Phenylacetylglutaminate (PG) and Phenylacetate (PN) are metabolites of Phenylbutyrate (PB) and are constituents of antineoplaston AS2-1. These are sodium salts of amino acid derivative and carboxylic acid that inhibit the growth of neoplastic cells without growth inhibitory effect in normal cells. The aim of this study was to identify molecular pathways involved in the anti-proliferative effect of antineoplastons. Using a total human genome microarray we have found that 1) Vitamin D3 upregulated protein (VDUP1) is significantly upregulated in response to PG and PN in the U87 glioblastoma cells; 2) Isobologram analysis shows that PG and PN act in an additive or synergistic manner to effectively suppress proliferation of U87 cells; 3) PG and PN cause cell cycle arrest, changes in expression of several cell cycle genes and suppress expression and activity of the G2/M checkpoint kinase, CHK1. The multiple cellular targets possibly make these compounds effective anti-proliferative agents. We propose that PG and PN in combination target important cellular pathways and upregulate VDUP1 leading to detachment-induced apoptosis in cancer cells.
Integrins have become a target for novel therapeutic strategies against malignant gliomas. Cilengitide, a synthetic Arg-Gly-Asp (RGD)-motif peptide, interferes with ligand binding to avb3 and avb5 integrins and is currently investigated in clinical trials. Integrins may also be involved in the activation of transforming growth factor (TGF)-b, a mediator of invasiveness and immune escape of glioma cells. Using flow cytometry, we demonstrate that the target integrins of cilengitide are expressed not only in glioblastoma blood vessels, but also by tumor cells. After exposure of glioma cells to cilengitide, we noticed reduced phosphorylation of Smad2 in most glioma cell lines, including stem-like glioma cells. Phophorylation of Smad2, but not cilengitide-induced detachment, is rescued by addition of recombinant TGF-b. Administration of cilengitide to glioma cells results in reduced TGF-b-mediated reporter gene activity. Furthermore, exposure to cilengitide leads to decreased TGF-b 1 and TGF-b 2 mRNA and protein expression. These effects are mimicked by blocking av, b3 or b5 antibodies or by silencing of integrins av, b3, b5 or b8 using RNA interference. Treatment of mice bearing experimental LN-308 glioma xenografts with cilengitide results in reduced pSmad2 levels. Taken together, cilengitide may exert anti-invasive and immune stimulatory activity in human glioblastoma patients by its anti-TGF-b properties.
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