Department of Internal Medicine II-Campus Grosshadern, University Hospital of Munich, Munich, Germany.
J Nucl Med. 2013 Aug;54(8):1450-7. doi: 10.2967/jnumed.112.115493. Epub 2013 Jul 10.
Currently, major limitations for the clinical application of adenovirus-mediated gene therapy are high prevalence of neutralizing antibodies, widespread expression of the coxsackie-adenovirus receptor (CAR), and adenovirus sequestration by the liver. In the current study, we used the sodium iodide symporter (NIS) as a theranostic gene to investigate whether coating of adenovirus with synthetic dendrimers could be useful to overcome these hurdles in order to develop adenoviral vectors for combination of systemic oncolytic virotherapy and NIS-mediated radiotherapy.
We coated replication-deficient (Ad5-CMV/NIS) (CMV is cytomegalovirus) and replication-selective (Ad5-E1/AFP-E3/NIS) adenovirus serotype 5 carrying the hNIS gene with poly(amidoamine) dendrimers generation 5 (PAMAM-G5) in order to investigate transduction efficacy and altered tropism of these coated virus particles by (123)I scintigraphy and to evaluate their therapeutic potential for systemic radiovirotherapy in a liver cancer xenograft mouse model.
After dendrimer coating, Ad5-CMV/NIS demonstrated partial protection from neutralizing antibodies and enhanced transduction efficacy in CAR-negative cells in vitro. In vivo (123)I scintigraphy of nude mice revealed significantly reduced levels of hepatic transgene expression after intravenous injection of dendrimer-coated Ad5-CMV/NIS (dcAd5-CMV/NIS). Evasion from liver accumulation resulted in significantly reduced liver toxicity and increased transduction efficiency of dcAd5-CMV/NIS in hepatoma xenografts. After PAMAM-G5 coating of the replication-selective Ad5-E1/AFP-E3/NIS, a significantly enhanced oncolytic effect was observed after intravenous application (virotherapy) that was further increased by additional treatment with a therapeutic dose of (131)I (radiovirotherapy) and was associated with markedly improved survival.
These results demonstrate efficient liver detargeting and tumor retargeting of adenoviral vectors after coating with synthetic dendrimers, thereby representing a promising innovative strategy for systemic NIS gene therapy. Moreover, our study-based on the function of NIS as a theranostic gene allowing the noninvasive imaging of NIS expression by (123)I scintigraphy-provides detailed characterization of in vivo vector biodistribution and localization, level, and duration of transgene expression, essential prerequisites for exact planning and monitoring of clinical gene therapy trials that aim to individualize the NIS gene therapy concept.
目前，腺病毒介导的基因治疗的主要临床应用限制包括中和抗体的高发生率、柯萨奇病毒-腺病毒受体（CAR）的广泛表达以及肝脏对腺病毒的隔离。在本研究中，我们使用钠碘转运体（NIS）作为治疗性基因，研究用合成树突状聚合物对腺病毒进行涂层处理是否有助于克服这些障碍，从而开发用于全身溶瘤病毒治疗和 NIS 介导的放射治疗相结合的腺病毒载体。
我们用聚（酰胺-胺）树枝状聚合物第五代（PAMAM-G5）对携带 hNIS 基因的复制缺陷型（Ad5-CMV/NIS）（CMV 为巨细胞病毒）和复制选择性（Ad5-E1/AFP-E3/NIS）腺病毒血清型 5 进行涂层处理，以通过（123）I 闪烁扫描研究这些涂覆病毒颗粒的转导效率和改变的嗜性，并评估其在肝癌异种移植小鼠模型中的全身放射病毒治疗的治疗潜力。
经树突状聚合物涂层处理后，Ad5-CMV/NIS 表现出对中和抗体的部分保护作用，并在 CAR 阴性细胞中增强了转导效率。静脉注射树枝状聚合物涂层的 Ad5-CMV/NIS（dcAd5-CMV/NIS）后，裸鼠体内（123）I 闪烁扫描显示肝内转基因表达水平显著降低。从肝脏积累中逃逸导致 dcAd5-CMV/NIS 在肝癌异种移植中的肝毒性显著降低和转导效率增加。用合成的 PAMAM-G5 对复制选择性的 Ad5-E1/AFP-E3/NIS 进行涂层处理后，静脉应用（病毒治疗）后观察到明显增强的溶瘤作用，通过用治疗剂量（131）I（放射病毒治疗）进一步增加，与明显改善的生存相关。
这些结果表明，用合成树突状聚合物对腺病毒载体进行涂层处理可有效实现肝脏去靶向和肿瘤再靶向，这代表了一种用于全身 NIS 基因治疗的有前途的创新策略。此外，我们的研究基于 NIS 的功能作为治疗性基因，允许通过（123）I 闪烁扫描对 NIS 表达进行非侵入性成像，提供了体内载体生物分布和定位、转导基因表达的水平和持续时间的详细特征，这是精确规划和监测旨在个体化 NIS 基因治疗概念的临床基因治疗试验的基本前提。
