PET radiopharmaceuticals for metabolic imaging in oncology

Early detection is critical to successful treatment and long-term cure of cancer. Detection relies on a broad array of mutually supporting diagnostic modalities, including visual detection of superficial lesions, quantification of biological and metabolic markers, and noninvasive imaging. The advantage of imaging techniques over circulating markers is that imaging defines the precise location of the tumor. Of the imaging techniques available today, positron emission tomography (PET) offers the best combination of selectivity, specificity, and sensitivity when used with appropriate molecular radiopharmaceuticals. In addition, PET images can be analyzed to provide quantitative kinetic data (parametric imaging) and biochemical knowledge at physiological molecular concentrations. This information is invaluable in staging, therapy planning, and therapeutic monitoring of cancer. Bioenergetics, genomics, and proteomics present unique opportunities to study and characterize cell growth and proliferation using PET. 2-[F-18]FDG, a probe of one component of cellular glycolysis, is the major PET tracer used in clinical oncology today. However, the potential contributions of PET to oncology extend well beyond 2-[F-18]FDG and other F-18-labeled tracers. Chemical classes of PET radiotracers commonly used in preclinical and clinical experimental oncology include carbohydrates, fatty acids, nucleosides, oligonucleotides, nitroimidazoles, amino acids, peptides, proteins, and antibodies. Fluorine-18, C-11, and radiometals are the most frequently used radionuclides. These PET radiopharmaceuticals are useful in the assessment of tissue bioenergetics, hypoxia, proliferation, and function. The following paragraphs present an overview of hexose-based measurement of glucose metabolism as an indicator of tumor viability, and nitroimidazole-based compounds as markers of regional tissue hypoxia, using PET. Emphasis is placed on the use of [F-18]-fluorodeoxyglucose (FDG) and [F-18] fluoroazomycin arabinoside (FAZA) in oncology. (C) 2004 Elsevier B.V. All rights reserved.