The assessment of tumor hypoxia variation after radiotherapy with 99Tcm-MNLS in mice tumor model

Objective To investigate the feasibility of monitoring the tumor's hypoxic changes by 99Tcm-2-(2-methyl-5-nitro-1H-imidazol-1-yl) ethyl eihydrogen phosphate (MNLS) imaging after radiotherapy.Methods (1) H22 cells were cultured and mice model with liver cancer xenografte was made.The mice were imaged at 0.5,1,2,3,4,6 and 8 h (six mice in each group) after injected with 7.4 MBq 99TcmMNLS when the tumor size reach about 1 cm.Then the mice were sacrificed.The T/NT and ％ID/g of each time point was calculated.(2) The liver cancer bearing mice of radiotherapy group (25 Gy) and control group were imaged at 0,24,48 h,and then the technique of ROI was adopted to calculate the T/NT at each time point in the two groups.Immunohistochemical stain method was used to evaluate the expression level of HIF-1α in liver cancer.(3) One-way analysis of variance,the least significant difference t test,two-sample t test and Spearman correlation analysis were performed.Results (1) The uptake of 99TcmMNLS in the liver cancer bearing mice was significant at 2 h after injection and the ％ID/g was the highest.99Tcm-MNLS was excreted mainly through kidneys.(2) The T/NT and HIF-1α expression level in radiotherapy group at 24 h (2.65±0.27,(50.62±3.78)％) were lower than those at the instant (3.35±0.19,(85.32±0.94)％,t=5.640,6.701,both P＜0.05),but higher than those at 48 h (2.23±0.52,(21.69±0.75)％,t=7.674,4.911,both P＜0.05).The T/NT and HIF-1α expression in the radiotherapy group were significantly higher than those in the control group at the instant (2.74 ± 0.29,(28.26 ± 1.70) ％,t =4.235,3.473,both P＜0.05) but lower at 48 h (3.15±0.88,(67.64±3.55) ％,t =7.902,3.258,both P＜0.05).However,no significant difference was observed at 24 h between radiotherapy group and the control group (2.98±0.16,(58.45±0.98) ％,t =0.525,2.043,both P＞0.05).The change of T/NT closely correlated with the expression of HIF-1α in both the radiotherapy group and control group(r,=0.793,0.756,both P＜0.05).Conclusion 99Tcm-MNLS hypoxia imaging has potential to monitor changes of hypoxia in tumor after radiotherapy. Key words: Liver neoplasms, experimental;  Radiotherapy;  Cell hypoxia;  Radionuclide imaging; Mice;  MNLS