Biomedical subjects

W K Alfred Yung

Publications and source records attributed to W K Alfred Yung.

At least 19 recordsLinked to original sources

PubMed2006

PTEN enhances TNF-induced apoptosis through modulation of nuclear factor-kappaB signaling pathway in human glioma cells.

The PTEN tumor suppressor gene modulates cell growth and survival known to be regulated by the activation of the transcription factor NFkappaB, suggesting PTEN might affect the NFkappaB activation pathway. We found that PTEN inhibited NFkappaB activation induced by TNF. The suppression of NFkappaB activation correlated with sequential inhibition of the tumor necrosis factor-induced expression of NFkappaB-regulated anti-apoptotic (IAP1, IAP2, Bcl-2, Bcl-xL, cFLIP, Bfl-1/A1, and survivin) gene products. Downregulation of the antiapoptotic genes by PTEN increased TNF-induced apoptosis, as indicated by caspase activation, TUNEL, annexin staining, and esterase assay. We conclude that the ectopic expression of PTEN enhances TNF-induced apoptosis and downregulates the proliferation of glioma cells through the suppression of various molecules including NFkappaB, and various mediators of cellular survival and proliferation, and that this targets might be essential for its central role in the growth and survival of glioma cancer cells.

Apoptosis↗

PubMed2006

Phase I/II study of imatinib mesylate for recurrent malignant gliomas: North American Brain Tumor Consortium Study 99-08.

PURPOSE: Phase I: To determine the maximum tolerated doses, toxicities, and pharmacokinetics of imatinib mesylate (Gleevec) in patients with malignant gliomas taking enzyme-inducing antiepileptic drugs (EIAED) or not taking EIAED. Phase II: To determine the therapeutic efficacy of imatinib. EXPERIMENTAL DESIGN: Phase I component used an interpatient dose escalation scheme. End points of the phase II component were 6-month progression-free survival and response. RESULTS: Fifty patients enrolled in the phase I component (27 EIAED and 23 non-EIAED). The maximum tolerated dose for non-EIAED patients was 800 mg/d. Dose-limiting toxicities were neutropenia, rash, and elevated alanine aminotransferase. EIAED patients received up to 1,200 mg/d imatinib without developing dose-limiting toxicity. Plasma exposure of imatinib was reduced by approximately 68% in EIAED patients compared with non-EIAED patients. Fifty-five non-EIAED patients (34 glioblastoma multiforme and 21 anaplastic glioma) enrolled in the phase II component. Patients initially received 800 mg/d imatinib; 15 anaplastic glioma patients received 600 mg/d after hemorrhages were observed. There were 2 partial response and 6 stable disease among glioblastoma multiforme patients and 0 partial response and 5 stable disease among anaplastic glioma patients. Six-month progression-free survival was 3% for glioblastoma multiforme and 10% for anaplastic glioma patients. Five phase II patients developed intratumoral hemorrhages. CONCLUSIONS: Single-agent imatinib has minimal activity in malignant gliomas. CYP3A4 inducers, such as EIAEDs, substantially decreased plasma exposure of imatinib and should be avoided in patients receiving imatinib for chronic myelogenous leukemia and gastrointestinal stromal tumors. The evaluation of the activity of combination regimens incorporating imatinib is under way in phase II trials.

Adolescent↗

PubMed2006

Phase II Radiation Therapy Oncology Group trial of conventional radiation therapy followed by treatment with recombinant interferon-beta for supratentorial glioblastoma: results of RTOG 9710.

PURPOSE: The aim of this study was to determine whether recombinant human interferon beta-1a (rhIFN-beta), when given after radiation therapy, improves survival in glioblastoma. METHODS AND MATERIALS: After surgery, 109 patients with newly diagnosed supratentorial glioblastoma were enrolled and treated with radiation therapy (60 Gy). A total of 55 patients remained stable after radiation and were treated with rhIFN-beta (6 MU/day i.m., 3 times/week). Outcomes were compared with the Radiation Therapy Oncology Group glioma historical database. RESULTS: RhIFN-beta was well tolerated, with 1 Grade 4 toxicity and 8 other patients experiencing Grade 3 toxicity. Median survival time (MST) of the 55 rhIFN-beta-treated patients was 13.4 months. MST for the 34 rhIFN-beta-treated in RPA Classes III and IV was 16.9 vs. 12.4 months for historical controls (hazard ratio [HR] = 1.27, 95% confidence interval [CI] = 0.89-1.81). There was also a trend toward improved survival across all RPA Classes comparing the 55 rhIFN-beta treated patients and 1,658 historical controls (HR = 1.24, 95% CI = 0.94-1.63). The high rate of early failures (54/109) after radiation and before initiation of rhIFN-beta was likely caused by stricter interpretation of early radiographic changes in the current study. Matched-pair and intent-to-treat analyses performed to try to address this bias showed no difference in survival between study patients and controls. CONCLUSION: RhIFN-beta given after conventional radiation therapy was well tolerated, with a trend toward survival benefit in patients who remained stable after radiation therapy. These data suggest that rhIFN-beta warrants further evaluation in additional studies, possibly in combination with current temozolomide-based regimens.

