN/12-1 in SKBR-3 cells by triggering apoptosis. Importantly, VN/12-1 (5 mg/kg twice weekly) and the combination of VN/12-1 (5 mg/kg twice weekly) + chloroquine (50 mg/kg twice weekly) significantly suppressed established SKBR-3 tumor growth by 81.4% (P < 0.001 vs. control) and 96.2% (P < 0.001 vs. control), respectively. Our novel findings suggest that VN/12-1 may be useful as a single agent or in combination with autophagy inhibitors for treating human breast cancers. Our data provides a strong rationale for clinical evaluation of VN/12-1 as single agent or in combination with autophagy inhibitors.

The pan erbB inhibitor PD168393 enhances lysosomal dysfunction-induced apoptotic death in malignant peripheral nerve sheath tumor cells

Malignant peripheral nerve sheath tumors (MPNSTs) are rapidly progressive Schwann cell neoplasms. The erbB family of membrane tyrosine kinases has been implicated in MPNST mitogenesis and invasion and, thus, is a potential therapeutic target. However, tyrosine kinase inhibitors (TKIs) used alone have limited tumoricidal activity. Manipulating the autophagy lysosomal pathway in cells treated with cytostatic agents can promote apoptotic cell death in some cases. The goal of this study was to establish a mechanistic basis for formulating drug combinations to effectively trigger death in MPNST cells. We assessed the effects of the pan erbB inhibitor PD168393 on MPNST cell survival, caspase activation, and autophagy. PD168393 induced a cytostatic but not a cytotoxic response in MPNST cells that was accompanied by suppression of Akt and mTOR activation and increased autophagic activity. The effects of autophagy modulation on MPNST survival were then assessed following the induction of chloroquine (CQ)-induced lysosomal stress. In CQ-treated cells, suppression of autophagy was accompanied by increased caspase activation. In contrast, increased autophagy induction by inhibition of mTOR did not trigger cytotoxicity, possibly because of Akt activation. We thus hypothesized that dual targeting of mTOR and Akt by PD168393 would significantly increase cytotoxicity in cells exposed to lysosomal stress. We found that PD168393 and CQ in combination significantly increased cytotoxicity. We conclude that combinatorial therapies with erbB inhibitors and agents inducing lysosomal dysfunction may be an effective means of treating MPNSTs.

Autophagy as a mediator of chemotherapy-induced cell death in cancer

Since the 1940s, chemotherapy has been the treatment of choice for metastatic disease. Chemotherapeutic agents target proliferating cells, inducing cell death. For most of the history of chemotherapy, apoptosis was thought to be the only mechanism of drug-induced cell death. More recently, a second type of cell death pathway has emerged: autophagy, also called type II programmed cell death. Autophagy is a tightly regulated process by which selected components of a cell are degraded. It primarily functions as a cell survival adaptive mechanism during stress conditions. However, persistent stress can also promote extensive autophagy, leading to cell death, hence its name. Alterations in the autophagy pathway have been described in cancer cells that suggest a tumor-suppressive function in early tumorigenesis, but a tumor-promoting function in established tumors. Moreover, accumulating data indicate a role for autophagy in chemotherapy-induced cancer cell death. Here, we discuss some of the evidence showing autophagy-dependent cell death induced by anti-neoplastic agents in different cancer models. On the other hand, in some other examples, autophagy dampens treatment efficacy, hence providing a therapeutic target to enhance cancer cell killing. In this paper, we propose a putative mechanism that could reconcile these two opposite observations.

The role of autophagy in cancer: therapeutic implications

Autophagy is a homeostatic, catabolic degradation process whereby cellular proteins and organelles are engulfed by autophagosomes, digested in lysosomes, and recycled to sustain cellular metabolism. Autophagy has dual roles in cancer, acting as both a tumor suppressor by preventing the accumulation of damaged proteins and organelles and as a mechanism of cell survival that can promote the growth of established tumors. Tumor cells activate autophagy in response to cellular stress and/or increased metabolic demands related to rapid cell proliferation. Autophagy-related stress tolerance can enable cell survival by maintaining energy production that can lead to tumor growth and therapeutic resistance. As shown in preclinical models, inhibition of autophagy restored chemosensitivity and enhanced tumor cell death. These results established autophagy as a therapeutic target and led to multiple early phase clinical trials in humans to evaluate autophagy inhibition using hydroxychloroquine in combination with chemotherapy or targeted agents. Targeting autophagy in cancer will provide new opportunities for drug development, because more potent and specific inhibitors of autophagy are needed. The role of autophagy and its regulation in cancer cells continues to emerge, and studies aim to define optimal strategies to modulate autophagy for therapeutic advantage.

