McKie J H, Douglas K T, Chan C, Roser S A, Yates R, Read M, Hyde J E, Dascombe M J, Yuthavong Y, Sirawaraporn W
School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Manchester M13 9PL, U.K.
J Med Chem. 1998 Apr 23;41(9):1367-70. doi: 10.1021/jm970845u.
Pyrimethamine acts by selectively inhibiting malarial dihydrofolate reductase-thymidylate synthase (DHFR-TS). Resistance in the most important human parasite, Plasmodium falciparum, initially results from an S108N mutation in the DHFR domain, with additional mutation (most commonly C59R or N51I or both) imparting much greater resistance. From a homology model of the 3-D structure of DHFR-TS, rational drug design techniques have been used to design and subsequently synthesize inhibitors able to overcome malarial pyrimethamine resistance. Compared to pyrimethamine (Ki 1.5 nM) with purified recombinant DHFR fromP. falciparum, the Ki value of the m-methoxy analogue of pyrimethamine was 1.07 nM, but against the DHFR bearing the double mutation (C59R + S108N), the Ki values for pyrimethamine and the m-methoxy analogue were 71.7 and 14.0 nM, respectively. The m-chloro analogue of pyrimethamine was a stronger inhibitor of both wild-type DHFR (with Ki 0.30 nM) and the doubly mutant (C59R +S108N) purified enzyme (with Ki 2.40 nM). Growth of parasite cultures of P. falciparum in vitro was also strongly inhibited by these compounds with 50% inhibition of growth occurring at 3.7 microM for the m-methoxy and 0.6 microM for the m-chloro compounds with the K1 parasite line bearing the double mutation (S108N + C59R), compared to 10.2 microM for pyrimethamine. These inhibitors were also found in preliminary studies to retain antimalarial activity in vivo in P. berghei-infected mice.
乙胺嘧啶通过选择性抑制疟原虫二氢叶酸还原酶-胸苷酸合成酶（DHFR-TS）发挥作用。在最重要的人体寄生虫恶性疟原虫中，耐药性最初源于DHFR结构域中的S108N突变，额外的突变（最常见的是C59R或N51I或两者兼有）会赋予更强的耐药性。基于DHFR-TS三维结构的同源模型，已运用合理药物设计技术来设计并随后合成能够克服疟原虫对乙胺嘧啶耐药性的抑制剂。与乙胺嘧啶（Ki为1.5 nM）和来自恶性疟原虫的纯化重组DHFR相比，乙胺嘧啶的间甲氧基类似物的Ki值为1.07 nM，但对于携带双重突变（C59R + S108N）的DHFR，乙胺嘧啶和间甲氧基类似物的Ki值分别为71.7 nM和14.0 nM。乙胺嘧啶的间氯类似物对野生型DHFR（Ki为0.30 nM）和双突变（C59R + S108N）纯化酶（Ki为2.40 nM）均是更强的抑制剂。这些化合物也强烈抑制恶性疟原虫体外培养物的生长，对于携带双重突变（S108N + C59R）的K1寄生虫株系，间甲氧基化合物在3.7 microM时出现50%的生长抑制，间氯化合物在0.6 microM时出现50%的生长抑制，而乙胺嘧啶则为10.2 microM。在初步研究中还发现，这些抑制剂在感染伯氏疟原虫的小鼠体内保留了抗疟活性。
