Development of new antimalarial endoperoxides and it's antimalarial mechanism

疟疾控制变得更加复杂，因为致病因子恶性疟原虫对几乎所有可用的抗疟疾药物都产生了抗药性。随着疟疾寄生虫对更常见和更有效的生物碱药物的抗药性日益增强，人们对倍半萜青蒿素等非生物碱化合物及其相关的内过氧化物质的抗疟疾特性的兴趣正在迅速增长。因此，寻找针对特定寄生虫靶点的新型抗疟疾药物是一项紧迫的任务。疟疾寄生虫在感染的红细胞阶段侵入人的红细胞。当寄生在红细胞中时，寄生虫依靠血红蛋白作为食物来源，用一系列的蛋白酶消化它。两种同源的天冬氨酸蛋白酶被称为纤溶酶I和II，通过在高度保守的铰链区裂解天然的血红蛋白分子来启动降解过程。半胱氨酸蛋白酶FalciPain-2和金属蛋白酶Falcilysin在该途径的下游进一步作用以降解…从更多的血红蛋白到小肽。抑制这些酶在培养和动物模型中杀死寄生虫，表明血红蛋白降解酶是化疗的有效靶点。在这项研究中，我们使用大约300个合成内氧化物的类似物来研究新的抗疟疾内氧化物的开发和选择。因此，用体外抗恶性疟原虫和体内抗伯氏疟原虫的方法筛选了合成的内过氧化物(N-)的抗疟疾活性。在体外，N-89对氯喹敏感株(FCR-3)和氯喹抗性株(K1)具有较强的抗疟活性，其半数抑制浓度(IC_(30))分别为28 nM和26 nM。该化合物的体内抗疟活性也很显著，ED50和ED90分别为20mgkg~(-1)和40mgkg~(-1)。在体外不同发育阶段表现出不同的效应。N-89对早期和中期寄生虫较敏感，对晚期和裂殖体寄生虫较不敏感。这种影响与明显的形态变化有关。虽然晚期和裂殖体阶段的寄生虫进入了第2个周期，但它们的再次入侵受到了损害。与阶段特异性效应一致，在成熟期寄生虫比裂殖体更明显地抑制了血吸虫的形成。当滋养体中期与过氧化内酯孵育时，寄生虫裂解物中有血红蛋白积聚。疟疾寄生虫天冬氨酸蛋白酶抑制剂胃抑素A可逆转其血红蛋白蓄积活性，与N-89联用时显示拮抗作用。我们的结果解释了N-89的抗疟疾活性可能与血红蛋白的降解有关。较少

Malaria control become more complexes because causal agent Plasmodium falciparum has developed resistance to nearly all available antimalarial drugs. As malaria parasite are increasingly resistance to more common and effective alkaloid drugs, interest in the antimalarial properties of nonalkaloid compounds such as sesquiterpene artemisinin and the related endoperoxides is rapidly growing. The search for novel antimalarial drugs against specific parasite target is thus an urgent task to pursue.Malaria parasites invade human erythrocytes in the erythrocytic stage of infection. While residing in erythrocytes, the parasites depend on hemoglobin as a source of food, digesting it with a series of proteases. Two homologous aspartic proteases called plasmepsin I and II initiate the degradative process by cleaving the native hemoglobin molecule in a highly conserved hinge region. A cysteine protease falcipain-2, and a metalloprotease falcilysin, act further downstream in the pathway to degrade … More hemoglobin to small peptides. Inhibition of these proteases kill parasites in culture and animal model, suggesting that hemoglobin degrading proteases are valid targets for chemotherapy.In this study, we studied development and selection of new antimalarial endopeoxides using about 300 analogs of synthetic endoperoxides. As a results, antimalarial activity of a synthetic endoperoxide, (N-89) was selected using in vitro against Plasmodium falciparum and in vivo against P. bergheii. In vitro N-89 exhibited potent antimalarial activity against chloroquine-sensitive (FCR-3) and chloroquine-resistant (K1) strain, estimated 50% growth inhibitory concentration (IC_<30>) was 28 nM and 26 nM, respectively. In vivo antimalarial activity of the compound was also remarkable, ED_<50> and ED_<90> were 20 mgkg^<-1> and 40 mgkg^<-1>, respectively. Differential effect was found at different developmental stages in vitro. N-89 is more sensitive on early and middle stages parasites and less sensitive on late and schizont stage parasites. The effect was associated with distinct morphological changes. Although late and schizonts stage parasites entered 2^<nd> cycle, their re-invasion was impaired. Consistence with stage-specific effect, inhibition of hemozoin formation is pronounced at mature stage parasites than schizonts. When middle trophozoites stage parasites was incubated with endoperoxide hemoglobin accumulation was found in parasite lysates. An aspartic protease inhibitor of malaria parasite pepstatin A could reverse its hemoglobin accumulation activity, and pepstatin A showed antagonistic effect when combined with N-89. Our results explain antimalarial activity of N-89 may be related to hemoglobin degradation. Less