Enhancement of methylcholanthrene-induced neoplastic transformation in murine C3H 10T1/2 fibroblasts by antisense phosphorothioate oligodeoxynucleotide sequences

Antisense phosphorothioate oligodeoxynucleotides (ODNs) are increasingly us ed to target specific proteins for inhibition. Previous reports of antisens e inhibition of the inducible nitric oxide synthase (iNOS) gene suggested i ts utility in defining the role of nitric oxide (NO) in carcinogenesis, as NO is mutagenic and chemical inhibitors of iNOS block neoplastic transforma tion in C3H 10T1/2 fibroblasts. Treatment with ODNs (0.025-25 mu M) directe d against 15mer sequences in the iNOS coding region decreased NO production consistent with a reduction of iNOS protein and iNOS mRNA, however, contro l ODNs (2.5 mu M) also showed considerable nonspecific inhibition of NO syn thesis. Treatment with both iNOS antisense and missense ODNs during the pro motional phase of the C3H10T1/2 transformation assay significantly increase d the number of neoplastic foci in 3-methylcholanthrene (MCA) treated cells which corresponded with the ability of the ODN to inhibit NO production. E nhanced neoplastic transformation and non-specific inhibition of NO synthes is resulting from exposure to antisense ODNs suggest Limitations to their l ong-term use in humans at higher doses. (C) 1999 Elsevier Science Ireland L td. All rights reserved.