Cancer research
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We have examined whether inhibition of phosphatidylinositol-3 kinase (PI3K) and its target, the serine/threonine kinase Akt, play a role in the antitumor effect of the HER2 antibody Herceptin. Herceptin inhibited colony formation, down-regulated cyclin D1, and increased p27 protein levels in the HER2 gene-amplified BT-474 and SKBR-3 human breast cancer cells. These effects were temporally associated with the inhibition of PI3K activity in vitro as well as Akt function as measured by steady-state levels of phospho-Ser473 Akt and kinase activity against glycogen synthase kinase (GSK)-3beta. ⋯ Transduction of BT-474 cells with an adenovirus-encoding active (myristoylated) Akt (Myr-Akt), but not with a beta-galactosidase control adenovirus, prevented the Herceptin- or LY294002-induced down-regulation of cyclin D1 and of phosphorylated GSK-3beta and prevented the accumulation of p27 in the nucleus and cytosol. In addition, Myr-Akt prevented Herceptin-induced inhibition of the cell proliferation of BT-474 cells and Herceptin-induced apoptosis of SKBR-3 cells. These data suggest that (a) changes in cell cycle- and apoptosis-regulatory molecules after HER2 blockade with Herceptin result, at least in part, from the inhibition of Akt; and (b) disabling PI3K and Akt is required for the antitumor effect of HER2 inhibitors.
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Glioblastoma multiforme, the most common form of malignant brain tumor,is resistant to all forms of therapy and causes death within 9-12 months of diagnosis. Glioblastomas are known to contain numerous genetic and physiological alterations affecting cell survival and proliferation; one of the most common alterations being platelet-derived growth factor (PDGF) autocrine signaling characterized by coexpression of PDGF and its receptor. The PDGF family consists of four members, PDGF-A, -B, -C, and -D, that signal through the alpha and beta PDGF receptor (PDGFR) tyrosine kinases. ⋯ This study of glioblastoma cells and primary tissues is the first to implicate PDGF-C and -D in brain tumor formation and confirms the existence of autocrine signaling by PDGF-A and -B. More importantly, treatment with the PDGFR antagonist CT52923 inhibited survival and/or mitogenic pathways in all of the glioblastoma cell lines tested and prevented glioma formation in a nude mouse xenograft model. Together these findings demonstrate the potential therapeutic utility of this class of compounds for the treatment of glioblastoma.