Apoptosis Modulation in Prodrug Activation Gene Therapy

描述（由申请方提供）：旁观者细胞毒性效应，定义为肿瘤内局部产生的活化前药的杀伤效应延伸至周围肿瘤细胞，是癌症基因导向酶前药治疗（GDEPT）的关键特征，因为目前基因递送技术的局限性仅允许用治疗基因转导小百分比的肿瘤细胞。 最近在Waxman博士实验室进行的研究表明，通过在单层培养系统中将抗凋亡因子p35引入大鼠胶质肉瘤9 L细胞中，可以实现基于细胞色素P450的GDEPT与抗癌前药环磷酰胺组合的显著增强的旁观者效应。 该提议的主要目的是1）研究杆状病毒半胱天冬酶抑制剂p35在基于细胞色素P450的GDEPT的临床前模型中增强癌症化疗药物环磷酰胺的旁观者杀伤效应中的效用，2）使用复制病毒辅助系统在人肿瘤异种移植模型中实施该基因治疗，以及3）确定在P450 GDEPT系统中用p35观察到的增强的旁观者活性是否可以广泛应用于其它GDEPT系统，例如单纯疱疹病毒胸苷激酶与更昔洛韦和E.大肠杆菌胞嘧啶脱氨酶与5-氟胞嘧啶组合，这两种药物通过不同的机制发挥其肿瘤杀伤和/或旁观者效应。 根据这一建议获得的结果可能会提供有价值的信息铺平道路，在临床上实施这种基因治疗策略。

DESCRIPTION (provided by applicant): The bystander cytotoxic effect, defined as the extension of the killing effects of an activated prodrug produced locally within a tumor to surrounding tumor cells, is a key feature of gene-directed enzyme prodrug therapy (GDEPT) for cancer, given that the limitation of current technologies for gene delivery allows for only a small percentage of tumor cells to be transduced with a therapeutic gene. Recent studies conducted in Dr. Waxman's laboratory suggest that a significantly enhanced bystander effect can be achieved for cytochrome P450-based GDEPT in combination with the anti-cancer prodrug cyclophosphamide by introduction of an anti-apoptotic factor, p35, into rat gliosarcoma 9L cells in a monolayer culture system. The major goals of this proposal are 1) to investigate the utility of a baculoviral caspase inhibitor, p35, in augmenting the bystander killing effect of the cancer chemotherapeutic drug cyclophosphamide in a preclinical model of cytochrome P450-based GDEPT, 2) to implement this gene therapy in a human tumor xenograft model using a replicating viral helper system, and 3) to determine whether the enhanced bystander activity seen with p35 in the P450 GDEPT system can be broadly applied to other GDEPT systems, such as herpes simplex virus thymidine kinase in combination with ganciclovir and E. coli cytosine deaminase in combination with 5-flurocytosine, both of which exert their tumor killing and/or bystander effect via distinct mechanisms. Findings obtained under this proposal may provide valuable information for paving the way of implementing this gene therapeutic strategy in the clinic.