Parental U251 Cells Research Articles

Neuropilin-1 enhances temozolomide resistance in glioblastoma via the STAT1/p53/p21 axis.

Glioblastoma (GBM) is the most prevalent primary intracranial tumor. Temozolomide (TMZ) is the first-line chemotherapy for GBM. Nonetheless, the development of TMZ resistance has become a main cause of treatment failure in GBM patients. Evidence suggests that neuropilin-1 (NRP-1) silencing can attenuate GBM cell resistance to TMZ. This study aims to determine potential mechanisms by which NRP-1 affects TMZ resistance in GBM. The parental U251 and LN229 GBM cells were exposed to increasing concentrations of TMZ to construct TMZ-resistant GBM cells (U251/TMZ, LN229/TMZ). BALB/c nude mice were injected with U251/TMZ cells to establish the xenograft mouse model. Functional experiments were carried out to examine NRP-1 functions. Western blotting and real-time quantitative polymerase chain reaction were used to evaluate molecular protein and mRNA expression, respectively. Immunohistochemical staining showed NRP-1 and STAT1 expression in mouse tumors. The results showed that NRP-1 was highly expressed in TMZ-resistant cells. Moreover, knocking down NRP-1 attenuated the TMZ resistance of U251/TMZ cells, while upregulating NRP-1 enhanced TMZ resistance of the parental cells. NRP-1 silencing elevated GBM cell sensitivity to TMZ in tumor-bearing mice. Depleting NRP-1 reduced STAT1, p53, and p21 expression in U251/TMZ cells. STAT1 depletion offset NRP-1 silencing evoked attenuation of GBM cell resistance to TMZ. Collectively, our study reveals that NRP-1 enhances TMZ resistance in GBM possibly by regulating the STAT1/p53/p21 axis.

Downregulation of miR-125b promotes resistance of glioma cells to TRAIL through overexpression of Tafazzin which is a mitochondrial protein.

Overexpression of Tafazzin (TAZ), a mitochondrial protein, is often observed in many cancers. However, the association between aberrant expression of TAZ and drug resistance remains unclear. The aim of this study is to explore the role of TAZ in regulating the TRAIL resistance in glioma. We thus established the TRAIL resistance models on glioma by using the U87 and U251 cell lines (U87/R and U251/R). As the results, obvious overexpression of TAZ was observed in U87/R and U251/R cells. However, knockdown of TAZ increased the sensitivity of U87/R and U251/R cells to TRAIL-induced apoptosis. By contrast, expression of miR-125b was downregulated in U87/R and U251/R cells compared to the parental U87 and U251 cells. Furthermore, decrease of miR-125b was responsible for overexpression of TAZ, because the results of dual-luciferase reporter assays verified that TAZ was targeted by miR-125b. We then showed that enforced expression of miR-125b resensitized the U87/R and U251/R cells to TRAIL-dependent damage of mitochondria and activation of caspase-9 and -3. We demonstrated that overexpression of TAZ caused by downregulation of miR-125b promoted resistance of glioma cells to TRAIL. MiR-125b/TAZ axis may represent a potential strategy to reverse the TRAIL in glioma.

Preliminary Study on Relationship Between Temozolomide Chemotherapy-Resistant Cells and Stem Cells in Gliomas.

To study the relationship between temozolomide (TMZ) chemotherapy-resistant cells and stem cells in gliomas. The U251 glioma cell line was exposed to TMZ to generate TMZ-resistant colonies (U251/TMZ cell line) using the pulse drug method. The TMZ sensitivity of U251/TMZ and parental cells was examined using an MTT assay. The cell growth curve was drawn to show the growth of the two kinds of cells. Glioma stem cells (GSCs) were cultured and differentiated in vitro. Immunofluorescence assays were used to identify the expression of CD133, Nestin, and ABCG2 in U251/TM and U251 cells. Western blot analysis was used to analyse protein expression levels. The U251/TMZ cell line was successfully cultured in vitro. The IC50 value of the U251/TMZ cell line is 8.1 times that of the parental U251 cell line (t=-63.28, p=0.00). The doubling time of U251/TMZ cells was long compared with the parental cells. GSC tumour spheres were successfully cultured in vitro, and they differentiated in medium containing serum. The expression of CD133, Nestin, and ABCG2 in U251/TMZ cells was significantly higher than that in the parental U251 cells (t=43.35, p=0.00; t=12.31, p=0.00; t=11.49, p=0.00). Immunofluorescence staining of CD133, Nestin, and ABCG2 was significantly higher in U251/TMZ than in the parental U251 cells (t=43.35, p=0.00; t=12.31, p=0.00; t=11.49, p=0.00). Moreover, Western blot results showed that CD133, Nestin, and ABCG2 expression was significantly higher in U251/TMZ cells than that in the parental U251 cells (t=17.76, p=0.00; t=18.78, p=0.00; t=6.19, p=0.00). The U251/TMZ cell line has the biological characteristics of GSCs. The relationship between GSCs and chemotherapy-resistant cells has been preliminary proven to be partially overlapping, which can provide a new perspective when using appropriate cell subpopulations as targets for glioma.

