Albumin

1.2.1.3 Albumin

Technetium-99m-microspheres (99mTc-microspheres) of human serum albumin (HSA)
have been widely used for clinical nuclear medicine, particularly for lung scanning,
since 1969 (25,26). 188Re labeled HSA microspheres used by Wunderlich et al. [25]
are uniform in size, with a mean diameter of 25 μm, and are biocompatible and
biodegradable. However, the labeling process is time-consuming and depends on
SnCl2.2H2O and gentisic acid concentration. On the surface of the microspheres a
shell of about 1 μm thickness was seen, probably consisting of precipitated tin
hydroxide. The particle labeling (coating) may be achieved by a combination of the
reduction reaction of Re(VII) with Sn(II) and a particle surface-related coprecipitation
effect of tin hydroxide colloid with high adsorption capacity and reduced, hydrolysed
rhenium. The labeling yield under optimal reaction conditions is more than 70%.
Biodistribution experiments in rats, using the lungs as a model for a well-perfused
tumour, resulted in excellent in vivo stability.
As well as rhenium, yttrium was bound to HSA for internal radiotherapy [27]. 90Yacetate
and macroaggregates of HSA (MAA) (Macrokit®, Dainabot, Tokyo, Japan)
were suspended in sodium acetate buffer and incubated at room temperature.
Experiments in mice were carried out in order to investigate the possibility of using
90Y-MAA as an internal radiotherapeutic agent for whole-lung irradiation. Yttriumactivity
in the lung was cleared within 72h post injection and activity was

redistributed in other organs, especially in the bone, but this could be prevented by the
combined use of CaNa3DTPA. Based on its rapid clearance 90Y-MAA was suggested
as being useful for fractionated internal radiotherapy of the lung.