Antineoplastic Agents↗

PubMed2006

Phase II trial of tipifarnib in patients with recurrent malignant glioma either receiving or not receiving enzyme-inducing antiepileptic drugs: a North American Brain Tumor Consortium Study.

PURPOSE: A phase II study was undertaken in patients with recurrent malignant glioma to determine the efficacy and safety of tipifarnib, a farnesyltransferase inhibitor, dosed at the respective maximum-tolerated dose (MTD) for patients receiving and not receiving enzyme-inducing antiepileptic drugs (EIAEDs). Because tipifarnib undergoes extensive hepatic metabolism, MTD is doubled in patients on EIAEDs. The population included 67 patients with glioblastoma multiforme (GBM) and an exploratory group of 22 patients with anaplastic glioma (AG). PATIENTS AND METHODS: Patients received tipifarnib (300 and 600 mg bid for 21 days every 4 weeks in non-EIAED and EIAED patients, respectively). All patients were assessable for efficacy and safety. RESULTS: Two AG patients (9.1%) and eight GBM patients (11.9%) had progression-free survival (PFS) more than 6 months. Among the latter eight GBM patients, six of 36 patients (16.7%; 95% CI, 7% to 32%) were not receiving EIAEDs and two of 31 patients (6.5%; 95% CI, 1% to 20%) were receiving EIAEDs. Four patients had partial responses in group A GBM and one patient had a partial response group B GBM. An exploratory comparison of PFS between GBM groups A and B was statistically significant (P = .01). Patients not receiving EIAEDs had a higher incidence and increased severity of hematologic events. However, the incidence and severity of rash (the previously determined dose-limiting toxicity in patients receiving EIAEDs) seemed similar in EIAED and non-EIAED subgroups. CONCLUSION: Tipifarnib (300 mg bid for 21 days every 4 weeks) shows modest evidence of activity in patients with recurrent GBM who are not receiving EIAEDs and is generally well tolerated in this population.

Adult↗

PubMed2006

Prognostic associations of activated mitogen-activated protein kinase and Akt pathways in glioblastoma.

PURPOSE: Activation of mitogen-activated protein kinase (MAPK) and members of the Akt pathway have been shown to promote cell proliferation, survival, and resistance to radiation. This study was conducted to determine whether any of these markers are associated with survival time and response to radiation in glioblastoma. EXPERIMENTAL DESIGN: The expression of phosphorylated (p-)Akt, mammalian target of rapamycin (p-mTOR), p-p70S6K, and p-MAPK were assessed by immunohistochemical staining in 268 cases of newly diagnosed glioblastoma. YKL-40, a prognostic marker previously examined in these tumors, was also included in the analysis. Expression data were tested for correlations with response to radiation therapy in 131 subtotally resected cases and overall survival (in all cases). Results were validated in an analysis of 60 patients enrolled in clinical trials at a second institution. RESULTS: Elevated p-MAPK expression was most strongly associated with poor response to radiotherapy, a finding corroborated in the validation cohort. For survival, higher expressions of p-mTOR, p-p70S6K, and p-MAPK were associated with worse outcome (all P < 0.03). YKL-40 expression was associated with the expressions of p-MAPK, p-mTOR, and p-p70S6K (all P < 0.02), with a trend toward association with p-Akt expression (P = 0.095). When known clinical variables were added to a multivariate analysis, only age, Karnofsky performance score, and p-MAPK expression emerged as independent prognostic factors. CONCLUSIONS: p-MAPK and activated members of the Akt pathway are markers of outcome in glioblastoma. Elevated expression of p-MAPK is associated with increased radiation resistance and represents an independent prognostic factor in these tumors.

