Resveratrol activates autophagic cell death in prostate cancer cells via downregulation of STIM1 and the mTOR pathway

Resveratrol (RSV), a natural polyphenol, has been suggested to induce cell cycle arrest and activate apoptosis‐mediated cell death in several cancer cells, including prostate cancer. However, several molecular mechanisms have been proposed on its chemopreventive action, the precise mechanisms by which RSV exerts its anti‐proliferative effect in androgen‐independent prostate cancer cells remain questionable. In the present study, we show that RSV activates autophagic cell death in PC3 and DU145 cells, which was dependent on stromal interaction molecule 1 (STIM1) expression. RSV treatment decreases STIM1 expression in a time‐dependent manner and attenuates STIM1 association with TRPC1 and Orai1. Furthermore, RSV treatment also decreases ER calcium storage and store operated calcium entry (SOCE), which induces endoplasmic reticulum (ER) stress, thereby, activating AMPK and inhibiting the AKT/mTOR pathway. Similarly, inhibition of SOCE by SKF‐96365 decreases the survival and proliferation of PC3 and DU145 cells and inhibits AKT/mTOR pathway and induces autophagic cell death. Importantly, SOCE inhibition and subsequent autophagic cell death caused by RSV was reversed by STIM1 overexpression. STIM1 overexpression restored SOCE, prevents the loss of mTOR phosphorylation and decreased the expression of CHOP and LC3A in PC3 cells. Taken together, for the first time, our results revealed that RSV induces autophagy‐mediated cell death in PC3 and DU145 cells through regulation of SOCE mechanisms, including downregulating STIM1 expression and trigger ER stress by depleting ER calcium pool. © 2015 The Authors. Molecular Carcinogenesis, published by Wiley Periodicals, Inc.     

Celecoxib enhances radiosensitivity of hypoxic glioblastoma cells through endoplasmic reticulum stress

Background

Refractoriness of glioblastoma multiforme (GBM) largely depends on its radioresistance. We investigated the radiosensitizing effects of celecoxib on GBM cell lines under both normoxic and hypoxic conditions.

Methods

Two human GBM cell lines, U87MG and U251MG, and a mouse GBM cell line, GL261, were treated with celecoxib or γ-irradiation either alone or in combination under normoxic and hypoxic conditions. Radiosensitizing effects were analyzed by clonogenic survival assays and cell growth assays and by assessing apoptosis and autophagy. Expression of apoptosis-, autophagy-, and endoplasmic reticulum (ER) stress–related genes was analyzed by immunoblotting.

Results

Celecoxib significantly enhanced the radiosensitivity of GBM cells under both normoxic and hypoxic conditions. In addition, combined treatment with celecoxib and γ-irradiation induced marked autophagy, particularly in hypoxic cells. The mechanism underlying the radiosensitizing effect of celecoxib was determined to be ER stress loading on GBM cells.

Conclusion

Celecoxib enhances the radiosensitivity of GBM cells by a mechanism that is different from cyclooxygenase-2 inhibition. Our results indicate that celecoxib may be a promising radiosensitizing drug for clinical use in patients with GBM.     

Adaptive response of resistant cancer cells to chemotherapy

Despite advances in cancer therapeutics and the integration of personalized medicine, the development of chemoresistance in many patients remains a significant contributing factor to cancer mortality. Upon treatment with chemotherapeutics, the disruption of homeostasis in cancer cells triggers the adaptive response which has emerged as a key resistance mechanism. In this review, we summarize the mechanistic studies investigating the three major components of the adaptive response, autophagy, endoplasmic reticulum (ER) stress signaling, and senescence, in response to cancer chemotherapy. We will discuss the development of potential cancer therapeutic strategies in the context of these adaptive resistance mechanisms, with the goal of stimulating research that may facilitate the development of effective cancer therapy.     

