Chapter 24 - Chemistry of Molecular Imaging: An Overview

Abstract

Molecular Imaging (MI) protocols require the availability of tailored probes that are specific for reporting on the selected event. The design of imaging probes relies on the setup of synthetic procedures for the preparation of the imaging reporters and the targeting vectors, as well as efficient bioconjugation routes to link the targeting and reporting moieties, eventually organized in nanosized macromolecular and supramolecular systems. The design of molecular imaging probes is dictated by the chosen imaging modality. Several chemical factors must be optimized in order to affect their in vivo behavior such as (i) the intravascular half-life (to allow the agents to accumulate at the target site), (ii) the binding affinity eventually through the design of multivalency systems, (iii) the capacity to carry a high payload of probe molecules able to generate strong contrast effects (particularly relevant for imaging modalities endowed with low sensitivity or for targeting procedures involving a low number of targeting epitopes); (iv) to modulate biodistribution, excretion, and toxicity properties. Special attention must be devoted to search for efficient conjugation procedures that occur under mild experimental conditions and selected examples of activated procedures (including the application of click chemistry applications) are reported. The chapter surveys also agents and procedures for cellular labeling including endosomal uptake by pinocytosis and electroporation, receptor-mediated endocytosis, phagocytosis and labeling at the outer cell surface.