MIXED BACKBONE ANTISENSE OLIGONUCLEOTIDES - DESIGN, BIOCHEMICAL AND BIOLOGICAL PROPERTIES OF OLIGONUCLEOTIDES CONTAINING 2'-5'-RIBORIBONUCLEOTIDE AND 3'-5'-DEOXYRIBONUCLEOTIDE SEGMENTS

We have designed and synthesized mixed backbone oligonucleotides (MBOs ) containing 2'-5'-ribo- and 3'-5'-deoxyribonucleotide segments. Therm al melting studies of the phosphodiester MBOs (three 2'-5' linkages at each end) with the complementary 3'-5'-DNA and -RNA target strands su ggest that 2'-5'-ribonucleoside incorporation into 3'-5'-oligodeoxyrib onucleotides reduces binding to the target strands compared with an al l 3'-5'-oligodeoxyribonucleotide of the same sequence and length, Incr easing the number of 2'-5' linkages (from six to nine) further reduces binding to the DNA target strand more than the RNA target strand [Kan dimalla,E.R. and Agrawal,S., (1996) Nucleic Acids Symp. Ser., 35, 125- 126]. Phosphorothioate (PS) analogs of MBOs destabilize the duplex wit h the DNA target strand more than the duplex with the RNA target stran d, Circular dichroism studies indicate that the duplexes of MBOs with the DNA and RNA target strands have spectral characteristics of both A - and B-type conformations, Compared with the control oligonucleotide, MBOs exhibit moderately higher stability against snake venom phosphod iesterase, S1 nuclease and in fetal calf serum, Although 2'-5' modific ation does not evoke RNase H activity, this modification does not effe ct the RNase H activation property of the 3'-5'-deoxyribonucleotide se gment adjacent to the modification, In vitro studies with MBOs suggest that they have lesser effects on cell proliferation, clotting prolong ation and hemolytic complement lysis than do control PS oligodeoxyribo nucleotides, PS analogs of MBOs show HIV-1 inhibition comparable with that of a control PS oligodeoxyribonucleotide with all 3'-5' linkages, The current results suggest that a limited number of 2'-5' linkages c ould be used in conjunction with PS oligonucleotides to further modula te the properties of antisense oligonucleotides as therapeutic agents.