Acquisition of temozolomide chemoresistance in gliomas leads to remodeling of mitochondrial electron transport chain

Addition of carbonic anhydrase 9 inhibitor SLC-0111 to temozolomide treatment delays glioblastoma growth in vivo

Tumor microenvironments can promote stem cell maintenance, tumor growth, and therapeutic resistance, findings linked by the tumor-initiating cell hypothesis. Standard of care for glioblastoma (GBM) includes temozolomide chemotherapy, which is not curative, due, in part, to residual therapy-resistant brain tumor-initiating cells (BTICs). Temozolomide efficacy may be increased by targeting carbonic anhydrase 9 (CA9), a hypoxia-responsive gene important for maintaining the altered pH gradient of tumor cells. Using patient-derived GBM xenograft cells, we explored whether CA9 and CA12 inhibitor SLC-0111 could decrease GBM growth in combination with temozolomide or influence percentages of BTICs after chemotherapy. In multiple GBMs, SLC-0111 used concurrently with temozolomide reduced cell growth and induced cell cycle arrest via DNA damage in vitro. In addition, this treatment shifted tumor metabolism to a suppressed bioenergetic state in vivo. SLC-0111 also inhibited the enrichment of BTICs after temozolomide treatment determined via CD133 expression and neurosphere formation capacity. GBM xenografts treated with SLC-0111 in combination with temozolomide regressed significantly, and this effect was greater than that of temozolomide or SLC-0111 alone. We determined that SLC-0111 improves the efficacy of temozolomide to extend survival of GBM-bearing mice and should be explored as a treatment strategy in combination with current standard of care.

Novel Targeting of Transcription and Metabolism in Glioblastoma

Purpose: Glioblastoma (GBM) is highly resistant to treatment, largely due to disease heterogeneity and resistance mechanisms. We sought to investigate a promising drug that can inhibit multiple aspects of cancer cell survival mechanisms and become an effective therapeutic for GBM patients.Experimental Design: To investigate TG02, an agent with known penetration of the blood-brain barrier, we examined the effects as single agent and in combination with temozolomide, a commonly used chemotherapy in GBM. We used human GBM cells and a syngeneic mouse orthotopic GBM model, evaluating survival and the pharmacodynamics of TG02. Mechanistic studies included TG02-induced transcriptional regulation, apoptosis, and RNA sequencing in treated GBM cells as well as the investigation of mitochondrial and glycolytic function assays.Results: We demonstrated that TG02 inhibited cell proliferation, induced cell death, and synergized with temozolomide in GBM cells with different genetic background but not in astrocytes. TG02-induced cytotoxicity was blocked by the overexpression of phosphorylated CDK9, suggesting a CDK9-dependent cell killing. TG02 suppressed transcriptional progression of antiapoptotic proteins and induced apoptosis in GBM cells. We further demonstrated that TG02 caused mitochondrial dysfunction and glycolytic suppression and ultimately ATP depletion in GBM. A prolonged survival was observed in GBM mice receiving combined treatment of TG02 and temozolomide. The TG02-induced decrease of CDK9 phosphorylation was confirmed in the brain tumor tissue.Conclusions: TG02 inhibits multiple survival mechanisms and synergistically decreases energy production with temozolomide, representing a promising therapeutic strategy in GBM, currently under investigation in an ongoing clinical trial. Clin Cancer Res; 24(5); 1124-37. ©2017 AACR.

Inhibition of HIF1α and PDK Induces Cell Death of Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most common and aggressive form of brain tumors. GBMs, like other tumors, rely relatively less on mitochondrial oxidative phosphorylation (OXPHOS) and utilize more aerobic glycolysis, and this metabolic shift becomes augmented under hypoxia. In the present study, we investigated the physiological significance of altered glucose metabolism and hypoxic adaptation in the GBM cell line U251 and two newly established primary GBMs (GBM28 and GBM37). We found that these three GBMs exhibited differential growth rates under hypoxia compared to those under normoxia. Under normoxia, the basal expressions of HIF1α and the glycolysis-associated genes, PDK1, PDK3, and GLUT1, were relatively low in U251 and GBM28, while their basal expressions were high in GBM37. Under hypoxia, the expressions of these genes were enhanced further in all three GBMs. Treatment with dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinase (PDK), induced cell death in GBM28 and GBM37 maintained under normoxia, whereas DCA effects disappeared under hypoxia, suggesting that hypoxic adaptation dominated DCA effects in these GBMs. In contrast, the inhibition of HIF1α with chrysin suppressed the expression of PDK1, PDK3, and GLUT1 and markedly promoted cell death of all GBMs under both normoxia and hypoxia. Interestingly, however, GBMs treated with chrysin under hypoxia still sustained higher viability than those under normoxia, and chrysin and DCA co-treatment was unable to eliminate this hypoxia-dependent resistance. Together, these results suggest that hypoxic adaptation is critical for maintaining viability of GBMs, and targeting hypoxic adaptation can be an important treatment option for GBMs.

Specificity protein 1-modulated superoxide dismutase 2 enhances temozolomide resistance in glioblastoma, which is independent of O6-methylguanine-DNA methyltransferase

Acquisition of temozolomide (TMZ) resistance is a major factor leading to the failure of glioblastoma (GBM) treatment. The exact mechanism by which GBM evades TMZ toxicity is not always related to the expression of the DNA repair enzyme O⁶-methylguanine-DNA methyltransferase (MGMT), and so remains unclear. In this study, TMZ-resistant variants derived from MGMT-negative GBM clinical samples and cell lines were studied, revealing there to be increased specificity protein 1 (Sp1) expression associated with reduced reactive oxygen species (ROS) accumulation following TMZ treatment. Analysis of gene expression databases along with cell studies identified the ROS scavenger superoxide dismutase 2 (SOD2) as being disease-related. SOD2 expression was also increased, and it was found to be co-expressed with Sp1 in TMZ-resistant cells. Investigation of the SOD2 promoter revealed Sp1 as a critical transcriptional activator that enhances SOD2 gene expression. Co-treatment with an Sp1 inhibitor restored the inhibitory effects of TMZ, and decreased SOD2 levels in TMZ-resistant cells. This treatment strategy restored susceptibility to TMZ in xenograft animals, leading to prolonged survival in an orthotopic model. Thus, our results suggest that Sp1 modulates ROS scavengers as a novel mechanism to increase cancer malignancy and resistance to chemotherapy. Inhibition of this pathway may represent a potential therapeutic target for restoring treatment susceptibility in GBM.

Downregulation of cytochrome c oxidase 1 induced radioresistance in esophageal squamous cell carcinoma

Comprehensive gene screening with transposons is a novel procedure for the systematic identification of resistant genes. The present study aimed to use this technique to identify candidate radioresistant genes in esophageal squamous cell carcinoma. A transposon is a base sequence that can translocate to another location in the genome at random. By inserting the cytomegalovirus promotor as a transcriptional activator in the transposon, the following gene in the new location becomes overexpressed and the gene located at the transposon insertion site is downregulated. Consequently, various transposon-tagged cells, which have differentially overexpressed or downregulated genes using the transposon method can be obtained. Following the irradiation of transposon-tagged cells, candidate radioresistant genes can be selected in order to detect the location of the transposon in the cells that have survived. A total of 11 genes were detected as candidate radioresistant genes. Cytochrome c oxidase 1 (MT-CO1), an enzyme involved in apoptosis through the activation of the caspase cascade, was one of the candidate genes identified. The relative expression level of MT-CO1 was 0.12 in MT-CO1-downregulated cells which was significantly lower compared with the expression level in parent TE4 cells (P<0.001). The survival rate was 28.7% in MT-CO1-downregulated cells and 10.5% in parent TE4 cells 9 days following 5-Gy irradiation. The activity of cytochrome c and caspase-3 following irradiation was significantly lower in the MT-CO1-downregulated radioresistant cells compared with in TE4 cells. In conclusion, the novel gene screening technique demonstrated to be useful for detecting candidate radioresistant genes in esophageal squamous cell carcinoma. The results of the present study revealed that the downregulation of MT-CO1 induced radioresistance occurs by inhibiting the activation of the caspase cascade in radioresistant esophageal cancer cells.

Glioma sensitive or chemoresistant to temozolomide differentially modulate macrophage protumor activities

BACKGROUND

Glioblastomas are the most devastating brain tumor characterized by chemoresistance development and poor prognosis. Macrophages are a component of tumor microenvironment related to glioma malignancy. The relation among inflammation, innate immunity and cancer is accepted; however, molecular and cellular mechanisms mediating this relation and chemoresistance remain unresolved.

OBJECTIVE

Here we evaluated whether glioma sensitive or resistant to temozolomide (TMZ) modulate macrophage polarization and inflammatory pathways associated. The impact of glioma-macrophage crosstalk on glioma proliferation was also investigated.

METHODS

GL261 glioma chemoresistance was developed by exposing cells to increasing TMZ concentrations over a period of 6months. Mouse peritoneal macrophages were exposed to glioma-conditioned medium or co-cultured directly with glioma sensitive (GL) or chemoresistant (GLTMZ). Macrophage polarization, in vitro and in vivo glioma proliferation, redox parameters, ectonucleotidase activity and ATP cytotoxicity were performed.

