Glioblastoma multiforme: the role of DSB repair between genotype and phenotype

Genotype-environment associations reveal genes potentially linked to avian malaria infection in populations of an endemic island bird

Patterns of pathogen prevalence are, at least partially, the result of coevolutionary host-pathogen interactions. Thus, exploring the distribution of host genetic variation in relation to infection by a pathogen within and across populations can provide important insights into mechanisms of host defence and adaptation. Here, we use a landscape genomics approach (Bayenv) in conjunction with genome-wide data (ddRADseq) to test for associations between avian malaria (Plasmodium) prevalence and host genetic variation across 13 populations of the island endemic Berthelot's pipit (Anthus berthelotii). Considerable and consistent spatial heterogeneity in malaria prevalence was observed among populations over a period of 15 years. The prevalence of malaria infection was also strongly positively correlated with pox (Avipoxvirus) prevalence. Multiple host loci showed significant associations with malaria prevalence after controlling for genome-wide neutral genetic structure. These sites were located near to or within genes linked to metabolism, stress response, transcriptional regulation, complement activity and the inflammatory response, many previously implicated in vertebrate responses to malarial infection. Our findings identify diverse genes - not just limited to the immune system - that may be involved in host protection against malaria and suggest that spatially variable pathogen pressure may be an important evolutionary driver of genetic divergence among wild animal populations, such as Berthelot's pipit. Furthermore, our data indicate that spatio-temporal variation in multiple different pathogens (e.g. malaria and pox in this case) may have to be studied together to develop a more holistic understanding of host pathogen-mediated evolution.

Hypoxanthine phosphoribosyl transferase 1 metabolizes temozolomide to activate AMPK for driving chemoresistance of glioblastomas

Temozolomide (TMZ) is a standard treatment for glioblastoma (GBM) patients. However, TMZ has moderate therapeutic effects due to chemoresistance of GBM cells through less clarified mechanisms. Here, we demonstrate that TMZ-derived 5-aminoimidazole-4-carboxamide (AICA) is converted to AICA ribosyl-5-phosphate (AICAR) in GBM cells. This conversion is catalyzed by hypoxanthine phosphoribosyl transferase 1 (HPRT1), which is highly expressed in human GBMs. As the bona fide activator of AMP-activated protein kinase (AMPK), TMZ-derived AICAR activates AMPK to phosphorylate threonine 52 (T52) of RRM1, the catalytic subunit of ribonucleotide reductase (RNR), leading to RNR activation and increased production of dNTPs to fuel the repairment of TMZ-induced-DNA damage. RRM1 T52A expression, genetic interruption of HPRT1-mediated AICAR production, or administration of 6-mercaptopurine (6-MP), a clinically approved inhibitor of HPRT1, blocks TMZ-induced AMPK activation and sensitizes brain tumor cells to TMZ treatment in mice. In addition, HPRT1 expression levels are positively correlated with poor prognosis in GBM patients who received TMZ treatment. These results uncover a critical bifunctional role of TMZ in GBM treatment that leads to chemoresistance. Our findings underscore the potential of combined administration of clinically available 6-MP to overcome TMZ chemoresistance and improve GBM treatment.

Evaluation of Proton-Induced DNA Damage in 3D-Engineered Glioblastoma Microenvironments

