PROJECT SUMMARY Brain cancers are the leading cause of disease-related death in children and in adults under the age of 40 years old. Even with aggressive treatments that include maximal surgical resection, stereotactic radiosurgery, whole-brain radiation therapy, chemotherapy, molecularly targeted therapeutics, and immunotherapies, the recurrence rates for many brain cancers are nearly 100%. Despite the hundreds of clinical trials and combination therapies tested, the mortality rates have only slightly decreased. According to the American Cancer Society, it is estimated that there will be over 24,000 adults and children with primary brain cancer in the US in 2023 with no available medications that can reverse drug resistant brain cancer recurrences. When secondary brain metastases from other primary cancers like breast, melanoma and lung are included, it is estimated that there will be over 300,000 patients with secondary brain metastases this year in the US. These patients are confronted with a mixed blessing of longer initial treatment survival but an increased incidence of secondary, drug resistant brain tumors. Much like primary brain cancer, when other cancers metastasize to the brain, they are almost always lethal. New therapies that can target adult and pediatric drug resistant recurrent primary and secondary brain cancers are badly needed. Creative BioTherapeutics, has discovered that recurrent drug resistant cancers up-regulate a survival pathway resulting in the expression and secretion of an extracellular Glucose-Regulated Protein 78 (ecGRP78) in the tumor microenvironment. Our research shows that ecGRP78 is important for drug and immune resistance as well as glioma stem cell formation. Cell surface bound ecGRP78 has been found on breast, lung, ovarian, prostate, melanoma, multiple myeloma, colon, pediatric and adult brain tumors and not on normal cells. We have found that ecGRP78 stabilizes essential oncofetal proteins, ROR1 and Cripto, along with the checkpoint protein, PD-L1, on tumor and immune cell surfaces inducing a cascade of events to increase drug resistance, immune suppression, and cancer stem cell formation. As such, we designed and developed several anti-cancer therapies to specifically block the N-terminal domain of ecGRP78 from binding to and stabilizing these pro-tumorigenic proteins on the tumor surface without disrupting normal cell function. We can now show that our lead inhibitor, CBT300, in vitro can a) induce apoptosis of drug resistant tumor cells, b) eliminate drug and immune resistance showing synergistic effects with chemotherapy and immunotherapy, c) decrease the amount of chemotherapy needed, thus lowering the toxic side effects. Our in vivo results with human high grade glioma tumors in mice treated with one of our ecGRP78 inhibitors displayed an increase in pathological complete responses of over 65% and an increase in median survival of 12 days or an estimated 2 years for human patients with no observa...