RESULTS

GLTMZ cells were more effective than GL in induce M2-like macrophage polarization and in promote a strong immunosuppressive environment characterized by high IL-10 release and increased antioxidant potential, which may contribute to glioma chemoresistance and proliferation. Interestingly, macrophage-GLTMZ crosstalk enhanced in vitro and in vivo proliferation of chemoresistant cells, decreased ectonucleotidase activities, which was followed by increased macrophage sensitivity to ATP induced death.

CONCLUSIONS

Results suggest a differential macrophage modulation by GLTMZ cells, which may favor the maintenance of immunosuppressive tumor microenvironment and glioma proliferation.

GENERAL SIGNIFICANCE

The induction of immunosuppressive environment and macrophage education by chemoresistant gliomas may be important for tumor recovery after chemotherapy and could be considered to overcome chemoresistance development.

Stress-Adaptive Response in Ovarian Cancer Drug Resistance: Role of TRAP1 in Oxidative Metabolism-Driven Inflammation

Metabolic reprogramming is one of the most frequent stress-adaptive response of cancer cells to survive environmental changes and meet increasing nutrient requirements during their growth. These modifications involve cellular bioenergetics and cross talk with surrounding microenvironment, in a dynamic network that connect different molecular processes, such as energy production, inflammatory response, and drug resistance. Even though the Warburg effect has long been considered the main metabolic feature of cancer cells, recent reports identify mitochondrial oxidative metabolism as a driving force for tumor growth in an increasing number of cellular contexts. In recent years, oxidative phosphorylation has been linked to a remodeling of inflammatory response due to autocrine or paracrine secretion of interleukines that, in turn, induces a regulation of gene expression involving, among others, molecules responsible for the onset of drug resistance. This process is especially relevant in ovarian cancer, characterized by low survival, high frequency of disease relapse and chemoresistance. Recently, the molecular chaperone TRAP1 (tumor necrosis factor-associated protein 1) has been identified as a key junction molecule in these processes in ovarian cancer: in fact, TRAP1 mediates a metabolic switch toward oxidative phosphorylation that, in turn, triggers cytokines secretion, with consequent gene expression remodeling, finally leading to cisplatin resistance and epithelial-to-mesenchymal transition in ovarian cancer models. This review summarizes how metabolism, chemoresistance, inflammation, and epithelial-to-mesenchymal transition are strictly interconnected, and how TRAP1 stays at the crossroads of these processes, thus shedding new lights on molecular networks at the basis of ovarian cancer.

Redox biology and the interface between bioenergetics, autophagy and circadian control of metabolism

Understanding molecular mechanisms that underlie the recent emergence of metabolic diseases such as diabetes and heart failure has revealed the need for a multi-disciplinary research integrating the key metabolic pathways which change the susceptibility to environmental or pathologic stress. At the physiological level these include the circadian control of metabolism which aligns metabolism with temporal demand. The mitochondria play an important role in integrating the redox signals and metabolic flux in response to the changing activities associated with chronobiology, exercise and diet. At the molecular level this involves dynamic post-translational modifications regulating transcription, metabolism and autophagy. In this review we will discuss different examples of mechanisms which link these processes together. An important pathway capable of linking signaling to metabolism is the post-translational modification of proteins by O-linked N-acetylglucosamine (O-GlcNAc). This is a nutrient regulated protein modification that plays an important role in impaired cellular stress responses. Circadian clocks have also emerged as critical regulators of numerous cardiometabolic processes, including glucose/lipid homeostasis, hormone secretion, redox status and cardiovascular function. Central to these pathways are the response of autophagy, bioenergetics to oxidative stress, regulated by Keap1/Nrf2 and mechanisms of metabolic control. The extension of these ideas to the emerging concept of bioenergetic health will be discussed.

Mitochondrial oncobioenergetic index: A potential biomarker to predict progression from indolent to aggressive prostate cancer

Mitochondrial function is influenced by alterations in oncogenes and tumor suppressor genes and changes in the microenvironment occurring during tumorigenesis. Therefore, we hypothesized that mitochondrial function will be stably and dynamically altered at each stage of the prostate tumor development. We tested this hypothesis in RWPE-1 cells and its tumorigenic clones with progressive malignant characteristics (RWPE-1 < WPE-NA22 < WPE-NB14 < WPE-NB11 < WPE-NB26) using high-throughput respirometry. Our studies demonstrate that mitochondrial content do not change with increasing malignancy. In premalignant cells (WPE-NA22 and WPE-NB14), OXPHOS is elevated in presence of glucose or glutamine alone or in combination compared to RWPE-1 cells and decreases with increasing malignancy. Glutamine maintained higher OXPHOS than glucose and suggests that it may be an important substrate for the growth and proliferation of prostate epithelial cells. Glycolysis significantly increases with malignancy and follow a classical Warburg phenomenon. Fatty acid oxidation (FAO) is significantly lower in tumorigenic clones and invasive WPE-NB26 does not utilize FAO at all. In this paper, we introduce for the first time the mitochondrial oncobioenergetic index (MOBI), a mathematical representation of oncobioenergetic profile of a cancer cell, which increases significantly upon transformation into localized premalignant form and rapidly falls below the normal as they become aggressive in prostate tumorigenesis. We have validated this in five prostate cancer cell lines and MOBI appears to be not related to androgen dependence or mitochondrial content, but rather dependent on the stage of the cancer. Altogether, we propose that MOBI could be a potential biomarker to distinguish aggressive cancer from that of indolent disease.

Analysis of expression and prognostic significance of vimentin and the response to temozolomide in glioma patients

Gliomas are the most common primary intracranial malignant tumors in adults. Surgical resection followed by optional radiotherapy and chemotherapy is the current standard therapy for glioma patients. Vimentin, a protein of intermediate filament family, could maintain the cellular integrity and participate in several cell signal pathways to modulate the motility and invasion of cancer cells. The purpose of the present research was to identify the relationship between vimentin expression and clinical characteristics and detect the prognostic and predictive ability of vimentin in patients with glioma. To determine the expression of vimentin in glioma tissues, paraffin-embedded blocks from glioma patients by surgical resection were obtained and evaluated by immunohistochemistry. To further investigate the association of vimentin expression with survival, we employed mRNA expression of vimentin genes from the Chinese Glioma Genome Atlas (CGGA) and the GSE 16011 dataset. Kaplan-Meier analysis and Cox regression model were used to statistical analysis. We detected positive vimentin straining in 84 % of high-grade compared to 47 % in low-grade glioma patients. Additionally, vimentin mRNA expression was correlated with glioma grade in both CGGA and GSE16011 dataset. Patients with low vimentin expression have longer survival than high expression. In multivariate analysis, vimentin was an independent significant prognostic factor for high-grade glioma patients. We also identified that glioblastoma patients with low vimentin expression had a better response to temozolomide therapy. Vimentin expression has a significant association with tumor grade and overall survival of high-grade glioma patients. Low vimentin expression may benefit from temozolomide therapy.

Identification of Small Molecule Inhibitors of Human Cytochrome c Oxidase That Target Chemoresistant Glioma Cells

The enzyme cytochrome c oxidase (CcO) or complex IV (EC 1.9.3.1) is a large transmembrane protein complex that serves as the last enzyme in the respiratory electron transport chain of eukaryotic mitochondria. CcO promotes the switch from glycolytic to oxidative phosphorylation (OXPHOS) metabolism and has been associated with increased self-renewal characteristics in gliomas. Increased CcO activity in tumors has been associated with tumor progression after chemotherapy failure, and patients with primary glioblastoma multiforme and high tumor CcO activity have worse clinical outcomes than those with low tumor CcO activity. Therefore, CcO is an attractive target for cancer therapy. We report here the characterization of a CcO inhibitor (ADDA 5) that was identified using a high throughput screening paradigm. ADDA 5 demonstrated specificity for CcO, with no inhibition of other mitochondrial complexes or other relevant enzymes, and biochemical characterization showed that this compound is a non-competitive inhibitor of cytochrome c When tested in cellular assays, ADDA 5 dose-dependently inhibited the proliferation of chemosensitive and chemoresistant glioma cells but did not display toxicity against non-cancer cells. Furthermore, treatment with ADDA 5 led to significant inhibition of tumor growth in flank xenograft mouse models. Importantly, ADDA 5 inhibited CcO activity and blocked cell proliferation and neurosphere formation in cultures of glioma stem cells, the cells implicated in tumor recurrence and resistance to therapy in patients with glioblastoma. In summary, we have identified ADDA 5 as a lead CcO inhibitor for further optimization as a novel approach for the treatment of glioblastoma and related cancers.

