Co-encapsulation of bromelain and doxorubicin in acid-responsive nanogels for enhanced chemotherapy via tumor ECM degradation

The therapeutic efficacy of chemotherapy in solid tumors such as osteosarcoma is hindered by the dense, collagen-rich extracellular matrix (ECM). In this work, we report an acid-responsive nanogel that co-encapsulates bromelain (BL), a proteolytic enzyme, and doxorubicin (DOX) with spatially distinct localization and independent pH-responsive release mechanisms. BL is encapsulated within the nanogel network, whereas DOX is covalently grafted onto the nanogel surface via an acid-labile linker, enabling the nanocarrier (ng(BL-DOX)) to remain stable under physiological conditions while promoting controlled release in the mildly acidic tumor microenvironment. The released BL degrades collagenous ECM components and reduces matrix density, thereby improving the penetration and intratumoral distribution of the concurrently released DOX. In a murine osteosarcoma model, the PEG-rich nanogels showed prolonged circulation and increased tumor accumulation via the enhanced permeability and retention (EPR) effect, accompanied by collagen I degradation and effective tumor growth inhibition, with final tumor volumes reduced to approximately one-tenth of those in the control group and without observable systemic toxicity. This microencapsulation approach provides an enzyme-drug co- encapsulation system that combines ECM degradation with chemotherapy in a single nanogel platform and may be adapted to other proteolytic enzymes and cytotoxic agents for the treatment of stroma-rich solid tumors.