The influence of isotopic and nonisotopic carriers on the biodistribution and biokinetics of M3+-citrate complexes

Uptake of 169Yb complexes in normal and tumour cells: influence of ligand and metabolic cell activity and stability of cellular association

For better understanding of the accumulation of trivalent radiometal tracers in tumours, studies of uptake of different 169Yb complexes into cultured normal (V79/4) and tumour (KTCTL-2) cells were performed. Cellular uptake of 169Yb3+ is dependent on both the metabolic activity of the cells and the nature of the ligand used. Uptake of 169Yb3+ from the citrate complex is an active cellular transport process but not tumour-specific. The 169Yb-aminopolycarboxylic acid complexes are taken up via a different, unknown mechanism, and in higher amounts by the tumour cells than by the V79/4 cell line, but the general features of uptake were principally the same with the normal and the tumour cells. Uptake of the complexes studied leads to a stable association of cellular components, which is a good premise for the therapeutic use of trivalent radiometals.

Stabilities of lanthanide-protein complexes

After incubation of both serum and HSA solutions with radioactive lanthanide complexes the binding constants of the corresponding lanthanide-protein complexes formed in the protein solutions under physiologic conditions, pH: 7.4, temperature: 310 K, isotonic ionic strength: 0.15 mol/L, were determined. The association constants of the lanthanide-protein complexes formed both in serum and HSA-solutions are equal within the experimental error. In conclusion, serum albumin binding predominates for the radiolanthanides. With the decrease of the ionic radii from 1.034 A (Ce) to 0.858 (Yb) the association constants increased by five orders of magnitude from 1 g Kpr = 4.90 (Ce) to 1 g Kpr = 9.54 (Yb). Further, a serum fractionation with alcohol was carried out to prove that the albumin fraction of serum is responsible for the lanthanide binding in blood.