In vivo imaging of oligonucleotides with nuclear tomography

Positron emission tomography (PET) and single photon emission tomography (SPECT) are high-resolution, sensitive, molecular and functional imaging techniques that permit repeated, noninvasive assessment and quantification of specific biological and pharmacological processes in humans. PET and SPECT are also the most advanced technologies currently available for studying in vivo molecular interactions and therefore can advantageously play a key role in both drug discovery and development of pharmaceuticals, by assessing their in vivo distribution, pharmacokinetics, and dynamics, once labeled with a positron or gamma-emitter. Recent advances in positron and gamma-emitter labeling of bioconjugates allow the design and development of complex high-molecular-weight bioactive chemical structures as radiopharmaceuticals including single-stranded oligonucleotides. Besides, the introduction of high-resolution tomographic devices for imaging the distribution of radioactivity in small animal models such as mice and rats offers a unique opportunity to study the biological behavior of labeled compounds in integrated, unperturbed living systems. The present review illustrates the current technologies for labeling oligonucleotides with various radioisotopes, and their use as in vivo probes of oligonucleotide distribution and molecular interactions in target tissues. Emphasis will be also given to the role which could be played by these technologies in the development of oligonucleotide-based drugs.