Characterization and chemosensitivity of two cell lines derived from human glioblastomas

In vivo magnetic resonance imaging of sodium and diffusion in rat glioma at 21.1 T

Sodium and diffusion magnetic resonance imaging (MRI) in intracranial rat 9L gliomas were evaluated over 6-8 days using the advanced sensitivity of sodium MRI at 21.1 T. Glioma doubling time was 2.4-2.6 days. Glioma sodium signal was detected using the ultra-short echo time of 0.15 ms. The high resolution 3D sodium MRI with pixels of 0.125 μL allowed for minimizing a partial volume effect often relevant to the MRI of low intensity signals. Tumor sodium and diffusion MRI were evaluated for two separate subclones of 9L cells with different resistance to 1,3-bis(2-chloroethyl)-1-nitrosurea detected by pre-surgery assays. In vivo, after implantation, resistant 9L cells created tumors with significantly reduced sodium concentrations (57 ± 3 mM) compared with nonresistant 9L cells (78 ± 3 mM). The corresponding differences in diffusion were less, but also statistically significant. During tumor progression, an increase of glioma sodium concentration was observed in both cell types with a rate of 2.4-5.8 %/day relative to normal brain. Tumor diffusion was not significantly changed at this time, indicative of no alterations in glioma cellularity. Thus, changes in sodium during tumor progression reflect increasing intracellular sodium concentration and mounting metabolic stress. These experiments also demonstrate an enhanced sensitivity of sodium MRI to reflect tumor cell resistance.

Changes in the immunologic phenotype of human malignant glioma cells after passaging in vitro

Although immunotherapeutic strategies against glioblastomas have been promising both in vitro and in animal models, similar successes have not been realized in human clinical trials. One reason may be that immunotherapeutic strategies are based on prior studies that primarily have used human glioblastoma cell lines passaged in vitro, which may not accurately reflect the in vivo properties of glioblastoma cells. In this report, we used flow cytometry to quantify the expression of immunological cell surface molecules on human glioblastomas directly ex vivo (prior to any in vitro culturing) and after varying passages in vitro. Furthermore, we used ELISA to quantitate cytokine secretion after various passages in vitro. We demonstrate that in vitro culturing of established cell lines led to increases in the cell surface expression of MHC class I and ICAM-1 and secretion of IL-6 and TGF-beta(2). Furthermore, there were significant changes in the expression of MHC class I, MHC class II, B7-2, ICAM-1, and FasL when comparing ex vivo tumor cells to those after a single passage in vitro. After passaging once in vitro, there were also significant changes in the secretion of TGF-beta(2) and IL-10. This report indicates that in vitro culturing leads to significant changes in both cell surface molecules and secreted cytokines, which are known to affect the ability of immune cells to initiate an anti-tumor immune response. These changes in the immunological phenotype of glioblastomas after in vitro culturing may in part explain the limited success of immunotherapeutic strategies against glioblastomas in human clinical trials.

Anticancer drug resistance in primary human brain tumors

The difficult clinical situation still associated with most types of primary human brain tumors has fostered significant interest in defining novel therapeutic modalities for this heterogeneous group of neoplasms. Beginning in the 1980s chemotherapy has been incorporated into the treatment protocol of a number of intractable brain tumors. However, it has predominantly failed to improve patient outcome. The unsatisfactory results with chemotherapeutic intervention have chiefly been attributed to tumor cell resistance. In recent years, there has been a literal explosion in our understanding about the mechanisms by which cancer cells become chemoresistant. During the course of their evolution (intrinsic resistance) or in response to chemotherapy (acquired resistance) these cells may follow a number of pathways of genetic alterations to possess a common (multidrug) or drug-specific (individual drug) resistant phenotype. Genomic aberrations, deregulation of membrane transporting proteins and cellular enzymes, and an altered susceptibility to commit to apoptosis are among the steps on the way that contribute to the genesis of chemotherapeutic treatment failure. Although, through the years we have come to yield information and inferences as to the roles that different molecular events may have in the resistance phenotype of cancer cells, the actual involvement of single genetic alterations in conferring drug resistance in primary brain tumors remains debatable. This uncertainty and, besides, the lack of proper drug resistance diagnostics, in a vicious circle, hinder the development of effective resistance-modulation strategies. Clinical non-responsiveness to chemotherapy remains a formidable obstacle to the successful treatment of brain tumors and one of the most serious problems to be solved in the therapy of these lesions. Future advances in the chemotherapeutic management of these neoplasms will come with an improved understanding of the significance and interrelationship of the multiple biological systems operative in promoting resistance to this treatment modality. The focus of this review is to summarize current knowledge concerning major drug resistance-related markers, to describe their functional interaction en route to chemoresistance, and to discuss their implication in rendering human brain tumor cells resistant to chemotherapy.