Glioblastoma (GBM) is a devastating cancer of the brain with an extremely poor prognosis. For this reason, besides clinical and preclinical studies, novel in vitro models for the assessment of cancer response to drugs and radiation are being developed. In such context, three-dimensional (3D)-engineered cellular microenvironments, compared to unrealistic two-dimensional (2D) monolayer cell culture, provide a model closer to the in vivo configuration. Concerning cancer treatment, while X-ray radiotherapy and chemotherapy remain the current standard, proton beam therapy is an appealing alternative as protons can be efficiently targeted to destroy cancer cells while sparing the surrounding healthy tissue. However, despite the treatment's compelling biological and medical rationale, little is known about the effects of protons on GBM at the cellular level. In this work, we designed novel 3D-engineered scaffolds inspired by the geometry of brain blood vessels, which cover a vital role in the colonization mechanisms of GBM cells. The architectures were fabricated by two-photon polymerization (2PP), cultured with U-251 GBM cells and integrated for the first time in the context of proton radiation experiments to assess their response to treatment. We employed Gamma H2A.X as a fluorescent biomarker to identify the DNA damage induced in the cells by proton beams. The results show a higher DNA double-strand breakage in 2D cell monolayers as compared to cells cultured in 3D. The discrepancy in terms of proton radiation response could indicate a difference in the radioresistance of the GBM cells or in the rate of repair kinetics between 2D cell monolayers and 3D cell networks. Thus, these biomimetic-engineered 3D scaffolds pave the way for the realization of a benchmark tool that can be used to routinely assess the effects of proton therapy on 3D GBM cell networks and other types of cancer cells.

N-cadherin upregulation mediates adaptive radioresistance in glioblastoma

Glioblastoma (GBM) is composed of heterogeneous tumor cell populations, including those with stem cell properties, termed glioma stem cells (GSCs). GSCs are innately less radiation sensitive than the tumor bulk and are believed to drive GBM formation and recurrence after repeated irradiation. However, it is unclear how GSCs adapt to escape the toxicity of repeated irradiation used in clinical practice. To identify important mediators of adaptive radioresistance in GBM, we generated radioresistant human and mouse GSCs by exposing them to repeat cycles of irradiation. Surviving subpopulations acquired strong radioresistance in vivo, which was accompanied by a reduction in cell proliferation and an increase in cell-cell adhesion and N-cadherin expression. Increasing N-cadherin expression rendered parental GSCs radioresistant, reduced their proliferation, and increased their stemness and intercellular adhesive properties. Conversely, radioresistant GSCs lost their acquired phenotypes upon CRISPR/Cas9-mediated knockout of N-cadherin. Mechanistically, elevated N-cadherin expression resulted in the accumulation of β-catenin at the cell surface, which suppressed Wnt/β-catenin proliferative signaling, reduced neural differentiation, and protected against apoptosis through Clusterin secretion. N-cadherin upregulation was induced by radiation-induced IGF1 secretion, and the radiation resistance phenotype could be reverted with picropodophyllin, a clinically applicable blood-brain-barrier permeable IGF1 receptor inhibitor, supporting clinical translation.

A Phase 1 dose-escalation study to evaluate safety, pharmacokinetics and pharmacodynamics of AsiDNA, a first-in-class DNA repair inhibitor, administered intravenously in patients with advanced solid tumours

Background

AsiDNA, a first-in-class oligonucleotide-mimicking double-stranded DNA breaks, acts as a decoy agonist to DNA damage response in tumour cells. It also activates DNA-dependent protein kinase and poly (adenosine diphosphate [ADP]-ribose) polymerase enzymes that induce phosphorylation of H2AX and protein PARylation.

Methods

The aim of this Phase 1 study was to determine dose-limiting toxicities (DLTs), maximum tolerated dose (MTD), safety and pharmacokinetics/pharmacodynamics of AsiDNA administered daily for 3 days in the first week then weekly thereafter. Twenty-two patients with advanced solid tumours were enrolled in 5 dose levels: 200, 400, 600, 900, and 1300 mg, using a 3 + 3 design.

Results

The MTD was not reached. IV AsiDNA was safe. Two DLTs (grade 4 and grade 3 hepatic enzymes increased at 900 and 1300 mg), and two related SAE at 900 mg (grade 3 hypotension and grade 4 hepatic enzymes increased) were reported. AsiDNA PK increased proportionally with dose. A robust activation of DNA-PK by a significant posttreatment increase of γH2AX was evidenced in tumour biopsies.

Conclusion

The dose of 600 mg was identified as the optimal dose for further clinical development.

