Radioimmunoscintigraphy using an anti-prostate monoclonal antibody (E4): a dosimetric evaluation

The aim of this study was to evaluate different strategies to increase the tumour radiation dose for experimental radioimmunotherapy using ¹²⁵I-labelled monoclonal antibody (MAb) E4 in a nude mice model xenografted with DU-145 tumours. The effects from a single injection of the ¹²⁵I-labelled MAb E4, the same total amount of radiolabelled MAb E4 divided into three repeated injections, and the effect of pre-targeting with non-labelled MAb E4 for reducing the amount of shed antigen were investigated. Based on repetitive quantitative radioimmunoscintigraphies, calculation of the tumour radiation dose delivered from the ¹²⁵I-nuclide was performed for each strategy. The single injection strategy without pretargeting rendered the highest mean tumour radiation dose, i.e. 0.23 Gy/MBq. Pretargeting with non-labelled MAb E4 before a single injection of [¹²⁵I]E4 resulted in a slightly lower mean tumour radiation dose, i.e. 0.19 Gy/MBq, compared to the single injection alone. An even lower mean tumour radiation dose, i.e. 0.14 Gy/MBq, was obtained when the same total administered amount of activity was divided into three separate injections given in 10-day intervals. We concluded that the single injection strategy is the most efficient when using MAb E4 in this tumour model. The tumour radiation doses were not increased by dividing the same amount of activity into three injections or by pretargeting with non-labelled MAb E4. Received: 30 October 2000 / Accepted: 23 February 2001