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Malignant gliomas are highly proliferative and invasive tumors with poor prognosis. We investigated the influence of Interferon-gamma (IFN-gamma) on the human malignant glioma cell line A172, measuring cell viability (MTT-test), proliferation (3H-thymidine-uptake), cell death (FACS) adhesion to hyaluronic acid (HA, adhesion-assay) and migration (Boyden-chamber). IFN-gamma significantly decreased cell viability and proliferation. Measured by FACS, an up-regulation of CD95 expression has been shown in combination with an increased rate of cell death, first seen after 96 hours IFN-gamma treatment. Adhesion to HA was decreased after pre-treatment with IFN-gamma. This was not mediated by down-regulation of the main HA-receptor CD44, since IFN-gamma did not change CD44 expression. IFN-gamma-treated cells showed a significantly diminished migration rate through a native or HA-coated 8-microm polycarbonate membrane. To summarise, IFN-gamma influences both the main characteristics of malignancy: it decreases cell proliferation and induces cell death, further it diminishes migration of A172 human glioblastoma cells.

Valproic acid (VPA) has been considered as a possible treatment agent for malignant gliomas. In order to characterise the possibilities of VPA, we investigated the effects on cell migration and proliferation. Human cell lines T98G, A172, 85HG66 and 86HG39 were treated with VPA or left untreated, afterwards Boyden chamber assay was used for measuring vertical migration. In a second assay cells were stimulated to create spheroids and spheroid migration was measured. Proliferation was assessed using a cell counter. VPA decreased proliferation of 86HG39 > A172 > 85HG66 cells, whereas T98G remained uninfluenced. The influence of VPA on migration was different; whereas VPA dose-dependently stimulated migration of 86HG39 cells, migration of T98G and 85HG66 decreased, whereas A172 cells remained uninfluenced. Only 86HG39 and A172 cells created spheroids. In both cell lines Boyden-chamber-findings were confirmed by analysing the influence of VPA on spheroid migration. These non-uniform data demonstrate that the benefit of VPA in glioma treatment is not clear and needs further investigation.

Recently we were able to show that valproic acid (VPA) induces growth-arrest and differentiation of human neuroblastoma cells. Hence we investigated in vitro the antitumoral effects of VPA on malignant gliomas by determining cell proliferation and expression of CD56 and CD44 of human T98G, A172, 85HG66, 86HG39 and rat C6 cell lines. VPA at concentrations ranging from 0.1 to 1 mM strongly inhibited proliferation of A172, 86HG39, 85HG66 and C6 cells in a dose-dependent manner, whereas T98G cell growth remained unchanged. All human glioma cells were highly positive for CD44, whereas CD56 was differently expressed. After 7 days of incubation with 1mM VPA CD56 expression was markedly increased in T98G, A172 and 85HG66 cells, whereas CD44 expression was decreased in all human cell lines. These data suggest that VPA has antitumoral effects on malignant glioma cells. Therefore we consider VPA as a potent therapeutic agent for treatment of these tumors.

The mechanisms underlying the rapid invasive growth of malignant gliomas are poorly understood. Adhesion to extracellular hyaluronic acid (HA) has been implicated in the invasive properties of tumor cells. We investigated the HA binding capacity of human (T98G, A172, U87MG, 86HG39, 85HG66) and rat (C6, 9L) glioma cell lines by means of HA coated, bovine serum albumin (BSA)-blocked (HA/BSA) and only BSA-blocked culture plates. Results were compared with adhesion to native wells (100% adhesion). Adhesion to HA/BSA was high for T98G (84.4%), medium for 86HG39 (36%), 9L (33.1%), A172 (35.5%) and low for 85HG66 (21.3%) and U87MG (26.8%). Adhesion to only BSA-coated wells was significantly lower in all these cell lines, suggesting a specific HA-adhesion. Only C6 showed similar adhesion to HA/BSA and BSA alone, therefore, C6 failed to bind HA specifically. These results suggest that adhesion to extracellular HA might be involved in the invasion of some gliomas.

Malignant gliomas are relatively resistant to radiation and chemotherapy. To investigate whether cisplatin (cis-diamminedichloroplatinum(II), CDDP) causes resistance we pretreated C6 cells with 10(-6) M CDDP for 24 hours and then tested their sensitivity in a colorimetric assay. Pretreated cells developed resistance to CDDP (resistance factor 2.0) and radiation (survival after 9 Gy 60Co: 36.4% +/- 5.5 versus 28.6% +/- 5.2, p = 0.005). Glutathione levels of pretreated cells were higher (51.7 +/- 13.8 ng/mg protein) than in wt cells (40.4 +/- 13.2, p = 0.029). Addressing the mechanisms we established 4 wild type subclones with different CDDP sensitivities. However, cross-resistance to CDDP (survival: 60.7% +/- 3.5 versus 7.2% +/- 0.5, respectively p = < 0.001) and radiation (29.7% +/- 2.6 versus 12.9% +/- 0.8, p = < 0.001) could also be induced in a subclone showing involvement of mutation. These data suggest that CDDP can induce resistance mediated via induced mutation and increased GSH levels.

Malignant gliomas are often treated with cisplatin (cis-diamminedichloroplatinum(II), CDDP) and radiation but results remain unsatisfactory. To investigate whether CDDP induces radioresistance in glioma, T98G human glioblastoma cells were pretreated 5 times with 10(-6)M CDDP for 24 hours and then the sensitivity of wild type (wt) and pretreated cells towards radiation (9Gy 60Co) and CDDP was tested in a colorimetric assay (MIT). The growth rates of wt and pretreated cells were 1.8 +/-0.2 and 3.1 +/- 0.2 respectively (p = 0.000155) 216 hours post radiation. Pretreated cells also developed resistance to CDDP (resistance factor 2.35). Glutathione (GSH) which potentially mediates resistance to both treatments was measured. Incubation for 6 hours with 10(-5) M CDDP increased GSH levels by a factor of 2.28 (p < 0.0001). However, neither basal nor increased levels differed between wt and pretreated cells. These data show that CDDP pretreatment can induce resistance against radiation and CDDP independently of GSH.