Thiazolidin-4-ones from 4-(methylthio)benzaldehyde and 4-(methylsulfonyl)benzaldehyde: Synthesis, antiglioma activity and cytotoxicity

The present study assessed the biological potential of fourteen 1,3-thiazolidin-4-ones evaluating the antiglioma effect through decreasing of cell viability of glioblastoma multiform cells. The new compounds were efficient synthesized through multicomponent or multicomponent one-pot procedures in moderate to good yields (22-86%) from two arenealdehydes (4-(methylthio)benzaldehyde and 4-(methylsulfonyl)benzaldehyde), seven amines (aromatic and aliphatic) and mercaptoacetic acid. The compounds were identified and characterized by GC/MS and NMR, five of them by HRMS. Six thiazolidinones showed significant effect of decreasing cell viability compared to standard drug TMZ at 100 μM in 72 h in C6 cell line by MTT assay. The compounds 5b, 5e, 5g and 6e showed the best results in the screening at 100 μM and were analyzed at different concentrations (5, 25, 50, 100 and 250 μM). Compounds 5b and 5e showed statistical difference at 5 μM, 6e at 25 μM and 5g at 50 μM in 72 h of treatment. The cytotoxicity study in primary astrocytes cells was evaluated and none of fourteen compounds showed toxicity at 100 μM, eight of them were not cytotoxic at 250 μM, both in 72 h. In addition, the propidium iodide assay demonstrated that the compounds might induce cell death by necrosis. In conclusion, this work reports at least four compounds (5b, 5e, 5g and 6e) with potential anti-tumor effect against glioblastoma multiform cell presenting activity at low concentrations and safe profile of cytotoxicity.

Expression of dynein, cytoplasmic 2, heavy chain 1 (DHC2) associated with glioblastoma cell resistance to temozolomide

Temozolomide (TMZ) is the main chemotherapeutic drug utilized for the treatment of glioblastoma multiforme (GMB), however, drug resistance often leads to tumor recurrence and poor outcomes. GMB cell lines were treated with TMZ for up to two weeks and then subjected to proteomics analysis to identify the underlying molecular pathology that is associated with TMZ resistance. Proteomics data showed that TMZ altered expression of proteins that related to cytoskeleton structure and function, such as DHC2 and KIF2B. qRT-PCR and immunofluorescence were used to verify expression of DHC2 and KIF2B in these cells. Immunohistochemistry was used to verify expression of these two proteins in xenografts of a nude mouse model, and ex vivo GBM tissue samples. Their expression was knocked down using siRNA to confirm their role in the regulation of GBM cell sensitivity to TMZ. Knockdown of DHC2 expression enhanced sensitivity of U87 cells to TMZ treatment. Ex vivo data showed that DHC2 expression in GBM tissue samples was associated with tumor recurrence after TMZ chemotherapy. These results indicated cytoskeleton related protein DHC2 reduced sensitivity of GBM cells to TMZ treatment. Further studies should assess DHC2 as a novel target in GBM for TMZ combination treatment.

Saponin 6 derived from Anemone taipaiensis induces U87 human malignant glioblastoma cell apoptosis via regulation of Fas and Bcl‑2 family proteins

Glioblastoma multiforme (GBM) is the most common and aggressive type of brain tumor, and is associated with a poor prognosis. Saponin 6, derived from Anemone taipaiensis, exerts potent cytotoxic effects against the human hepatocellular carcinoma HepG2 cell line and the human promyelocytic leukemia HL‑60 cell line; however, the effects of saponin 6 on glioblastoma remain unknown. The present study aimed to evaluate the effects of saponin 6 on human U87 malignant glioblastoma (U87 MG) cells. The current study revealed that saponin 6 induced U87 MG cell death in a dose‑ and time‑dependent manner, with a half maximal inhibitory concentration (IC50) value of 2.83 µM after treatment for 48 h. However, saponin 6 was needed to be used at a lesser potency in HT‑22 cells, with an IC50 value of 6.24 µM. Cell apoptosis was assessed by flow cytometry using Annexin V‑fluorescein isothiocyanate/propidium iodide double staining. DNA fragmentation and alterations in nuclear morphology were examined by terminal deoxynucleotidyl transferase‑mediated dUTP nick end labeling and transmission electron microscopy, respectively. The present study demonstrated that treatment with saponin 6 induced cell apoptosis in U87 MG cells, and resulted in DNA fragmentation and nuclear morphological alterations typical of apoptosis. In addition, flow cytometric analysis revealed that saponin 6 was able to induce cell cycle arrest. The present study also demonstrated that saponin 6‑induced apoptosis of U87 MG cells was attributed to increases in the protein expression levels of Fas, Fas ligand, and cleaved caspase‑3, ‑8 and ‑9, and decreases in the levels of B‑cell lymphoma 2. The current study indicated that saponin 6 may exhibit selective cytotoxicity toward U87 MG cells by activating apoptosis via the extrinsic and intrinsic pathways. Therefore, saponin 6 derived from A. taipaiensis may possess therapeutic potential for the treatment of GBM.

Temozolomide resistance in glioblastoma multiforme

Temozolomide (TMZ) is an oral alkylating agent used to treat glioblastoma multiforme (GBM) and astrocytomas. However, at least 50% of TMZ treated patients do not respond to TMZ. This is due primarily to the over-expression of O⁶-methylguanine methyltransferase (MGMT) and/or lack of a DNA repair pathway in GBM cells. Multiple GBM cell lines are known to contain TMZ resistant cells and several acquired TMZ resistant GBM cell lines have been developed for use in experiments designed to define the mechanism of TMZ resistance and the testing of potential therapeutics. However, the characteristics of intrinsic and adaptive TMZ resistant GBM cells have not been systemically compared. This article reviews the characteristics and mechanisms of TMZ resistance in natural and adapted TMZ resistant GBM cell lines. It also summarizes potential treatment options for TMZ resistant GBMs.

Temozolomide promotes genomic and phenotypic changes in glioblastoma cells

BACKGROUND

Temozolomide (TMZ) is a first-line drug for the treatment of glioblastoma. Long-term TMZ-treated tumour cells acquire TMZ resistance by profound reprogramming of the transcriptome, proteome, kinome, metabolism, and demonstrate versatile and opposite changes in proliferation, invasion, in vivo growth, and drug cross-resistance. We hypothesized that chromosomal instability (CIN) may be implicated in the generation of TMZ-driven molecular and phenotype diversity. CIN refers to the rate (cell-to-cell variability) with which whole chromosomes or portions of chromosomes are gained or lost.

METHODS

The long-term TMZ-treated cell lines were established in vitro (U251TMZ1, U251TMZ2, T98GTMZ and C6TMZ) and in vivo (C6R2TMZ). A glioma model was achieved by the intracerebral stereotactic implantation of C6 cells into the striatum region of rats. Genomic and phenotypic changes were analyzed by conventional cytogenetics, array CGH, trypan blue exclusion assay, soft agar colony formation assay, scratch wound healing assay, transwell invasion assay, quantitative polymerase chain reaction, and Western blotting.

RESULTS

Long-term TMZ treatment increased CIN-mediated genomic diversity in U251TMZ1, U251TMZ2 and T98GTMZ cells but reduced it in C6TMZ and C6R2TMZ cells. U251TMZ1 and U251TMZ2 cell lines, established in parallel with a similar treatment procedure with the only difference in the duration of treatment, underwent individual phenotypic changes. U251TMZ1 had a reduced proliferation and invasion but increased migration, whereas U251TMZ2 had an enhanced proliferation and invasion but no changes in migration. U251TMZ1 and U251TMZ2 cells demonstrated individual patterns in expression/activation of signal transduction proteins (e.g., MDM2, p53, ERK, AKT, and ASK). C6TMZ and C6R2TMZ cells had lower proliferation, colony formation efficiency and migration, whereas T98GTMZ cells had increased colony formation efficiency without any changes in proliferation, migration, and invasion. TMZ-treated lines demonstrated a differential response to a reduction in glucose concentration and an increased resistance to TMZ re-challenge but not temsirolimus (mTOR inhibitor) or U0126 (MEK1/2 inhibitor) treatment.

CONCLUSION

Long-term TMZ treatment selected resistant genotype-phenotype variants or generated novel versatile phenotypes by increasing CIN. An increase of resistance to TMZ re-challenge seems to be the only predictable trait intrinsic to all long-term TMZ-treated tumour cells. Changes in genomic diversity may be responsible for heterogeneous phenotypes of TMZ-treated cell lines.

Bevacizumab is superior to Temozolomide in causing mitochondrial dysfunction in human brain tumors

OBJECTIVE

Current chemotherapy treatments available for treating high-grade brain tumors, Temozolomide (TMZ) or Bevacizumab (BEV), not only have specific anti-tumor mechanisms, but also have an effect on mitochondria. However, effects of both drugs on mitochondria isolated from human brain tumors have not been thoroughly investigated. This study determined the direct effects of TMZ and BEV as well as the neurotoxic condition (calcium overload), on the function of mitochondria and compared these effects on mitochondria isolated from low- and high-grade human brain tumors.

METHODS

Mitochondria were isolated from either low- or high-grade human primary brain tumors. Calcium overload conditions (100 or 200 μM), TMZ (300 μM), and BEV (2 mg/mL) were applied to isolated mitochondria from low- and high-grade brain tumors. Following the treatment, mitochondrial function, including reactive oxygen species production, membrane potential changes, and swelling, were determined. The mitochondrial morphology was also examined.

RESULTS

In calcium overload conditions, mitochondrial dysfunction was only found to have occurred in low-grade tumors. In TMZ and BEV treatment, BEV, rather than TMZ, caused greater membrane depolarization and mitochondrial swelling in both grades of brain tumors.

