Volume 271, Number 24,
Issue of June 14, 1996
pp. 14533-14540
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
Nuclease Resistance and Antisense Activity of Modified
Oligonucleotides Targeted to Ha-ras
(Received for publication, January 3, 1996, and in revised form, March 27, 1996)
Brett P.
Monia
,
Joseph F.
Johnston
,
Henri
Sasmor
¶
and
Lendell L.
Cummins
¶
From the
Department of Molecular Pharmacology and
¶ Division of Medicinal Chemistry, Isis Pharmaceuticals,
Carlsbad, California 92008
We have previously described structure-activity
studies on a 17-mer uniform phosphorothioate antisense sequence
targeted to human Ha-ras. In an effort to further improve
the pharmacological properties of antisense oligonucleotides,
structure-activity studies on this 17-mer sequence were expanded to
examine both the effects of replacing phosphorothioate backbone
linkages with phosphodiester linkages and the effects of incorporating
various 2
-sugar modifications into phosphorothioate and phosphodiester
oligonucleotides on oligonucleotide stability against nucleases
in vitro and on antisense activity in cells. Replacement of
three or more phosphorothioate linkages with phosphodiester linkages
greatly compromised both nuclease resistance and antisense activity,
and these effects correlated directly with the number of phosphodiester
linkages incorporated into the oligonucleotide. However, substantial
nuclease resistance, sufficient for obtaining potent antisense effects
in cells, was conferred to phosphodiester oligonucleotides by
incorporation of appropriate 2
-alkoxy sugar modifications. Nuclease
stability and antisense activity imparted by these sugar modifications
in phosphodiester backbones correlated with the size of the 2
-alkoxy
substituent (pentoxy > propoxy > methoxy > deoxy).
Furthermore, antisense activity mediated by oligonucleotides that
exhibit partial resistance to nucleolytic degradation was dependent on
both oligonucleotide concentration and the duration of oligonucleotide
treatment.