Heterogeneity in 2-deoxy-D-glucose-induced modifications in energetics andradiation responses of human tumor cell lines

Purpose: The glucose analog and glycolytic inhibitor, 2-deoxy-D-glucose (2- DG), has been shown to differentially enhance the radiation damage in tumor cells by inhibiting the postirradiation repair processes. The present stud y was undertaken to examine the relationship between 2-DG-induced modificat ion of energy metabolism and cellular radioresponses and to identify the mo st relevant parameter(s) for predicting the tumor response to the combined treatment of radiation + 2-DG. Methods and Materials: Six human tumor cell Lines (glioma: BMG-1 and U-87, squamous cell carcinoma: 4451 and 4197, and melanoma: MeWo and Be-11) were investigated. Cells were exposed to 2 Gy of Co-60 gamma -rays or 250 kVP X- rays and maintained under liquid-holding conditions 2-4 h to facilitate rep air. 2-DG (5 mM, equimolar with glucose) that was added at the time of irra diation was present during the liquid holding. Glucose utilization, lactate production (enzymatic assays), and adenine nucleotides (high performance l iquid chromatography and capillary isotachophoresis) were investigated as p arameters of energy metabolism. Induction and repair of DNA damage (comet a ssay), cytogenetic damage (micronuclei formation), and cell death (macrocol ony assay) were analyzed as parameters of radiation response. Results: The glucose consumption and lactate production of glioma cell line s (BMG-1 and U-87) were nearly 2-fold higher than the squamous carcinoma ce ll lines (4197 and 4451), The ATP content varied from 3.0 to 6.5 femto mole s/cell among these lines, whereas the energy charge (0.86-0.90) did not sho w much variation. Presence of 2-DG inhibited the rate of glucose usage and glycolysis by 30-40% in glioma cell lines and by 15-20% in squamous carcino ma lines, while ATP levels reduced by nearly 40% in all the four cell lines . ATP:ADP ratios decreased to a greater extent (similar to 40%) in glioma c ells than in squamous carcinoma 4451 and MeWo cells; in contrast, presence of 2-DG reduced ADP:AMP ratios by 3-fold in the squamous carcinoma 4451, wh ereas an increase was noted in the glioma cell line BMG-1. 2-DG significant ly reduced the initial rates of DNA repair in all cells, resulting in an ex cess residual damage after 2 h of repair in BMG-1, U-87, and 4451 cell line s, whereas no significant differences could be observed in the other cell l ines. Recovery from potentially lethal damage was also significantly inhibi ted in BMG-1 cells. 2-DG increased the radiation-induced micronuclei format ion in the melanoma line (MeWo) by nearly 60%, while a moderate (25-40%) in crease was observed in the glioma cell lines (BMG-1 and U-87). Presence of 2-DG during liquid holding (4 h) enhanced the radiation-induced cell death by nearly 40% in both the glioma cell lines, while significant effects were not observed in others. Conclusions: The modifications in energetics and radiation responses by 2-D G vary considerably among different human tumor cell Lines, and the relatio nships between energy metabolism and various radiobiologic parameters are c omplex in nature. The 2-DG-induced modification of radiation response does not strictly correlate with changes in the levels of ATP. However, a signif icant enhancement of the radiation damage by 2-DG was observed in cells wit h high rates of glucose usage and glycolysis, which appear to be the two mo st important factors determining the tumor response to the combined treatme nt of 2-DG + radiation therapy. (C) 2001 Elsevier Science Inc.