Bacteria targeting cancer therapy: Salmonella typhimurium-VNP20009 with its unique characteristic of accumulating in nutrient-rich or hypoxic tissues can be adapted to tumor targeted therapy. However, recent researches revealed that S. typhimurium can survive in other normal tissues, resulting in damage or inflammatory response. Our project aims to improve the therapeutic property of S. typhimurium by modifying its amino acids-synthesizing genes and screen highly tumor-targeted strains. Then we standardize them to construct a general element used specifically in hypoxic tissues. The hypoxic feature in the core areas of tumors made it possible for S. typhimurium to target tumors specifically. Our goal is to screen the anaerobic promoter that can express efficiently in S. typhimurium and ligate it with genes of anti-cancer drugs. The double properties of the strains and promoters enable anti-cancer drugs to express specifically in tumors, fulfilling our goal of decreasing toxic and side effects of the drugs.