Engineering probiotic biohydrogen micro-factories to initiate reductive stress for boosting tumor vulnerability

Disruption of redox homeostasis profoundly affects cellular metabolism and functions. While oxidative stress is extensively studied in cancer therapies, research on reductive stress is still in its infancy. Molecular hydrogen (H2) as a typical antioxidant holds great potential in eliciting reductive stress. However, it is still a great challenge to engineer a sustainable H2 delivery system in cancer. Herein, we proposed a micro-factory through engineering a gel-based microcapsule encapsulating of probiotic Enterobacter aerogenes, a.k.a. probiotic biohydrogen microcapsules (PBMCs), enabling the sustained and sufficient H2 generation within tumor microenvironment. Notably, PBMCs effectively suppressed the proliferation of six distinct tumor cell types as well as drug-resistant cancer cells. The PBMCs were demonstrated to induce apoptosis through eliciting reductive stress by marked elevation of GSH/GSSG ratio, as evidenced by a significant increase in the GSH/GSSG ratio. This led to cell cycle arrest, with a 1.5-fold increase in the G0/G1 phase and a 2.3-fold decrease in the S phase. Notably, PBMCs exhibited synergistic effects in combination with doxorubicin in breast cancer, resulting in robust inhibitions of preinvasive carcinoma growth and commonly associated pulmonary metastasis. Overall, our study introduces an innovative strategy to manipulate aberrant reductive stress within tumors through in situ generation of H2 using a bio-safe probiotic strain, thus enhancing tumor vulnerability.