New Antimalarial Drug Research for Multidrug-resistant Malaria

疟疾在世界发展中地区仍然是一个主要的健康问题，对氯喹、甲氟喹、普鲁愈乃和许多其他现有药物产生抗药性的疟疾进一步蔓延，极大地限制了我们控制疟疾的能力。这种可怕的情况促使人们迫切需要开发新的抗疟疾药物，优化利用现有药物，并开发新的抗疟疾化疗方法。在这项研究中，我研究了内氧化物作为新的抗疟药，并分析了甲氟喹的耐药性机制和药物相互作用。合成的内氧化物1，2，6，7-四氧螺(7.11)十一烷(N-89)在体外(IC_50 28 NM，FCR-3株)和体内(ED_50 20 mg·kg~(-1)&gt；)具有显著的抗疟疾活性。N-89对早中期滋养体期寄生虫的治疗效果优于晚期滋养体和裂殖体期寄生虫。与阶段特异性效应一致，在成熟的…中显著抑制血球蛋白的形成E期寄生虫多于裂殖体。在用N-89处理的成熟期寄生虫中，发现血红蛋白消化被抑制。此外，与蛋白酶抑制剂联合使用时发现拮抗作用，解释了N-抑制寄生虫血红蛋白降解的原因。在与青蒿素的联合研究中，N-89在体外对氯喹耐药株(K-1)和氯喹敏感株(FCR-3)显示了协同作用。N-89与青蒿素联用能明显降低伯氏疟原虫感染小鼠的寄生虫血症，延长小鼠存活率。在体外，这种组合能够完全预防寄生虫的复发，其中任何一种药物都有很高的复发率。结果表明，N-89与青蒿素、氟喹啉有协同作用，与奎宁有相加作用，与氯喹、甲氟喹、乙胺嘧啶有拮抗作用。为了了解恶性疟原虫对甲氟喹的抗性机制，分析了恶性疟原虫高抗甲氟喹克隆24中pfmdr1基因的序列多态性和表达水平。甲氟喹抗性克隆/24对甲氟喹、氟苯喹、奎宁、青蒿素的敏感性降低，对氯喹的敏感性增加。甲氟喹敏感株与甲氟喹抗性克隆/24的第86、184、1034、1042和1246位氨基酸残基的pfmdr1基因序列没有差异。相反，我们在克隆/24的pfmdr1基因上发现了新的T到C突变。此外，pfmdr1基因的mRNA在抗性克隆/24中的表达高于敏感品系。Pfmdr1基因的表达水平和点突变可能与甲氟喹耐药机制有关。较少

Malaria remains a major health problem throughout developing parts of the world, Further spread of drug-resistant malaria against chloroquine, mefloquine, proguanile and many other available drugs, extremely limited our ability to control malaria. This terrible situation has stimulated urgent need for the development of novel antimalarial drugs, optimal use of existing drugs and development of new approach to antimalarial chemotherapy. In this study, I investigated endoperoxides as new antiplasmodial agents and analysis of mefloquine resistance mechanisms and drug interactions.Synthesized endoperoxide 1,2,6,7-Tetraoxaspiro (7.11) nonadecane (N-89) exhibited significant antimalarial activity in vitro (IC_50 28 nM, FCR-3 strain) and in vivo (ED_50 20 mgkg^<-1>). N-89 is more effective on early and middle trophozoites stage parasites than that of late trophozoites and schizonts stage parasites. Consistance with stage-specific effect, inhibition of hemozoin formation is pronounced at matur … More e stage parasites than schizonts. Inhibition of hemoglobin digestion was found in mature stage parasites with N-89 treatment. Furthermore, antagonistic effects found when combined with protease inhibitors and explain N-89 inhibits parasite hemoglobin degradation. In a combination study with artemisinin, N-89 exhibited synergistic effect in vitro against chloroquine-resistant (K-1) and chloroquine-sensitive (FCR-3) strains. N-89 and artemisinin combination led marked decline of parasitemia and extends survival rate of mice infected with P. berghei. In vitro this combination able to complete prevention of parasites recrudescence where either drug associate with high rate of recrudesince. N-89 showed synergistic effects with artemisinin and halofantrine; additive effect with quinine; and antagonistic effect with chloroquine, mefloquine and pyrimethamine.Sequence polymorphisms and expression level of pfmdr1 gene in highly mefloquine-resistant clone 24 were analyzed to understand underlying mefloquine resistance mechanisms in Plasmodium falciparum. The mefloquine-resistant clone/24 exerted decreased sensitivity to mefloquine, halofantrine, quinine, artemisinin, and increased sensitivity to chloroquine. There were no difference of pfmdr1 gene sequences of amino acid residues 86, 184, 1034, 1042 and 1246 among mefloquine-sensitive strain and mefloquine-resistant clone/24. In contrast, we found new mutation of T to C in pfmdr1 gene of clone/24. Furthermore, over expression of mRNA of pfmdr1 gene has been observed in resistant clone/24 than sensitive strain. It is likely that expression level and point mutation of pfmdr1 gene may be related to mefloquine resistance mechanism. Less