CONCLUSIONS

TMZ and BEV can directly cause the dysfunction of mitochondria isolated from human brain tumors. However, BEV has a greater ability to disturb mitochondrial function in mitochondria isolated from human brain tumors than either TMZ or calcium overload conditions.

Temozolomide-based combination for advanced neuroendocrine neoplasms: a systematic review of the literature

BACKGROUND

In this systematic review, we explored the value of using temozolomide (TMZ)-based combinations for advanced neuroendocrine neoplasms (NENs).

METHODS

Database search were conducted using the terms 'NENs' and 'TMZ' and 'systemic therapy.' Outcomes of interest included progression-free survival and overall survival, toxicities and tumor response.

RESULTS

In total, 16 trials including 348 patients were included. Median progression-free survival ranged from 6 to 31 months. The disease control rate ranged from 65 to 100%. Frequently reported grade 3/4 toxicities were leukopenia, lymphopenia and elevated transaminases.

CONCLUSION

The published clinical data suggest that TMZ-based combination with some anticancer agents (especially capecitabine) could be an effective treatment option for advanced low-intermediate grade NENs.

Clinical relevance of autophagic therapy in cancer: Investigating the current trends, challenges, and future prospects

Oncophagy (cancer-related autophagy) has a complex dual character at different stages of tumor progression. It remains an important clinical problem to unravel the reasons that propel the shift in the role of oncophagy from tumor inhibition to a protective mechanism that shields full-blown malignancy. Most treatment strategies emphasize curbing protective oncophagy while triggering the oncophagy that is lethal to tumor cells. In this review, we focus on the trends in current therapeutics as well as various challenges in clinical trials to address the oncophagic dilemma and evaluate the potential of these developing therapies. A detailed analysis of the clinical and pre-clinical scenario of the anticancer medicines highlights the various inducers and inhibitors of autophagy. The ways in which tumor stage, the microenvironment and combination drug treatment continue to play an important tactical role are discussed. Moreover, autophagy targets also play a crucial role in developing the best possible solution to this oncophagy paradox. In this review, we provide a comprehensive update on the current clinical impact of autophagy-based cancer therapeutic drugs and try to lessen the gap between translational medicine and clinical science.

Expression and clinical significance of cytochrome c oxidase subunit IV in colorectal cancer patients

INTRODUCTION

Previous studies have demonstrated that the expression of cytochrome c oxidase (COX) subunits encoded by mitochondrial DNA is elevated in colorectal cancer (CRC). However, the expression of nuclear DNA-encoded COX IV and its clinical significance have not yet been investigated in CRC.

MATERIAL AND METHODS

We examined COX IV expression in paired CRC samples (cancer and pericancerous tissues) by quantitative real-time polymerase chain reaction (qPCR), Western blot and immunohistochemical staining and analyzed its clinical significance.

RESULTS

qPCR and Western blot analyses showed that COX IV expression was significantly elevated at both the mRNA (p = 0.05) and protein levels in CRC tissue samples when compared with those in paired pericancerous tissues. Immunohistochemistry also revealed that COX IV expression was significantly increased in CRC tissues (p < 0.001). Association analyses showed that there was no significant association between COX IV expression and clinical parameters of CRC patients except for gender (p = 0.017). Moreover, we did not find any association between COX IV expression and overall survival or recurrence-free survival of CRC patients. Further analysis showed no significant relationship between the expression of COX IV and proliferating cell nuclear antigen (PCNA), a marker of cell proliferation.

CONCLUSIONS

Our findings suggest that elevated COX IV expression may play an important role in colorectal carcinogenesis, but not in progression, which warrants further investigation in future studies.

Nuclear-encoded cytochrome c oxidase subunit 4 regulates BMI1 expression and determines proliferative capacity of high-grade gliomas

Nuclear-encoded cytochrome c oxidase subunit 4 (COX4) is a key regulatory subunit of mammalian cytochrome c oxidase, and recent studies have demonstrated that COX4 isoform 1 (COX4-1) could have a role in glioma chemoresistance. The Polycomb complex protein BMI1 is a stem cell regulatory gene implicated in the pathogenesis of many aggressive cancers, including glioma. This study sought to determine if COX4 regulates BMI1 and modulates tumor cell proliferation. Using The Cancer Genome Atlas database and a retrospective data set from patients with glioblastoma multiforme, we found that BMI1 expression levels positively correlated with COX4-1 expression and overall survival. Whereas COX4-1 promoted cell growth by increasing BMI1 expression, COX4-2 inhibited cell growth even in cells overexpressing BMI1. We also demonstrate that COX4-1 attenuates mitochondrial reactive oxygen species (ROS) production, which is required for COX4-1-mediated effects on BMI1 expression and cell proliferation. Notably, mice bearing COX4-1-expressing glioma cell xenografts quickly developed invasive tumors characterized by the presence of multiple lesions positive for Ki-67, BMI1, and COX4-1, whereas mice bearing COX4-2-expressing xenografts rarely developed tumors by this point. COX4-1 also promoted the self-renewal of glioma stem-like cells, consistent with the reported role of BMI1 in stem cell growth. Taken together, these findings identify a novel COX4-1-mitochondrial ROS axis, in which differential expression of COX4 isoforms regulates mitochondrial ROS production and controls BMI1 expression.

5-fluorouracil resistant colon cancer cells are addicted to OXPHOS to survive and enhance stem-like traits

Despite marked tumor shrinkage after 5-FU treatment, the frequency of colon cancer relapse indicates that a fraction of tumor cells survives treatment causing tumor recurrence. The majority of cancer cells divert metabolites into anabolic pathways through Warburg behavior giving an advantage in terms of tumor growth. Here, we report that treatment of colon cancer cell with 5-FU selects for cells with mesenchymal stem-like properties that undergo a metabolic reprogramming resulting in addiction to OXPHOS to meet energy demands. 5-FU treatment-resistant cells show a de novo expression of pyruvate kinase M1 (PKM1) and repression of PKM2, correlating with repression of the pentose phosphate pathway, decrease in NADPH level and in antioxidant defenses, promoting PKM2 oxidation and acquisition of stem-like phenotype. Response to 5-FU in a xenotransplantation model of human colon cancer confirms activation of mitochondrial function. Combined treatment with 5-FU and a pharmacological inhibitor of OXPHOS abolished the spherogenic potential of colon cancer cells and diminished the expression of stem-like markers. These findings suggest that inhibition of OXPHOS in combination with 5-FU is a rational combination strategy to achieve durable treatment response in colon cancer.

Prediction of Response to Temozolomide in Low-Grade Glioma Patients Based on Tumor Size Dynamics and Genetic Characteristics

Both molecular profiling of tumors and longitudinal tumor size data modeling are relevant strategies to predict cancer patients' response to treatment. Herein we propose a model of tumor growth inhibition integrating a tumor's genetic characteristics (p53 mutation and 1p/19q codeletion) that successfully describes the time course of tumor size in patients with low-grade gliomas treated with first-line temozolomide chemotherapy. The model captures potential tumor progression under chemotherapy by accounting for the emergence of tissue resistance to treatment following prolonged exposure to temozolomide. Using information on individual tumors' genetic characteristics, in addition to early tumor size measurements, the model was able to predict the duration and magnitude of response, especially in those patients in whom repeated assessment of tumor response was obtained during the first 3 months of treatment. Combining longitudinal tumor size quantitative modeling with a tumor''s genetic characterization appears as a promising strategy to personalize treatments in patients with low-grade gliomas.

Pitfalls of the MTT assay: Direct and off-target effects of inhibitors can result in over/underestimation of cell viability

The MTT assay (to a less degree MTS, XTT or WST) is a widely exploited approach for measuring cell viability/drug cytotoxicity. MTT reduction occurs throughout a cell and can be significantly affected by a number of factors, including metabolic and energy perturbations, changes in the activity of oxidoreductases, endo-/exocytosis and intracellular trafficking. Over/underestimation of cell viability by the MTT assay may be due to both adaptive metabolic and mitochondrial reprogramming of cells subjected to drug treatment-mediated stress and inhibitor off-target effects. Previously, imatinib, rottlerin, ursolic acid, verapamil, resveratrol, genistein nanoparticles and some polypeptides were shown to interfere with MTT reduction rate resulting in inconsistent results between the MTT assay and alternative assays. Here, to test the under/overestimation of viability by the MTT assay, we compared results derived from the MTT assay with the trypan blue exclusion assay after treatment of glioblastoma U251, T98G and C6 cells with three widely used inhibitors with the known direct and side effects on energy and metabolic homeostasis - temozolomide (TMZ), a DNA-methylating agent, temsirolimus (TEM), an inhibitor of mTOR kinase, and U0126, an inhibitor of MEK1/2 kinases. Inhibitors were applied shortly as in IC50 evaluating studies or long as in studies focusing on drug resistance acquisition. We showed that over/underestimation of cell viability by the MTT assay and its significance depends on a cell line, a time point of viability measurement and other experimental parameters. Furthermore, we provided a comprehensive survey of factors that should be accounted in the MTT assay. To avoid result misinterpretation, supplementation of the tetrazolium salt-based assays with other non-metabolic assays is recommended.

