Preclinical development of biological pacemakers

摘要：慢性右室起搏可引起右室起搏诱发的心肌病。 从右室心尖部起搏的患者中，约有20%发生右室PIC，并伴有显著的收缩压下降。 功能。症状性心力衰竭并不少见，而且长期效果不佳。显然，替代方案 RV起搏是可取的，但目前还没有经过验证的RVPIC临床前模型来帮助理解机制 并指导治疗。在此，我们试图在猪的RVPIC模型中验证RVPIC的非心动过速起搏模型 并用此模型测试生物起搏器(BIOP)。基于基因的BIOP是第一个 十多年前描述的；各种结构的体细胞基因转移(显性-负性突变体 内向整流通道[Kir2.1AAA]、野生型HCN通道和转录因子[TBX18]) 已经被证明可以创造BIOP活动。然而，直到最近，体内临床前应用大多是 仅限于高度侵入性的开胸模型。我们已经开发出一种临床上可行的微创分娩方法。 技术，并用它在猪的完全性心脏传导阻滞模型中创建了Biop。在这里，我们建议使用这个 比较两个具有根本不同作用机制的“入围”候选治疗方法。 第一种是野生型离子通道(Hcn2)，它可以人工诱导心肌细胞的自律性。 通过功能重组。其目标不是创造一个起搏器细胞的忠实复制品，而是 操纵膜通道谱系的单个组分，以在 可兴奋但正常静止的细胞。第二个候选治疗药物Tbx18的有效成分， 将心室肌细胞重编程为窦房结(SAN)样起搏细胞(诱导窦房结 单元格)。没有一个决定兴奋性的因素选择性地过度表达：整个基因表达程序是 改变，从而导致基本细胞生理和形态的改变。这项建议利用了上述 上述经皮给药方法的改进和验证，在RVPIC的大动物模型中， 移植到临床所需的方法。我们将表征和比较起搏效率和 HCN2和TBX18衍生的Biop的安全性，验证了Isan细胞将提供优越的变时性的假设 与hcn2相比，支持。一旦确定了最有希望的治疗候选者，我们将进行测试 Biop在RVPIC设置中的应用。我们假设通过希氏束恢复前传传导 BIOP起搏可以减轻或逆转与右室相关的不利的室壁重构 快步走。这项研究计划旨在为测试优化的BIOP奠定临床前基础 有RVPIC风险的患者。

Abstract: Chronic right ventricular (RV) pacing can cause RV pacing-induced cardiomyopathy (RPVIC). Approximately 20% of patients paced from the RV apex develop RVPIC, with a dramatic depression of systolic function. Symptomatic heart failure is not infrequent, and long-term outcomes are poor. Clearly, alternatives to RV pacing are desirable, but there are no validated preclinical models of RVPIC to help understand mechanisms and to guide therapy. Here we seek to validate a non-tachycardic pacing model of RVPIC in a porcine model of complete heart block, and to use this model to test biological pacemakers (BioP). Gene-based BioP were first described more than a decade ago; somatic gene transfer of various constructs (a dominant-negative mutant of the inward rectifier channel [Kir2.1AAA], wild-type HCN channels, and a transcription factor [Tbx18]) have all been shown to create BioP activity. However, until recently, in vivo preclinical applications have been mostly limited to highly-invasive open-chest models. We have developed a clinically-realistic minimally-invasive delivery technique and used it to create BioP in a porcine model of complete heart block. Here, we propose to use this approach to compare two “finalist” therapeutic candidates with fundamentally different mechanisms of action. The first one is a wild-type ion channel (HCN2) that artificially induces automaticity in ventricular cardiomyocytes by functional re-engineering. The goal is not to create a faithful replica of a pacemaker cell, but rather to manipulate a single component of the membrane channel repertoire so as to induce spontaneous firing in an excitable but normally-quiescent cell. The active principle of the second therapeutic candidate, Tbx18, reprograms ventricular cardiomyocytes into sinoatrial node (SAN)-like pacemaker cells (induced SAN [iSAN] cells). No one determinant of excitability is selectively over-expressed: the entire gene expression program is altered, with resultant changes in fundamental cell physiology and morphology. This proposal utilizes the above mentioned percutaneous delivery method to reduce to refine and validate, in a large-animal model of RVPIC, the approaches required for translation to the clinic. We will characterize and compare the pacing efficacy and safety of HCN2 and Tbx18-derived BioP, testing the hypothesis that iSAN cells will provide superior chronotropic support as compared to HCN2. Once designating the most promising therapeutic candidate, we will then test the utility of BioP in the setting of RVPIC. We hypothesize that restoring antegrade conduction by his-bundle pacing with a BioP can attenuate or reverse the adverse ventricular remodeling associated with right ventricular pacing. This research proposal is designed to lay the pre-clinical groundwork for testing of an optimized BioP in patients at risk for RVPIC.