Improved efficacy of doxycycline in liposomes against Plasmodium falciparum in culture and Plasmodium berghei infection in mice

The rate at which Plasmodium falciparum is developing resistance to clinically used antimalarial drugs is alarming. Therefore, there is a compelling need to develop an efficient drug delivery system to improve the efficacy of existing antimalarial agents and circumvent drug resistance. Here, we report the antibacterial drug doxycycline (DOXY) in liposomal formulations exhibits enhanced antiplasmodial activity against blood stage forms of P. falciparum (3D7) in culture and established Plasmodium berghei NK-65 infection in murine model. Parasite killing on blood stage forms in culture was determined by a radiolabeled [^{3}H] hypoxanthine incorporation assay and infected erythrocytes stained with Giemsa were counted using microscopy in vivo. The 50% inhibitory concentration (IC_{50}) of DOXY-stearylamine liposome (IC_{50} 0.36 μM) and DOXY-SPC:Chol-liposome (IC_{50} 0.85 μM) exhibited marked growth inhibition of parasites compared with free DOXY (IC_{50} 14 μM), with minimal toxicity to normal erythrocytes. Administration of polyethylene glycol distearoyl phosphatidylethanolamine-methoxy-polyethylene glycol2000 (DSPE-mPEG-2000) coated liposomes loaded with DOXY at 2.5 mg/kg per day resulted in efficacious killing of blood parasites with improved survival in mice relative to the free drug in both chloroquine sensitive and resistant strains of P. berghei infection. This is the first report to demonstrate that DOXY in liposomal system has immense chemotherapeutic potential against plasmodial infections at lower dosages.