Src family kinases and paclitaxel sensitivity

Src-family Kinases (SFKs) participate in the regulation of proliferation, differentiation, apoptosis, autophagy, adhesion, migration, invasion and angiogenesis in normal and cancer cells. Abnormal expression of SFKs has been documented in cancers that arise in breast, colon, ovary, melanocyte, gastric mucosa, head and neck, pancreas, lung, and brain. Targeting SFKs in cancer cells has been shown to be a promising therapeutic strategy in solid tumors, particularly in ovarian, colon and breast cancers. Paclitaxel is one of most widely used chemotherapeutic agents for the management of ovarian, breast, lung and head/neck cancers. As a microtubule-stabilizing agent, paclitaxel possesses both mitosis-dependent and mitosis-independent activities against cancer cells. A variety of mechanisms such as deregulation of P-glycoprotein, alteration of tubulin isotypes, alteration of microtubule-regulatory proteins, deregulation of apoptotic signaling pathways, mutation of tubulins and overexpression of copper transporters have been implicated in the development of primary or secondary resistance to paclitaxel. By affecting cancer cell survival, proliferation, autophagy, microtubule stability, motility, and/or angiogenesis, SFKs interact with mechanisms that regulate paclitaxel sensitivity. Inhibition of SFKs can potentiate the anti-tumor activity of paclitaxel by enhancing apoptosis, autophagy and microtubule stability. Based on pre-clinical observations, administration of SFK inhibitors in combination with paclitaxel could improve treatment for ovarian, breast, lung and head/neck cancers. Identification and validation of predictive biomarkers could also permit personalization of the therapy.

Suppression of autophagy sensitizes multidrug resistant cells towards Src tyrosine kinase specific inhibitor PP2

Upregulated Src activity has been implicated in a variety of cancers. Thus, Src family tyrosine kinase (SFK) inhibitors are often effective cancer treatments. Here, we employed 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), a selective SFK inhibitor, to determine the possible involvement of tyrosine phosphorylation in the modulation of autophagy, for overcoming multidrug resistance. We found that multidrug-resistant v-Ha-ras-transformed NIH 3T3 cells (Ras-NIH 3T3/Mdr) were more susceptible to PP2 treatment than were their parental cells (Ras-NIH 3T3). The antiproliferative activity of PP2 appeared to be due to cell-cycle arrest at G1/S without induction of apoptosis. Interestingly, PP2 preferentially induced autophagy in Ras-NIH 3T3 cells but not in Ras-NIH 3T3/Mdr cells, which implies that a high level of autophagy may protect PP2-treated cells from undergoing cell death. PP2-induced autophagy in Ras-NIH 3T3 cells is accompanied by an inhibition of the mTOR signaling pathway. However, we found that in Ras-NIH 3T3/Mdr cells, PP2-induced mTOR inhibition was uncoupled from the induction of autophagy-likely due to the hyperactivation of AMPK by delayed Raf activation. We also found that PP2-induced dissociation of Beclin 1 from Bcl-2 leads to autophagy in Ras-NIH 3T3 cells. Taken together, these results suggest that functional autophagy in response to PP2 may lead to cell survival in Ras-NIH 3T3 cells, while defective autophagy may contribute to inhibition of growth in Ras-NIH 3T3/Mdr cells. Thus, modulators of autophagy may be used beneficially as adjunctive therapeutic agents during the treatment of cancers with SFK inhibitors.

EGFR tyrosine kinase inhibitors activate autophagy as a cytoprotective response in human lung cancer cells

Epidermal growth factor receptor tyrosine kinase inhibitors gefitinib and erlotinib have been widely used in patients with non-small-cell lung cancer. Unfortunately, the efficacy of EGFR-TKIs is limited because of natural and acquired resistance. As a novel cytoprotective mechanism for tumor cell to survive under unfavorable conditions, autophagy has been proposed to play a role in drug resistance of tumor cells. Whether autophagy can be activated by gefitinib or erlotinib and thereby impair the sensitivity of targeted therapy to lung cancer cells remains unknown. Here, we first report that gefitinib or erlotinib can induce a high level of autophagy, which was accompanied by the inhibition of the PI3K/Akt/mTOR signaling pathway. Moreover, cytotoxicity induced by gefitinib or erlotinib was greatly enhanced after autophagy inhibition by the pharmacological inhibitor chloroquine (CQ) and siRNAs targeting ATG5 and ATG7, the most important components for the formation of autophagosome. Interestingly, EGFR-TKIs can still induce cell autophagy even after EGFR expression was reduced by EGFR specific siRNAs. In conclusion, we found that autophagy can be activated by EGFR-TKIs in lung cancer cells and inhibition of autophagy augmented the growth inhibitory effect of EGFR-TKIs. Autophagy inhibition thus represents a promising approach to improve the efficacy of EGFR-TKIs in the treatment of patients with advanced non-small-cell lung cancer.

