Induction of autophagic cell death and radiosensitization by the pharmacological inhibition of nuclear factor-kappa B activation in human glioma cell lines

Feedback loop between hypoxia and energy metabolic reprogramming aggravates the radioresistance of cancer cells

Radiotherapy is one of the mainstream approaches for cancer treatment, although the clinical outcomes are limited due to the radioresistance of tumor cells. Hypoxia and metabolic reprogramming are the hallmarks of tumor initiation and progression and are closely linked to radioresistance. Inside a tumor, the rate of angiogenesis lags behind cell proliferation, and the underdevelopment and abnormal functions of blood vessels in some loci result in oxygen deficiency in cancer cells, i.e., hypoxia. This prevents radiation from effectively eliminating the hypoxic cancer cells. Cancer cells switch to glycolysis as the main source of energy, a phenomenon known as the Warburg effect, to sustain their rapid proliferation rates. Therefore, pathways involved in metabolic reprogramming and hypoxia-induced radioresistance are promising intervention targets for cancer treatment. In this review, we discussed the mechanisms and pathways underlying radioresistance due to hypoxia and metabolic reprogramming in detail, including DNA repair, role of cancer stem cells, oxidative stress relief, autophagy regulation, angiogenesis and immune escape. In addition, we proposed the existence of a feedback loop between energy metabolic reprogramming and hypoxia, which is associated with the development and exacerbation of radioresistance in tumors. Simultaneous blockade of this feedback loop and other tumor-specific targets can be an effective approach to overcome radioresistance of cancer cells. This comprehensive overview provides new insights into the mechanisms underlying tumor radiosensitivity and progression.

Deciphering the impact of circRNA-mediated autophagy on tumor therapeutic resistance: a novel perspective

Cancer therapeutic resistance remains a significant challenge in the pursuit of effective treatment strategies. Circular RNAs (circRNAs), a class of non-coding RNAs, have recently emerged as key regulators of various biological processes, including cancer progression and drug resistance. This review highlights the emerging role of circRNAs-mediated autophagy in cancer therapeutic resistance, a cellular process that plays a dual role in cancer by promoting both cell survival and death. Increasing evidence suggests that circRNAs can modulate autophagy pathways, thereby influencing the response of cancer cells to therapeutic agents. In this context, the intricate interplay between circRNAs, autophagy, and therapeutic resistance is explored. Various mechanisms are discussed through which circRNAs can impact autophagy, including direct interactions with autophagy-related genes, modulation of signaling pathways, and cross-talk with other non-coding RNAs. Furthermore, the review delves into specific examples of how circRNA-mediated autophagy regulation can contribute to resistance against chemotherapy and radiotherapy. Understanding these intricate molecular interactions provides valuable insights into potential strategies for overcoming therapeutic resistance in cancer. Exploiting circRNAs as therapeutic targets or utilizing them as diagnostic and predictive biomarkers opens new avenues for developing personalized treatment approaches. In summary, this review underscores the importance of circRNA-mediated autophagy in cancer therapeutic resistance and proposes future directions for research in this exciting and rapidly evolving field.

Pitavastatin loaded nanoparticles: a suitable ophthalmic treatment for Acanthamoeba Keratitis inducing cell death and autophagy in Acanthamoeba polyphaga

Statins are effective sterol lowering agents with high amoebicidal activity. Nevertheless, due to their poor aqueous solubility, they remain underused especially in eye drop formulation. The aim of the present study is to develop Pitavastatin loaded nanoparticles suitable for ophthalmic administration and designed for the management of Acanthamoeba Keratitis. These nanocarriers are aimed to solve both the ophthalmic route-associated problems and the limited aqueous drug solubility issues of Pitavastatin. Nanoparticles were obtained by a nanoprecipitation-solvent displacement method and their amoebicidal activity was evaluated against four strains of Acanthamoeba: A. castellanii Neff, A. polyphaga, A. griffini and A. quina. In Acanthamoeba polyphaga, the effect of the present nanoparticles was investigated with respect to the microtubule distribution and several programmed cell death features. Nanoparticles were able to eliminate all the tested strains and Acanthamoeba polyphaga was determined to be the most resistance strain. Nanoparticles induced chromatin condensation, autophagic vacuoles and mitochondria dysfunction.

Statins and Gliomas: A Systematic Review of the Preclinical Studies and Meta-Analysis of the Clinical Literature

BACKGROUND

Gliomas represent most common primary brain tumors. Glioblastoma (GBM) is the most common subtype and carries a poor prognosis. There is growing interest in the anti-glioma properties of statins. The aim of this study was to conduct a systematic review of the preclinical literature and to meta-analyze existing clinical studies to determine what benefit, if any, statins may confer in the context of glioma.

METHODS

The PubMed, Embase, Cochrane, and Web of Science libraries were queried in May 2021. Preclinical studies were included if they investigated the anti-cancer effects of statins in glioma in vitro and in vivo. Clinical studies were included if they reported incidence rates of glioma by statin use, or mortality outcomes among GBM patients by statin use. Pooled point estimates were calculated using a random-effects model.

RESULTS

In total, 64 publications, 51 preclinical and 13 clinical, were included. Preclinical studies indicated that statins inhibited glioma cell proliferation, migration, and invasion. These effects were time- and concentration-dependent. Synergistic anti-glioma effects were observed when statins were combined with other anti-cancer therapies. Clinical observational studies showed an inverse, albeit non-statistically significant, association between statin use and incidence rate of glioma (HR = 0.84, 95% CI 0.62-1.13, I² = 72%, p-heterogeneity = 0.003, 6 studies). Statin use was not associated with better overall survival following GBM surgery (HR = 1.05, 95% CI 0.85-1.30, I² = 30%, p-heterogeneity = 0.23, 4 studies).

CONCLUSION

Statins were potent anti-cancer drugs that suppressed glioma growth through various mechanisms in vitro; these effects have translated into the clinical realm, clinically but not statistically, in terms of glioma incidence but not GBM survival.

The complexity of biological control systems: An autophagy case study

Autophagy and YAP1-WWTR1/TAZ signalling are tightly linked in a complex control system of forward and feedback pathways which determine different cellular outcomes in differing cell types at different time-points after perturbations. Here we extend our previous experimental and modelling approaches to consider two possibilities. First, we have performed additional mathematical modelling to explore how the autophagy-YAP1 crosstalk may be controlled by posttranslational modifications of components of the pathways. Second, since analogous contrasting results have also been reported for autophagy as a regulator of other transduction pathways engaged in tumorigenesis (Wnt/β-catenin, TGF-β/Smads, NF-kB or XIAP/cIAPs), we have considered if such discrepancies may be explicable through situations involving competing pathways and feedback loops in different cell types, analogous to the autophagy-YAP/TAZ situation. Since distinct posttranslational modifications dominate those pathways in distinct cells, these need to be understood to enable appropriate cell type-specific therapeutic strategies for cancers and other diseases.

Synergistic Anticancer Effects of Gemcitabine with Pitavastatin on Pancreatic Cancer Cell Line MIA PaCa-2 in vitro and in vivo

Background

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with an overall 5-year survival rate of 9.3%, and this malignancy is expected to become the second leading cause of cancer-related death by 2030. Gemcitabine resistance develops within weeks of PDAC patient’s chemotherapeutic initiation. Statins, including pitavastatin, have been indicated to have anticancer effects in numerous human cancer cell lines. Thus, in this study, we hypothesized that a combination of gemcitabine and pitavastatin may have a greater anticancer effect than gemcitabine alone on the human pancreatic carcinoma cell line MIA PaCa-2.

