Use of Radiolabeled Liposomes for PEG-Liposome-Based Drug Targeting and Diagnostic Imaging Applications

Abstract

The development of new targeted diagnostic and therapeutic imaging agents is at the cutting edge of diagnostic imaging (Torchilin, 1995). When a specific targeted agent accumulates in pathological tissue, the diagnostic imaging physician is able to determine simultaneously that a disease process is present and its location in the body. Usually, the uptake of a targeted agent is due to alteration of a physiological process, and hence a disease process may be detected prior to manifestation of any anatomical changes. Targeted diagnostic imaging, therefore, has the ability to be more sensitive for the detection of some disease processes in early stages. Although targeted diagnostic imaging agents are currently being developed for use in imaging modalities such as computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound, nuclear medicine is the branch of diagnostic medicine with the longest history and the largest number of diagnostic and therapeutic targeted agents. This success in the field of nuclear medicine with targeted diagnostic imaging agents is probably due to the high signal response generated from an atomic decay which requires localization of only a small number of atoms at a particular body location in order for the photon emissions to be detected. While CT requires 10 to 100 mg of contrast agent per study and MRI requires 10-1 to 10-3, nuclear medicine imaging requires only 10-7 to 10-9 mg for diagnostic imaging (Wolf, 1995). Targeted agents developed for nuclear scintigraphy can be used in virtually all the organs of the body including bones, heart, liver, gallbladder, kidney, brain, soft tissues and tumors.