Aptamers offer advantages over other
oligonucleotide-based approaches that artificially interfere with target gene function due to their ability to bind
protein products of these genes with high affinity and specificity. However,
RNA aptamers are limited in their ability to target intracellular
proteins since even nuclease-resistant aptamers do not efficiently enter the intracellular compartments. Moreover, attempts at expressing
RNA aptamers within mammalian cells through vector-based approaches have been hampered by the presence of additional flanking sequences in expressed
RNA aptamers, which may alter their functional conformation. In this report, we successfully expressed a 'pure'
RNA aptamer specific for
NF-kappaB p50
protein (A-p50) utilizing an adenoviral vector employing the H1
RNA polymerase III promoter. Binding of the expressed aptamer to its target and subsequent inhibition of
NF-kappaB mediated intracellular events were demonstrated in human
lung adenocarcinoma cells (A549), murine mammary
carcinoma cells (4T1) as well as a human
tumor xenograft model. This success highlights the promise of
RNA aptamers to effectively target intracellular
proteins for in vitro discovery and in vivo applications.