A randomized, double-blind, dose-finding, multicenter, phase 2 study of radium chloride (Ra 223) in patients with bone metastases and castration-resistant prostate cancer.

Background: Patients with castration-resistant prostate cancer (CRPC) and bone metastases have an unmet clinical need for effective treatments that improve quality of life and survival with a favorable safety profile.

Objective: To prospectively evaluate the efficacy and safety of three different doses of radium chloride (Ra 223) in patients with CRPC and bone metastases.

Design, Setting, And Participants: In this phase 2 double-blind multicenter study, 122 patients were randomized to receive three injections of Ra 223 at 6-wk intervals, at doses of 25 kBq/kg (n=41), 50 kBq/kg (n=39), or 80 kBq/kg (n=42). The study compared the proportion of patients in each dose group who had a confirmed decrease of ≥ 50% in baseline prostate-specific antigen (PSA) levels.

Outcome Measurements And Statistical Analysis: Efficacy was evaluated using blood samples to measure PSA and other tumor markers, recorded skeletal-related events, and pain assessments. Safety was evaluated using adverse events (AEs), physical examination, and clinical laboratory tests. The Jonckheere-Terpstra test assessed trends between groups.

Results And Limitations: The study met its primary end point with a statistically significant dose-response relationship in confirmed ≥ 50% PSA declines for no patients (0%) in the 25-kBq/kg dose group, two patients (6%) in the 50-kBq/kg dose group, and five patients (13%) in the 80-kBq/kg dose group (p=0.0297). A ≥ 50% decrease in bone alkaline phosphatase levels was identified in six patients (16%), 24 patients (67%), and 25 patients (66%) in the 25-, 50-, and 80-kBq/kg dose groups, respectively (p<0.0001). The most common treatment-related AEs (≥ 10%) occurring up to week 24 across all dose groups were diarrhea (21%), nausea (16%), and anemia (14%). No difference in incidence of hematologic events was seen among dose groups. Potential limitations include small patient numbers and differences among dose groups at baseline.

Conclusions: Ra 223 had a dose-dependent effect on serum markers of CRPC activity, suggesting that control of bone disease with Ra 223 may affect cancer-related outcomes. Ra 223 was well tolerated at all doses.

Trial Registration: ClinicalTrials.gov: NCT00337155.