Re-engineered Mitochondrially Targeted p53 Gene Therapy in Liver Cancer

摘要：肝细胞癌是最常见的肝脏肿瘤，是引起人类疾病的第三大原因。 世界范围内的癌症死亡。在美国，肝细胞癌的总体5年存活率仅为17%，远端肝细胞癌仅为3% 转移性肝癌。手术切除和肝移植是目前治疗肝癌的标准治疗方法，但 由于肝硬变，只有5%的人有资格接受切除。有限的器官供应也严重限制了 移植。包括激酶抑制剂和免疫疗法在内的治疗肝癌的新靶向药物显示出希望，但 使用靶向药物的患者将不可避免地产生耐药性。治疗肝癌的有效新疗法是 急需之物。我们提出了一种新的、重新设计的p53抑癌基因-凋亡蛋白杂合体。 肝癌的治疗被称为P53-Bad*。野生型p53被批准作为Gendicine®用于治疗癌症 中国的成功有限。有限的疗效可能与突变型p53的显性负效应有关 对wt p53施加影响。由于核P53的活性依赖于同源四聚体，因此在癌细胞中突变的P53 也可以与wt p53四聚，使其失活。突变型P53还可以具有功能增益和其他 可以对抗wt p53影响的活动。为了克服这一限制，一种有效的p53融合蛋白与 这里提出了新的作用机制，克服了显性的负面抑制并导致了细胞凋亡。 与癌细胞的P53状态无关。通过将P53与凋亡的BH3蛋白融合 线粒体靶向信号，如Bad，这通过结合凋亡效应进一步增加细胞凋亡 线粒体P53与促凋亡的BH3蛋白的差异。P53-Bad*(Bad的突变版本，增加了 线粒体定位)是我们最重要的杀死癌细胞的结构。我们假设P53的结合 和线粒体上的BH3蛋白，由修饰的甲胎蛋白(AFP)驱动的肝癌特异性 启动子，将在体外(与P53状态无关)和体内诱导肝癌细胞凋亡 斑马鱼和老鼠模型。斑马鱼是研究人类癌症的理想模型系统，具有组织学 斑马鱼和人类肿瘤之间的遗传相似性“，而原位异种移植小鼠模型是一个 向翻译迈出的重要一步。目标1：a.P53-BH3融合(P53-Bad*)将 定位于线粒体并引起相关肝细胞癌细胞系的有效凋亡 无论细胞内P53状态如何；B.使用修饰/组合的AFP启动子将使肝癌细胞 特异性和杀伤肝癌细胞，而不是正常人类细胞。目的2：肝脏特异表达P53-Bad* 在斑马鱼中，启动子Fabp10a与肝癌斑马鱼模型杂交将产生的后代具有减少的 肝癌特异性表型的表达。目的3：P53-Bad*(在腺病毒中的表达及其优化 肝癌特异性启动子)将缩小肝癌原位移植小鼠模型中的肝肿瘤(使用AFP- 表达人肝细胞癌细胞，Hep3B)。本研究的最终目的是开发一种新的、有效的 全球肝细胞癌患者的治疗方法。

Abstract: Hepatocellular carcinoma (HCC), the most common cancer of the liver, is the third leading cause of cancer death worldwide. In the U.S., the overall 5-year survival rate for HCC is only 17% and only 3% for distantly metastasized HCC. Surgical resection and liver transplantation are the current standard of care for HCC, but only ~5% qualify for resection due to cirrhosis. Limited organ availability also severely restricts the number of transplants. New targeted agents for HCC including kinase inhibitors and immunotherapies show promise, but patients using targeted agents will inevitably develop drug resistance. Effective new therapies for HCC are urgently needed. We propose a new, re-engineered p53 tumor suppressor-apoptotic protein hybrid for gene therapy of HCC called p53-Bad*. Wild-type p53 was approved for gene therapy as Gendicine® for cancers in China with limited success. Limited efficacy may be related to the dominant negative effect that mutant p53 exerts over wt p53. As nuclear p53 activity is dependent on homo-tetramerization, mutant p53 in cancer cells can also tetramerize with wt p53 to cause its inactivation. Mutant p53 can also have gain-of-function and other activities that can counter the effects of wt p53. To overcome this limitation, a potent p53 fusion protein with novel mechanisms of action is proposed here that overcomes dominant negative inhibition and causes apoptosis regardless of the p53 status of cancer cells. By fusing p53 to an apoptotic BH3 protein with an inherent mitochondrial targeting signal, such as Bad, this increases apoptosis further by combining the apoptotic effects of mitochondrial p53 with those of pro-apoptotic BH3 proteins. p53-Bad* (a mutant version of Bad with increased mitochondrial localization) is our top cancer cell-killing construct. We hypothesize that the combination of p53 and BH3 proteins at the mitochondria, with liver cancer specificity driven by a modified alpha fetoprotein (AFP) promoter, will potently induce apoptosis in liver cancer both in vitro (regardless of p53 status), and in vivo in zebrafish and mouse models. Zebrafish are an ideal model system for studying human cancer, with “histologic and genetic similarities between zebrafish and human tumors” while an orthotopic xenograft mouse model is an important step toward translation. The following aims are proposed: Aim 1: a. p53-BH3 fusion (p53-Bad*) will localize to the mitochondria and cause potent apoptosis in relevant hepatocellular carcinoma (HCC) cell lines regardless of cellular p53 status; b. the use of modified/combination AFP promoters will confer liver cancer cell specificity and kill HCC cells and not normal human cells. Aim 2: Expression of p53-Bad* under the liver specific promoter fabp10a in zebrafish, crossed with a liver cancer zebrafish model will produce offspring with reduced expression of liver cancer specific phenotypes. Aim 3: p53-Bad* (expressed in adenovirus with the optimized HCC specific promoter) will shrink liver tumors in an orthotopic xenograft mouse model of HCC (using AFP- expressing human HCC liver cells, Hep3B). The ultimate goal of this study is the development of a new, effective therapy for treatment of HCC patients worldwide.