Radiation-induced apoptosis of tumor cells is facilitated by inhibition of the interaction between Survivin and Smac/DIABLO

ILP-2: A New Bane and Therapeutic Target for Human Cancers

Inhibitor of apoptosis protein-related-like protein-2 (ILP-2), also known as BIRC-8, is a member of the inhibitor of apoptosis protein (IAPs) family, which mainly encodes the negative regulator of apoptosis. It is selectively overexpressed in a variety of human tumors and can help tumor cells evade apoptosis, promote tumor cell growth, increase tumor cell aggressiveness, and appears to be involved in tumor cell resistance to chemotherapeutic drugs. Several studies have shown that downregulation of ILP-2 expression increases apoptosis, inhibits metastasis, reduces cell growth potential, and sensitizes tumor cells to chemotherapeutic drugs. In addition, ILP-2 inhibits apoptosis in a unique manner; it does not directly inhibit the activity of caspases but induces apoptosis by cooperating with other apoptosis-related proteins. Here, we review the current understanding of the various roles of ILP-2 in the apoptotic cascade and explore the use of interfering ILP-2, and the combination of related anti-tumor agents, as a novel strategy for cancer therapy.

The Ectopic Expression of SurvivinT34A and FilC Can Enhance the Oncolytic Effects of Vaccinia Virus in Murine Gastric Cancer

Background/Aims

Anti-tumor vaccines have been shown to be effective in cancer therapeutics ever since the anti-HPV vaccine was developed. Compared to conventional chemotherapy, anti-tumor vaccines can specifically target cancer cells and they have lower side effects. We developed a recombinant vaccinia virus (VACV) (Western Reserve) WR strain, and we tested its anti-tumor effects in an animal model.

Methods

A recombinant VACV WR strain expressing mutant survivin T34A (SurT34A) and FilC was constructed and validated. Its oncolytic effect was tested in vitro using a CCK-8 assay, and its tolerance and anti-tumor effects were tested in a murine gastric cancer model. The proportion of lymphocytes in the spleen and tumor was determined after antibody-mediated immuno-depletion.

Results

The recombinant VACV showed a stronger replication ability in tumor cells, and it was safe in vivo, even at high doses. The combination of vv-SurT34A and vv-FilC resulted in a stronger anti-tumor effect compared to either construct alone. However, the inhibitory effect of vv-SurT34A was stronger than the combination. The recombinant VACV activated the host immune response, as indicated by lymphocyte infiltration in the spleen and tumor tissues.

Conclusion

The recombinant VACV WR strain expressing SurT34A and FilC is a safe and effective anti-tumor vaccine.

Niclosamide sensitizes triple-negative breast cancer cells to ionizing radiation in association with the inhibition of Wnt/β-catenin signaling

Triple-negative breast cancer (TNBC) is one of the most difficult breast cancers to treat because there is no targeted treatment, and conventional cytotoxic chemotherapy followed by adjuvant radiation therapy is the standard of care for patients with TNBC. We herein reported that ionizing radiation (IR) induced Wnt3a, LRP6 and β-catenin expression and consequently activated Wnt/β-catenin signaling in TNBC MDA-MB-231, MDA-MB-468 and Hs578T cells. Moreover, depletion of β-catenin by shRNA sensitized TNBC cells to IR, whereas treatment of Wnt3a protein or overexpression of β-catenin resulted in radioresistance of TNBC cells. Niclosamide, a potent inhibitor of Wnt/β-catenin signaling, not only inhibited constitutive Wnt/β-catenin signaling, but also blocked IR-induced Wnt/β-catenin signaling in TNBC cells. In addition, niclosamide sensitized TNBC cells to IR, prevented Wnt3a-induced radioresistance, and overcame β-catenin-induced radioresistance in TNBC cells. Importantly, animals treated with the combination of niclosamide and γ-ray local tumor irradiation had significant inhibition of MDA-MB-231 tumor growth compared with treated with local tumor irradiation alone. These findings indicate that Wnt/β-catenin signaling pathway plays an important role in the development of radioresistance of TNBC cells, and that niclosamide had significant radiosensitizing effects by inhibiting Wnt/β-catenin signaling in TNBC cells. Our study also provides rationale for further preclinical and clinical evaluation of niclosamide in TNBC management.

