**Dr. Rahul Shukla, PhD**

Assistant Professor, Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research, Raebareli, Lucknow, India

## **Dr. Neeraj K. Garg**

Formulation Scientist, Sun Pharmaceutical Industries Limited, Vadodara, India

#### **Prakash S. Bisen**

Professor and Advisor, Institute of Medical Sciences, Jaipur National University, Jaipur

Emeritus Professor, School of Studies in Biotechnology, Jiwaji University, Gwalior

**1**

**Chapter 1**

**Abstract**

small molecule drugs.

**1. Introduction**

renal clearance, high-throughput

three-dimensional shape, stacking and hydrogen bonds.

Opportunities

Aptamers for Targeted Delivery:

Aptamers are synthetic ssDNA/RNA molecules that are emerging as novel tools for the development of therapeutics, especially for targeted delivery. Aptamers are comparable to monoclonal antibodies, which are well-established therapeutic molecules, in terms of specificity and affinity to their target. The advantage of aptamers over antibodies includes their high stability, ease of synthesis, less batchto-batch variation, easy chemical modifications that allow different conjugation chemistries, small size for better tissue penetration and low immunogenicity. These advantages make aptamers an important tool for use in therapeutics for targeted delivery. However, aptamers do have some limitations that have hindered their widespread clinical use as a therapeutic agent. Some of their common limitations include serum stability, renal filtration and endocytic escape. Other limitations that are more specific to aptamers include lack of diversity in the aptamer library, nuclease susceptibility and claims of aptamer specificity as well. This book chapter sheds light on these challenges, and using examples, it explains the scientific advancements that have been achieved in overcoming these limitations. We will end this chapter by discussing the use of high-throughput technology, which is the only way of truly industrializing the aptamer technology akin to the development of

**Keywords:** aptamers, SELEX, targeted delivery, serum stability, endosomal escape,

Aptamers are small single-stranded RNA or DNA oligonucleotides that specifically bind to their target due to their unique 3-dimensional structure. They were first independently developed by the groups of Gold and Szostak in 1990 [1, 2]. Aptamers are selected from a pool of random oligonucleotide library (>1015 random sequences) by iterative rounds of selection and amplification by a process called Systematic Evolution of Ligands by EXponential Enrichment (SELEX). Different intermolecular interactions facilitate the interaction of aptamers with their target including van der Waal's forces, electrostatic interactions between charged groups,

Functionally aptamers are same as antibodies; however, their advantages over antibodies include small size, less immunogenicity, ease of synthesis, easy chemical

Current Challenges and Future

*Chetan Chandola and Muniasamy Neerathilingam*
