Susceptibility of Leishmania amazonensis Axenic Amastigotes to the Calpain Inhibitor MDL28170

Leishmaniasis encompasses a group of neglected diseases caused by flagellated protozoa belonging to the <i>Leishmania</i> genus, associated with high morbidity and mortality. The search for compounds with anti-<i>Leishmania</i> activity that exhibit lower toxicity and can overcome the emergence of resistant strains remains a significant goal. In this context, the calpain inhibitor MDL28170 has previously demonstrated deleterious effects against promastigote forms of <i>Leishmania amazonensis</i>, which led us to investigate its role on axenic amastigote forms. The calpain inhibitor MDL28170 was able to decrease the viability of amastigotes in a typically dose-dependent manner. The treatment with the IC₅₀ dose (13.5 μM) for 72 h led to significant amastigote lysis and increased cell-to-cell aggregation. Ultrastructural analysis revealed several cellular alterations, including disruption of the <i>trans</i>-Golgi network and the formation of autophagosomes when treated with MDL28170 at ½ × IC₅₀ dose. Additionally, mitochondrial swelling and the formation of concentric membranous structures inside the mitochondrion were observed after incubation with the IC₅₀ dose. These results reinforce the potential application of the calpain inhibitor MDL28170 against <i>L. amazonensis</i>, highlighting its effectiveness and possible mechanism of action against the parasite.