Adipokines↗

PubMed2006

E2F1 and telomerase: alliance in the dark side.

Cancer arises from a stepwise accumulation of genetic changes. Among these changes, deregulation of the Rb/E2F1 pathway and constitutively active telomerase are pivotal milestones for the attainment of immortality and maintaining the neoplastic phenotype. We recently showed the Rb/E2F1 pathway to be a direct modulator of telomerase activity in normal and cancer cells, specifically in malignant gliomas. In addition, we reported that the correlation between the levels of expression of E2F1 and hTERT -the catalytic subunit of telomerase- in a subset of patients with glioblastoma multiforme confers clinical relevance to the role of E2F1 in triggering or maintaining hTERT expression. Here we review the evidence supporting the mechanistic linkage between E2F1 and telomerase activation. We also consider the clinical implications of this association in terms of prognostic significance and opportunities for the development of new and more rational therapeutic strategies.

Biomarkers, Tumor↗

PubMed2006

Randomized, double-blind, placebo-controlled trial of marimastat in glioblastoma multiforme patients following surgery and irradiation.

PURPOSE: Because raised matrix metalloprotease (MMP) levels are associated with glioma invasion and angiogenesis, we tested the efficacy of marimastat (MT) an orally active drug that can reduce MMP levels, in patients with gliomas. PATIENTS AND METHODS: A total of 162 patients with intracranial glioblastoma multiforme or gliosarcomas who had undergone surgery and radiotherapy participated in this multicenter, double-blind, placebo-controlled, parallel group study conducted at 20 institutions. Seventy-nine patients (57 male, 22 female, median age 58 years) were randomized to receive placebo (PB), and 83 patients (51 male, 32 female, median age 57 years) were randomized to receive MT, 10 mg orally twice daily, until tumor progression. RESULTS: This intention-to-treat efficacy analysis showed no statistically significant difference between MT and PB groups with respect to survival (P = 0.38, log rank test). The median survival time from protocol initiation was 37.9 weeks for the PB group and 42.9 weeks for the MT group, with a hazard ratio of 1.16 (95% CI 0.83 to 1.60). There were no statistically significant differences in quality of life between the PB and MT groups, as assessed by the FACT-BR questionnaire. Musculoskeletal toxicities led to dose modification or withdrawal in 20% of MT-treated and 1.2% of PB-treated patients. CONCLUSION: MT does not improve survival in patients with glioblastoma or gliosarcoma following surgery and radiotherapy. Therefore, single-agent MT appears unwarranted; however, MT in combination with cytotoxic chemotherapy may be warranted, as suggested by observations in our study and other studies.

Adult↗

PubMed2006

Phase II trial of temozolomide plus marimastat for recurrent anaplastic gliomas: a relationship among efficacy, joint toxicity and anticonvulsant status.

PURPOSE: Since anaplastic gliomas (AG) depend on matrix metalloproteinases for tumor cell invasion and angiogenesis, we undertook this phase II study to evaluate the matrix metalloproteinase inhibitor marimastat (MT), combined with the alkylator temozolomide (TMZ) in patients with recurrent AG, looking for improved outcomes. PATIENTS AND METHODS: Patients were treated every 28 days with TMZ at 150-200 mg/m2 once daily on days 1-5 and MT at 25 mg twice daily on days 8-28. Results were compared to our database of anaplastic glioma patients treated at recurrence. A subanalysis of the relationship between MT-induced joint-related toxicity and anticonvulsant status was carried out. RESULTS: Forty-nine patients were enrolled; all were assessable for toxicity, and 46 were included in the efficacy analysis. Joint and muscle complaints occurred in 32 patients (65%); 1 patient was removed from the study due to toxicity. The best protocol response was a complete response in 1 patient and a partial response in 2 patients (3/46=7%, 95% confidence interval (CI)=1, 18). Median time to progression was 24 weeks (95% CI=16, 56), and the progression-free survival (PFS) rate was 48% at 6 months (95% CI=35%, 65%), which surpassed the protocol objective of 40%. Sub-analysis showed a positive impact of joint-related toxicity due to MT on PFS whether or not patients were taking CYP450 enzyme-inducing anticonvulsants. CONCLUSIONS: Even though this regimen is more efficacious than our comparator of historical controls in recurrent AG, the regimen was roughly equivalent to single-agent TMZ and was associated with additional toxicity. The sub-analysis suggests pharmacokinetic and drug-drug interactions which may positively impact responses to MT.

