Cell blotting and isoelectric focusing of neuroblastoma-derived heparin-binding neurotrophic activities: detection of basic fibroblast growth factor protein and mRNA

Novel agents targeting the IGF-1R/PI3K pathway impair cell proliferation and survival in subsets of medulloblastoma and neuroblastoma

The receptor tyrosine kinase (RTK)/phosphoinositide 3-kinase (PI3K) pathway is fundamental for cancer cell proliferation and is known to be frequently altered and activated in neoplasia, including embryonal tumors. Based on the high frequency of alterations, targeting components of the PI3K signaling pathway is considered to be a promising therapeutic approach for cancer treatment. Here, we have investigated the potential of targeting the axis of the insulin-like growth factor-1 receptor (IGF-1R) and PI3K signaling in two common cancers of childhood: neuroblastoma, the most common extracranial tumor in children and medulloblastoma, the most frequent malignant childhood brain tumor. By treating neuroblastoma and medulloblastoma cells with R1507, a specific humanized monoclonal antibody against the IGF-1R, we could observe cell line-specific responses and in some cases a strong decrease in cell proliferation. In contrast, targeting the PI3K p110α with the specific inhibitor PIK75 resulted in broad anti-proliferative effects in a panel of neuro- and medulloblastoma cell lines. Additionally, sensitization to commonly used chemotherapeutic agents occurred in neuroblastoma cells upon treatment with R1507 or PIK75. Furthermore, by studying the expression and phosphorylation state of IGF-1R/PI3K downstream signaling targets we found down-regulated signaling pathway activation. In addition, apoptosis occurred in embryonal tumor cells after treatment with PIK75 or R1507. Together, our studies demonstrate the potential of targeting the IGF-1R/PI3K signaling axis in embryonal tumors. Hopefully, this knowledge will contribute to the development of urgently required new targeted therapies for embryonal tumors.

Protein kinase B modulates the sensitivity of human neuroblastoma cells to insulin-like growth factor receptor inhibition

The potential of the novel insulin-like growth factor receptor (IGF-IR) inhibitor NVP-AEW541 as an antiproliferative agent in human neuroblastoma was investigated. Proliferation of a panel of neuroblastoma cell lines was inhibited by NVP-AEW541 with IC(50) values ranging from 0.15 to 5 microM. Experiments using an IGF-IR neutralizing antibody confirmed that the IGF-IR was essential to support growth of neuroblastoma cell lines. The expression levels of the IGF-IR in individual neuroblastoma cell lines did not correlate with the sensitivities to NVP-AEW541, while coexpression of the IGF-IR and the insulin receptor (IR) correlated with lower sensitivity to the inhibitor in some cell lines. Intriguingly, high levels of activation of Akt/protein kinase B (PKB) and phosphorylation of the ribosomal S6 protein were observed in neuroblastoma cell lines with decreased sensitivities to NVP-AEW541. Inhibition of Akt/PKB activity restored the sensitivity of neuroblastoma cells to the IGF-IR inhibitor. Transfection of neuroblastoma cells with activated Akt or ribosomal protein S6 kinase (S6K) decreased the sensitivity of the cells to NVP-AEW541. IGF-I-stimulated proliferation of neuroblastoma cell lines was completely blocked by NVP-AEW541, or by a combination of an inhibitor of phosphoinositide 3-kinase and rapamycin. In addition to its antiproliferative effects, NVP-AEW541 sensitized neuroblastoma cells to cisplatin-induced apoptosis. Together, our data demonstrate that NVP-AEW541 in combination with Akt/PKB inhibitors or chemotherapeutic agents may represent a novel approach to target human neuroblastoma cell proliferation.

Identification and characterization of differentiation-dependent Schwann cell surface antigens by novel monoclonal antibodies: introduction of a marker common to the non-myelin-forming phenotype

In an attempt to identify and characterize novel Schwann cell surface molecules with putative functions during development, maintenance, and regeneration of the peripheral nervous system (PNS), we have produced monoclonal antibodies against viable neonatal rat Schwann cells. Using a sensitive live cell ELISA protocol, three monoclonal antibodies reactive with cultured Schwann cells, designated 27B10, 26F2, and 27C7 were isolated. The 27B10 and 26F2 antibodies specifically labelled forskolin-stimulated secondary Schwann cells in vitro as determined by live cell ELISA implying that the expression of the antigens in situ is regulated by axonal contact. The observation that the antigens seemed to be associated with both Schwann cell phenotypes clearly discriminated them from the well characterized myelin proteins as well as from molecules known to be confined to the non-myelin-forming phenotype. Interestingly, both antigens were found to be concentrated at the nodes of Ranvier. Further studies therefore have to show whether the identified antigens share structural or functional homology with adhesion or channel molecules, which display a similar distribution. Following transection of the adult sciatic nerve, the 26F2 antigen was rapidly down-regulated in the distal nerve stump. The 27C7 antibody reacted with an 80 kDa cell surface molecule common to non-myelin-forming Schwann cells. No differences in expression of the antigen between forskolin-treated and untreated Schwann cells in vitro were found, suggesting that the antigen is expressed independently from axonal contact. Two weeks after nerve transection in the absence of myelinating Schwann cells, the antigen was associated with S-100-positive Schwann cells of the distal nerve stump. The antigen was found to be expressed also by non-neuronal tissues, the level of the protein declined towards the adult stage. Comparison of the 27C7 antigen with previously described marker molecules suggests that we have identified a novel Schwann cell surface antigen of the non-myelin-forming phenotype.

