Unveiling the molecular mechanism of pH-dependent interactions of human serum albumin with chemotherapeutic agent doxorubicin: A combined spectroscopic and constant-pH molecular dynamics study

Doxorubicin (DOX) is a potent and clinically approved chemotherapeutic agent for cancers. Although human serum albumin (HSA) has been frequently used as a promising drug vehicle for DOX to reduce its doses and toxicities, the pH-dependent binding mechanism of HSA with DOX is still poorly understood. This hampers the rational design of smart HSA-based cancer microenvironment-responsive DOX delivery systems for clinical applications. Here, the molecular interactions of DOX with HSA at various pH levels were systematically investigated using spectroscopic and in silico techniques. Our experiments showed that the binding of DOX to HSA was governed by static quenching mechanism and highly affected by environmental pH. The change of pH altered the conformational states of HSA, which may regulate the binding of DOX onto HSA. In agreement with experimental observations, 1000 ns-long constant-pH molecular dynamics simulations elucidated the structural basis of DOX bound to HSA at different pH. The computational results revealed that the favored binding of DOX at slight alkaline pH may be attributed to the intact structure of HSA and increased intermolecular hydrogen bonding. In contrast, at acidic conditions, the extension of HSA global conformation and drop of local structural identity reduced the number of intermolecular hydrogen bonds. Our study provided novel structural insights into the molecular mechanism of pH-dependent interactions of HSA with DOX, which may be helpful for the design of novel HSA-based microenvironment-responsive drug delivery systems for anticancer therapeutic applications. (C) 2021 Elsevier B.V. All rights reserved.