Design of dual stimuli-responsive ion pair self-assembled nanocarriers responsive to nitroreductase and reduction conditions

The tumor microenvironment (TME) exhibits reductive and distinctive biochemical characteristics that can be exploited to design stimuli-responsive nanocarriers sensitive to tumor-specific conditions. In this study, a nitroreductase (NTR) and reduction-responsive ion-pair self-assembly (IPSAM) was developed using poly(diallyldimethylammonium chloride) (PDADMAC) and 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB). Electrostatic interactions between the quaternary ammonium groups of PDADMAC and the carboxyl groups of DTNB generated amphiphilic ion pairs, which spontaneously self-assembled into micellar structures in aqueous solution. Ion-pair formation was confirmed by FT-IR and 1H NMR spectroscopy, and the spherical micellar structures and particle sizes were observed and analyzed using TEM and DLS. IPSAM(7/3) exhibited an upper critical solution temperature (UCST) at 40.9 °C, and the UCST gradually decreased with increasing concentrations of dithiothreitol (DTT), indicating cleavage of the disulfide bonds in DTNB. Under nitroreductase (NTR) treatment in the presence of NADH, the nitro groups of DTNB were reduced to amino groups, leading to the loss of amphiphilicity, micellar disassembly, and an increase in absorbance. Surface tension measurements also revealed a concentration-dependent decrease after DTT and NTR treatment, supporting the structural destabilization of the micelles. Release experiments demonstrated that IPSAM exhibited concentration-dependent release behaviors under both reductive and NTR conditions.