This is a multicenter, open-label, dose-escalation, dose-expansion Phase 1 study of PRT811, a PRMT5 inhibitor, in subjects with advanced cancers without any approved or available treatment options including solid tumors, CNS lymphoma, and /or high-grade gliomas. The study will consist of 2 parts, a dose escalation part evaluating subjects with advanced solid tumors, CNS lymphoma, and/or high-grade glioma and a cohort expansion part which will evaluate the safety and efficacy of PRT811 in subjects with advanced solid tumors, and glioblastoma multiforme. For subjects, the study will include a screening phase, a treatment phase, and a post treatment follow-up phase. An end-of-study visit will be conducted within 30 days after the last dose of PRT811.