FIGURE 1.

In vitro cytotoxicity by luminometry. Antigenic blockade was performed with 50 μg/mL application of unlabeled rituximab for 24 h before dosing with varying amounts of activity. Dose-dependent ²¹³Bi-rituximab cell kill is substantially blocked with cold rituximab. x-axis represents days of assessment (0–6 d). Controls (not shown), antigen (CD-20) blocked ²¹³Bi-rituximab (74 and 370 kBq did not vary from one another over 6 d, P = not statistically significant). Two, 10, and 740 kBq of ²¹³Bi-rituximab and 740 kBq of ²¹³Bi had significant antitumor effects vs. control and 74- and 370-kBq ²¹³Bi-rituximab–blocked groups (P < 0.01). ²¹³Bi-rituximab and free ²¹³Bi at 740-kBq dose were comparable (P = not statistically significant). 1 μCi = 37 kBq.