Hematoporphyrin derivatives potentiate the radiosensitizing effects of 2-deoxy-D-glucose in cancer cells

PURPOSE: Two deoxy-D-glucose (2-DG), an inhibitor of glucose transport and glycolysis, has been shown to differentially inhibit the repair of radiation damage in cancer cells by reducing the flow of metabolic energy. Since hematoporphyrin derivatives (Hpd) inhibit certain enzymes of the respiratory metabolism, resulting in an increase in the glucose usage and glycolysis, Hpd could possibly enhance the energy-linked radiosensitizing effects of 2-DG in cancer cells. The purpose of the present work was to verify this suggestion. METHODS AND MATERIALS: Two human tumor cell lines (cerebral glioma, BMG-1 and squamous cell carcinoma, 4197) and a murine tumor cell line (Ehrlich ascites tumor [EAT], F-15) in vitro were investigated. A commercially available preparation of Hpd, Photosan-3 (PS-3) was used in the present studies. Cells incubated with 0-10 microg/ml PS-3 for 0-24 h before irradiation were exposed to 2.5 Gy of Co-60 gamma rays and maintained under liquid holding conditions for 1-4 h to facilitate repair. 2-DG (0-5 mM) added at the time of irradiation was present during the liquid holding. Radiation-induced cytogenetic damage (micronuclei formation) and cell death (macrocolony assay) were analyzed as parameters of radiation response. Effects of these radiosensitizers on glucose usage and glycolysis were also studied by measuring the glucose consumption and lactate production using enzymatic assays. RESULTS: The glucose consumption and lactate production of BMG-1 cells (0.83 and 1.43 pmole/cell/h) were twofold higher than in the 4197 cells (0.38 and 0.63 pmole/cell/h). Presence of PS-3 (10 microg/ml) enhanced the rate of glycolysis (glucose consumption and lactate production) in these cells by 35% to 65%, which was reduced by 20% to 40% in the presence of 5 mM 2-DG. In exponentially growing BMG-1 and EAT cells, presence of 2-DG (5 mM; equimolar with glucose) for 4 hours after irradiation increased the radiation-induced micronuclei formation and cell death by nearly 40%, whereas no significant effects could be observed in 4197 cells. In EAT cells, radiation was also observed to induce apoptotic death, which was significantly increased in the presence of the combination (PS-3 + 2-DG). The combination (PS-3 + 2-DG) enhanced the radiation damage in all three cell systems by 60-100%. Furthermore, the radiosensitizing effects of the combination (PS-3 + 2-DG) were higher at pH 6.7 as compared to pH 7. 4. In the plateau phase, presence of 2-DG alone did not significantly influence the radiation response of either BMG-1 or of 4197 cells, whereas in combination with PS-3, 2-DG enhanced the radiation damage in both these cell lines by 40% to 50%. Furthermore, in BMG-1 cells, the effects of 2-DG were observed to be reversible to a very great extent, while that of the combination were mostly irreversible. CONCLUSION: The hematoporphyrin derivative PS-3 enhances the radiosensitizing effects of 2-DG in cancer cells, possibly by further reducing the energy supply leading to an irreversible inhibition of DNA repair, and increased cytogenetic damage and cell death. Since both these compounds have been used in clinical practice, further studies to investigate their use in improving radiotherapy of tumors are warranted.     

富勒烯对斑马鱼60Coγ辐射生物效应修饰作用的研究

目的 研究富勒烯化合物对斑马鱼受到γ射线照射后的存活率、畸形发生率的影响及其机制,以了解富勒烯类化合物对辐射生物效应的修饰作用。方法 ⁶⁰Coγ射线照射下富勒烯母体纳米颗粒对斑马鱼成鱼存活率的改变,同时利用斑马鱼胚胎-幼体比较该化合物对不同照射条件下斑马鱼鱼卵及幼体畸形发生率的影响,并从活性氧(ROS)生成的改变及DNA链断裂形成探讨了其可能的作用机制。结果 光照期给药500×10^－9的富勒烯母体(nano-C₆₀)能增强γ射线照射对成鱼的杀伤作用,在此条件下活性氧生成和DNA损伤增加,且抑制胚胎的孵出率和导致畸形的发生率增加;但避光期用药对射线效应没有明显的增强作用,除了高浓度5000×10^－9会抑制幼鱼的孵出率,并导致发育畸形增加。结论 富勒烯母体对斑马鱼的辐射损伤效应有增强作用,其机制可能是在光照期用药后活化并导致活性氧生成增加,并导致DNA氧化损伤增强。