Visualization of ceramide channels in lysosomes following endogenous palmitoyl-ceramide accumulation as an initial step in the induction of necrosis

In this study, we showed that the dual addition of glucosyl ceramide synthase and ceramidase inhibitors to A549 cell culture led to the possibility of ceramide channel formation via endogenous palmitoyl-ceramide accumulation with an increase in cholesterol contents in the lysosome membrane as an initial step prior to initiation of necrotic cell death. In addition, the dual addition led to black circular structures of 10-20 nm, interpreted as stain-filled cylindrical channels on transmission electron microscopy. The formation of palmitoyl-ceramide channels in the lysosome membrane causes the liberation of cathepsin B from lysosomes for necrotic cell death. On the other hand, necrotic cell death in the dual addition was not caused by oxidative stress or cathepsin B activity, and the cell death was free from the contribution of the translation of Bax protein to the lysosome membrane.

Palmitoyl-ceramide accumulation with necrotic cell death in A549 cells, followed by a steep increase in sphinganine content

Ceramides (Cers) have recently been identified as key signaling molecules that mediate biological functions such as cell growth, differentiation, senescence, apoptosis, and autophagy. However, the functions of Cer accumulation in necrotic cell death remain unknown. The aim of this study was to clarify the relationship between Cer accumulation with inhibition of the conversion pathway of Cer and concomitant necrotic cell death. In order to minimize the effect of apoptosis against necrotic cell death, A549 cells having the inhibiting effect of caspase 9 by survivin were used in this study. Consequently, Cer accumulation in A549 cells would likely be associated with a pathway other than the mitochondrial caspase-dependent pathway of apoptosis. Here, we showed that the dual addition of a glucosyl-Cer synthase inhibitor and a ceramidase inhibitor to A549 cell culture induced palmitoyl-Cer accumulation with Cer synthase 5 expression and necrotic cell death with lysosomal rupture together with leakage of cathepsin B/alkalization after 2–3 h, although it is unknown in this study whether the necrotic cell death was caused by the lysosomal rupture. This Cer accumulation was followed by a steep increase in sphinganine base levels via the activation of serine palmitoyltransferase activity brought about by the increase in palmitoyl-coenzyme A concentration as a substrate after 5–6 h. The increase in palmitoyl-coenzyme A concentration was achieved by activation of the fatty acid synthetic pathway from acetyl coenzyme A.

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Palmitoylceramide accumulation with necrosis is studied.

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The accumulation is with ceramide synthase 5 expression.

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The accumulation is followed by high sphinganine levels.

Multisite mutation of monomer survivin with enhanced effect on apoptosis regulation of breast cancer cells

Survivin is an important protein in regulating both cell apoptosis and proliferation. It has attracted growing attentions in recent years as a promising target for cancer therapy. Previous studies have revealed that monomeric survivin regulated apoptosis in a more significant way than the wild-type survivin that generally contains a large portion of its dimers. In order to investigate the roles of monomeric mutant survivin apoptosis and cell cycle regulation of human cancer cells, we developed and tested three dominant-negative mutants with multisite mutations (MSM) including TAT-survivin(34/101/102), TAT-survivin(34/117/101/102) and TAT-survivin(117/101/102). Results revealed that MSM mutants remained as monomers under ambient conditions, and induced cells (breast cancer Bcap-37 cells) apoptosis even more efficiently, primarily through the caspase-dependent and Bcl-2-related pathways, than non-monomeric mutants. We further identified that the TAT-survivin(34/101/102) and TAT-survivin(117/101/102) MSM significantly inhibited the proliferation of Bcap-37 cells and arrested cells in S and G2/M phases, while TAT-survivin(34/117/101/102) arrested cells in G2/M phase. It appeared to us that TAT-survivin(34/101/102) and TAT-survivin(117/101/102) also inhibited cell proliferation more significantly. These findings suggest that such MSM afford monomeric survivin with promising potentials for cancer therapy.

