EFFECTS OF ANTISENSE C-MYB OLIGONUCLEOTIDES ON VASCULAR SMOOTH-MUSCLECELL-PROLIFERATION AND RESPONSE TO VESSEL WALL INJURY

The process of restenosis after arterial balloon dilatation has been d emonstrated to involve smooth muscle cell hyperplasia. Initial reports with antisense oligonucleotides directed against the proto-oncogene c -myb suggest marked in vitro specificity and in vivo efficacy. In the present study, we sought to confirm and extend the hypothesis that ant isense to c-myb results in a specific antiproliferative effect with a comprehensive assessment by using different oligonucleotide preparatio ns, different species, and tissue and cellular uptake experiments. Pho sphorothioate-protected oligonucleotides representing the appropriate sequence for antisense to c-myb and multiple controls were used to inh ibit proliferation of platelet-derived growth factor- and fetal bovine serum-stimulated rat, dog, and human aortic smooth muscle cells in vi tro and neointimal proliferation in the rat carotid injury model. In v itro experiments using identical culture conditions in rat, dog, and h uman aortic smooth muscle cells failed to show specificity as well as consistency in growth inhibitory effects that could be attributed to a n antisense mechanism. Proliferation of smooth muscle cell growth in c ulture was consistently inhibited with oligomers containing a contiguo us 4-guanosine residue motif. In vivo, the rat carotid injury neointim al hyperplasia was similar for antisense c-myb (0.095+/-0.009 mm(2)) a nd sense c-myb (0.090+/-0.009 mm(2)). Fluorescent-labeled oligonucleot ides were present in tissue after local delivery via pluronic gel, and their activity rapidly declined over a 72-hour period. Our findings p oint to the potential nonspecificity and lack of consistency of the an tisense oligonucleotide to c-myb in vitro and in vivo. An alternative nonantisense mechanism for the inhibition of smooth muscle cell prolif eration, involving contiguous 4-guanosine residues, is proposed.