Studies on the toxic effects of three regioisomeric methoxylated xanthones against Trypanosoma cruzi amastigotes and their binding with human serum albumin

Abstract

The synthetic 1-methoxyxanthone, 2-methoxyxanthone, and 4-methoxyxanthone (compounds 1, 2, and 3, respectively) were tested against amastigotes of Trypanosoma cruzi (C2C4, LacZ), showing an activity profile that depends on the position of the methoxy group in the xanthone ring, targeting pteridine reductase 1 of T. cruzi (TcPTR1). The initial pharmacokinetic assessment involved biophysical characterization of the interaction between the xanthones and human serum albumin (HSA, the main globular protein responsible for drug distribution), using circular dichroism (CD), steady-state and time-resolved fluorescence measurements, combined with in silico calculations. Monomethoxyxanthone 3 exhibited the highest potency (37.37 ± 1.25 μM) against T. cruzi amastigotes, likely due to its ability to form the most hydrogen bonds with TcPTR1. Both HSA:1-3 interactions involved spontaneous and strong binding, with minimal disruption to albumin's secondary structure. The methoxy group at position 4 of the xanthone aromatic ring reduces binding affinity by approximately tenfold. Nonetheless, all methoxyxanthones demonstrated higher binding affinity than the reported synthetic dimethoxyxanthones. The main binding site was identified in the positive electrostatic potential pocket in subdomain IIA (site I), suggesting that compounds 1-3 could be transported in the human bloodstream via albumin.

Keywords: Antiparasitic chemotherapy; Biophysical characterization; HSA-binding.