Tian Hu,1,* Linsong Zhang,2,* Yun Lu,1 Kang Xiong,1 Qian Wen,1 Jingrong Huang,1 Hongjun Deng,1 Kewei Xiang,1 Ping Zhou,3 Shaozhi Fu1,4 

1Department of Oncology, the Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan, 646000, People’s Republic of China; 2Department of Oncology, The Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University, Luzhou, Sichuan, 646000, People’s Republic of China; 3Department of Radiology, the Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan, 646000, People’s Republic of China; 4Nuclear Medicine and Molecular Imaging Key Laboratory of Sichuan Province, Luzhou, Sichuan, 646000, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Ping Zhou, Email zhouping1@126.com Shaozhi Fu, Email shaozhifu513@163.com

Background: The hypoxic tumor microenvironment (TME) significantly impacts the effectiveness of various therapies on breast cancer. Conventional chemotherapeutic agents are unable to target hypoxic tumor tissue specifically, leading to reduced treatment efficacy and severe systemic toxicity. In order to improve drug targeting ability, we developed a bioactive biomotors system (MDPP@Bif) for chemoimmunotherapy against breast cancer. Utilizing the self-driving properties of the anaerobic Bifidobacterium infantis (B. infantis, Bif), both doxorubicin (DOX) and anti-programmed cell death protein ligand-1 (αPD-L1) antibody can be delivered simultaneously to tumor tissues to exert an anti-tumor effect on breast cancer.
Methods: The physicochemical properties of diverse nano-formulations were systematically characterized. In vitro anti-tumor efficacy of the MDPP@Bif biomotors was assessed through comprehensive biological evaluations, including 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, live/dead staining, c cellular uptake analysis, apoptosis quantification, and wound healing assays to evaluate the in vitro anti-tumor activity of the MDPP@Bif biomotors. Furthermore, the therapeutic potential of the MDPP@Bif biohybrids was validated in vivo using a murine breast cancer model by monitoring of tumor growth kinetics, body weight fluctuations, and survival outcomes. Immunofluorescence staining was also used to further validate T-cells infiltration in the tumor tissues.
Results: The developed MDPP@Bif biomotors can actively colonize hypoxic tumor tissues through Bif’s inherent targeting ability, releasing DOX to inhibit tumor growth. The released αPD-L1 antibody specifically binds to PD-L1, reducing immune escape and activating T cells. The concentration of DOX in tumor tissues of the MDPP@Bif group was 2.5 times higher than in tumors treated with free DOX, significantly prolonging the median survival of mice to 62 days and reducing the toxic side effects of DOX.
Conclusion: The novel bacteria-propelled biomotor MDPP@Bif shows great potential in treating solid tumors through synergistic chemotherapy and immunotherapy.

Keywords: anaerobic bacteria, mesoporous silica nanoparticles, doxorubicin, anti-PD-L1 antibody, breast cancer, chemoimmunotherapy