Anticonvulsants↗

PubMed2006

Delta-24 increases the expression and activity of topoisomerase I and enhances the antiglioma effect of irinotecan.

PURPOSE: In this study, we sought to determine whether Delta-24 could sensitize glioma cells to the topoisomerase I inhibitor irinotecan (CPT-11) and to identify the mechanisms underlying this enhanced anticancer effect. EXPERIMENTAL DESIGN: We used human glioblastoma cell lines for the in vitro studies. The expression of topoisomerase I was determined in Western blot analyses, and topoisomerase I activity was determined by measuring the relaxation of a supercoiled DNA. The cell cycle distribution of cells was determined by flow cytometry analysis of the cellular DNA content. Cell viability was quantified by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Tissue culture infection dose assays were used to quantitate adenovirus replication. For the in vivo studies, athymic mice received intracranial/intratumoral injections of Delta-24 in combination with CPT-11, after which animal survival was monitored. RESULTS: Delta-24 infection caused human glioma cells to accumulate in the S phase and induced the expression and activity of topoisomerase I as shown by Western blot and in vitro enzymatic activity assays. Further, we showed that the sequential administration of Delta-24 and CPT-11 to human glioma cell cultures potentiated the CPT-11-mediated anticancer effect in vitro without modifying the replicative phenotype of the oncolytic adenovirus. In vivo experiments showed that the single intratumoral administration of Delta-24 to intracranially implanted human glioma xenografts followed by the systemic administration of CPT-11 resulted in significantly prolonged animal survival. CONCLUSIONS: The combination of Delta-24 treatment with CPT-11 showed an enhanced anticancer effect, which suggests that the interaction between adenoviral and human proteins can be exploited in rational anticancer therapies comprising replication-competent adenoviruses and conventional chemotherapeutic agents.

Adenoviridae↗

PubMed2006

Inhibition of Akt survival pathway by a small-molecule inhibitor in human glioblastoma.

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and Akt are important regulators of the phosphatidylinositol 3-kinase (PI3K) pathway and thus are important to the regulation of a wide spectrum of tumor-related biological processes. Akt regulates several critical cellular functions, including cell cycle progression; cell migration, invasion, and survival; and angiogenesis. Decreased expression of PTEN and overexpression of the Akt proto-oncogene, which is located downstream of PI3K, have been shown in a variety of cancers, including glioblastoma. Novel small-molecule inhibitors of receptors and signaling pathways, including inhibitors of the PI3K pathway, have shown antitumor activity, but inhibitors of Akt have not been examined. In this study, we tested our hypothesis that the pharmacologic inhibition of Akt has an antiproliferative effect on gliomas. We showed that two newly developed Akt inhibitors, KP-372-1 and KP-372-2 (herein called KP-1 and KP-2), effectively inhibited the PI3K/Akt signaling cascade. KP-1 and KP-2 blocked both the basal and epidermal growth factor-induced phosphorylation of Akt Ser473 at 125 and 250 nmol/L, which, in turn, reduced the activation of intracellular downstream targets of Akt, including GSK-3beta and p70s6k. Furthermore, the treatment of U87 and U251 glioma cells with 125 to 250 nmol/L KP-1 and KP2 for 48 hours inhibited cell growth by approximately 50%. This decrease in cell growth stemmed from the induction of apoptosis. Collectively, these results provide a strong rationale for the pharmacologic targeting of Akt for the treatment of gliomas.

Apoptosis Regulatory Proteins↗

PubMed2006

Sustained angiopoietin-2 expression disrupts vessel formation and inhibits glioma growth.

Systematic analyses of the expression of angiogenic regulators in cancer models should yield useful information for the development of novel therapies for malignant gliomas. In this study, we analyzed tumor growth, vascularization, and angiopoietin-2 (Ang2) expression during the development of U-87 MG xenografts. We found that tumoral angiogenesis in this model follows a multistage process characterized by avascular, prolific peripheral angiogenesis, and late vascular phases. On day 4, we observed an area of central necrosis, a peripheral ring of Ang2-positive glioma cells, and reactive Ang2-positive vascular structures in the tumor/brain interface. When the tumor had developed a vascular network, Ang2 was expressed only in peripheral vascular structures. Because Ang2 expression was downmodulated in the late stages of development, probably to maintain a stable tumoral vasculature, we next studied whether sustained Ang2 expression might impair vascular development and, ultimately, tumor growth. Ang2 prevented the formation of capillary-like structures by and impaired angiogenesis in a chorioallantoic membrane chicken model. Finally, we tested the effect of sustained Ang2 expression on U-87 MG xenograft development. Ang2 significantly prolonged the survival of intracranial U-87 MG tumor-bearing animals. Examination of Ang2-treated xenografts revealed areas of tumor necrosis and vascular damage. We therefore conclude that deregulated Ang2 expression during gliomagenesis hindered successful angiogenesis and that therapies that sustain Ang2 expression might be effective against malignant gliomas.