Clinical trial registration

Clinical trial registration (NCT number): NCT03579628.

Enhancement of resistance to chemo-radiation by hsa-miR-1290 expression in glioblastoma cells

One of the resistance mechanisms to chemo-radiation is the efficiency of the DNA repair systems. MicroRNAs can alter the expression of their involved proteins; therefore, it may lead to a change in the response of cancer cells to adjuvant treatments. Here, the present study is aimed to investigate the role of hsa-miR-1290 on the chemo-radiation resistance and the target genes in the glioblastoma cells. First, we altered miR-1290 expression in the U-87 cells by using hsa-miR-1290 mimic and anti-miR-1290. Then, the Annexin V, CCK-8, MTT, colony formation, invasion, migration, and wound healing tests were utilized to study hsa-miR-1290 influences on cellular behavior such as proliferation, apoptosis, and metastasis. Moreover, the qRT-PCR and Western blot analyses were used to evaluate the effects of miR-1290 on the SOCS4 gene expression. Our results represented that the overexpression of miR-1290 could increase cell proliferation, migration, invasion, and resistance to chemo-radiation. The results showed miR-1290 directly targeted the 3՛UTR of the SOCS4 gene and suppressed its expression. Moreover, the suppression of hsa-miR-1290 led to an increase of apoptosis and cellular sensitivity to chemotherapy drugs and could also lead to decrease cell proliferation, migration, and invasion. Our findings proposed that miR-1290 can function as a novel oncomiR in glioblastoma cells by regulating its downstream genes such as SOCS4. Moreover, hsa-miR-1290 may be employed as a therapeutic target for clinical therapy of glioblastoma.

miR-548x and miR-4698 controlled cell proliferation by affecting the PI3K/AKT signaling pathway in Glioblastoma cell lines

Glioblastoma multiforme (GBM) is the most aggressive and prevalent form of brain tumor cancers that originate from glial cells. This study proposed to investigate the effect of miR-548x and miR-4698 on the proliferation and the PI3K/AKT signaling pathway in glioblastoma cell lines. The molecular features of glioblastoma were studied using KEGG and TCGA sites. Next, by using miRwalk 2.0 and TargetScan version 7.1, the microRNAs that target critical genes in the PI3k/AKT pathway were selected according to score. The pre-miR-548x and pre-miR-4698 were cloned in a pCDH plasmid to produced lentiviral vector. The expression levels of miR-548x, miR-4698 and target genes were detected by qRT-PCR. The MTT, cell cycle, annexin and colony formation assay was used to detect the cell proliferation. MiR-548x and miR-4698 predicted target genes (Rheb, AKT1, mTOR, PDK1) were also evaluated by luciferase assay. The expression of AKT was detected by western blotting. Our results described that overexpression of miR-548x and miR-4698 could inhibit proliferation of A-172 and U251 cells. Also, miR-548x promoted the cell cycle arrest of GBM cell lines. The luciferase reporter assay results showed the 3′ UTR of PDK1, RHEB, and mTOR are direct targets of the miR-548x and miR-4698. Too, the western blot analysis revealed that miR-548x and miR-4698 could downregulate the AKT1 protein expression. Overall, our findings suggest that miR-548x and miR-4698 could function as tumor suppressor genes in glioblastoma by controlling the PI3K/AKT signaling pathway and may act as gene therapy for clinical treatment of glioblastoma multiforme.

Polymeric Nanoparticles for the Treatment of Malignant Gliomas

Malignant gliomas are one of the deadliest forms of brain cancer and despite advancements in treatment, patient prognosis remains poor, with an average survival of 15 months. Treatment using conventional chemotherapy does not deliver the required drug dose to the tumour site, owing to insufficient blood brain barrier (BBB) penetration, especially by hydrophilic drugs. Additionally, low molecular weight drugs cannot achieve specific accumulation in cancerous tissues and are characterized by a short circulation half-life. Nanoparticles can be designed to cross the BBB and deliver their drugs within the brain, thus improving their effectiveness for treatment when compared to administration of the free drug. The efficacy of nanoparticles can be enhanced by surface PEGylation to allow more specificity towards tumour receptors. This review will provide an overview of the different therapeutic strategies for the treatment of malignant gliomas, risk factors entailing them as well as the latest developments for brain drug delivery. It will also address the potential of polymeric nanoparticles in the treatment of malignant gliomas, including the importance of their coating and functionalization on their ability to cross the BBB and the chemistry underlying that.

