Antiplasmodial properties of acyl-lysyl oligomers in culture and animal models of malaria

Our previous analysis of antiplasmodial properties exhibited by dodecanoyl-based oligo-acyl-lysyls (OAKs) has outlined basic attributes implicated in potent inhibition of parasite growth and underlined the critical role of excess hydrophobicity in hemotoxicity. To dissociate hemolysis from antiplasmodial effect, we screened >50 OAKs for in vitro growth inhibition of Plasmodium falciparum strains, thus revealing the minimal requirements for antiplasmodial potency in terms of sequence and composition, as confirmed by efficacy studies in vivo. The most active sequence, dodecanoyllysyl- bis(aminooctanoyllysyl)-amide (C ₁₂K-2α ₈), inhibited parasite growth at submicromolar concentrations (50% inhibitory concentration [IC ₅₀], 0.3 ± 0.1 μM) and was devoid of hemolytic activity (<0.4% hemolysis at 150 μM). Unlike the case of dodecanoyl-based analogs, which equally affect ring and trophozoite stages of the parasite developmental cycle, the ability of various octanoyl-based OAKs to distinctively affect these stages (rings were 4- to 5-fold more sensitive) suggests a distinct antiplasmodial mechanism, nonmembranolytic to host red blood cells (RBCs). Upon intraperitoneal administration to mice, C ₁₂K-2α ₈ demonstrated sustainable high concentrations in blood (e.g., 0.1 mM at 25 mg/kg of body weight). In Plasmodium vinckei-infected mice, C ₁₂K- 2α ₈ significantly affected parasite growth (50% effective dose [ED ₅₀], 22 mg/kg) but also caused mortality in 2/3 mice at high doses (50 mg/kg/day x 4).