Publications by authors named "Dimpy Koul"

43 Publications

The promise of DNA damage response inhibitors for the treatment of glioblastoma.

Neurooncol Adv 2021 Jan-Dec;3(1):vdab015. Epub 2021 Feb 4.

Department of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

Glioblastoma (GBM), the most aggressive primary brain tumor, has a dismal prognosis. Despite our growing knowledge of genomic and epigenomic alterations in GBM, standard therapies and outcomes have not changed significantly in the past two decades. There is therefore an urgent unmet need to develop novel therapies for GBM. The inter- and intratumoral heterogeneity of GBM, inadequate drug concentrations in the tumor owing to the blood-brain barrier, redundant signaling pathways contributing to resistance to conventional therapies, and an immunosuppressive tumor microenvironment, have all hindered the development of novel therapies for GBM. Given the high frequency of DNA damage pathway alterations in GBM, researchers have focused their efforts on pharmacologically targeting key enzymes, including poly(ADP-ribose) polymerase (PARP), DNA-dependent protein kinase, ataxia telangiectasia-mutated, and ataxia telangiectasia and Rad3-related. The mainstays of GBM treatment, ionizing radiation and alkylating chemotherapy, generate DNA damage that is repaired through the upregulation and activation of DNA damage response (DDR) enzymes. Therefore, the use of PARP and other DDR inhibitors to render GBM cells more vulnerable to conventional treatments is an area of intense investigation. In this review, we highlight the growing body of data behind DDR inhibitors in GBM, with a focus on putative predictive biomarkers of response. We also discuss the challenges involved in the successful development of DDR inhibitors for GBM, including the intracranial location and predicted overlapping toxicities of DDR agents with current standards of care, and propose promising strategies to overcome these hurdles.
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http://dx.doi.org/10.1093/noajnl/vdab015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7954093PMC
February 2021

PARP mediated PARylation of MGMT is critical to promote repair of temozolomide-induced O6-methylguanine DNA damage in glioblastoma.

Neuro Oncol 2021 Jan 12. Epub 2021 Jan 12.

Department of Neuro-Oncology, Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

Background: Temozolomide (TMZ) resistance in Glioblastoma (GBM) is mediated by the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). MGMT promoter methylation (occurs in about 40% patients) is associated with loss of MGMT expression (MGMT-) that compromises DNA repair, leading to a favorable response to TMZ therapy. The 60% of patients with unmethylated MGMT (MGMT+) GBM experience resistance to TMZ; in these patients, understanding the mechanism of MGMT mediated repair and modulating MGMT activity may lead to enhanced TMZ activity. Here, we report a novel mode of regulation of MGMT protein activity by poly-ADP-ribose polymerase (PARP).

Methods: MGMT-PARP interaction was detected by co-immunoprecipitation (IP). PARylation of MGMT and PARP was detected by co-immunoprecipitation with anti-PAR antibody. O 6-methylguanine (O 6-MetG) adducts were quantified by immunofluorescence assay. In vivo studies were conducted in mice to determine the effectiveness of PARP inhibition in sensitizing GBM to TMZ.

Results: We demonstrated that PARP physically binds with MGMT and PARylates MGMT in response to TMZ treatment. In addition, PARylation of MGMT by PARP is required for MGMT binding to chromatin to enhance the removal of O 6-MetG adducts from DNA after TMZ treatment. PARP inhibitors reduced PARP-MGMT binding and MGMT PARylation, silencing MGMT activity to repair O 6-MetG. PARP inhibition restored TMZ sensitivity in vivo in MGMT expressing GBM.

Conclusion: This study demonstrated that PARylation of MGMT by PARP is critical for repairing TMZ-induced O6-MetG, and inhibition of PARylation by PARP inhibitor reduces MGMT function rendering sensitization to TMZ, providing a rationale for combining PARP inhibitors to sensitize TMZ in MGMT unmethylated GBM.
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http://dx.doi.org/10.1093/neuonc/noab003DOI Listing
January 2021

Integrated analysis of telomerase enzymatic activity unravels an association with cancer stemness and proliferation.

Nat Commun 2021 01 8;12(1):139. Epub 2021 Jan 8.

Greehey Children's Cancer Research Institute, UT Health San Antonio, San Antonio, TX, USA.

Active telomerase is essential for stem cells and most cancers to maintain telomeres. The enzymatic activity of telomerase is related but not equivalent to the expression of TERT, the catalytic subunit of the complex. Here we show that telomerase enzymatic activity can be robustly estimated from the expression of a 13-gene signature. We demonstrate the validity of the expression-based approach, named EXTEND, using cell lines, cancer samples, and non-neoplastic samples. When applied to over 9,000 tumors and single cells, we find a strong correlation between telomerase activity and cancer stemness. This correlation is largely driven by a small population of proliferating cancer cells that exhibits both high telomerase activity and cancer stemness. This study establishes a computational framework for quantifying telomerase enzymatic activity and provides new insights into the relationships among telomerase, cancer proliferation, and stemness.
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http://dx.doi.org/10.1038/s41467-020-20474-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7794223PMC
January 2021

Amplification Induces Increased DNA Damage Response and Renders Selective Sensitivity to Talazoparib (PARP Inhibitor) in Glioblastoma.

Clin Cancer Res 2020 03 18;26(6):1395-1407. Epub 2019 Dec 18.

Department of Neuro-Oncology, Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas.

Purpose: Exploration of novel strategies to extend the benefit of PARP inhibitors beyond -mutant cancers is of great interest in personalized medicine. Here, we identified amplification as a potential biomarker to predict sensitivity to PARP inhibition, providing selection for the glioblastoma (GBM) patient population who will benefit from PARP inhibition therapy.

Experimental Design: Selective sensitivity to the PARP inhibitor talazoparib was screened and validated in two sets [test set ( = 14) and validation set ( = 13)] of well-characterized patient-derived glioma sphere-forming cells (GSC). FISH was used to detect copy number. DNA damage response following talazoparib treatment was evaluated by γH2AX and 53BP1 staining and neutral comet assay. PARP-DNA trapping was analyzed by subcellular fractionation. The selective monotherapy of talazoparib was confirmed using glioma models.

Results: -amplified GSCs showed remarkable sensitivity to talazoparib treatment. amplification was associated with increased reactive oxygen species (ROS) and subsequent increased basal expression of DNA-repair pathways to counterelevated oxidative stress, and thus rendered vulnerability to PARP inhibition. Following talazoparib treatment, -amplified GSCs showed enhanced DNA damage and increased PARP-DNA trapping, which augmented the cytotoxicity. amplification-associated selective sensitivity was further supported by the experimental results showing that talazoparib significantly suppressed tumor growth in -amplified subcutaneous models but not in nonamplified models.