Exosomal transfer of long non-coding RNA SBF2-AS1 enhances chemoresistance to temozolomide in glioblastoma

Background

Acquired drug resistance is a constraining factor in clinical treatment of glioblastoma (GBM). However, the mechanisms of chemoresponsive tumors acquire therapeutic resistance remain poorly understood. Here, we aim to investigate whether temozolomide (TMZ) resistance of chemoresponsive GBM was enhanced by long non-coding RNA SBF2 antisense RNA 1 (lncRNA SBF2-AS1) enriched exosomes.

Method

LncSBF2-AS1 level in TMZ-resistance or TMZ-sensitive GBM tissues and cells were analyzed by qRT-PCR and FISH assays. A series of in vitro assay and xenograft tumor models were performed to observe the effect of lncSBF2-AS1 on TMZ-resistance in GBM. CHIP assay were used to investigate the correlation of SBF2-AS1 and transcription factor zinc finger E-box binding homeobox 1 (ZEB1). Dual-luciferase reporter, RNA immunoprecipitation (RIP), immunofluorescence and western blotting were performed to verify the relation between lncSBF2-AS1, miR-151a-3p and XRCC4. Comet assay and immunoblotting were performed to expound the effect of lncSBF2-AS1 on DNA double-stand break (DSB) repair. A series of in vitro assay and intracranial xenografts tumor model were used to determined the function of exosomal lncSBF2-AS1.

Result

It was found that SBF2-AS1 was upregulated in TMZ-resistant GBM cells and tissues, and overexpression of SBF2-AS1 led to the promotion of TMZ resistance, whereas its inhibition sensitized resistant GBM cells to TMZ. Transcription factor ZEB1 was found to directly bind to the SBF2-AS1 promoter region to regulate SBF2-AS1 level and affected TMZ resistance in GBM cells. SBF2-AS1 functions as a ceRNA for miR-151a-3p, leading to the disinhibition of its endogenous target, X-ray repair cross complementing 4 (XRCC4), which enhances DSB repair in GBM cells. Exosomes selected from temozolomide-resistant GBM cells had high levels of SBF2-AS1 and spread TMZ resistance to chemoresponsive GBM cells. Clinically, high levels of lncSBF2-AS1 in serum exosomes were associated with poor response to TMZ treatment in GBM patients.

Conclusion

We can conclude that GBM cells remodel the tumor microenvironment to promote tumor chemotherapy-resistance by secreting the oncogenic lncSBF2-AS1-enriched exosomes. Thus, exosomal lncSBF2-AS1 in human serum may serve as a possible diagnostic marker for therapy-refractory GBM.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1139-6) contains supplementary material, which is available to authorized users.

NUAK2 is a critical YAP target in liver cancer

The Hippo-YAP signaling pathway is a critical regulator of proliferation, apoptosis, and cell fate. The main downstream effector of this pathway, YAP, has been shown to be misregulated in human cancer and has emerged as an attractive target for therapeutics. A significant insufficiency in our understanding of the pathway is the identity of transcriptional targets of YAP that drive its potent growth phenotypes. Here, using liver cancer as a model, we identify NUAK2 as an essential mediator of YAP-driven hepatomegaly and tumorigenesis in vivo. By evaluating several human cancer cell lines we determine that NUAK2 is selectively required for YAP-driven growth. Mechanistically, we found that NUAK2 participates in a feedback loop to maximize YAP activity via promotion of actin polymerization and myosin activity. Additionally, pharmacological inactivation of NUAK2 suppresses YAP-dependent cancer cell proliferation and liver overgrowth. Importantly, our work here identifies a specific, potent, and actionable target for YAP-driven malignancies.