The nuclear transcription factor nuclear factor-κB inhibitor in glioma cells reversed the resistance of glioma cell lines to temozolomide

Objective To reduce the expression of nuclear factor-κB (NF-κB) by inhibiting IκBα, and thereby reverse the temozolomide (TMZ) resistance of glioblastoma multiforme (GBM) cells, as well as to explore the relationship between NF-κB pathways and the expression of O6-methylguanine-DNA methytransferase (MGMT) in TMZ resistant cell lines. Methods We used U251 cells to build anti TMZ model TR-U251. Western blotting was used to detect the expression of NF-κB and MGMT in both cell lines, and we also observed changes in the level of resistance to TMZ by inhibiting the expression of NF-κB. Chi-square test of statistical methods was used for analysis. Results TR-U251 cell line model was successfully constructed. MGMT was highly expressed in TR-U251 cells, but was almost undetectable or very low in parental U251 cells. Likewise, phosphorylated p65 showed the same expression tendency. Compared with the parental U251 cell line, the expression of the sub-structure p65 of NF-κB in TR-U251 cells was 5.4 times higher that of the parental cells. When exposed to 80 μmol/L TMZ for 24 to 96 h, the survival rate of TR-U251 cells decreased slowly from (97.6±1.4)% to (78.3±3.6)%, while exposure to 50 μmol/L of bay11-7082, the survival rate decreased from (97.9±4.4)% to (64.2±2.3)%. However, the survival rate of cells exposed to 80 μmol/L TMZ combined with 50 μmol/L bay11-7082 decreased from (91.6±1.9)% to (27.8±5.7)% (P=0.004). The combination of TMZ and BAY11-7082 treatment significantly decreased the survival of cells as compared with TMZ alone or BAY11-7082 TMZ alone. Conclusion NF-κB activation has obvious relevance with the expression of MGMT degree in glioma. NF-κB and MGMT involved in the regulation of TMZ resistance of glioma cell lines. Inhibition of NF-κB decreased the activity of MGMT. Key words: Glioma; Nuclear factor-κ B; O6-methylguanine-DNA methytransferase; Temozolomide; Tolerance

Characterizing the molecular mechanisms of acquired temozolomide resistance in the U251 glioblastoma cell line by protein microarray.

Acquired chemoresistance refers to tumor cells gradually losing their sensitivity to anticancer drugs during the course of treatment, resulting in tumor progression or recurrence. This phenomenon, which has deleterious outcomes for the patient, has long been observed in patients with glioblastoma receiving temozolomide(TMZ)-based radiochemotherapy. Currently, the mechanisms for acquired TMZ chemoresistance are not fully understood. In the present study, a TMZ-resistant cell line U251R with a 4-fold50% inhibition concentration compared with its TMZ-sensitive parent cell line was isolated by incremental long-time TMZ treatment in the human glioblastoma cell lineU251. Fluorescence-activated cell sorting analysis indicated G2/Marrest and a lower proportion of cells in the Sphase, accompanied by a decreased apoptosis rate in the U251Rcell line compared with the parental U251cell line. In addition, a sphere-formation assay indicated an increased self-renewal capacity in U251R cells. Furthermore, a high-throughput protein microarray unveiled more than 200differentially expressed proteins as potential molecular targets accounting for acquired TMZ resistance. Subsequent bioinformatics analysis illustrated the molecular and signaling networks and revealed the central role of SRC. Immunoblotting and reverse-transcription quantitative polymerase chain reaction analysis further confirmed the expressional upregulation of SRC family kinases. Moreover, SRC knockdown led to partial reversal of TMZ resistance in the U251Rcell line and sensitization in the U373cell line. These data helped to develop a comprehensive understanding of survival strategies, particularly with respect to pro-stemness regulation, which could be potential targets for overcoming TMZ resistance.