Conclusions: -amplified cells are highly sensitive to talazoparib. Our data provide insight into the potential of using amplification as a selection biomarker for the development of personalized therapy.
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http://dx.doi.org/10.1158/1078-0432.CCR-19-2549DOI Listing
March 2020

BRCA1 identified as a modulator of temozolomide resistance in P53 wild-type GBM using a high-throughput shRNA-based synthetic lethality screening.

Am J Cancer Res 2019 1;9(11):2428-2441. Epub 2019 Nov 1.

Department of Neuro-Oncology, Brain Tumor Center, The University of Texas MD Anderson Cancer Center Houston, Texas, USA.

Glioblastoma multiforme (GBM), the most common type of primary brain tumor, is universally fatal, with a median survival duration ranging from 12-15 months despite maximum treatment efforts. Temozolomide (TMZ) is the current standard of care for GBM patients; however patients usually develop resistance to TMZ and limits its benefit. The identification of novel synergistic targets in GBM will lead to the development of new targeted drugs, which could be combined with broad-spectrum cytotoxic agents. In this study, we used a high-throughput synthetic lethality screen with a pooled short hairpin DNA repair library, in combination with TMZ, to identify targets that will enhance TMZ-induced antitumor effects. Using an unbiased bioinformatical analysis, we identified BRCA1 as a potential promising candidate gene that induced synthetic lethality with TMZ in glioma sphere-forming cells (GSCs). BRCA1 knockdown resulted in antitumor activity with TMZ in P53 wild-type GSCs but not in P53 mutant GSCs. TMZ treatment induced a DNA damage repair response; the activation of BRCA1 DNA repair pathway targets and knockdown of BRCA1, together with TMZ, led to increased DNA damage and cell death in P53 wild-type GSCs. Our study identified BRCA1 as a potential target that sensitizes TMZ-induced cell death in P53 wild-type GBM, suggesting that the combined inhibition of BRCA1 and TMZ treatment will be a successful targeted therapy for GBM patients.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6895442PMC
November 2019

Wild-type defined gamma-secretase inhibitor sensitivity and synergistic activity with doxorubicin in GSCs.

Am J Cancer Res 2019 1;9(8):1734-1745. Epub 2019 Aug 1.

Department of Neuro-Oncology, Brain Tumor Center, The University of Texas MD Anderson Cancer Center Houston, TX, USA.

Glioblastoma (GBM) is the most common and lethal primary intracranial tumor. Aggressive surgical resection plus radiotherapy and temozolomide have prolonged patients' median survival to only 14.6 months. Therefore, there is a critical need to develop novel therapeutic strategies for GBM. In this study, we evaluated the effect of NOTCH signaling intervention by gamma-secretase inhibitors (GSIs) on glioma sphere-forming cells (GSCs). GSI sensitivity exhibited remarkable selectivity among wild-type (wt-p53) GSCs. GSIs significantly impaired the sphere formation of GSCs harboring wt-p53. We also identified a concurrence between GSI sensitivity, NOTCH1 expression, and wt-p53 activity in GSCs. Through a series of gene editing and drug treatment experiments, we found that wt-p53 did not modulate NOTCH1 pathway, whereas NOTCH1 signaling positively regulated wt-p53 expression and activity in GSCs. Finally, GSIs (targeting NOTCH signaling) synergized with doxorubicin (activating wt-p53) to inhibit proliferation and induce apoptosis in wt-p53 GSCs. Taken together, we identified wt-p53 as a potential marker for GSI sensitivity in GSCs. Combining GSI with doxorubicin synergistically inhibited the proliferation and survival of GSCs harboring wt-p53.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6726980PMC
August 2019

Tie2-FGFR1 Interaction Induces Adaptive PI3K Inhibitor Resistance by Upregulating Aurora A/PLK1/CDK1 Signaling in Glioblastoma.

Cancer Res 2019 10 15;79(19):5088-5101. Epub 2019 Aug 15.

Brain Tumor Center, Departments of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.

PI3K-targeting therapy represents one of the most sought-after therapies for glioblastoma (GBM). Several small-molecule inhibitors have been evaluated in clinical trials, however, the emergence of resistance limits treatment potential. Here, we generated a patient-derived glioma sphere-forming cell (GSC) xenograft model resistant to the PI3K-specific inhibitor BKM-120. Integrated RNA sequencing and high-throughput drug screening revealed that the Aurora A kinase (Aurora A)/Polo-like kinase 1 (PLK1)/cyclin-dependent kinase 1 (CDK1) signaling pathway was the main driver of PI3K inhibitor resistance in the resistant xenografts. Aurora kinase was upregulated and pCDK1 was downregulated in resistant tumors from both xenografts and tumor tissues from patients treated with the PI3K inhibitor. Mechanistically, the tyrosine kinase receptor Tie2 physically interacted with FGFR1, promoting STAT3 phosphorylation and binding to the promoter, which increased Aurora A expression in resistant GSCs. Concurrent inhibition of Aurora A and PI3K signaling overcame PI3K inhibitor-induced resistance. This study offers a proof of concept to target PI3K and the collateral-activated pathway to improve GBM therapy. SIGNIFICANCE: These findings provide novel insights into the mechanisms of PI3K inhibitor resistance in glioblastoma.
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http://dx.doi.org/10.1158/0008-5472.CAN-19-0325DOI Listing
October 2019

Buparlisib in Patients With Recurrent Glioblastoma Harboring Phosphatidylinositol 3-Kinase Pathway Activation: An Open-Label, Multicenter, Multi-Arm, Phase II Trial.

J Clin Oncol 2019 03 4;37(9):741-750. Epub 2019 Feb 4.

1 Dana-Farber Cancer Institute, Boston, MA.

Purpose: Phosphatidylinositol 3-kinase (PI3K) signaling is highly active in glioblastomas. We assessed pharmacokinetics, pharmacodynamics, and efficacy of the pan-PI3K inhibitor buparlisib in patients with recurrent glioblastoma with PI3K pathway activation.

Methods: This study was a multicenter, open-label, multi-arm, phase II trial in patients with PI3K pathway-activated glioblastoma at first or second recurrence. In cohort 1, patients scheduled for re-operation after progression received buparlisib for 7 to 13 days before surgery to evaluate brain penetration and modulation of the PI3K pathway in resected tumor tissue. In cohort 2, patients not eligible for re-operation received buparlisib until progression or unacceptable toxicity. Once daily oral buparlisib 100 mg was administered on a continuous 28-day schedule. Primary end points were PI3K pathway inhibition in tumor tissue and buparlisib pharmacokinetics in cohort 1 and 6-month progression-free survival (PFS6) in cohort 2.

