Influence Of Salmonella Mutants Defficiency In The Intra-macrophage Survival-or TCA Cycle-related Genes On The Tumor-targeting Ability And Anticancer Potency Of Salmonella VNP20009

Attenuated Salmonella Typhimurium VNP20009 can preferentially accumulate and replicate in hypoxic tumor region and suppress the growth of the tumor,is a typical representative of tumor-therapeutic bacteria which is rapidly developed recently.And it is now widely used as an anticancer agent.In the first part of our study,we knocked out five genes relating to its survival within macrophage on the background of VNP20009 respectively.These genes perform different functions within macrophage.Their tumor-targeting and anti-cancer activities were evaluated.Macrophages are responsible for the clearance and destruction of Salmonella.The attenuates that cannot survive within the macrophage are avirulent.Although all the mutants showed reduced fitness in the normal organ,they showed different tumor-targeting ability.What’s more important,all of their anticancer capacity were partially or completely abrogated.The infiltration of the immune cell,such as CD4+ T cell,macrophage and granulocyte was less in the tumor of mice infected with the mutant strains than that of their parental,and the mutant strains may elicit different immune responses.Thus the immune system plays a vital role in the bacterial cancer therapy and identifying the mutants that elicit varied immune responses may provide tools for the better understanding of the mechanism of bacterial cancer therapy.In the second part,we genetically modified the tricarboxylic acid(TCA)cycle of VNP20009 to obtain the strain with better tumor-targeting property or higher level of antitumor effect.We constructed two gene knockout Salmonella Typhimurium strains based on the genetic background of VNP20009 named kgd and gltA.a-ketoglutarate decarboxylase(kgd)is El component of a-ketoglutarate dehydrogenase(KDH)complex which is an important regulatory point within the tricarboxylic acid(TCA)cycle and plays an important regulatory role in aerobic energy metabolism.Citrate synthase(gltA)is the first enzyme of the TCA cycle and catalyzes the condensation of acetyl coenzyme A with oxaloacetate to form citrate,which is an important control point for determining the metabolic rate of the cell.Our results showed that kgd and gltA exhibited a high level of biological safety and a better tumor-targeting property.But their antitumor effects were almost completely abrogated.Therefore,kgd and gltA genes contribute to the antitumor effect of VNP20009,and they could be better gene therapy delivery systems to further research in oncotherapy.