Inhibitor of Apoptosis (IAP) proteins as therapeutic targets for radiosensitization of human cancers

Radiotherapy initiates a variety of signaling events in cancer cells that eventually lead to cell death in case the DNA damage cannot be repaired. However, the signal transduction pathways that mediate cell death in response to radiation-inflicted DNA damage are frequently disturbed in human cancers, contributing to radioresistance. For example, aberrant activation of antiapoptotic programs such as high expression of Inhibitor of Apoptosis (IAP) proteins has been shown to interfere with the efficacy of radiotherapy. Since IAP proteins have been linked to radioresistance in several malignancies, therapeutic targeting of IAP proteins may open new perspectives to overcome radioresistance. Therefore, molecular targeting of IAP proteins may provide novel opportunities to reactivate cell death pathways that mediate radiation-induced cytotoxicity. A number of strategies have been developed in recent years to antagonize IAP proteins for the treatment of cancers. Some of these approaches have already been translated into a clinical application. While IAP protein-targeting agents are currently being evaluated in early clinical trials alone or in combination with conventional chemotherapy, they have not yet been tested in combination with radiation therapy. Therefore, it is a timely subject to discuss the opportunities of antagonizing IAP proteins for radiosensitization. Preclinical studies demonstrating the potential of this concept in relevant in vitro and in vivo models underscore that this combination approach warrants further clinical investigation. Thus, combination protocols using IAP antagonists together with radiotherapy may pave the avenue to more effective radiation-based treatment options for cancer patients.

Bidirectional function of shenghe powder on repair of radiation-induced DNA damage in glioma and astrocyte

The study assessed the effect of Chinese herbs of Shenghe Powder (SHP) on the repair capacity of gamma-radiation-induced DNA damage in rat glioma cells (C6) compared with normal human astrocytes (NHA). C6 and NHA Cells treated with SHP and irradiated with 2Gy of gamma radiation. Cells growth inhibition were analysed by MTT assay, DNA damage and repair were evaluated using phosphorylated histone H2AX (γH2AX) at the appointed time. Apoptosis was observed by flow cytometry, and the expression of DNA-dependent protein kinase (DNA-PK) and surviving proteins were assessed by Western blot analysis. SHP depressed the radiation-induced DNA double-strand break and enhanced the DNA repair capacity in NHA, which correlated with promotion of DNA-PK phosphorylation. In contrast, SHP enhanced radiosensitivity of C6 cells, the pre-treatment with SHP resulted in reduced numbers of γH2AX foci in irradiated C6 cells, and decreased the expression of DNA-PK and survivn(P<0.005). It significant effect on inhibition of C6 cell proliferation and induced C6 cells apoptosis in a time-depdendent manner than radiation alone (P<0.001). SHP showed a novel bidirectional function to improve the radioresistance of NHA and enhanced radiosensitivity of C6 cells. This implies that SHP can protect the NHA from radiant damage and enhanced the sensitivity of C6 cells to radiation, which could be attributed to the alteration of survivin DNA-PK in DNA repair processes.

8-Aminoadenosine enhances radiation-induced cell death in human lung carcinoma A549 cells

The combination of a chemotherapeutic agent and radiation is widely applied to enhance cell death in solid tumor cells in cancer treatment. The purine analogue 8-aminoadenosine (8-NH(2)-Ado) is known to be a transcription inhibitor that has proved very effective in multiple myeloma cell lines and primary indolent leukemia cells. In this report, to examine whether 8-NH(2)-Ado had the ability to enhance the radiation-induced cell killing in solid tumor cells, human lung adenocarcinoma A549 cells were irradiated in the presence and absence of 8-NH(2)-Ado. 8-NH(2)-Ado significantly increased reproductive cell death and apoptosis in A549 cells exposed to X-rays. When peptide inhibitors against caspase-3, -8, and -9 were utilized to evaluate the involvement of caspases, all inhibitors suppressed the enhancement of radiation-induced apoptosis, suggesting that not only mitochondria-mediated apoptotic signal transduction pathways but also death receptor-mediated pathways were involved in this enhancement of apoptosis. In addition, in the cells exposed to the treatment combining X-irradiation and 8-NH(2)-Ado, reduction of the intracellular ATP concentration was essential for survival, and down-regulation of the expression of antiapoptotic proteins such as survivin and XIAP was observed. These results indicate that 8-NH(2)-Ado has potential not only as an anti-tumor drug for leukemia and lymphoma but also as a radiosensitizing agent for solid tumors.

