Design of Orally Bioavailable IAP Antagonists for Cancer Treatment

说明书(申请人提供)：凋亡抑制蛋白(IAPs)是一类重要的细胞凋亡调节因子。在这些IAP蛋白中，细胞IAP-1(CIAP-1)和细胞IAP-2(CIAP-2)在死亡受体介导的细胞凋亡的调节中起关键作用，而X-连锁IAP(XIAP)是死亡受体介导的和线粒体介导的凋亡途径的中枢调节因子。XIAP和CIAP-1/2因其作为细胞凋亡调节因子的核心作用，有望成为肿瘤治疗的靶点。Smac是这些IAP蛋白的内源性拮抗剂，并通过其AVPI四肽结合基序与它们相互作用。近年来，大量的研究工作致力于设计和开发被称为Smac模拟物的小分子，它模拟AVPI结合基序并作为IAP蛋白的拮抗剂。Smac类似物不仅能够使癌细胞对其他治疗药物诱导的细胞凋亡敏感，而且在体外和体内作为单一药物在不同肿瘤类型的癌细胞亚群中诱导凋亡也是有效的。Smac类药物作为一类新型抗癌药物被认为具有很大的开发潜力。在这一R01竞争更新中，我们建议评估一类新的有效的、口服活性的、有前景的Smac模拟物作为治疗人类癌症的新疗法。我们的初步数据表明，我们有希望的先导化合物与XIAP和CIAP-1/2以低纳摩尔范围内的亲和力结合，有效地诱导癌细胞凋亡，对正常细胞具有最小的毒性，并且具有与靶向IAP蛋白诱导细胞凋亡高度一致的细胞机制。我们的一种先导化合物作为口服剂在诱导异种移植瘤组织凋亡和抑制MDA-MB-231异种移植瘤模型中的肿瘤生长方面非常有效，而在高效剂量下对动物没有任何毒性。我们在这个项目中的最终目标是开发一种高效的、口服活性的Smac模拟物，作为治疗人类癌症的一种新疗法。为了在最有效地利用资源的同时最大限度地实现我们的最终目标，我们将实施以下具体目标：目标1：测定几种最有希望的先导化合物在多种人类癌症异种移植模型中的体外稳定性、动物毒性和药代动力学以及抗肿瘤活性。目的2：阐明几种最有希望的Smac模拟物在诱导癌细胞凋亡中的作用机制。目的3：基于最有前景的化合物进行基于结构的新类似物的设计和合成，以进一步确定这类有前景的Smac模拟物的构效关系，并为体内研究寻找更多的新的和更好的类似物。目的4：对目标3中得到的新类似物，测定它们与IAP蛋白的结合亲和力和特异性，它们对XIAP的拮抗活性，它们在癌细胞系中的活性和对正常细胞的选择性。我们的初步数据为我们的中心假设、研究设计和策略提供了强有力的支持，为本项目的成功奠定了坚实的基础。该项目的成功实施，将使至少1-2种有效的、特征良好的、高度优化的、口服活性的Smac模拟物进入高级临床前开发，作为一种治疗多种人类癌症的新型抗癌疗法。

DESCRIPTION (provided by applicant): Inhibitor of apoptosis proteins (IAPs) are a class of key apoptosis regulators. Among these IAP proteins, cellular IAP-1 (cIAP-1) and cellular IAP-2 (cIAP-2) play critical roles in the regulation of death-receptor-mediated apoptosis, and X-linked IAP (XIAP) is a central regulator of both death-receptor-mediated and mitochondria-mediated apoptosis pathways. Because of their central role as apoptosis regulators, XIAP and cIAP-1/2 are promising cancer therapeutic targets. Smac is an endogenous antagonist of these IAP proteins and interacts with them via its AVPI tetrapeptide binding motif. In recent years, intense research efforts have been devoted to the design and development of small molecules known as Smac mimetics, which mimic the AVPI binding motif and function as antagonists of IAP proteins. Smac mimetics are not only capable of sensitizing cancer cells to induction of apoptosis by other therapeutic agents but also are effective as single agents in induction of apoptosis in vitro and in vivo in a subset of cancer cell lines of diverse tumor types. Smac mimetics are considered to have great potential for development as a new class of anticancer drugs. In this R01 competing renewal, we propose to evaluate a novel class of potent, orally active, promising Smac mimetics as new therapies for the treatment of human cancer. Our preliminary data have shown that our promising lead compounds bind to XIAP and cIAP-1/2 with affinities in the low nanomolar range, effectively induce apoptosis in cancer cells, possess minimal toxicity to normal cells and have a cellular mechanism of action highly consistent with targeting IAP proteins for apoptosis induction. One of our lead compounds is highly effective as an oral agent in induction of apoptosis in xenograft tumor tissues and in inhibition of tumor growth in the MDA- MB-231 xenograft model, while showing no toxicity to animals at highly efficacious doses. Our ultimate goal in this project is to develop a highly potent, orally active Smac mimetic as a new therapy for the treatment of human cancer. To maximize the probability of achieving our ultimate goal while using resources most efficiently, we will carry out the following specific Aims: Aim 1: Determination of the microsomal and plasma stability in vitro, toxicity and pharmacokinetics in animals, and antitumor activity in multiple xenograft models of human cancer for several of the most promising lead compounds. Aim 2: Elucidation, for several of the most promising Smac mimetics, of the cellular mechanism of action for apoptosis induction in cancer cells. Aim 3: Structure-based design and synthesis of new analogues based upon the most promising leads to further define the structure-activity relationship for this class of promising Smac mimetics and to identify additional new and superior analogues for in vivo studies. Aim 4: For the new analogues obtained in Aim 3, determination of the binding affinities and specificity to IAP proteins, their activity in antagonizing XIAP, their activity in cancer cell lines and selectivity over normal cells. Our preliminary data provide strong support for our central hypothesis, research design and strategy and have laid a solid foundation for the success of this project. Successfully carried out, this project will bring, at a minimum, 1-2 potent, well-characterized, highly optimized, orally active Smac mimetics into advanced preclinical development as a new class of anticancer therapy for the treatment of many types of human cancer.