RA5 and RG2 have reduced apoptosis to high LET-emitting constructs ²²⁵Ac-lintuzumab and ¹²⁵I-dUdr. Cells were treated in log-phase growth with indicated concentrations of radioimmunotherapy construct for 48 hours in a 96-well plate and then assayed by the ATP Lite viability assay. (A) Treatment with ²²⁵Ac-lintuzumab. (B) Treatment in the presence of 100-fold excess unlabeled antibody. Data are mean ± SD of a representative experiment repeated 3 times. The curves were fitted using sigmoidal dose-response nonlinear regression with variable slope. The corresponding IC₅₀ values for HL60, RA5, and RG2 were 0.59, 5.25, and 8.7 kBq/mL, respectively. (C) Cells were treated with indicated doses of ¹²⁵I-Udr, and cell viability was measured by scoring of nuclear morphology, normalized to controls. (D) Percent uptake of ¹²⁵I-Udr at 24 and 48 hours after treatment. ¹²⁵I-Udr experiments are mean ± SEM from 2 independent experiments. A 2-way, repeated-measures ANOVA was performed to determine significance at each dose. *P < .05. **P < .01. ***P < .001.