PROJECT SUMMARY Diffuse midline gliomas (DMG), including diffuse intrinsic pontine gliomas (DIPG), are deleterious malignant pediatric tumors of the brainstem. DMG is the leading cause of death among pediatric brain tumors and the second most common malignant brain cancer afflicting children. DMG has a dismal prognosis of less than 1% survival within a year of diagnosis, even when using the most aggressive treatments. Approximately 400 children will be diagnosed with DIPG in the United States in 2022, all of whom will have a median survival of between 8 and 11 months. DMG disease outcomes have plateaued over the past decade due to the lack of effective treatments and limited diagnostic tools. Many failed clinical trials and therapeutic strategies in DMG can be attributed to two critical concerns: 1) the selectively penetrable blood brain barrier (BBB) restricts drug delivery to central nervous system, and 2) despite there being distinct genetic alterations between DMG and adult high- grade gliomas (aHGG), the agents considered for DMG clinical trials have been derived by extrapolation from aHGG data, without grounds for the therapeutic translation. Studies have revealed extracellular signal-regulated protein kinases (ERK), a downstream receptor tyrosine kinase of mitogen-activated protein kinase (MEK), is upregulated in DMG, raising questions about whether targeting the MAPK/ERK pathway can have anti-tumor effects in DMG. Targeting MEK in combination with aminolevulinic acid-photodynamic therapy (5-ALA-PDT) is of interest because inhibition of MEK has been found to significantly enhance protoporphyrin IX (PpIX) accumulation in vitro and in vivo in a tumor-specific manner. This proposal uses an innovative multimodal treatment approach that addresses the barriers to successful DMG clinical trials and exploits the molecular composition of DMG cells to reduce morbidity and mortality. By targeting MEK and employing 5-ALA-PDT, we anticipate MEK inhibition will synergize with 5-ALA-PDT efficacy by eliciting direct tumor cell killing, vascular shutdown and immune response, ultimately increasing overall patient survival. If successful, this treatment can be applied to other inoperable CNS tumors.

PROJECT NARRATIVE Diffuse midline glioma (DMG) is the leading cause of death among pediatric brain tumors yet disease outcomes have not improved due to the lack of effective treatments and limited diagnostic tools. This proposal uses an innovative, multimodal treatment approach, involving mitogen- activated protein kinase (MEK) inhibition and aminolevulinic acid-photodynamic therapy, that addresses the barriers to successful DMG clinical trials and exploits the molecular composition of DMG cells to reduce morbidity and mortality. If successful, this treatment can be applied to other inoperable central nervous system (CNS) tumors.