Realizing the potential of the Actinium-225 radionuclide generator in targeted alpha particle therapy applications

Abstract

Alpha particle-emitting isotopes have been proposed as novel cytotoxic agents for augmenting targeted therapy. Properties of alpha particle radiation such as their limited range in tissue of a few cell diameters and their high linear energy transfer leading to dense radiation damage along each alpha track are promising in the treatment of cancer, especially when single cells or clusters of tumor cells are targeted. Actinium-225 (225 Ac) is an alpha particle-emitting radionuclide that generates 4 net alpha particle isotopes in a short decay chain to stable 209 Bi, and as such can be described as an alpha particle nanogenerator. This article reviews the literature pertaining to the research, development, and utilization of targeted 225 Ac to potently and specifically affect cancer.

Figure 1

The ²²⁹Th decay scheme.

Figure 2

An illustration of the ²²⁵Ac nanogenerator system.

Figure 3

Murine biodistribution data at 24 hours for ²²⁵Ac-acetate, [²²⁵Ac]DOTA-SCN, and [²²⁵Ac]DOTA-HuM195.

Figure 4

Biodistribution data at 24 hours for [²²⁵Ac]DOTA-HuM195 administered to two cynomolgus monkeys. Note the reduction in the renal ²¹³Bi activity in the DMPS-treated monkey as compared to an untreated (no DMPS) animal.