Differential Characterization of Temozolomide-Resistant Human Glioma Cells.

Glioblastoma multiforme (GBM) is the most common type of primary and malignant tumor occurring in the adult central nervous system. Temozolomide (TMZ) has been considered to be one of the most effective chemotherapeutic agents to prolong the survival of patients with glioblastoma. Many glioma cells develop drug-resistance against TMZ that is mediated by increasing O-6-methylguanine-DNA methyltransferase (MGMT) levels. The expression of connexin 43 was increased in the resistant U251 subline compared with the parental U251 cells. The expression of epithelial–mesenchymal transition (EMT)-associated regulators, including vimentin, N-cadherin, and β-catenin, was reduced in the resistant U251 subline. In addition, the resistant U251 subline exhibited decreased cell migratory activity and monocyte adhesion ability compared to the parental U251 cells. Furthermore, the resistant U251 subline also expressed lower levels of vascular cell adhesion molecule (VCAM)-1 after treatment with recombinant tumor necrosis factor (TNF)-α. These findings suggest differential characteristics in the drug-resistant GBM from the parental glioma cells.

Acquired temozolomide resistance in human glioblastoma cell line U251 is caused by mismatch repair deficiency and can be overcome by lomustine.

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor in adults. While the alkylating agent temozolomide (TMZ) has prolonged overall survival, resistance evolution represents an important clinical problem. Therefore, we studied the effectiveness of radiotherapy and CCNU in an in vitro model of acquired TMZ resistance. We studied the MGMT-methylated GBM cell line U251 and its in vitro derived TMZ-resistant subline, U251/TMZ-R. Cytotoxicity of TMZ, CCNU, and radiation was tested. Both cell lines were analyzed for MGMT promotor status and expression of mismatch repair genes (MMR). The influence of MMR inhibition by cadmium chloride (CdCl2) on the effects of both drugs was evaluated. During the resistance evolution process in vitro, U251/TMZ-R developed MMR deficiency, but MGMT status did not change. U251/TMZ-R cells were more resistant to TMZ than parental U251 cells (cell viability: 92.0% in U251/TMZ-R/69.2% in U251; p=0.032) yet more sensitive to CCNU (56.4%/80.8%; p=0.023). The effectiveness of radiotherapy was not reduced in the TMZ-resistant cell line. Combination of CCNU and TMZ showed promising results for both cell lines and overcame resistance. CdCl2-induced MMR deficiency increased cytotoxicity of CCNU. Our results confirm MMR deficiency as a crucial process for resistance evolution to TMZ. MMR-deficient TMZ-resistant GBM cells were particularly sensitive to CCNU and to combined CCNU/TMZ. Effectiveness of radiotherapy was preserved in TMZ-resistant cells. Consequently, CCNU might be preferentially considered as a treatment option for recurrent MGMT-methylated GBM and may even be suitable for prevention of resistance evolution in primary treatment.

DNMT1 mediates chemosensitivity by reducing methylation of miRNA-20a promoter in glioma cells.

Although methyltransferase has been recognized as a major element that governs the epigenetic regulation of the genome during temozolomide (TMZ) chemotherapy in glioblastoma multiforme (GBM) patients, its regulatory effect on glioblastoma chemoresistance has not been well defined. This study investigated whether DNA methyltransferase (DNMT) expression was associated with TMZ sensitivity in glioma cells and elucidated the underlying mechanism. DNMT expression was analyzed by western blotting. miR-20a promoter methylation was evaluated by methylation-specific PCR. Cell viability and apoptosis were assessed using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) and TdT-mediated dUTP-biotin nick end labeling assays, respectively. The results showed that compared with parental U251 cells, DNMT1 expression was downregulated, miR-20a promoter methylation was attenuated and miR-20a levels were elevated in TMZ-resistant U251 cells. Methyltransferase inhibition by 5-aza-2′-deoxycytidine treatment reduced TMZ sensitivity in U251 cells. In U251/TM cells, DNMT1 expression was negatively correlated with miR-20a expression and positively correlated with TMZ sensitivity and leucine-rich repeats and immunoglobulin-like domains 1 expression; these effects were reversed by changes in miR-20a expression. DNMT1 overexpression induced an increase in U251/TM cell apoptosis that was inhibited by the miR-20a mimic, whereas DNMT1 silencing attenuated U251/TM cell apoptosis in a manner that was abrogated by miR-20a inhibitor treatment. Tumor growth of the U251/TM xenograft was inhibited by pcDNA-DNMT1 pretreatment and boosted by DNMT1-small hairpin RNA pretreatment. In summary, DNMT1 mediated chemosensitivity by reducing methylation of the microRNA-20a promoter in glioma cells.

