Liposomes as Carriers of Radionuclides: From Imaging to Therapy

Abstract

Liposomes have been studied quite extensively during the last twenty years or so as carriers for a variety of diagnostic molecules, in order to enhance the obtained in vivo target-to-background contrast, thus improve imaging resolution. In such applications, unlike chemotherapy and even more radiotherapy, low radiation doses are generally administered hence, apart from risk assessment purposes, the need for radiation dosimetry is not critical for their success. In the present article we will try to present and analyze critical factors that may affect any attempt to construct and investigate liposomes as carriers of particle-emitting radionuclides for radiotherapeutic purposes. Since dosimetric considerations for this kind of applications are considered essential for establishing radiotoxicity levels and dose-response relations for both healthy and tumor tissues, a description of current dosimetry methodologies will be included. It is aimed that the conceptual differences between imaging and therapy using radiolabeled liposome conjugates, along with those between chemotherapy and radiotherapy will be elucidated. The complex interplay of different pharmacokinetic (liposome biodistribution), physical (radionuclide half-life, particle emission characteristics), physicochemical (liposome particle size, surface charge), and physiological (tumor dimensions, vasculature, pH) parameters will be qualitatively investigated towards optimal selection and design of liposome-radionuclide complexes.