Exploring the selective incorporation of 15β-senecioyloxi-ent-kaurenoic acid methyl ester in Langmuir monolayers mimicking cell membranes.

A natural product isolated from Brazilian plant species Baccharis retusa (Asteraceae), 15β-senecioyloxi-ent-kaurenoic acid (1), demonstrated activity against trypomastigotes of the parasite Trypanosoma cruzi but it was inactive against intracellular forms. In the present work, compound 1a, a methyl ester derivative of 1, exhibited activity against intracellular amastigotes (EC₅₀ = 11.8 μM), similar to that determined by the standard drug benznidazol (EC₅₀ = 16.2 μM) and no toxicity against NCTC cells (CC₅₀ > 200 μM). Based on this selectivity, compound 1a was incorporated into Langmuir monolayers of three lipids, DPPC, DPPE, and DPPS, to characterize the interaction of the compound with each lipid as model for cell membranes. For that, we used tensiometry, surface potential measurements, and infrared spectroscopy. Our results showed that incorporating the drug into DPPC monolayers significantly altered the physicochemical properties, resulting in more condensed monolayers. In contrast, the incorporation of the drug into DPPE and DPPS monolayers led to their expansion. The effects on DPPC were more pronounced than on the other lipids, inducing a viscoelastic monolayer with lower alignment of the alkyl chains, as observed through surface potential measurements and infrared spectroscopy. These changes indicate a more cohesive DPPC monolayer upon drug incorporation, forming domains in a strip shape. We believe these results contribute to understanding the interaction between 1a and lipid interfaces, especially those involved in biological interactions with amastigotes of parasite T. cruzi.