Survivin-T34A: molecular mechanism and therapeutic potential

The inhibitor of apoptosis protein survivin’s threonine 34 to alanine (T34A) mutation abolishes a phosphorylation site for p34(cdc2)–cyclin B1, resulting in initiation of the mitochondrial apoptotic pathway in cancer cells; however, it has little known direct effects on normal cells. The possibility that targeting survivin in this way may provide a novel approach for selective cancer gene therapy has yet to be fully evaluated. Although a flurry of work was undertaken in the late 1990s and early 2000s, only minor advances on this mutant have recently taken place. We recently described that cells generated to express a stable form of the mutant protein released this survivin-T34A to the conditioned medium. When this conditioned medium was collected and deposited on naive tumor cells, conditioned medium T34A was as effective as some chemotherapeutics in the induction of tumor cell apoptosis, and when combined with other forms of genotoxic stressors potentiated their killing effects. We hope with this review to revitalize the T34A field, as there is still much that needs to be investigated. In addition to determining the therapeutic dose and the duration of drug therapy required at the disease site, a better understanding of other key factors is also important. These include knowledge of target cell populations, cell-surface receptors, changes that occur in the target tissue at the molecular and cellular level with progression of the disease, and the mechanism and site of therapeutic action.

Survivin mediates self-protection through ROS/cdc25c/CDK1 signaling pathway during tumor cell apoptosis induced by high fluence low-power laser irradiation

Survivin, an important member of inhibitor-of-apoptosis (IAP) family, can be up-regulated by various pro-apoptotic stimuli, such as UV, photodynamic therapy (PDT) and cisplatin. High fluence low-power laser irradiation (HF-LPLI) is a newly discovered pro-apoptotic stimulator. The anti-apoptotic mechanism of survivin during HF-LPLI-induced apoptosis is still not investigated. Here, we report that HF-LPLI up-regulates survivin activity through reactive oxygen species (ROS)/cdc25c protein phosphatase (cdc25c)/cyclin-dependent kinase (CDK1) signaling pathway in human lung adenocarcinoma cells (ASTC-a-1). The up-regulation of survivin activity can reduce HF-LPLI-induced apoptosis, while down-regulation of the activity can promote the apoptosis. In addition, activated survivin delays mitochondrial depolarization, cytochrome c release, caspase-9 and Bax activation, all of which are typical pro-apoptotic events of cell apoptosis induced by HF-LPLI. On the basis of the present studies, we conclude that survivin can mediate self-protection during tumor cell apoptosis caused by HF-LPLI.

Molecular biology of breast cancer stem cells: potential clinical applications

Breast cancer stem cells (CSC) have been postulated recently as responsible for failure of breast cancer treatment. The purpose of this study is to review breast CSCs molecular biology with respect to their mechanism of resistance to conventional therapy, and to develop treatment strategies that may improve survival of breast cancer patients. A literature search has identified in vitro and in vivo studies of breast CSCs. Breast CSCs overexpress breast cancer resistance protein (BCRP) which allows cancer cells to transport actively chemotherapy agents out of the cells. Radioresistance is modulated through activation of Wnt signaling pathway and overexpression of genes coding for glutathione. Lapatinib can selectively target HER-2 positive breast CSCs and improves disease-free survival in these patients. Metformin may target basal type breast CSCs. Parthenolide and oncolytic viruses are promising targeting agents for breast CSCs. Future clinical trials for breast cancer should include anti-cancer stem cells targeting agents in addition to conventional chemotherapy. Hypofractionation radiotherapy may be indicated for residual disease post chemotherapy.

