Novel Antifolates against AIDS-associated Tuberculosis

描述(由申请人提供)：该项目的总体目标是开发有效和选择性的抗结核分枝杆菌(Mtb)，结核分枝杆菌是一种已知会导致艾滋病患者发病率和死亡率的机会性病原体。具体地说，该项目将侧重于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，设计新型的抗叶酸，有机合成，并评价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。最近对抑制叶酸途径酶的药物的临床研究，包括DHFR，证明了对艾滋病相关结核病患者的治疗效果。高效力的DHFR抑制剂是可用的，但由于其低选择性而具有毒性。为了提高选择性，需要一个新的药效团模型，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潜在的靶点，允许设计选择性抑制剂。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体系，我们设计了一系列具有特殊功能的分子，它们能与Mtb DHFR上的这些位点紧密而特异地结合，但不太可能与人类酶上的相同位点结合。在这项拟议的研究中，将合成这些设计的分子，并评估它们对DHFR的抑制作用和对MTB细胞生长的影响。活性和选择性抑制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由X射线结晶学确定。对这些化合物的结构分析将揭示这些化合物与靶的配体结合方式以及由这些化合物的结合引起的靶结构的变化，这对于先导化合物的优化是至关重要的。本研究为抗分枝杆菌感染的抗叶酸类药物的设计提供了新的方向。这项研究还将为进一步开发高效和选择性抗结核分枝杆菌的化合物提供分子基础，并有可能用于结核病的治疗。

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.