Glioblastoma is the most lethal primary malignant brain tumor, and current therapies fail to effectively treat the disease. One reason that glioblastoma is difficult to treat is the presence of therapeutically resistant cancer stem cells (CSCs) within the tumors. Our long-term objective is to target glioblastoma cancer stem cells (CSCs) by creating small molecule drugs. Based on our results showing its importance in both cultured glioblastoma CSCs and glioblastoma organoid models, we aim to target the protein WDR5, which plays a role in modifying cellular DNA, thereby regulating gene expression. We plan to accomplish this goal by (1) designing new compounds to target WDR5 that are able to pass through the blood-brain barrier to reach the tumor and (2) thoroughly testing our new compounds for their ability to target WDR5 and CSCs both in cultured cells and mouse models of glioblastoma. In Aim 1, we will develop new compounds (current and future compounds are protected by a provisional patent) by optimizing brain penetration and potency and decreasing off-target effects. In Aim 2, we will test a lead candidate we have developed, as well as other synthesized compounds, for their ability to stop CSC growth and to increase survival in animal models. We will also test whether these compounds target WDR5 as we predict. Together, these studies will develop and begin to translate new compounds targeting WDR5 to prevent CSC-mediated glioblastoma therapeutic resistance and recurrence after treatment.