Rui-Min Long,1,2,* Qing-Lei Dai,1,* Xia Zhou,1,* Duan-Hua Cai,1 Ya-Zhen Hong,1–3 Shi-Bin Wang,1–4 Yuan-Gang Liu1–3 1College of Chemical Engineering, Huaqiao University, Xiamen 361021, China; 2Fujian Provincial Key Laboratory of Biochemical Technology, Huaqiao University, Xiamen 361021, China; 3Institute of Pharmaceutical Engineering, Huaqiao University, Xiamen 361021, China; 4Institute of Biomaterials and Tissue Engineering, Huaqiao University, Xiamen 361021, China *These authors contributed equally to this work Abstract: In recent times, co-delivery of therapeutics has emerged as a promising strategy for treating dreadful diseases such as cancer.Materials and methods: In this study, we developed a novel nanocarrier based on bacterial magnetosomes (BMs) that co-loaded with siRNA and doxorubicin (DOX) using polyethyleneimine (PEI) as a cross-linker (BMs/DP/siRNA). The delivery efficiency of siRNA as well as the pH-responsive release of DOX, and synergistic efficacy of these therapeutics in vitro were systematically investigated.Results: The structure of DOX–PEI (DP) conjugates that synthesized via hydrazone bond formation was confirmed by 1H nuclear magnetic resonance (NMR). The in vitro release experiments showed that the DP conjugate (DOX-loading efficiency – 5.77%±0.08%) exhibited the long-term release behavior. Furthermore, the optimal BMs/DP/siRNA particle size of 107.2 nm and the zeta potential value of 31.1±1.0 mV facilitated enhanced cellular internalization efficiency. Moreover, the agarose gel electrophoresis showed that the co-delivery system could protect siRNA from degradation in serum and RNase A. In addition, the cytotoxicity assay showed that BMs/DP/siRNA could achieve an excellent synergistic effect compared to that of siRNA delivery alone. The acridine orange (AO)/ethidium bromide (EB) double staining assay also showed that BMs/DP/siRNA complex could induce cells in a stage of late apoptosis and nanocomplex located in the proximity of the nucleus.Conclusion: The combination of gene and chemotherapeutic drug using BMs is highly efficient, and the BMs/DP/siRNA would be a promising therapeutic strategy for the future therapeutics. Keywords: bacterial magnetosomes, co-delivery, gene therapy, pH-responsive release