Background: Herbal medicine has been a rich source of new drugs exemplified by quinine and artemisinin. In this study, a variety of Japanese traditional herbal medicine ('Kampo') were examined for their potential anti-malarial activities. Methods: A comprehensive screening methods were designed to identify novel anti-malarial drugs from a library of Kampo herbal extracts (n = 120) and related compounds (n = 96). The anti-malarial activity was initially evaluated in vitro against chloroquine/mefloquine-sensitive (3D7) and-resistant (Dd2) strains of Plasmodium falciparum. The cytotoxicity was also evaluated using primary adult mouse brain cells. After being selected through the first in vitro assay, positive extracts and compounds were examined for possible in vivo anti-malarial activity. Results: Out of 120 herbal extracts, Coptis rhizome showed the highest anti-malarial activity (IC 50 1.9 µg/mL of 3D7 and 4.85 µg/mL of Dd2) with a high selectivity index (SI) > 263 (3D7) and > 103 (Dd2). Three major chlorinated compounds (coptisine, berberine, and palmatine) related to Coptis rhizome also showed anti-malarial activities with IC 50 1.1, 2.6, and 6.0 µM (against 3D7) and 3.1, 6.3, and 11.8 µM (against Dd2), respectively. Among them, coptisine chloride exhibited the highest anti-malarial activity (IC 50 1.1 µM against 3D7 and 3.1 µM against Dd2) with SI of 37.8 and 13.2, respectively. Finally, the herbal extract of Coptis rhizome and its major active compound coptisine chloride exhibited significant anti-malarial activity in mice infected with Plasmodium yoelii 17X strain with respect to its activity on parasite suppression consistently from day 3 to day 7 post-challenge. The effect ranged from 50.38 to 72.13% (P < 0.05) for Coptis rhizome and from 81 to 89% (P < 0.01) for coptisine chloride. Conclusion: Coptis rhizome and its major active compound coptisine chloride showed promising anti-malarial activity against chloroquine-sensitive (3D7) and-resistant (Dd2) strains in vitro as well as in vivo mouse malaria model. Thus, Kampo herbal medicine is a potential natural resource for novel anti-malarial agents.

緒 言 Despite significant advances in the prevention and treatment of malaria, it remains to be one of the calamitous global health and socioeconomic concern. Several drugs are currently available for malaria treatment, however parasites began to develop resistance against most of these drugs including the first line drug, Artemisinin. A newly approved vaccine, RTS, S, has raised hope for preventive therapy, yet suffered with limited efficacy (shorter and stage-specific immunity). As a result, look for new small molecule drug candidates with novel target/mechanism of action has become pivotal. There are various phenotypic screening methods to identify novel antimalarials, however, most of them are time-consuming, costly and laborious. In contrary, in silico approach found to be effective to screen millions of compounds comparatively at shorter time and less expensive way than conventional screening. Therefore, in this study, we developed new prediction models for in silico antimalarial compound screening based on the physicochemical properties of small chemical compounds (hemozoin inhibitors) identified from our previous study. 対象と方法In this study, 224 positive hemozoin inhibitors (obtained from our previous study), were tested for in vitro erythrocytic antimalarial activity against chloroquine -mefloquine sensitive Plasmodium falciparum strain, 3D7A and their antihemozoin activity. The physicochemical properties of the active compounds (antimalarials and hemozoin inhibitors) were extracted from ChemSpider and SciFinder databases. To develop the model, univariable logistic regression was performed to examine the association between physicochemical properties (variables) and antimalarial activity of the compounds (outcome). Subsequently, to find independent predictors, variables P<0.1 and/or significant variables in previous study, were subjected to multivariable analysis using Bayesian model averaging (BMA) based on the Bayesian information criterion (BIC), where the smaller BIC value indicates the better model. The data were randomly divided into two sets -training and testing, with a ratio of 70:30. The BMA models were developed using training set and validated by testing data set. The data were analysed by using RStudio 1.0.44

Background Emergence of cross-resistance to current anti-malarial drugs has led to an urgent need for identification of potential compounds with novel modes of action and anti-malarial activity against the resistant strains. One of the most promising therapeutic targets of anti-malarial agents related to food vacuole of malaria parasite is haemozoin, a product formed by the parasite through haemoglobin degradation. Methods With this in mind, this study developed two-dimensional-quantitative structure–activity relationships (QSAR) models of a series of 21 haemozoin inhibitors to explore the useful physicochemical parameters of the active compounds for estimation of anti-malarial activities. The 2D-QSAR model with good statistical quality using partial least square method was generated after removing the outliers. Results Five two-dimensional descriptors of the training set were selected: atom count (a_ICM); adjacency and distance matrix descriptor (GCUT_SLOGP_2: the third GCUT descriptor using atomic contribution to logP); average total charge sum (h_pavgQ) in pKa prediction (pH = 7); a very low negative partial charge, including aromatic carbons which have a heteroatom-substitution in “ortho” position (PEOE_VSA-0) and molecular descriptor (rsynth: estimating the synthesizability of molecules as the fraction of heavy atoms that can be traced back to starting material fragments resulting from retrosynthetic rules), respectively. The model suggests that the anti-malarial activity of haemozoin inhibitors increases with molecules that have higher average total charge sum in pKa prediction (pH = 7). QSAR model also highlights that the descriptor using atomic contribution to logP or the distance matrix descriptor (GCUT_SLOGP_2), and structural component of the molecules, including topological descriptors does make for better anti-malarial activity. Conclusions The model is capable of predicting the anti-malarial activities of anti-haemozoin compounds. In addition, the selected molecular descriptors in this QSAR model are helpful in designing more efficient compounds against the P. falciparum 3D7A strain.