Results: Sixty-five patients were treated (cohort 1, n = 15; cohort 2, n = 50). In cohort 1, reduction of phosphorylated AKT immunohistochemistry score was achieved in six (42.8%) of 14 patients, but effects on phosphoribosomal protein S6 and proliferation were not significant. Tumor-to-plasma drug level was 1.0. In cohort 2, four (8%) of 50 patients reached 6-month PFS6, and the median PFS was 1.7 months (95% CI, 1.4 to 1.8 months). The most common grade 3 or greater adverse events related to treatment were lipase elevation (n = 7 [10.8%]), fatigue (n = 4 [6.2%]), hyperglycemia (n = 3 [4.6%]), and elevated ALT (n = 3 [4.6%]).

Conclusion: Buparlisib had minimal single-agent efficacy in patients with PI3K-activated recurrent glioblastoma. Although buparlisib achieved significant brain penetration, the lack of clinical efficacy was explained by incomplete blockade of the PI3K pathway in tumor tissue. Integrative results suggest that additional study of PI3K inhibitors that achieve more-complete pathway inhibition may still be warranted.
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http://dx.doi.org/10.1200/JCO.18.01207DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6553812PMC
March 2019

PAF promotes stemness and radioresistance of glioma stem cells.

Proc Natl Acad Sci U S A 2017 10 9;114(43):E9086-E9095. Epub 2017 Oct 9.

Department of Cancer Biology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030;

An integrated genomic and functional analysis to elucidate DNA damage signaling factors promoting self-renewal of glioma stem cells (GSCs) identified proliferating cell nuclear antigen (PCNA)-associated factor () up-regulation in glioblastoma. PAF is preferentially overexpressed in GSCs. Its depletion impairs maintenance of self-renewal without promoting differentiation and reduces tumor-initiating cell frequency. Combined transcriptomic and metabolomic analyses revealed that PAF supports GSC maintenance, in part, by influencing DNA replication and pyrimidine metabolism pathways. PAF interacts with PCNA and regulates PCNA-associated DNA translesion synthesis (TLS); consequently, PAF depletion in combination with radiation generated fewer tumorspheres compared with radiation alone. Correspondingly, pharmacological impairment of DNA replication and TLS phenocopied the effect of PAF depletion in compromising GSC self-renewal and radioresistance, providing preclinical proof of principle that combined TLS inhibition and radiation therapy may be a viable therapeutic option in the treatment of glioblastoma multiforme (GBM).
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http://dx.doi.org/10.1073/pnas.1708122114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5664518PMC
October 2017

Activation of WEE1 confers resistance to PI3K inhibition in glioblastoma.

Neuro Oncol 2018 01;20(1):78-91

Brain Tumor Center, Departments of Neuro-Oncology.

Background: Oncogenic activation of phosphatidylinositol-3 kinase (PI3K) signaling plays a pivotal role in the development of glioblastoma (GBM). However, pharmacological inhibition of PI3K has so far not been therapeutically successful due to adaptive resistance through a rapid rewiring of cancer cell signaling. Here we identified that WEE1 is activated after transient exposure to PI3K inhibition and confers resistance to PI3K inhibition in GBM.

Methods: Patient-derived glioma-initiating cells and established GBM cells were treated with PI3K inhibitor or WEE1 inhibitor alone or in combination, and cell proliferation was evaluated by CellTiter-Blue assay. Cell apoptosis was analyzed by TUNEL, annexin V staining, and blotting of cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase. Both subcutaneous xenograft and orthotropic xenograft studies were conducted to evaluate the effects of the combination on tumorigenesis; the tumor growth was monitored by bioluminescence imaging, and tumor tissue was analyzed by immunohistochemistry to validate signaling changes.

Results: PI3K inhibition activates WEE1 kinase, which in turn phosphorylates cell division control protein 2 homolog (Cdc2) at Tyr15 and inhibits Cdc2 activity, leading to G2/M arrest in a p53-independent manner. WEE1 inhibition abrogated the G2/M arrest and propelled cells to prematurely enter into mitosis and consequent cell death through mitotic catastrophe and apoptosis. Additionally, combination treatment significantly suppressed tumor growth in a subcutaneous model but not in an intracranial model due to limited blood-brain barrier penetration.

Conclusions: Our findings highlight WEE1 as an adaptive resistant gene activated after PI3K inhibition, and inhibition of WEE1 potentiated the effectiveness of PI3K targeted inhibition, suggesting that a combinational inhibition of WEE1 and PI3K might allow successful targeted therapy in GBM.
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http://dx.doi.org/10.1093/neuonc/nox128DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5761544PMC
January 2018

APOBEC3G acts as a therapeutic target in mesenchymal gliomas by sensitizing cells to radiation-induced cell death.

Oncotarget 2017 Aug 21;8(33):54285-54296. Epub 2017 Apr 21.

Brain Tumor Center, Departments of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

Genomic, transcriptional, and proteomic analyses of brain tumors reveal that subtypes differ in their pathway activity, progression, and response to therapy. We performed an expression profiling of Glioma Initiating Cells (GICs) and comparative analysis between different groups of GICs indicates major variations in gene expression. Hierarchical clustering analysis revealed groups of GICs reflecting their heterogeneity, and among some of the genes as major regulators of mesenchymal phenotype, we identified ABOBEC3G as one of the most discriminating genes in mesenchymal group. ABOBEC3G revealed a strong correlation with overall survival in TCGA GBM patient cohorts. APOBEC3G regulates cell invasion and silencing of this gene in GICs inhibits cell invasion and also glioma sphere initiation. APOBEC3G controls invasion through TGFβ/Smad2 pathway by regulating Smad2 target genes Thrombospondin 1, matrix metallopeptidase 2 and TIMP metallopeptidase inhibitor 1. We also show that targeting APOBEC3G can sensitize cancer cells to radiation induced cell death by attenuating activation of the DNA repair pathway. This response is mainly shown by decreased pChk2 expression in knockdown APOBEC3G cells. Taken together, we show that APOBEC3G gene is a mesenchymal enriched gene that controls invasion and knockdown of APOBEC3G sensitizes cells to radiation induced cell death, suggesting that APOBEC3G can be considered for use in stratifying patients with GBM for prognostic considerations.
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http://dx.doi.org/10.18632/oncotarget.17348DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5589580PMC
August 2017

Preclinical therapeutic efficacy of a novel blood-brain barrier-penetrant dual PI3K/mTOR inhibitor with preferential response in PI3K/PTEN mutant glioma.