Methods

The anticancer effects of gemcitabine with pitavastatin were evaluated using human MIA PaCa-2 cell line in vitro and in vivo Balb/c murine xenograft tumor model. Cell viability was assessed with CCK-8, and cell migration was stained by crystal violet. Cell cycle distribution, apoptosis and mitochondrial membrane potential were examined by flow cytometry. Activation of drug transporters (hENTs, hCNTs), intracellular drug activating (dCK) and inhibition of inactivating enzymes (RRMs) pathways were assessed by Western blotting analysis. Molecular mechanisms and signaling pathways of apoptosis, necrosis and autophagy also were assessed by Western blotting.

Results

We observed that gemcitabine and pitavastatin synergistically suppressed the proliferation of MIA PaCa-2 cells through causing sub-G1 and S phase cell cycle arrest. Activation of apoptosis/necrosis was confirmed by annexin V/propidium iodide double staining, which showed increasing levels of active caspase 3, cleaved poly(ADP-ribose) polymerase and the RIP1–RIP3–MLKL complex. Moreover, gemcitabine–pitavastatin-mediated S phase arrest downregulated cyclin A2/CDK2 and upregulated p21/p27 in MIA PaCa-2 cells. Furthermore, this combination improved drug cellular metabolism pathway, mitochondria function and activated autophagy as part of the cell death mechanism. In vivo, gemcitabine-pitavastatin effectively inhibited tumor growth in a nude mouse mode of Mia PaCa-2 xenografts without observed adverse effect.

Conclusion

Combined gemcitabine–pitavastatin may be an effective novel treatment option for pancreatic cancer.

Combination Therapy With Charged Particles and Molecular Targeting: A Promising Avenue to Overcome Radioresistance

Radiotherapy plays a central role in the treatment of cancer patients. Over the past decades, remarkable technological progress has been made in the field of conventional radiotherapy. In addition, the use of charged particles (e.g., protons and carbon ions) makes it possible to further improve dose deposition to the tumor, while sparing the surrounding healthy tissues. Despite these improvements, radioresistance and tumor recurrence are still observed. Although the mechanisms underlying resistance to conventional radiotherapy are well-studied, scientific evidence on the impact of charged particle therapy on cancer cell radioresistance is restricted. The purpose of this review is to discuss the potential role that charged particles could play to overcome radioresistance. This review will focus on hypoxia, cancer stem cells, and specific signaling pathways of EGFR, NFκB, and Hedgehog as well as DNA damage signaling involving PARP, as mechanisms of radioresistance for which pharmacological targets have been identified. Finally, new lines of future research will be proposed, with a focus on novel molecular inhibitors that could be used in combination with charged particle therapy as a novel treatment option for radioresistant tumors.

mTOR-Mediated Antioxidant Activation in Solid Tumor Radioresistance

Radiotherapy is widely used for the treatment of cancer patients, but tumor radioresistance presents serious therapy challenges. Tumor radioresistance is closely related to high levels of mTOR signaling in tumor tissues. Therefore, targeting the mTOR pathway might be a strategy to promote solid tumor sensitivity to ionizing radiation. Radioresistance is associated with enhanced antioxidant mechanisms in cancer cells. Therefore, examination of the relationship between mTOR signaling and antioxidant mechanism-linked radioresistance is required for effective radiotherapy. In particular, the effect of mTOR signaling on antioxidant glutathione induction by the Keap1-NRF2-xCT pathway is described in this review. This review is expected to assist in the identification of therapeutic adjuvants to increase the efficacy of radiotherapy.

Duocarmycin SA, a potent antitumor antibiotic, sensitizes glioblastoma cells to proton radiation

New treatment modalities for glioblastoma multiforme (GBM) are urgently needed. Proton therapy is considered one of the most effective forms of radiation therapy for GBM. DNA alkylating agents such as temozolomide (TMZ) are known to increase the radiosensitivity of GBM to photon radiation. TMZ is a fairly impotent agent, while duocarmycin SA (DSA) is an extremely potent cytotoxic agent capable of inducing a sequence-selective alkylation of duplex DNA. Here, the effects of sub-nM concentrations of DSA on the radiosensitivity of a human GBM cell line (U-138) to proton irradiation were examined. Radiation sensitivity was determined by viability, apoptosis, necrosis and clonogenic assays. DSA concentrations as low as 0.001 nM significantly sensitized U-138 cells to proton irradiation. DSA demonstrates synergistic cytotoxicity against GBM cells treated with proton radiation in vitro, which may represent a novel therapeutic alternative for the treatment of GBM.

Combined pitavastatin and dacarbazine treatment activates apoptosis and autophagy resulting in synergistic cytotoxicity in melanoma cells

Melanoma is an aggressive skin cancer and its incidence is increasing faster than any other type of cancer. Whilst dacarbazine (DTIC) is the standard chemotherapy for metastatic melanoma, it has limited success. Statins, including pitavastatin, have been demonstrated to have a range of anti-cancer effects in a number of human cancer cell lines. The present study therefore explored the anti-cancer activity of combined DTIC and pitavastatin in A375 and WM115 human melanoma cells. Cell survival assays demonstrated that combined DTIC and pitavastatin treatment resulted in synergistic cell death. Cell cycle analyses further revealed that this combined treatment resulted in a G1 cell cycle arrest, as well as a sub-G1 population, indicative of apoptosis. Activation of apoptosis was confirmed by Annexin V-fluorescein isothiocyanate/propidium iodide double-staining and an increase in the levels of active caspase 3 and cleaved poly (ADP-ribose) polymerase. Furthermore, it was demonstrated that apoptosis occurs through the intrinsic pathway, evident from the release of cytochrome c. Finally, combined DTIC and pitavastatin treatment was demonstrated to also activate autophagy as part of a cell death mechanism. The present study provides novel evidence to suggest that the combined treatment of DTIC and pitavastatin may be effective in the treatment of melanoma.

Rho inhibition by lovastatin affects apoptosis and DSB repair of primary human lung cells in vitro and lung tissue in vivo following fractionated irradiation

Thoracic radiotherapy causes damage of normal lung tissue, which limits the cumulative radiation dose and, hence, confines the anticancer efficacy of radiotherapy and impacts the quality of life of tumor patients. Ras-homologous (Rho) small GTPases regulate multiple stress responses and cell death. Therefore, we investigated whether pharmacological targeting of Rho signaling by the HMG-CoA-reductase inhibitor lovastatin influences ionizing radiation (IR)-induced toxicity in primary human lung fibroblasts, lung epithelial and lung microvascular endothelial cells in vitro and subchronic mouse lung tissue damage following hypo-fractionated irradiation (4x4 Gy). The statin improved the repair of radiation-induced DNA double-strand breaks (DSBs) in all cell types and, moreover, protected lung endothelial cells from IR-induced caspase-dependent apoptosis, likely involving p53-regulated mechanisms. Under the in vivo situation, treatment with lovastatin or the Rac1-specific small molecule inhibitor EHT1864 attenuated the IR-induced increase in breathing frequency and reduced the percentage of γH2AX and 53BP1-positive cells. This indicates that inhibition of Rac1 signaling lowers IR-induced residual DNA damage by promoting DNA repair. Moreover, lovastatin and EHT1864 protected lung tissue from IR-triggered apoptosis and mitigated the IR-stimulated increase in regenerative proliferation. Our data document beneficial anti-apoptotic and genoprotective effects of pharmacological targeting of Rho signaling following hypo-fractionated irradiation of lung cells in vitro and in vivo. Rac1-targeting drugs might be particular useful for supportive care in radiation oncology and, moreover, applicable to improve the anticancer efficacy of radiotherapy by widening the therapeutic window of thoracic radiation exposure.

