Purpose: To determine the dose-limiting toxicity and maximum-tolerated dose of the proteasome inhibitor bortezomib administered intravenously weekly for 4 every 5 weeks; to determine the bortezomib pharmacokinetics and pharmacodynamics using plasma levels and an assay for 20S proteasome inhibition (PI) in whole blood; to correlate toxicity with bortezomib dose and degree of 20S PI; and to conduct a preliminary determination of the antitumor activity of bortezomib in patients with androgen independent prostate cancer (AIPCa). Patients and Methods: Fifty-three patients (48 with AIPCa) received 128 cycles of bortezomib in doses ranging from 0.13 to 2.0 mg/m2/dose, utilizing a careful escalation scheme with a continuous reassessment method. Pharmacokinetic and pharmacodynamic studies were performed in 24 patients (at 1.45 to 2.0 mg/m 2). Results: A dose-related 20S PI was seen, with dose-limiting toxicity at 2.0 mg/m2 (diarrhea, hypotension) occurring at an average 1-hour post-dose of ≥ 75% 20S PI. Other side effects were fatigue, hypertension, constipation, nausea, and vomiting. No relationship was seen between body-surface area and bortezomib clearance over the narrow dose range tested. There was evidence of biologic activity (decline in serum prostate-specific antigen and interleukin-6 levels) at & 50% 20S PI. Two patients with AIPCa had prostate-specific antigen response and two patients had partial response in lymph nodes. Conclusion: The maximum-tolerated dose and recommended phase II dose of bortezomib in this schedule is 1.6 mg/m 2. Biologic activity (inhibition of nuclear factor-kappa B-related markers) and antitumor activity is seen in AIPCa at tolerated doses of bortezomib. This agent should be further explored with chemotherapy agents in advanced prostate cancer.
ASJC Scopus subject areas
- Cancer Research