Azithromycin enhances the cytotoxicity of DNA-damaging drugs via lysosomal membrane permeabilization in lung cancer cells

Cancer cells use autophagy for growth, survival, and cytoprotection from chemotherapy. Therefore, autophagy inhibitors appear to be good candidates for cancer treatment. Our group previously reported that macrolide antibiotics, especially azithromycin (AZM), have potent autophagy inhibitory effects, and combination treatment with tyrosine kinase inhibitors or proteasome inhibitors enhances their anti–cancer activity. In this study, we evaluated the effect of combination therapy with DNA-damaging drugs and AZM in non–small-cell lung cancer (NSCLC) cells. We found that the cytotoxic activities of DNA-damaging drugs, such as doxorubicin (DOX), etoposide, and carboplatin, were enhanced in the presence of AZM in NSCLC cell lines, whereas AZM alone exhibited almost no cytotoxicity. This enhanced cell death was dependent on wild-type-p53 status and autophagosome-forming ability because TP53 knockout (KO) and ATG5-KO cells attenuated AZM-enhanced cytotoxicity. DOX treatment upregulated lysosomal biogenesis by activating TFEB and led to lysosomal membrane damage as assessed by galectin 3 puncta assay and cytoplasmic leakage of lysosomal enzymes. In contrast, AZM treatment blocked autophagy, which resulted in the accumulation of lysosomes/autolysosomes. Thus, the effects of DOX and AZM were integrated into the marked increase in damaged lysosomes/autolysosomes, leading to prominent lysosomal membrane permeabilization (LMP) for apoptosis induction. Our data suggest that concomitant treatment with DNA-damaging drugs and AZM is a promising strategy for NSCLC treatment via pronounced LMP induction.     

Osthole induces apoptosis of the HT-29 cells via endoplasmic reticulum stress and autophagy

Endoplasmic reticulum stress (ERS) and autophagy are important pathways, which induce apoptosis of tumor cells. Osthole has been demonstrated to exert anticancer effects via the induction of apoptosis in several human colon cancer lines, but the mechanism underlying its involvement in the induction of ERS and autophagy in the human HT-29 colorectal cancer cell line remains unknown. The present study aimed to identify the possible signaling pathways involved in osthole-induced apoptosis of HT29 cells. Methodologically, colony formation and Cell Counting Kit-8 assays were used to assess cell proliferation and viability, respectively, while flow cytometry was performed to investigate apoptosis. Signaling pathways, including apoptosis, autophagy and ERS, were also investigated in the HT-29 cell line using western blot analysis. The results demonstrated that osthole inhibited cellular proliferation and viability in a dose-dependent manner. In addition, osthole induced the expression level of proteins associated with mitochondria-mediated cell apoptosis, autophagy and ERS. The association between autophagy and ERS in osthole-induced apoptosis in the HT-29 cell line was further clarified. Inhibiting cell autophagy with the inhibitor, 3-methyladenine, suppressed osthole-induced cell apoptosis and enhanced osthole-induced ERS. By contrast, alleviating ERS with the inhibitor, 4-phenylbutyric acid attenuated osthole-induced cell apoptosis and autophagy. In conclusion, osthole could significantly suppress the proliferation and viability of the HT-29 colorectal cancer cell line and induce cell apoptosis via autophagy and ERS. Furthermore, ERS may play a more important role in osthole-induced cell apoptosis.     

Acceleration of invasive activity via matrix metalloproteinases by transfection of the estrogen receptor-alpha gene in endometrial carcinoma cells

It is well known that the functions of reproductive organs are regulated by sex steroids and their receptors and it is hypothesized that the progression of neoplasms that originate from the reproductive organs is influenced by them. However, the correlation between sex steroids and tumor progression, especially tumor invasion, is not well known in endometrial carcinoma. In our study, we focused on the influence of estrogen and its receptor in invasion and matrix metalloproteinases (MMPs), which are known to be important in tumor invasion, as well as on endometrial carcinoma cells. The growth of Ishikawa cells, to which an estrogen receptor-alpha expressing vector was transfected, was accelerated by 17 beta-estradiol as was the acceleration of the expression of cyclin D1. By invasion assay, in conditions with 17 beta-estradiol, the invasiveness of Ishikawa cells was enhanced. Furthermore, according to the accelerated invasiveness, the expression of MMP-1, -7 and -9 and Ets-1 was enhanced. These results suggest that activation of ER-alpha by estrogen results in tumor progression by stimulating cell growth and invasiveness via acceleration of the expression of MMPs.     