NF-κB inhibitor reverses temozolomide resistance in human glioma TR/U251 cells.

Glioblastoma multiforme (GBM) demonstrates an unsatisfactory clinical prognosis due to the intrinsic or acquired resistance to temozolomide (TMZ) exhibited by the tumors. One possible cause of TMZ resistance in GBM is the overexpression of O6-methylguanine-DNA methyltransferase (MGMT), which can repair the TMZ-induced guanine damage in DNA. Additionally, excessive activated NF-κB is reported to be a component of the major inflammatory transcription pathway that is associated with TMZ resistance in GBM. However, the association between the NF-κB pathway and MGMT expression in GBM cells is unknown. Therefore, in the present study, the TMZ resistant (TR) U251 cell line (TR/U251) was successfully constructed to detect how the TR/U251 cell line and the parental U251 cell line each interact with TMZ in vitro. The TR/U251 cells were approximately five times more resistant to TMZ compared with the parental cells. Furthermore, it was found that the NF-κB inhibitor BAY 11-7082 suppressed the expression of MGMT in TR/U251 cells and enhanced TMZ-induced cytotoxicity and apoptosis, thereby indicating that the NF-κB pathway and MGMT interact to promote TMZ resistance. The inhibition of NF-κB may be a promising strategy to reverse drug resistance in TR glioma cells. The present results propose a potential mechanism for using the NF-κB inhibitor BAY 11-7082 as a potential therapy for the treatment of TR glioma. Although BAY 11-7082 is a well-known NF-κB inhibitor, the present study further investigated its underlying mechanisms through a series of new experiments.

Polymerase I and transcript release factor acts as an essential modulator of glioblastoma chemoresistance.

ObjectivesThis study is to investigate if polymerase I and transcript release factor (PTRF) acts as a modulator in glioblastoma (GBM) chemoresistance.MethodsMultidrug resistant (MDR) GBM cell line U251AR was established by exposing the U251 cell line to imatinib. The 2D-DIGE and MALDI-TOF/TOF-MS were performed on U251 and U251AR cell lines to screen MDR-related proteins. The expression of PTRF was determined by Western blot and quantitative RT-PCR analyses.ResultsWhen compared with the parental U251 cells, expression of 21 proteins was significantly altered in U251AR cells. Among the 21 differentially expressed proteins, the expression of PTRF was up-regulated by 2.14 folds in U251AR cells when compared with that in the parental U251 cells. Knockdown of PTRF in GBM cell lines significantly increased chemosensitivity of cells to various chemical drugs and decreased the expression levels of caveolin1, a major structural component of caveolae. Expression levels of PTRF and caveolin1 were significantly up-regulated in the relapsed GBM patients. The mRNA level of PTRF and caveolin1 showed a positive correlation in the same GBM specimens.ConclusionsOur results indicate that PTRF acts as a modulator in GBM chemoresistance.

Let-7b expression determines response to chemotherapy through the regulation of Cyclin D1 in Glioblastoma