Hippo-YAP pathway plays an important role in cancers; however the in vivo relevance of YAP/TAZ target genes is unclear. Here, the authors show that NUAK2 is a target of YAP and participates in a feedback loop to maximize YAP activity. Inhibition of NUAK2 suppresses YAP-driven hepatomegaly and liver cancer growth, offering a new target for cancer therapy.

Polμ deficiency induces moderate shortening of P53-/- mouse lifespan and modifies tumor spectrum

Non-homologous end joining (NHEJ) is the main mechanism for double strand break (DSB) DNA repair. The error-prone DNA polymerase mu (Polμ) is involved in immunoglobulin variable region rearrangement and in general, NHEJ in non-lymphoid cells. Deletion of NHEJ factors in P53^-/- mice, which are highly prone to development of T cell lymphoma, generally increases cancer incidence and shifts the tumor spectrum towards aggressive pro-B lymphoma. In contrast, Polμ deletion increased sarcoma incidence, proportionally reducing pro-B lymphoma development on the P53-deficient background. Array comparative genomic hybridization (aCGH) analyses showed DNA copy number alterations in both P53^-/- and Polμ^-/-P53^-/- lymphomas. Our results also indicate that the increase in sarcoma incidence in Polμ^-/-P53^-/- mice could be associated with Cdk4 and Kub3 amplification and overexpression. These results identify a role for Polμ in the prevention of sarcomagenesis on a murine P53-deficient background, in contrast to most other NHEJ factors.

Evidence for L1-associated DNA rearrangements and negligible L1 retrotransposition in glioblastoma multiforme

Background

LINE-1 (L1) retrotransposons are a notable endogenous source of mutagenesis in mammals. Notably, cancer cells can support unusual L1 retrotransposition and L1-associated sequence rearrangement mechanisms following DNA damage. Recent reports suggest that L1 is mobile in epithelial tumours and neural cells but, paradoxically, not in brain cancers.

Results

Here, using retrotransposon capture sequencing (RC-seq), we surveyed L1 mutations in 14 tumours classified as glioblastoma multiforme (GBM) or as a lower grade glioma. In four GBM tumours, we characterised one probable endonuclease-independent L1 insertion, two L1-associated rearrangements and one likely Alu-Alu recombination event adjacent to an L1. These mutations included PCR validated intronic events in MeCP2 and EGFR. Despite sequencing L1 integration sites at up to 250× depth by RC-seq, we found no tumour-specific, endonuclease-dependent L1 insertions. Whole genome sequencing analysis of the tumours carrying the MeCP2 and EGFR L1 mutations also revealed no endonuclease-dependent L1 insertions. In a complementary in vitro assay, wild-type and endonuclease mutant L1 reporter constructs each mobilised very inefficiently in four cultured GBM cell lines.

Conclusions

These experiments altogether highlight the consistent absence of canonical L1 retrotransposition in GBM tumours and cultured cell lines, as well as atypical L1-associated sequence rearrangements following DNA damage in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s13100-016-0076-6) contains supplementary material, which is available to authorized users.

