We seek to determine whether Indirubins (IRs), a class of chemicals with relative selective inhibitory activity against glycogen synthase kinase-3 (GSK-3), exhibit activity against malignant gliomas. These tumors remain amongst the most formidable cancers to treat, particularly due to their propensity to invade and infiltrate into normal brain. Based on data showing reduced glioma motility in vitro using lithium, a GSK-3 inhibitor that is FDA-approved for the treatment of bipolar disorders, we have initiated a bi-institutional phase 2 clinical trial, where lithium is added to standard cytotoxic therapy in patiets with newly diagnosed malignant glioma, to determine whether it will reduce glioma invasion. However, lithium has a narrow therapeutic index and its inhibitory activity for GSK-3 is not as specific. We thus have screened other GSK-3 inhibitors and discovered that the IRs are more potent than lithium and appear to be well tolerated in mice models of gliomas. Our pilot data shows that IRs a- inhibit glycogen synthase kinase- 3 (GSK-3) activity more potently than lithium; b- lead to the translocation of β-catenin from the membrane to the nucleus; c- change the expression of several β-catenin responsive genes related to cell-cell adhesion and invasion, including claudin-1, d-significantly reduce invasion of glioma cells both in vitro and invivo; e- reduce the number of microvessels in gliomas; and f- reduce endothelial motility, at least in vitro. IR treatment significantly increases the survival of animals with orthotopic glioma and reduces the volume of ectopic flank gliomas. We thus propose to further study IRs in order to provide preclinical data related to their efficacy and toxicity and to understand their mechanism of action in glioma initiating cells (GICs) rather than cell lines. Our overall hypothesis is that IRs represent a novel class of agents with anti-invasive action for both the tumor and endothelial stromal components of the gliomas. We thus propose to: Aim 1-Determine whether the combination of IRs and cytotoxic agents/radiation leads to a significant anticancer effect in glioma models; Aim 2- Test IR's mode of action, as it relates to a GSK-3/β-catenin/claudin-1 signaling pathway, in a panel of glioma initiating cells (GICs); and Aim 3- Determine the cellular and biologic mechanisms responsible for IR-mediated reduction of glioma microvessel density and their physiological effects.