Oncotarget 2017 Mar;8(13):21741-21753

Brain Tumor Center, Department of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

Glioblastoma (GBM) is an ideal candidate disease for signal transduction targeted therapy because the majority of these tumors harbor genetic alterations that result in aberrant activation of growth factor signaling pathways. Loss of heterozygosity of chromosome 10, mutations in the tumor suppressor gene PTEN, and PI3K mutations are molecular hallmarks of GBM and indicate poor prognostic outcomes in many cancers. Consequently, inhibiting the PI3K pathway may provide therapeutic benefit in these cancers. PI3K inhibitors generally block proliferation rather than induce apoptosis. To restore the sensitivity of GBM to apoptosis induction, targeted agents have been combined with conventional therapy. However, the molecular heterogeneity and infiltrative nature of GBM make it resistant to traditional single agent therapy. Our objectives were to test a dual PI3K/mTOR inhibitor that may cross the blood-brain barrier (BBB) and provide the rationale for using this inhibitor in combination regimens to chemotherapy-induced synergism in GBM. Here we report the preclinical potential of a novel, orally bioavailable PI3K/mTOR dual inhibitor, DS7423 (hereafter DS), in in-vitro and in-vivo studies. DS was tested in mice, and DS plasma and brain concentrations were determined. DS crossed the BBB and led to potent suppression of PI3K pathway biomarkers in the brain. The physiologically relevant concentration of DS was tested in 9 glioma cell lines and 22 glioma-initiating cell (GIC) lines. DS inhibited the growth of glioma tumor cell lines and GICs at mean 50% inhibitory concentration values of less than 250 nmol/L. We found that PI3K mutations and PTEN alterations were associated with cellular response to DS treatment; with preferential inhibition of cell growth in PI3KCA-mutant and PTEN altered cell lines. DS showed efficacy and survival benefit in the U87 and GSC11 orthotopic models of GBM. Furthermore, administration of DS enhanced the antitumor efficacy of temozolomide against GBM in U87 glioma models, which shows that PI3K/mTOR inhibitors may enhance alkylating agent-mediated cytotoxicity, providing a novel regimen for the treatment of GBM. Our present findings establish that DS can specifically be used in patients who have PI3K pathway activation and/or loss of PTEN function. Further studies are warranted to determine the potential of DS for glioma treatment.
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http://dx.doi.org/10.18632/oncotarget.15566DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5400620PMC
March 2017

MSK1-Mediated β-Catenin Phosphorylation Confers Resistance to PI3K/mTOR Inhibitors in Glioblastoma.

Mol Cancer Ther 2016 07 22;15(7):1656-68. Epub 2016 Apr 22.

Brain Tumor Center, Department of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.

Glioblastoma (GBM) represents a compelling disease for kinase inhibitor therapy because most of these tumors harbor genetic alterations that result in aberrant activation of growth factor-signaling pathways. The PI3K/mammalian target of the rapamycin (mTOR) pathway is dysregulated in over 50% of human GBM but remains a challenging clinical target. Inhibitors against PI3K/mTOR mediators have limited clinical efficacy as single agents. We investigated potential bypass mechanisms to PI3K/mTOR inhibition using gene expression profiling before and after PI3K inhibitor treatment by Affymetrix microarrays. Mitogen- and stress-activated protein kinase 1 (MSK1) was markedly induced after PI3K/mTOR inhibitor treatment and disruption of MSK1 by specific shRNAs attenuated resistance to PI3K/mTOR inhibitors in glioma-initiating cells (GIC). Further investigation showed that MSK1 phosphorylates β-catenin and regulates its nuclear translocation and transcriptional activity. The depletion of β-catenin potentiated PI3K/mTOR inhibitor-induced cytotoxicity and the inhibition of MSK1 synergized with PI3K/mTOR inhibitors to extend survival in an intracranial animal model and decreased phosphorylation of β-catenin at Ser(552) These observations suggest that MSK1/β-catenin signaling serves as an escape survival signal upon PI3K/mTOR inhibition and provides a strong rationale for the combined use of PI3K/mTOR and MSK1/β-catenin inhibition to induce lethal growth inhibition in human GBM. Mol Cancer Ther; 15(7); 1656-68. ©2016 AACR.
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http://dx.doi.org/10.1158/1535-7163.MCT-15-0857DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4936927PMC
July 2016

A high Notch pathway activation predicts response to γ secretase inhibitors in proneural subtype of glioma tumor-initiating cells.

Stem Cells 2014 Jan;32(1):301-12

Department of Neuro-Oncology, Brain Tumor Center, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

Genomic, transcriptional, and proteomic analyses of brain tumors reveal subtypes that differ in pathway activity, progression, and response to therapy. However, a number of small molecule inhibitors under development vary in strength of subset and pathway-specificity, with molecularly targeted experimental agents tending toward stronger specificity. The Notch signaling pathway is an evolutionarily conserved pathway that plays an important role in multiple cellular and developmental processes. We investigated the effects of Notch pathway inhibition in glioma tumor-initiating cell (GIC, hereafter GIC) populations using γ secretase inhibitors. Drug cytotoxicity testing of 16 GICs showed differential growth responses to the inhibitors, stratifying GICs into responders and nonresponders. Responder GICs had an enriched proneural gene signature in comparison to nonresponders. Also gene set enrichment analysis revealed 17 genes set representing active Notch signaling components NOTCH1, NOTCH3, HES1, MAML1, DLL-3, JAG2, and so on, enriched in responder group. Analysis of The Cancer Genome Atlas expression dataset identified a group (43.9%) of tumors with proneural signature showing high Notch pathway activation suggesting γ secretase inhibitors might be of potential value to treat that particular group of proneural glioblastoma (GBM). Inhibition of Notch pathway by γ secretase inhibitor treatment attenuated proliferation and self-renewal of responder GICs and induces both neuronal and astrocytic differentiation. In vivo evaluation demonstrated prolongation of median survival in an intracranial mouse model. Our results suggest that proneural GBM characterized by high Notch pathway activation may exhibit greater sensitivity to γ secretase inhibitor treatment, holding a promise to improve the efficiency of current glioma therapy.
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http://dx.doi.org/10.1002/stem.1528DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3947402PMC
January 2014

A survey of intragenic breakpoints in glioblastoma identifies a distinct subset associated with poor survival.

Genes Dev 2013 Jul 24;27(13):1462-72. Epub 2013 Jun 24.

Department of Bioinformatics and Computational Biology.