Angiopoietin-2↗

PubMed2005

Expression of transcription factor E2F1 and telomerase in glioblastomas: mechanistic linkage and prognostic significance.

BACKGROUND: Several tumor suppressor pathways have been identified as modulators of telomerase function. We examined the functional role of the retinoblastoma-E2F1 pathway in regulating telomerase activity in malignant gliomas. METHODS: Adenovirus vectors were used to transfer cDNAs into human glioblastoma and sarcoma cells. Telomerase activity was assessed with a telomere repeat amplification protocol. Promoter activity in cancer cells was assessed with promoter-luciferase reporter constructs. Promoter binding was assessed with the chromatin immunoprecipitation (ChIP) assay. We isolated astrocytes from E2F1 transgenic mice and normal mice for in vivo studies. We evaluated the expression of E2F1 and hTERT (the catalytic subunit of human telomerase) mRNAs by reverse transcriptase-polymerase chain reaction and proteins in human glioblastoma samples by immunoblot analysis. Associations between survival among 61 glioblastoma multiforme patients and expression of E2F1 and hTERT mRNA and protein were examined with Kaplan-Meier analysis, the log-rank test, and Cox proportional hazards regression models. All statistical tests were two-sided. RESULTS: Ectopic E2F1 expression increased hTERT promoter activity in cancer cells. We detected an interaction between E2F1 protein and the hTERT promoter. Transgenic E2F1 astrocytes contained functional telomerase protein. E2F1 mRNA expression and hTERT mRNA expression were statistically significantly correlated in human glioblastoma specimens (R = .8; P < .001). Longer median survival was statistically significantly associated with lower E2F1 mRNA expression in tumors (103.6 weeks) rather than with higher expression (46.1 weeks) (difference = 57.5 weeks; 95% confidence interval [CI] = 14.7 to 159.7; log-rank P = .002). E2F1 mRNA was the only factor that was statistically significantly associated with overall survival in a multivariable model (P = .04). Among 27 patients with glioblastoma multiforme samples, the expression of E2F1 protein was statistically significantly associated with survival (log-rank P < .001). CONCLUSIONS: E2F1 may participate in telomerase activity regulation in malignant glioma cells. Its expression appears to be strongly associated with the survival of patients with malignant brain tumors.

Animals↗

PubMed2005

Integrated array-comparative genomic hybridization and expression array profiles identify clinically relevant molecular subtypes of glioblastoma.

Glioblastoma, the most aggressive primary brain tumor in humans, exhibits a large degree of molecular heterogeneity. Understanding the molecular pathology of a tumor and its linkage to behavior is an important foundation for developing and evaluating approaches to clinical management. Here we integrate array-comparative genomic hybridization and array-based gene expression profiles to identify relationships between DNA copy number aberrations, gene expression alterations, and survival in 34 patients with glioblastoma. Unsupervised clustering on either profile resulted in similar groups of patients, and groups defined by either method were associated with survival. The high concordance between these separate molecular classifications suggested a strong association between alterations on the DNA and RNA levels. We therefore investigated relationships between DNA copy number and gene expression changes. Loss of chromosome 10, a predominant genetic change, was associated not only with changes in the expression of genes located on chromosome 10 but also with genome-wide differences in gene expression. We found that CHI3L1/YKL-40 was significantly associated with both chromosome 10 copy number loss and poorer survival. Immortalized human astrocytes stably transfected with CHI3L1/YKL-40 exhibited changes in gene expression similar to patterns observed in human tumors and conferred radioresistance and increased invasion in vitro. Taken together, the results indicate that integrating DNA and mRNA-based tumor profiles offers the potential for a clinically relevant classification more robust than either method alone and provides a basis for identifying genes important in glioma pathogenesis.