A Randomized Controlled Open-Label Pilot Study of Simvastatin Addition to Whole-Brain Radiation Therapy in Patients With Brain Metastases

Statins have been reported to have a potential radiosensitizing effect that has not been evaluated in clinical trials. The aim of this study was to evaluate the efficacy and safety of simvastatin in addition to whole-brain radiation therapy (WBRT) in patients with brain metastases (BM). A prospective randomized, controlled, open-label pilot study was conducted on 50 Egyptian patients with BM who were randomly assigned to receive 30-Gy WBRT (control group: 25 patients) or 30 Gy WBRT + simvastatin 80 mg/day for the WBRT period (simvastatin group: 25 patients). The primary outcome was radiological response at 4 weeks after WBRT. Secondary outcomes were 1-year progression-free survival (PFS), 1-year overall survival (OS), and health-related quality of life (HRQL) that was assessed using the European Organization for the Research and Treatment of Cancer Quality of Life Questionnaire C30 (EORTC QLQ-C30) and its brain module (BN-20), at baseline, after WBRT, and 4 weeks after WBRT. The addition of simvastatin was tolerated. Twenty-one patients were not evaluated for radiological response because of death (n = 16), noncompliance to follow-up (n = 4), and clinical deterioration (n = 1). Response rates were 60% and 78.6% (p = 0.427), 1-year PFS rates were 5.2% and 17.7% (p = 0.392), and 1-year OS rates were 12% and 8% (p = 0.880) for the control group and simvastatin group, respectively. Nonsignificant differences were found between the two arms regarding HRQL scales. The addition of simvastatin 80 mg/day did not improve the clinical outcomes of patients with BM receiving WBRT.

Pitavastatin suppressed liver cancer cells in vitro and in vivo

Pitavastatin classically functions as a blood cholesterol-lowering drug. Previously, it was discovered with antiglioma stem cell properties through drug screening. However, whether it can be used for liver cancer cell therapy has never been reported. In this study, the cell viability and colony formation assay were utilized to analyze the cytotoxicity of pitavastatin on liver cancer cells. The cell cycle alteration was checked after pitavastatin treatment. Apoptosis-related protein expression and the effect of caspase inhibitor were also checked. The in vivo inhibitory effect of pitavastatin on the growth of liver tumor was also tested. It was found that pitavastatin inhibited growth and colony formation of liver cancer Huh-7 cells and SMMC7721 cells. It induced arrest of liver cancer cells at the G1 phase. Increased proportion of sub-G1 cells was observed after pitavastatin treatment. Pitavastatin promoted caspase-9 cleavage and caspase-3 cleavage in liver cancer cells. Caspase inhibitor Z-VAD-FMK reversed the cleavage of cytotoxic effect of pitavastatin. Moreover, pitavastatin decreased the tumor growth and improved the survival of tumor-bearing mice. This study suggested the antiliver cancer effect of the old drug pitavastatin. It may be developed as a drug for liver cancer therapy.

TLR9-ERK-mTOR signaling is critical for autophagic cell death induced by CpG oligodeoxynucleotide 107 combined with irradiation in glioma cells

Synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG ODN) function as potential radiosensitizers for glioma treatment, although the underlying mechanism is unclear. It was observed that CpG ODN107, when combined with irradiation, did not induce apoptosis. Herein, the effect of CpG ODN107 + irradiation on autophagy and the related signaling pathways was investigated. In vitro, CpG ODN107 + irradiation induced autophagosome formation, increased the ratio of LC3 II/LC3 I, beclin 1 and decreased p62 expression in U87 cells. Meanwhile, CpG ODN107 also increased LC3 II/LC3 I expression in U251 and CHG-5 cells. In vivo, CpG ODN107 combined with local radiotherapy induced autophagosome formation in orthotopic transplantation tumor. Investigation of the molecular mechanisms demonstrated that CpG ODN107 + irradiation increased the levels of TLR9 and p-ERK, and decreased the level of p-mTOR in glioma cells. Further, TLR9-specific siRNA could affect the expressions of p-ERK and autophagy-related proteins in glioma cells. Taken together, CpG ODN107 combined with irradiation could induce autophagic cell death, and this effect was closely related to the TLR9-ERK-mTOR signaling pathway in glioma cells, providing new insights into the investigation mechanism of CpG ODN.

Engineering a Three-Dimensional In Vitro Drug Testing Platform for Glioblastoma

Three-dimensional (3D) in vivo cell culture modeling is quickly emerging as a platform to replace two-dimensional (2D) monolayer cell culture in vitro tests. Three-dimensional tumor models mimic physiological conditions and provide valuable insight of the tumor cell response to drug discovery application. In this study, we used poly(ethylene glycol) (PEG) hydrogel microwells to generate 3D brain cancer spheroids and studied their treatment with anticancer drugs in single or combination treatment. Glioblastoma (GBM) spheroids were grown through 14 days before infecting with two drugs: Pitavastatin and Irinotecan at various concentrations. A significant cell lysis was observed and cell viability decreased to lower than 7% when drugs were combined at the concentration Pitavastatin 10 μM and Irinotecan 50 μM to infect after 7 days. These findings demonstrate a promising platform—PEG hydrogel microwells—that should be an efficient way to test the drug sensitivity in vitro as well as application in different studies.

The Combination of α-Tocopheryl Succinate and Sodium Selenite on Breast Cancer: A Merit or a Demerit?

α-Tocopheryl succinate (α-TOS), a mitochondria-targeting agent, induces apoptosis in malignant cells in vitro and in vivo. Selenite is a nutritional supplement that has been shown to stimulate apoptosis in cancer cells. This study was designed to investigate the cytotoxic effect of combined treatment of α-TOS and sodium selenite (SSe) in vitro and in vivo and to explore their effect on apoptosis and autophagy in breast cancer. The type of interaction between α-TOS and SSe was evaluated and levels of oxidative stress and apoptotic and autophagic markers were determined. SSe alone showed varying degrees of cytotoxicity on all the tested cell lines. Its combination with α-TOS was antagonistic in vitro in MCF7 and in vivo in mice bearing Ehrlich tumor compared to α-TOS-treated one. Combination of TOS with 2 μM of SSe increased the level of glutathione without changes in antiapoptotic markers Bcl-2 and Mcl-1 at 16 and 48 hrs. SSe decreased caspase 3 activity and protein level of caspases 7 and 9, while it increased autophagic markers beclin-1 and LC3B protein levels of MCF7 cells treated with α-TOS. In conclusion, SSe antagonizes α-TOS-induced apoptosis via inhibition of oxidative stress and promoting prosurvival machinery of autophagy.