With the advent of high-throughput sequencing technologies, much progress has been made in the identification of somatic structural rearrangements in cancer genomes. However, characterization of the complex alterations and their associated mechanisms remains inadequate. Here, we report a comprehensive analysis of whole-genome sequencing and DNA copy number data sets from The Cancer Genome Atlas to relate chromosomal alterations to imbalances in DNA dosage and describe the landscape of intragenic breakpoints in glioblastoma multiforme (GBM). Gene length, guanine-cytosine (GC) content, and local presence of a copy number alteration were closely associated with breakpoint susceptibility. A dense pattern of repeated focal amplifications involving the murine double minute 2 (MDM2)/cyclin-dependent kinase 4 (CDK4) oncogenes and associated with poor survival was identified in 5% of GBMs. Gene fusions and rearrangements were detected concomitant within the breakpoint-enriched region. At the gene level, we noted recurrent breakpoints in genes such as apoptosis regulator FAF1. Structural alterations of the FAF1 gene disrupted expression and led to protein depletion. Restoration of the FAF1 protein in glioma cell lines significantly increased the FAS-mediated apoptosis response. Our study uncovered a previously underappreciated genomic mechanism of gene deregulation that can confer growth advantages on tumor cells and may generate cancer-specific vulnerabilities in subsets of GBM.
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http://dx.doi.org/10.1101/gad.213686.113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3713427PMC
July 2013

Identification of prognostic gene signatures of glioblastoma: a study based on TCGA data analysis.

Neuro Oncol 2013 Jul 15;15(7):829-39. Epub 2013 Mar 15.

Cancer Research Institute of Medical Science, The Catholic University of Korea, Seoul, Korea.

Background: The Cancer Genome Atlas (TCGA) project is a large-scale effort with the goal of identifying novel molecular aberrations in glioblastoma (GBM).

Methods: Here, we describe an in-depth analysis of gene expression data and copy number aberration (CNA) data to classify GBMs into prognostic groups to determine correlates of subtypes that may be biologically significant.

Results: To identify predictive survival models, we searched TCGA in 173 patients and identified 42 probe sets (P = .0005) that could be used to divide the tumor samples into 3 groups and showed a significantly (P = .0006) improved overall survival. Kaplan-Meier plots showed that the median survival of group 3 was markedly longer (127 weeks) than that of groups 1 and 2 (47 and 52 weeks, respectively). We then validated the 42 probe sets to stratify the patients according to survival in other public GBM gene expression datasets (eg, GSE4290 dataset). An overall analysis of the gene expression and copy number aberration using a multivariate Cox regression model showed that the 42 probe sets had a significant (P < .018) prognostic value independent of other variables.

Conclusions: By integrating multidimensional genomic data from TCGA, we identified a specific survival model in a new prognostic group of GBM and suggest that molecular stratification of patients with GBM into homogeneous subgroups may provide opportunities for the development of new treatment modalities.
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http://dx.doi.org/10.1093/neuonc/not024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3688008PMC
July 2013

Novel HSP90 inhibitor NVP-HSP990 targets cell-cycle regulators to ablate Olig2-positive glioma tumor-initiating cells.

Cancer Res 2013 May 14;73(10):3062-74. Epub 2013 Mar 14.

Brain Tumor Center, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.

Genetic heterogeneity and signaling alterations diminish the effectiveness of single-agent therapies in glioblastoma multiforme (GBM). HSP90 is a molecular chaperone for several signaling proteins that are deregulated in glioma cells. Thus, HSP90 inhibition may offer an approach to coordinately correct multiple signaling pathways as a strategy for GBM therapy. In this study, we evaluated the effects of a novel HSP90 inhibitor, NVP-HSP990, in glioma tumor-initiating cell (GIC) populations, which are strongly implicated in the root pathobiology of GBM. In GIC cultures, NVP-HSP990 elicited a dose-dependent growth inhibition with IC50 values in the low nanomolar range. Two GIC subgroups with different responses were observed with an Olig2-expressing subset relatively more sensitive to treatment. We also showed that Olig2 is a functional marker associated with cell proliferation and response to NVP-HSP990, as NVP-HSP990 attenuated cell proliferation in Olig2-high GIC lines. In addition, NVP-HSP990 disrupted cell-cycle control mechanism by decreasing CDK2 and CDK4 and elevating apoptosis-related molecules. Mechanistic investigations revealed molecular interactions between CDK2/CDK4 and Olig2. Inhibition of CDK2/CDK4 activity disrupted Olig2-CDK2/CDK4 interactions and attenuated Olig2 protein stability. In vivo evaluation showed a relative prolongation of median survival in an intracranial model of GIC growth. Our results suggest that GBM characterized by high-expressing Olig2 GIC may exhibit greater sensitivity to NVP-HSP990 treatment, establishing a foundation for further investigation of the role of HSP90 signaling in GBM.
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http://dx.doi.org/10.1158/0008-5472.CAN-12-2033DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3655088PMC
May 2013

Antitumor activity of NVP-BKM120--a selective pan class I PI3 kinase inhibitor showed differential forms of cell death based on p53 status of glioma cells.

Clin Cancer Res 2012 Jan 7;18(1):184-95. Epub 2011 Nov 7.

Department of Neuro-Oncology, Brain Tumor Center, The University of Texas M D Anderson Cancer Center, Houston, Texas 77030, USA.

Purpose: The aim of this study was to show preclinical efficacy and clinical development potential of NVP-BKM120, a selective pan class I phosphatidylinositol-3 kinase (PI3K) inhibitor in human glioblastoma (GBM) cells in vitro and in vivo.

Experimental Design: The effect of NVP-BKM120 on cellular growth was assessed by CellTiter-Blue assay. Flow cytometric analyses were carried out to measure the cell-cycle, apoptosis, and mitotic index. Mitotic catastrophe was detected by immunofluorescence. The efficacy of NVP-BKM120 was tested using intracranial U87 glioma model.

Results: We tested the biologic effects of a selective PI3K inhibitor NVP-BKM120 in a set of glioma cell lines. NVP-BKM120 treatment for 72 hours resulted in a dose-dependent growth inhibition and effectively blocked the PI3K/Akt signaling cascade. Although we found no obvious relationship between the cell line's sensitivity to NVP-BKM120 and the phosphatase and tensin homolog (PTEN) and epidermal growth factor receptor (EGFR) statuses, we did observe a differential sensitivity pattern with respect to p53 status, with glioma cells containing wild-type p53 more sensitive than cells with mutated or deleted p53. NVP-BKM120 showed differential forms of cell death on the basis of p53 status of the cells with p53 wild-type cells undergoing apoptotic cell death and p53 mutant/deleted cells having a mitotic catastrophe cell death. NVP-BKM120 mediates mitotic catastrophe mainly through Aurora B kinase. Knockdown of p53 in p53 wild-type U87 glioma cells displayed microtubule misalignment, multiple centrosomes, and mitotic catastrophe cell death. Parallel to the assessment of the compound in in vitro settings, in vivo efficacy studies using an intracranial U87 tumor model showed an increased median survival from 26 days (control cohort) to 38 and 48 days (treated cohorts).