Identification of a small-molecule inhibitor of the interaction between Survivin and Smac/DIABLO

The protein Survivin is selectively overexpressed in a variety of cancers, but not in normal tissues. It has been reported to be involved in cell survival and cell division. However, the molecular mechanisms involved in its function are not clear, although several binding partner proteins have been proposed to date. Here, we report the identification of a novel small molecule Survivin antagonist, which disrupts the Survivin-Smac/DIABLO interaction in cells. In order to identify Survivin-directed antagonists, we developed a high-throughput screening system based on AlphaScreen technology, which allows the identification of small molecules with the ability to inhibit the interaction of Survivin with Smac/DIABLO or INCENP in vitro. We screened chemical libraries, generated in-house, using this system and identified a 5-deazaflavin analog (compound 1) as a hit compound that selectively inhibited the interaction of Survivin with Smac/DIABLO but not INCENP. In cultured cells, compound 1 abrogated the formation of the complex between Survivin and Smac/DIABLO. In addition, this compound was able to sensitize cultured cells to doxorubicin-mediated DNA damage stress and synergistically enhance apoptotic cell death. Thus, the small-molecule inhibitor described here may serve as a proof-of-principle agent for discriminating between the multiple functions of Survivin.

Extracellular, cell-permeable survivin inhibits apoptosis while promoting proliferative and metastatic potential

The tumour microenvironment is believed to be involved in development, growth, metastasis, and therapy resistance of many cancers. Here we show survivin, a member of the inhibitor of apoptosis protein (IAP) family, implicated in apoptosis inhibition and the regulation of mitosis in cancer cells, exists in a novel extracellular pool in tumour cells. Furthermore, we have constructed stable cell lines that provide the extracellular pool with either wild-type survivin (Surv-WT) or the previously described dominant-negative mutant survivin (Surv-T34A), which has proven pro-apoptotic effects in cancer cells but not in normal proliferating cells. Cancer cells grown in conditioned medium (CM) taken from Surv-WT cells absorbed survivin and experienced enhanced protection against genotoxic stresses. These cells also exhibited an increased replicative and metastatic potential, suggesting that survivin in the tumour microenvironment may be directly associated with malignant progression, further supporting survivin's function in tumourigenesis. Alternatively, cancer cells grown in CM taken from the Surv-T34A cells began to apoptose through a caspase-2- and caspase-9-dependent pathway that was further enhanced by the addition of other chemo- and radiotherapeutic modalities. Together our findings suggest a novel microenvironmental function for survivin in the control of cancer aggressiveness and spread, and should result in the genesis of additional cancer treatment modalities.

Inhibition of HIF-1alpha by the anticancer drug TAS106 enhances X-ray-induced apoptosis in vitro and in vivo

In a previous study, we showed that a novel anticancer drug, 1-(3-C-ethynyl-β-D-ribo-pentofuranosyl)cytosine (TAS106, ECyd) increased the antitumour efficacy of X-irradiation. However, its effects on hypoxic cells in tumours remain unclarified. Here, we show that TAS106 enhances the induction of apoptosis in X-irradiated human gastric adenocarcinoma MKN45 and MKN28 cells under hypoxia in vitro. At the same time, the accumulation of HIF-1α observed under hypoxia was shown to be decreased to the level of normoxia in the presence of 0.1 μM TAS106. To study the function of HIF-1α protein in apoptosis of hypoxic cells, we employed an HIF-1α reductive approach using its specific antisense oligodeoxynucleotide. The reduction of HIF-1α gene expression dramatically enhanced X-ray-induced apoptosis in hypoxic cells. In in vivo experiments in which MKN45 cells were transplanted into severe combined immunodeficient (SCID) mice, TAS106 (0.5 mg kg⁻¹) suppressed HIF-1α expression and subsequently reduced the area of the hypoxic region in the tumour and enhanced the induction of apoptosis in the hypoxic region when combined with 2 Gy of X-irradiation. These results suggest the possibility that TAS106 acts as a potent radiosensitiser through the inhibition of HIF-1α expression and can be a useful agent against radiotherapy-resistant hypoxic cells in solid tumours.