Antisense Oligonucleotides and RNA Interference - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 360

efforts have been made in previous and ongoing research to judicially modify anti-
sense agents and to develop an effective formulation for the desired application.
Therapeutic silencing of various endogenous genes by systemic administration by
the delivery of modified siRNAs was studied. To study antitumor activity, protamine-
antibody-mediated siRNA was injected intravenously and intratumorally in rodents
[204] . siRNA-targeting Fas protein protects mice against renal ischemia-reperfusion
injury and fulminant hepatitis [205,206] . Caspase 8 siRNA was targeted to liver via
systemic administration to prevent acute liver failure in mice [207] .
7.9 Applications of Antisense Drugs
Antisense technology can potentially be applied to treat various diseases, especially
viral infections and cancers. However, with rapid progress in antisense technology,
the technique has found newer applications to treat several other infections, which
we discuss here in detail.
7.9.1 Genetic Research
AS ODNs are now being widely used in basic research to elucidate the general splicing
patterns of various genes, which in turn may help in treating genetic disorders [99,208] .
Oligonucleotides splice out specific introns from a pre-mRNA by interfering with the
assembly of a spliceosome. A spliceosome is complex comprising various proteins and
small nuclear RNA (snRNA) and is formed for each splicing event. Thus, AS ODNs
can be used to elucidate the various pathways involved in the synthesis of a protein
and to determine the various possible mutagenic splicing sites alterations that result in
inappropriate protein production. In genetic disorders, point mutations result in new
splice sites within the introns, directing the splicing machinery to rupture the splicing
pathways, resulting in the formation of a defective mRNA and an inappropriate protein
product [209] . Blocking of these splice sites using AS ODNs thus prevents inappropri-
ate protein expression. However, oligonucleotides must not activate RNase H enzyme
when used to alter these splicing patterns. This is usually achieved by inducing certain
chemical modifications in the AS ODNs such that the oligonucleotide RNA duplex is
not recognized by the RNase H [210] . Examples of such enzymes include methylphos-
phonate derivatives, O -alkyl oligonucleotides, and PNAs [211] . Using antisense tech-
nology, O -alkyl oligonucleotides or morpholino-oligonucleotides have been reported to
treat genetic blood disorder -thelassemia completely [212,213] .
7.9.2 CNS Protein Function
The application of antisense technology to investigate protein function in the liv-
ing brain has recently been reported. This technology has been successfully used to
study central nervous system (CNS) proteins such as transmembrane receptors, ion
channels, transporters, G proteins, and growth factors [214] . Many of these belong