Pathogen-Centric Activation of an Azoreductase-Responsive Antibody-Antibiotic Conjugate for the Targeted Eradication of MRSA.

Antibody-antibiotic conjugates (AACs) provide a transformative platform for eradicating intracellular methicillin-resistant Staphylococcus aureus (MRSA). However, current AACs largely follow antibody-drug conjugates (ADCs) design principles and rely on host-lysosomal proteases for activation, rendering them ineffective against extracellular (planktonic) bacteria. Furthermore, we demonstrate that high bacterial burden induces host-lysosomal dysfunction, fundamentally compromising the efficacy of host-dependent AACs against intracellular reservoirs. To address these limitations, we developed a pathogen-centric AAC (AZO-AAC) featuring an azobenzene-based linker that is triggered by bacterial-secreted azoreductase. This strategy shifts the activation mechanism from host-cell machinery to the pathogen itself, enabling antibiotic release independent of host-cell integrity. Surprisingly, our designed AZO-AAC achieves nanomolar-scale eradication of both planktonic and intracellular MRSA, reaching levels below the limit of detection in scenarios where traditional AACs fail. In murine models of peritonitis and septicemia, a single dose (60 mg/kg) of AZO-AAC resulted in a six-log reduction in bacterial burden and the preservation of normal tissue architecture. By decoupling activation from host-cell status, this pathogen-responsive platform provides a robust strategy for the targeted elimination of complex, multi-niche MRSA infections.