Monoclonal antibody 3E1.2 was coupled with the bifunctional chelate, cyclic DTPA anhydride, at molar ratios (cOTPAA:3E1.2) of 1:1, lO:l, 1OO:l and 1oOO:l. The desired substitution level of less than one mol of D"PA/bl of 3E1.2 was achieved at a molar ratio of 1O:l and a coupling efficiency of 9.9t3.38 percent. The DTPA-coupled antibody was purified by dialysis before labelling with l1lIn acetate. The labelling efficiency was 38.7f3.59 percent. The radiolabelled antibody was purified by -10 Sephadex G25M chromatography then sterilized by filtration through a 0.22 un filter (Millex-or Millex-GV).
A substantial adsorption effect (87.4f3.84 percent) occurs with the Millex-filter but to a much smaller extent (26.8f5.58 percent) with the Millex-filter. The radiochemical purity of the product was 80-90 percent depending on the method of analysis. The product was tested and found to be sterile and non-pyrogenic. Key Wrds: M O ~O C ~O M ~ antibodies, 111In, Bifunctional Chelates IWRCXXKTION Radiolabelled mnoclonal antibodies directed against tumour-specif ic antigens have undergone mnsiderable study in recent years as tunour imaging radiopharmaceuticals (1). Using bifunctional chelates it is IKW possible to label m0nocl0~1 antibodies with metallic radionuclides such as ll1In (2-6).
The use of ll1In as the radiolabel offers may advantages: efficient detection by the ganna camera, a physical half-life sufficiently long to permit delayed imaging and a relatively low radiation dose to the patient. In addition, the in-vivo stability of monoclonal antibodies labelled with ll1In using bifunctional chelates is excellent (2,4). There is also negligible loss of immunoreactivity after labelling provided the substitution level of the *To whom correspondence should be addressed.