Molecular Imaging Companion Diagnostics

Abstract The status of certain proteins (e.g., expression and mutations) and/or biochemical processes in tumor samples is necessary to initiate specific anticancer therapies. This information is generally obtained by assays of biopsied or surgically resected tissues of primary and/or metastatic tumor lesions. The use of biopsied samples does not allow assessment of the entire tissue, which is particularly important when the aim is to detect heterogeneous and dynamic biomarkers of the tumors. Molecular imaging of tumor receptors and/or biochemical processes using radiolabeled small molecules, peptides, and antibodies has demonstrated potential as a companion diagnostic. This chapter discusses the use of nuclear and multiplexed imaging to evaluate tumors at both an anatomical and molecular level. The chapter starts by discussing small molecule imaging probes, and how probes that are radiolabeled analogs of endogenous substrates can be used for cancer diagnosis, staging, and patient selection of targeted therapies. It then describes how peptide imaging and therapeutic agents are developed as theranostic pairs for companion diagnostic purposes. The last section of the chapter discusses the main advantages and disadvantages of using radiolabeled antibodies for tumor diagnosis and to monitor treatment responses. In addition, this section highlights the problems of shedding antigens as biomarkers for tumor diagnosis and illustrates the ways by which pretargeting in vivo strategies can be promising in the imaging of this type of target.