Improved Animal Models for Cell-Specific Regenerative Medicine Paradigms

 描述（由申请人提供）：我们提出了对我们开发的强大靶向细胞消融系统的实质性改进，以创建用于再生医学研究的新型动物模型，并提供相应的通用新工具集。该系统独特地促进了：1）研究几乎任何细胞亚型的细胞特异性再生; 2）诱导性退行性疾病建模;和3）再生疗法的全生物体HTS发现。重要的是，这种方法可以部署在任何转基因动物模型系统中，并且能够模拟与特定细胞或组织类型的损失相关的任何疾病。该系统采用了前药转化硝基还原酶（NTR）酶，该酶最初被开发用于[通过基因治疗根除人类癌细胞]。为了产生新的细胞特异性再生范例，将NTR酶和荧光报告基因置于转基因生物中细胞类型特异性启动子的控制下[（即，仅在靶细胞/组织中表达）]。NTR表达选择性地使那些细胞对产生细胞毒性衍生物的前药敏感[（例如，甲硝哒唑），使精确的]靶向细胞消融，在[需求，不伤害周围细胞]。该报告允许随后的再生过程进行详细表征。这种通用的NTR系统已经适应于多个物种，促进了广泛的细胞特异性再生范例和退行性疾病模型。然而，不充分的前药活化损害了这种方法的全部潜力;这限制了可以消融的细胞类型，减缓了细胞损失动力学，并且需要半毒性前药方案，这可能混淆关键数据。我们建议开发NTR/前药系统的上级迭代，其将：1）提供细胞靶向的额外维度; 2）加速细胞消融动力学，以促进再生动力学的更好解决;和3）减轻与当前前药治疗方案相关的全身半毒性。本研究的具体目的是：1）鉴定具有改善的细胞特异性消融功效的NTR变体; 2）定义选择性NTR前药对以促进多种细胞类型的独立消融;和3）开发泛物种转基因[载体以创建改善的] NTR资源。为了实现这些目标，我们已经组装了一个从24个细菌物种的NTR变体库，使用定向进化（在单基因水平上的随机诱变，然后选择改进的酶变体），以定制所需的NTR活性，确定新的前药底物，并开发了高通量的方法，以量化比较试验中的消融功效。我们将应用这些资源开发具有改善的酶活性的NTR [变体，和具有增强的特异性的新型NTR/前药对。我们改进的NTR将：1）促进改进的动物模型的创建，以产生对细胞特异性再生的见解; 2）能够识别调节离散干细胞小生境的再生潜力的因素;以及3）帮助开发与特定细胞损失相关的许多退行性疾病的治愈性疗法。

 DESCRIPTION (provided by applicant): We propose substantial improvements to a powerful targeted cell ablation system we developed to create novel animal models for regenerative medicine research, and to provide a corresponding set of versatile new toolsets. This system uniquely facilitates: 1) Studies of cell-specific regeneration for nearly any cellular subtype; 2) Inducible degenerative disease modeling; and 3) Whole organism HTS discovery of regenerative therapeutics. Importantly, this approach can be deployed in any transgenic animal model system, and is capable of modeling any disease linked to the loss of specific cell or tissue types. The system employs a prodrug converting nitroreductase (NTR) enzyme, which was first developed to [eradicate human cancer cells via gene therapy.] To create novel cell-specific regeneration paradigms, a NTR enzyme and a fluorescent reporter gene are placed under the control of a cell-type specific promoter in a transgenic organism [(i.e., only expressed in the targeted cells/tissues)]. NTR expression selectively sensitizes those cells to prodrugs that produce cytotoxic derivatives [(e.g., metronidazole), enabling precise] targeted cell ablation, on [demand, without harming surrounding cells]. The reporter allows subsequent regenerative processes to be characterized in detail. This versatile NTR system has been adapted] to multiple species, promoting a wide array of cell-specific regeneration paradigms and degenerative disease models. However, inadequate prodrug activation compromises the full potential of this approach; this limits the types of cells that can be ablated, slows cell loss kinetics, and necessitates semi-toxic prodrug regimens that can confound key data. We propose to develop superior iterations of NTR/prodrug systems that will: 1) Provide additional dimensions of cell targeting; 2) Accelerate cell ablation kinetics, to facilitate better resolutionof regeneration kinetics; and 3) Alleviate systemic semi-toxicity associated with current prodrug treatment regimens. The specific aims of this study are: 1) Identify NTR variants with improved cell-specific ablation efficacy; 2) Define selective NTR prodrug pairs to facilitate independent ablation of multiple cell types; and 3) Develop pan-species transgenic [vectors to create improved] NTR resources. To achieve these aims we have assembled a library of NTR variants from 24 bacterial species, used directed evolution (random mutagenesis at a single-gene level, followed by selection for improved enzyme variants) to tailor desirable NTR activities, identified new prodrug substrates, and developed high-throughput methods to quantify ablation efficacy in comparative assays. We will apply these resources to develop NTR [variants with improved enzymatic activity, and novel NTR/prodrug pairs with enhanced specificity. Our improved NTRs will: 1) Facilitate the creation of improved animal models to yield insights] into cell-specific regeneration; 2) Enable identification of factors that regulate the regenerative potential of discrete stem cell niches; and 3) Aid development of curative therapies for the many degenerative conditions linked to the loss of specific cells.