BackgroundGlioblastoma is the most common type of primary brain tumors. Cisplatin is a commonly used chemotherapeutic agent for Glioblastoma patients. Despite a consistent rate of initial responses, cisplatin treatment often develops chemoresistance, leading to therapeutic failure. Cellular resistance to cisplatin is of great concern and understanding the molecular mechanisms is an utter need.MethodsGlioblastoma cell line U251 cells were exposed to increasing doses of cisplatin for 6 months to establish cisplatin-resistant cell line U251R. The differential miRNA expression profiles in U251 and U251R cell lines were identified by microarray analysis and confirmed by Q-PCR. MiRNA mimics were transfected into U251R cells, and cellular response to cisplatin-induced apoptosis and cell cycle distribution were examined by FACS analysis.ResultsU251R cells showed 3.1-fold increase in cisplatin resistance compared to its parental U251 cells. Microarray analysis identified Let-7b and other miRNAs significantly down-regulated in U251R cells compared to U251 cells. Transfection of Let-7b mimics greatly re-sensitized U251R cells to cisplatin, while transfection of other miRNAs has no effect or slightly effect. Cyclin D1 is predicted as a target of Let-7b through bioinformatics analysis. Over-expression of Let-7b mimics suppressed cyclin D1 protein expression and inhibited cyclin D1-3’-UTR luciferase activity. Knockdown of cyclin D1 expression significantly increased cisplatin-induced G1 arrest and apoptosis.ConclusionsCollectively, our results indicated that cisplatin treatment leads to Let-7b suppression, which in turn up-regulates cyclin D1 expression. Let-7b may serve as a marker of cisplatin resistance, and can enhance the therapeutic benefit of cisplatin in glioblastoma cells.

MiR-296-3p regulates cell growth and multi-drug resistance of human glioblastoma by targeting ether-à-go-go (EAG1)

MicroRNAs (miRNAs) – short non-coding RNA molecules – post-transcriptionally regulate gene expressions and play crucial roles in diverse biological processes such as development, differentiation, apoptosis and proliferation. In order to investigate the possible role of miRNAs in the development of multi-drug resistance (MDR) in human glioblastoma, we first detected (by Western blotting, real-time polymerase chain reaction [RT-PCR] and immunohistochemistry) the expression of miR-296-3p and ether-à-go-go (EAG1 or KCNH1) in U251 cells, U251/imatinib mesylate (U251AR cells) and clinical specimens. The results showed that miR-296-3p was down-regulated in U251AR cells, concurrent with the up-regulation of EAG1 protein, compared with the parental U251 cell line. In vitro drug sensitivity assay demonstrated that over-expression of miR-296-3p sensitised glioblastoma (GBM) cells to anticancer drugs, whereas down-expression using antisense oligonucleotides conferred MDR. Ectopic expression of miR-296-3p reduced EAG1 expression and suppressed cell proliferation drug resistance, and the luciferase activity of an EAG1 3′-untranslated region-based reporter construct in U251AR cells, whereas EAG1 over-expression rescued the suppressive effect of miR-296-3p in U251AR cells. We also found that EAG1 was widely over-expressed and inversely correlated with miR-296-3p in clinical specimens. Taken together, our findings suggest that miR-296-3p may play a role of MDR in glioblastoma at least in part by targeting EAG1.

MiR-221/222 is the regulator of Cx43 expression in human glioblastoma cells

The miR-221/222 cluster is significantly upregulated in malignant glioma cells and regulates the expression of multiple genes associated with glioma cell proliferation, invasion and apoptosis, which was shown in our previous studies. Cx43 has been identified as a tumor suppressor and major component for the establishment of gap junction intercellular communication (GJIC) in glial cells, which is frequently reduced or deleted in high-grade gliomas. According to bioinformatic analysis, connexin 43 (Cx43) may be one of the target genes of miR-221/222. The aim of the present study was to validate Cx43 as a target gene of miR-221/222 and to determine whether overexpression of miR-221/222 is one of the molecular mechanisms for the reduced expression of Cx43 in malignant gliomas. We transfected miR-221/222 antisense oligonucleotides (AS-miR-221/222) into U251 human glioblastoma cells using a lipofectamine method. Northern blot analysis was conducted to detect the expression of the miR-221/222 cluster. Luciferase reporter assays were exploited to confirm Cx43 as a target gene of miR-221/222. Cx43 expression was assessed by western blotting and immunofluorescence staining. Scrape loading and dye transfer (SLDT) assays were used for examination of GJIC. Proliferation and invasion of U251 cells were evaluated by MTT and transwell assays, respectively. Cell cycle kinetics and apoptosis were determined with flow cytometry. We found that expression of the miR-221/222 cluster was significantly reduced while Cx43 expression was upregulated in U251 cells transfected with AS-miR-221/222, and the GJIC deficiency in parental U251 cells was re-established. Moreover, the luciferase activity determined by the luciferase reporter assay was enhanced in AS-miR-221/222-treated cells, and cell proliferation and invasion were suppressed while apoptosis was induced. We conclude that miR-221/222 function as oncogenic microRNAs in human gliomas, at least in part, by targeting Cx43.

