Attachment of radio-metals to LDL with lipid analogues of EDTA or DTPA type complexing agents. Comparison of two labelling procedures

In order to take advantage of the tumor cell's affinity for LDL particles and target imaging agents via LDL for diagnostic applications, different methods have been proposed for labelling LDL with a metal ion. In this work, two methods are compared for labeling LDL with a radio-metal (M 111In, 153Gd) through a liquid anchor (L). Three EDTA or DTPA type complexing agents derived from stearylamine or phosphatidyl-ethanolamine were used. In procedure A, the L-LDL conjugate is first prepared and then labeled with M. In procedure B, the complex M-L is first prepared and then inserted into the LDL. In both procedures the final particle IS M-L-LDL. After precipitation of free radio-metals (adding trophone) or of the M-L-LDL particles (adding heparin), radioactivity counting shows that 55 to 92 % or 55 to 85 % of the initial amount of M remains attached to the M-L-LDL particles in procedures A and B, respectively. These two procedures may be used for labeling LDL with a radio-metal. (authors)