TEMPORARY EX-VIVO INHIBITION OF THE EXPRESSION OF THE HUMAN ONCOGENE HER2(NEU) BY A TRIPLE HELIX-FORMING OLIGONUCLEOTIDE

A 28-base phosphodiester triple helix-forming oligonucleotide, mostly G and A containing, targeted to a polypurine tract interrupted by a pu rine-pyrimidine inversion, situated upstream from the TATA box of the promoter of the human HER2 gene, was conceived by computer modeling, T he ''energetically best choice'' was oligo 28(C), which formed the tri ple helix in vitro, as proved by gel retardation and Fourier transform infrared spectroscopy, When administered as a complex with lipofectin , fluorescence confocal microscopy and electrophoresis confirmed the d elivery and persistence of this unprotected oligonucleotide inside MCF 7 (breast cancer) cells. At a concentration of 2 mu M, the oligonucleo tide reduced within 6 h the HER2 mRNA level to 42% (Northern blot) but did not interfere with the transcription of a housekeeping gene, glyc eraldehyde-3-phosphate dehydrogenase, During the first day of administ ration at 0.22 mu M, it lowered to 59% the HER2 protein in treated, as compared to nontreated, cells (ELISA), The effect was sequence specif ic when compared to that of five different negative controls, and it w as target selective when compared to the expression of a related, nont argeted protein, the epidermal growth factor receptor, By day 2, the i nhibitory effect was overcome by replenishment reactions.