Cyclic Peptide Natural Product Inspired Inhibitors of the Free-Living Amoeba <i>Balamuthia mandrillaris</i>

<i>Balamuthia mandrillaris</i> is a pathogenic free-living amoeba (pFLA) that can cause infection of the central nervous system (CNS), called <i>Balamuthia</i> amoebic encephalitis (BAE), as well as cutaneous and systemic diseases. Patients infected with <i>B. mandrillaris</i> have a high mortality rate due to a lack of effective treatments. A nonoptimized antimicrobial drug regimen is typically recommended; however, it has poor antiparasitic activity and can cause various and severe side effects. Cyclic peptides exhibit a broad spectrum of antimicrobial activities but are underexplored for their antiamoebic activity. In this study, we evaluated the anti-<i>B. mandrillaris</i> effect of Synthetic Natural Product Inspired Cyclic Peptides (SNaPP) mined from ∼500 biosynthetic gene clusters of various bacterial species. The predicted natural product-43 (pNP-43; BICyP1), identified from the SNaPP library, and its derivates displayed a significant inhibition against <i>B. mandrillaris</i> trophozoites, with five pNPs having IC₅₀s ≤ 5 μM. Furthermore, all hit natural product inspired peptides demonstrated minimal to no hemolytic and cytotoxic effects on human red blood cells (RBCs) and immortalized human carcinoma cells, respectfully. Our study is the first to demonstrate the anti-<i>B. mandrillaris</i> effects of cyclic peptides, offering a promising new direction for drug development.