Conclusion: Our present findings establish that NVP-BKM120 inhibits the PI3K signaling pathways, leading to different forms of cell death on the basis of p53 statuses. Further studies are warranted to determine if NVP-BKM120 has potential as a glioma treatment.
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http://dx.doi.org/10.1158/1078-0432.CCR-11-1558DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785365PMC
January 2012

An integrated in vitro and in vivo high-throughput screen identifies treatment leads for ependymoma.

Cancer Cell 2011 Sep;20(3):384-99

Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.

Using a mouse model of ependymoma-a chemoresistant brain tumor-we combined multicell high-throughput screening (HTS), kinome-wide binding assays, and in vivo efficacy studies, to identify potential treatments with predicted toxicity against neural stem cells (NSC). We identified kinases within the insulin signaling pathway and centrosome cycle as regulators of ependymoma cell proliferation, and their corresponding inhibitors as potential therapies. FDA approved drugs not currently used to treat ependymoma were also identified that posses selective toxicity against ependymoma cells relative to normal NSCs both in vitro and in vivo, e.g., 5-fluorouracil. Our comprehensive approach advances understanding of the biology and treatment of ependymoma including the discovery of several treatment leads for immediate clinical translation.
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http://dx.doi.org/10.1016/j.ccr.2011.08.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3172881PMC
September 2011

Establishment and characterization of clinically relevant models of ependymoma: a true challenge for targeted therapy.

Neuro Oncol 2011 Jul 8;13(7):748-58. Epub 2011 Jun 8.

Brain Tumor Center, Department of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

The development of new therapies for ependymoma is dramatically limited by the absence of optimal in vivo and in vitro models. Successful ependymoma treatment requires a profound understanding of the disease's biological characteristics. This study focuses on the establishment and characterization of in vivo and in vitro models of ependymoma to study the molecular pathways necessary for growth and progression in ependymoma. In addition, this study also emphasizes the use of these models for therapeutic intervention of ependymomas. We established optimal conditions for the long-term growth of 2 tumor xenografts and cultures of 2 human ependymoma cell lines. This study also describes the establishment of in vivo models. Histopathologic features of tumors from both intracranial and subcutaneous sites in mice revealed perivascular pseudorosettes and ependymal rosettes, which are typical morphologic features of ependymoma similar to those observed in human specimens. The in vitro models revealed glial fibrillary acidic protein and vimentin expression, and ultrastructural studies demonstrated numerous microvilli, caveolae, and microfilaments commonly seen in human ependymoma. To study signaling pathway alterations in ependymoma, we profiled established ependymoma models with Western blot analysis that demonstrated aberrant activation mainly of the phosphoinositide 3-kinase and epidermal growth factor receptor signaling pathways. Targeting phosphoinositide 3-kinase and epidermal growth factor receptor signaling pathways with small molecule inhibitors showed growth inhibitory effects. These models can also be used to study the standard therapies used for ependymomas, as shown by some of the drugs used in this study. Therefore, the models developed will assist in the biological studies and preclinical drug screening for ependymomas.
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http://dx.doi.org/10.1093/neuonc/nor037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3129270PMC
July 2011

Induction of MUC5AC mucin by conjugated bile acids in the esophagus involves the phosphatidylinositol 3-kinase/protein kinase C/activator protein-1 pathway.

Cancer 2011 Jun 14;117(11):2386-97. Epub 2010 Dec 14.

Department of Gastroenterology, Hepatology, and Nutrition, The University of Texas M. D. Anderson Cancer Center, Houston, Texas.

Background: Bile reflux contributes to the development of esophageal injury and neoplasia. The mucin 5AC (MUC5AC) is absent in the normal squamous epithelium of the esophagus but is strongly expressed in Barrett esophagus (BE). The objective of this study was to determine whether and how bile acids influence the expression of MUC5AC in the esophagus.

Methods: MUC5AC expression was studied by immunohistochemistry and immunoblotting in human tissues, in tissues from a rat model of BE, and in SKGT-4 cultured esophageal epithelial cells. MUC5AC transcription was studied by real-time polymerase chain reaction and transient transfection assays.

Results: MUC5AC was absent from normal squamous epithelium but was present in 100% of Barrett specimens and in 61.5% of human esophageal adenocarcinoma tissues that were examined. MUC5AC protein expression was induced to a greater degree by conjugated bile acids than by unconjugated bile acids, and this occurred at the transcriptional level. In the rat reflux model, MUC5AC mucin was expressed abundantly in tissues of BE stimulated by duodenoesophageal reflux. Conjugated bile acids induced AKT phosphorylation in SKGT-4 cells but had no effect on extracellular signal-regulated protein kinases 1 and 2, c-Jun N-terminal kinase, or protein-38 kinase phosphorylation. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and a dominant-negative protein kinase C (AKT) construct prevented the induction of MUC5AC by conjugated bile acids. Transactivation of AP-1 by conjugated bile acids coincided with MUC5AC induction, and cotransfection with a dominant-negative activator protein-1 (AP-1) vector decreased MUC5AC transcription and its induction.

Conclusions: Conjugated bile acids in the bile refluxate contribute to MUC5AC induction in the esophagus. This occurs at the level of transcription and involves activation of the PI3K/AKT/AP-1 pathway.
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http://dx.doi.org/10.1002/cncr.25796DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3116027PMC
June 2011

Identification of novel synergistic targets for rational drug combinations with PI3 kinase inhibitors using siRNA synthetic lethality screening against GBM.

Neuro Oncol 2011 Apr;13(4):367-75

Brain Tumor Center, Department of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.

