The Mechanism Of Curative Bias Of Engineered Anti-tumor Bacteria On Solid Tumor

To date,the incidence of cancer is still rising rapidly worldwide,with one person diagnosed with cancer around every 8 minutes,and more than 95% of malignant cancers are solid tumors.However,classical therapies like surgery,radiotherapy or chemotherapy,and state-of-the-art therapies like small molecule targeted agents,gene therapy or immunotherapy,still can’t meet all need in the treatment to malignant solid tumors.Due to the potential ability of tumor targeting,solid tumor penetration and cell destruction possessed by bacteria,bacterial anti-tumor therapy becomes one of the most promising tumor treatment methods.In the meanwhile,synthetic biology also serves as a powerful tool for the genetic engineering and optimization of anti-tumor bacteria.Bacterial anti-tumor therapy has been developed for more than one century.In the beginning,researchers focused on the design and modification of bacteria,hoping to construct a strain with enhanced tumor-targeting ability,improved safety and optimized therapeutic effect.But it was found that there was always a gap between the results and expectations,and it is difficult to balance the relationship between the toxicity and therapeutic effect of bacteria.Then scientists began to study the mechanism of bacterial treatment to tumors,hoping to clarify the essence of bacterial anti-tumor therapy,so as to design the anti-tumor bacteria in a more rational way.Based on existing studies on bacterial anti-tumor therapy,the curative bias of engineered anti-tumor bacteria on different solid tumors is well-recognized,but the reason has not been clarified.To find out the reason why there are differences among the treatment effects of bacteria therapy to different types of solid tumors,in this study,we used engineered anti-tumor DB1,which has been constructed based on Salmonella typhimurium in the previous study,4T1 breast tumor model and CT26 colon tumor model,to explores the key factors and mechanism theories behind the curative bias.Firstly,the direct effect of DB1 on two kinds of tumor cells was explored by the co-culture experiment in vitro.And then the relationship between the treatment effects and intratumoral immunity was analyzed by CT26-4T1 double-tumor model treatment experiment and immune factor analysis experiment.Furthermore,the content and distribution pattern of the innate immune cells within tumor were analyzed by flow cytometry and the immunofluorescence staining of tumor sections.finally,neutrophil neutralization experiments were used to verify the hypothesis that the neutrophil content in 4T1 tumors affected the treatment efficacy of DB1.In this study,the abundance of neutrophil within tumor was proved to be a key factor affecting the therapeutic effect of bacterial therapy on these two kinds of tumor models.Reducing neutrophil content in the solid tumor can help improve the therapeutic effect of engineered anti-tumor bacteria on solid tumor.This study preliminarily explored the immune mechanism of bacterial anti-tumor therapy,contributed to indication selection of the bacterial therapy and provided a direction for further modification of anti-tumor bacterial.