An image guided small animal radiation therapy platform (SmART) to monitor glioblastoma progression and therapy response

BACKGROUND AND PURPOSE

Glioblastoma multiforme is the most common malignant brain tumor. Standard treatment including surgery, radiotherapy and chemotherapy with temozolomide is not curative. There is a great need for in vitro and in vivo models closely mimicking clinical practice to ensure better translation of novel preclinical findings.

METHODS AND MATERIALS

A 3D spheroid model was established using the U87MG cell line. The efficacy of temozolomide, RT and combinations was assessed using growth delay assays. Orthotopic glioblastoma tumors were established, different radiation doses delivered based on micro-CT based treatment planning (SmART-plan) and dose volume histograms (DVH) were determined. Tumor growth was monitored using bioluminescent imaging.

RESULTS

3D spheroid cultures showed a dose-dependent growth delay upon single and combination treatments. Precise uniform radiation was achieved in all in vivo treatment groups at all doses tested, and DVHs showed accurate dose coverage in the planning target volume which resulted in tumor growth delay.

CONCLUSION

We demonstrate that 3D spheroid technology can be reliably used for treatment efficacy evaluation and that mimicking a clinical setting is also possible in small animals. Both these in vitro and in vivo techniques can be combined for clinically relevant testing of novel drugs combined with radiation.

A novel class of mitochondria-targeted soft electrophiles modifies mitochondrial proteins and inhibits mitochondrial metabolism in breast cancer cells through redox mechanisms

Despite advances in screening and treatment over the past several years, breast cancer remains a leading cause of cancer-related death among women in the United States. A major goal in breast cancer treatment is to develop safe and clinically useful therapeutic agents that will prevent the recurrence of breast cancers after front-line therapeutics have failed. Ideally, these agents would have relatively low toxicity against normal cells, and will specifically inhibit the growth and proliferation of cancer cells. Our group and others have previously demonstrated that breast cancer cells exhibit increased mitochondrial oxygen consumption compared with non-tumorigenic breast epithelial cells. This suggests that it may be possible to deliver redox active compounds to the mitochondria to selectively inhibit cancer cell metabolism. To demonstrate proof-of-principle, a series of mitochondria-targeted soft electrophiles (MTSEs) has been designed which selectively accumulate within the mitochondria of highly energetic breast cancer cells and modify mitochondrial proteins. A prototype MTSE, IBTP, significantly inhibits mitochondrial oxidative phosphorylation, resulting in decreased breast cancer cell proliferation, cell attachment, and migration in vitro. These results suggest MTSEs may represent a novel class of anti-cancer agents that prevent cancer cell growth by modification of specific mitochondrial proteins.

Inhibition of oxidative metabolism leads to p53 genetic inactivation and transformation in neural stem cells

Alterations of mitochondrial metabolism and genomic instability have been implicated in tumorigenesis in multiple tissues. High-grade glioma (HGG), one of the most lethal human neoplasms, displays genetic modifications of Krebs cycle components as well as electron transport chain (ETC) alterations. Furthermore, the p53 tumor suppressor, which has emerged as a key regulator of mitochondrial respiration at the expense of glycolysis, is genetically inactivated in a large proportion of HGG cases. Therefore, it is becoming evident that genetic modifications can affect cell metabolism in HGG; however, it is currently unclear whether mitochondrial metabolism alterations could vice versa promote genomic instability as a mechanism for neoplastic transformation. Here, we show that, in neural progenitor/stem cells (NPCs), which can act as HGG cell of origin, inhibition of mitochondrial metabolism leads to p53 genetic inactivation. Impairment of respiration via inhibition of complex I or decreased mitochondrial DNA copy number leads to p53 genetic loss and a glycolytic switch. p53 genetic inactivation in ETC-impaired neural stem cells is caused by increased reactive oxygen species and associated oxidative DNA damage. ETC-impaired cells display a marked growth advantage in the presence or absence of oncogenic RAS, and form undifferentiated tumors when transplanted into the mouse brain. Finally, p53 mutations correlated with alterations in ETC subunit composition and activity in primary glioma-initiating neural stem cells. Together, these findings provide previously unidentified insights into the relationship between mitochondria, genomic stability, and tumor suppressive control, with implications for our understanding of brain cancer pathogenesis.

Berberine induces senescence of human glioblastoma cells by downregulating the EGFR-MEK-ERK signaling pathway

Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor and has a poor prognosis. We, here, report a potent antitumor effect of berberine, an isoquinoline alkaloid, on GBM. Berberine was found to have an IC50 that is much lower than temozolomide in vitro in U87, U251, and U118 glioblastoma cells. Although previous studies showed that berberine primarily exerts its anticancer effect by inducing cell-cycle arrest, apoptosis, and autophagy, we observed that the antitumor effect of berberine on glioblastoma cells was primarily achieved through induction of cellular senescence. In glioblastoma cells treated with berberine, the level of epidermal growth factor receptor (EGFR) was greatly reduced. Examination of the activities of the kinases downstream of EGFR revealed that the RAF-MEK-ERK signaling pathway was remarkably inhibited, whereas AKT phosphorylation was not altered. Pharmacologic inhibition or RNA interference of EGFR similarly induced cellular senescence of glioblastoma cells. Furthermore, the cellular senescence induced by berberine could be rescued by introduction of a constitutive active MKK. Berberine also potently inhibited the growth of tumor xenografts, which was accompanied by downregulation of EGFR and induction of senescence. Our findings thus revealed a new route by which berberine exerts its anticancer activity. Because EGFR is commonly upregulated in glioblastoma, the demonstration of effective inhibition of EGFR by berberine points to the possibility of using berberine in the treatment of patients with glioblastoma.

Therapeutic efficacy of aldoxorubicin in an intracranial xenograft mouse model of human glioblastoma

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor with a median survival of 12 to 15 months after diagnosis. Acquired chemoresistance, high systemic toxicity, and low penetration of the blood brain barrier by many anticancer drugs contribute to the failure of anti-GBM therapies. To circumvent some of these obstacles, we tested a novel prodrug approach to evaluate anti-GBM efficacy by utilizing serum albumin-binding doxorubicin (Doxo), aldoxorubicin (Aldoxo), which is less toxic, is released from albumin in an acidic environment and accumulates in tumor tissues. A human GBM cell line that expresses a luciferase reporter (U87-luc) was stereotactically injected into the left striatum of the brain of immunodeficient mice. Following initial tumor growth for 12 days, mice were injected once a week in the tail-vein with Aldoxo [24 mg/kg or 18 mg/kg of doxorubicin equivalents—3/4 maximum tolerated dose (MTD)], Doxo [6 mg/kg (3/4 MTD)], or vehicle. Aldoxo-treated mice demonstrated significantly slower growth of the tumor when compared to vehicle-treated or Doxo-treated mice. Five out of eight Aldoxo-treated mice remained alive more than 60 days with a median survival of 62 days, while the median survival of vehicle- and Doxo-treated mice was only 26 days. Importantly, Aldoxo-treated mice exhibited high levels of Doxo within the tumor tissue, accompanied by low tumor cell proliferation (Ki67) and abundant intratumoral programmed cell death (cleaved caspase-3). Effective accumulation of Aldoxo in brain tumor tissues but not normal brain, its anti-tumor efficacy, and low toxicity, provide a strong rationale for evaluating this novel drug conjugate as a treatment for patients afflicted with GBM.

Contemporary murine models in preclinical astrocytoma drug development

Despite 6 decades of research, only 3 drugs have been approved for astrocytomas, the most common malignant primary brain tumors. However, clinical drug development is accelerating with the transition from empirical, cytotoxic therapy to precision, targeted medicine. Preclinical animal model studies are critical for prioritizing drug candidates for clinical development and, ultimately, for their regulatory approval. For decades, only murine models with established tumor cell lines were available for such studies. However, these poorly represent the genomic and biological properties of human astrocytomas, and their preclinical use fails to accurately predict efficacy in clinical trials. Newer models developed over the last 2 decades, including patient-derived xenografts, genetically engineered mice, and genetically engineered cells purified from human brains, more faithfully phenocopy the genomics and biology of human astrocytomas. Harnessing the unique benefits of these models will be required to identify drug targets, define combination therapies that circumvent inherent and acquired resistance mechanisms, and develop molecular biomarkers predictive of drug response and resistance. With increasing recognition of the molecular heterogeneity of astrocytomas, employing multiple, contemporary models in preclinical drug studies promises to increase the efficiency of drug development for specific, molecularly defined subsets of tumors.

Current evidence of temozolomide and bevacizumab in treatment of gliomas

OBJECTIVE

This review article summarizes in vitro, in vivo, and clinical evidence pertaining to temozolomide (TMZ) and bevacizumab (BEV) efficacy and mechanism of action in gliomas.

METHODS

Relevant publications published before June 2013 in PubMed database were reviewed.

RESULTS

Temozolomide and BEV are current chemotherapeutic agents treating patients with high-grade glioma, including glioblastoma. In vitro and in vivo studies have proposed discordant cell death pathways for TMZ as either apoptosis or autophagy using different experimental setting details or cell lines. In addition, BEV may cause cell death through hypoxia-induced autophagy or unspecific indirect effects on cancer cells. The complexity of cancer cells in glioma has contributed to their resistance of both chemotherapies. In clinical trials, overall survival duration in glioma patients with recurrence (8-9 months) is lower than that in newly diagnosed patients (12-15 months).

