Albumin-stabilized manganese-based nanocomposites with sensitive tumor microenvironment responsivity and their application for efficient SiRNA delivery in brain tumors.

Mn(iv)-Based nanoparticles (NPs) are effective in improving tumor oxygenation (hypoxia) and reducing endogenous hydrogen peroxide and acidity in the tumor region. However, the optimized reduction conditions of conventional Mn(iv)-based NPs are generally reported at pH <= 6.5, while the usual pH range of the tumor microenvironment (TME) is 6.5-7.0. The dissatisfactory imaging performance in the weakly acidic environment may limit their further application in tumor diagnosis. In this study, Mn(iii) was introduced in a nanoplatform, because it is reduced into Mn(ii) in weakly acidic environments. Arg-Gly-Asp (RGD) peptide-decorated bovine serum albumin (BSA) was employed as the stabilizer and scaffold to fabricate Mn(iii)- and Mn(iv)-integrated nanocomposites (RGD-BMnNPs) with suitable size, good stability, and excellent biocompatibility. The as-prepared NPs showed clear contrast enhancement at pH 6.5-6.9 in vitro as well as sensitive and rapid T-1-weighted imaging performance within the tumor region in a glioblastoma (U87MG) orthotopic model, owing to the intrinsic disproportionation reaction of Mn(iii) in the weakly acidic environment. In addition, these NPs could be used for efficient siRNA delivery. They showed superior advantages in this process, including increased tumour uptake, improved tumor accumulation and enhanced therapeutic effects with the modulation of the TME. These novel albumin-stabilized manganese-based NPs combined with efficient drug delivery capacity hold great potential to serve as intelligent theranostic agents for further clinical translation.