Therapeutic interactions of autophagy with radiation and temozolomide in glioblastoma: evidence and issues to resolve

Glioblastoma is a unique model of non-metastasising disease that kills the vast majority of patients through local growth, despite surgery and local irradiation. Glioblastoma cells are resistant to apoptotic stimuli, and their death occurs through autophagy. This review aims to critically present our knowledge regarding the autophagic response of glioblastoma cells to radiation and temozolomide (TMZ) and to delineate eventual research directions to follow, in the quest of improving the curability of this incurable, as yet, disease. Radiation and TMZ interfere with the autophagic machinery, but whether cell response is driven to autophagy flux acceleration or blockage is disputable and may depend on both cell individuality and radiotherapy fractionation or TMZ schedules. Potent agents that block autophagy at an early phase of initiation or at a late phase of autolysosomal fusion are available aside to agents that induce functional autophagy, or even demethylating agents that may unblock the function of autophagy-initiating genes in a subset of tumours. All these create a maze, which if properly investigated can open new insights for the application of novel radio- and chemosensitising policies, exploiting the autophagic pathways that glioblastomas use to escape death.

Therapeutic Implications for Overcoming Radiation Resistance in Cancer Therapy

Ionizing radiation (IR), such as X-rays and gamma (γ)-rays, mediates various forms of cancer cell death such as apoptosis, necrosis, autophagy, mitotic catastrophe, and senescence. Among them, apoptosis and mitotic catastrophe are the main mechanisms of IR action. DNA damage and genomic instability contribute to IR-induced cancer cell death. Although IR therapy may be curative in a number of cancer types, the resistance of cancer cells to radiation remains a major therapeutic problem. In this review, we describe the morphological and molecular aspects of various IR-induced types of cell death. We also discuss cytogenetic variations representative of IR-induced DNA damage and genomic instability. Most importantly, we focus on several pathways and their associated marker proteins responsible for cancer resistance and its therapeutic implications in terms of cancer cell death of various types and characteristics. Finally, we propose radiation-sensitization strategies, such as the modification of fractionation, inflammation, and hypoxia and the combined treatment, that can counteract the resistance of tumors to IR.

Discovery of Power-Law Growth in the Self-Renewal of Heterogeneous Glioma Stem Cell Populations

Background

Accumulating evidence indicates that cancer stem cells (CSCs) drive tumorigenesis. This suggests that CSCs should make ideal therapeutic targets. However, because CSC populations in tumors appear heterogeneous, it remains unclear how CSCs might be effectively targeted. To investigate the mechanisms by which CSC populations maintain heterogeneity during self-renewal, we established a glioma sphere (GS) forming model, to generate a population in which glioma stem cells (GSCs) become enriched. We hypothesized, based on the clonal evolution concept, that with each passage in culture, heterogeneous clonal sublines of GSs are generated that progressively show increased proliferative ability.

Methodology/Principal Findings

To test this hypothesis, we determined whether, with each passage, glioma neurosphere culture generated from four different glioma cell lines become progressively proliferative (i.e., enriched in large spheres). Rather than monitoring self-renewal, we measured heterogeneity based on neurosphere clone sizes (#cells/clone). Log-log plots of distributions of clone sizes yielded a good fit (r>0.90) to a straight line (log(% total clones) = k*log(#cells/clone)) indicating that the system follows a power-law (y = x^k) with a specific degree exponent (k = −1.42). Repeated passaging of the total GS population showed that the same power-law was maintained over six passages (CV = −1.01 to −1.17). Surprisingly, passage of either isolated small or large subclones generated fully heterogeneous populations that retained the original power-law-dependent heterogeneity. The anti-GSC agent Temozolomide, which is well known as a standard therapy for glioblastoma multiforme (GBM), suppressed the self-renewal of clones, but it never disrupted the power-law behavior of a GS population.

Conclusions/Significance

Although the data above did not support the stated hypothesis, they did strongly suggest a novel mechanism that underlies CSC heterogeneity. They indicate that power-law growth governs the self-renewal of heterogeneous glioma stem cell populations. That the data always fit a power-law suggests that: (i) clone sizes follow continuous, non-random, and scale-free hierarchy; (ii) precise biologic rules that reflect self-organizing emergent behaviors govern the generation of neurospheres. That the power-law behavior and the original GS heterogeneity are maintained over multiple passages indicates that these rules are invariant. These self-organizing mechanisms very likely underlie tumor heterogeneity during tumor growth. Discovery of this power-law behavior provides a mechanism that could be targeted in the development of new, more effective, anti-cancer agents.

Novel anti-glioblastoma agents and therapeutic combinations identified from a collection of FDA approved drugs

Background

Glioblastoma (GBM) is a therapeutic challenge, associated with high mortality. More effective GBM therapeutic options are urgently needed. Hence, we screened a large multi-class drug panel comprising the NIH clinical collection (NCC) that includes 446 FDA-approved drugs, with the goal of identifying new GBM therapeutics for rapid entry into clinical trials for GBM.

Methods

Screens using human GBM cell lines revealed 22 drugs with potent anti-GBM activity, including serotonergic blockers, cholesterol-lowering agents (statins), antineoplastics, anti-infective, anti-inflammatories, and hormonal modulators. We tested the 8 most potent drugs using patient-derived GBM cancer stem cell-like lines. Notably, the statins were active in vitro; they inhibited GBM cell proliferation and induced cellular autophagy. Moreover, the statins enhanced, by 40-70 fold, the pro-apoptotic activity of irinotecan, a topoisomerase 1 inhibitor currently used to treat a variety of cancers including GBM. Our data suggest that the mechanism of action of statins was prevention of multi-drug resistance protein MDR-1 glycosylation. This drug combination was synergistic in inhibiting tumor growth in vivo. Compared to animals treated with high dose irinotecan, the drug combination showed significantly less toxicity.

Results

Our data identifies a novel combination from among FDA-approved drugs. In addition, this combination is safer and well tolerated compared to single agent irinotecan.

Conclusions

Our study newly identifies several FDA-approved compounds that may potentially be useful in GBM treatment. Our findings provide the basis for the rational combination of statins and topoisomerase inhibitors in GBM.

Nrf2 is a potential therapeutic target in radioresistance in human cancer

Radiation therapy can effectively kill cancer cells through ROS generation. Cancer cells with upregulated antioxidant systems can develop high radioresistance ability, and the transcription factor NF-E2-related factor 2 (Nrf2) is a key regulator of the antioxidant system. Currently, there are numerous data indicating the important role of Nrf2 in cancer radioresistance. In this review, we summarize the aberrant regulation of Nrf2 in radioresistant cells and discuss the effects and underlying mechanism of Nrf2 in promoting radioresistance. These findings suggest that Nrf2 might be a potential therapeutic target in cancer radiation resistance or a promising radioprotector for normal organs during radiation therapy in the future.

Endoplasmic reticulum stress sensitizes human esophageal cancer cell to radiation

AIM: To investigate the role of endoplasmic reticulum (ER) stress in cancer radiotherapy and its molecular mechanism.

METHODS: Tunicamycin (TM) was applied to induce ER stress in human esophageal cancer cell line EC109, and the radiosensitization effects were detected by acute cell death and clonogenic survival assay. Cell cycle arrest induced by TM was determined by flow cytometric analysis after the cellular DNA content was labeled with propidium iodide. Apoptosis of EC109 cells induced by TM was detected by annexin V staining and Western blotting of caspase-3 and its substrate poly ADP-ribose polymerase. Autophagic response was determined by acridine orange (AO) staining and Western blotting of microtubule-associated protein-1 light chain-3 (LC3) and autophagy related gene 5 (ATG5). In order to test the biological function of autophagy, specific inhibitor or Beclin-1 knockdown was used to inhibit autophagy, and its effect on cell apoptosis was thus detected. Additionally, involvement of the phosphatidylinositol-3 kinase (PI3K)/Akt/mammalian target of the rapamycin (mTOR) pathway was also detected by Western blotting. Finally, male nude mice inoculated subcutaneously with EC109 cells were used to confirm cell model observations.

