Developing Low Molecular Weight PET and SPECT Imaging Agents

Imaging agents for positron emission tomography (PET) and single‐photon emission computerized tomography (SPECT) have shown their utility in many situations, answering clinical questions related to drug development and medical considerations. The discovery and development of imaging agents follow a well‐understood process, with variations related to available starting points and to the envisaged imaging application. This article describes the general development path leading from the expression of an imaging need and project initiation to a clinically usable imaging agent. The definition of the project rationale, the design and optimization of early leads, and the assessment of the imaging potential of an imaging agent candidate are followed by preclinical and clinical development activities that differ from those required for therapeutic agents. These include radiolabeling with a positron emitter and first‐in‐human clinical studies, to rapidly evaluate the ability of a new imaging agent to address the questions it was designed to answer. From a clinical need to an imaging agent. PET and SPECT imaging agents are exceptionally useful tools to understand human biology and support the development of clinically efficacious drug candidates. This article describes the process starting from a clinical need, the optimization of an imaging agent, and how, after initial confirmation of its fitness for imaging purposes, they can uniquely address both drug‐ and disease‐related clinical questions.