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

Abstract

Intra-arterial administration of particulates labeled with -emitting radionuclides is one of the promising modalities for the treatment of liver cancer. 166Ho [T1/2=26.9 hours, E(max) = 1.85 MeV, Egamma = 81keV (6.4%)] could be envisioned as an attractive radionuclide for use in liver cancer therapy owing to its high energy 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 micros were chosen as the particulate carrier due to their biocompatibility and ease of labeling with lanthanides. 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 of166Ho-HA was tested in normal Wistar rats by carrying out biodistribution and imaging studies. 166Ho was produced with a specific activity of 5.55-6.48 TBq/g and radionuclidic purity of approximately 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 (approximately 89% of injected activity after 2 days) with insignificant uptake in any other major organ/tissue. 166Ho-HA exhibited promising features as an agent for liver cancer therapy in preliminary studies and warrants further investigation