THERANOSTICS FOR PEDIATRIC BRAIN CANCER Glioblastoma (GBM) is the most frequently diagnosed primary malignant brain tumor in children with median survival of less than one year. Disease recurrence is common and is caused by the presence of glioma-initiating cells (GICs) that are unreceptive to conventional therapies, underscoring the urgent need for new therapeutic options. We aim to develop a novel strategy to specifically disrupt the lifeline of GICs, without causing toxic effects to the normal brain. The highly vascularized nature of GBMs and the critical function of the perivascular niche for nutritional supply of GICs have spurred much interest in novel vascular-disruptive agents (VDAs). Intravenously administered VDAs easily reach GBM vessels and do not rely on the enhanced permeability and retention effect, which can limit the delivery of macromolecules to the tumor tissue. VDA-mediated blood vessel disruption causes efficient drug delivery to the GIC niche and starvation of many tumor cells. In contrast to classical anti-angiogenesis drugs, VDAs not only disrupt the tumor vasculature, but also cause significant GIC apoptosis through direct cytotoxic effects. While being highly effective for cancer treatment, initial VDA formulations also caused significant toxicity to the normal brain. This is particularly concerning for children, as the developing brain is more vulnerable to toxic side effects compared to the adult brain. To solve this problem, we developed novel VDA-loaded theranostic (combined therapeutic and diagnostic) nanoparticles, which are specifically activated in brain tumors by matrix metalloproteinases 14 (MMP-14). The normal brain does not express MMP-14 and therefore, does not activate the theranostic drug, thereby creating highly effective cancer therapy without side effects. The major goal of our project is to develop MMP-14-activatable theranostic nanoparticles (TNPs) for curative treatment of GBM, without causing toxicity to the normal brain. The approach relies on the high prevalence of MMP-14 in GBM, a proven MMP-14-activatable prodrug strategy, and a nanocarrier platform based on FDA-approved iron oxide nanoparticles. We hypothesize that our TNPs will be converted to an active therapeutic agent only within MMP-14-expressing tumors, releasing the therapeutic drug azademethylcolchicine and causing significant antitumor effects. In addition, we postulate that the iron oxide nanoparticle moiety will allow real-time monitoring of drug accumulation and localization at tumors with magnetic resonance imaging (MRI). In aim 1, we will evaluate whether TNP dose and VDA payload affect VDA mediated vascular disruption, blood brain barrier (BBB) breakdown and cancer-specific toxicity. In aim 2, we will investigate the link between VDA-mediated tumor microvessel disruption, microvascular endothelial cell death and GIC death. TNPs hold the potential to substantially improving therapeutic efficacy whilst simultaneously reducing dose-...