Adipokines↗

PubMed2005

The excitatory amino acid transporter-2 induces apoptosis and decreases glioma growth in vitro and in vivo.

Accumulating evidence suggests that glutamate plays a key role in the proliferation and invasion of glioblastoma tumors. Astrocytic tumors have been shown to release glutamate at high levels, which may stimulate tumor cell proliferation and motility via activation of glutamate receptors. Excess glutamate has also been found to facilitate tumor invasion by causing excitotoxic damage to normal brain thereby paving a pathway for tumor migration. Results from tissue microarray analyses showed decreased excitatory amino acid transporter-2 (EAAT-2) expression in high-grade glial tumors compared with low-grade astrocytomas and normal brain. EAAT-2 expression was inversely correlated with tumor grade, implicating its potential role in glial tumor progression, which was reflected by an undetectable level of EAAT-2 protein in glioma cell lines. In this study, we sought to investigate the effect of reconstituted EAAT-2 on glioma cell growth in vitro and in vivo by adenoviral-mediated gene transfer. Infection of glioma cells with Ad-EAAT-2 resulted in a physiologic level of functional EAAT-2, and a subsequent dose-dependent reduction in cell proliferation in all glioma cell lines tested compared with controls. Interestingly, results from analyses of Annexin V staining, detection of poly(ADP-ribose)polymerase cleavage and caspase-3 activation all indicated that Ad-EAAT-2 infection elicited apoptosis in glioma cells. Ex vivo experiments in nude mice showed a total suppression of tumor growth at sites that received Ad-EAAT-2-infected cells. Collectively, our results uncovered a new function of EAAT-2 in controlling glioma proliferation. Further studies will improve our knowledge of the role of glutamate in glioma growth and may provide useful prognostic information and alternative therapeutic targets for the treatment of glioma.

Adenoviridae↗

PubMed2005

PAX6 suppresses growth of human glioblastoma cells.

PURPOSE: Glioblastomas (GBMs) are the most common primary malignant brain tumors. Majority of GBMs has loss of heterozygosity of chromosome 10. The PAX6 encodes a transcription factor that involves in development of the brain, where its expression persists. We have reported that the expression of PAX6 was significantly reduced in GBMs and that a low level of PAX6 expression is a harbinger of an unfavorable prognosis for patients with malignant astrocytic glioma. Interestingly, PAX6 expression was increased in suppressed somatic cell hybrids derived from introducing a normal human chromosome 10 into U251 GBM cells. Thus it is interesting to determine if repression of PAX6 expression is involved in anti-tumor suppression function in GBM. EXPERIMENTAL DESIGN: We overexpressed PAX6 in a GBM cell line U251HF via either stable transfection or infection with recombinant adenovirus, and examined cell growth in vitro and in vivo. RESULT: Although we did not observe changes in the cell doubling time for PAX6-stable transfectants, significantly fewer numbers of PAX6-positive colonies grew in soft agar. Transient overexpression of PAX6 via adenovirus, however, suppressed cell growth by increasing the number of cells in G1 and by decreasing the number of cells in S-phase, and later on caused a dramatic level of cell death. Repeated subcutaneous and intracranial implantation experiments in nude mice using PAX6-stable transfectants provided solid evidence that PAX6 suppressed tumor growth in vivo and significantly extended mouse survival. CONCLUSION: Our data demonstrate that PAX6exerts a tumor suppressor function that limits the growth of GBM cells.

Animals↗

PubMed2005

Delta24-hyCD adenovirus suppresses glioma growth in vivo by combining oncolysis and chemosensitization.

Replication-competent adenoviruses could provide an efficient method for delivering therapeutic genes to tumors. The most promising strategies among adenovirus-based oncolytic systems are designed to exploit free E2F-1 activity in cancer cells, which in the absence of pRb activates transcription and regulates the expression of genes involved in differentiation, proliferation, and apoptosis. We previously developed Delta24, an E1A-mutant, conditionally replicative oncolytic adenovirus. Here, we examine the ability of a second-generation Delta24 (Delta24-hyCD) engineered to express a humanized form of the Saccharomyces cerevisiae cytosine deaminase gene (hyCD). Real-time quantitative PCR, Western blotting, thin-layer chromatography, and radioisotope quantitative enzymatic assays confirmed the production of a catalytically active hyCD enzyme in the setting of an oncolytic infection in vitro; other experiments assessing local production of 5-fluorouracil and a concomitant bystander effect showed improved cytotoxicity. The IC50 dose of 5-fluorocytosine (5-FC) required for a complete cytopathic effect by the Delta24-hyCD virus was fivefold lower than with Delta24 alone in U251MG and U87MG malignant glioma (MG) cell lines. Intratumoral treatment of mice bearing intracranial U87MG xenografts with Delta24-hyCD+5-FC significantly improved survival, confirming that Delta24-hyCD with 5-FC is a more efficient anticancer tool than Delta24 alone. Histopathologically, Delta24-hyCD replication was accompanied by progressively augmented oncolysis and drug-induced necrosis. These findings demonstrate that Delta24-hyCD with concomitant systemic 5-FC is a significant improvement over the earlier Delta24 oncolytic tumor-selective strategy for therapy of experimental gliomas.

