[4] Technetium-99m labeling of albumin microspheres intended for drug targeting

Publisher Summary This chapter discusses 99m Tc labeling procedures, the mechanism of labeling, and the labeling and biological fate of chemically stabilized HSA microspheres. The chapter presents a study that has shown that human serum albumin microspheres, crosslinked by 2,3-butadione and glutaraldehyde, can be efficiently labeled with the radioisotope technetium-99m. It has been found that reduction with sodium thiosulfate needs to be carried out at 100° in an acidic environment for several minutes, and although the method leads to long retention of label on the microspheres, the cleaning procedures are a problem and lead to only a 30% labeling efficiency. The use of stannous chloride as reducing agent has many advantages, although, to avoid the formation of radiocolloid either during or after labeling, it needs to be coated on the surface of the microspheres. Such coated HSA microspheres can be labeled with technetium-99m at neutral pH in saline. To label HSA microspheres with technetium, it is necessary to first convert heptavalent Tc(VII) to one of its lower oxidation states.