Tumor VX-702 growth in nude mice bearing a human GBM xenograft. Significantly ISA27 was non-toxic both in vitro in a normal human cell model and in vivo in a mouse model. The direct and specific activation of the p53 pathway without inducing collateral DNA damage offers a tantalising solution to the shortcomings of current therapeutic regimens and appears to be a reasonable approach for GBM therapy in view of the infrequent occurrence of p53 gene mutations. The cumulative evidence of aberrantly increased activity of the primary p53 inhibitor MDM2 in GBM prompted us to examine the effects of targeted inhibition of the MDM2-p53 interaction by the spiro-oxindole analogue ISA27, a recently described smallmolecule inhibitor of MDM2. Little is known about the effects of MDM2 inhibitors on the in vitro growth of GBM cells. Recently, Nutlin-3, the first potent small-molecule inhibitor of MDM2, was reported to be effective at inhibiting GBM cell growth in vitro, suggesting the validity of this experimental approach for the treatment of GBM. In this study, we investigated whether ISA27 affected the growth of GBM cells and explored the intracellular events following ISA27 treatment. The U87MG and U343MG cell lines overexpress MDM2 and maintain wild-type p53 and were chosen as a cell culture model of human GBM. In these cell lines, the primary mechanism of p53 inactivation is the high nuclear MDM2 levels caused by a lack of PTEN, a tumor suppressor protein that normally counteracts MDM2 translocation into the nucleus. The lack of PTEN makes these cell lines a suitable representative model of GBM, as the loss of the PTEN gene locus has been found in up to 80 of GBM cases. This is the first report to MK-8245 demonstrate that ISA27 is a potent inhibitor of GBM cell growth. Previous studies have shown that ISA27 activates p53, resulting in growth inhibition in HEK-293 transformed human embryonic kidney, M14 human melanoma and U937 human monocyte lymphoma cell lines. Our results demonstrate that ISA27 blocks the cell cycle and triggers an apoptotic cell death program in the GBM cells, responses that are similar to those obtained in human M14 melanoma cells. We observed a dose-dependent antiproliferative effect of ISA27 in U87MG and U343 cells following short-term treatments with incre
