Inclusion Criteria:

          1. Confirmed histopathology of recurrent GBM (WHO Grade IV), following primary treatment
             with TMZ and radiotherapy (minimum of 50 Gy) and at least two cycles of maintenance
             TMZ (5 days of a 28 day cycle).

          2. Patients must have tumor tissue samples available from the GBM surgery or open biopsy
             for O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation status analysis
             or must have medical record available to document MGMT status.

          3. Unequivocal radiographic evidence of tumor progression by MRI

          4. At least one measurable lesion per RANO criteria within 21 days prior to registration.

          5. No more than one prior line of therapy for glioblastoma.

          6. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2

          7. Full recovery (≤ grade 1) from the toxic effects.

          8. Adequate renal, liver and bone marrow function:

               -  Hemoglobin >9.0 g/dL

               -  Leukocytes >3,000/mcL

               -  Absolute neutrophil count >1,500/mcL

               -  Platelets >100,000/mcL

               -  Total bilirubin ≤ 1.5 × upper limit of normal (ULN)

               -  AST (SGOT) / ALT (SGPT) ≤2.5 × ULN

               -  Creatinine clearance ≥ 60 mL/min

        10. Patients must be ≥18 years of age

        Exclusion Criteria:

          1. Early discontinuation of TMZ in first line due to treatment related Adverse events
             (AEs).

          2. Second primary malignancy expected to require treatment within a 6 month period
             (except adequately treated basal cell carcinoma of the skin).

          3. Have received treatment within the last 28 days with a drug that has not received
             regulatory approval for any indication at the time of study entry.

          4. Serious concomitant systemic disorders

          5. Patients with abnormal sodium, potassium, or creatinine levels ≥ grade 2.

          6. Patients with prothrombin time/partial thromboplastin time (PT/PTT) or International
             normalized ratio (INR) above the ULN.

          7. Inability to comply with protocol or study procedures.