A Unique c-myc-Targeted Triplex-Forming Oligonucleotide Inhibits the Growth of Ovarian and Cervical Carcinomas in Vitro

A 27-base pair triplex forming oligonucleotide (G27-oligonucleotide) targeted to the "puf" regulatory protein-binding domain of the human c-myc oncogene has been conjugated with the DNA-binding molecule acridine (G27-conjugate) in order to obtain a drug with high binding affinity as well as high sequence specificity. Both the triplex-forming oligonucleotide and its acridine conjugate are shown to form triple-stranded DNA at the site of the target sequence by DNase 1 footprinting. When the cervical carcinoma cell line HeLa was exposed to 4 microM concentrations of the G27-oligonucleotide the viable cell count fell to 89, 56, and 49% of control at 25, 50, and 72 hr. After exposure to 1 microM G27-conjugate the viable cell count fell to 87, 50, and 33% of control. Nonspecific reductions in cell number were found for the control oligonucleotides to 79 and 82% of control. When SKOV-3 cells were exposed to the same concentrations of oligonucleotides, viable cell count in relation to control fell to 43, 50, and 67% with the G27-oligonucleotide and 57, 52, and 53% with the G27-conjugate at 24, 48, and 72 hr. The control oligonucleotides again caused a small nonspecific drop in the viable cell number.