The combination of tephrosin with 2-deoxy-D-glucose enhances the cytotoxicity via accelerating ATP depletion and blunting autophagy in human cancer cells

2-Deoxy-D-glucose (2-DG), a synthetic glucose analog that acts as a glycolytic inhibitor, is currently under clinical evaluation for targeting tumor cells. Tephrosin (TSN), a plant rotenoid, is known as an anticancer agent. In this study, we describe that the addition of TSN to 2-DG enhanced the cytotoxic activity of 2-DG against various types of cancer cells by accelerating ATP depletion and blunting autophagy. TSN increased the sensitivity of cancer cells to the cytotoxic effect of 2-DG. The combination of TSN and 2-DG induced acceleration of intracellular ATP depletion and the drastic activation of AMP-activated protein kinase (AMPK), which resulted in the inactivation of the mammalian target of rapamycin (mTOR) pathway. Of particular interest, TSN suppressed 2-DG-induced autophagy, a cell survival process in response to nutrient deprivation. We also showed that TSN inhibited 2-DG-induced activation of elongation factor-2 kinase (eEF-2K), which has been known to regulate 2-DG-induced autophagy. Inhibition of eEF-2K by RNA interference blunted 2-DG-induced autophagy and increased the sensitivity of cancer cells to the cytotoxic effect of 2-DG. The addition of TSN to 2-DG, however, did not enhance the cytotoxic activity of 2-DG by knockdown of eEF-2K, suggesting that inhibition of eEF-2K by tephrsoin could be a critical role in the potentiating effect of TSN on the cytotoxicity of 2-DG. Furthermore, we showed that the blunted autophagy and enhanced cytotoxicity of 2-DG was accompanied by the augmentation of apoptosis. These results show that TSN may be valuable for augmenting the therapeutic efficacy of 2-DG.     

ABC294640, a sphingosine kinase 2 inhibitor,enhances the antitumor effects of TRAIL in non-small cell lung cancer

Evidences suggest that tumor microenvironment may play an important role in cancer drug resistance. Sphingosine kinase 2 (SphK2) is proposed to be the key regulator of sphingolipid signaling. This study is aimed to investigate whether the combination of molecular targeting therapy using a specific inhibitor of SphK2 (ABC294640), with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can enhance the apoptosis of non-small cell lung cancer (NSCLC) cells. Our results revealed that NSCLC cells'' sensitivity to TRAIL is correlated with the level of SphK2. Compared with TRAIL alone, the combination therapy enhanced the apoptosis induced by TRAIL, and knockdown of SphK2 by siRNA presented a similar effect. Combination therapy with ABC294640 increased the activity of caspase-3/8 and up-regulated the expression of death receptors (DR). Additional investigations revealed that translocation of DR4/5 to the cell membrane surface was promoted by adding ABC294640. However, expression of anti-apoptosis proteins such as Bcl^-2 and IAPs was not significantly modified by this SphK2 inhibitor. Overall, this work demonstrates that SphK2 may contribute to the apoptosis resistance in NSCLC, thus indicating a new therapeutic target for resistant NSCLC cells.     

