Role of Phosphoramidate Antisense in Specific Inhibition of K562 Leukemic Cell Line

Telomeres are specialized heterochromatin structures that act as protective caps at the ends of the chromosomes. Telomere maintenance in the majority of tumor cells is achieved by telomerase, a reverse transcriptase enzyme that catalyzes the synthesis of further telomeric DNA. Telomerase is detected in the majority of malignant cells. Thus, telomerase may represent a very good candidate for targeted therapy in cancer. To inhibit telomere maintenance by telomerase, approaches that directly target either telomerase and telomeres or the telomerase regulatory mechanisms have been used. Moreover, strategies targeting telomerase-positive cells as a means to directly kill the tumor cells have been tested. The aim of this study was to evaluate effects of antisense against the template region in the, telomerase RNA (hTR). The K562 cells were cultured and to inhibit telomerase activity, a 19-mer antisense oligonucleotide, complementary to hTR was designed. The modification of this sequence was N3′→P5′ phosphoramidate and FuGENE6 was used as transfection reagent. Telomerase activity was measured using TRAP assay. Telomerase activity decreased using both sense and antisense hTR after 3 days with 1 µM comparing to the scramble oligonucleotides. There was morphological changes observed in K562 cells and MTT assay demonstrated that treatment of these cells efficiently reduced cell viability. Our results clearly demonstrated that antisense phosphoramidate is a very good candidate for targeted therapy in K562 leukemic cell line. The applied antisense inhibits transcription of hTR efficiently and can be considered as a potential therapeutic approach for leukemia treatment.