Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0017636 (glioblastoma)
 18,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Deregulation of protein kinase activity has been shown to play a central role in the pathogenesis of human cancer. The molecular pathogenesis of chronic myelogenous leukemia (CML) in particular, depends on formation of the bcr-abl oncogene, leading to constitutive expression of the tyrosine kinase fusion protein, Bcr-Abl. Based on these observations, imatinib was developed as a specific inhibitor for the Bcr-Abl protein tyrosine kinase. The expanding understanding of the basis of imatinib-mediated tyrosine kinase inhibition has revealed a spectrum of potential new antitumor applications beyond the powerful activity already reported in the treatment of CML. Imatinib has shown activity in vivo against PDGF-driven tumor models including glioblastoma, dermatofibrosarcoma protuberans and chronic myelomonocytic leukemia. Antiangiogenic effects have been demonstrated by inhibition of PDGF-, VEGF (vascular endothelial growth factor)- and bFGF- (basic fibroblast growth factor) induced angiogenesis in vivo, and by inhibition of angiogenesis and tumor growth in an experimental bone metastasis model. Imatinib has been shown to reduce interstitial fluid pressure in an experimental colonic carcinoma model by blocking PDGF-mediated effects on tumor-associated blood vessels and stromal tissue. It is also a potent inhibitor of the Kit receptor tyrosine kinase, and has demonstrated activity clinically against the Kit-driven gastrointestinal stromal tumor (GIST) and experimentally in small-cell lung cancer cell lines. The pharmacology of imatinib and its activity in various tumor models is discussed.
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PMID:Pharmacology of imatinib (STI571). 1252 70

Imatinib mesylate is a small molecule inhibitor of the c-Abl, platelet-derived growth factor (PDGF) receptor and c-Kit tyrosine kinases that is approved for the treatment of Philadelphia chromosome-positive chronic myeloid leukemia (CML) and gastrointestinal stromal tumors. Glioblastoma multiforme is a highly malignant primary brain tumor that is usually treated with surgery and/or radiotherapy. Previous studies implicate an autocrine loop caused by high expression of PDGF and its receptor, PDGFR, in the proliferation of some glioblastomas. Here, we demonstrate that pretreatment of a human glioblastoma cell line, RuSi RS1, with imatinib significantly enhanced the cytotoxic effect of ionizing radiation. This effect was not seen in human breast cancer (BT20) and colon cancer (WiDr) cell lines. Whereas c-Abl and c-Kit were expressed about equally in the three cell lines, RuSi RS1 cells showed significantly higher expression of PDGFR-beta protein in comparison to BT20 and WiDr. Imatinib treatment of RuSi RS1 cells decreased overall levels of cellular tyrosine phosphorylation and specifically inhibited phosphorylation of PDGFR-beta, while c-Abl was not prominently activated in these cells. These results suggest that imatinib may have clinical utility as a radiosensitizer in the treatment of human glioblastoma, possibly through disruption of an autocrine PDGF/PDGFR loop.
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PMID:Imatinib mesylate radiosensitizes human glioblastoma cells through inhibition of platelet-derived growth factor receptor. 1572 3

Imatinib mesylate (signal transduction inhibitor 571, Gleevec) is a potent and selective tyrosine kinase inhibitor, which was shown to effectively inhibit platelet-derived growth factor-induced glioblastoma cell growth preclinically. However, in patients, a limited penetration of imatinib into the brain has been reported. Imatinib is transported in vitro and in vivo by P-glycoprotein (P-gp; ABCB1), which thereby limits its distribution into the brain in mice. Previously, imatinib was shown to potently inhibit human breast cancer resistance protein (BCRP; ABCG2). Here, we show that imatinib is efficiently transported by mouse Bcrp1 in transfected Madin-Darby canine kidney strain II (MDCKII) monolayers. Furthermore, we show that the clearance of i.v. imatinib is significantly decreased 1.6-fold in Bcrp1 knockout mice compared with wild-type mice. At t = 2 hours, the brain penetration of i.v. imatinib was significantly 2.5-fold increased in Bcrp1 knockout mice compared with control mice. We tested the hypothesis that P-gp and BCRP inhibitors, such as elacridar and pantoprazole, improve the brain penetration of imatinib. Firstly, we showed in vitro that pantoprazole and elacridar inhibit the Bcrp1-mediated transport of imatinib in MDCKII-Bcrp1 cells. Secondly, we showed that co-administration of pantoprazole or elacridar significantly reduced the clearance of i.v. imatinib in wild-type mice by respectively 1.7-fold and 1.5-fold. Finally, in wild-type mice treated with pantoprazole or elacridar, the brain penetration of i.v. imatinib significantly increased 1.8-fold and 4.2-fold, respectively. Moreover, the brain penetration of p.o. imatinib increased 5.2-fold when pantoprazole was co-administered in wild-type mice. Our results suggest that co-administration of BCRP and P-gp inhibitors may improve delivery of imatinib to malignant gliomas.
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PMID:The effect of Bcrp1 (Abcg2) on the in vivo pharmacokinetics and brain penetration of imatinib mesylate (Gleevec): implications for the use of breast cancer resistance protein and P-glycoprotein inhibitors to enable the brain penetration of imatinib in patients. 1580 52

