人脐带间充质干细胞运载呼肠孤病毒对人慢性髓系白血病K562细胞溶瘤作用的研究

Oncolytic effect of human umbilical cord mesenchymal stem cells delivering reovirus on chronic myeloid leukemia K562 cells

目的:探讨人脐带间充质干细胞(hUMSCs)运载3型呼肠孤病毒(Reo3)对人慢性髓系白血病K562细胞的溶瘤效应。方法:流式细胞术检测hUMSCs和K562细胞表面Reo3易感受体——连接黏附分子A(JAM-A)表达情况,电镜观察Reo3感染hUMSCs 72 h后胞内病毒包涵体分布。将不同(0、1、2和3)感染复数(MOI)的Reo3感染hUMSCs 24、48、72、96和120 h后利用CCK-8法筛选最适MOI。选择最适滴度的Reo3感染hUMSCs 24、48、72、96和120 h后收集上清液,利用小鼠成纤维细胞系L929结合半数组织培养感染剂量(TCID50)法测定各组上清液中Reo3病毒滴度以确定最适感染时间。将K562细胞分为对照组、hUMSCs组、Reo3组和hUMSCs-Reo3组,hUMSCs组和hUMSCs-Reo3组设置hUMSCs与K562细胞作用的低、中、高比例(5∶1、10∶1和20∶1)。CCK-8法分析hUMSCs-Reo3与K562细胞共培养24、48、72 h后K562细胞活力的变化。流式细胞术评估细胞凋亡。利用L929细胞确定抗Reo3单克隆抗体的半数效应浓度(EC50);验证在体外抗体存在条件下hUMSCs-Reo3对K562细胞溶瘤作用的变化。Western blot检测运载体作用于K562细胞后胞内Bcl-2、Bax、survivin和cleaved caspase-3蛋白水平。构建K562细胞的BALB/c裸鼠皮下荷瘤模型(每组6只),分析hUMSCs-Reo3在体内对K562细胞的抑瘤效果。结果:hUMSCs和K562细胞表面JAM-A分子表达量分别为11.0%和99.0%。电镜显示Reo3感染hUMSCs 72 h后胞内出现大量病毒包涵体。在120 h范围内,与未感染组相比,MOI=1的Reo3对hUMSCs活力无显著影响,故最佳MOI为1;TCID50结果显示,MOI=1的Reo3感染hUMSCs 48 h后细胞裂解液中病毒滴度最高,故最适感染时间为48 h。hUMSCs-Reo3作用24、48和72 h后K562细胞活力呈现剂量与时间依赖性抑制。抗Reo3单克隆抗体的EC50为1∶34;在体外不同浓度(1∶34、1∶300和1∶600)抗体存在条件下,hUMSCs仍能运载Reo3抑制K562细胞活力并诱导凋亡发生。与对照组相比,hUMSCs-Reo3作用48 h后K562细胞中Bcl-2和survivin表达水平显著下调(P<0.05),Bax和cleaved caspase-3表达水平显著上调(P<0.05或P<0.01)。在BALB/c裸鼠荷瘤模型中,荷瘤体积测定、肿瘤组织和主要脏器病理学分析及小动物活体成像仪检测组织蛋白酶B/L活性结果表明,运载体在体内对K562细胞具有溶瘤效应而对正常组织无不良影响。结论:hUMSCs可有效运载Reo3,该运载体系在体内、外实验中能够释放足量Reo3抑制K562细胞恶性增殖并促进细胞凋亡,从而发挥溶瘤效应。

AIM:To investigate the oncolytic effect of human umbilical cord mesenchymal stem cells(hUMSCs)delivering reovirus type 3(Reo3)on chronic myeloid leukemia(CML)K562 cells.METHODS:The expression of junc‐tional adhesion molecule-A(JAM-A),a receptor susceptible to Reo3,on the surface of hUMSCs and K562 cells was assessed by flow cytometry.Intracellular viral inclusion body distribution 72 h after Reo3 infection in hUMSCs was observed by electron microscopy.The hUMSCs were infected with various multiplicities of infection(MOI)of Reo3(MOI=0,1,2 and 3)for 24,48,72,96 and 120 h,and the most suitable MOI was identified by CCK-8 assay.Subsequently,hUMSCs were infected with the optimal titer of Reo3 for the same durations,and supernatants were collected.The titer of Reo3 in the supernatant from each group was measured using mouse fibroblast L929 cells combined with median tissue culture infectious dose(TCID50)method,determining the optimal infection time.The K562 cells were divided into 4 groups:control group,hUMSCs group,Reo3 group,and hUMSCs-Reo3 group.Ratios of hUMSCs to K562 cells in hUMSCs group and hUMSCs-Reo3 group were set at low,medium and high(5∶1,10∶1 and 20∶1).The changes of K562 cell viability after co-cultured with hUMSCs-Reo3 for 24,48 and 72 h were analyzed by CCK-8 assay.The apoptosis of K562 cells was evaluated by flow cytometry.The half maximal effective concentration(EC50)of anti-Reo3 monoclonal antibody was determined using L929 cells.The oncolytic effect of hUMSCs-Reo3 on K562 cells with antibody present in vitro was verified.Western blot analysis was used to detect the protein levels of Bcl-2,Bax,survivin and cleaved caspase-3 in K562 cells after treatment.A BALB/c nude mouse subcutaneous tumor model was constructed with K562 cells(n=6)to analyze the in vivo anti-tumor effect of hUMSCs-Reo3.RESULTS:The expression levels of JAM-A on the surfaces of hUMSCs and K562 cells were found to be 11.0%and 99.0%,respectively.Electron microscopy revealed a significant presence of viral inclusion bodies within hUMSCs 72 h following infection with Reo3.Within 120 h,no statistically significant difference was observed in the viability of hUMSCs between Reo3(MOI=1)group and uninfected group,establishing the optimal MOI.The TCID50 results indicated that the highest virus titer in the lysate of hUMSCs in Reo3(MOI=1)group occurred 48 h after infection,determining 48 h as the optimal infection time.The K562 cells co-cultured with hUMSCs-Reo3 for 24,48 and 72 h showed a dose-and time-dependent inhibition of cell viability.The EC50 of the anti-Reo3 monoclonal antibody was found to be 1∶34.Even in the presence of antibodies at various concentrations(1∶34,1∶300 and 1∶600),hUMSCs were capable of transporting Reo3 to inhibit K562 cell viability and induce apoptosis in vitro.Compared with control group,significant down-regulation of Bcl-2 and survivin expression levels in K562 cells was noted after 48 h of co-culture with hUMSCs-Reo3(P<0.05),while Bax and cleaved caspase-3 expression levels were significantly up-regulated(P<0.05 or P<0.01).In the BALB/c nude mouse tumor-bearing model,determination of tumor volume changes,pathological examination of tumor tissue and major organs,and assessment of cathepsin B/L activity using a small animal live imaging system confirmed the oncolytic effect of hUMSCs-Reo3 on K562 cells in vivo without adverse effects on normal tissues.CONCLUSION:The hUMSCs are effective in transporting Reo3,and this delivery system is capable of releasing sufficient quantities of Reo3 in both in vivo and in vitro settings to inhibit the malignant proliferation of K562 cells and promote apoptosis,thereby exerting an oncolytic effect.