Novel Antifolates against AIDS-associated Tuberculosis

描述（由申请人提供）：本项目的总体目标是开发针对结核分枝杆菌（Mtb）的有效和选择性抗叶酸剂，已知结核分枝杆菌是导致艾滋病患者发病和死亡的机会致病菌。具体而言，该项目将侧重于新的抗叶酸剂的设计，通过基于结构的方法，根据最近解决的Mtb二氢叶酸还原酶（DHFR）的晶体结构，有机合成，并评估合成化合物的生物活性。DHFR是叶酸代谢途径的关键酶，是原核和真核细胞生长所必需的。最近对叶酸途径酶抑制剂（包括DHFR）的临床研究表明，对艾滋病相关结核病患者具有治疗效果。高效的DHFR抑制剂是可用的，但由于其低选择性而有毒。为了提高选择性，需要一种新的药效团模型，该模型严重依赖于宿主和病原体酶之间的结构差异。宿主和病原体DHFR酶的可用结构之间的比较揭示了允许设计选择性抑制剂的潜在靶位点。以DHFR家族常见的结合基序为平台，如2，4-二氨基嘧啶和二氨基蝶啶杂环系统，我们设计了一系列具有特殊功能的分子，这些分子将紧密和特异性地结合到Mtb DHFR上的这些位点，但不太可能与人酶上的相同位点结合。在这项拟议的研究中，这些设计的分子将被合成并评估其对DHFR的抑制作用及其对Mtb细胞生长的影响。主动和选择性抑制Mtb的先导化合物将与Mtb DHFR共结晶。这些配合物的晶体结构将通过X射线晶体学确定。这些复合物的结构分析将揭示配体与靶标的结合模式以及由这些化合物的结合引起的靶标的结构变化，这对于先导化合物的优化至关重要。本研究为叶酸类抗分枝杆菌药物的设计提供了一个新的方向。这项研究还将为进一步开发对Mtb具有高度有效性和选择性的化合物提供分子基础，并可能用于TB治疗。

DESCRIPTION (provided by applicant): The overall goal of this project is to develop both potent and selective antifolates against Mycobacterium tuberculosis (Mtb), an opportunistic pathogen known to cause morbidity and mortality in AIDS patients. Specifically this project will focus on design of novel antifolates, through a structure-based approach in light of the recently solved crystal structure of Mtb dihydrofolate reductase (DHFR), organic synthesis, and evaluation of the synthetic compounds for their biological activity. DHFR is a key enzyme of the folate metabolic pathway and is required for both prokaryotic and eukaryotic cell-growth. Recent clinical studies of agents inhibiting enzymes of the folate pathway, including DHFR, demonstrated therapeutic effect in AIDS-associated TB patients. Highly potent DHFR inhibitors are available but are toxic due to their low selectivity. To increase the selectivity, a new pharmacophore model is needed, which relies critically on structural differences between the host and pathogen enzymes. The comparison between the available structures of the host and the pathogen DHFR enzymes has revealed potential target sites that allow for the design of selective inhibitors. With the common binding motifs of the DHFR family as platforms, such as 2,4-diaminopyrimidine and diaminopteridine heterocyclic systems, we have designed a series of molecules with special features that would bind tightly and specifically to these sites on Mtb DHFR but unlikely to the same sites on the human enzyme. In this proposed research, these designed molecules will be synthesized and evaluated for their inhibition of DHFR and their effect on Mtb cell growth. Lead compounds that actively and selectively inhibit Mtb will be co-crystallized with Mtb DHFR. The crystal structures of these complexes will be determined by X-ray crystallography. The structural analysis of these complexes will reveal the ligand binding mode to the target and the structural changes in the target induced by the binding of these compounds, which is critically useful for the lead-compound optimization. This study presents a new direction in the design of antifolates against mycobacterial infection. This study will also provide the molecular basis for further developing compounds that are highly potent and selective against Mtb and are potentially useful for the TB treatment.