Epigenetically regulated stemness program and stem cell niche as targets in pediatric DIPG

Understanding the role of cancer stem cells (CSCs) in diffuse intrinsic pontine glioma (DIPG) is crucial for preventing treatment resistance and tumor progression and for devising therapies that may prolong the lives of the 200-400 pediatric DIPG patients diagnosed each year. Radiotherapy remains the standard of care, but tumors recur in 100% of patients, resulting in dismal patient survival of 8-11 months. Over 250 clinical trials have failed to move these numbers. Mechanistic research is urgently needed to understand the underlying biology of CSCs and how they drive treatment resistance to develop innovative combinatorial therapies that can change the natural history of DIPG. Extensive preliminary data and existing literature, support the overarching hypothesis that aldehyde hydrogenase positive (ALDH+) CSC cause therapeutic resistance and drive tumor progression. We propose, in mechanistic studies, to characterize an epigenetically regulated stemness program and stem cell niche (Aim 1 and 2) as potential targets (Aim 3) in pediatric DIPG. Specifically, in Aim 1, we will determine the role and regulation of ALDH-positive CSCs in DIPG. We will evaluate the regulation of specific ALDH isoforms, particularly ALDH1A3 and ALDH2 by H3 K27M mutation, and by IL1β secreted by microglia, respectively, in carefully designed in vitro and in vivo assays using isogenic DIPG models. We will define the role of specific ALDH isoforms, including ALDH1A3 and ALDH2, in cell differentiation, tumor initiation and progression, and immunity. In Aim 2 we will evaluate whether ALDH+ CSCs are the cause of therapeutic resistance and responsible for tumor progression. We will modulate expression of disease relevant ALDH isoforms and evaluate whether therapeutic sensitivity can be restored. We will characterize the therapy induced stem cell niche and mechanisms of immune evasion with cutting-edge technologies, including single cell RNA sequencing (scRNA-seq) and CyTOF. In Aim 3, we will target ALDH+ CSCs as the cause of resistance to prevent tumor progression. In preclinical proof-of concept studies we will target ALDH (Disulfiram) and PI3K/mTOR (GDC- 0084), a cell intrinsic signaling of ALDH+ CSC, to enhance outcomes from standard of care (radiotherapy) and to prevent progression. Therefore, our studies will (1) confirm that CSCs present a mechanism of resistance and (2) provide a rationale to target these cells specifically and (3) address an unmet clinical need for efficacious therapies. In summary, our proposal will mechanistically address the role of ALDH+ CSCs in therapeutic resistance and tumor relapse of DIPG and provide druggable targets, which can accelerate clinical translation against this devastating pediatric disease.