This phase II trial was undertaken to evaluate the efficacy of TLN-4601 in patients with glioblastoma (GBM) at first progression. TLN-4601 inhibits the Ras-MAPK signaling pathway, and in animal models crosses the blood-brain barrier and accumulates in implanted gliomas, possibly by binding specifically to the peripheral benzodiazepine receptor. A maximum of 40 patients with recurrent GBM were to be enrolled in this study. TLN-4601 was administered at a dose of 480 mg/m(2)/day by continuous intravenous (CIV) administration. Each 21-day cycle consisted of a 14-day CIV administration and a 7-day recovery period. Samples were obtained from all patients for pharmacokinetic evaluations (PK) and for Raf-1 and pERK biomarker assessment using immunohistochemistry and flow cytometry. Following enrollment of 20 patients, this study was terminated due to a lack of efficacy. Of 17 evaluable patients, 14 had MR scans performed after two cycles of TLN-4601. Of these 14 patients, three had stable disease and 11 had disease progression. Only three patients had MR scans performed after four cycles and all had evidence of radiographic progression. Serum PKs confirmed that patients were exposed to TLN-4601 at targeted drug levels. TLN-4601 was generally well tolerated although two patients discontinued treatment due to adverse events. Biomarker analysis did not show consistent changes. TLN-4601 infused via CIV at 480 mg/m(2)/day for 14 of 21 days is well tolerated by patients with progressive GBM. However, this agent is ineffective in progressive GBM when administered as monotherapy in this schedule.