Background: The herbal medicine has been a rich source of new drugs exemplified by quinine and artemisinin. In this study, examined a variety of Japanese traditional herbal medicine (Kampo) for their potential antimalarial activities. Methods: We designed a comprehensive screening to identify novel antimalarial drugs from a library of Kampo herbal extracts (n = 120) and related compounds (n=96). The antimalarial activity was initially evaluated in vitro against chloroquine/mefloquine-sensitive (3D7) and -resistant (Dd2) strains of Plasmodium falciparum . The cytotoxicity was also evaluated using primary Adult Mouse Brain cells. After being selected through the first in vitro assay, positive extracts and compounds were examined for possible in vivo antimalarial activity. Results: Out of 120 herbal extracts, Coptis Rhizome showed the highest antimalarial activity (IC 50 1.9 µg/mL of 3D7 and 4.85 µg/mL of Dd2) with a high selectivity index (SI) > 263 (3D7) and > 103 (Dd2). Three major chlorinated compounds (coptisine, berberine, and palmatine) related to Coptis Rhizome also showed antimalarial activities with IC 50 1.1, 2.6, and 6.0 µM (against 3D7) and 3.1, 6.3, and 11.8 µM (against Dd2), respectively. Among them, coptisine chloride exhibited the highest antimalarial activity (IC 50 1.1 µM against 3D7 and 3.1 µM against Dd2) with SI of 37.8 and 13.2, respectively. . Finally, the herbal extract of Coptis Rhizome and its major active compound coptisine chloride exhibited significant antimalarial activity in mice infected with P. yoelii 17X strain with respect to its activity on parasite suppression consistently from day 3 to day 7 post-challenge. The effect ranged from 50.38 to 72.13% (P <.05) for Coptis Rhizome and from 81 to 89% (P <.01) for coptisine chloride. Conclusion: Coptis Rhizome and its major active compound coptisine chloride showed promising antimalarial activity against chloroquine-sensitive (3D7) and -resistant (Dd2) strains in vitro as well as in vivo mouse malaria model. Thus Kampo herbal medicine is a potential natural resource for novel antipathogenic agents.

Background: The herbal medicine has been an attractive source of new antimalarial drugs exemplified by quinine and artemisinin, thus we examined a variety of Japanese traditional herbal medicine (Kampo) for their potential antimalarial activities.Methods: We designed a comprehensive screening to identify novel antimalarial drugs from a library of Kampo crude drug extracts (n = 120). The antimalarial activity was initially evaluated in vitro against chloroquine/mefloquine-sensitive (3D7) and -resistant (Dd2) strains of Plasmodium falciparum. The cytotoxicity was also evaluated using primary Adult Mouse Brain cells. Subsequently, major active components of Kampo crude drug extracts showing high antimalarial activities and low cytotoxicity were further evaluated. Finally, the in vivo antimalarial activities of promising Kampo crude drug extract was investigated using P. yoelii infected mouse model in a seven-day suppressive test (treatment start two hours after challenge infection and continue for seven days).Results: Out of 120 extracts, Coptis Rhizome showed the highest antimalarial activity (IC50 1.9 µg/mL of 3D7 and 4.85 µg/mL of Dd2) with a high selectivity index (SI) > 263 (3D7) and > 103 (Dd2). Three major components in Coptis Rhizome also showed antimalarial activities with IC50 ranging from 1.1 to 6.0 µM (against 3D7) and from 3.1 to 11.8 µM (against Dd2). Among them, coptisine chloride exhibited the highest antimalarial activity (IC50 1.1 µM against 3D7 and 3.1 µM against Dd2) with SI of 37.8 and 13.2, respectively. Furthermore, Coptis Rhizome exhibited significant antimalarial activity in mice infected with P. yoelii 17X strain with respect to its activity on parasite suppression consistently throughout the entire test period (P < 0.05).Conclusion: Coptis Rhizome showed a significant in vivo antimalarial activity in mice infected with P. Yoelii, thus it is a potential natural resource for antimalarials and its component coptisine chloride is a promising antimalarial lead compound.