Preface

Oligonucleotides are comprised of nucleoside bases, sugars, and triphosphates. These nucleic acids are biological macromolecules found in all life forms encoding genetic information.

The chemical composition of nucleic acids was extensively studied in the early 1900s and five nucleotide bases including uracil have been identified. Although the elemental compositions were known, the correct structures were not established until the chemical synthesis of nucleotides was performed. Following various milestone inventions by eminent scientists like Emil Fischer and Albert Kossel, James Watson, Francis Crick, and Rosalind Franklin discovered the double helical structure of DNA, for which Watson and Crick were awarded the Nobel Prize. This discovery helped to solve the most significant biological riddle of the time and advance oligonucleotide-based research.

In recent decades, a plethora of modified nucleotides have been synthesized using nucleic acid chemistry. These molecules have proved to be useful for gene therapy and DNA-based diagnostics. Diverse forms of structures, chemistries, and mechanisms of action exist for oligonucleotide-based therapeutics. These drug candidates target either mRNAs or proteins. Antisense oligonucleotides (ASOs), siRNAs, antagomirs, splice-switching oligonucleotides, and DNAzymes target mainly RNA moiety, while immunostimulatory sequences and aptamers target proteins. The recent approval of many oligonucleotide-based drug candidates is indicative of the extensive vitality of the field. The unique base-pairing properties of nucleic acids have already been exploited to develop biosensors for disease diagnosis. The ability of single-stranded oligonucleotides or aptamers to self-assemble into complex structures may possess enormous potential in future nanoscale engineering and DNA-based computing. This book discusses the various biological processes targeted and the corresponding oligonucleotide interventions. It includes six chapters that discuss new developments in modified oligonucleotides and various theranostic applications of oligonucleotides.

I would like to give my heartfelt thanks to all the authors and contributors as well as the staff at IntechOpen. I believe that the case studies of modified bases, cutting-edge fluorescence in situ hybridization (FISH) technology and other techniques discussed in this book will provide guidance and support to researchers in the field as well as future developers in the oligonucleotide industry.

> **Arghya Sett** Postdoc Research Scientist, Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Prague, Czech Republic

**1**

Section 1

Introduction

Section 1 Introduction
