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取得成功效果的关键。癌胚抗原(CEA)启动子已被广泛用于此目的，但肿瘤特异性启动子如CEA启动子的表达水平普遍较低。在本研究中，我们使用了Cre/loxP系统，结果表明CEA启动子的LacZ表达显著增强，同时利用Cre/loxP系统保持其特异性。首次将Cre/loxP系统应用于胞嘧啶脱氨酶(CD)基因的选择性表达，作为一种自杀基因治疗CEA产生细胞。CEA启动子控制下表达Cre重组酶的AxCEANCre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CEA产生的肿瘤细胞，使CEA产生的肿瘤细胞对5-FC(5-氟胞嘧啶)的敏感性比单一感染由CEA启动子驱动表达CD基因的AxCEACD提高13倍。治疗效果…在人胃癌原位模型上评价了增强型CD/5-F-C自杀基因治疗的敏感性。将腺病毒载体(1×10~(-9)pfu)腹腔注射小鼠3次，然后连续10天腹腔注射5-FC。与模型组和AxCEACD组相比，AxCEANCre和AxCALNLCD组小鼠的肿瘤体积和重量显著减少(p&lt；0.0001)。AxCEANCre和AxCALNLCD/5-FC组小鼠的存活时间明显长于Mock组和AxCEACD/5-FC组(p&lt；0.01)。此外，在人结肠癌原位模型中，与Mock或AxCEACD相比，AxCEANCre和AxCALNLCD的双重给药完全抑制了肝转移，并显著减少了原发肿瘤的体积。这些结果表明，Cre/loxP系统的应用可能为CD/5-FC的增强型选择性自杀基因治疗提供一条新的途径。较少

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