Labelling and control of biomolecules with 188Re and 153Sm

The aim of this work was to develop and/or standardize the labelling of different biomolecules with beta emitters as well as their radiochemical and biological quality control methods. Lanreotide was labelled with 188Re with yields >90% with good stability using SnF2 in the presence of ascorbic acid and HEDP (molar ratio HEDP/lanreotide=260 and SnF2/lanreotide=40) at pH 1-2. In order to conduct indirect labelling, the synthesis of 188Re-MAG3-TFP ester was done. Lanreotide was also labelled with 125I by chloramine-T method and Bolton-Hunter method with yield >95% and RCP >98% after purification. Somatostatin receptors from rat brain cortex were prepared, their control with 125I-somatostatin gave maximum binding capacity near to 100%. 188Re-lanreotide binding was low and could be inhibited with unlabelled lanreotide but not with somatostatin. 153Sm-EB1 was obtained with RCP >90%, without affecting the binding site for avidin-biotin complex using molar ratio EB1-153Sm 20:1, at 80 deg C, 10 min. Conjugation of 83D4 and IgG bovine with cDTPA was done and labelled with 153Sm (yield <20%). Radioiodination (chloramine-T method) of native and biotinylated 83D4, scFv and VH with BMCC-biotin in 1:50, 1:25 and 1:25 molar ratios respectively, were achieved with yields >50%. Their binding capacity with respect to Tn structure and avidin by immnunoradiochemical analysis and by formation of triple complex [AcB]-[avidin]-[111In-DTPA-biotin] was higher for 83D4 than for the recombinant fragments:%B/T=36 for native and%B/T=38 for 83D4-biotin. The highest affinity constant, determined by surface plasmon resonance, was obtained for 83D4-biotin, KA=1x1010 M-1, while the value for the 83D4 was 109 M-1. In order to gain experience and then switch to therapeutic applications by replacing 99Tcm with 188Re, the labelling conditions of 99Tcm-N4-Lys-Biotin were investigated. The best results were obtained using 50 μg of the ligand (61 μmol), 50 μg of SnCl2 (224μmol) at pH 12, incubating a RT. A diagnostic study in a patient with colon carcinoma by using a pretargeting system showed the location of the tumour at 2 h and a predominant renal excretion of the labelled molecule. Bifunctional chelating agents cDTPA and TETA were synthesized. (author)