Comparative binding studies of bacosine with human serum albumin and α-1-acid glycoprotein biophysical evaluation and computational approach

Bacosine (BAC) is a natural product isolated from a herb and used in the Ayurvedic system of medicine. It is reported to have a wide array of biological activities, which has generated interest in its therapeutic potential. To better understand how BAC may operate as a potential anti-cancer therapeutic, we examined its anti-cancer properties in the human breast cancer cell line, MCF-7. In order to get an idea of how it may behave in vivo, we also evaluated its interaction with human serum albumin (HSA) and alpha-1-acid glycoprotein (AGP) using fluorescence spectroscopy and in silico molecular modelling. Based on our in vitro studies, we found that BAC inhibited MCF-7 cell growth in a dose-dependent manner with an IC50 value of 9 mu M. In addition, the intrinsic fluorescence of HSA and AGP was quenched by BAC, consistent with a static quenching mechanism. Fluorescence emission spectroscopy revealed a binding of 2.97 +/- 0.01 x 10(4) M-1 for HSA-BAC which corresponded to a free energy change of - 6.07 kcal/mol at 25 degrees C. In addition, we found that BAC had a binding constant of 1.8 +/- 0.02 x 10(3) M-1 to AGP which corresponded to a change in free energy - 4.42 kcal/mol at 25 degrees C. We also identified the site of BAC binding to the HSA protein using the site-specific marker, phenylbutazone, along with molecular docking studies. Circular dichroism spectra revealed partial changes in the secondary structure of HSA in the presence of BAC suggesting direct interactions. Molecular dynamics simulations demonstrated that the HSA-BAC complex reaches an equilibration state at around 4 ns, suggesting that the HSA-BAC complex is quite stable. Our results provide evidence that serum proteins can act as a carrier protein for BAC, potentially impacting its development as an anti-cancer agent. (C) 2021 Elsevier B.V. All rights reserved.