Optimizing radiation therapy of brain tumours by combination of 5-bromo-2-deoxy-uridine & 2-deoxy-D-glucose

The effects of 5-bromo-2-deoxy-uridine (BrdU) and 2-deoxy-D-glucose (2-DG) on 60Co-gamma ray induced damage were studied in a human glioma cell line grown as monolayer. Radiation induced micronuclei formation was used as an index of cytogenetic damage. Exponentially growing cells (doubling time 16-20 h) were incubated in the presence of BrdU (0.8 microM, in dark) for 24 h. After removing BrdU, cells were irradiated (1-4 Gy), incubated with or without 2-DG (2-3 h), and grown further (for 18, 24, 30 or 45 h) for assay of damage. It was observed that (i) BrdU and 2-DG treatments did not induce micronuclei formation in unirradiated cultures; (ii) pre-irradiation presence of BrdU increased the gamma-ray induced micronuclei formation; (iii) incubation of irradiated cells under sub-optimal growth conditions [Dulbecco's modified minimal essential medium (DMEM) + 1% serum, or DMEM alone] instead of growth medium (DMEM + 5% serum) progressively decreased micronuclei formation; and (iv) post-irradiation presence of 2-DG (1.25, 2.5, 5 mM, 2-3 h in DMEM + 1% serum) enhanced the radiation damage with and without BrdU treatment at all the time points studied. These observations suggest that (i) radiation induced lesions leading to micronuclei formation in proliferating cells are, at least, partly repairable; (ii) the presence of 2-DG (2DG/glucose > or = 0.25) for short intervals (approximately 2 h), could enhance radiation damage in proliferating brain tumour cells, in the absence as well as presence of BrdU incorporation; and (iii) the combination of 2-DG could reduce BrdU doses required for radiosensitization of brain tumours, reducing, thereby, its toxic side effects.