High-grade gliomas, including glioblastomas, are malignant brain tumors for which improved treatment is urgently needed. Genetic studies have demonstrated the existence of biologically distinct subsets. Preliminary studies have indicated that platelet-derived growth factor (PDGF) receptor signaling contributes to the growth of some of these tumors. In this study, human high-grade glioma primary cultures were analysed for sensitivity to treatment with the PDGF receptor inhibitor imatinib/Glivec/Gleevec/STI571. Six out of 15 cultures displayed more than 40% growth inhibition after imatinib treatment, whereas seven cultures showed less than 20% growth inhibition. In the sensitive cultures, apoptosis contributed to growth inhibition. Platelet-derived growth factor receptor status correlated with imatinib sensitivity. Supervised analyses of gene expression profiles and real-time PCR analyses identified expression of the chemokine CXCL12/SDF-1 (stromal cell-derived factor 1) as a predictor of imatinib sensitivity. Exogenous addition of CXCL12 to imatinib-insensitive cultures conferred some imatinib sensitivity. Finally, coregulation of CXCL12 and PDGF alpha-receptor was observed in glioblastoma biopsies. We have thus defined the characteristics of a novel imatinib-sensitive subset of glioma cultures, and provided evidence for a functional relationship between imatinib sensitivity and chemokine signaling. These findings will assist in the design and evaluation of clinical trials exploring therapeutic effects of imatinib on malignant brain tumors.
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PMID:Characterization of an imatinib-sensitive subset of high-grade human glioma cultures. 1654 94

In vitro and in vivo studies have demonstrated inhibition of glioblastoma growth by imatinib mesylate (Gleevec). Imatinib is an inhibitor of the tyrosine kinase activities of platelet-derived growth factor receptor (PDGF-r), which is involved in glioblastoma aggressiveness. In this study, we have investigated the link between 99mTc-(V)-DMSA, an imaging agent used in Single Photon Emission Computed Tomography, cellular accumulation and the biological effects of imatinib mediated by PDGF-r in a human glioblastoma cell line U87-MG. Cells treated with imatinib showed significant decreases in proliferation, invasion, migration and PDGF-rbeta expression. 99mTc-(V)-DMSA cellular uptake studies showed that the specific action of imatinib on PDGF-r signal pathway, in the human glioblastoma cell line U87-MG, could be followed by radioactive tracer. Furthermore, strong correlations between cellular 99mTc-(V)-DMSA uptake and the effect of imatinib therapy on U87-MG proliferation (r=0.896), invasion (r=0.621) and migration (r=0.822) were obtained, likewise for 99mTc-(V)-DMSA uptake and PDGF-r expression (r=0.958). Our results show that the biological effects of imatinib therapy on tumour cells properties are linked to PDGF-r phosphorylation and could be traced with 99mTc-(V)-DMSA, which also seems to be a potential tracer to evaluate the response to imatinib therapy in glioblastoma.
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PMID:Evaluation of imatinib mesylate effects on glioblastoma aggressiveness with SPECT radiotracer 99mTc-(v)-DMSA. 1656 90

Glioblastomas are intrinsically resistant to conventional radiation therapy. The present study investigated the possibility that the tyrosine kinase inhibitor, imatinib, could enhance radiation sensitivity and influence proliferative recovery after irradiation in glioblastoma cells. Radiosensitivity was evaluated by clonogenic survival; apoptotic cell death was evaluated using flow cytometric analysis; proliferative recovery was monitored based on viable cell number subsequent to radiation-induced growth arrest; activation of p44/42 MAPK was based on phosphorylation of the protein. Glioblastoma cells pretreated with imatinib demonstrated an enhanced sensitivity to radiation. Imatinib also delayed proliferative recovery in irradiated glioblastoma cells. Imatinib promoted suppression of p44/42 MAPK signaling both when added prior to and post-irradiation. Increased sensitivity to radiation and delayed proliferative recovery in irradiated glioblastoma cells exposed to imatinib may be a consequence of the capacity of imatinib to interfere with p44/42 MAPK kinase signaling. Imatinib may prove to have clinical utility as a neoadjuvant and adjuvant in the treatment of glioblastomas that receive radiation therapy.
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PMID:Enhancement of radiation sensitivity, delay of proliferative recovery after radiation and abrogation of MAPK (p44/42) signaling by imatinib in glioblastoma cells. 1682 Aug 83

