Department of Parasitology and Entomology, Faculty of Public Health, Mahidol University, Bangkok, Thailand.
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Mahidol University, Bangkok, 10400, Thailand.
Malar J. 2023 Mar 23;22(1):105. doi: 10.1186/s12936-023-04532-3.
New anti-malarial drugs are needed urgently to address the increasing challenges of drug-resistant falciparum malaria. Two rhinacanthin analogues containing a naphthoquinone moiety resembling atovaquone showed promising in-vitro activity against a P. falciparum laboratory reference strain (K1). The anti-malarial activity of these 2 compounds was further evaluated for P. falciparum field isolates from an area of multi-drug resistance in Northeast Thailand.
Using a pLDH enzyme-linked immunosorbent assay, four P. falciparum isolates from Northeast Thailand in 2018 were tested for in vitro sensitivity to the two synthetic rhinacanthin analogues 1 and 2 as well as established anti-malarials. Mutations in the P. falciparum cytochrome b gene, a marker for atovaquone (ATQ) resistance, were genotyped in all four field isolates as well as 100 other clinical isolates from the same area using PCR-artificial Restriction Fragment Length Polymorphisms. Pfkelch13 mutations, a marker for artemisinin (ART) resistance, were also examined in all isolates.
The 50% inhibitory concentrations (IC) of P. falciparum field isolates for rhinacanthin analogue 1 was 321.9-791.1 nM (median = 403.1 nM). Parasites were more sensitive to analogue 2: IC 48.6-63.3 nM (median = 52.2 nM). Similar results were obtained against P. falciparum reference laboratory strains 3D7 and W2. The ART-resistant IPC-5202 laboratory strain was more sensitive to these compounds with a median IC 45.9 and 3.3 nM for rhinacanthin analogues 1 and 2, respectively. The ATQ-resistant C2B laboratory strain showed high-grade resistance towards both compounds (IC > 15,000 nM), and there was a strong positive correlation between the IC values for these compounds and ATQ (r = 0.83-0.97, P < 0.001). There were no P. falciparum cytochrome b mutations observed in the field isolates, indicating that P. falciparum isolates from this area remained ATQ-sensitive. Pfkelch13 mutations and the ring-stage survival assay confirmed that most isolates were resistant to ART.
Two rhinacanthin analogues showed parasiticidal activity against multi-drug resistant P. falciparum isolates, although less potent than ATQ. Rhinacanthin analogue 2 was more potent than analogue 1, and can be a lead compound for further optimization as an anti-malarial in areas with multidrug resistance.
需要新的抗疟药物来应对日益严重的耐青蒿素恶性疟原虫的挑战。两种含有类似阿托伐醌的萘醌部分的瑞那辛类似物在体外对恶性疟原虫实验室参考株（K1）表现出有希望的活性。对来自泰国东北部多药耐药地区的四种恶性疟原虫临床分离株进一步评估了这两种化合物的抗疟活性。
使用 pLDH 酶联免疫吸附试验，对来自泰国东北部的 2018 年的四种疟原虫分离株进行了体外敏感性测试，测试了两种合成的瑞那辛类似物 1 和 2 以及已建立的抗疟药物。对所有四个现场分离株以及来自同一地区的 100 个其他临床分离株进行了疟原虫细胞色素 b 基因的基因分型，该基因是阿托伐醌（ATQ）耐药的标志物。还在所有分离株中检查了疟原虫 Kelch13 突变，这是抗青蒿素（ART）耐药的标志物。
瑞那辛类似物 1 对恶性疟原虫现场分离株的 50%抑制浓度（IC）为 321.9-791.1 nM（中位数= 403.1 nM）。类似物 2 对寄生虫的敏感性更高：IC 48.6-63.3 nM（中位数= 52.2 nM）。对恶性疟原虫参考实验室株 3D7 和 W2 也得到了类似的结果。ART 耐药的 IPC-5202 实验室株对这些化合物更敏感，瑞那辛类似物 1 和 2 的中位 IC 分别为 45.9 和 3.3 nM。ATQ 耐药的 C2B 实验室株对这两种化合物表现出高等级耐药性（IC>15000 nM），并且这两种化合物的 IC 值与 ATQ 之间存在很强的正相关（r=0.83-0.97，P<0.001）。在现场分离株中未观察到疟原虫细胞色素 b 突变，表明该地区的疟原虫分离株仍对 ATQ 敏感。Pfkelch13 突变和环期存活试验证实，大多数分离株对 ART 耐药。
两种瑞那辛类似物对多药耐药恶性疟原虫分离株表现出杀寄生虫活性，尽管其效力低于 ATQ。瑞那辛类似物 2 比类似物 1 更有效，可作为在多药耐药地区进一步优化的抗疟先导化合物。
