CLRM-05 FEASIBILITY OF EVALUATING ABEMACICLIB NEUROPHARMACOKINETICS OF DIFFUSE MIDLINE GLIOMA USING INTRATUMORAL MICRODIALYSIS

INTRODUCTION: Diffuse midline gliomas are the most aggressive brain tumors of childhood and young adults, with documented 2 year survival rates of <10%. Treatment failure is due in part to the presence of the blood-brain barrier (BBB), which limits permeability of varied agents. Efforts to evaluate drug delivery across the BBB in midline gliomas have been restricted to post biopsy specimens. Intracerebral microdialysis sampling of cortical tissue has been shown to be a highly effective tool in determining neuropharmacokinetics in adult brain tumors. METHODS: All participants will take abemaciclib pre-operatively for 4.5 days at twice daily dosing. A maximally safe surgical resection for cortical high grade glioma or stereotactic needle biopsy for midline glioma will be performed in the OR and verified by brain CT. Continuous microdialysis sampling will be obtained over the course of the next 48 hours. We propose to evaluate 5 participants. RESULTS: This is a safety and feasibility study to evaluate tumor pharmacokinetics (PK) and pharmacodynamics (PD) of abemaciclib in recurrent high grade glioma and midline glioma participants in need of surgical resection or biopsy respectively. If intratumoral or PK brain dialysate sampling concentrations are >10nmol/L, or PD findings suggest CDK inhibition (decreased expression of Rb and/or topoIIα), then restart of abemaciclib therapy along with temozolomide will be administered for maintenance therapy post resection or biopsy. After every 3 cycles, repeat brain MRI’s will be obtained to evaluate treatment response and disease progression. Exploratory aims include catheter stability testing, tissue genomic sequencing and PDX modeling. CONCLUSION: We propose a trial using clinical microdialysis, placed in diffuse midline glioma tissue post biopsy, as an experimental research tool, to assess CNS drug entry and targeted inhibition with abemaciclib. These studies will be the first of their kind focused on the dynamic nature of CNS drug delivery with the overall intent to inform future clinical therapies.