Several small molecules that inhibit the PI3 kinase (PI3K)-Akt signaling pathway are in clinical development. Although many of these molecules have been effective in preclinical models, it remains unclear whether this strategy alone will be sufficient to interrupt the molecular events initiated and maintained by signaling along the pathways because of the activation of other pathways that compensate for the inhibition of the targeted kinase. In this study, we performed a synthetic lethality screen to identify genes or pathways whose inactivation, in combination with the PI3K inhibitors PX-866 and NVPBEZ-235, might result in a lethal phenotype in glioblastoma multiforme (GBM) cells. We screened GBM cells (U87, U251, and T98G) with a large-scale, short hairpin RNA library (GeneNet), which contains 43 800 small interfering RNA sequences targeting 8500 well-characterized human genes. To decrease off-target effects, we selected overlapping genes among the 3 cell lines that synergized with PX-866 to induce cell death. To facilitate the identification of potential targets, we used a GSE4290 dataset and The Cancer Genome Atlas GBM dataset, identifying 15 target genes overexpressed in GBM tissues. We further analyzed the selected genes using Ingenuity Pathway Analysis software and showed that the 15 genes were closely related to cancer-promoting pathways, and a highly interconnected network of aberrations along the MYC, P38MAPK, and ERK signaling pathways were identified. Our findings suggest that inhibition of these pathways might increase tumor sensitivity to PX-866 and therefore represent a potential clinical therapeutic strategy.
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http://dx.doi.org/10.1093/neuonc/nor012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3064700PMC
April 2011

Combined action of the dinuclear platinum compound BBR3610 with the PI3-K inhibitor PX-866 in glioblastoma.

Int J Cancer 2011 Feb;128(4):787-96

Department of Neurosurgery, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.

Polynuclear platinum compounds are more effective at killing glioblastoma cells than cisplatin, work by a different mechanism, and typically do not induce high levels of apoptosis at early time points after exposure. Here, we tested the hypothesis that combining BBR3610, the most potent polynuclear platinum, with a phosphoinositide-3-kinase (PI3K) inhibitor would promote apoptosis and enhance the impact on glioblastoma cells. The PI3K pathway is commonly activated in glioblastoma and promotes tumor cell survival, suggesting that its inhibition would make cells more sensitive to cytotoxic agents. We chose PX-866 as a PI3K inhibitor as it is a clinically promising agent being evaluated for brain tumor therapy. Combining BBR3610 and PX-866 resulted in synergistic killing of cultured glioma cells and an extension of survival in an orthotopic xenograft animal model. Both agents alone induced autophagy, and this appeared to be saturated, because when they were combined no additional autophagy was observed. However, the combination of PX-866 and BBR3610 did induce statistically significant increases in the level of apoptosis, associated with a reduction in pAkt and pBad, as well as inhibition of transwell migration. We conclude that combining polynuclear platinums with PI3K inhibitors has translational potential and alters the cellular response to include early apoptosis.
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http://dx.doi.org/10.1002/ijc.25394DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2990813PMC
February 2011

Cellular and in vivo activity of a novel PI3K inhibitor, PX-866, against human glioblastoma.

Neuro Oncol 2010 Jun 15;12(6):559-69. Epub 2010 Feb 15.

Department of Neuro-Oncology, Unit 100, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.

The phosphatidylinositol-3-kinase (PI3K)/Akt oncogenic pathway is critical in glioblastomas. Loss of PTEN, a negative regulator of the PI3K pathway or activated PI3K/Akt pathway that drive increased proliferation, survival, neovascularization, glycolysis, and invasion is found in 70%-80% of malignant gliomas. Thus, PI3K is an attractive therapeutic target for malignant glioma. We report that a new irreversible PI3K inhibitor, PX-866, shows potent inhibitory effects on the PI3K/Akt signaling pathway in glioblastoma. PX-866 did not induce any apoptosis in glioma cells; however, an increase in autophagy was observed. PX-866 inhibited the invasive and angiogenic capabilities of cultured glioblastoma cells. In vivo, PX-866 inhibited subcutaneous tumor growth and increased the median survival time of animals with intracranial tumors. We also assessed the potential of proton magnetic resonance spectroscopy (MRS) as a noninvasive method to monitor response to PX-866. Our findings show that PX-866 treatment causes a drop in the MRS-detectable choline-to-NAA, ratio and identify this partial normalization of the tumor metabolic profile as a biomarker of molecular drug action. Our studies affirm that the PI3K pathway is a highly specific molecular target for therapies for glioblastoma and other cancers with aberrant PI3K/PTEN expression.
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http://dx.doi.org/10.1093/neuonc/nop058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2940638PMC
June 2010

NVP-BEZ235, a novel dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor, elicits multifaceted antitumor activities in human gliomas.

Mol Cancer Ther 2009 Aug 11;8(8):2204-10. Epub 2009 Aug 11.

Department of Neuro-Oncology, The University of Texas M. D. Anderson Cancer Center, Unit 431, 1515 Holcombe Boulevard, Houston, TX 77030.

Aberrant genetic alternations in human gliomas, such as amplification of epidermal growth factor receptor, mutation and/or deletion of tumor suppressor gene PTEN, and mutations of PIK3CA, contribute to constitutive activation of the phosphatidylinositol 3-kinase (PI3K) pathway. We investigated the potential antitumor activity of NVP-BEZ235, which is a novel dual PI3K/mammalian target of rapamycin (mTOR) inhibitor in gliomas. The compound suppressed glioma cell proliferation with IC(50) values in the low nanomolar range by specifically inhibiting the activity of target proteins including Akt, S6K1, S6, and 4EBP1 in the PI3K/Akt/mTOR signaling pathway. NVP-BEZ235 treatment of glioma cell lines led to G(1) cell cycle arrest and induced autophagy. Furthermore, expression of the vascular endothelial growth factor (VEGF), which is an important angiogenic modulator in glioma cells, was significantly decreased, suggesting that NVP-BEZ235 may also exert an antiangiogenic effect. Preclinical testing of the therapeutic efficacy of NVP-BEZ235 showed that it significantly prolonged the survival of tumor-bearing animals without causing any obvious toxicity. Tumor extracts harvested from animals after treatment showed that the compound inhibited the activity of target proteins in the PI3K/Akt/mTOR cascade. Immunohistochemical analyses also showed a significant reduction in staining for VEGF von Willebrand factor (factor VIII) in NVP-BEZ235-treated tumor sections compared with controls, further confirming that NVP-BEZ235 has an antiangiogenic effect in vivo. We conclude from these findings that NVP-BEZ235 antagonizes PI3K and mTOR signaling and induces cell cycle arrest, down-regulation of VEGF, and autophagy. These results warrant further development of NVP-BEZ235 for clinical trials for human gliomas or other advanced cancers with altered PI3K/Akt/mTOR signaling.
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http://dx.doi.org/10.1158/1535-7163.MCT-09-0160DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2752877PMC
August 2009

Exploratory analysis of the copy number alterations in glioblastoma multiforme.

PLoS One 2008 30;3(12):e4076. Epub 2008 Dec 30.