PD‐1 blockade enhances the antitumor efficacy of GM‐CSF surface‐modified bladder cancer stem cells vaccine

Eliminating cancer stem cells (CSCs) is a key issue in eradicating tumor. The streptavidin–granulocyte‐macrophage‐colony stimulating factor (SA–GM‐CSF) surface‐modified bladder CSCs vaccine previously developed using our protein–anchor technology could effectively induce specific immune response for eliminating CSCs. However, program death receptor‐1 (PD‐1)/program death ligand 1 (PD‐L1) signaling in tumor microenvironment results in tumor‐adaptive immune resistance. Although the CSCs vaccine could increase the number of CD8⁺T cells, a part of these CD8⁺T cells expressed PD‐1. Moreover, the CSCs vaccine upregulated the PD‐L1 expression of tumor cells, resulting in immune resistance. Adding PD‐1 blockade to the CSCs vaccine therapy increased the population of CD4⁺, CD8⁺ and CD8⁺IFN‐γ⁺ but not CD4⁺ Foxp3⁺T cells and induced the highest production of IFN‐γ. PD‐1 blockade could effectively enhance the functions of tumor‐specific T lymphocytes generated by the CSCs vaccine. This combination therapy improved the cure rate among mice and effectively protected the mice against a second CSCs cell challenge, but not a RM‐1 cell challenge. These results indicate that PD‐1 blockade combined with the GM‐CSF‐modified CSCs vaccine effectively induced a strong and specific antitumor immune response against bladder cancer.     

Lenvatinib enhances antitumor immunity by promoting the infiltration of TCF1+ CD8+ T cells in HCC via blocking VEGFR2

Lenvatinib is the favorable treatment for advanced hepatocellular carcinoma (HCC), and it is currently undergoing phase III clinical trials. However, the specific effects of lenvatinib on PD1⁺ CD8⁺ T cells in HCC microenvironment have not been systematically studied. Here, we established an orthotopic hepa1-6 mouse model treated with lenvatinib to investigate CD8⁺ T cells’ role in the tumor and spleen. We found an increasing proportion of TCF-1⁺ in PD1⁺ CD8⁺ T cells and proliferation of PD1⁺ CD8⁺ T cells after lenvatinib treatment. Meanwhile, lenvatinib treatment upregulated the expression of granzyme B on PD1⁺ CD8⁺ T cells both in vitro and in vivo. Lenvatinib activated the endogenous mTOR pathway of exhausted CD8⁺ T cells, and mTOR pathway blockade eliminated the antitumor effect of lenvatinib and function of PD1⁺ CD8⁺ T cells. The effects of the mTOR pathway on PD1⁺ CD8⁺ T cells after lenvatinib treatment were mediated by VEGFR2 inhibition. Overall, our work provides insight into the mechanism of lenvatinib's antitumor efficacy through exhausted CD8⁺ T cells in HCC treatment.     

SCD1 inhibition enhances the effector functions of CD8+ T cells via ACAT1-dependent reduction of esterified cholesterol

We previously reported that the inhibition of stearoyl-CoA desaturase 1 (SCD1) enhances the antitumor function of CD8⁺ T cells indirectly via restoring production of DC recruiting chemokines by cancer cells and subsequent induction of antitumor CD8⁺ T cells. In this study, we investigated the molecular mechanism of direct enhancing effects of SCD1 inhibitors on CD8⁺ T cells. In vitro treatment of CD8⁺ T cells with SCD1 inhibitors enhanced IFN-γ production and cytotoxic activity of T cells along with decreased oleic acid and esterified cholesterol, which is generated by cholesterol esterase, acetyl-CoA acetyltransferase 1 (ACAT1), in CD8⁺ T cells. The addition of oleic acid or cholesteryl oleate reversed the enhanced functions of CD8⁺ T cells treated with SCD1 inhibitors. Systemic administration of SCD1 inhibitor to MCA205 tumor-bearing mice enhanced IFN-γ production of tumor-infiltrating CD8⁺ T cells, in which oleic acid and esterified cholesterol, but not cholesterol, were decreased. These results indicated that SCD1 suppressed effector functions of CD8⁺ T cells through the increased esterified cholesterol in an ACAT1-dependent manner, and SCD1 inhibition enhanced T cell activity directly through decreased esterified cholesterol. Finally, SCD1 inhibitors or ACAT1 inhibitors synergistically enhanced the antitumor effects of anti-PD-1 antibody therapy or CAR-T cell therapy in mouse tumor models. Therefore, the SCD1–ACAT1 axis is regulating effector functions of CD8⁺ T cells, and SCD1 inhibitors, and ACAT1 inhibitors are attractive drugs for cancer immunotherapy.     

