he challenges encountered in developing applications of antisense technologies are numerous: enhanced stability, efficient delivery, identification of selective sites in the target RNAs, and minimization of off-target effects.
Nuclease attack: To inhibit translation, the antisense oligonucleotides must reach the interior of the cell unaltered. That ability depends upon stability of the oligonucleotide toward extra and intracellular enzymes. Combating nuclease attack is one of the prime requirements for maintaining the efficiency of antisense agents. Natural phosphodiester oligodeoxynucleotides (or oligoribonucleotides) are quickly digested by nucleases both in vitro and in vivo and thus the overall activity of antisense is compromised. A vast number of chemically-modified nucleotides have been used in antisense experiments; fortunately it has been found that the chemical modification usually helps antisense molecules circumvent nuclease digestion.4, 6, 10