Abstract 2706: Engineered tumor-targeting bacteria expressing cancer-killing protein for breast cancer

Abstract Despite significant advancements in the treatment of advanced breast cancer, therapies using chemotherapeutic agents still face considerable challenges. One key issue is the hypoxic tumor microenvironment (TME), characterized by insufficient blood flow and oxygen supply within tumors. This hypoxia reduces the sensitivity of breast tumors to treatment, diminishes therapeutic efficacy, and promotes resistance and metastasis. Approximately 25-40% of invasive breast cancers exhibit hypoxic tumors, which are strongly associated with increased risks of metastasis and chemotherapy resistance. Therefore, there is a pressing clinical need for novel strategies to specifically target these hypoxic tumor regions. To address this limitation, our objective is to develop an innovative approach using tumor-targeting bacteria carrying cancer-killing protein, controlled by an engineered hypoxia-inducible expression system. In this study, four Escherichia coli strains from the probiotic Symbioflor® 2 were isolated and characterized based on colony morphology and PCR results. These strains were transformed with luciferase gene, and luciferase activity was monitored to determine biodistributions of each E. coli after intravenous injection into mice. Our data showed that G5 strain preferentially colonized in xenografted triple-negative breast tumors. To specifically express cancer-killing azurin gene within the hypoxic tumor TME, we optimized the hypoxia-inducible promoter in E. coli G5 cells. To test its anti-tumor efficacy, TNBC cells were orthotopically injected into the mammary fat pads of immunodeficient mice. The engineered E. coli G5Hyp*-azurin strain was administered at varying concentrations (1×105, 1×106, and 1×107 CFU/mouse) through weekly tail vein injections over three weeks. Our results demonstrated that E. coli G5Hyp*-azurin, at doses of 1×107 and 1×106 CFU, effectively inhibited tumor progression. In contrast, lower dose (1×105 CFU) showed no significant effect. Additionally, no noticeable side effects were observed, as there was no evidence of weight loss. Overall, our results highlight the potential of our newly designed bacterial approach to develop an innovative treatment strategy. Citation Format: Duy Binh Tran, Konstantin Christov, Balaji Ganesh, Jing Wang, Albert Green, Tohru Yamada. Engineered tumor-targeting bacteria expressing cancer-killing protein for breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2706.