166 Ho-Labeled Hydroxyapatite Particles: A Possible Agent for Liver Cancer Therapy

Abstract

Purpose:

Intra-arterial administration of particulates labeled with β ⁻-emitting radionuclides is one of the promising modalities for the treatment of liver cancer. ¹⁶⁶Ho [T_1/2 = 26.9 hours, E _β(max) = 1.85 MeV, E _γ = 81 keV (6.4%)] could be envisioned as an attractive radionuclide for use in liver cancer therapy owing to its high-energy β ⁻ emission, short half-life, and feasibility of its production with adequately high specific activity and radionuclidic purity. Hydroxyapatite (HA) particles in the size range of 20–60 μ were chosen as the particulate carrier due to their biocompatibility and ease of labeling with lanthanides.

Methods:

¹⁶⁶Ho was produced by thermal neutron bombardment on a natural holmium target. HA particles of the desired size range were synthesized, characterized, and radiolabeled with ¹⁶⁶Ho. The biologic behavior of ¹⁶⁶Ho-HA was tested in normal Wistar rats by carrying out biodistribution and imaging studies.

Results:

¹⁶⁶Ho was produced with a specific activity of 5.55–6.48 TBq/g and radionuclidic purity of ∼100%. HA particles were labeled with ¹⁶⁶Ho with a high radiochemical purity of >99% and good in vitro stability up to 7 days. The biodistribution and imaging studies revealed satisfactory hepatic retention (∼89% of injected activity after 2 days) with insignificant uptake in any other major organ/tissue.

Conclusions:

¹⁶⁶Ho-HA exhibited promising features as an agent for liver cancer therapy in preliminary studies and warrants further investigation.