2. Histologically confirmed GBM or World Health Organization (WHO) Grade IV variants (gliosarcoma, glioblastoma with oligodendroglial features, or giant cell glioblas toma). 3. Unequivocal evidence of a first tumor recurrence or progression on the initial treatment regimen (prior to enrollment on this study), consisting of surgical intervention (biopsy and/or resection), radiation, and TMZ chemotherapy, as assessed by MRI or CT scan of the brain with and without contrast within 14 days prior to the start of SL-701. If receiving corticosteroids, the dose must be stable or decreasing for at least 5 days prior to the scan. Patients unable to undergo MRI because of non-compatible devices can be enrolled, provided CT scans are obtained and are of sufficient quality. Patients without non- compatible devices may not have CT scans performed to meet this requirement. For each patient, the same imaging technique should be performed throughout the study for purposes of assessing tumor response or PD. 4. For patients who have undergone resection of recurrent or progressive tumor prior to study enrollment, the following conditions must apply:  Recovery from the effects of surgery  Residual disease following resection of recurrent tumor is not mandated for eligibil ity into the study. To best assess the extent of residual disease post-operatively, an MRI should be performed: o No later than 96 hours in the immediate post-operative period; or o At least 4 weeks post-craniotomy (7 days for stereotactic biopsy), within 14 days prior to the start of SL-701, and on a corticosteroid dosage that has been stable or decreasing for at least 5 days. 5.