Relevance of Rac1-regulated mechanisms for adverse tissue damage caused by conventional anticancer drugs and radiotherapy

常规(即遗传毒性)抗癌药物对正常组织有许多副作用。这些不良反应是剂量限制的，严重影响癌症患者的生活质量。为了拓宽放化疗联合治疗的窗口，从而使恶性疾病的治疗更有效和更易耐受，从药理上抑制不良组织损伤将是优先的。自身的初步数据表明，HMG-CoA还原酶抑制剂(即他汀类药物)被认为通过靶向RAC/Rho信号转导而具有多效性胆固醇非依赖性作用，在广泛使用的抗癌药物(如阿霉素、顺铂)和放射(IR)治疗后，在体外和临床前体内模型中减轻非恶性肿瘤细胞和特定组织的不良细胞毒性和遗传毒性以及炎症和促纤维化反应。考虑到他汀类药物和RAC特异性小分子抑制剂对不同类型的遗传毒性药物和不同类型的组织/细胞类型的多重保护作用，我们假设这些药物干扰了抗癌治疗导致的急性和慢性正常组织损伤的病理生理过程中的高级分子机制。其他药理学研究的结果提供了累积证据，表明RAS同源GTPase rac1在这方面可能具有特别的相关性。然而，这一假说的遗传证据仍然缺乏。然而，基因数据本质上是激励新药临床开发所必需的。因此，提交的提案旨在通过使用一种遗传的rac1基因敲除小鼠模型来验证rac1作为预防抗癌治疗引起的不良组织反应的有希望的靶点。为此，我们打算使用已经为申请人提供的rac1flx/flx/Mx1-Cre小鼠模型来实现可诱导的rac1基因的遗传缺失。利用这种Poly-I：C可诱导模型系统，rac1可以在多种细胞类型中被广泛删除。然后，我们将使用熟悉的和缺乏rac1的动物进行比较分析，以阐明rac1对(I)阿霉素对心脏的毒性作用、(Ii)顺铂的肾毒性作用和(Iii)肺分次照射引起的毒性作用的影响。工作假设是，在抗癌治疗引起的急性和慢性正常组织损伤中，rac1调节的信号通路是必需的。换句话说，我们推测，在使用常规药物和放射治疗的抗癌治疗中，rac1缺乏是一种器官保护作用。该项目旨在验证rac1作为跨组织预防放化疗的多种不良反应的治疗靶点。

Conventional (i.e. genotoxic) anticancer drugs cause numerous side effects on normal tissue. These adverse effects are dose-limiting and severely impact the quality of life of cancer patients. Pharmacological inhibition of adverse tissue damage would be preferential in order to widen the therapeutic window of combined radio-chemotherapy and, in consequence, enable more efficient and better tolerable therapy of malignant diseases. Own preliminary data demonstrate that HMG-CoA reductase inhibitors (i.e. statins), which are believed to have pleiotropic cholesterol-independent effects by targeting Rac/Rho-signaling, mitigate adverse cytotoxic and genotoxic as well as inflammatory and pro-fibrotic responses of non-malignant cells in vitro and selected tissues in preclinical in vivo models following treatment with widely used anticancer drugs (e.g. doxorubicin, cisplatin) and irradiation (IR). Bearing in mind the multiple protective effects of statins and Rac-specific small-molecule inhibitors against different types of genotoxic drugs and towards different types of tissues/cell types, we hypothesize that these drugs interfere with superior molecular mechanisms involved in the pathophysiology of acute and chronic normal tissue damage resulting from anticancer therapeutics. The results of additional pharmacological studies provide cumulative evidence that the Ras-homologous GTPase Rac1 might be of particular relevance in this context. However, genetic evidence for this hypothesis is still missing. Yet, genetic data are essentially required to motivate novel clinical drug development. Therefore, the submitted proposal aims to verify Rac1 as promising target for the prevention of anticancer therapy-induced adverse tissue responses by employing a genetic rac1 knock-out mouse model. To this end, we intend to accomplish an inducible genetic deletion of the rac1 gene using the Rac1flox/flox/Mx1-Cre mouse model, which is already available to the applicant. Employing this poly-I:C inducible model system, rac1 can be extensively deleted in multiple cell types. Afterwards, comparative analyses using Rac1 proficient and Rac1 deficient animals will be performed to elucidate the impact of Rac1 on (i) the toxic effects of doxorubicin on the heart, (ii) the nephrotoxic effects of cisplatin and (iii) the toxic effects caused by fractionated irradiation of the lung. The working hypothesis is that Rac1-regulated signaling pathways are required for both acute and chronic normal tissue damage induced by anticancer therapeutics. In other words, we speculate that Rac1 deficiency is organoprotective in the context of anticancer therapy employing conventional drugs and irradiation. The project aims to validate Rac1 as therapeutic target for a tissue-overspanning prevention of multiple adverse effects of radio-chemotherapy.