Pharmacological inhibition of DNA repair enzymes differentially modulates telomerase activity and apoptosis in two human leukaemia cell lines

Purpose: To investigate the effect of wortmannin and 3-aminobenzamide (3-AB) on telomerase activity and apoptosis in two human leukaemia cells. Materials and methods: MOLT-4 (p53-wild type) and KG1a (p53-null) cells were irradiated with (gamma)-rays (3 Gy at 1.57 Gy min^-1) and the effects of wortmannin and 3-AB were evaluated. Telomerase activity was measured by polymerase chain reaction and the expression of human telomerase reverse transcriptase, human telomerase RNA and telomerase-associated protein 1 was assessed by reverse transcriptase-polymerase chain reaction. poptosis was evaluated by fluorescence microscopy and flow cytometry. Results: A radiation-induced up-regulation of telomerase activity was observed from 4 h post-irradiation in both cell lines. This up-regulation was abrogated by wortmannin and 3-AB. Telomerase activity was maximal 24 h post-irradiation, coinciding with an accumulation of human telomerase reverse transcriptase mRNA. poptosis and G2/M arrest were evident from A4 h post-irradiation in MOLT-4 cells. KG1a cells exhibited a G2/M block at 24 h post-irradiation and apoptosis increased between 24 and 48 h post-irradiation. 3-AB abolished G2/M blockage and enhanced radiation-induced apoptosis in both cell lines, while wortmannin ncreased apoptosis only in MOLT-4 cells. Conclusions: 3-AB inhibits the radiation-associated telomerase activity increase and enhances apoptosis in MOLT-4 and KG1a cells. Wortmannin, which also inhibits the radiation-associated telomerase activity increase in both cell lines, does not modify radiation-induced apoptosis in KG1a cells. DNA repair enzymes might be selective targets for enhancing radiosensitivity in certain tumour cells.