Preparation of γ-immunoglobulins coupled with DTPA and their labelling with trivalent metal radionuclides for radiotherapy

The scope of the report is as follows: immunoglobulin coupling with cDTPAA and labelling of the conjugate with 90Y; Acid-base and complexation equilibria in the coupled immunoglobulin solution; Theory of the complex equilibrium of yttrium between coupled immunoglobulin and EDTA; and Procedures and results of recent experiments. The following was achieved: (i) The dependence of the bovine immunoglobulin on the cDTPAA/IgG coupling ratio and immunoglobulin concentration was obtained; (ii) A procedure aimed to free phosphate buffer from ubiquitous trivalent cations was tested; (iii) The procedure of lyophilization of coupled bovine IgG-DTPA in a phosphate buffer at pH 7.34 and I = 0.16 mol.l-1.was elaborated. (iv) A procedure for lyophilization of the coupled CD20 monoclonal antibody in the same phosphate buffer was elaborated. (v) Acid-base and complexation equilibria were calculated for citrate and phosphate buffer solutions in the presence of coupled immunoglobulin. ( vi) A theory of the complexation equilibrium of yttrium between coupled immunoglobulin and EDTA was developed. (vii) Experiments were performed leading to the determination of a so far unknown constant of complexity of yttrium to DTPA coupled to immunoglobulin; its 3rd and 4th dissociation constants. (viii) The method sub (vii) can be applied to the determination of the complexity constants of other radionuclides with DTPA coupled to immunoglobulin; the 3rd and 4th dissociation constants of IgG-DTPA will not have to be sought any more. (ix) Samples of lyophilizate of the Y-CD20-DTPA complex can be sent to the biochemical laboratory for immunoreactivity determination. (x) Lyophilizates from experiments (iv-vi) are stored in a refrigerator at 4 deg C to be used for labelling with 177Lu. (xi) The results obtained can be used to plan an experiment with CD20 in which a specific radioactivity of 400 MBq 177Lu per mg CD20 will be achieved. (P.A.)