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

传统的（即基因毒性的）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。对不良组织损伤的药理学抑制将是优先的，以便扩大放化疗联合的治疗窗口，从而使恶性疾病的治疗更有效和更耐受。自己的初步数据表明，HMG-CoA还原酶抑制剂（即他汀类药物）被认为通过靶向Rac/ rho信号传导具有多效胆固醇非依赖性作用，在体外和临床前体内模型中使用广泛使用的抗癌药物（如阿霉素、顺铂）和辐照（IR）治疗后，可减轻非恶性细胞的不良细胞毒性和基因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基因毒性药物和不同类型的组织/细胞的多重保护作用，我们假设这些药物干扰了抗癌治疗引起的急性和慢性正常组织损伤的病理生理学中涉及的优越分子机制。其他药理学研究的结果提供了累积证据，表明ras同源GTPase Rac1可能在这种情况下具有特殊的相关性。然而，这一假设的遗传证据仍然缺失。然而，基因数据是推动新的临床药物开发的基本需要。因此，提交的提案旨在通过采用Rac1基因敲除小鼠模型来验证Rac1作为预防抗癌治疗诱导的不良组织反应的有希望的靶点。为此，我们打算使用Rac1flox/flox/Mx1-Cre小鼠模型完成rac1基因的诱导性基因缺失，该模型已经提供给申请人。采用这种poly-I:C诱导模型系统，rac1可以在多种细胞类型中广泛删除。随后，将使用Rac1熟练和缺乏的动物进行对比分析，以阐明Rac1对(i)阿霉素对心脏的毒性作用，（ii）顺铂的肾毒性作用以及（iii）肺部分级照射引起的毒性作用的影响。工作假设是rac1调节的信号通路是抗癌治疗引起的急性和慢性正常组织损伤所必需的。换句话说，我们推测在采用常规药物和照射的抗癌治疗背景下，Rac1缺乏具有器官保护作用。该项目旨在验证Rac1作为跨组织预防放化疗多重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.