Engineering lactic acid bacteria for tumour targeted delivery of anticancer agents

The lack of efficient delivery of drugs to cancer cells in vivo remains one of the main challenges in achieving a good therapeutic outcome and reducing side effects of anticancer agents. The release mechanisms of conventional delivery systems are triggered by factors that are independent of pathophysiological conditions of the tumour and its location. This results in lower concentrations of drug delivered to tumour tissue and increased side effects in healthy tissues. Targeted bacterial delivery systems with high selectivity for cancer cells can increase the accumulation of the administered therapeutic agent in the tumour microenvironment and limit its activity on the tumour tissue, while sparing healthy tissues from toxic effects of the drug. In the proposed project, we aim to endow the safe lactic acid bacterium Lactococcus lactis with the ability to specifically target cancer cells and induce selective cell death by delivering an encoded cytotoxic protein to cancer cells. Tumour targeting will be achieved by displaying on the surface of bacteria cancer‐cell specific peptide that will be isolated from phage display peptide libraries by whole‐cell biopanning. As a cytotoxic agent, we will use a proapoptotic protein (tumour necrosis factor-related apoptosis-inducing ligand, TRAIL), which has been shown to possess potent anticancer activity against various types of cancer. The engineered bacteria will be assessed for specific adhesion and selective killing of cancer cells in vitro on colon cancer cell models and in vivo on tumour xenograft mouse model. Our proposal represents a novel approach that uses L. lactis functionalized with cancer cell-specific peptide ligand as a delivery vector for cytotoxic proteins. The feasibility of the approach is well supported by our previous research. We have previously engineered L. lactis to simultaneously display small protein binders of tumour antigens for targeting and cytokine‐binding proteins for anti‐inflammatory activity. This work will be upgraded in the proposed project by the use of targeting ligands, capable of discriminating between cancer and normal cells, rather than recognizing single tumour surface receptor only. In vivo administration of developed tumour‐targeting bacteria could enable the accumulation and prolonged retention of high concentrations of cytotoxic proteins in tumour tissue. The local cytotoxic activity mediated by the engineered bacteria would cause fewer systemic side effects, especially compared to currently used treatment regimens. The reduced side effects should allow for an increase in the administered dose and thus better efficacy. Furthermore, the probiotic and immunoregulatory activity of lactococci may provide additional beneficial effects in some type of cancers, particularly those associated with inflammation, such as colorectal cancer.