Tona Schnee

The combination of ionizing radiation and peripheral vaccination produces long-term survival of mice bearing established invasive GL261 gliomas.

Purpose: High-grade glioma treatment includes ionizing radiation therapy. The high invasiveness of glioma cells precludes their eradication and is responsible for the dismal prognosis. Recently, we reported the down-regulation of MHC class I (MHC-I) products in invading tumor cells in human and mouse GL261 gliomas. Here, we tested the hypothesis that whole-brain radiotherapy (WBRT) up-regulates MHC-I expression on GL261 tumors and enhances the effectiveness of immunotherapy. Experimental Design: MHC-I molecule expression on GL261 cells was analyzed in vitro and in vivo by flow cytometry and immunohistochemistry, respectively. To test the response of established GL261 gliomas to treatment, mice with measurable (at CT imaging) brain tumors were randomly assigned to four groups receiving (a) no treatment, (b) WBRT in two fractions of 4 Gy, (c) vaccination with irradiated GL261 cells secreting granulocyte-macrophage colony-stimulating factor, or (d) WBRT and vaccination. Endpoints were tumor response and survival. Results: An ionizing radiation dose of 4 Gy maximally up-regulated MHC-I molecules on GL261 cells in vitro. In vivo, WBRT induced the expression of the β2-microglobulin light chain subunit of the MHC class I complex on glioma cells invading normal brain and increased CD4+ and CD8+ T cell infiltration. However, the survival advantage obtained with WBRT or vaccination alone was minimal. In contrast, WBRT in combination with vaccination increased long-term survival to 40% to 80%, compared with 0% to 10% in the other groups (P < 0.002). Surviving animals showed antitumor immunity by rejecting challenge tumors. Conclusion: Ionizing radiation can be successfully combined with peripheral vaccination for the treatment of established high-grade gliomas.

Flavopiridol downregulates hypoxia-mediated hypoxia-inducible factor-1α expression in human glioma cells by a proteasome-independent pathway: Implications for in vivo therapy

Angiogenesis is a critical step required for sustained tumor growth and tumor progression. The stimulation of endothelial cells by cytokines secreted by tumor cells such as vascular endothelial growth factor (VEGF) induces their proliferation and migration. This is a prominent feature of high-grade gliomas. The secretion of VEGF is greatly upregulated under conditions of hypoxia because of the transcription factor hypoxiainducible factor (HIF)-1alpha, which controls the expression of many genes, allowing rapid adaptation of cells to their hypoxic microenvironment. Flavopiridol, a novel cyclin-dependent kinase inhibitor, has been attributed with antiangiogenic properties in some cancer cell lines by its ability to inhibit VEGF production. Here, we show that flavopiridol treatment of human U87MG and T98G glioma cell lines decreases hypoxia-mediated HIF-1alpha expression, VEGF secretion, and tumor cell migration. These in vitro results correlate with reduced vascularity of intracranial syngeneic GL261 gliomas from animals treated with flavopiridol. In addition, we show that flavopiridol downregulates HIF-1alpha expression in the presence of a proteasome inhibitor, an agent that normally results in the accumulation and overexpression of HIF-1alpha. The potential to downregulate HIF-1alpha expression with flavopiridol treatment in combination with a proteasome inhibitor makes this an extremely attractive anticancer treatment strategy for tumors with high angiogenic activity, such as gliomas.

Flavopiridol inhibits the Growth of GL261 Gliomas In Vivo: Implications for Malignant Glioma Therapy

The mechanism of action of many chemotherapeutic agents targets the cell cycle. Recently, we demonstrated cytotoxic and other anti-tumor effects of flavopiridol, the first synthetic cyclin dependent kinase (CDK) inhibitor to enter clinical trials, on the murine GL261 glioma cell line in vitro (Newcomb et al., Cell Cycle 2003; 2:243). Given that flavopiridol has demonstrated anti-tumor activity in several human xenograft models, we wanted to evaluate it for anti-glioma activity in vivo in our established subcutaneous and intracranial GL261 experimental tumor models. In particular, the intracranial animal model recapitulates many of the histopathological and biological features of human high-grade glioma including both necrosis with pseudopalisading and invasion of the brain adjacent to tumor. Here we tested the activity of flavopiridol against tumors formed by GL261 cells, first as subcutaneous implants, and then in the intracranial model. We demonstrate efficacy of flavopiridol as a single modality treatment in delaying tumor growth in both animal models. We hypothesize that flavopiridol treatment induced tumor growth delay by two possible mechanisms involving growth arrest combined with recruitment of tumor cells to S-phase. Based on our findings, flavopiridol should be considered as a treatment approach for patients with high-grade glioma.

Noscapine induces apoptosis in human glioma cells by an apoptosis-inducing factor-dependent pathway.

Previously, we identified noscapine as a small molecule inhibitor of the hypoxia-inducible factor-1 pathway in hypoxic human glioma cells and human umbilical vein endothelial cells. Noscapine is a nontoxic ingredient in cough medicine currently used in clinical trials for patients with non-Hodgkins lymphoma or chronic lymphocytic leukemia to assess antitumor efficacy. Here, we have evaluated the sensitivity of four human glioma cell lines to noscapine-induced apoptosis. Noscapine was a potent inhibitor of proliferation and inducer of apoptosis. Induction of apoptosis was associated with activation of the c-jun N-terminal kinase signaling pathway concomitant with inactivation of the extracellular signal regulated kinase signaling pathway and phosphorylation of the antiapoptotic protein Bcl-2. Noscapine-induced apoptosis was associated with the release of mitochondrial proteins apoptosis-inducing factor (AIF) and/or cytochrome c. In some glioma cell lines, only AIF release occurred without cytochrome c release or poly (ADP-ribose) polymerase cleavage. Knock-down of AIF decreased noscapine-induced apoptosis. Our results suggest the potential importance of noscapine as a novel agent for use in patients with glioblastoma owing to its low toxicity profile and its potent anticancer activity.