Chemoresistance to Temozolomide in Human Glioma Cell Line U251 is Associated with Increased Activity of O 6-methylguanine-DNA Methyltransferase and Can be Overcome by Metronomic Temozolomide Regimen

Temozolomide (TMZ) is a novel cytotoxic alkylating agent for chemotherapy of malignant gliomas. However, intrinsic or acquired resistance to TMZ often defines poor efficacy of chemotherapy in malignant gliomas. A growing number of studies indicate that expression of O(6)-methylguanine-DNA methyltransferase (MGMT) is one of the principal mechanisms responsible for this chemoresistance. In the present study, we evaluated the relationship between expression of MGMT and resistance to TMZ. We generated a TMZ-resistant cell line, U251/TR, by stepwise (8 months) exposure of parental U251 cells to TMZ. The resistance to TMZ was quantified using SRB assay. MGMT expression was evaluated at mRNA (RT-PCR) and protein (Western blot) levels. U251/TR cells showed increased (~ sevenfold) resistance to TMZ. The MGMT expression (both mRNA and protein) was significantly (P < 0.01) increased in U251/TR cells compared with parental U251 cells. Further, MGMT expression fluctuated during exposure of U251/TR cells to TMZ. The resistance of U251/TR cells to TMZ could be overcome by application of elevated doses of TMZ when MGMT expression was at the lowest level. In conclusion, our results demonstrate that the primary mechanism responsible for resistance of U251/TR cells to TMZ is associated with increased expression of MGMT. Resistance of malignant gliomas to TMZ can be overcome by synchronizing metronomic TMZ regimen with MGMT expression.

Abstract LB-115: EphA2/ephrinA1 system may regulate invadopodia formation of glioblastoma multiforme (GBM) cells

Abstract Background. Grade IV astrocytoma, or glioblastoma multiforme (GBM), is the most common, most malignant primary brain tumor in humans. With a median survival of approximately14 months, GBMs are characterized for their aggressive and highly invasive nature. We have previously explored the function of the EphA2 receptor and its ligand ephrinA1 in GBM. EphA2 was found to be over-expressed in various GBM cells, but not normal brain. EphrinA1, a naturally occurring GPI-linked protein originally found on epithelial cells, plays a tumor suppressive function by binding to and down-regulating cell surface expression of EphA2, leading to a subsequent decrease in cell migration and invasion. Invadopodia are electron-dense, actin-rich protrusions that bind to and proteolytically degrade extracellular matrix (ECM) proteins, potentially allowing for increased invasion. We have thus begun exploring the role of the EphA2/ephrinA1 complex in invadopodia formation and matrix degradation. Methods. Invadopodia formation and matrix degradation were assessed by an in situ gelatin zymography assay combined with fluorescence microscopy. Expression of the EphA2 receptor was examined by immunoblot using the following GBM cell lines: parental, vector control and ephrinA1-expressing U-251 cells, A-172, G48a, and Snb-19. Invadopodia-mediated degradation of the gelatin matrix was examined by fluorescence microscopy at various time points for each cell line. Src-transformed NIH3T3 (Src3T3) cells were used as a positive control. Results. The Snb-19 cells showed the most degradation of gelatin matrix among the GBM cell lines tested, closely mimicking control Src3T3 cells. This punctate pattern of gelatin degradation started to form as early as 2 hr after cell plating and continued until at least 72 hr. Other GBM cell lines degraded the matrix in the following order: Snb-19 ≫ A-127 &amp;gt; U-251 ephrinA1 &amp;gt; U-251 vector &amp;gt; U-251 parental &amp;gt; G-48a. Unexpectedly, immunoblot analysis showed low levels of EphA2 among the cells that degraded the most ECM. In preliminary experiments, diminishing levels of EphA2, either by knockdown or ligand activation, evoked more prominent gelatin-degrading invadopodia activity. Conclusions. GBM cells form invadopodia-like structures that degrade the ECM, with the Snb-19 cell line exhibiting the greatest degradation activity among the tested cell lines. Our preliminary results suggest a significant involvement of the EphA2/ephrinA1 system in invadopodia function based on an inverse correlation between matrix degradation and EphA2 expression. These findings have potentially important implications concerning the role of the EphA2/ephrinA1 complex in brain tumor migration and invasion. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-115. doi:10.1158/1538-7445.AM2011-LB-115

