In vitro anti-radiation effects of antisense thiodeoxyoligonucleotides targeted to Bax mRNA

Objective: The ratio of Bcl-2/Bax proteins is a key checkpoint of apoptotic initiation by radiation. The goal of the present study was to increase the ratio of Bcl-2/Bax proteins through reducing translation of Bax protein by antisense thiodeoxyoligonucleotides targeted to Bax mRNA, and thus to inhibit radiation-induced apoptosis and to enhance cell survival. Methods: Immediately after exposure of human embryonic lung fibroblast (HELF) and mice to γ-radiation, the HELF and mouse bone marrow cells were treated with Bax antisense deoxyoligonucleotides for 6 h (final concentration was 100 nmol/L). The survival profile of HELF was determined with MTT and SRB assay, the mouse CFU-GM with CFU-GM colony formation. With RT-PCR and flow cytometry, the alteration of Bax mRNA expression and cell cycle of HELF were examined in order to explore its mechanisms of action. Results: The survival rate of treated HELF increased by 24.4% (MTT) and 12.8% (SRB) (P<0.01). The count of CFU-GM colonies in treated group was significantly higher than that in control (72 ± 17 vs 13± 6, P<0.01). The result of RT-PCR showed that the ratio between Bax and β-actin in treated group and control was 43.9% and 68.6%, respectively. The proportion of total S-phase of HELF of treated group and control was 24.2% and 7.7% determined by flow cytometry. The above suggested that the number of copies of Bax mRNA be lower in treated cells than in control cells, and the treated cells may have more active proliferation. Conclusions: the antisense thiodeoxyoligonucleotides could promote the survival of cells exposed to γ-ray, and its mechanisms might involve reducing expression of Bax protein secondary to damage of target mRNA, inhibiting apoptotic initiation and enhancing active proliferation