Phase I Trial Using Proteasome Inhibitor Bortezomib and Concurrent Temozolomide and Radiotherapy for Central Nervous System Malignancies

Purpose: To evaluate the toxicity and response rate of bortezomib with concurrent radiotherapy and temozolomide in the treatment of patients with central nervous system malignancies. Patients and Methods: This open-label, dose-escalation, Phase I clinical study evaluated the safety of three dose levels of intravenously administered bortezomib (0.7, 1.0, and 1.3 mg/m²/dose) on Days 1, 4, 8, and 11 of a 21-day cycle, in addition to concurrent radiotherapy and temozolomide at a daily dose of 75 mg/m² starting on Day 1. The primary endpoint was dose-limiting toxicity, defined as any Grade 4-5 toxicity or Grade 3 toxicity directly attributable to protocol treatment, requiring hospitalization and/or radiotherapy interruption. The secondary endpoints included feasibility, non-dose-limiting toxicity, and treatment response. Results: A total of 27 patients were enrolled, 23 of whom had high-grade glioma (10 recurrent and 13 newly diagnosed). No dose-limiting toxicities were noted in any dose group, including the highest (1.3 mg/m²/dose). The most frequent toxicities were Grade 1 and 2 stomatitis, erythema, and alopecia. All 27 patients were evaluable for response. At a median follow-up of 15.0 months, 9 patients were still alive, with a median survival of 17.4 months for all patients and 15.0 months for patients with high-grade glioma. Conclusion: Bortezomib administered at its typical "systemic" dose (1.3 mg/m²) is well tolerated and safe combined with temozolomide and radiotherapy when used in the treatment of central nervous system malignancies. A Phase II study to characterize efficacy is warranted.