CONCLUSION

Our collected data support the addition of radiotherapy, BEV, and other targeted agents to TMZ treatment, indicating prolonged survival duration in newly diagnosed patients. However, the optimal regimen for treating high-grade glioma cannot be concluded without more clinical trials.

Kinomic exploration of temozolomide and radiation resistance in Glioblastoma multiforme xenolines

BACKGROUND AND PURPOSE

Glioblastoma multiforme (GBM) represents the most common and deadly primary brain malignancy, particularly due to temozolomide (TMZ) and radiation (RT) resistance. To better understand resistance mechanisms, we examined global kinase activity (kinomic profiling) in both treatment sensitive and resistant human GBM patient-derived xenografts (PDX or "xenolines").

MATERIALS AND METHODS

Thirteen orthotopically-implanted xenolines were examined including 8 with known RT sensitivity/resistance, while 5 TMZ resistant xenolines were generated through serial TMZ treatment in vivo. Tumors were harvested, prepared as total protein lysates, and kinomically analyzed on a PamStation®12 high-throughput microarray platform with subsequent upstream kinase prediction and network modeling.

RESULTS

Kinomic profiles indicated elevated tyrosine kinase activity associated with the radiation resistance phenotype, including FAK and FGFR1. Furthermore, network modeling showed VEGFR1/2 and c-Raf hubs could be involved. Analysis of acquired TMZ resistance revealed more kinomic variability among TMZ resistant tumors. Two of the five tumors displayed significantly altered kinase activity in the TMZ resistant xenolines and network modeling indicated PKC, JAK1, PI3K, CDK2, and VEGFR as potential mediators of this resistance.

CONCLUSION

GBM xenolines provide a phenotypic model for GBM drug response and resistance that when paired with kinomic profiling identified targetable pathways to inherent (radiation) or acquired (TMZ) resistance.

Mitochondrial protein ATPase family, AAA domain containing 3A correlates with radioresistance in glioblastoma

BACKGROUND

ATPase-family, AAA domain containing 3A (ATAD3A) is located on human chromosome 1p36.33, and high endogenous expression may associate with radio- and chemosensitivity. This study was conducted to investigate the significance of ATAD3A in glioblastoma multiforme (GBM).

METHODS

Clinical significance of ATAD3A expression was assessed by immunohistochemistry in 67 GBM specimens, and prognostic value was assessed in 32 GBM patients statistically. To investigate in vitro phenotypic effects of ATAD3A, cell viability was measured using a clonogenic survival assay under either knockdown or ectopic expression of ATAD3A in GBM cell lines. The effects of ATAD3A knockdown on targeted DNA repair-associated proteins in T98G cells were evaluated using immunofluorescence and Western blotting.

RESULTS

Clinically, high expression of ATAD3A was independent of O(6)-DNA methylguanine-methyltransferase methylation status and correlated with worse prognosis. In vitro, high ATAD3A-expressing T98G cells were more resistant to radiation-induced cell death compared with control and low endogenous ATAD3A U87MG cells. After silencing ATAD3A, T98G cells became more sensitive to radiation. On the other hand, enforced ATAD3A expression in U87MG cells exhibited increased radioresistance. ATAD3A may coordinate with aldo-keto reductase genes and participate in bioactivation or detoxication of temozolomide. Surprisingly, deficient DNA repair after irradiation was observed in T98G/ATAD3A knockdown as a result of decreased nuclear ataxia telangiectasia mutated kinase and histones H2AX and H3, which was also evidenced by the sustained elevation of poly (ADP-ribose) polymerase prior to and after radiation treatment.

CONCLUSION

Our data suggest that high expression of ATAD3A is an independent biomarker for radioresistance in GBM. ATAD3A could be a potential target for therapy.

A mitochondrial RNAi screen defines cellular bioenergetic determinants and identifies an adenylate kinase as a key regulator of ATP levels

Altered cellular bioenergetics and mitochondrial function are major features of several diseases, including cancer, diabetes, and neurodegenerative disorders. Given this important link to human health, we sought to define proteins within mitochondria that are critical for maintaining homeostatic ATP levels. We screened an RNAi library targeting >1,000 nuclear-encoded genes whose protein products localize to the mitochondria in multiple metabolic conditions in order to examine their effects on cellular ATP levels. We identified a mechanism by which electron transport chain (ETC) perturbation under glycolytic conditions increased ATP production through enhanced glycolytic flux, thereby highlighting the cellular potential for metabolic plasticity. Additionally, we identified a mitochondrial adenylate kinase (AK4) that regulates cellular ATP levels and AMPK signaling and whose expression significantly correlates with glioma patient survival. This study maps the bioenergetic landscape of >1,000 mitochondrial proteins in the context of varied metabolic substrates and begins to link key metabolic genes with clinical outcome.

Differential expression of miR200a-3p and miR21 in grade II-III and grade IV gliomas: evidence that miR200a-3p is regulated by O⁶-methylguanine methyltransferase and promotes temozolomide responsiveness

Glioblastoma multiforme (GBM) is the most common primary brain tumor and is among the deadliest of human cancers. Dysregulation of microRNAs (miRNAs) expression is an important step in tumor progression as miRNAs can act as tumor suppressors or oncogenes and may affect cell sensitivity to chemotherapy. Whereas the oncogenic miR21 has been shown to be overexpressed in gliomas, the expression and function of the tumor-supressor miR200a in GBMs remains unknown. In this study, we show that miR21 is upregulated in grade IV (GBMs) vs. grade II-III (LGs) gliomas, confirming that miR21 expression level is correlated with tumor grade, and that it may be considered as a marker of tumor progression. Conversely, miR200a is demonstrated for the first time to be downregulated in GBMs compared with LGs, and overexpression of miR200a in GBM cells is shown to promote TMZ-sensitivity. Interestingly, miR200a but not miR21 expression level is significantly higher in TMZ-responsive vs. -unresponsive tumoral glial cells in primary culture. Furthermore, miR200a appears negatively correlated with the expression of the DNA repair enzyme O (6)-methylguanine methyltransferase (MGMT), and the inhibition of MGMT activity results in an increase of miR200a expression in GBM cells. Taken together, these data strongly suggest that miR200a is likely to act as a crucial antitumoral factor regarding glioma progression. Interplay between miR200a and MGMT should be considered as potential mechanism involved in therapeutic response.

The lignan, (-)-sesamin reveals cytotoxicity toward cancer cells: pharmacogenomic determination of genes associated with sensitivity or resistance

(-)-Sesamin is a lignan present in sesam oil and a number of medicinal plants. It exerts various pharmacological effects, such as prevention of hyperlipidemia, hypertension, and carcinogenesis. Moreover, (-)-sesamin has chemopreventive and anticancer activity in vitro and in vivo. Multidrug resistance (MDR) of tumors leads to fatal treatment outcome in many patients and novel drugs able to kill multidrug-resistant cells are urgently needed. P-glycoprotein (MDR1/ABCB1) is the best known ATP-binding cassette (ABC) drug transporter mediating MDR. ABCB5 is a close relative to ABCB1, which also mediates MDR. We found that the mRNA expressions of ABCB1 and ABCB5 were not related to the 50% inhibition concentrations (IC50) for (-)-sesamin in a panel of 55 cell lines of the National Cancer Institute, USA. Furthermore, (-)-sesamin inhibited ABCB1- or ABCB5-overexpressing cells with similar efficacy than their drug-sensitive parental counterparts. In addition to ABC transporter-mediated MDR, we attempted to identify other molecular determinants of (-)-sesamin resistance. For this reason, we performed COMPARE and hierarchical cluster analyses of the transcriptome-wide microarray-based mRNA expression of the NCI cell panel. Twenty-three genes were identified, whose mRNA expression correlated with the IC50 values for (-)-sesamin. These genes code for proteins of different biological functions, i.e. ribosomal proteins, components of the mitochondrial respiratory chain, proteins involved in RNA metabolism, protein biosynthesis, or glucose and fatty acid metabolism. Subjecting this set of genes to cluster analysis showed that the cell lines were assembled in the resulting dendrogram according to their responsiveness to (-)-sesamin. In conclusion, (-)-sesamin is not involved in MDR mediated by ABCB1 or ABCB5 and may be valuable to bypass chemoresistance of refractory tumors. The microarray expression profile, which predicted sensitivity or resistance of tumor cells to (-)-sesamin consisted of genes, which do not belong to the classical resistance mechanisms to established anticancer drugs.

