Aptamers as smart ligands for the development of cancer-targeting nanocarriers

The short single-strand nucleic acids, so-called aptamers (Aps), are selected through systematic evolution of ligands by exponential enrichment (SELEX) using a pool of randomized sequences of oligonucleotides. Aps can form three-dimensional nanostructures and interact with their cognate biological targets with high affinity and specificity. The SELEX can be applied for in vitro, cell-based, and in vivo selection of Aps. Their unique physicochemical and biological characteristics make Aps excellent homing entities that can be used to target a wide range of molecular markers, making them comparable to monoclonal antibodies (mAbs) and Ab fragments. Nanoscale Ap-decorated drug delivery systems have widely been used to specifically deliver diagnostic/therapeutic agents to the intended diseased cells/tissues, including several types of malignancies. These nanosystems (NSs) can be used for the delivery of genes or drugs to modify the anomalous expression of designated genes or induce cytotoxic effects on tumor cells. Ap-based multifunctional NSs might serve as robust targeted therapies in combating intimidating cancers. These advanced NSs can be engineered to simultaneously target multiple biological targets in cancerous cells, causing desired inhibitory impacts on tumor cells. In this chapter, we provide comprehensive insights into smart multifunctional Ap-armed nanomedicines and theranostics and discuss their applications in cancer diagnosis and therapy.