Evidence of cancer-promoting roles for AMPK and related kinases

The discovery that the 5'AMP-activated protein kinase (AMPK) serves to link the tumour suppressors LKB1 and the tuberous sclerosis complex and functions to slow macromolecular synthesis through attenuation of the mechanistic target of rapamycin complex 1 revealed a role for AMPK in tumour suppression. On the other hand, the well-recognized role of AMPK in maintaining ATP homeostasis, through suppression of anabolism and promotion of catabolism, as well as the role of AMPK in neutralizing reactive oxygen species, via maintenance of NADPH-dependent reductive capacity, point to tumour-protective roles in the context of metabolic stress, which is a key feature of many solid tumours. A growing number of studies thus suggest a duality of functions for AMPK that are either pro- or anti-cancer, depending upon context. Importantly, AMPK is composed of three subunits, and multiple isoforms exist for all three, allowing for different permutations to assemble and the potential for specific AMPK complexes to regulate distinct cellular processes. Moreover, certain subunits of the AMPK complex are frequently overexpressed in a spectrum of human cancer types, suggesting an outright oncogenic function for specific AMPK complexes. Adding complexity to this picture, the catalytic AMPK alpha subunits belong to a family of 14 kinases that can all be activated by LKB1 and studies are beginning to reveal a similar duality of roles in cancer for other members of the AMPK-related kinase family.

Investigation of ICAM-1 and β3 integrin gene variations in patients with brain tumors

BACKGROUND

Primary brain tumors constitute a small percent of all malignant cancers, but their etiology remains poorly understood. β3 integrin (ITGB3) has been recognized to play influential roles in angiogenesis, tumor growth and metastasis. Intercellular adhesion molecule-1 (ICAM-1) is a surface glycoprotein important for tumor invasion and angiogenesis. The aim of this study was to investigate whether specific genetic polymorphisms of ICAM-1 and ITGB3 could be associated with brain cancer development and progression in a Turkish population. Our study is the first to our knowledge to investigate the relationship between brain tumor risk and ICAM-1 and β3 integrin gene polymorphisms.

MATERIALS AND METHODS

The study covered 92 patients with primary brain tumors and 92 age-matched healthy control subjects. Evaluation of β3 integrin (Leu33Pro (rs5918)) and ICAM-1 (R241G (rs1799969) and K469E (rs5498)) gene polymorphisms was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

According to results of our research, the A allele of the ICAM-1 R241G gene polymorphism appeared to be a risk factor for primary brain tumors (p<0.001). Similarly, the frequency of the A mutant allele of ICAM-1 R241G was statistically significant in patients with brain tumors classified as glioma (p<0.001). When allele and genotype distributions of ICAM- 1 K469E, ICAM-1 R241G and β3 integrin Leu33Pro gene polymorphisms were evaluated with age, sex, and smoking, there were no statistically significant differences. Haplotype analysis revealed that the frequencies of GAC (rs1799969-rs5498-rs5918) and GAT (rs1799969-rs5498-rs5918) haplotypes were significantly lower in patients as compared with controls (p=0.001; p=0.036 respectively).

CONCLUSIONS

This study provides the first evidence that ICAM-1 R241G SNP significantly contributes to the risk of primary brain tumors in a Turkish population. In addition, our results suggest that ICAM-1 R241G in combination ICAM-1 K469E may have protective effects against the development of brain cancer.

Enhanced accumulation of curcumin and temozolomide loaded magnetic nanoparticles executes profound cytotoxic effect in glioblastoma spheroid model

Glioblastomas (GBMs) are highly lethal primary brain tumours. Treatment of these malignant gliomas remains ineffective as these are extremely resistant to chemotherapeutic applications. Furthermore, combination therapy for cancer treatment is becoming more popular because it generates synergistic anticancer effects, by reducing individual drug-related toxicity and associated side effects. Currently, magnetic nanoparticles (MNPs) based drug delivery system has attracted much more attention owing to its intrinsic magnetic properties and drug loading capacity. In the present study, MNPs based drug delivery approach for co-delivering of potent chemotherapeutic drugs such as Curcumin (herbal drug) and Temozolomide (DNA methylating agent) has been implemented. The dual drug loaded MNPs formulations were evaluated in two-dimensional (2-D) monolayer culture and three-dimensional (3-D) tumour spheroid culture of T-98G cells for understanding the therapeutic discrepancy. The dual drug loaded MNPs formulations demonstrated higher cytotoxic effect than single drug loaded MNPs formulations as compared to their corresponding native drugs in 2-D and 3-D culture. The combination index (CI) analysis revealed synergistic mode of action of dual drug loaded MNPs formulations, which was further confirmed by cell death induction assay mediated by acridine orange (AO)/propidium iodide (PI) staining, illustrating higher efficacy of the formulation towards GBM therapy.

