Abstract
2039 Background: Platelet-derived growth factor signaling is important in gliomagenesis and PDGFR-β is expressed on >90% of endothelial cells in glioblastoma specimens. Methods: We report the results of a feasibility and phase I study of tandutinib (MLN518), an orally bioavailable, quinazoline-based inhibitor of type III receptor tyrosine kinases including PDGFR-β, FLT-3, and c-Kit, in patients with recurrent glioblastoma (GBM) conducted in the New Approaches to Brain Tumor Therapy (NABTT) consortium. Results: A feasibility study was conducted in 6 recurrent GBM patients in whom resection was clinically indicated. These patients received tandutinib 500-mg BID for 7 days prior to resection. In these patients, the drug was measured in tumor tissue and plasma samples obtained shortly before and after the resection by LC/MS. The mean ± SD concentration of tandutinib in tumor tissue was 7.2 ± 3.2 μg/mL and the mean ratio of its concentration in brain tumor-to-plasma was 9.6 ± 7.7. A phase I study was conducted in 19 patients to determine the MTD in this recurrent GBM population with sequential assessment of the following dose levels: 500-, 600-, and 700-mg BID. Four patients were replaced due to early withdrawal unrelated to toxicity. Dose limiting toxicities were observed in 1/6 patients at 500-mg BID (grade 3 phosphorous, grade 3 fatigue, grade 3 somnolence in 1 patient); 1/6 patients at 600-mg BID (grade 3 phosphorous); 2/3 patients at 700-mg BID (grade 3 fatigue, grade 3 weakness). 600-mg BID was declared the MTD and a phase II study has been initiated at this dose level. Conclusions: The mean brain tumor tissue-to-plasma ratio of tandutinib in GBM patients receiving 500-mg BID exceeded the estimated threshold ratio of 0.33 that was considered as being necessary to achieve local cytotoxic concentrations in brain tumors. The MTD of tandutinib in the recurrent GBM population is 600-mg BID. A phase II trial has been initiated at this dose level. [Table: see text]
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