Bisleuconothine A as a potential plasma alpha-2-macroglobulin ligand and apoptosis inducer in glioma: Structural and...

Exploring protein binding reveals insights into drug transport, stability, and bioavailability, while studying anticancer effects uncovers cellular mechanisms and efficacy. Both aspects are essential for understanding and optimizing a drug's therapeutic potential in cancer. This study investigates the interaction of bisleuconothine A (Bis-A), a promising bisindole alkaloid, with the plasma protein alpha-2-macroglobulin (α₂M) and its effects on U373 MG human glioma cells. Spectroscopic and thermodynamic assays revealed a spontaneous, exothermic binding interaction (ΔG < 0) between Bis-A and α₂M, characterized by a single high-affinity binding site. Molecular dynamics (MD) simulations (300 ns trajectory) elucidated the structural basis of this interaction, demonstrating that Bis-A binding promotes global conformational stabilization of α₂M. This stabilization was reflected by reduced conformational fluctuations (RMSD: 0.50 nm vs. 0.53 nm for free α₂M), a decreased radius of gyration, and a reduced solvent-accessible surface area (SASA). Hydrogen bond analysis identified Trp-739 as a key residue involved in transient interactions (0-6 bonds; average 1.5), stabilizing the binding pocket while maintaining α₂M's inherent flexibility. Concurrently, Bis-A exhibited potent anticancer effects in U373 glioma cells (IC₅₀: 5.95 μM), inducing apoptosis via ROS-mediated activation of the Bax-caspase-9-caspase-3 pathway. This was supported by increased ROS levels, an altered GSH/GSSG ratio, suppressed SOD activity, and upregulated pro-apoptotic gene expression (Bax/Bcl-2 ratio, caspase-3/-9). The strong binding affinity of Bis-A for α₂M, corroborated by both thermodynamic data and MD-derived structural insights, suggests its potential for efficient plasma transport while preserving anticancer activity. These findings establish Bis-A as a dual-functional agent: a selective α₂M ligand and a redox-driven apoptosis inducer in glioma, highlighting its therapeutic promise for further preclinical development.