THE ANTIPROLIFERATIVE ACTIVITY OF C-MYB AND C-MYC ANTISENSE OLIGONUCLEOTIDES IN SMOOTH-MUSCLE CELLS IS CAUSED BY A NONANTISENSE MECHANISM

Smooth muscle cell (SMC) proliferation is thought to play a major role in vascular restenosis after angioplasty and is a serious complicatio n of the procedure. Developing antisense (AS) oligonucleotides as ther apeutics is attractive because of the potentially high specificity of binding to their targets, and several investigators have reported inhi bition of SMC proliferation in vitro and in vivo by using AS strategie s. We report here the results of our experiments on vascular SMCs usin g AS oligonucleotides directed toward c-myb and c-myc. We found that s ignificant inhibition of SMC proliferation occurred with these specifi c AS sequences but that this inhibition was dearly not via a hybridiza tion-dependent AS mechanism, Rather, inhibition was due to the presenc e of four contiguous guanosine residues in the oligonucleotide sequenc e, This nas demonstrated in vitro in primary cultures of SMCs and in a rteries ex vivo, The ex vivo model developed here provides a rapid and effective system in which to screen potential oligonucleotide drugs f or restenosis. We have further explored the sequence requirements of t his non-AS effect and determined that phosphorothioate oligonucleotide s containing at least two sets of three or four consecutive guanosine residues inhibit SMC proliferation in vitro and ex vivo. These results suggest that previous AS data obtained using these and similar, conti guous guanosine-containing AS sequences be reevaluated and that there may be an additional class of nucleic acid compounds that have potenti al as antirestenosis therapeutics.