The adherens junction-associated protein 1 is a negative transcriptional regulator of MAGEA2, which potentiates temozolomide-induced apoptosis in GBM

Previous studies identified the frequent loss of adherens junction-associated protein 1 (AJAP1) expression in glioblastoma (GBM) and its correlation with worse survival. AJAP1 may suppress glioma cell migration, which plays an important role in tumor progression in malignant gliomas such as GBM. However, the role of AJAP1 in cell cycle arrest or apoptosis and resistance to chemotherapy remains unclear. Based on microarray screening results, quantitative PCR and luciferase plasmid reporter constructs were used to evaluate the possible regulatory role of AJAP1 on MAGEA2 expression and function. Cell death assays, TUNEL and other markers of apoptosis were utilized to detect cell apoptosis. Restoration of AJAP1 expression in glioma cells was analyzed after temozolomide exposure. AJAP1 suppressed the expression of MAGEA2 and inhibited the transcriptional activity of MAGEA2 in glioma cells. As AJAP1 expression decreased MAGEA2 protein expression apoptosis increased moderately. Consistent with increased cell death, the induced loss of MAGEA2 expression correlated with increased caspase 3/7 activity, BCL2/BAX ratio and TUNEL signal. AJAP1 expression enhanced cell death in the presence of temozolomide. This study suggests AJAP1 may also function as a pro-apoptotic factor and potentiate cell death by temozolomide in glioma cells. This effect may be partially explained by AJAP1-mediated gene regulation of MAGEA2.

miR-218 opposes a critical RTK-HIF pathway in mesenchymal glioblastoma

Glioblastoma multiforme (GBM) and the mesenchymal GBM subtype in particular are highly malignant tumors that frequently exhibit regions of severe hypoxia and necrosis. Because these features correlate with poor prognosis, we investigated microRNAs whose expression might regulate hypoxic GBM cell survival and growth. We determined that the expression of microRNA-218 (miR-218) is decreased significantly in highly necrotic mesenchymal GBM, and orthotopic tumor studies revealed that reduced miR-218 levels confer GBM resistance to chemotherapy. Importantly, miR-218 targets multiple components of receptor tyrosine kinase (RTK) signaling pathways, and miR-218 repression increases the abundance and activity of multiple RTK effectors. This elevated RTK signaling also promotes the activation of hypoxia-inducible factor (HIF), most notably HIF2α. We further show that RTK-mediated HIF2α regulation is JNK dependent, via jun proto-oncogene. Collectively, our results identify an miR-218-RTK-HIF2α signaling axis that promotes GBM cell survival and tumor angiogenesis, particularly in necrotic mesenchymal tumors.

O6-methylguanine DNA methyltransferase as a promising target for the treatment of temozolomide-resistant gliomas

Temozolomide (TMZ) is an alkylating agent currently used as first-line therapy for gliomas treatment due to its DNA-damaging effect. However, drug resistance occurs, preventing multi-cycle use of this chemotherapeutic agent. One of the major mechanisms of cancer drug resistance is enhanced activity of a DNA repair enzyme, O(6)-methylguanine-DNA-methyltransferase (MGMT), which counteracts chemotherapy-induced DNA alkylation and is a key component of chemoresistance. MGMT repairs TMZ-induced DNA lesions, O(6)-meG, by transferring the alkyl group from guanine to a cysteine residue. This review provides an overview of recent advances in the field, with particular emphasis on the inhibitors of MGMT and underlying mechanisms. Literature search was performed through PubMed and all relevant articles were reviewed, with particular attention to MGMT, its role in TMZ-resistant gliomas, effects of MGMT inhibitors and the underlying mechanisms. Several strategies are currently being pursued to improve the therapeutic efficacy of TMZ via inhibition of MGMT to reduce chemoresistance and improve overall survival. MGMT may be a promising target for the treatment of TMZ-resistant gliomas.

Dysfunctional mitochondrial bioenergetics and oxidative stress in Akita(+/Ins2)-derived β-cells

Insulin release from pancreatic β-cells plays a critical role in blood glucose homeostasis, and β-cell dysfunction leads to the development of diabetes mellitus. In cases of monogenic type 1 diabetes mellitus (T1DM) that involve mutations in the insulin gene, we hypothesized that misfolding of insulin could result in endoplasmic reticulum (ER) stress, oxidant production, and mitochondrial damage. To address this, we used the Akita(+/Ins2) T1DM model in which misfolding of the insulin 2 gene leads to ER stress-mediated β-cell death and thapsigargin to induce ER stress in two different β-cell lines and in intact mouse islets. Using transformed pancreatic β-cell lines generated from wild-type Ins2(+/+) (WT) and Akita(+/Ins2) mice, we evaluated cellular bioenergetics, oxidative stress, mitochondrial protein levels, and autophagic flux to determine whether changes in these processes contribute to β-cell dysfunction. In addition, we induced ER stress pharmacologically using thapsigargin in WT β-cells, INS-1 cells, and intact mouse islets to examine the effects of ER stress on mitochondrial function. Our data reveal that Akita(+/Ins2)-derived β-cells have increased mitochondrial dysfunction, oxidant production, mtDNA damage, and alterations in mitochondrial protein levels that are not corrected by autophagy. Together, these findings suggest that deterioration in mitochondrial function due to an oxidative environment and ER stress contributes to β-cell dysfunction and could contribute to T1DM in which mutations in insulin occur.

Oncocytic glioblastoma: a glioblastoma showing oncocytic changes and increased mitochondrial DNA copy number

Ten cases of glioblastomas showing oncocytic changes are described. The tumors showed mononuclear to multinuclear cells and abundant, granular, eosinophilic cytoplasm. The cytoplasm of these same cells was filled by strongly immunoreactive mitochondria. At ultrastructure, numerous mitochondria, some of which were large, were evidenced in the cytoplasm of neoplastic cells. Finally, 9 of 10 of these cases had a significantly high mitochondrial DNA content compared with control tissue (P < .01). It seems that, for these tumors, the designation of oncocytic glioblastoma is appropriate. To the best of our knowledge, oncocytic changes have not been previously reported in such neoplasms. Oncocytic glioblastomas have to be added to the long list of various tumors that can manifest "unexpected" oncocytic changes in different organs. Albeit failing to show statistical significance (log-rank test, P = .597; Wilcoxon test, P = .233), we observed a trend for longer median survival in oncocytic glioblastomas, when compared with "ordinary" glioblastomas (median survival of 16 versus 8.7 months). Thus, it seems that the definition of neoplasms showing oncocytic changes, currently based on classic morphological parameters (ie, histology, ultrastructure, and immunohistochemistry), can be expanded by including the quantitative assessment of mitochondrial DNA content.

Connexin43 confers Temozolomide resistance in human glioma cells by modulating the mitochondrial apoptosis pathway

Glioblastoma multiforme (GBM) is the most aggressive astrocytoma, and therapeutic options are generally limited to surgical resection, radiotherapy, and Temozolomide (TMZ) chemotherapy. TMZ is a DNA alkylating agent that causes DNA damage and induces cell death. Unfortunately, glioma cells often develop resistance to TMZ treatment, with DNA de-methylation of the MGMT promoter identified as the primary reason. However, the contributions from proteins that normally protect cells against cytotoxic stress in TMZ-induced apoptosis have not been extensively explored. Here, we showed that increasing the level of the gap junction protein, Cx43, in human LN18 and LN229 glioma cells enhances resistance to TMZ treatment while knockdown of Cx43 in these same cells sensitizes them to TMZ treatment. By expressing a channel-dead or a C-terminal truncation mutant of Cx43, we show that Cx43-mediated TMZ resistance involves both channel dependent and independent functions. Expression of Cx43 in LN229 cells decreases TMZ-induced apoptosis, as determined by Annexin V staining. Cx43-mediated chemoresistance appears to be acting via a mitochondrial apoptosis pathway as manifested by the reduction in Bax/Bcl-2 ratio and the release of cytochrome C. Our findings highlight additional mechanisms and proteins that contribute to TMZ resistance, and raise the possibility of increasing TMZ efficiency by targeting Cx43 protein. This article is part of the Special Issue Section entitled 'Current Pharmacology of Gap Junction Channels and Hemichannels'.

Prognostic relevance of cytochrome C oxidase in primary glioblastoma multiforme

Patients with primary glioblastoma multiforme (GBM) have one of the lowest overall survival rates among cancer patients, and reliable biomarkers are necessary to predict patient outcome. Cytochrome c oxidase (CcO) promotes the switch from glycolytic to OXPHOS metabolism, and increased CcO activity in tumors has been associated with tumor progression after chemotherapy failure. Thus, we investigated the relationship between tumor CcO activity and the survival of patients diagnosed with primary GBM. A total of 84 patients with grade IV glioma were evaluated in this retrospective cohort study. Cumulative survival was calculated by the Kaplan-Meier method and analyzed by the log-rank test, and univariate and multivariate analyses were performed with the Cox regression model. Mitochondrial CcO activity was determined by spectrophotometrically measuring the oxidation of cytochrome c. High CcO activity was detected in a subset of glioma tumors (∼30%), and was an independent prognostic factor for shorter progression-free survival and overall survival [P = 0.0087 by the log-rank test, hazard ratio = 3.57 for progression-free survival; P<0.001 by the log-rank test, hazard ratio = 10.75 for overall survival]. The median survival time for patients with low tumor CcO activity was 14.3 months, compared with 6.3 months for patients with high tumor CcO activity. High CcO activity occurs in a significant subset of high-grade glioma patients and is an independent predictor of poor outcome. Thus, CcO activity may serve as a useful molecular marker for the categorization and targeted therapy of GBMs.

