Three-dimensional growth of glial cell lines affects growth factor and growth factor receptor mRNA levels

Beta-glucan enhanced killing of renal cell carcinoma micrometastases by monoclonal antibody G250 directed complement activation

Metastases from renal cell carcinomas (RCC) are resistant to radiation and chemotherapy but are relatively immunogenic. We have investigated the possibility to eliminate human RCC micrometastases using MAb G250. G250 penetrates human micrometastases completely in a spheroid model and induces complement deposition rapidly on the outmost cell layers. However, complement dependent cytotoxicity (CDC) was barely detected using either (51)chromium release assays or confocal microscopy, due to relatively low expression of the G250 antigen and the effect of membrane bound complement regulatory proteins. Addition of blocking anti-CD59 MAbs enhanced formation of C5b-9 and consequently complement mediated lysis (13%). Complement assisted cellular cytotoxicity (CACC) was not detectable, although the iC3b ligand and CR3 receptor were present on respectively target and effector cells. Addition of soluble beta-glucan induced the killing of MAb and iC3b opsonized spheroids by effector cells (6-21%). Despite a lower affinity for G250 antigen, a bispecific anti-G250*anti-CD55 MAb enhanced cell killing in spheroids comparable to the parental G250 MAb. Our results suggest that complement-activating G250 in combination with anti-mCRP MAbs is able to kill human RCC cells in micrometastasis in vitro. For CACC the presence of CR3-priming beta-glucan seems to be obligatory. In vivo, bi-MAb may be more effective as therapeutic agent due to its increased C5a generating properties.

The development of necrosis and apoptosis in glioma: experimental findings using spheroid culture systems

Cell death in gliomas may occur either by apoptosis, or, in the case of high grade tumours, by necrosis, but questions remain as to the pathogenesis and relationship between these processes. The development of cell death was investigated in multicellular glioma spheroid cultures. Spheroids model the development of cell death due to diffusion gradients in a three-dimensional system without confounding influences of immune response, pressure gradients, etc. Spheroid cultures were established from four malignant glioma cell lines: U87, U373, MOG-G-CCM and A172; harvested from culture at weekly intervals and stained with Haematoxylin and Eosin (H&E), TdT-mediated dUTP-X nick end labelling (TUNEL) and by immunohistochemistry for vimentin, Glial Fibrillary Acidic Protein (GFAP) and Ki67. Annexin V flow cytometry and counts of apoptotic cells on H & E stained sections were performed to assess levels of apoptosis. Modes of cell death were also characterized by electron microscopy. Spatially separate zones of proliferation, differentiation and central cell death developed with increasing spheroid diameter. Central cell death developed at a predictable radius (300-400 microm) for each cell line. Ultrastructural examination showed this to be necrotic in type. Apoptosis was most reliably assayed by morphological counts using H & E. Basal levels of apoptosis were low (< 0.5%), but increased with increasing spheroid diameter (> 2% in U87). In particular, levels of apoptosis rose following development of central necrosis and apoptoses were most abundant in the peri-necrotic zone. There were quantitative differences in the levels of apoptosis and necrosis between glioma cell lines. The predictable onset of necrosis in the spheroids will allow us to investigate the pathogenesis of necrosis and events in prenecrotic cells. There is a relationship between the development of necrosis and apoptosis in this model and these processes can be separately assayed. Further in vitro and genetic studies will enable us to study these events and interactions in greater detail than is possible using other cell culture and in vivo systems.

Central role of epidermal growth factor (EGF) receptor density in anchorage-independent growth of normal rat kidney cells

Epidermal growth factor (EGF) receptor levels are known to play a central role in density dependent growth regulation of normal rat kidney (NRK) fibroblasts. Here we show that EGF receptor expression is strongly decreased when NRK cells are cultured under anchorage independent conditions, and that expression is returned to original levels upon cell readherence. Agents that stimulate anchorage independent growth (AIG) of NRK cells in the presence of EGF are shown to upregulate both EGF receptor promoter activity and (125)I-EGF binding capacity. These data show that two aspects of phenotypic transformation of NRK cells, namely density arrest and AIG, can both directly be correlated to EGF receptor levels.

