16. Engineering Aptamers for Biomedical Applications: Part II

The development of new targeting means for the specific and safe delivery of drugs to diseased cells or tissues has become a need with potential widespread applications in medicine. Because of their high specificity of targeting, aptamers offer an innovative highly promising option as delivery agents for nanoparticles, siRNA bioconjugates, chemotherapeutic cargos, and molecular imaging probes. Indeed, aptamers are short, single-stranded oligonucleotides (ODNs) that have been shown as high-affinity ligands and potential antagonists of disease-associated proteins. They discriminate between closely related targets and are characterized by high specificity, convenient synthesis and modification with high batch fidelity, rapid tissue penetration, and long-term stability. Further, nucleic acid aptamer-based drugs show low in vivo immunogenicity, a major obstacle in the development of protein-based therapeutics. As such, aptamers couple the advantages of the specific binding of monoclonal antibodies to the chemical nature of nucleic acids. Here, we will focus on the development of multifunctional aptamer-based bioconjugates for targeted delivery of therapeutics and imaging agents to diseased cells and tissues. The broad spectrum of ways for aptamer engineering will be discussed in light of the pros and cons for biomedical developments in terms of in vivo specificity, efficacy, stability, and toxicity.