Development of new tumor specific gene therapy in gastrointestinal carcinoma

肿瘤特异性基因传递是自杀基因治疗成功的关键。癌胚抗原（CEA）启动子已被广泛用于此目的，但CEA启动子等肿瘤特异性启动子的表达水平普遍较低。在本研究中，我们采用Cre/loxP系统，发现Cre/loxP调节系统显著增强了CEA启动子LacZ的表达，同时保持了其特异性。并且，Cre/loxP系统首次应用于增加胞嘧啶脱氨酶（CD）基因的选择性表达，作为一种自杀基因治疗cea产生细胞。在CEA启动子控制下表达Cre重组酶的axceacre和CAG启动子控制下表达CD基因的AxCALNLCD通过Cre开关系统双重感染，产生CEA的肿瘤细胞对5-FC（5-氟胞嘧啶）的敏感性比在CEA启动子驱动下表达CD基因的AxCEACD单感染的肿瘤细胞高13倍。在人胃癌原位模型中评价了强化CD/5- fc自杀基因治疗的疗效。腺病毒载体（1 × 10^9 pfu）灌胃小鼠3次，5-FC灌胃10 d。AxCEANCre和AxCALNLCD治疗小鼠的肿瘤体积和重量均显著低于Mock和AxCEACD治疗小鼠（p < 0.0001）。AxCEANCre和AxCALNLCD /5-FC处理小鼠的生存期明显长于Mock和AxCEACD/5-FC处理小鼠（p < 0.01）。此外，在人结肠癌原位模型中，与给药Mock或AxCEACD相比，AxCEANCre和AxCALNLCD双重给药完全抑制肝转移，并显著减少原发肿瘤体积。上述结果提示，应用Cre/loxP系统可为CD/5-FC的选择性自杀基因强化治疗人胃肠道癌提供新的途径。少

Tumor-specific gene delivery is crucial to achieving successful effects in suicide gene therapy. Carcinoembryonic antigen (CEA) promoter has been widely used for this purpose, but the expression level of tumor-specific promoters such as CEA promoter is generally low. In this study, we employed the Cre/loxP system, and showed that LacZ expression by CEA promoter was remarkably enhanced while maintaining its specificity using Cre/loxP regulation system. And, the Cre/loxP system was first applied to augmentation of selective expression of cytosine deaminase (CD) gene as a suicide gene therapy in CEA-producing cells. The double infection with AxCEANCre expressing Cre recombinase under control of CEA promoter and AxCALNLCD expressing CD gene under control of CAG promoter by the Cre-switching ststem rendered CEA-producing tumor cells 13-fold more sensitive to 5-FC (5-fluorocytosine) compared with the single infection with AxCEACD expressing CD gene driven by CEA promoter. The therapeutic eff … More icacy of the enhanced CD/5-F Csuicide gene therapy was evaluated in orthotopic models of human gastric carcinoma. Adenovirus vectors (1 × 10^9 pfu) were administered i. p. into mice three times, and then 5-FC was administered i. p. for the next 10 days. Tumor volume and weight in mice treated with AxCEANCre and AxCALNLCD were significantly reduced as compared with those in mice treated not only with Mock but also with AxCEACD (p < 0.0001). The survival periods of the mice treated with AxCEANCre and AxCALNLCD /5-FC were longer than those in mice treated with Mock or AxCEACD/5-FC (p < 0.01). Moreover, in orthotopic models of human colon carcinoma, the double administration of AxCEANCre and AxCALNLCD completely inhibited liver metastases, and significantly reduced primary tumor volume compared to the administration of Mock or AxCEACD. These results suggested that the application of Cre/loxP system could provide a new approach for enhanced selective suicide gene therapy of CD/5-FC for the treatment of human gastrointestinal carcinoma. Less