Induction of autophagy by drug-resistant esophageal cancer cells promotes their survival and recovery following treatment with chemotherapeutics

We investigated the cell-death mechanisms induced in esophageal cancer cells in response to the chemotherapeutic drugs, 5-fluorouracil (5-FU) and cisplatin. Chemosensitive cell lines exhibited apoptosis whereas chemoresistant populations exhibited autophagy and a morphology resembling type II programmed cell death (PCD). Cell populations that respond with autophagy are more resistant and will recover following withdrawal of the chemotherapeutic agents. Specific inhibition of early autophagy induction with siRNA targeted to Beclin 1 and ATG7 significantly enhanced the effect of 5-FU and reduced the recovery of drug-treated cells. Pharmacological inhibitors of autophagy were evaluated for their ability to improve chemotherapeutic effect. The PtdIns 3-kinase inhibitor 3-methyladenine did not enhance the cytotoxicity of 5-FU. Disruption of lysosomal activity with bafilomycin A 1 or chloroquine caused extensive vesicular accumulation but did not improve chemotherapeutic effect. These observations suggest that an autophagic response to chemotherapy is a survival mechanism that promotes chemoresistance and recovery and that selective inhibition of autophagy regulators has the potential to improve chemotherapeutic regimes. Currently available indirect inhibitors of autophagy are, however, ineffective at modulating chemosensitivity in these esophageal cancer cell lines.

Autophagy modulation for cancer therapy

Autophagy is a homeostatic and catabolic process that enables the sequestration and lysosomal degradation of cytoplasmic organelles and proteins that is important for the maintenance of genomic stability and cell survival. Beclin 1 (+/- ) gene knockout mice are tumor prone, indicating a tumor suppressor role for autophagy. Autophagy is also mechanism of stress tolerance that maintains cell viability and can lead to tumor dormancy, progression, and therapeutic resistance. Many anticancer drugs induce cytotoxic stress that can activate pro-survival autophagy. In some contexts, excessive or prolonged autophagy can lead to tumor cell death. Inhibition of cytoprotective autophagy by genetic or pharmacological means has been shown to enhance anticancer drug-induced cell death, suggesting a novel therapeutic strategy. Studies are ongoing to define optimal strategies to modulate autophagy for cancer prevention and therapy, and to exploit it as a target for anticancer drug discovery.

Statins and prostate cancer: role of cholesterol inhibition vs. prevention of small GTP-binding proteins

Prostate cancer (PCa) is initially regulated by androgens, such as testosterone and dihydrotestosterone, which regulates cell proliferation and survival by activating the androgen receptor (AR), but later progresses to an aggressive, metastatic, androgen-independent stage for which, currently, there is no cure. Here, we argue that prevention of PCa progression is a better strategy compared to trying to cure the disease once it has already progressed. Statins inhibit the mevalonate pathway, thus preventing the synthesis of cholesterol, geranylgeranyl pyrophosphate and farnesyl pyrophosphate. Multiple clinical studies have shown an inverse relationship between statin use and PCa risk, especially the risk for developing advanced metastatic cancer. Biochemical investigations have largely corroborated the positive effect of statins on PCa risk, showing that statins inhibited cell proliferation, induced apoptosis, and decreased cell migration and invasion in PCa cells in vitro. However, investigations of the biochemical mechanism of statin action in preventing advanced/high risk PCa remains inconclusive, as statins can act through cholesterol, geranylgeranyl, or farnesyl mediated signals. This review discusses the current clinical and biochemical findings on the use of statins in preventing PCa. Evidence of statin action through cholesterol as well as geranylgeranylation and farnesylation has been discussed. As cholesterol is a precursor of androgen production, it can reduce PCa risk by decreasing the levels of circulating testosterone, which in turn reduces the levels of interprostatic dihydrotestosterone, a strong ligand for the AR. Cholesterol was also shown to accumulate in lipid rafts and regulate the activation of the phosphatidylinositol 3-kinase/Akt pathway. However, clinical evidence from multiple studies also point to the existence of cholesterol-independent pathways mediating statin action in PCa patients. In particular, ligand-activated AR activation is seen in early stage PCa and activation of the cholesterol pathway did not indicate an effect on metastasis. Cell migration and invasion, on the other hand, is regulated strongly by members of the Ras superfamily of small GTPases, especially the Rho family, which is geranylgeranylated. This review, therefore, also compares the effects of statins on both cholesterol and geranylgeranylated and farnesylated small GTPases regulating tumor progression and metastasis in biochemical and clinical studies.

