This is a Phase 1 dose-escalation study of PRT811, a protein arginine N-methyltransferase (PRMT) 5 inhibitor, in subjects with advanced cancers and high-grade gliomas who have exhausted available treatment options. The purpose of this study is to define a safe dose and schedule to be used in subsequent development of PRT811.

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.

Inclusion Criteria:

• Malignancies that are refractory to or intolerant of established therapies known to provide clinical benefit for the malignancy in question, or in the opinion of the Investigator, not be a candidate for such therapies
• Subjects must have recovered from the effects of any prior investigational system therapies
• For subjects with recurrent high-grade glioma or GBM, must have biopsy proven evidence (WHO Grade III or IV) and received external bean fractionated radiotherapy and at least 2 cycles of adjuvant temozolomide chemotherapy. Mutant Glioma must comply with biomarker defined enrollment criterias.
• For biomarker-selected solid tumors: must meet enrollment criteria
• Eastern Cooperative Oncology Group (ECOG) Performance Score of 0 or 1
• Adequate organ function (bone marrow, hepatic, renal, cardiovascular)
• Female subjects of childbearing potential must have a negative pregnancy test within 7 days of the start of treatment and must agree to use an effective method of contraception during the trial

Exclusion Criteria:

• Untreated concurrent malignancies or malignancies that have been in complete remission for less than one year
• Treatment with strong inhibitors of CYP3A4 for which there are no therapeutic substitutions
• Inflammatory disorders of the gastrointestinal tract, or subjects with GI malabsorption
• HIV positive; known active hepatitis B or C
• Known hypersensitivity to any of the components of PRT811