全反式维甲酸靶向增强自杀基因对髓母细胞瘤的杀伤作用

Because of the invasive nature of medulloblastoma, the prognosis with conventional treatment is poor.Suicided gene therapy has been considered as one of the most promising therapeutic strategies for brain tumor, but the therapeutic efficacy is not so good in medulloblastoma. The low expression of Cx43 between tumor cells is a key factor that affect the efficacy.How to improve the expression of Cx43 is a problem which urgent needs to solve. Our previous study has shown that ATRA can improve the expression of Cx43,but the side effect of ATRA is great.In this study we try to use mesenchymal stem cells as carrier, MSCs carry ATRA and suicided gene at the same time,to realize the purpose of targeted therapy and lower the drug side effect.We first use liposome to pack ATRA, and use a peptide to connect the MSCs cells with ATRA liposome, then plus a peptide that can be cut by the MMPs enzyme which is secreted by MB cells,When MSCs carry ATRA moved close to MB, MMP substrate peptide was cut by the MMPs enzyme, ATRA was released near the tumor ,and increase the expression of Cx43 between tumor cells, thereby enhance the treatment effect of suicided gene therapy.This study provides theoretical basis for improving the therapeutic effect of suicide gene system in MB.

髓母细胞瘤(MB)呈侵润性生长，现有治疗手段疗效较差。自杀基因疗法被认为是很有希望的治疗方法，但该法在MB中疗效不佳。究其原因，肿瘤细胞间Cx43的低表达是影响其疗效的关键。如何提高Cx43在肿瘤细胞间的表达是目前迫切需要解决的问题。前期研究中我们发现全反式维甲酸（ATRA）能显著增强肿瘤细胞间Cx43的表达，但ATRA全身应用副作用大，生物利用率低。本课题尝试利用骨髓间充质干细胞做载体，携带ATRA与自杀基因，靶向给药，降低药物副作用的同时增强自杀基因治疗效果。我们首先将ATRA用脂质体包裹，通过亲和肽-基质金属蛋白酶（MMP）底物肽与导入自杀基因的骨髓间充质干细胞相连，当干细胞携带ATRA到达髓母细胞瘤局部时，MMP底物肽被瘤细胞分泌的MMP酶切，ATRA在局部被释放，增强瘤细胞间Cx43的表达，提高自杀基因的杀伤效率。本课题的研究工作为提高自杀基因系统在MB中的疗效研究提供理论依据。

颅内恶性肿瘤呈侵润性生长，现有治疗手段疗效较差。自杀基因疗法被认为是很有希望的治疗方法，但临床实验效果不佳。肿瘤细胞间缝隙连接蛋白Cx43的低表达，而导致毒性物质不能在细胞间广泛扩散，是影响其疗效的重要因素。如何提高Cx43在肿瘤细胞间的表达是本课题要重点解决的问题。我们的实验中自杀基因联合应用全反式维甲酸(ATRA)，结果发现ATRA能显著增强肿瘤细胞间Cx43的表达，并增强自杀基因对肿瘤的杀伤作用。同时，前期研究表明，神经干细胞因其具有肿瘤趋向性，是基因治疗的良好载体。本课题中我们继续应用神经干细胞作为TK基因治疗的载体，检测神经干细胞与肿瘤细胞间Cx43蛋白的表达，比较干细胞载体与肿瘤细胞载体对肿瘤细胞杀伤作用的强弱。结果发现神经干细胞与肿瘤细胞之间能够建立更为广泛的缝细连接，且干细胞载体较肿瘤细胞载体对肿瘤细胞有更强的杀伤作用。该研究进一步证明干细胞作为载体在自杀基因治疗中的优越性，为提高自杀基因系统在颅内恶性肿瘤中的疗效提供依据。