Onchocerciasis, or river blindness, is a neglected tropical disease caused by the filarial nematode
Onchocerca volvulus
that affects more than 37 million people, mainly in third world countries. Currently, the only approved drug available for mass treatment is ivermectin, however, drug resistance is beginning to emerge, thus, new therapeutic targets and agents are desperately needed to treat and cure this devastating disease. Chitin metabolism plays a central role in invertebrate biology due to the critical structural function of chitin for the organism. Taken together with its absence in mammals, targeting chitin is an appealing therapeutic avenue. Importantly, the chitinase OvCHT1 from
O. volvulus
was recently discovered, however, its exact role in the worm’s metabolism remains unknown. A screening effort against OvCHT1 was conducted using the Johns Hopkins Clinical Compound Library that contains over 1,500 existing drugs. Closantel, a veterinary anthelmintic with known proton ionophore activities, was identified as a potent and specific inhibitor of filarial chitinases, an activity not previously reported for this compound. Notably, closantel was found also to completely inhibit molting of
O. volvulus
infective L3 stage larvae. Closantel appears to target two important biochemical processes essential to filarial parasites. To begin to unravel closantel’s effects, a retro-fragment-based study was used to define structural elements critical for closantel’s chitinase inhibitor function. As resources towards the development of new agents that target neglected tropical diseases are scant, the finding of an existing drug with impact against
O. volvulus
provides promise in the hunt for new therapies against river blindness.
河盲症是一种由丝虫寄生虫Onchocerca volvulus引起的热带病,主要影响第三世界国家的超过3700万人。目前,唯一获批用于大规模治疗的药物是伊维菌素,但药物耐药性开始出现,因此迫切需要新的治疗靶点和药物来治疗和治愈这种毁灭性的疾病。由于几丁质对生物体的关键结构功能,因此几丁质代谢在无脊椎动物生物学中起着核心作用。结合哺乳动物中的缺失,靶向几丁质是一种吸引人的治疗途径。重要的是,最近发现了来自O. volvulus的几丁质酶OvCHT1,但其在虫体代谢中的确切作用尚不清楚。使用约翰霍普金斯临床化合物库进行了针对OvCHT1的筛选工作,该库包含超过1500种现有药物。发现克罗山特尔是一种具有已知质子离子载体活性的兽医驱虫药,是一种有效且特异性的丝虫几丁质酶抑制剂,这种活性以前从未报道过。值得注意的是,发现克罗山特尔还完全抑制了O. volvulus感染性L3期幼虫的蜕皮。克罗山特尔似乎靶向了丝虫寄生虫所必需的两个重要生化过程。为了开始解开克罗山特尔的作用,使用基于反向片段的研究来定义对克罗山特尔几丁质酶抑制剂功能至关重要的结构元素。由于针对忽视的热带病开发新药物的资源匮乏,发现一种对O. volvulus产生影响的现有药物,为寻找治疗河盲症的新疗法提供了希望。