A phase I pharmacodynamic trial of bortezomib in combination with doxorubicin in patients with advanced cancer

Purpose: This phase I trial sought to define the toxicity, maximally tolerated dose (MTD) and pharmacodynamics of a combination of bortezomib and doxorubicin in patients with advanced malignancies. Patients and methods: Twenty-six patients were treated with bortezomib intravenously on days 1, 4, 8 and 11, with doxorubicin also administered intravenously on days 1 and 8, both in a 21-day cycle. Dosing ranged from 1.0 mg/m² of bortezomib with 15 mg/m² of doxorubicin to 1.5 mg/m² of bortezomib with 20 mg/m² of doxorubicin. Pharmacodynamic studies performed included assessment of levels of 20S proteasome activity and ubiquitin-protein conjugates. Results: The combination of bortezomib and doxorubicin was generally well tolerated. There were two dose limiting toxicities (DLT) at dose cohort 3 (1.3 mg/m² bortezomib, 20 mg/m² doxorubicin) and 2 DLT at dose cohort 3a (1.5 mg/m² bortezomib, 15 mg/m² doxorubicin). DLT seen included neutropenia, thrombocytopenia, and neuropathy. In addition, one patient developed grade 3 central nervous system toxicity in cycle 2 (not a DLT). One patient with hormone refractory prostate cancer had a partial response. Proteasome inhibition in whole blood was demonstrated and an increase in ubiquitin-protein conjugates was observed in peripheral blood mononuclear cells of most patients. Conclusions: Bortezomib and doxorubicin can be administered safely. The recommended phase II dose for this 21-day cycle is bortezomib 1.3 mg/m² intravenously on days 1, 4, 8 and 11, and doxorubicin 20 mg/m² intravenously on days 1 and 8. This combination may be of special interest in multiple myeloma, given the activity of both drugs in that disease.