Background The Plasmodium falciparum dihydrofolate reductase (PfDHFR) inhibitors pyrimethamine and cycloguanil (the active metabolite of proguanil) have important roles in malaria chemoprevention, but drug resistance challenges their efficacies. A new compound, P218, was designed to overcome resistance, but drug-susceptibility data for P falciparum field isolates are limited. Methods We studied ex vivo PfDHFR inhibitor susceptibilities of 559 isolates from Tororo and Busia districts, Uganda, from 2016 to 2020, sequenced 383 isolates, and assessed associations between genotypes and drug-susceptibility phenotypes. Results Median half-maximal inhibitory concentrations (IC50s) were 42 100 nM for pyrimethamine, 1200 nM for cycloguanil, 13000 nM for proguanil, and 0.6 nM for P218. Among sequenced isolates, 3 PfDHFR mutations, 51I (100%), 59R (93.7%), and 108N (100%), were very common, as previously seen in Uganda, and another mutation, 164L (12.8%), had moderate prevalence. Increasing numbers of mutations were associated with decreasing susceptibility to pyrimethamine, cycloguanil, and P218, but not proguanil, which does not act directly against PfDHFR. Differences in P218 susceptibilities were modest, with median IC50s of 1.4 nM for parasites with mixed genotype at position 164 and 5.7 nM for pure quadruple mutant (51I/59R/108N/164L) parasites. Conclusions Resistance-mediating PfDHFR mutations were common in Ugandan isolates, but P218 retained excellent activity against mutant parasites.

中文翻译：

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乌干达恶性疟原虫分离株对与遗传多态性相关的二氢叶酸还原酶抑制剂的敏感性降低

背景 恶性疟原​​虫二氢叶酸还原酶 (PfDHFR) 抑制剂乙胺嘧啶和环胍（氯胍的活性代谢物）在疟疾化学预防中具有重要作用，但耐药性挑战了它们的功效。一种新化合物 P218 旨在克服耐药性，但恶性疟原虫野外分离株的药物敏感性数据有限。方法 我们研究了 2016 年至 2020 年来自乌干达 Tororo 和 Busia 地区的 559 株分离株的体外 PfDHFR 抑制剂敏感性，对 383 株分离株进行了测序，并评估了基因型与药物敏感性表型之间的关联。结果 乙胺嘧啶的中位半数最大抑制浓度 (IC50) 为 42100 nM，环胍为 1200 nM，氯胍为 13000 nM，P218 为 0.6 nM。在测序的分离株中，3 个 PfDHFR 突变，51I (100%)，59R (93.7%)，和 108N (100%) 非常常见，如之前在乌干达所见，另一种突变 164L (12.8%) 的流行率中等。越来越多的突变与乙胺嘧啶、环胍和 P218 的易感性降低有关，但与氯胍无关，氯胍不直接作用于 PfDHFR。P218 敏感性的差异不大，164 位混合基因型寄生虫的 IC50 中位数为 1.4 nM，纯四重突变体 (51I/59R/108N/164L) 寄生虫的 IC50 中位数为 5.7 nM。结论 耐药介导的 PfDHFR 突变在乌干达分离株中很常见，但 P218 保留了对突变寄生虫的优异活性。越来越多的突变与乙胺嘧啶、环胍和 P218 的易感性降低有关，但与氯胍无关，氯胍不直接作用于 PfDHFR。P218 敏感性的差异不大，164 位混合基因型寄生虫的 IC50 中位数为 1.4 nM，纯四重突变体 (51I/59R/108N/164L) 寄生虫的 IC50 中位数为 5.7 nM。结论 耐药介导的 PfDHFR 突变在乌干达分离株中很常见，但 P218 保留了对突变寄生虫的优异活性。越来越多的突变与乙胺嘧啶、环胍和 P218 的易感性降低有关，但与氯胍无关，氯胍不直接作用于 PfDHFR。P218 敏感性的差异不大，164 位混合基因型寄生虫的 IC50 中位数为 1.4 nM，纯四重突变体 (51I/59R/108N/164L) 寄生虫的 IC50 中位数为 5.7 nM。结论 耐药介导的 PfDHFR 突变在乌干达分离株中很常见，但 P218 保留了对突变寄生虫的优异活性。