ECM-targeting bacteria enhance chemotherapeutic drug efficacy by lowering IFP in tumor mouse models

Bacterial cancer therapies aim to manipulate bacteria to effectively deploy therapeutic payloads to tumors. Attenuated bacteria alone often cannot eradicate solid tumors. Attenuated Salmonella can be engineered to deliver cytotoxic drugs to either trigger an immune response or increase antitumor efficacy when combined with chemotherapeutic drugs. However, the extracellular matrix (ECM) surrounding cancer cells forms a barrier that often limits the ability of chemotherapeutic and cytotoxic drugs to penetrate and eliminate tumors. To overcome this limitation, we developed a strategy to combine chemotherapy with an attenuated Salmonella typhimurium strain engineered to secrete HysA protein (from Staphylococcus aureus; Hyaluronidase, HAase) in tumors. The engineered Salmonella effectively degraded hyaluronan (HA), which is a major ECM constituent in tumors, and suppressed tumor growth in mouse models of pancreatic adenocarcinoma (ASPC-1) and breast cancer (4T1). Furthermore, it prolonged survival when combined with chemotherapeutic drugs (doxorubicin or gemcitabine). Upon bacterial colonization, the HAase-mediated ECM degradation decreased interstitial fluid pressure (IFP) in the tumor microenvironment. Additionally, HA degradation using HAase-expressing bacteria in vivo led to decreased binding to the receptor, CD44, expressed in tumors. This may modulate proliferation- and apoptosis-related signal pathways. Therefore, ECM-targeting bacteria can be used as a synergistic anticancer therapeutic agent to maximize chemotherapeutic drug delivery into highly invasive tumors.