Dual E1A oncolytic adenovirus: targeting tumor heterogeneity with two independent cancer-specific promoter elements, DF3/MUC1 and hTERT

The therapeutic utility of oncolytic adenoviruses controlled by a single, tumor-specific regulatory element may be limited by the intra- and inter-tumoral heterogeneity that characterizes many cancers. To address this issue, we constructed an oncolytic adenovirus that uses two distinct tumor-specific promoters (DF3/Muc1 and hTERT) to drive separate E1A expression cassettes, in combination with deletion of the viral E1B region, which confers additional tumor selectivity and increased oncolytic activity. The resultant virus, Adeno-DF3-E1A/hTERT-E1A, induced higher levels of E1A oncoprotein, enhanced oncolysis, and an earlier and higher apoptotic index in infected tumor cells than following infection with Adeno-hTERT-E1A, which harbors a single hTERT promoter-driven E1A cassette. In isolated U251 human gliosarcoma cell holoclones (putative cancer stem cells), where DF3/Muc1 expression is substantially enriched and hTERT expression is decreased compared to the parental U251 cell population, E1A production and oncolysis were strongly decreased following infection with Adeno-hTERT-E1A but not Adeno-DF3-E1A/hTERT-E1A. The strong oncolytic activity of Adeno-DF3-E1A/hTERT-E1A translated into superior anti-tumor activity over Adeno-hTERT-E1A in vivo in a U251 solid tumor xenograft model, where hTERT levels were >90% suppressed and the DF3/Muc1 to hTERT expression ratio was substantially increased compared to cultured U251 cells. The enhanced anti-tumor activity of the dual-targeted Adeno-DF3-E1A/hTERT-E1A was achieved despite premature viral host cell death and decreased production of functional viral progeny, which limited tumor cell spread of the viral infection. These findings highlight the therapeutic benefit of targeting oncolytic viruses to heterogeneous tumor cell populations.

Cancer stem-like cells of glioblastoma characteristically express MMP-13 and display highly invasive activity

Glioblastoma is the most malignant type of primary brain tumor that has been shown to contain a small population of cancer stem cells. Recent studies have suggested that cancer stem cells cause tumor recurrence based on their resistance to radiotherapy and chemotherapy. Although the highly invasive nature of glioblastoma cells is also implicated in the failure of current therapies, it is not clear whether cancer stem cells are involved in invasiveness. In this study, we isolated tumor sphere-forming cells bearing cancer stem-like characteristics such as self-renewal, multipotency, drug-resistibility, and in vivo tumorigenicity, from the human glioblastoma cell line U251, under serum-free neural stem cell culture condition, and assessed their migratory and invasive ability. These cells showed enhanced migratory and invasive ability on both Matrigel and organotypic brain slices compared to parental U251 cells. The expression of matrix metalloproteinase (MMP)-13 was specifically expressed in tumor sphere-forming cells derived from U251 and primary human glioma cells. Knockdown of MMP-13 expression by shRNA suppressed the migration and invasion of these cells. The results suggest that the highly invasive potential of cancer stem cells depends on MMP-13 enzymatic activity, thus MMP-13 might be a potential therapeutic target for glioblastomas.

