A Hypoxia-Activated Supramolecular Albumin Conjugate for Tumor-Selective Chemotherapy via Host-Guest Recognition and Reductive Drug Release.

Tumor hypoxia provides a unique biochemical cue for the development of microenvironment-responsive drug delivery systems with enhanced selectivity and therapeutic efficacy. Herein, we report a hypoxia-responsive supramolecular albumin conjugate (MAC) constructed by covalently grafting an azo-functionalized calixarene derivative (SAC4A) onto bovine serum albumin (BSA). In this design, SAC4A serves as both a supramolecular host for drug encapsulation and a reductive "molecular switch" that enables hypoxia-triggered activation, while albumin provides a biocompatible and tumor-affinitive transport scaffold. MAC preserves the strong host-guest recognition capability of SAC4A toward a wide range of chemotherapeutic agents and fluorescent probes, with binding constants in the 104-106 M-1 range. Rigorous global fitting and residual analysis confirm the reliability of the binding models. Under reductive conditions, the azo bonds in SAC4A are efficiently cleaved, leading to pronounced structural transformation, surface charge reversal, and controllable dissociation of guest molecules. Both chemical (sodium dithionite, SDT) and enzymatic (DT-diaphorase (NQO1)/NADPH) reduction experiments demonstrate that MAC exhibits high sensitivity and selectivity toward hypoxic environments. Using mitomycin C (MMC) as a model drug, we show that MAC enables precise hypoxia-triggered intracellular drug release, efficient lysosomal escape, and enhanced mitochondrial dysfunction. In vitro cytotoxicity assays reveal that MMC-MAC displays markedly amplified antitumor activity under hypoxic conditions, whereas free MMC shows no oxygen dependence, indicating that hypoxia selectivity is introduced by the carrier rather than the drug itself. In vivo studies further demonstrate that MMC-MAC achieves rapid and sustained tumor accumulation, significantly suppresses tumor growth, induces robust apoptosis, alleviates tumor hypoxia, and exhibits improved systemic biosafety compared with free MMC. This work establishes a supramolecular-biological hybrid strategy that integrates host-guest chemistry, albumin-based delivery, and hypoxia-responsive activation into a single platform, providing a modular and generalizable paradigm for constructing tumor microenvironment-selective nanomedicines with enhanced therapeutic index.