Radiosensitization by 6-aminonicotinamide and 2-deoxy-D-glucose in human cancer cells

The aim was to exploit simultaneous inhibition of glycolytic and pentose phosphate pathways of energy production for radiosensitization using 2-deoxy-D-glucose (2-DG) and 6-aminonicotinamide (6-AN) in transformed mammalian cells. Two human tumour cell lines ( cerebral glioma, BMG-1 and squamous carcinoma cells 4197) were investigated. 2-DG and/ or 6-AN added at the time of irradiation were present for 4 h after radiation. Radiation-induced cell death (macrocolony assay), cytogenetic damage ( micronuclei formation), cell cycle delay ( bromodeoxyuridne ( BrdU) pulse chase), apoptosis ( externalization of phosphotidylserine (PS) by annexin V), chromatin-bound proliferation cell nuclear antigen ( PCNA) and cellular glutathione (GSH) levels were investigated as parameters of radiation response. The presence of 2-DG ( 5 mM) during and for 4 h after irradiation increased the radiation-induced micronuclei formation and cell death, and caused a time-dependent decrease in GSH levels in BMG-1 cells while no significant effects could be observed in 4197 cells. 6-AN ( 5 mu M) enhanced the radiosensitivity of both cell lines and reduced the GSH content by nearly 50% in gamma-irradiated 4197 cells. Combining 2-DG and 6-AN caused a profound decrease in the GSH content and enhanced the radiation damage in both the cell lines by increasing mitotic and apoptotic cell death. Further, the combination (2-DG +6-AN) enhanced the radiation-induced G2 block, besides arresting cells in S phase and inhibited the recruitment of PCNA. The combination of 2-DG and 6-AN enhances radiation damage by modifying damage response pathways and has the potential for improving radiotherapy of cancer.