Squalene Synthase As a Target for Chagas Disease Therapeutics

Trypanosomatid parasites are the causative agents of many neglected tropical diseases and there is currently considerable interest in targeting endogenous sterol biosynthesis in these organisms as a route to the development of novel anti-infective drugs. Here, we report the first x-ray crystallographic structures of the enzyme squalene synthase (SQS) from a trypanosomatid parasite, Trypanosoma cruzi, the causative agent of Chagas disease. We obtained five structures of T. cruzi SQS and eight structures of human SQS with four classes of inhibitors: the substrate-analog S-thiolo-farnesyl diphosphate, the quinuclidines E5700 and ER119884, several lipophilic bisphosphonates, and the thiocyanate WC-9, with the structures of the two very potent quinuclidines suggesting strategies for selective inhibitor development. We also show that the lipophilic bisphosphonates have low nM activity against T. cruzi and inhibit endogenous sterol biosynthesis and that E5700 acts synergistically with the azole drug, posaconazole. The determination of the structures of trypanosomatid and human SQS enzymes with a diverse set of inhibitors active in cells provides insights into SQS inhibition, of interest in the context of the development of drugs against Chagas disease.锥虫科（Trypanosomatid）寄生虫是多种被忽视热带病的致病原，目前学界对靶向这类生物的内源性固醇生物合成途径以开发新型抗感染药物有着浓厚兴趣。本研究首次解析了锥虫科寄生虫克氏锥虫（Trypanosoma cruzi，恰加斯病的致病原）的鲨烯合酶（squalene synthase, SQS）的X射线晶体结构。我们共获得了5组克氏锥虫SQS结构与8组人源SQS结构，所使用的抑制剂分为四类：底物类似物S-硫醇法尼基焦磷酸（S-thiolo-farnesyl diphosphate）、奎宁环类（quinuclidines）抑制剂E5700与ER119884、多种亲脂性双膦酸盐，以及硫氰酸盐WC-9；其中两种强效奎宁环类抑制剂的结构为选择性抑制剂开发提供了可行策略。本研究同时证实，亲脂性双膦酸盐对克氏锥虫具有纳摩尔级的强效活性，可抑制内源性固醇生物合成；且E5700与唑类药物泊沙康唑（posaconazole）具有协同作用。本研究通过多种细胞活性抑制剂解析了锥虫科与人类SQS酶的结构，为SQS抑制机制研究提供了新见解，这对于恰加斯病的抗药物开发具有重要意义。