RESULTS: Our results showed that TM treatment enhanced cell death and reduced the colony survival fraction induced by ionizing radiation (IR), which suggested an obvious radiosensitization effect of TM. Moreover, TM and IR combination treatment led to a significant increase of G2/M phase and apoptotic cells, compared with IR alone. We also observed an increase of AO positive cells, and the protein level of LC3-II and ATG5 was induced by TM treatment, which suggested an autophagic response in EC109 cells. However, inhibition of autophagy by using a chemical inhibitor or Beclin-1 silencing led to increased cell apoptosis and decreased cell viability, which suggested a cytoprotective role of autophagy in stressed EC109 cells. Furthermore, TM treatment also activated mTORC1, and in turn reduced Akt phosphorylation, which suggested the PI3K/Akt/mTOR signal pathway was involved in the TM-induced autophagic response in EC109 cells. Tumor xenograft results also showed synergistic retarded tumor growth by TM treatment and IR, as well as the involvement of the PI3K/Akt/mTOR pathway.

CONCLUSION: Our data showed that TM treatment sensitized human esophageal cancer cells to radiation via apoptosis and autophagy both in vitro and in vivo.

Silencing of mitochondrial NADP(+)-dependent isocitrate dehydrogenase gene enhances glioma radiosensitivity

Reactive oxygen species (ROS) levels are elevated in organisms that have been exposed to ionizing radiation and are protagonists in the induction of cell death. Recently, we demonstrated that the control of mitochondrial redox balance and the cellular defense against oxidative damage are primary functions of mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm) via the supply of NADPH for antioxidant systems. In the present study, we report an autophagic response to ionizing radiation in A172 glioma cells transfected with small interfering RNA (siRNA) targeting the IDPm gene. Autophagy in A172 transfectant cells was associated with enhanced autophagolysosome formation and GFP-LC3 punctuation/aggregation. Furthermore, we found that the inhibition of autophagy by chloroquine augmented apoptotic cell death of irradiated A172 cells transfected with IDPm siRNA. Taken together, our data suggest that autophagy functions as a survival mechanism in A172 cells against ionizing radiation-induced apoptosis and the sensitizing effect of IDPm siRNA and autophagy inhibitor on the ionizing radiation-induced apoptotic cell death of glioma cells offers a novel redox-active therapeutic strategy for the treatment of cancer.

Modulating autophagy: a strategy for cancer therapy

Autophagy is a process in which long-lived proteins, damaged cell organelles, and other cellular particles are sequestered and degraded. This process is important for maintaining the cellular microenvironment when the cell is under stress. Many studies have shown that autophagy plays a complex role in human diseases, especially in cancer, where it is known to have paradoxical effects. Namely, autophagy provides the energy for metabolism and tumor growth and leads to cell death that promotes tumor suppression. The link between autophagy and cancer is also evident in that some of the genes that regulate Carcinogenesis, oncogenes and tumor suppressor genes, participate in or impact the autophagy process. Therefore, modulating autophagy will be a valuable topic for cancer therapy. Many studies have shown that autophagy can inhibit the tumor growth when autophagy modulators are combined with radiotherapy and/or chemotherapy. These findings suggest that autophagy may be a potent target for cancer therapy.

Gene therapy-mediated reprogramming tumor infiltrating T cells using IL-2 and inhibiting NF-κB signaling improves the efficacy of immunotherapy in a brain cancer model

Immune-mediated gene therapy using adenovirus expressing Flt3 ligand and thymidine kinase followed by ganciclovir administration (Flt3/TK) effectively elicits tumor regression in preclinical glioma models. Herein, we assessed new strategies to optimize Flt3L/TK therapeutic efficacy in a refractory RG2 orthotopic glioblastoma model. Specifically, we aimed to optimize the therapeutic efficacy of Flt3L/TK treatment in the RG2 model by overexpressing the following genes within the brain tumor microenvironment: 1) a TK mutant with enhanced cytotoxicity (SR39 mutant TK), 2) Flt3L-IgG fusion protein that has a longer half-life, 3) CD40L to stimulate DC maturation, 4) T helper cell type 1 polarizing dendritic cell cytokines interleukin-12 or C-X-C motif ligand 10 chemokine (CXCL)-10, 5) C-C motif ligand 2 chemokine (CCL2) or C-C motif ligand 3 chemokine (CCL3) to enhance dendritic cell recruitment into the tumor microenvironment, 6) T helper cell type 1 cytokines interferon-γ or interleukin-2 to enhance effector T-cell functions, and 7) IκBα or p65RHD (nuclear factor kappa-B [NF-κB] inhibitors) to suppress the function of Foxp3+ Tregs and enhanced effector T-cell functions. Anti-tumor immunity and tumor specific effector T-cell functions were assessed by cytotoxic T lymphocyte assay and intracellular IFN-γ staining. Our data showed that overexpression of interferon-γ or interleukin-2, or inhibition of the nuclear factor kappa-B within the tumor microenvironment, enhanced cytotoxic T lymphocyte-mediated immune responses and successfully extended the median survival of rats bearing intracranial RG2 when combined with Flt3L/TK. These findings indicate that enhancement of T-cell functions constitutes a critical therapeutic target to overcome immune evasion and enhance therapeutic efficacy for brain cancer. In addition, our study provides novel targets to be used in combination with immune-therapeutic strategies for glioblastoma, which are currently being tested in the clinic.

Context-Dependent Regulation of Autophagy by IKK-NF-κB Signaling: Impact on the Aging Process

The NF-κB signaling system and the autophagic degradation pathway are crucial cellular survival mechanisms, both being well conserved during evolution. Emerging studies have indicated that the IKK/NF-κB signaling axis regulates autophagy in a context-dependent manner. IKK complex and NF-κB can enhance the expression of Beclin 1 and other autophagy-related proteins and stimulate autophagy whereas as a feedback response, autophagy can degrade IKK components. Moreover, NF-κB signaling activates the expression of autophagy inhibitors (e.g., A20 and Bcl-2/xL) and represses the activators of autophagy (BNIP3, JNK1, and ROS). Several studies have indicated that NF-κB signaling is enhanced both during aging and cellular senescence, inducing a proinflammatory phenotype. The aging process is also associated with a decline in autophagic degradation. It seems that the activity of Beclin 1 initiation complex could be impaired with aging, since the expression of Beclin 1 decreases as does the activity of type III PI3K. On the other hand, the expression of inhibitory Bcl-2/xL proteins increases with aging. We will review the recent literature on the control mechanisms of autophagy through IKK/NF-κB signaling and emphasize that NF-κB signaling could be a potent repressor of autophagy with ageing.