Targeting autophagy during cancer therapy to improve clinical outcomes

Autophagy is a catabolic process that turns over long-lived proteins and organelles and contributes to cell and organism survival in times of stress. Current cancer therapies including chemotherapy and radiation are known to induce autophagy within tumor cells. This is therefore an attractive process to target during cancer therapy as there are safe, clinically available drugs known to both inhibit and stimulate autophagy. However, there are conflicting positive and negative effects of autophagy and no current consensus on how to manipulate autophagy to improve clinical outcomes. Careful and rigorous evaluation of autophagy with a focus on how to translate laboratory findings into relevant clinical therapies remains an important aspect of improving clinical outcomes in patients with malignant disease.

Autophagy as a therapeutic target in cancer

Autophagy is a self-catabolic process that maintains intracellular homeostasis and prolongs cell survival under stress via lysosomal degradation of cytoplasmic constituents and recycling of amino acids and energy. Autophagy is intricately involved in many aspects of human health and disease, including cancer. Autophagy is a double-edged sword in tumorigenesis, acting both as a tumor suppressor and a protector of cancer cell survival, and elucidation of its exact role at different stages of cancer progression and in treatment responsiveness is a complex and challenging task. Better understanding of autophagy regulation and its impact on treatment outcome will potentially allow us to identify novel therapeutic targets in cancer. In this review, we summarize current knowledge on the regulation and dual function of autophagy in tumorigenesis, as well as ongoing efforts in modulating autophagy for cancer treatment and prevention. This is a very exciting and highly promising area of cancer research, as pharmacologic modulation of autophagy appears to augment the efficacy of currently available anticancer regimens and opens the way to the development of new combinatorial therapeutic strategies that will hopefully contribute to cancer eradication.

Targeting tyrosine kinases and autophagy in prostate cancer

Tyrosine kinases play significant roles in tumor progression and therapy resistance. Inhibitors of tyrosine kinases are on the forefront of targeted therapy. For prostate cancer, tyrosine kinases play an additional role in the development of castration-resistant disease state, the most troubling aspect of prostate cancinogenesis which presently defies any effective treatment. Among the 30 or so tyrosine kinases expressed in a typical prostate cancer cell, nearly one third of them have been implicated in prostate carcinogenesis. Interestingly, most of them channel signals through a trio of non-receptor tyrosine kinases, Src/Etk/FAK, referred here as Src tyrosine kinase complex. This complex has been shown to play a significant role in the aberrant activation of androgen receptor (AR) mediated by growth factors (e.g., epidermal growth factor (EGF)), cytokines (interleukin (IL)-6), chemokines (IL-8), and neurokines (gastrin-releasing peptide). These factors are induced and released from the prostate cancer to the stromal cells upon androgen withdrawal. The Src kinase complex has the ability to phosphorylate androgen receptor, resulting in the nuclear translocation and stabilization of un-liganded androgen receptor. Indeed, tyrosine kinase inhibitors targeting Src can inhibit androgen-independent growth of prostate cancer cells in vitro and in preclinical xenograft model. While effective in inducing growth arrest and inhibiting metastasis of castration-resistant tumors, Src inhibitors rarely induce a significant level of apoptosis. This is also reflected by the general ineffectiveness of tyrosine kinase inhibitors as monotherapy in clinical trials. One of the underlying causes of apoptosis resistance is "autophagy," which is induced by tyrosine kinase inhibitors and by androgen withdrawal. Autophagy is a self-digesting process to regenerate energy by removal of long-lived proteins and retired organelles to provide a survival mechanism to cells encountering stresses. Excessive autophagy, sometimes, could lead to type II programmed cell death. We demonstrated that autophagy blockade sensitizes prostate cancer cells toward Src tyrosine kinase inhibitor. Thus, a combination therapy based on Src tyrosine kinase inhibitor and autophagy modulator deserves further attention as a potential treatment for relapsed prostate cancer.

