Preparation of 166Ho-oxine-lipiodol and its preliminary bioevaluation for the potential application in therapy of liver cancer.

Objective: Intra-arterial administration of beta-emitting radionuclides in the form of suitable radiopharmaceuticals is one of the promising modalities for the treatment of liver cancer. Ho [T1/2=26.9 h, Ebeta(max)=1.85 MeV, Egamma=81 keV (6.4%)] could be envisaged as an attractive radionuclide for the use in liver cancer therapy owing to its high-energy beta-emission, short half-life and feasibility of its production with adequately high specific activity and radionuclidic purity using moderate flux reactors. Lipiodol is chosen as the vehicle to deliver localized doses of ionizing radiation to liver cancer cells after intra-arterial hepatic infusion as it is selectively retained in the vascular periphery of the proliferating cells.
Methods: Ho was produced by thermal neutron bombardment on a natural Ho2O3 target at a flux of approximately 6 x 10 n/cm.s for 7 days. Radiolabelled lipiodol was prepared by dispersing the Ho-oxine complex in lipiodol. The biological behaviour of Ho-oxine-lipiodol was studied by biodistribution and imaging studies in normal Wistar rats.
Results: Ho was produced with a specific activity of 9.25-11.10 TBq/g and radionuclidic purity of approximately 100%. The Ho-labelled oxine complex was prepared in high yield (approximately 97%). Approximately, 95% of the Ho activity was dispersed in lipiodol within 30 min. The resulting radiolabelled preparation was found to exhibit good stability in physiological saline and human serum up to 3 days. The biodistribution and imaging studies revealed satisfactory hepatic retention (88.43+/-2.85% of injected activity after 2 days) with insignificant uptake in any other major organ/tissue except skeleton (6.44+/-1.07% at 2 days postinjection).
Conclusion: The Ho-oxine-lipiodol preparation exhibited promising features in preliminary studies and warrants further investigation.