CpG ODN107 potentiates radiosensitivity of human glioma cells via TLR9-mediated NF-κB activation and NO production

Radiotherapy is a standard treatment for glioma patient with or without surgery; radiosensitizer can increase tumor sensitivity for radiotherapy. Herein, a synthetic oligodeoxynucleotide containing unmethylated CpG dinucleotides (CpG ODN107) as a radiosensitizer was investigated in vitro and in vivo, and the possible mechanisms were studied in vitro. In the present experiments, the human glioma U87 cell line used herein was resistant to 5 Gy of β-ray irradiation. The results showed that 10 μg/ml of CpG ODN107 in combination with irradiation significantly inhibited cell proliferation both in MTT assay and colony formation experiments. Tumor growth was inhibited by CpG ODN107 in combination with local irradiation but not by local irradiation or CpG ODN107 alone in human glioma xenograft model in nude mice. The inhibition ratio of tumor growth produced by CpG ODN107 (1.7, 5, and 15 mg/kg) in combination with irradiation was 27.3, 67.0, and 65.5 %, respectively. Further molecular mechanisms were studied in vitro. The results showed that the expressions of iNOS, NO, TLR9 mRNA, and NF-κB p50/p65 increased in the cells treated with CpG ODN107 in combination with irradiation. CpG ODN107 in combination with irradiation did not induce apoptosis but induced cell cycle arrest at G(1) phase. The said results demonstrated that CpG ODN107 possessed a radiosensitizing effect via TLR9-mediated NF-κB activation and NO production in the tumor cells, leading to cell cycle arrest. Therefore, CpG ODN107 is a potential candidate as radiosensitizer for human glioma.

Radiation, inflammation, and immune responses in cancer

Chronic inflammation has emerged as one of the hallmarks of cancer. Inflammation also plays a pivotal role in modulating radiation responsiveness of tumors. As discussed in this review, ionizing radiation (IR) leads to activation of several transcription factors modulating the expression of numerous mediators in tumor cells and cells of the microenvironment promoting cancer development. Novel therapeutic approaches thus aim to interfere with the activity or expression of these factors, either in single-agent or combinatorial treatment or as supplements of the existing therapeutic concepts. Among them, NF-κB, STAT-3, and HIF-1 play a crucial role in radiation-induced inflammatory responses embedded in a complex inflammatory network. A great variety of classical or novel drugs including nutraceuticals such as plant phytochemicals have the capacity to interfere with the inflammatory network in cancer and are considered as putative radiosensitizers. Thus, targeting the inflammatory signaling pathways induced by IR offers the opportunity to improve the clinical outcome of radiation therapy by enhancing radiosensitivity and decreasing putative metabolic effects. Since inflammation and sex steroids also impact tumorigenesis, a therapeutic approach targeting glucocorticoid receptors and radiation-induced production of tumorigenic factors might be effective in sensitizing certain tumors to IR.

Casein kinase 2 inhibition modulates the DNA damage response but fails to radiosensitize malignant glioma cells

Inhibitors of casein kinase 2 (CK2), a regulator of cell proliferation and mediator of the DNA damage response, are being evaluated in clinical trials for the treatment of cancers. Apigenin was capable of inhibiting the activation of CK2 following γ irradiation in LN18 and U87 malignant glioma cells. Apigenin and siRNA-mediated CK2 protein depletion further inhibited NF-κB activation and altered the Tyr68 phosphorylation of Chk2 kinase, a DNA damage response checkpoint kinase, following irradiation. However, CK2 inhibition did not decrease the ability of these glioma cells to repair double-strand DNA breaks, as assessed by COMET assays and γ-H2Ax staining. Likewise, apigenin and siRNA-induced depletion of CK2 failed to sensitize glioma cells to the cytotoxic effect of 2 to 10 G-rays of γ irradiation, as assessed by clonogenic assays. These results contrast with those found in other cancer types, and urge to prudence regarding the inclusion of malignant glioma patients in clinical trials that assess the radiosensitizing role of CK2 inhibitors in solid cancers.

Acriflavine enhances radiosensitivity of colon cancer cells through endoplasmic reticulum stress-mediated apoptosis

Radiotherapy (RT) is one of the most effective tools in the clinical treatment of cancer. Because the tumor suppressor p53 plays a central role in radiation-mediated responses, including cell cycle-arrest and apoptosis, a number of studies have suggested that p53 could be a useful therapeutic target of anti-cancer agents. Accordingly, we sought to discover a new agent capable of increasing p53 activity. HCT116 colon cancer cells, containing wild-type p53, were stably transfected with a p53 responsive-luciferase (p53-Luc) reporter gene. A cell-based high-throughput screen of 7920 synthetic small molecules was performed in duplicate. Of the screened compounds, acriflavine (ACF) significantly increased p53-Luc activity in a concentration-dependent manner without causing toxicity. Pretreatment with ACF enhanced the induction of p53 protein expression and phosphorylation on serine 15 by γ-irradiation. Clonogenic assays showed that ACF pretreatment also potentiated radiation-induced cell death. The combination of irradiation and ACF treatment induced mitochondrial release of cytochrome c and significant activation of caspase-3 with PARP cleavage in colon cancer cells, demonstrating typical apoptotic cell death. Combined treatment with ACF and radiation increased the expression of Bax and Bad, while decreasing expression of Bcl-2. In addition, the ACF/radiation treatment combination induced endoplasmic reticulum (ER) stress responses mediated by IRE1α (inositol-requiring transmembrane kinase and endonuclease 1α), eIF-2α (eukaryotic initiation factor 2α), caspase-2/12, and CHOP (C/EBP homologous protein). The knockdown of IRE1α by siRNA inhibited the apoptotic cell death induced by ACF/radiation treatment. In vivo studies showed that combined treatment with ACF and radiation significantly inhibited the growth of tumors in colorectal cancer xenografted mice. These results indicate that ACF acts through p53-dependent mitochondrial pathways and ER stress signals, and could be a promising radiosensitizer.

Autophagy activation: a novel mechanism of atorvastatin to protect mesenchymal stem cells from hypoxia and serum deprivation via AMP-activated protein kinase/mammalian target of rapamycin pathway

Autophagy is a complex "self-eating" process and could be utilized for cell survival under stresses. Statins, which could reduce apoptosis in mesenchymal stem cells (MSCs) during both ischemia and hypoxia/serum deprivation (H/SD), have been proved to induce autophagy in some cell lines. We have previously shown that atorvastatin (ATV) could regulate AMP-activated protein kinase (AMPK), a positive modulator of autophagy, in MSCs. Thus, we hypothesized that autophagy activation through AMPK and its downstream molecule mammalian target of rapamycin (mTOR) may be a novel mechanism of ATV to protect MSCs from apoptosis during H/SD. Here, we demonstrated that H/SD induced autophagy in MSCs significantly as identified by increasing acidic vesicular organelle-positive cells, type II of light chain 3 (LC3-II) expression, and autophagosome formation. The levels of H/SD-induced apoptosis were increased by autophagy inhibitor 3-methyladenine (3-MA) while decreased by rapamycin, an autophagic inducer. ATV further enhanced the autophagic activity observed in MSCs exposed to H/SD. Treatment with 3-MA attenuated ATV-induced autophagy and abrogated the protective effects of ATV on MSC apoptosis, while rapamycin failed to cause additional effects on either autophagy or apoptosis compared with ATV alone. The phosphorylation of AMPK was upregulated whereas the phosphorylation of mTOR was downregulated in ATV-treated MSCs, which were both attenuated by AMPK inhibitor compound C. Further, treatment with compound C reduced the ATV-induced autophagy in MSCs under H/SD. These data suggest that autophagy plays a protective role in H/SD-induced apoptosis of MSCs, and ATV could effectively activate autophagy via AMPK/mTOR pathway to enhance MSC survival during H/SD.

