Specific elimination of tumor stem cells using oncolytic viruses

在肿瘤组织内，一小部分细胞已被证明具有干细胞的行为。这些所谓的肿瘤干细胞被描述为重新启动肿瘤，甚至产生肿瘤血管。CD133等表面标志物正被用于识别和丰富肿瘤干细胞。在肝细胞癌和胶质母细胞瘤中，CD133阳性的肿瘤细胞在肿瘤组织中很少见，但具有很高的肿瘤起始潜能，并被描述为对放射和化疗耐药。因此，针对肿瘤干细胞的抗肿瘤药物是非常理想的。申请者小组开发了独特的方法，实现了将溶瘤病毒重定向到任何细胞类型和所选的细胞表面受体。为了实现这项提议的目标，申请者小组首次产生了一种使用CD133作为细胞进入受体的溶瘤病毒。这种病毒被称为MV-CD133，是从麻疹病毒(MV)衍生而来的，它选择性地感染和溶解CD133阳性的肿瘤细胞。对荷人肝癌皮下移植瘤小鼠的初步研究表明，MV-CD133具有较强的抗肿瘤作用。值得注意的是，MV-CD133比母体麻疹病毒更有效地抑制肿瘤生长，后者目前正在进行许多临床试验，用于治疗不同的肿瘤实体。该建议旨在开发一种对CD133阳性肿瘤细胞具有绝对特异性的新型抗肿瘤药物。根据CD133作为肿瘤干细胞标志物的相关性，MV-CD133可能是第一个选择性感染和杀伤肿瘤干细胞的溶瘤病毒。到目前为止，还没有关于任何类型的溶瘤病毒的肿瘤干细胞特异性病毒的描述。基于初步数据，我们假设以CD133为靶点可增强溶瘤病毒治疗肝细胞癌的抗肿瘤潜能。除了肝癌，我们还将探索MV-CD133对胶质母细胞瘤的活性，CD133也被认为是肿瘤干细胞标记物。为了进一步增强MV-CD133的溶瘤活性，我们将用自杀基因武装病毒，并将其趋向性扩展到CD133阴性的肿瘤细胞。病毒的抗肿瘤效果将通过细胞杀伤试验和监测不同小鼠肿瘤模型中的肿瘤生长来量化。将特别强调评估含有不同程度CD133阳性细胞的原代肿瘤细胞，当这些样本中的CD133阳性细胞被病毒感染时，它们形成肿瘤和转移的能力。MV-CD133的活性也将在多灶性肿瘤模型中进行评估，这些模型与临床应用更相关。我们期望从这个项目中更好地理解CD133作为肿瘤干细胞标记物的相关性，并为肿瘤治疗的新的创新策略奠定基础。

Within tumor tissue a small fraction of cells has been demonstrated to behave like stem cells. These so called tumor stem cells have been described to reinitiate tumors and to even generate tumor vasculature. Surface markers such as CD133 are being used to identify and enrich tumor stem cells. CD133-positive tumor cells in hepatocellular cancer and glioblastoma are rare in tumor tissue but have a high potential for tumor initiation and were described to be resistant against radio- and chemotherapy. Anti-tumoral drugs targeted to tumor stem cells are therefore highly desirable.The applicants group has developed unique methods to achieve the retargeting of oncolytic viruses to any cell type and cellular surface receptor of choice. Towards the goals of this proposal, the applicants group generated for the first time an oncolytic virus that uses CD133 as receptor for cell entry. This virus termed MV-CD133 has been derived from measles virus (MV) and infects and lyses selectively CD133-positive tumor cells. Initial studies in mice carrying subcutaneously growing human hepatocellular carcinoma cells showed that MV-CD133 is able to exert a strong anti-tumoral effect. Notably, MV-CD133 reduced tumor growth more efficiently than the parental measles virus which is currently investigated in numerous clinical trials for the treatment of different tumor entities. This proposal aims at generating a novel anti-tumoral agent with absolute specificity for CD133-positive tumor cells. Based on the relevance of CD133 as marker for tumor stem cells, MV-CD133 may be the first oncolytic virus that selectively infects and kills tumor stem cells. By now, a tumor stem cell specific virus has not been described for any type of oncolytic virus. Based on preliminary data, we hypothesize that CD133-targeting enhances the anti-tumoral potential of oncolytic viruses for the treatment of hepatocellular cancer (HCC). Beyond HCC, we will explore the activity of MV-CD133 against glioblastoma for which CD133 has been suggested as tumor stem cell marker as well. To further enhance the oncolytic activity of MV-CD133 we will arm the virus with suicide genes and extend its tropism to CD133-negative tumor cells. The anti-tumoral efficacy of the viruses will be quantified in cell killing assays and by monitoring tumor growth in different mouse tumor models. Special emphasis will be put on the evaluation of primary tumor cells containing varying degrees of CD133-positive cells for their ability to form tumors and metastases when the CD133-positive cells in these samples have been infected by the virus. The activity of MV-CD133 will also be assessed in multi-focal tumor models which are more relevant for clinical applications. We expect from this project an improved understanding of the relevance of CD133 as marker of tumor stem cells as well as the basis for a novel innovative strategy in tumor therapy.