Targeting against epidermal growth factor receptors. Cellular processing of astatinated EGF after binding to cultured carcinoma cells.

BACKGROUND The alpha-emitting nuclide 211At is of great interest for radionuclide therapy when coupled to a tumor-targeting biomolecule, e.g. epidermal growth factor (EGF) the receptors of which are overexpressed in many malignancies. However, almost no information concerning the cellular processing of astatinated targeting agents is available. MATERIALS AND METHODS We indirectly astatinated EGF ([211At]-benzoate-EGF) and studied its cellular processing in A-431 carcinoma cells in comparison with data concerning [125I]-benzoate-EGF. RESULTS The biological half-life of astatine (3.5 h) was longer than the half-life of the iodine label (1.5 h). The increase of the half-life was due to longer retention of the internalised astatine radioactivity. The maximum accumulation for the astatine label occurred later (4-6h) than that for the iodine label (2-4h), indicating a slower excretion of astatine that was confirmed in experiment with 211At/1251-benzoate-EGF. CONCLUSION The long retention of astatine might be advantageous for radionuclide therapy.