ABSTRACT
Objective To study the increased radiosensitivity of tumor cells by triterpene acids of loquat leaf (TAL) and mechanism.Methods C6 and MG63 cells were pretreated by TAL,and then were exposed to X-rays at 1,2,3,5,7 Gy.Clonogenic assay was used to evaluate those tumor cells survival fraction (SF) to calculate the sensitization enhancement ratios (SER) of TAL.The cellular micronuclei ratios of tumor cells were analyzed by micronuclei assay.Additionally,the changes of Rad51 and XRCC4 levels were observed by RT-PCR and Western blot.Results D0 values were decreased to 1.31 and 2.85 Gy in C6 and MG63 cells by TAL pretreatment respectively.The SER value of the effect of TAL on C6 and MG63 cells was 1.73 and 2.04,respectively.There was a statistical difference in the cellular micronuclei ratios between tumor cells with TAL above 2 Gy and those without TAL (C6:t =-8.372--2.476,P ＜0.05 ; MG63:t =-4.03--2.557,P ＜ 0.05).TAL attenuated the expression of XRCC4 at transcriptional and translational level,but not for Rad51,a key gene in homologous recombination repair (HRR).Conclusions TAL pretreatment could increase the lethal effect of X-rays on tumor cells in vitro.The mechanism might be involved in the inhibition of non-homologous end joining (NHEJ).