A combined DNA-affinic molecule and N-mustard alkylating agent has an anti-cancer effect and induces autophagy in oral cancer cells

Although surgery or the combination of chemotherapy and radiation are reported to improve the quality of life and reduce symptoms in patients with oral cancer, the prognosis of oral cancer remains generally poor. DNA alkylating agents, such as N-mustard, play an important role in cancer drug development. BO-1051 is a new 9-anilinoacridine N-mustard-derivative anti-cancer drug that can effectively target a variety of cancer cell lines and inhibit tumorigenesis in vivo. However, the underlying mechanism of BO-1051-mediated tumor suppression remains undetermined. In the present study, BO-1051 suppressed cell viability with a low IC(50) in oral cancer cells, but not in normal gingival fibroblasts. Cell cycle analysis revealed that the tumor suppression by BO-1051 was accompanied by cell cycle arrest and downregulation of stemness genes. The enhanced conversion of LC3-I to LC3-II and the formation of acidic vesicular organelles indicated that BO-1501 induced autophagy. The expression of checkpoint kinases was upregulated as demonstrated with Western blot analysis, showing that BO-1051 could induce DNA damage and participate in DNA repair mechanisms. Furthermore, BO-1051 treatment alone exhibited a moderate tumor suppressive effect against xenograft tumor growth in immunocompromised mice. Importantly, the combination of BO-1051 and radiation led to a potent inhibition on xenograft tumorigenesis. Collectively, our findings demonstrated that BO-1051 exhibited a cytotoxic effect via cell cycle arrest and the induction of autophagy. Thus, the combination of BO-1051 and radiotherapy may be a feasible therapeutic strategy against oral cancer in the future.

An NF-κB p65-cIAP2 link is necessary for mediating resistance to TNF-α induced cell death in gliomas

Malignant gliomas are diffusively infiltrative and remain among the deadliest of all cancers. NF-κB is a transcription factor that mediates cell growth, migration and invasion, angiogenesis and resistance to apoptosis. Normally, the activity of NF-κB is tightly regulated by numerous mechanisms. However, in many cancers, NF-κB is constitutively activated and may function as a tumor promoter. Herein, we show that in gliomas, NF-κB is constitutively activated and the levels of cIAP2, Bcl-2, Bcl-xL and Survivin are elevated. These genes are regulated by NF-κB and can inhibit apoptosis. To understand the potential role of NF-κB p65 in suppressing apoptosis, we generated human glioma cell lines that inducibly express shRNA molecules specific for p65. We demonstrate that in the absence of p65, TNF-α induced cIAP2 expression is significantly reduced while the levels of Bcl-2, Bcl-xL and Survivin are not affected. These data suggest that of these genes, only cIAP2 is a direct target of p65, which was confirmed using RT-PCR and chromatin immunoprecipitation (ChIP) assays. By reducing the levels of p65 and/or cIAP2 levels, we demonstrate that the levels of RIP poly-ubiquitination are reduced, and that p65-deficient glioma cells are more sensitive to the cytotoxic effects of TNF-α. Specifically, in the presence of TNF-α glioma cells lacking p65 and/or cIAP2 showed cellular proliferation defects and underwent cell death. These data suggest that NF-κB and/or cIAP2 may be therapeutically relevant targets for the treatment of malignant gliomas.

Strategies to improve radiotherapy with targeted drugs

Radiotherapy is used to treat approximately 50% of all cancer patients, with varying success. The dose of ionizing radiation that can be given to the tumour is determined by the sensitivity of the surrounding normal tissues. Strategies to improve radiotherapy therefore aim to increase the effect on the tumour or to decrease the effects on normal tissues. These aims must be achieved without sensitizing the normal tissues in the first approach and without protecting the tumour in the second approach. Two factors have made such approaches feasible: namely, an improved understanding of the molecular response of cells and tissues to ionizing radiation and a new appreciation of the exploitable genetic alterations in tumours. These have led to the development of treatments combining pharmacological interventions with ionizing radiation that more specifically target either tumour or normal tissue, leading to improvements in efficacy.

Prognostic significance of kappaB-Ras1 expression in gliomas

Nuclear factor (NF)-kappa-B is a pleiotropic transcriptional regulator that plays important roles in cell differentiation, growth, tumorigenesis, and apoptosis. Constitutive NF-kappa-B is overexpressed and activated in various tumors, including gliomas. Here, we investigated the expression of NF-kappa-B inhibitor interacting ras-like protein 1 (κB-Ras1), which is one of the most important negative modulators of NF-kappa-B, and a well-known proliferation biomarker survivin protein. We performed immunohistochemistry and western blot analysis on 154 glioma specimens and 3 non-neoplastic brain parenchyma specimens. Immunohistochemistry showed a strong-to-weak range of κB-Ras1 staining with increasing pathologic grade of glioma (P = 0.000). Immunoreactivity scores of κB-Ras1 were 8.15 ± 0.72 in non-neoplastic brain parenchyma, 5.00 ± 0.29 in low-grade gliomas, 3.89 ± 0.30 in anaplasia astrocytomas, and 2.78 ± 0.25 in glioblastomas. In contrast, the immunoreactivity of survivin increased with pathological grade in gliomas. The immunohistochemical data were in line with the results from western blot analysis. Moreover, a non-parametric analysis revealed that the attenuated κB-Ras1 expression was correlated with elevated survivin expression, large tumor diameter, frequent intra-tumor necrosis, and worse overall survival. These results indicated that κB-Ras1 was down-regulated in gliomas compared to non-neoplastic brain parenchyma, and the expression was even lower in glioblastomas. In addition, multivariate analysis showed that κB-Ras1 expression and intra-tumor necrosis were two important prognostic factors identified by the Cox proportional hazards model. Taken together, our study suggests that glioma patients with lower κB-Ras1 expression have a worse prognosis, which is partly due to NF-kappa-B pathway-mediated aberrant proliferation of tumor cells.

Enhancement of radiosensitivity in human glioblastoma cells by the DNA N-mustard alkylating agent BO-1051 through augmented and sustained DNA damage response

Background

1-{4-[Bis(2-chloroethyl)amino]phenyl}-3-[2-methyl-5-(4-methylacridin-9-ylamino)phenyl]urea (BO-1051) is an N-mustard DNA alkylating agent reported to exhibit antitumor activity. Here we further investigate the effects of this compound on radiation responses of human gliomas, which are notorious for the high resistance to radiotherapy.

Methods

The clonogenic assay was used to determine the IC₅₀ and radiosensitivity of human glioma cell lines (U87MG, U251MG and GBM-3) following BO-1051. DNA histogram and propidium iodide-Annexin V staining were used to determine the cell cycle distribution and the apoptosis, respectively. DNA damage and repair state were determined by γ-H2AX foci, and mitotic catastrophe was measure using nuclear fragmentation. Xenograft tumors were measured with a caliper, and the survival rate was determined using Kaplan-Meier method.

Results

BO-1051 inhibited growth of human gliomas in a dose- and time-dependent manner. Using the dosage at IC₅₀, BO-1051 significantly enhanced radiosensitivity to different extents [The sensitizer enhancement ratio was between 1.24 and 1.50 at 10% of survival fraction]. The radiosensitive G₂/M population was raised by BO-1051, whereas apoptosis and mitotic catastrophe were not affected. γ-H2AX foci was greatly increased and sustained by combined BO-1051 and γ-rays, suggested that DNA damage or repair capacity was impaired during treatment. In vivo studies further demonstrated that BO-1051 enhanced the radiotherapeutic effects on GBM-3-beared xenograft tumors, by which the sensitizer enhancement ratio was 1.97. The survival rate of treated mice was also increased accordingly.