Chapter seven--Cancer treatment with gene therapy and radiation therapy

Radiation therapy methods have evolved remarkably in recent years which have resulted in more effective local tumor control with negligible toxicity of surrounding normal tissues. However, local recurrence and distant metastasis often occur following radiation therapy mostly due to the development of radioresistance through the deregulation of the cell cycle, apoptosis, and inhibition of DNA damage repair mechanisms. Over the last decade, extensive progress in radiotherapy and gene therapy combinatorial approaches has been achieved to overcome resistance of tumor cells to radiation. In this review, we summarize the results from experimental cancer therapy studies on the combination of radiation therapy and gene therapy.

Complex DNA repair pathways as possible therapeutic targets to overcome temozolomide resistance in glioblastoma

Many conventional chemotherapeutic drugs exert their cytotoxic function by inducing DNA damage in the tumor cell. Therefore, a cell-inherent DNA repair pathway, which reverses the DNA-damaging effect of the cytotoxic drugs, can mediate therapeutic resistance to chemotherapy. The monofunctional DNA-alkylating agent temozolomide (TMZ) is a commonly used chemotherapeutic drug and the gold standard treatment for glioblastoma (GBM). Although the activity of DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) has been described as the main modulator to determine the sensitivity of GBM to TMZ, a subset of GBM does not respond despite MGMT inactivation, suggesting that another DNA repair mechanism may also modulate the tolerance to TMZ. Considerable interest has focused on MGMT, mismatch repair (MMR), and the base excision repair (BER) pathway in the mechanism of mediating TMZ resistance, but emerging roles for the DNA strand-break repair pathway have been demonstrated. In the first part of this review article, we briefly review the significant role of MGMT, MMR, and the BER pathway in the tolerance to TMZ; in the last part, we review the recent publications that demonstrate possible roles of DNA strand-break repair pathways, such as single-strand break repair and double-strand break repair, as well as the Fanconi anemia pathway in the repair process after alkylating agent-based therapy. It is possible that all of these repair pathways have a potential to modulate the sensitivity to TMZ and aid in overcoming the therapeutic resistance in the clinic.

Microwaves from Mobile Phones Inhibit 53BP1 Focus Formation in Human Stem Cells More Strongly Than in Differentiated Cells: Possible Mechanistic Link to Cancer Risk

BACKGROUND

It is widely accepted that DNA double-strand breaks (DSBs) and their misrepair in stem cells are critical events in the multistage origination of various leukemias and tumors, including gliomas.

OBJECTIVES

We studied whether microwaves from mobile telephones of the Global System for Mobile Communication (GSM) and the Universal Global Telecommunications System (UMTS) induce DSBs or affect DSB repair in stem cells.

METHODS

We analyzed tumor suppressor TP53 binding protein 1 (53BP1) foci that are typically formed at the sites of DSB location (referred to as DNA repair foci) by laser confocal microscopy.

RESULTS

Microwaves from mobile phones inhibited formation of 53BP1 foci in human primary fibroblasts and mesenchymal stem cells. These data parallel our previous findings for human lymphocytes. Importantly, the same GSM carrier frequency (915 MHz) and UMTS frequency band (1947.4 MHz) were effective for all cell types. Exposure at 905 MHz did not inhibit 53BP1 foci in differentiated cells, either fibroblasts or lymphocytes, whereas some effects were seen in stem cells at 905 MHz. Contrary to fibroblasts, stem cells did not adapt to chronic exposure during 2 weeks.

CONCLUSIONS

The strongest microwave effects were always observed in stem cells. This result may suggest both significant misbalance in DSB repair and severe stress response. Our findings that stem cells are most sensitive to microwave exposure and react to more frequencies than do differentiated cells may be important for cancer risk assessment and indicate that stem cells are the most relevant cellular model for validating safe mobile communication signals.

