Transition-State Analogue Inhibitors of Dihydrofolate Synthetase for MDR/XDR TB

描述（由申请人提供）：结核分枝杆菌（Mtb）是一种臭名昭著的病原体，其对抗生素的耐药性日益增强，与艾滋病合并的致死率提高，使其成为世界范围内的主要健康问题。耐多药Mtb的选择和传播持续了几十年，导致两种不同形式的选择和传播，即耐多药（MDR-TB）和广泛耐药（XDR-TB）。2007年全球耐多药结核病和广泛耐药结核病病例的估计数分别为50万和4万。鉴于结核病在世界范围内的流行和耐药菌株的出现，使用目前的抗菌剂来根除耐多药结核病和广泛耐药结核病是站不住脚的。因此，迫切需要发现作用于新的药物靶点且对任何现有药物没有交叉耐药性的新型抗结核药物，以对抗耐多药/广泛耐药结核病。一种治疗耐多药/广泛耐药结核病的新抗菌素的潜在影响预计将是重大的，可能影响数十万患者。靶向叶酸生物合成途径是一种已被证实的治疗多种疾病的策略，包括癌症、细菌感染和寄生虫感染。对人类来说，叶酸的需求必须完全从饮食中获得。相反，结核分枝杆菌和其他细菌从头合成叶酸，并具有催化叶酸组装的酶，这是人类所缺乏的。这种酶是二氢叶酸合成酶（Mtb- dhfs），它催化谷氨酸与二氢叶酸（DHP）的结合产生二氢叶酸（DHF）。因此，人类完全缺乏DHFS，但它对结核分枝杆菌的生长至关重要。因此，针对DHFS是开发治疗MDR/XDR-TB的一种非常有吸引力的策略，因为(1)DHFS不涉及对任何现有抗mtb药物的交叉耐药，(2)据预测，使用高剂量的DHFS抑制剂可以有效地消毒细菌的避难所，达到杀菌浓度，而不会对患者产生剂量限制性毒性。基于已知的Mtb-DHFS中催化和dhp结合位点的催化机制和结构模型，我们假设我们将能够开发出有效的、选择性的过渡态类似物抑制剂。因此，SBIR一期提案的两年实验计划旨在快速启动发现活动，以确定Mtb-DHFS的有效和选择性抑制剂。我们将在为期2年的第一阶段阶段测试的假设是，基于已知的催化机制和催化和dhp结合位点的结构模型，我们将能够开发出有效的、选择性的Mtb-DHFS过渡态类似抑制剂。

DESCRIPTION (provided by applicant): Mycobacterium tuberculosis (Mtb) is a notorious pathogen whose increasing resistance to antibiotics and heightened lethality in combination with AIDS makes it a major health concern worldwide. The selection and spread of multiple drug resistant Mtb continued for decades leading to selection and spread of two operationally distinct forms, multiple drug resistant (MDR-TB) and extensively drug resistant (XDR-TB). The estimate for global MDR-TB and XDR-TB cases for 2007 were 500,000 and 40,000 respectively. Given the worldwide epidemic in tuberculosis and emergence of drug resistant strains, eradicating MDR-TB and XDR-TB using the current armamentarium of antimicrobials is untenable. Thus, the discovery of new types of anti-Mtb drugs acting on novel drug targets with no cross-resistance to any existing drugs is urgently needed to combat MDR/XDR-TB. The potential impact of a new antimicrobial to treat MDR/XDR-TB would be expected to be major, potentially affecting hundreds of thousands of patients. Targeting the folate biosynthetic pathway is an established and proven therapeutic strategy in a variety of diseases including cancer, bacterial infections and parasitic infections. In humans, folate requirements must be met entirely from dietary sources. In contrast, Mtb and other bacteria synthesize folates de novo and have enzymes that catalyze the assembly of folate that are absent from humans. One such enzyme in Mtb is dihydrofolate synthetase (Mtb-DHFS) that catalyzes the addition of glutamate to dihydropteroate (DHP) to produce dihydrofolate (DHF). Accordingly, humans completely lack DHFS, but it is essential for the growth of Mtb. Targeting DHFS is therefore a highly attractive strategy for developing therapy for treating MDR/XDR-TB, because (1) DHFS is not involved in cross- resistance to any existing anti-Mtb drugs, and (2) it is predicted that bacterial sanctuary sites could be effectively sterilized using high doses of a DHFS inhibitor to achieve bactericidal concentrations without causing dose-limiting toxicities to the patient. Based on the known catalytic mechanism and structural models of the catalytic and DHP-binding sites in Mtb-DHFS, it is our hypothesis that we will be able to develop potent and selective transition-state analogue inhibitors. Thus, the two-year experimental plan in this SBIR Phase 1 proposal aims to jumpstart the discovery campaign to identify potent and selective inhibitors of Mtb-DHFS. The hypothesis we will test during the 2-year Phase 1 segment is that based on the known catalytic mechanism and structural models of the catalytic and DHP-binding sites, we will be able to develop potent and selective transition-state analogue inhibitors to Mtb-DHFS. PUBLIC HEALTH RELEVANCE: Multidrug-resistant tuberculosis and extensively drug resistant tuberculosis are a major health concern worldwide. The proposed DHRS inhibitors may lead to effective new treatments for resistant tuberculosis.