In vivo binding specificity of111In-DTPA-11B6 in NRMI nude mice. (a) Dot plot of tumour accumulation in blocked LNCaP, non-blocked LNCaP xenografts (hK2+) and DU145 (hK2-). There was a significant difference in active uptake between non-blocked LNCaP xenografts and the other groups. (b) Distribution of 111In-DTPA-11B6 48 h post-injection in LNCaP xenografted NMRI mice, shown as %IA/g ± SEM with pre-dosing of 0.8 mg of cold 11B6 antibody. (c) Dot plot with linear regression for pre-dosing and no pre-dosing as function of tumour weight. This shows that %IA increases with tumour weight for both pre-dosed and normal uptake but that the uptake increases more in tumours with no pre-dosing. The slope calculated from linear regression was 6.1 ± 0.27%IA/g for the pre-dosed groups and 14 ± 1.2%IA/g with no pre-dosing. The R2 value was 0.97 for the pre-dosed groups and 0.99 for xenografts without pre-dosing. As %IA/g increases with smaller tumour volume this could explain the large difference seen in (b) between the different pre-dosing groups. By analysing %IA instead, it seems that the effect of pre-dosing is retained over the studied time interval and that 11B6 in fact has a long tumour retention.