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Much research was done in the past decade on the potential therapeutic feasibility
of oligonucleotide-based medicine such as antisense DNA, ribozyme and small interring
RNA (siRNA). After deciphering the entire human gene sequence, the trend
of oligonucleotide-based medicine and gene therapy have been accepted with a positive
reaction in the medical arena. Synthetic oligonucleotides have greater potential to become a
new type of rationally designed therapeutic agent (Matthews and Kricka, 1988; and
Uhlmann and Peyman, 1990). The synthetic oligonucleotides interfere with the expression of a
selected gene through interaction with a genomic DNA or regulatory proteins and mRNA (Harel et al., 1989; Bielinska et al., 1990; Tuerk and Gold, 1990; Wetmur, 1991; and
Bock et al., 1992). The recognition of antisense oligonucleotides with target mRNA sequences is
through Watson-Crick hydrogen bonding between A and T; and G and C. This type of
recognition is highly specific in nature and may lead to the development of site specific and less
toxic therapeutic agents (Stephenson and Zamecnik, 1978). Diseases which are due to
virus protein, aberrant proliferate protein, and inflammatory cytokines can be eliminated
by oligonucleotide-based medicine. The oligonucleotide-based medicine has been in
the mainstream pharmaceutical product line since the introduction of
Vitravene, the first antisense DNA against cytomegalovirus retinitis
(CMV), which appeared in the market in 1998. Rural life in India and elsewhere has poor sanitary conditions and lack
of education and medical facilities. Because of these problems, the rural population, cattle and
plants most often acquire various types of viral diseases. Therefore, the development
of oligonucleotide-based therapeutics such as Vitravene will be useful for the rural society.
The length of the antisense oligonucleotide affects its specificity for the target
sequence. An oligonucleotide containing 13 or more bases may recognize a unique sequence
that occurs only once in a eukaryotic mRNA pool (Helene and Toulme, 1989).
Theoretically, there should be an increase in the sequence specificity as the length of the
oligonucleotide (less than 15 mer) increases. But it has been observed that an increase in the length of
an antisense oligonucleotide beyond a minimum length which can hybridize with the
target (11-14 bases) might decrease in its specificity (Helene and Toulme, 1989;
Herschlag, 1991; and Woolf et al., 1992). A decrease in hybridization specificity might lead to
non-sequence-specific effects and subsequent increased toxicity (Woolf et al., 1992; and Stein and Chang, 1993). Cooperative interactions such as hydrogen bonding,
hydrophobic interactions and π-π* stacking have been used to improve the binding of
synthetic oligonucleotide to a single stranded DNA or RNA through duplex formation (Maher
and Dolnick, 1988; Grgaznov and Lloyed, 1993; and Kandimalla et al., 1995) or a double stranded DNA through triplex formation (Strobel and Dervan, 1989; Distefano et al., 1991; Distefano and Dervan, 1992; Colocci and Distefano, 1993; and Colocci and
Dervan 1994). Here, we describe the modulation of oligonucleotide duplex DNA/DNA and
DNA/RNA stability via a disulfide bond between the two adjacent thiol groups
containing oligonucleotides. Figure 1 shows the disulfide bond in oligonucleotides. |
