Antisense oligodeoxynucleotides targeting internal exon sequences efficiently regulate TNF-α expression

Exon sequences upstream of splice sites play a critical role in mRNA processing, which is dependent on spliceosome interactions with these sites. Using antisense oligodeoxynucleotides (ODN), we targeted these and other sequences of the proinflammatory tumor necrosis factor-alpha (TNF-alpha) gene because it is multiply spliced and has been difficult to regulate with ODN in the past. ODN targeting exon sequences upstream of the donor splice sites of internal exons 2 (ORF4) and 3 (ORF6) significantly reduced TNF-alpha levels in stimulated U937 cells by 62% +/- 7% and 51% +/- 9%, respectively, in a dose-dependent manner but did not affect interleukin-6 (IL-6) levels. In contrast, ODN targeting the exon sequences downstream of the acceptor splice sites of exons 1, 2, and 3 failed to reduce TNF-alpha levels significantly under the same conditions, End-phosphorothioated ORF4 (ORF4-PE) significantly reduced TNF-alpha mRNA levels by greater than 80% (p < 0.001) and protein levels by 60% (p < 0.001) in U937 cells. ORF4-PE reduced newly synthesized TNF-a protein levels by >80% in lipopolysaccharide (LPS)-stimulated human macrophages, by greater than 60% in phorbol myristate acetate/phytohemagglutinin (PMA/PHA)-stimulated human peripheral blood mononuclear cells (PBMC), and by approximately 50% in LPS-stimulated murine monocytes, These results suggest that exon sequences nanking donor splice sites are highly susceptible target domains for antisense inhibition of TNF-alpha gene expression.