An improved cell-ELISA for the differential screening of antibodies against cell surface molecules of viable adherent Schwann cells

In this report we describe a highly sensitive large-scale screening assay that uses viable adherent cells. The newly developed test design combines the advantages of live cell immunocytochemistry with the versatility of a conventional ELISA technique. Culturing of target cells as well as incubation with antibodies is done in the same microtiter plate. No processing of cells prior to incubation with the antibodies, such as fixation or enzymatic detachment of the cells, is performed. This eliminates possible factors that might interfere with antibody-antigen recognition and results in a dramatically increased sensitivity that is comparable to cell-free ELISA procedures with an assay detection limit reproducibly between 0.004 and 0.002 micrograms/ml. Furthermore, this test design is convenient for the rapid identification of antibodies against differentiation-dependent antigens. Incubation in parallel with the same antibody of different cell types (forskolin-stimulated Schwann cells or fibroblasts) or cells grown under different conditions (forskolin-stimulated and non-stimulated Schwann cells) facilitates the selection of antibodies displaying genotypic or phenotypic specificity. Since culture of target cells and the detection of antibodies is done on one microtiter plate, it is not only possible to detect cell surface molecules but also secreted molecules that remain bound to the cell surface or the culture substrate. Compared to other previously introduced cell-ELISAs, our protocol offers the following advantages: (i) increased sensitivity, (ii) convenience for large-scale screening, (iii) optimal identification of antibodies reacting with native molecules, and (iv) identification of differentiation-dependent antigens. Since this assay could also be used in studies examining the regulation of cell surface molecules at a semiquantitative level it may be of general relevance.

Immunocytochemical localization of the heparin-binding growth-associated molecule (HB-GAM) in the developing and adult rat cerebellar cortex

The heparin-binding, growth-associated molecule (HB-GAM) is a developmentally regulated protein that belongs to a new family of heparin-binding molecules, not related to the fibroblast growth factors (FGFs), with putative functions during cell growth and differentiation. In order to further study the functional role of HB-GAM we have used a polyclonal antiserum, raised against the purified protein to localize HB-GAM in the developing and adult rat cerebellar cortex. During postnatal development HB-GAM-like immunoreactivity (IR) was found to be present in all layers of the cerebellar cortex. IR was mainly associated with processes or extracellular structures but not with cell bodies. Throughout all the stages examined the molecular layer was clearly labeled, whereas staining in the internal granular layer was diffuse. IR in the external granular layer on postnatal day 1 and 8 was found to be associated with radially oriented fibres connecting the internal granular layer with the pial surface of the cerebellum. The intensity of this staining seemed to increase from day 1 to 8. Staining of corresponding areas with an antiserum against the glial fibrillary acidic protein (GFAP) suggested that the HB-GAM antiserum in the developing cerebellar cortex labels Bergmann glia fibres of Golgi epithelial cells. Because of the diffuse staining of the molecular layer in the adult rat it was not possible to distinguish whether radial fibres in the adult contained any HB-GAM IR. Golgi epithelial cells are considered as crucial for the migration of granular cells during the differentiation of the cerebellar cortex. We therefore speculate that the association of HB-GAM-like IR may be of functional relevance. The fact that molecules, such as tenascin, known to be involved in morphogenetic events show a similar spatiotemporal distribution pattern further underscores this hypothesis. HB-GAM, which possesses a classical signal sequence, might be release in the extracellular space and could mediate adhesion phenomena by binding to heparin-like molecules associated with the neuronal membrane. Therefore, it will be important to investigate whether specific antibodies against HB-GAM are able to interfere with normal cerebellar development in vitro and in vivo.