Glucocorticoids downregulate Fyn and inhibit IP(3)-mediated calcium signaling to promote autophagy in T lymphocytes

T cell receptor activation induces inositol 1,4,5 trisphosphate (IP(3))-mediated calcium signaling that is essential for cell metabolism and survival. Moreover, inhibitors of IP(3) or pharmacological agents that disrupt calcium homeostasis readily induce autophagy. Using a glucocorticoid-sensitive CD4/CD8 positive T cell line, we found that dexamethasone prevented both IP(3)-mediated and spontaneous calcium signals within a timeframe that correlated with the induction of autophagy. We determined that this loss in IP(3)-mediated calcium signaling was dependent upon the downregulation of the Src kinase Fyn at the mRNA and protein level. Because it has previously been shown that Fyn positively regulates IP(3)-mediated calcium release by phosphorylating Type I IP(3) receptors (IP(3)R1), we investigated the effect of glucocorticoids on IP(3)R1 phosphorylation at Tyr353. Accordingly, glucocorticoid-mediated downregulation of Fyn prevented IP(3)R1 phosphorylation at Tyr353. Moreover, selective knockdown of Fyn or treatment with a Src inhibitor also attenuated IP(3)-mediated calcium release and induced autophagy. Collectively, these data indicate that glucocorticoids promote autophagy by inhibiting IP(3)-dependent calcium signals. These findings carry important therapeutic implications given the widespread use of dexamethasone as both a chemotherapeutic and immunosuppressive agent.

Interleukin-9 (IL-9) and NPM-ALK each generate mast cell hyperplasia as single 'hit' and cooperate in producing a mastocytosis-like disease in mice

Mast cell neoplasms are characterized by abnormal growth and focal accumulation of mast cells (MC) in one or more organs. Although several cytokines, including stem cell factor (SCF) and interleukin-9 (IL-9) have been implicated in growth of normal MC, little is known about pro-oncogenic molecules and conditions triggering differentiation and growth of MC far enough to lead to the histopathological picture of overt mastocytosis. The anaplastic lymphoma kinase (ALK) has recently been implicated in growth of neoplastic cells in malignant lymphomas. Here, we describe that transplantation of NPM-ALK-transplanted mouse bone marrow progenitors into lethally irradiated IL-9 transgenic mice not only results in lymphoma-formation, but also in the development of a neoplastic disease exhibiting histopathological features of systemic mastocytosis, including multifocal dense MC-infiltrates, occasionally with devastating growth in visceral organs. Transplantation of NPM-ALK-transduced progenitors into normal mice or maintenance of IL-9-transgenic mice without NPM-ALK each resulted in MC hyperplasia, but not in mastocytosis. Neoplastic MC in mice not only displayed IL-9, but also the IL-9 receptor, and the same was found to hold true for human neoplastic MC. Together, our data show that neoplastic MC express IL-9 receptors, that IL-9 and NPM-ALK upregulate MC-production in vivo, and that both'hits' act in concert to induce a mastocytosis-like disease in mice. These data may have pathogenetic and clinical implications and fit well with the observation that neoplastic MC in advanced SM strongly express NPM and multiple "lymphoid" antigens including CD25 and CD30.

Effect of the specific Src family kinase inhibitor saracatinib on osteolytic lesions using the PC-3 bone model

The hematogenous metastatic spread of prostate cancer is preferentially to bone and can result in significant patient morbidity. Although these metastatic lesions are typically osteoblastic, bone resorption is believed to have a prerequisite role in their development. Src kinase has been identified to contribute to prostate cancer tumor growth and metastasis. In addition, Src is also essential in bone metabolism, especially in bone resorption. We hypothesized that inhibiting Src activity with the specific Src family kinase inhibitor saracatinib (AZD0530) would inhibit tumor cell growth and osteoclast differentiation in the tumor-bone interface, thus providing a new approach for advanced prostate cancer. We found that saracatinib inhibited PC-3 cell growth and invasion in a dose-dependent manner. Phosphorylation of Src, focal adhesion kinase, and P38 kinases was inhibited by saracatinib at the submicromolar range. Saracatinib also inhibited the expression and secretion of invasion-related molecules interlukin-8, urokinase-type plasminogen activator, and matrix metalloprotease-9. Receptor activator of NF-kappaB ligand (RANKL)-induced osteoclastogenesis and signaling were inhibited by saracatinib in both macrophages and PC-3 cells. In in vivo studies, control mice developed more severe osteolytic lesions compared with the treatment group. Immunohistochemical and biochemical assays of bone metabolites confirmed that saracatinib preserved bone architecture in the presence of prostate cancer tumor cells. In summary, we have shown the inhibition of PC3 cell growth and invasion by saracatinib. Src inhibition also blocked the RANKL stimulatory pathway in osteoclasts and PC3 cells. The inhibition of Src thus targets multiple sites involved in prostate cancer bone metastasis, which may offer a therapeutic advantage in treating advanced prostate cancer.