Background: The caspase family of cysteine proteases play key roles in the initiation and execution of apoptosis. The activation of procaspase-3 to caspase-3 is critical in both the intrinsic and extrinsic apoptotic cascades. Procaspase-3 levels are elevated in many cancers, including glioblastoma (GBM). As a result, caspase-3 levels are abnormally low in these tumors; thus they avoid apoptosis. PAC-1 is a small molecule that directly activates procaspase-3 and induces apoptosis of cancer cells. PAC-1 has activity against a wide range of cancer cell lines, and in animal models of cancer. PAC-1 crosses the blood brain barrier and has been shown to synergize with TMZ in both canine malignant glioma and meningioma that arise spontaneously. Methods: This Phase I dose escalation study uses a modified- Fibonacci 3+3 design to determine the MTD of PAC-1 when combined with TMZ in patients with recurrent malignant gliomas: anaplastic astrocytoma (AA) and GBM (open to enrollment). Here, we focus on component 2 of the study. Primary objectives: to establish MTD of PAC-1 when combined with a fixed dose of TMZ, tolerability, and toxicity using CTCAE v.4. Secondary and correlative objectives: pharmacokinetics, pharmacodynamics, preliminary anti-tumor activity correlation with procaspase-3 expression in tumor tissue, radiographic response using the Response Assessment in Neuro-Oncology (RANO) criteria, and neurocognitive function using a validated test battery. Inclusion criteria: diagnosis of recurrent high grade glioma (AA or GBM), ECOG PS 0-2, adequate organ function. Exclusion criteria: received prior cytotoxic therapy in the last 3-6 weeks (duration based on prior therapy) or uncontrolled chronic illness. Administration and design, Component 2: PAC-1, orally administered, is dosed at 375-650 mg daily (up to 3 dose levels) on days 1-21 of each 28-day cycle. A fixed dose of TMZ, (150 mg/m2), is administered orally, days 8 -12 of each cycle. The study is currently enrolling patients for Component 2. Clinical trial information: NCT02355535