Heterogeneity of human neuroblastoma cell lines in their proliferative responses to basic FGF, NGF, and EGF: correlation with expression of growth factors and growth factor receptors

Growth factors can induce both proliferation or differentiation of neuroblastoma (NB) cells through interaction with specific receptors. Using two automated colorimetric assays for determinations of cell numbers, the present study demonstrates that a) different NB and neuroepithelioma cell lines show distinct responses, both qualitatively and quantitatively, to basic FGF (bFGF), NGF, and EGF; b) even closely related NB cell lines (e.g., SK-N-SH, SH-SY5Y, and SHEP) do not respond uniformly to these factors; c) responses of the two neuroepithelioma cell lines employed (SK-N-MC and CHP-100) differ, but match those of certain NB cell lines; and d) two growth factors, bFGF and EGF, may both stimulate or inhibit proliferation, depending on the cell line studied. Specifically, IMR-32, SK-N-SH, and SH-SY5Y showed a mitogenic response to each growth factor. Maximal proliferative responses ranged from 204-355% as compared to controls (100%). GICAN was stimulated by NGF (199%), and SK-N-MC and NMB by EGF (282 and 140%, respectively), but other factors were ineffective. CHP-100 and GIMEN were inhibited by bFGF. NGF and EGF were not effective on CHP-100 cells, while EGF caused an arrest of mitogenic activity in GIMEN cells, and NGF stimulated their proliferation. Cell lines SHEP and LAN1 did not respond to any factor. To begin to analyze putative relationships of growth factor responsiveness and growth factor/growth factor receptor expressions, IMR-32, GIMEN, and LAN1 cell lines were studied for the presence of bFGF, NGF, FGF receptors (R)-1 (flg) and FGFR-4, trk, and low-affinity NGF receptor (p75) mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

Establishment of a single-step hybridoma cloning protocol using an automated cell transfer system: comparison with limiting dilution

An easy-to-standardize single-step protocol of hybridoma cloning has been established using a recently introduced, commercially available cell transfer system. By controlling the volume of air within a sealed glass micropipette by means of a Peltier device, single cells are gently collected or ejected. The transfer of cells from a source dish to the wells of a target microplate is controlled by a microprocessor. Since collection as well as expulsion of cells is done under microscopic control seeding of single cells can be guaranteed. Monoclonality is therefore reproducibly achieved in a single step, reducing the time required for cloning enormously, and conserving man-power and material. Since the automated transfer of cells is time-saving and easy-to-standardize, it substantially facilitates cloning of hybridoma. The present protocol therefore represents an alternative to limiting-dilution cloning as well as to other previously introduced techniques of single-cell cloning. It is easily adapted to a wide spectrum of other cell types and can therefore be used in many other applications involving single cell manipulation.

Fibroblast growth factors: structure-activity on dopamine neurons in vitro

We investigated the effect of neurotrophic factors on dopamine (DA) cells in vitro. At concentrations of nanograms/c.c. basic fibroblast growth factor (bFGF) is a more potent DA-trophic agent than brain derived neurotrophic factor (BDNF) or epidermal growth factor (EGF) in fetal mid brain neurons. In these cells, bFGF produces a greater increase of DA levels and percentage of cells positive for tyrosine hydroxylase (TH+) than BDNF and EGF. Acidic fibroblast growth factor (aFGF) was not tested in fetal DA cells since aFGF requires heparin for its effect and fetal mid brain cultures do not grow well in the presence of a high concentration of heparin. We further investigated the effect of bFGF and aFGF, and two of their analogs, in catecholamine rich human neuroblastoma cells NB69. In these cells aFGF, at concentrations of picograms/c.c., increases DA levels, while its analogs, E118 and super short, have no effect. Acidic FGF also increases norepinephrine levels, the number of TH+ cells, and the percentage of TH+ with respect to the total number of nuclei. Basic fibroblast growth factor (bFGF) produced similar, but less potent effects. Acidic FGF was active only in the presence of heparin; the effect of bFGF was independent of heparin. FGFs are promising drugs for the treatment of PD, though further investigations with these compounds should be performed before their use in clinical trials.

Interleukin-1 beta and interferon gamma interact with fibroblast growth factor-2 in the control of neuroblastoma cell proliferation and differentiation

Based on our previous observations that neuroblastoma (NB) cells express fibroblast growth factor-2 (FGF-2; basic FGF) and respond to it [Janet T. et al. (submitted); Wewetzer K. et al. (1993) J. Neurosci. Res. 36, 209-215), we attempted to find to what extent selected cytokines [interleukin (IL)-1 beta and interferon gamma (IFN gamma)] may modulate FGF-mediated proliferative activity and differentiation. The NB cell lines IMR-32, SH-SY5Y, GIMEN and LAN-1 and colorimetric assays were used for the determination of cell numbers. IL-1 beta (and several other ILs, including IL-1 alpha, -2, -3, and 6) per se did not affect proliferation of any cell line studied. IFN gamma inhibited growth of GIMEN and LAN-1 cells, but was uneffective on IMR-32 and SH-SY5Y cells. FGF-2 was antimitogenic for GIMEN cells. IFN gamma reversed and IL-1 beta enhanced this antimitogenic effect of FGF-2. FGF-2 per se did not affect LAN-1 cells and did not modulate the growth inhibitory actions of IFN gamma on these cells. FGF-2 induced proliferation of IMR-32 and SH-SY5Y cells. This effect was not modulated by IFN gamma or IL-1 beta. These results suggest a heterogeneous response pattern of human NB cell lines towards the cytokines studied and complex interactions of FGF-2, IL-1 beta and IFN gamma.