Radiosensitization to X-ray radiation by telomerase inhibitor MST-312 in human hepatoma HepG2 cells.

Aims: Previous studies in malignant cells have shown that irradiation-induced upregulation of telomerase activity, not only protected damaged telomeres, but also contributed to DNA damage repair by chromosomal healing and increased resistance to irradiation. The purpose of the present study was to investigate the radiosensitizing effect of telomerase inhibitor MST-312 and the corresponding mechanism in the human hepatoma cell line HepG2.

Main Methods: Cell proliferation, telomerase activity, cell cycle distribution, DNA damage and repair, expression of p53, mitochondrial membrane potential, and cell apoptosis were measured with the MTT assay, real-time fluorescent quantitative PCR, flow cytometry, immunofluorescence, western blots, JC-1 staining, and Hoechst 33258 staining, respectively.

Key Findings: MST-312 effectively inhibited telomerase activity and showed relative weak toxicity to HepG2 cells at 4 μM. Compared with irradiation alone, 4 μM MST-312 pretreatment, followed by X-ray treatment, significantly reduced clonogenic potential. Aggravated DNA damage and increased sub-G1 cell fractions were observed. Further investigation found that homologous recombination (HR) repair protein Rad51 foci nuclear formation was blocked, and expression of p53 was elevated. These led to the collapse of mitochondrial membrane potential, and enhanced the apoptotic rate.

Significance: These data demonstrated that disturbances of telomerase function could enhance the radiosensitivity of HepG2 cells to X-ray irradiation by impairing HR repair processes. In addition, telomerase inhibitor MST-312 may be useful as an adjuvant treatment in combination with irradiation.