DNA repair and resistance of gliomas to chemotherapy and radiotherapy

The importance of DNA repair as a resistance mechanism in gliomas, the most aggressive form of brain tumor, is a clinically relevant topic. Recent studies show that not all cells are equally malignant in gliomas. Certain subpopulations are particularly prone to drive tumor progression and resist chemo- and radiotherapy. Those cells have been variably named cancer stem cells or cancer-initiating cells or tumor-propagating cells, owing to their possible (but still uncertain) origin from normal stem cells. Although DNA repair reduces the efficacy of chemotherapeutics and ionizing radiation toward bulk gliomas, its contribution to resistance of the rare glioma stem cell subpopulations is less clear. Mechanisms other than DNA repair (in particular low proliferation and activation of the DNA damage checkpoint response) are likely main players of resistance in glioma stem cells and their targeting might yield significant therapeutic gains.

Development of a three-dimensional in vitro model for longitudinal observation of cell behavior: monitoring by magnetic resonance imaging and optical imaging

Purpose

The aim of this study is the development of a three-dimensional multicellular spheroid cell culture model for the longitudinal comparative and large-scale screening of cancer cell proliferation with noninvasive molecular imaging techniques under controlled and quantifiable conditions.

Procedures

The human glioblastoma cell line Gli36ΔEGFR was genetically modified to constitutively express the fluorescence protein mCherry, and additionally labeled with iron oxide nanoparticles for high-field MRI detection. The proliferation of aggregates was longitudinally monitored with fluorescence imaging and correlated with aggregate size by light microscopy, while MRI measurements served localization in 3D space. Irradiation with γ-rays was used to detect proliferational response.

Results

Cell proliferation in the stationary three-dimensonal model can be observed over days with high accuracy. A linear relationship of fluorescence intensity with cell aggregate size was found, allowing absolute quantitation of cells in a wide range of cell amounts. Glioblastoma cells showed pronounced suppression of proliferation for several days following high-dose γ-irradiation.

Conclusions

Through the combination of two-dimensional optical imaging and 3D MRI, the position of individual cell aggregates and their corresponding light emission can be detected. This allows an exact quantification of cell proliferation, with a focus on very small cell amounts (below 100 cells) using high resolution noninvasive techniques as a well-controlled basis for further cell transplantation studies.

A different view on DNA amplifications indicates frequent, highly complex, and stable amplicons on 12q13-21 in glioma

To further understand the biological significance of amplifications for glioma development and recurrencies, we characterized amplicon frequency and size in low-grade glioma and amplicon stability in vivo in recurring glioblastoma. We developed a 12q13-21 amplicon-specific genomic microarray and a bioinformatics amplification prediction tool to analyze amplicon frequency, size, and maintenance in 40 glioma samples including 16 glioblastoma, 10 anaplastic astrocytoma, 7 astrocytoma WHO grade 2, and 7 pilocytic astrocytoma. Whereas previous studies reported two amplified subregions, we found a more complex situation with many amplified subregions. Analyzing 40 glioma, we found that all analyzed glioblastoma and the majority of pilocytic astrocytoma, grade 2 astrocytoma, and anaplastic astrocytoma showed at least one amplified subregion, indicating a much higher amplification frequency than previously suggested. Amplifications in low-grade glioma were smaller in size and displayed clearly different distribution patterns than amplifications in glioblastoma. One glioblastoma and its recurrencies revealed an amplified subregion of 5 Mb that was stable for 6 years. Expression analysis of the amplified region revealed 10 overexpressed genes (i.e., KUB3, CTDSP2, CDK4, OS-9, DCTN2, RAB3IP, FRS2, GAS41, MDM2, and RAP1B) that were consistently overexpressed in all cases that carried this amplification. Our data indicate that amplifications on 12q13-21 (a) are more frequent than previously thought and present in low-grade tumors and (b) are maintained as extended regions over long periods of time.