Drug resistance-associated factors in primary and secondary glioblastomas and their precursor tumors

Malignant gliomas are largely resistant to current chemotherapeutic strategies often displaying a multidrug-resistant phenotype. Mechanisms involved in drug resistance are reduced cellular drug accumulation through membrane efflux pumps, drug detoxification as well as alterations in drug target specificity. In 27 primary and 17 secondary glioblastomas and their astrocytic precursor tumors, we studied the immunohistochemical expression profile of P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), lung resistance-related protein (LRP), metallothionein, and topoisomerase II alpha. Glial tumor cells in all glioblastomas showed constant up-regulation of LRP, MRP, and topoisomerase II alpha. P-gp was found in 90% of the primary and 60% of the secondary glioblastomas. In precursor tumors, these drug resistance-related factors were expressed in varying proportions. Metallothionein, also found in normal and activated astrocytes, was retained in all neoplastic phenotypes. Furthermore, metallothionein, P-gp, LRP, and topoisomerase II alpha were strongly expressed by normal and neoplastic vessels which may confer to impaired penetration of therapeutic agents through the blood-brain and blood-tumor barrier. However, the expression profiles of drug resistance-related proteins neither differed between primary and secondary glioblastomas nor revealed any correlation to precursor or recurrent tumors. Nevertheless, inhibition of these factors may be promising approaches to the management of malignant gliomas.

Ex vivo malignant glioma cells are sensitive to Fas (CD95/APO-1) ligand-mediated apoptosis

Fas (also known as CD95/APO-1) is a cell surface receptor and member of the tumor necrosis factor receptor superfamily which mediates apoptosis in sensitive cells upon oligomerization by specific antibodies or by its ligand (FasL). Recently, human glioma cell lines were found to be susceptible to Fas-mediated apoptosis triggered by alpha-Fas antibodies. However, whether the Fas system can also be targeted in ex vivo high grade gliomas is at present unknown. In the present investigation, alpha-Fas antibodies and FasL were tested in short-term monolayer cultures or in colony forming assays established from freshly resected tumors of patients with anaplastic astrocytomas (WHO grade III) and glioblastoma multiforme (WHO grade IV). Anti-Fas antibodies induced only moderate apoptosis in four of the 19 tested glioma cell cultures. This contrasts FasL which induced apoptosis in all of the 19 tumor cell cultures analyzed. Mean cytotoxicity of glioma cell cultures treated for 48 h with alpha-Fas antibodies or FasL was 9.6% and 44.3%, respectively. Irrespective of whether alpha-Fas antibodies or FasL were used, pretreatment with recombinant hu (rhu) IFN-gamma and rhuTNF-alpha for 48 h did not sensitize glioma cells to Fas-mediated cytotoxicity. The long-term effect by FasL on tumor colony formation was more striking. FasL treatment resulted in more than 90% inhibition of clonal tumor cell growth of all the eight high grade gliomas analyzed. These results suggest that Fas targeting by FasL but not by alpha-Fas antibodies may provide a promising approach for locoregional glioma treatment.