Malarial dihydrofolate reductase (DHFR) is the target of antifolate antimalarial drugs such as pyrimethamine and cycloguanil, the clinical efficacy of which have been compromised by resistance arising through mutations at various sites on the enzyme. Here, we describe the use of cocrystal structures with inhibitors and substrates, along with efficacy and pharmacokinetic profiling for the design, characterization, and preclinical development of a selective, highly efficacious, and orally available antimalarial drug candidate that potently inhibits both wild-type and clinically relevant mutated forms of
Plasmodium falciparum
(Pf) DHFR. Important structural characteristics of P218 include pyrimidine side-chain flexibility and a carboxylate group that makes charge-mediated hydrogen bonds with conserved Arg122 (PfDHFR-TS amino acid numbering). An analogous interaction of P218 with human DHFR is disfavored because of three species-dependent amino acid substitutions in the vicinity of the conserved Arg. Thus, P218 binds to the active site of PfDHFR in a substantially different fashion from the human enzyme, which is the basis for its high selectivity. Unlike pyrimethamine, P218 binds both wild-type and mutant PfDHFR in a slow-on/slow-off tight-binding mode, which prolongs the target residence time. P218, when bound to PfDHFR-TS, resides almost entirely within the envelope mapped out by the dihydrofolate substrate, which may make it less susceptible to resistance mutations. The high in vivo efficacy in a SCID mouse model of
P. falciparum
malaria, good oral bioavailability, favorable enzyme selectivity, and good safety characteristics of P218 make it a potential candidate for further development.
疟原虫二氢叶酸还原酶(DHFR)是抗叶酸类抗疟药物如嘧啶嗪和环戊鸟苷的靶点,但其临床疗效已因酶上各个位点突变导致耐药性而受到影响。在此,我们描述了利用与抑制剂和底物的共晶结构,以及功效和药代动力学分析进行设计、表征和临床前开发的选择性、高效、口服可用的抗疟药候选药物,可有效抑制野生型和临床相关的突变型疟原虫(Pf)DHFR。 P218的重要结构特征包括嘧啶侧链的灵活性和羧酸基团,它与保守的Arg122(PfDHFR-TS氨基酸编号)形成电荷介导的氢键。P218与人类DHFR的类似相互作用不利于发生,因为在保守的Arg附近存在三个物种特异性氨基酸替换。因此,P218以与人类酶截然不同的方式结合于PfDHFR的活性位点,这是其高选择性的基础。与嘧啶嗪不同,P218以缓慢进入/缓慢离开的紧密结合模式结合于野生型和突变型PfDHFR,这延长了靶点驻留时间。当P218结合于PfDHFR-TS时,几乎完全处于二氢叶酸底物描绘的包络内,这可能使其不易受到耐药突变的影响。P218在SCID小鼠模型中对P. falciparum疟疾的高体内功效、良好的口服生物利用度、有利的酶选择性和良好的安全特性使其成为进一步开发的潜在候选药物。