A c‐myc Phosphorothioate Oligonucleotide Protects U87‐MG Glioblastoma Cells from Toxicity at High Concentrations of Lipofectin and Streptolysin O

Abstract

The pharmacological activity of an antisense oligodeoxynucleotide (ODN) targeted to c-myc (15mycAS) was evaluated in the glioblastoma-derived cell line U87-MG. ODNs with both phosphodiester (PO) and phosphorothioate (PS) backbones, and with 3′ hairpin sequences, were used with lipofectin and streptolysin O as transfection reagents. At non-toxic concentrations of lipofectin, cellular association was low and no evidence of an antisense mechanism was seen on evaluation of cell proliferation or c-Myc protein expression. At a high lipofectin concentration (25 μg mL−1), which resulted in loss of more than 50% cell viability, ODN uptake was enhanced, but no reduction in c-Myc protein expression was observed with any of the 15mycAS ODNs. However, treatment with the antisense PS ODN (15mycAS PS), specifically resulted in protection of the viable cell number. This cytoprotective effect was concentration- and chemistry-dependent. Three 15mer control PS ODNs, the PO form of 15mycAS, and the hairpin stabilized PO and PS forms (15mycASHP2 PO and 15mycASHP2 PS, respectively) did not show cytoprotection. A similar protective effect of 15mycAS PS was also seen with the transfection agent streptolysin O. These data demonstrate a potential source of misinterpretation in antisense experiments and emphasize the need to consider possible interactions of ODNs with lipids or cell membranes in the design of effective antisense strategies.