Highly penetrative nanocarrier modulates tumor bacteria to enhance oxygen-free photo immunotherapy in spinal metastatic cancer

Microbiome and transcriptome analyses revealed that Fusobacterium nucleatum (F.n) in clinical samples is associated with immune suppression and poor prognosis in triple-negative breast cancer spinal metastasis. However, its preferential localization in hypoxic tumor regions limits the efficacy of conventional antimicrobial therapies, which poorly penetrate solid tumors and function suboptimally under anaerobic conditions. Developing strategies that enable deep tumor penetration, eliminate anaerobic bacteria, and induce immunogenic cell death remains a major challenge. In this study, a novel charge-enrichment and light-activated biomimetic nanosystem, designated as polyion liquid-bridged eosin Y (PIL-BEY), was developed. On one hand, interionic hydrogen bonding and dynamic electrostatic interactions within polyionic liquids reduce the surface energy of the nanoprobe and synergistically remodel the dense tumor stromal microenvironment via photodynamic therapy, thereby facilitating the deep intratumoral penetration and accumulation of PIL-BEY. On the other hand, the novel photosensitizer BEY generates reactive oxygen species via electron transfer under hypoxic conditions, thereby effectively eradicating bacteria within hypoxic tumor regions. The resulting pathogen-associated molecular patterns, together with damage-associated molecular patterns, activate dendritic cells, promote cytotoxic T lymphocyte infiltration, trigger immunogenic cell death, and induce systemic antitumor immune responses with durable immune memory. This oxygen-independent, dual-functional nanoplatform offers a promising strategy for treating invasive metastatic tumors.