Background: Severe malaria caused by Plasmodium falciparum (P. falciparum) leads to most malaria-related deaths globally. Decoquinate (DQ) displays strong antimalarial activity against multistage infection by Plasmodium parasites. However, the development of DQ as an oral dosage form for the treatment of malaria at the blood stage has not been successful. In this study, we have created liposome formulations of DQ for intravenous (IV) injection to suppress Plasmodium parasites that cause severe malaria in mice.
Methods: DQ liposomes were prepared by conventional ethanol injection method with slight modifications and encapsulation efficiency evaluated by the well-established centrifugation method. Antimalarial potency of the DQ liposomes against P. falciparum was assessed in vitro using freshly isolated human red blood cells. The efficacy of the DQ liposomes against Plasmodium berghei (P. berghei) was examined in the mouse model of severe malaria.
Results: The DQ liposomes were around 150 nm in size and had the encapsulation efficiency rates > 95%. The freshly prepared and lyophilized liposomes were stable after storage at -20oC for 6 months. The liposomes were shown to have excellent activity against P. falciparum in vitro with DQ IC50 0.91±0.05 nM for 3D7 (chloroquine sensitive strain) and DQ IC50 1.33±0.14 nM for Dd2 (multidrug resistant strain), which were 18- and 14-fold more potent than artemisinin, respectively. Mice did not have any signs of toxicity after receiving high dose of the liposomes (DQ 500 mg/kg per mouse) by IV injection. In the mouse model of severe malaria, the liposomes had impressive efficacy against P. berghei with DQ ED50 of 0.720mg/kg.
Conclusion: The DQ liposomes prepared in this study were stable for long term storage and safe for IV injection in mammalian animals. The newly created liposome formulations had excellent activity against Plasmodium infection at the blood-stage, which encourages their application in the treatment of severe malaria.