Conclusions

These results indicate that BO-1051 can effectively enhance glioma cell radiosensitivity in vitro and in vivo. It suggests that BO-1051 is a potent radiosensitizer for treating human glioma cells.

Inactivation of ataxia telangiectasia mutated gene can increase intracellular reactive oxygen species levels and alter radiation-induced cell death pathways in human glioma cells

PURPOSE

To investigate the effects of ataxia telangiectasia mutated (ATM)-regulated reactive oxygen species (ROS) and cell death pathways on the response of U87MG glioma cells to ionising radiation (IR) and oxidative stress.

MATERIAL AND METHODS

ATM expression was blocked in U87MG glioma cells using a small interfering RNA (siRNA) technique. Cell survival, sub-lethal damage (SLD), and potential lethal damage (PLD) repair following IR were assessed by clonogenic assay while changes in intracellular ROS, the apoptosis, and autophagy were followed by flow cytometry and Western blotting.

RESULTS

Blocking ATM expression in U87MG cells increased intracellular ROS levels and sensitivity to the cytotoxic effects of IR and oxygen stress; effects that could be partly counteracted by the antioxidant N-acetylcysteine (NAC). Knock down of ATM rendered cells unable to repair sub-lethal or potentially lethal damage and DNA double strand breaks (DSB) after IR exposure; something that NAC could not counteract. ATM did control the pathways a cell used to die following IR and this did seem to be ROS-dependent.

CONCLUSION

ATM is involved in redox control but ROS elevations following ATM knock down seem more involved in the decision as to what cell death pathway is utilised after IR than DSB repair and radiosensitivity.

Targeting inflammatory pathways for tumor radiosensitization

Although radiation therapy (RT) is an integral component of treatment of patients with many types of cancer, inherent and/or acquired resistance to the cytotoxic effects of RT is increasingly recognized as a significant impediment to effective cancer treatment. Inherent resistance is mediated by constitutively activated oncogenic, proliferative and anti-apoptotic proteins/pathways whereas acquired resistance refers to transient induction of proteins/pathways following radiation exposure. To realize the full potential of RT, it is essential to understand the signaling pathways that mediate inducible radiation resistance, a poorly characterized phenomenon, and identify druggable targets for radiosensitization. Ionizing radiation induces a multilayered signaling response in mammalian cells by activating many pro-survival pathways that converge to transiently activate a few important transcription factors (TFs), including nuclear factor kappa B (NF-κB) and signal transducers and activators of transcription (STATs), the central mediators of inflammatory and carcinogenic signaling. Together, these TFs activate a wide spectrum of pro-survival genes regulating inflammation, anti-apoptosis, invasion and angiogenesis pathways, which confer tumor cell radioresistance. Equally, radiation-induced activation of pro-inflammatory cytokine network (including interleukin (IL)-1β, IL-6 and tumor necrosis factor-α) has been shown to mediate symptom burden (pain, fatigue, local inflammation) in cancer patients. Thus, targeting radiation-induced inflammatory pathways may exert a dual effect of accentuating the tumor radioresponse and reducing normal tissue side-effects, thereby increasing the therapeutic window of cancer treatment. We review recent data demonstrating the pivotal role played by inflammatory pathways in cancer progression and modulation of radiation response.

The inhibition of autophagy potentiates anti-angiogenic effects of sulforaphane by inducing apoptosis

BACKGROUND

Sulforaphane (SUL), a kind of isothiocyanate, has recently been focused due to its strong pro-apoptotic effect on cancer cells as well as tumor vascular endothelial cells (ECs). And recently, we demonstrated the induction of autophagy by colon cancer cells as a protective mechanism against SUL. In the present study, we aimed to investigate the possible role of autophagy induction by ECs as a defense mechanism against SUL.

METHODS

Human umbilical vein endothelial cells (HUVECs) were used as the in vitro model of angiogenic ECs. The induction of autophagy was evaluated by the detection of acidic vesicular organelles (AVOs) by flow-cytometry, after the staining with acridine orange, as well as the detection of light chain 3(LC3) by Western blot. Finally, the functional implication of autophagy inhibition and SUL treatment in ECs was investigated by their ability to form vascular-like structures on Matrigel.

RESULTS

Treatment of HUVECs with relatively low concentrations of SUL for 16 h resulted in the evident formation of AVOs and the recruitment of LC3 to autophagosomes, the pathognomonic features of autophagy. Co-treatment of cells with the specific autophagy inhibitor (3-methyladenine) potentiated the proapoptotic effect of SUL. And inhibition of autophagy potentiated the inhibitory effect of SUL on the ability of ECs to form capillary-like structures.

CONCLUSION

Similar to cancer cells, ECs induced autophagy in response to the pro-apoptotic agent, SUL, and the inhibition of autophagy potentiated the pro-apoptotic effect. These findings open premises for the use of autophagy inhibitors in combination with anti-angiogenic agents.

Nuclear factor-kappaB (NF-kappaB) is a novel positive transcriptional regulator of the oncogenic Wip1 phosphatase

The nuclear factor-kappaB (NF-kappaB) family of transcription factors plays a key role in inflammation and augments the initiation, promotion, and progression of cancer. NF-kappaB activation generally leads to transcriptional enhancement of genes important in cell survival and cell growth, which is exploited in cancer cells. In this study, we identify an additional oncogene, PPM1D, which encodes for Wip1, as a transcriptional target of NF-kappaB in breast cancer cells. Inhibition of NF-kappaB or activation of NF-kappaB resulted in decreased or increased Wip1 expression, respectively, at both the mRNA and protein levels. PPM1D promoter activity was positively regulated by NF-kappaB, and this regulation was dependent on the presence of the conserved kappaB site in the PPM1D promoter region. Chromatin immunoprecipitation analysis showed basal binding of the p65 NF-kappaB subunit to the PPM1D promoter region encompassing the kappaB site, which is enhanced after NF-kappaB activation by tumor necrosis factor-alpha. Finally, we show that Wip1 expression is induced in lipopolysaccharide-stimulated mouse splenic B-cells and is required for maximum proliferation. Taken together, these data suggest an additional mechanism by which NF-kappaB may promote tumorigenesis, support the selective use of NF-kappaB inhibitors as chemotherapeutic agents for the treatment of human cancers, and further define a function for Wip1 in inflammation.

Promotion of autophagy as a mechanism for radiation sensitization of breast tumor cells

Radiation has long been a useful component of the treatment regimen for solid tumors. However, some malignancies are relatively resistant to radiation treatment while even tumors that may initially respond (to both radiation and chemotherapy) may eventually recover proliferative capacity. A variety of approaches have been utilized in the efforts to enhance radiation sensitivity. Recent studies have identified autophagy as a cell death pathway that may mediate the radiosensitizing effects of selected treatments. Studies in our laboratory support the premise that radiosensitization of breast tumor cells by vitamin D or vitamin D analogs is mediated through autophagy. In addition, promotion of autophagic cell death by a vitamin D analog in irradiated breast tumor cells delays and attenuates the proliferative recovery that may be a preclinical indicator of disease recurrence.