Assessment of the effect of sphingosine kinase inhibitors on apoptosis,unfolded protein response and autophagy of T-cell acute lymphoblastic leukemia cells; indications for novel therapeutics

Sphingosine 1-phosphate (S1P) is a bioactive lipid that is formed by the phosphorylation of sphingosine and catalysed by sphingosine kinase 1 (SK1) or sphingosine kinase 2 (SK2). Sphingosine kinases play a fundamental role in many signaling pathways associated with cancer, suggesting that proteins belonging to this signaling network represent potential therapeutic targets. Over the last years, many improvements have been made in the treatment of T-cell acute lymphoblastic leukemia (T-ALL); however, novel and less toxic therapies are still needed, especially for relapsing and chemo-resistant patients. Here, we analyzed the therapeutic potential of SKi and ROMe, a sphingosine kinase 1 and 2 inhibitor and SK2-selective inhibitor, respectively. While SKi induced apoptosis, ROMe initiated an autophagic cell death in our in vitro cell models. SKi treatment induced an increase in SK1 protein levels in Molt-4 cells, whereas it activated the endoplasmic reticulum (ER) stress/unfolded protein response (UPR) pathway in Jurkat and CEM-R cells as protective mechanisms in a sub-population of T-ALL cells. Interestingly, we observed a synergistic effect of SKi with the classical chemotherapeutic drug vincristine. In addition, we reported that SKi affected signaling cascades implicated in survival, proliferation and stress response of cells. These findings indicate that SK1 or SK2 represent potential targets for treating T-ALL.     

Differential effects of the glycolysis inhibitor 2-deoxy-D-glucose on the activity of pro-apoptotic agents in metastatic melanoma cells, and induction of a cytoprotective autophagic response

2-Deoxy-D-glucose (2DG) is a synthetic glucose analogue that inhibits glycolysis and blocks cancer cell growth. In this report, we evaluated the role of 2DG in the induction of cell death in human metastatic melanoma cells. We have also examined the effects of 2DG in combined treatments with four different pro-apoptotic agents: (i) Temozolomide (TMZ), a chemotherapic drug commonly used to treat metastatic melanoma, (ii) Pyrimethamine (Pyr), a pro-apoptotic antifolate drug recently reappraised in cancer therapy, (iii) Cisplatin (CisPt), a drug capable of directly binding to DNA ultimately triggering apoptosis of cancer cells and (iv) the kinase inhibitor Staurosporine (STS), a prototypical inducer of mitochondria-mediated apoptosis. We found that 2DG per se: (i) induced a cell cycle arrest in G(0) /G(1) , (ii) promoted autophagy, (iii) was ineffective in inducing apoptosis in association with the chemotherapic drug TMZ, whereas (iv) it was synergistic with CisPt and STS pro-apoptotic drugs through a mechanism involving changes of mitochondrial homeostasis. Conversely, (v) 2DG hindered the pro-apoptotic effects of Pyr via a mechanism involving either the block of cell cycle in G(0) /G(1) or the modification of the free radical production of the cell, i.e., decreasing the production of reactive oxygen species (ROS) and increasing the production of reactive nitrogen species (RNS). Moreover, a clear-cut autophagic response involving endoplasmic reticulum remodelling was detectable. Since autophagic cytoprotection has been suggested to contribute to the induction of chemoresistance, these results could provide useful clues as concerns the use of 2DG as anticancer agent in combinatory protocols.