Anthelmintics are used to treat human and veterinary parasitic diseases, as well as to reduce crop and livestock production loss associated with parasitosis. The free-living nematode Caenorhabditis elegans, a model system for anthelmintic drug discovery, has a serotonin (5-HT)-gated chloride channel, MOD-1, which belongs to the Cys-loop receptor family and modulates locomotory and behavioral functions. Since MOD-1 is unique to nematodes, it is emerging as an attractive anthelmintic drug target, but details of MOD-1 function are unclear. Here, we revealed novel aspects of MOD-1 function from the molecular level to the organism level and identified compounds targeting this receptor, which may provide new directions for anthelmintic drug discovery. We used whole-cell current recordings from heterologously expressed MOD-1 to show that tryptamine, a weak partial agonist of vertebrate 5-HT₃ receptors, efficaciously activates MOD-1. A screen for modulators revealed that GABAergic ligands piperazine and muscimol reduce 5-HT-elicited currents, thus identifying novel MOD-1 allosteric inhibitors. Next, we performed locomotor activity assays, and we found 5-HT and tryptamine rapidly decrease worm motility, which is reversible only at low 5-HT concentrations. Mutants lacking MOD-1 are partially resistant to both drugs, demonstrating its key role in locomotion. Acting as an antagonist of MOD-1, we showed piperazine reduces the locomotor effects of exogenous 5-HT. Therefore, tryptamine- and piperazine-derived compounds, acting at MOD-1 through different molecular mechanisms, emerge as promising anthelmintic agents. This study enhances our knowledge of the function and drug selectivity of Cys-loop receptors and postulates MOD-1 as a potential target for anthelmintic therapy.

驱虫药用于治疗人类和兽医寄生虫病，以及减少与寄生虫病相关的农作物和牲畜生产损失。自由生活的线虫秀丽隐杆线虫（Caenorhabditis elegans ）是驱虫药物发现的模型系统，具有血清素（5-HT）门控氯离子通道MOD-1，属于半胱环受体家族并调节运动和行为功能。由于 MOD-1 是线虫所特有的，因此它正在成为一种有吸引力的驱虫药物靶点，但 MOD-1 功能的细节尚不清楚。在这里，我们从分子水平到生物水平揭示了MOD-1功能的新方面，并鉴定了针对该受体的化合物，这可能为驱虫药物的发现提供新的方向。我们使用异源表达的 MOD-1 的全细胞电流记录来表明色胺（脊椎动物 5-HT ₃受体的弱部分激动剂）可有效激活 MOD-1。调节剂筛选显示 GABA 配体哌嗪和蝇蕈醇可减少 5-HT 引发的电流，从而鉴定出新型 MOD-1 变构抑制剂。接下来，我们进行了运动活性测定，发现 5-HT 和色胺会迅速降低蠕虫的运动性，而这种情况只有在低 5-HT 浓度下才可逆转。缺乏 MOD-1 的突变体对这两种药物均具有部分耐药性，这证明了其在运动中的关键作用。作为 MOD-1 的拮抗剂，我们发现哌嗪可降低外源 5-HT 的运动效应。因此，色胺和哌嗪衍生的化合物通过不同的分子机制作用于MOD-1，成为有前途的驱虫剂。 这项研究增强了我们对 Cys 环受体的功能和药物选择性的了解，并假设 MOD-1 作为驱虫治疗的潜在靶点。