Aptamers as imaging agents

Aptamers are structured oligonucleotides able to bind with high affinity and specificity a wide range of targets. Over the last decade, aptamers have been developed as targeting agents for diagnostics. Advances in imaging methods have led to a new generation of targeting molecules such as aptamer-based probes.

Aptamers are selected through a combinatorial strategy termed SELEX (systematic evolution of ligands by exponential enrichment), and can be easily modified for generating new diagnostic tools or therapeutic agents. These modifications increase the nuclease resistance and improve the in vivo bioavailability, and conjugations of aptamer to appropriate labels provide colorimetric, fluorescent, or radiolabeled aptamers for the detection of cancer-related antigens.

This review reports on the different aptamer-based imaging probes developed for ex vivo and in vivo applications. The advantages and challenges in developing aptamer-based probes will be discussed.

The applications of aptamers range from diagnostic to therapeutic. Their binding properties, retention in the tumor region and clearance properties make them relevant tumor imaging probes.