Department of Bioinformatics and Computational Biology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.

Background: The Cancer Genome Atlas project (TCGA) has initiated the analysis of multiple samples of a variety of tumor types, starting with glioblastoma multiforme. The analytical methods encompass genomic and transcriptomic information, as well as demographic and clinical data about the sample donors. The data create the opportunity for a systematic screening of the components of the molecular machinery for features that may be associated with tumor formation. The wealth of existing mechanistic information about cancer cell biology provides a natural reference for the exploratory exercise.

Methodology/principal Findings: Glioblastoma multiforme DNA copy number data was generated by The Cancer Genome Atlas project for 167 patients using 227 aCGH experiments, and was analyzed to build a catalog of aberrant regions. Genome screening was performed using an information theory approach in order to quantify aberration as a deviation from a centrality without the bias of untested assumptions about its parametric nature. A novel Cancer Genome Browser software application was developed and is made public to provide a user-friendly graphical interface in which the reported results can be reproduced. The application source code and stand alone executable are available at (http://code.google.com/p/cancergenome) and (http://bioinformaticstation.org), respectively.

Conclusions/significance: The most important known copy number alterations for glioblastoma were correctly recovered using entropy as a measure of aberration. Additional alterations were identified in different pathways, such as cell proliferation, cell junctions and neural development. Moreover, novel candidates for oncogenes and tumor suppressors were also detected. A detailed map of aberrant regions is provided.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004076PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2605252PMC
February 2009

PTEN signaling pathways in glioblastoma.

Authors:
Dimpy Koul

Cancer Biol Ther 2008 Sep 8;7(9):1321-5. Epub 2008 Sep 8.

Brain Tumor Center, Department of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.

Malignant gliomas are the most common primary brain tumor in adults, but the prognosis for patients with these tumors remains poor despite advances in diagnosis and standard therapies such as surgery, radiation therapy, and chemotherapy. Progress in the treatment of gliomas now depends to a great extent on an increased understanding of the biology of these tumors. Recent insights into the biology of gliomas include the finding that tyrosine kinase receptors and signal transduction pathways play a role in tumor initiation and maintenance. Deregulation of phosphatidylinositol 3-kinase (PI3K) signaling pathways resulting from genetic alterations in the PTEN tumor suppressor gene on 10q23 at the level of LOH, mutation and methylation have been identified in at least 60% of glioblastoma. Loss of PTEN function by mutation or LOH correlates with poor survival in anaplastic astrocytoma and glioblastoma, suggesting that PTEN plays a role in patient outcome. Interestingly, amplification of Epidermal growth factor receptor (EGFR) in the background of heterozygous PTEN knockout mice develop invasive glioma very similar to human glioblastoma, demonstrating the importance of PTEN in glioma progression and providing a model system to evaluate the efficacy of targeting PTEN in glioblastoma.
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http://dx.doi.org/10.4161/cbt.7.9.6954DOI Listing
September 2008

Tissue transglutaminase regulates focal adhesion kinase/AKT activation by modulating PTEN expression in pancreatic cancer cells.

Clin Cancer Res 2008 Apr;14(7):1997-2005

Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center Houston, TX 77030, USA.

Purpose: Pancreatic ductal adenocarcinoma (PDAC) progresses rapidly and exhibits profound resistance to treatment. We recently reported that a great majority of PDAC tumors and tumor cell lines express elevated levels of tissue transglutaminase (TG2). Here, we provide first evidence that TG2 expression in PDAC cells results in constitutive activation of focal adhesion kinase/AKT by modulating the expression of the tumor suppressor phosphatase PTEN.

Experimental Design: Using PDAC cell lines, we determined the effect of TG2 overexpression on PTEN stability and functions. We confirmed the correlation between TG2 expression and PTEN levels in a few (n=51) PDAC tumor samples.

Results: We observed that expression of TG2 is inversely correlated with PTEN expression in PDAC cells. Ectopic expression of TG2 inhibited PTEN phosphorylation and promoted its degradation by ubiquitin-proteasomal pathway. Conversely, down-regulation of TG2 by small interfering RNA up-regulated PTEN expression. Clinical relevance of these results was evident in an athymic nude mouse model where down-regulation of endogenous TG2 caused a significant retardation in PDAC xenograft growth. Importantly, the analysis of 51 tumor samples from patients with stage II PDAC revealed that overexpression of TG2 was associated with loss of PTEN expression (P=0.023; odds ratio, 4.1). In multivariate analysis, TG2-mediated loss of PTEN was a prognostic factor for overall survival in patients with stage II pancreatic ductal carcinoma independent of tumor stage/lymph node status and tumor differentiation (P=0.01).

Conclusion: TG2 expression in PDAC promotes degradation of PTEN by ubiquitin-proteasomal pathway and results in constitutive activation of focal adhesion kinase/AKT cell survival signaling.
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http://dx.doi.org/10.1158/1078-0432.CCR-07-1533DOI Listing
April 2008

PTEN down regulates AP-1 and targets c-fos in human glioma cells via PI3-kinase/Akt pathway.

Mol Cell Biochem 2007 Jun 18;300(1-2):77-87. Epub 2007 Jan 18.

Department of Neuro-Oncology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.

The continual activation of signaling cascades results in dramatic consequences that include loss of cellular growth control and neoplastic transformation. We show here that phosphoinositide 3-kinase and its mediator Akt was constitutively activated in glioma and that this might be due to the aberrant expression of their natural antagonist PTEN. The PTEN (phosphatase and tensin homologue deleted on chromosome ten) tumor suppressor gene modulates cell growth and survival through mechanisms that are incompletely understood. In this study, we investigated the possibility that PTEN mediates its effects through modulation of transcription factor AP-1, which is in part due to decrease in c-fos expression which was dependent on PI3kinase activity. Consistent with a reduction in the c-fos levels, an AP-1 dependent reporter gene was poorly induced in the PTEN expressing cell lines. In contrast to its effect on c-fos, PTEN did not affect the expression of c-Jun and other fos family members. We also show that the effect of PTEN on c-fos expression was due to its ability to antagonize PI3-kinase and could be mimicked by the expression of dominant negative Akt mutant. Taken together, these data indicate that the aberrant expression of PTEN contributes to the activation of the PI3kinase/Akt pathway and its transcription factor mediators in glioma. We conclude that the ectopic expression of PTEN down regulates the proliferation of glioma cells through the suppression of AP-1 and that this target might be essential for its central role in the growth and survival of glioma cancer cells.
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http://dx.doi.org/10.1007/s11010-006-9371-8DOI Listing
June 2007