Activity of Lytic Peptides against Intracellular Trypanosoma cruzi Amastigotes In vitro and Parasitemias in Mice

Three cecropin-like lytic peptides (DC-1, DC-2, and DC-2R) were synthesized with virtually no sequence homology with the natural compound (cecropin B) while retaining the charge distribution, amphipathic, and hydrophobic properties of the natural compound. A fourth analog (α-Pi) without these later properties, but a similar molecular weight, was also synthesized as a nonlytic peptide control. The 3 lytic peptides were examined for their ability to kill Trypanosoma cruzi trypomastigotes in vitro, intracellular amastigotes in vitro, and their toxicity to a mammalian cell line. DC-2 at 5 µM and DC-1 and DC-2R at 10 µM were 100% effective in killing T. cruzi trypomastigotes in vitro, suggesting at least a 10-fold increase in lytic activity over previous tested lytic peptide analogues, SB-37 and Shiva-1. When T. cruzi-infected Vero cells were treated with a single or double exposure of low concentrations (2.5 µM) of DC-1, DC-2, and DC-2R there was a significant (P < 0.05) reduction in amastigote numbers/cell when compared to untreated and α-Pi-treated T. cruzi-infected cells. Vero cells alone treated with the lytic peptides showed no reduction in number or toxicity. One of the peptides (DC-1) was tested for its toxicity in AJ mice and its ability to reduce parasitemias in T. cruzi-infected AJ mice. No untoward effects were seen in AJ mice injected intravenously with 50 µg/mouse daily for 10 days. There was a significant (P < 0.05) reduction in parasitemia and mortality by day 14 postinoculation (from 100% to 0%) in T. cruzi-infected AJ mice given 25 µg of DC-1/mouse on days 2, 4, 6, 8, and 10 postinoculation.