Adenoviridae↗

PubMed2005

Nuclear PTEN-mediated growth suppression is independent of Akt down-regulation.

The tumor suppressor gene PTEN is a phosphoinositide phosphatase that is inactivated by deletion and/or mutation in diverse human tumors. Wild-type PTEN is expressed both in the cytoplasm and nucleus in normal cells, with a preferential nuclear localization in differentiated or resting cells. To elucidate the relationship between PTEN's subcellular localization and its biologic activities, we constructed different PTEN mutants that targeted PTEN protein into different subcellular compartments. Our data show that the subcellular localization patterns of a PTEN (deltaPDZB) mutant versus a G129R phosphatase mutant were indistinguishable from those of wild-type PTEN. In contrast, the Myr-PTEN mutant demonstrated an enhanced association with the cell membrane. We found that nuclear PTEN alone is capable of suppressing anchorage-independent growth and facilitating G1 arrest in U251MG cells without inhibiting Akt activity. Nuclear compartment-specific PTEN-induced growth suppression is dependent on possessing a functional lipid phosphatase domain. In addition, the down-regulation of p70S6K could be mediated, at least in part, through activation of AMP-activated protein kinase in an Akt-independent fashion. Introduction of a constitutively active mutant of Akt, Akt-DD, only partially rescues nuclear PTEN-mediated growth suppression. Our collective results provide the first direct evidence that PTEN can contribute to G1 growth arrest through an Akt-independent signaling pathway.

AMP-Activated Protein Kinase Kinases↗

PubMed2005

Targeting integrin-linked kinase inhibits Akt signaling pathways and decreases tumor progression of human glioblastoma.

The phosphatidylinositol 3-kinase pathway is an important regulator of a wide spectrum of tumor-related biological processes, including cell proliferation, survival, and motility, as well as neovascularization. Protein kinase B/Akt is activated in a complex manner through the phosphorylation of protein kinase B/Akt on Thr308 and Ser473. Although protein-dependent kinase-1 has been shown to phosphorylate Akt at Thr308, it is not clear whether there is a distinct kinase that exclusively phosphorylates Akt at Ser473. A possible candidate is integrin-linked kinase (ILK), which has been shown to phosphorylate Akt at Ser473 in vitro. ILK is a multidomain focal adhesion protein that is believed to be involved in signal transmission from integrin and growth factor receptors. Further, ILK is implicated in the regulation of anchorage-dependent cell growth/survival, cell cycle progression, invasion and migration, and tumor angiogenesis. In this study, we tested the hypothesis that ILK inhibition would inhibit these processes in gliomas in which it is constitutively expressed. We found that a newly developed small-molecule compound (QLT0267) effectively inhibited signaling through the ILK/Akt cascade in glioma cells by blocking the phosphorylation of Akt and downstream targets, including mammalian target of rapamycin and glycogen synthase kinase-3beta. Treatment of glioma cells with 12.5 micromol/L QLT0267 inhibited cell growth by 50% at 48 hours. An anchorage-dependent cell growth assay confirmed the cell growth-inhibitory effect of QLT0267. Further, the decrease in cell growth was associated with a dramatic accumulation of cells in the G2-M phase of the cell cycle. Although the cell growth-inhibitory effects of the ILK inhibitor were achieved only at a high concentration, the QLT0267 was able to reduce cellular invasion and angiogenesis at much lower concentrations as shown by in vitro invasion assays and vascular endothelial growth factor secretion. Thus, blocking the ILK/Akt pathway is a potential strategy for molecular targeted therapy for gliomas.

Blotting, Western↗