Inhibition of prolyl 4-hydroxylase, beta polypeptide (P4HB) attenuates temozolomide resistance in malignant glioma via the endoplasmic reticulum stress response (ERSR) pathways

BACKGROUND

Glioblastoma multiforme (GBM), the most aggressive malignant primary brain tumor of the central nervous system, is characterized by a relentless disease recurrence despite continued advancement in surgery, radiotherapy, and chemotherapy. Resistance to temozolomide (TMZ), a standard chemotherapeutic agent for GBM, remains a major challenge. Understanding the mechanisms behind TMZ resistance can direct the development of novel strategies for the prevention, monitoring, and treatment of tumor relapse.

METHODS AND RESULTS

Our research platform, based on the establishment of 2 pairs of TMZ-sensitive/resistant GBM cells (D54-S and D54-R; U87-S and U87-R), has successfully identified prolyl 4-hydroxylase, beta polypeptide (P4HB) over-expression to be associated with an increased IC50 of TMZ. Elevated P4HB expression was verified using in vivo xenografts developed from U87-R cells. Clinically, we found that P4HB was relatively up-regulated in the recurrent GBM specimens that were initially responsive to TMZ but later developed acquired resistance, when compared with treatment-naive tumors. Functionally, P4HB inhibition by RNAi knockdown and bacitracin inhibition could sensitize D54-R and U87-R cells to TMZ in vitro and in vivo, whereas over-expression of P4HB in vitro conferred resistance to TMZ in both D54-S and U87-S cells. Moreover, targeting P4HB blocked its protective function and sensitized glioma cells to TMZ through the PERK arm of the endoplasmic reticulum stress response.

CONCLUSIONS

Our study identified a novel target together with its functional pathway in the development of TMZ resistance. P4HB inhibition may be used alone or in combination with TMZ for the treatment of TMZ-resistant GBM.

The overexpression of hypomethylated miR-663 induces chemotherapy resistance in human breast cancer cells by targeting heparin sulfate proteoglycan 2 (HSPG2)

MicroRNAs are involved in regulating the biology of cancer cells, but their involvement in chemoresistance is not fully understood. We found that miR-663 was up-regulated in our induced multidrug-resistant MDA-MB-231/ADM cell line and that this up-regulation was closely related to chemosensitivity. In the present study, we aimed to clarify the role of miR-663 in regulating the chemoresistance of breast cancer. MicroRNA microarray and quantitative RT-PCR assays were used to identify differentially expressed microRNAs. Cell apoptosis was evaluated by annexin V/propidium iodide staining, TUNEL, and reactive oxygen species generation analysis. The expression of miR-663 and HSPG2 in breast cancer tissues was detected by in situ hybridization and immunohistochemistry. The potential targets of miR-663 were defined by a luciferase reporter assay. Bisulfite sequencing PCR was used to analyze the methylation status. We found that miR-663 was significantly elevated in MDA-MB-231/ADM cells, and the down-regulation of miR-663 sensitized MDA-MB-231/ADM cells to both cyclophosphamide and docetaxel. The overexpression of miR-663 in breast tumor tissues was associated with chemoresistance; in MDA-MB-231 cells, this chemoresistance was accompanied by the down-regulation of HSPG2, which was identified as a target of miR-663. MDA-MB-231/ADM contained fewer methylated CpG sites than its parental cell line, and miR-663 expression in MDA-MB-231 cells was reactivated by 5-aza-29-deoxycytidine treatment, indicating that DNA methylation may play a functional role in the expression of miR-663. Our findings suggest that the overexpression of hypomethylated miR-663 induced chemoresistance in breast cancer cells by down-regulating HSPG2, thus providing a potential target for the development of an microRNA-based approach for breast cancer therapy.

Integration of cellular bioenergetics with mitochondrial quality control and autophagy

Bioenergetic dysfunction is emerging as a cornerstone for establishing a framework for understanding the pathophysiology of cardiovascular disease, diabetes,cancer and neurodegeneration. Recent advances in cellular bioenergetics have shown that many cells maintain a substantial bioenergetic reserve capacity, which is a prospective index of ‘ healthy ’ mitochondrial populations.The bioenergetics of the cell are likely regulated by energy requirements and substrate availability. Additionally,the overall quality of the mitochondrial population and the relative abundance of mitochondria in cells and tissues also impinge on overall bioenergetic capacity and resistance to stress. Because mitochondria are susceptible to damage mediated by reactive oxygen/nitrogen and lipid species, maintaining a ‘ healthy ’ population of mitochondria through quality control mechanisms appears to be essential for cell survival under conditions of pathological stress. Accumulating evidence suggest that mitophagy is particularly important for preventing amplification of initial oxidative insults, which otherwise would further impair the respiratory chain or promote mutations in mitochondrial DNA (mtDNA). The processes underlying the regulation of mitophagy depend on several factors, including the integrity of mtDNA, electron transport chain activity, and the interaction and regulation of the autophagic machinery. The integration and interpretation of cellular bioenergetics in the context of mitochondrial quality control and genetics is the theme of this review.

Mitochondrial electron transport chain complex dysfunction in the colonic mucosa in ulcerative colitis

BACKGROUND

Ulcerative colitis (UC) is characterized by an energy deficiency state of the colonic epithelium. This study evaluated mitochondrial electron transport chain (ETC) complex activity in normal and disease mucosa in patients with UC. Alterations in ETC complexes were also investigated in experimental colitis in mice.

METHODS

Biopsies were obtained from macroscopically normal and diseased colonic mucosa of 43 patients with UC and 35 controls undergoing screening colonoscopy and ETC complex activity was assayed biochemically. ETC complex activities were also assayed in colonic epithelial cells isolated from Swiss albino mice with dextran sodium sulfate (DSS)-induced colitis at various stages of induction of colitis. Mucosal nitrite levels and protein carbonyl content were determined.

RESULTS

The activity of Complex II was significantly decreased in colonic biopsies from UC patients compared with controls, while activities of other mitochondrial complex were normal. Complex II activity was equally decreased in diseased and normal mucosa in UC; the degree of reduction did not correlate with clinical, endoscopic, or histological grading of disease activity. In DSS-fed mice, a reduction in activity of Complex IV and Complex II was observed. Activity of other complex was not affected. Administration of aminoguanidine, an inducible nitric oxide synthase (iNOS) inhibitor, attenuated all parameters of colitis as well as the reductions in Complex IV and Complex II activity.

CONCLUSIONS

Reduction in Complex II activity appears to be a specific change in UC, present in quiescent and active disease. Mitochondrial complex dysfunction occurs in DSS colitis in mice and appears to be mediated by nitric oxide.

Cancer cell growth and survival as a system-level property sustained by enhanced glycolysis and mitochondrial metabolic remodeling

Systems Biology holds that complex cellular functions are generated as system-level properties endowed with robustness, each involving large networks of molecular determinants, generally identified by “omics” analyses. In this paper we describe four basic cancer cell properties that can easily be investigated in vitro: enhanced proliferation, evasion from apoptosis, genomic instability, and inability to undergo oncogene-induced senescence. Focusing our analysis on a K-ras dependent transformation system, we show that enhanced proliferation and evasion from apoptosis are closely linked, and present findings that indicate how a large metabolic remodeling sustains the enhanced growth ability. Network analysis of transcriptional profiling gives the first indication on this remodeling, further supported by biochemical investigations and metabolic flux analysis (MFA). Enhanced glycolysis, down-regulation of TCA cycle, decoupling of glucose and glutamine utilization, with increased reductive carboxylation of glutamine, so to yield a sustained production of growth building blocks and glutathione, are the hallmarks of enhanced proliferation. Low glucose availability specifically induces cell death in K-ras transformed cells, while PKA activation reverts this effect, possibly through at least two mitochondrial targets. The central role of mitochondria in determining the two investigated cancer cell properties is finally discussed. Taken together the findings reported herein indicate that a system-level property is sustained by a cascade of interconnected biochemical pathways that behave differently in normal and in transformed cells.

Pyruvate fuels mitochondrial respiration and proliferation of breast cancer cells: effect of monocarboxylate transporter inhibition

Recent studies have highlighted the fact that cancer cells have an altered metabolic phenotype, and this metabolic reprogramming is required to drive the biosynthesis pathways necessary for rapid replication and proliferation. Specifically, the importance of citric acid cycle-generated intermediates in the regulation of cancer cell proliferation has been recently appreciated. One function of MCTs (monocarboxylate transporters) is to transport the citric acid cycle substrate pyruvate across the plasma membrane and into mitochondria, and inhibition of MCTs has been proposed as a therapeutic strategy to target metabolic pathways in cancer. In the present paper, we examined the effect of different metabolic substrates (glucose and pyruvate) on mitochondrial function and proliferation in breast cancer cells. We demonstrated that cancer cells proliferate more rapidly in the presence of exogenous pyruvate when compared with lactate. Pyruvate supplementation fuelled mitochondrial oxygen consumption and the reserve respiratory capacity, and this increase in mitochondrial function correlated with proliferative potential. In addition, inhibition of cellular pyruvate uptake using the MCT inhibitor α-cyano-4-hydroxycinnamic acid impaired mitochondrial respiration and decreased cell growth. These data demonstrate the importance of mitochondrial metabolism in proliferative responses and highlight a novel mechanism of action for MCT inhibitors through suppression of pyruvate-fuelled mitochondrial respiration.