Insulin-like growth factors (IGF) enhance three-dimensional (3D) growth of human glioblastomas

Human glioblastomas (gliomas) are characterized as rapidly growing brain tumors which are highly invasive but rarely metastatic. Human gliomas synthesize and secrete increased levels of insulin-like growth factors (IGFs) as well as expressing increased numbers of IGF receptors when compared to normal brain tissue. These observations suggest the existence of an IGF-mediated autocrine mechanism for glioma growth regulation. The purpose of this study was to examine the effect of human recombinant IGF (hrIGF) treatment on the in vitro growth of human glioma monolayer and three-dimensional (3D) multicellular spheroid cultures. The data demonstrate that hrIGF-I treatment of glioma cell lines slightly enhanced tumor monolayer proliferation as measured by [(3)H]thymidine incorporation. In contrast, treatment of glioma spheroids with hrIGF-I or hrDes(1-3)IGF-I, the truncated brain form of IGF-I, dramatically enhanced 3D tumor growth with a 1.5-2-fold reduction in spheroid doubling time (FRSDT). In addition, IGF-treated glioma spheroids were more densely packed than spheroids grown in media alone with no observed necrosis. These data suggest that IGFs will dramatically enhance glioma proliferation when 3D cell-cell contact occurs. This observed enhancement suggests that IGFs both synthesized in the brain and systemically support rapid proliferation of gliomas in vivo.

Resistance of ovarian teratocarcinoma cell spheroids to complement-mediated lysis

We have shown previously that it is possible to target complement-mediated killing against cultured ovarian tumour cells in vitro. As malignant ovarian cells usually grow in solid nodules in vivo, we have in the present study examined the effectiveness of complement killing against ovarian teratocarcinoma cells (PA-1) growing in three-dimensional tumour microspheroids (TMSs). Our study shows that PA-1 cells growing in TMSs are less susceptible to complement-mediated killing than cells growing in monolayer cultures, even after neutralization of protectin (CD59), the main inhibitor of complement lysis. Cells in suspension and cells growing in TMSs showed a similar expression of membrane co-factor protein (MCP, CD46) and CD59. Decay-accelerating factor (DAF, CD55) was not detected on the surface of cells in suspension, but appeared focally on the outermost cell layers of the TMSs. Complement-activating antibodies bound to all PA-1 cells in suspension but only to the most peripherally located cells in TMSs, even though the target antigens were similarly expressed in the two systems. Antibody-induced complement activation on PA-1 cells in suspension led to C3 and C5b-9 deposition on most cells, while C3 and C5b-9 were only found on the outermost layers of the TMSs. The increased complement resistance of tumour cells growing in three-dimensional spheroids is partly because of an insufficient penetration of antibodies and complement into the TMSs. TMSs are a useful model for the development of more efficient ways to kill malignant cells in micrometastases with monoclonal antibodies and complement.

Expression of platelet-derived growth factor (PDGF) receptor alpha-subunit in mouse brain: comparison of Patch mutants and normal littermates

1. Platelet-derived growth factor (PDGF) plays an important role not only in mesenchyme-derived tissues, but also in the mammalian central nervous system. The Patch mutant (Ph/+) lacks one copy of the PDGFR-alpha gene. However, it is not clear whether there are differences in expression of PDGF receptor alpha-subunit (PDGFR-alpha) in brain tissue of the Patch heterozygous (Ph/+) mutants compared to wild-type C57Bl (+/+) mice. 2. The level of PDGRF-alpha mRNA expression is slightly lower in Patch mutant than in normal littermate. 3. Protein and total RNA isolated from mouse brain tissue and primary type 1 astrocyte cultures were studied with Western and Northern blotting techniques. There was no measurable difference ir PDGFR-alpha protein expression between the Patch and wild-type mouse nervous system. Adjustment of transcriptional efficiency and messenger stability may contribute to this phenomenon, whose biological significance remains unclear. 4. Further, the expression of PDGRF-alpha protein and message in mouse brain tissues is developmentally regulated. Its level remains high during the embryonic period and declines below measurable levels in adult.

Effects of 1,25-dihydroxyvitamin D3 on transformed C3H/10T1/2 fibroblasts grown as multicellular spheroids

We have previously shown that 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) is able to modulate proliferation of C3H/10T1/2 fibroblasts grown in monolayer cell culture. The aim of this study was to investigate the effects of the hormone in a 3-dimensional culture system, which is considered to better reflect the cellular environment that is found in vivo. Two transformed cell lines of C3H/10T1/2 fibroblasts (C116 and TPA 482) were grown as multicellular spheroids, whereas the nontumorigenic C3H/10T1/2 C18 cells failed to form spheroids. The hormone had no effect on spheroids made of TPA 482 cells but had a biphasic effect on C116 spheroid growth with stimulation at low and inhibition at higher concentrations. In C116 spheroids, 10(-8) M 1,25-(OH)2D3 induced complete arrest of spheroid growth. Light and electron microscopic studies and immunocytochemistry showed that 10(-8) M 1,25-(OH)2D3 induced morphological changes in C116 spheroids, with a marked reduction in expression of fibronectin, laminin and the gap junction protein connexin 43. These effects were followed by a loosening of the spheroid structure, detachment of viable cells, and finally disaggregation of the spheroids. The results of this study, together with the data previously obtained in monolayer cell cultures, indicate that the effects of 1,25-(OH)2D3 may be conditioned by the cellular environment. Therefore, the spheroid model is an interesting tool for investigation of the antineoplastic effect of the hormone.