Abstract 3444: The role of p75ntr and TIMP-1 in U251 malignant glioma cells

Abstract The neurotrophin receptor p75NTR and trk receptors play an important role in the diverse functions of neurotrophins in the CNS. These include survival, differentiation, neurite outgrowth and development in the nervous system. More recently, an emerging role for the p75NTR has been described in tumor biology, both within the nervous system as well as in non-nervous system neoplasms. Investigative studies in vitro and in vivo have identified both tumor promoting and tumor inhibitory functions of p75NTR, related to specific tumor types. p75NTR has been implicated as a tumor and metastasis suppressor gene and in promoting apoptosis, particularly within the prostate. It has been suggested that p75NTR interactions in the microenvironment result in decreasing MMP2 and MMP9, with a concomitant increase in TIMP1 expression. These have a negative effect on tumor kinetics. However, these tumor promoting and tumor inhibitory functions of p75NTR have been reported in context of specific tumor types. Previously, we have shown that over-expressing TIMP1 in H2009, a lung adenocarcinoma cell line resulted in decreased expression of p75NTR in the clone HB1 compared to H2009. This clone was found to be more aggressive in both in vitro and in vivo studies. Extending these studies to glial neoplasms we sought to define a role of TIMP1in the modulation of p75NTR activities. To this end, we over-expressed TIMP1 in U251 glioma cell line. The resulting stable clones expressed decreased levels of p75 RNA and again behaved more aggressively in vitro with increased tumorigenicity and angiogenesis as evidenced by enhanced colony formation in soft agar as well as increased capillary network formation on Matrigel when serum-free conditioned media was used from the clone compared to parental U251 cell line. We have utilized p75 siRNA to knockdown the levels of p75NTR in U251 glioma cell line. Stable clones expressing reduced levels of p75 showed an increase in the number as well as the size of colonies in soft agar assay compared to the parental cell line suggesting increased tumorigenicity. Collectively our studies appear to define a tumor suppressor function for p75NTR. Additional studies are ongoing to further define the role of p75NTR and TIMP1. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3444.

Expression of matrix metalloproteinase-26 promotes human glioma U251 cell invasion in vitro and in vivo

MMP-26 is a novel member of the MMP family and is widely expressed in cancer cells of epithelial origin. Published research shows that MMP-26 contributes to tumor development and to the restoration of tissue injury. In this study, in order to identify the functions of MMP-26 that contribute to the biological phenotype and behavior of non-epithelial human glioma U251 cells, we established an MMP-26 overexpressing tumor cell model using gene transfection. We then used these cells to investigate the role of MMP-26 in tumor progression. Adherence and spreading assay, wound healing assay, Boyden chamber invasion assay, and in vivo tumorigenicity assay were performed to analyze the invasion ability of MMP-26 transfected U251 cells. Microvessel density analysis and tumor cell induced angiogenesis assay were employed to detect the function of MMP-26 in angiogenesis. Results showed that the spreading cell ratio of MMP-26 transfected cells was significantly higher than parental U251 cells. The relative migration distance of MMP-26 transfected cells on Matrigel was significantly higher than that of parental U251 cells. The Boyden chamber assay showed that MMP-26 could significantly enhance the ability of U251 cells to invade through Matrigel. MMP-26 could also enhance the local invasion ability of U251 cells in vivo. There was a significant increase of the microvessel density of tumor tissue derived from MMP-26 transfected U251 cells. The vessel numbe induced by MMP-26 transfected U251 cells in nude mice was also significantly higher than that induced by parental U251 cells. In conclusion, we successfully established an MMP-26 overexpressing cell model and confirmed that MMP-26 contributed to U251 cell invasion and migration in vitro. We also demonstrated that MMP-26 plays an important role in local invasion, and angiogenesis.

Increased spontaneous mutation frequency in human cells expressing the phage PBS2-encoded inhibitor of uracil-DNA glycosylase

The Ugi protein inhibitor of uracil-DNA glycosylase encoded by bacteriophage PBS2 inactivates human uracil-DNA glycosylases (UDG) by forming a tight enzyme:inhibitor complex. To create human cells that are impaired for UDG activity, the human glioma U251 cell line was engineered to produce active Ugi protein. In vitro assays of crude cell extracts from several Ugi-expressing clonal lines showed UDG inactivation under standard assay conditions as compared to control cells, and four of these UDG defective cell lines were characterized for their ability to conduct in vivo uracil-DNA repair. Whereas transfected plasmid DNA containing either a U:G mispair or U:A base pairs was efficiently repaired in the control lines, uracil-DNA repair was not evident in the lines producing Ugi. Experiments using a shuttle vector to detect mutations in a target gene showed that Ugi-expressing cells exhibited a 3-fold higher overall spontaneous mutation frequency compared to control cells, due to increased C:G to T:A base pair substitutions. The growth rate and cell cycle distribution of Ugi-expressing cells did not differ appreciably from their parental cell counterpart. Further in vitro examination revealed that a thymine DNA glycosylase (TDG) previously shown to mediate Ugi-insensitive excision of uracil bases from DNA was not detected in the parental U251 cells. However, a Ugi-insensitive UDG activity of unknown origin that recognizes U:G mispairs and to a lesser extent U:A base pairs in duplex DNA, but which was inactive toward uracil residues in single-stranded DNA, was detected under assay conditions previously shown to be efficient for detecting TDG.