The success of kinase inhibitor therapy in chronic myeloid leukemia (CML) has validated the long-held thesis in the cancer research community that a precise molecular understanding of cancer can directly affect cancer therapy. Now that several years have passed since the approval of imatinib/Gleevec for CML treatment, we have a greater appreciation for the challenges involved in effectively deploying these agents in the clinic. In this paper, I review recent events in the treatment of CML and highlight early applications of kinase inhibitor therapy to other diseases such as glioblastoma. I conclude with a vision that it may be possible, through analysis of tumor proteins secreted into serum, to track distinct molecular features of various cancers in order to select appropriate molecularly targeted therapy and measure treatment response. This new science of cancer biomarkers could radically transform the conduct of clinical trials and speed the evaluation of new molecularly targeted agents.
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PMID:Making progress through molecular attacks on cancer. 1686 86

The heat shock protein HSP90 serves as a chaperone for receptor protein kinases, steroid receptors, and other intracellular signaling molecules. Targeting HSP90 with ansamycin antibiotics disrupts the normal processing of clients of the HSP90 complex. The platelet-derived growth factor receptor alpha (PDGFRalpha) is a tyrosine kinase receptor up-regulated and activated in several malignancies. Here we show that the PDGFRalpha forms a complex with HSP90 and the co-chaperone cdc37 in ovarian, glioblastoma, and lung cancer cells. Treatment of cancer cell lines expressing the PDGFRalpha with the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) promotes degradation of the receptor. Likewise, phospho-Akt, a downstream target, is degraded after treatment with 17-AAG. In contrast, PDGFRalpha expression is not affected by 17-AAG in normal human smooth muscle cells or 3T3 fibroblasts. PDGFRalpha degradation by 17-AAG is inhibited by the proteasome inhibitor MG132. High molecular weight, ubiquitinated forms of the receptor are detected in cells treated with 17-AAG and MG132. Degradation of the receptor is also inhibited by a specific neutralizing antibody to the PDGFRalpha but not by a neutralizing antibody to PDGF or by imatinib mesylate (Gleevec). Ultimately, PDGFRalpha-mediated cell proliferation is inhibited by 17-AAG. These results show that 17-AAG promotes PDGFRalpha degradation selectively in transformed cells. Thus, not only mutated tyrosine kinases but also overexpressed receptors in cancer cells can be targeted by 17-AAG.
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PMID:The platelet-derived growth factor receptor alpha is destabilized by geldanamycins in cancer cells. 1707 30

The oncogenic epidermal growth factor receptor (EGFR) pathway triggers downstream phosphatidylinositol 3-kinase (PI3K)/RAS-mediated signaling cascades. In transgenic mice, glioblastoma cannot develop on single but only on simultaneous activation of the EGFR signaling mediators RAS and AKT. However, complete blockade of EGFR activation does not result in apoptosis in human glioblastoma cells, suggesting additional cross-talk between downstream pathways. Based on these observations, we investigated combination therapies using protein kinase inhibitors against EGFR, platelet-derived growth factor receptor, and mammalian target of rapamycin, assessing glioblastoma cell survival. Clinically relevant doses of AEE788, Gleevec (imatinib), and RAD001 (everolimus), alone or in combinations, did not induce glioblastoma cell apoptosis. In contrast, simultaneous inactivation of the EGFR downstream targets mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase and PI3K by U0126 and wortmannin triggered rapid tumor cell death. Blocking EGFR with AEE788 in combination with sublethal concentrations of the microtubule stabilizer patupilone also induced apoptosis and reduced cell proliferation in glioblastoma cells, accompanied by reduced AKT and ERK activity. These data underline the critical role of the PI3K/AKT and the RAS/RAF/mitogen-activated protein/ERK kinase/ERK signaling cascades in the cell-intrinsic survival program of sensitive glioblastoma cell lines. We conclude that drug combinations, which down-regulate both ERK and protein kinase B/AKT activity, may prove effective in overcoming cell resistance in a subgroup of glioblastoma.
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PMID:Combination of sublethal concentrations of epidermal growth factor receptor inhibitor and microtubule stabilizer induces apoptosis of glioblastoma cells. 1730 73

Glioblastoma (GBM) is a highly infiltrating, aggressive brain cancer with no available curative treatment. We developed a rapid assay for assessing the effect of various drugs on GBM stem cells. The assay uses a small number of separated CD133+ cells (20,000 in 0.2 ml) in 96-well plate that form neurospheres within 1-2 days. Various drugs disperse the neurospheres within 24-36 h, which can be quantified microscopically. We used the GBM cell line A-172 to develop the conditions for the assay, utilizing Gleevec, the gamma-secretase inhibitor DAPT, and the anti-bacterial peptide amph1D. The results show dispersion of the neurospheres leading to cell death, at relatively low drugs concentrations (<25 microM). Drug combination showed a synergistic effect and disruption of neurospheres under lower concentrations. We applied this assay to the CD133+ cells of surgical specimens from three patients that showed similar results. This assay facilitates a rapid test of drugs on small amounts of fractionated patient's GBM stem cells.
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PMID:A rapid assay for drug sensitivity of glioblastoma stem cells. 1751 5


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