Radiation Sensitivity of GL261 Murine Glioma Model and Enhanced Radiation Response by Flavopiridol

Response of a solid tumor to radiation treatment depends, in part, on the intrinsic radiosensitivity of tumor cells, the proliferation rate of tumor cells between radiation treatments and the hypoxic state of the tumor cells. A successful radiosensitizing agent would target S-phase cells and hypoxia. Recently, we demonstrated the anti-tumor effects of flavopiridol in the GL261 murine glioma model might involve 1) recruitment of tumor cells to S-phase (Newcomb et al., Cell Cycle 2004; 3:230-234) and 2) an anti-angiogenic effect on the tumor vasculature by downregulation of hypoxia-inducible factor -1? (HIF-1?) (Newcomb et al., Neuro-Oncology 2005; 7:225-235). Given that flavopiridol has demonstrated radiosensitizing activity in several murine tumor models, we tested whether it would enhance the response of GL261 tumors to radiation. In the present study, we evaluated the intrinsic radiation sensitivity of the GL261 glioma model using the tumor control/cure dose of radiation assay (TCD50). We found that a single dose of 65 Gy (CI 57.1-73.1) was required to cure 50% of the tumors locally. Using the tumor growth delay assay, fractionated radiation (5 fractions of 5 Gy over 10 days) combined with flavopiridol (5 mg/kg) given three times weekly for 3 cycles produced a significant growth delay. Our results indicate that the GL261 murine glioma model mimics the radioresistance encountered in human gliomas, and thus should prove useful in identifying promising new investigational radiosensitizers for use in the treatment of glioma patients.

The geldanamycin analogue 17-allylamino-17-demethoxygeldanamycin inhibits the growth of GL261 glioma cells in vitro and in vivo

Geldanamycin is a naturally occurring benzoquinone ansamycin product of Streptomyces geldanus that binds the protein chaperone heat shock protein 90. As geldanamycin binds to heat shock protein 90 interfering with its function and heat shock protein 90 is overexpressed in many cancers, heat shock protein 90 has become a target for cancer therapy. As the geldanamycin analogue 17-allylamino-17-demethoxygeldanamycin has a favorable toxicity profile, it is being tested extensively in clinical trials in patients with advanced cancer. In this study, GL261 glioma cells from C57BL/6 mice were used to investigate the anti-tumor effect of 17-allylamino-17-demethoxygeldanamycin both in vitro and in vivo. Heat shock protein 90 inhibitors possess potent anti-proliferative activity, usually at low nanomolar ranges, owing to their pharmacological characteristics of binding tightly to heat shock protein 90, coupled with a slow dissociation rate. We found that 17-allylamino-17-demethoxygeldanamycin at doses as low as 200 nmol/l showed anti-tumor activity within 24 h of treatment. Treatment with 17-allylamino-17-demethoxygeldanamycin arrested GL261 cells in the G2 phase of the cell cycle associated with the downregulation of cyclin B1. Low doses of 17-allylamino-17-demethoxygeldanamycin significantly inhibited migration of GL261 cells within 16 h of treatment, concomitant with the downregulation of phosphorylated focal adhesion kinase and matrix metalloproteinase 2 secretion. Using an orthotopic glioma model with well-established intracranial tumors, 3 weekly cycles of 17-allylamino-17-demethoxygeldanamycin significantly reduced tumor volumes of treated animals compared with untreated controls (P=0.002). Given these promising results, clinical testing of 17-allylamino-17-demethoxygeldanamycin or other novel heat shock protein 90 inhibitors being developed should be considered for glioma patients whose tumors remain refractory to most current treatment regimens.

Antiangiogenic Effects of Noscapine Enhance Radioresponse for GL261 Tumors

PURPOSE To assess the effects of noscapine, a tubulin-binding drug, in combination with radiation in a murine glioma model. METHODS AND MATERIALS The human T98G and murine GL261 glioma cell lines treated with noscapine, radiation, or both were assayed for clonogenic survival. Mice with established GL261 hind limb tumors were treated with noscapine, radiation, or both to evaluate the effect of noscapine on radioresponse. In a separate experiment with the same treatment groups, 7 days after radiation, tumors were resected and immunostained to measure proliferation rate, apoptosis, and angiogenic activity. RESULTS Noscapine reduced clonogenic survival without enhancement of radiosensitivity in vitro. Noscapine combined with radiation significantly increased tumor growth delay: 5, 8, 13, and 18 days for control, noscapine alone, radiation alone, and the combination treatment, respectively (p < 0.001). To assess the effect of the combination of noscapine plus radiation on the tumor vasculature, tubule formation by the murine endothelial 2H11 cells was tested. Noscapine with radiation significantly inhibited tubule formation compared with radiation alone. By immunohistochemistry, tumors treated with the combination of noscapine plus radiation showed a decrease in BrdU incorporation, an increase in apoptosis by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling, and a decrease in tumor vessel density compared with tumors treated with radiation alone. CONCLUSION Noscapine enhanced the sensitivity of GL261 glioma tumors to radiation, resulting in a significant tumor growth delay. An antiangiogenic mechanism contributed to the effect. These findings are clinically relevant, particularly in view of the mild toxicity profile of this drug.