New developments in the sequencing of viral genomes
have become popular in the past decade. These synthetic nucleosides,
nucleotides and nucleic acids have many applications in biology, biotechnology
and medicine. The development of antisense oligonucleotide technology as
therapeutic agents has recently gained approval from the Food and Drug
Administration for the commercialization and numerous clinical trials of these
therapeutic oligonucleotides4. The use of short fragments of nucleic
acids (oligonucleotides) as therapeutic agents or as tools to study gene
function is known as antisense technology1. In theory, antisense oligonucleotides can be designed to either interact
with proteins involved in the biosynthetic process or to bind to a
complementary sequence of the viral genome.
(Figure1)
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Figure 1: How Antisense Technology works.
Source: C&EN
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An antisense oligonucleotide is a short strand of deoxyribonculeotide
analogue that hybridizes with its complementary mRNA via the Watson-Crick
base-pairing model. Formation of this heteroduplex can either lead to
activation of RNAse H or the inhibition of ribosomal activity3. The
oligonucleotides must be able show resistance to naturally occurring nucleases
that cleave phosphodiester bonds2. The focus of current research
focuses on the chemical approaches to improve the properties of these
oligonucleotides, mainly concentrating on the increase of nuclease resistance
and mRNA binding affinity. Modifications of the oligonucleotides have been
made mainly on the phosphodiester backbone; as the hydrolytic cleavage of the
phosphodiester backbone is the main cause for the rapid degradation of
oligonucleotides by nucleases1. Replacement by other functional
groups has been one of the major strategies to improve stability; in addition backbone
modifications can influence other properties of oligonucleotides like RNA
binding affinity or behavior for cellular uptake5.
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Figure
2: A general synthetic Cycle of Oligonucleotide
Synthesis.
Source: www.exiqon.com
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Currently
at CSU Channel Islands, antisense research is being performed under the guidance
of Dr. Ahmed Awad and his research students; myself included. There are many
factors that play a role in determining the efficiency of oligonucleotides;
these properties are both intrinsic and extrinsic. The chemistry issues we
often find ourselves tackling in the laboratory are the intrinsic properties
such as length, size, net charge, sequence, and hybridization. The two most
common ribonucleosides dealt with in the laboratory are Uridine and Guanosine
who are respectively both the easiest and hardest to work with. The synthetic
routes to these modified ribonucleosides (RNG molecules) are straight forward
and include extensive use of a wide range of protecting groups in combination
with oxidation/reduction or substitution reactions (Figure 2).
The goal of
our research is to improve stability of these molecules by replacement of
different functional groups on the tertiary carbon of the ribose sugar. While we aren’t personally combating disease
in the laboratory, we are coming up with new ideas and pursing unusual routes
to these molecules. These qualities and
the specificity of binding make these techniques potentially powerful future
therapeutic tools for gene targeting and/ or expression regulation.
References
1 1. Eman M. Zaghloul, Andreas S. Madsen, Pedro M. D.
Moreno, Iulian I. Oprea, Samir El-Andaloussi, Burcu Bestas, Pankaj Gupta, Erik
B. Pedersen, Karin E. Lundin, Jesper Wengel, C. I. Edvard Smith,Nucleic Acids Res. 2011, 39(3), 1142–1154
2 2. Kurreck, J.; Eur, J.; Biochemistry. 2003, 270(8),1628-44. Review.
3 3. Lützelberger, M.; Kjems, J. Handbook of Experimental
Pharmacology. 2006, (173), 243-59. Review.
4 4. Popescu, F. D.; J Cell Mol Med. 2005, 9(4), 840-53.
Review.
Written by Jiovana Hermosillo
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