Progress in
oligonucleotide chemistry has provided second-generation
antisense oligonucleotides with increased efficacy and reduced non-antisense-related toxicity. The ability of the 2'-O-(2-methoxyethylribose) (2'-MOE)-modified phosphorothioate gapmer
oligonucleotide 4625, which matches the bcl-2
mRNA and has three base-mismatches to bcl-xL, to inhibit bcl-2 and bcl-xL expression and induce
tumor cell apoptosis has been described. Here we investigated the consequences of adding of 2'-MOE or 2'-Me modifications to
ribonucleotides at either the two ends of the sequence, or the center region together with different combinations of phosphodiester/phosphorothioate backbones on the activity of
oligonucleotide 4625. The ability of the various 4625 analogs, including the parental first-generation
oligonucleotide 3005, to inhibit bcl-2 and bcl-xL expression, and diminish cell growth or induce
tumor cell death was assessed in SW2
lung cancer cells using real-time PCR, Western blotting and cell viability assays. Only
oligonucleotide 4625 exhibited a potent bispecific antisense activity against bcl-2 and bcl-xL, which effectively reduced
tumor cell viability. The other
antisense oligonucleotides were either uniquely active against bcl-2 or completely inactive. Our data suggest that the 2'-MOE modification in combination with the phophorothioate gapmer chemistry is the optimal format of the 4625 sequence in terms of antisense activity and
biological efficacy.