ABSTRACT
ãIntravenously administered obligate anaerobic bacteria, such as bifidobacteria, grow specifically in tumor tissues. This specificity is attributed to the following: (1) Vascular walls in tumor tissues have nanometer- to micrometer-wide cracks, which allow the bacteria to pass through; (2) the intratumoral environment is hypoxic, due to poor vascularization, and therefore bifidobacteria can survive and proliferate in this anaerobic environment; (3) bifidobacteria cannot survive in well-oxygenated normal tissues. Moreover, unlike gram-negative bacteria, the gram-positive bifidobacteria do not produce endotoxins; therefore, there is no risk of endotoxin shock associated with their intravenous administration. Recently, the utility of bifidobacteria for specific drug delivery to tumor tissues has been highlighted. We have established a novel anti-cancer drug-delivery system using Bifidobacterium longum for the specific release of anti-tumor antibodies (e.g., antibody-drug complexes or single-chain antibodies) to targeted tumor tissues. Here, we introduce the results of our investigation.