Yttrium-90 and Rhenium-188 Radiopharmaceuticals for Radionuclide Therapy

10.3.1.1. Materials and methods
A direct labelling method was optimized by varying HEDP, MDP and DPD
concentration, pH of the labelling mixture, reaction temperature and reaction
time. The stock solution of polyphosphonate ligands was prepared by dissolving
the desired ligand (concentration 0.01–10 mg/mL) in double distilled water.
Then, the appropriate amount of 90 Y chloride solution (~370 MBq per vial) was
added. The pH values of the resulting reaction mixtures were adjusted to 6.5–7.5.
The total reaction volume in each vial was kept at 3 mL. Ascorbic acid (10 mg)
was used as the radiolytic stabilizer in all samples. The steps followed were:
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RCP studies: ITLC SG, mobile phase, 0.9% NaCl or CH 3 OH (R f = 0.9–1.0
for free 90 Y 3+ and R f = 0.0–0.2 for the 90 Y complex).
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Serum stability studies: Stability of 90 Y HEDP, 90 Y MDP and 90 Y DPD
in human serum was assessed by measuring the release of 90 Y from the
complex at 37°C over a period of 10 d.
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Organ distribution studies: Experiments were done as a distribution per
organ of animals (healthy male Wistar rats). Major tissues of the body were
removed and assayed for radioactivity. The radioactivity was measured
using a NaI(Tl) detector and percentages of injected dose in the tissues were
calculated. The results were expressed as percentages of injected activity
per organ or gram of tissue for blood, muscle and bone.
10.3.1.2. Results and discussion
The RCP for all 90 Y complexes was >95%. The serum stability results
showed that the complex was quite stable up to 10 d. There was no significant
dissociation of activity from the complex, i.e.