ABSTRACT
Imidazopyridazine compounds are potent, ATP-competitive inhibitors of calcium-dependent protein kinase 1 (CDPK1) and of
Plasmodium falciparum
parasite growth
in vitro
. Here, we show that these compounds can be divided into two classes depending on the nature of the aromatic linker between the core and the R2 substituent group. Class 1 compounds have a pyrimidine linker and inhibit parasite growth at late schizogony, whereas class 2 compounds have a nonpyrimidine linker and inhibit growth in the trophozoite stage, indicating different modes of action for the two classes. The compounds also inhibited cyclic GMP (cGMP)-dependent protein kinase (PKG), and their potency against this enzyme was greatly reduced by substitution of the enzyme's gatekeeper residue at the ATP binding site. The effectiveness of the class 1 compounds against a parasite line expressing the modified PKG was also substantially reduced, suggesting that these compounds kill the parasite primarily through inhibition of PKG rather than CDPK1. HSP90 was identified as a binding partner of class 2 compounds, and a representative compound bound to the ATP binding site in the N-terminal domain of HSP90. Reducing the size of the gatekeeper residue of CDPK1 enabled inhibition of the enzyme by bumped kinase inhibitors; however, a parasite line expressing the modified enzyme showed no change in sensitivity to these compounds. Taken together, these findings suggest that CDPK1 may not be a suitable target for further inhibitor development and that the primary mechanism through which the imidazopyridazines kill parasites is by inhibition of PKG or HSP90.
摘要
咪唑哒嗪化合物是钙依赖性蛋白激酶 1 (CDPK1) 的强效 ATP 竞争性抑制剂。
恶性疟原虫
寄生虫生长的
体外
.我们在此表明,根据核心与 R2 取代基之间芳香连接物的性质,这些化合物可分为两类。第 1 类化合物具有嘧啶连接基,抑制寄生虫在分裂后期的生长,而第 2 类化合物具有非嘧啶连接基,抑制滋养体阶段的生长,这表明这两类化合物具有不同的作用模式。这些化合物还能抑制环磷酸腺苷(cGMP)依赖性蛋白激酶(PKG),在 ATP 结合位点取代该酶的守门残基后,它们对该酶的抑制作用大大降低。1 类化合物对表达经修饰的 PKG 的寄生虫品系的效力也大大降低,这表明这些化合物主要通过抑制 PKG 而不是 CDPK1 来杀死寄生虫。HSP90 被确定为 2 类化合物的结合伙伴,一种代表性化合物与 HSP90 N 端结构域中的 ATP 结合位点结合。减小 CDPK1 守门残基的大小可使撞击激酶抑制剂抑制该酶;然而,表达修饰酶的寄生虫品系对这些化合物的敏感性没有变化。综上所述,这些发现表明 CDPK1 可能不是进一步开发抑制剂的合适靶点,咪唑并哒嗪类药物杀死寄生虫的主要机制是通过抑制 PKG 或 HSP90。