(621c) Quorum-Sensing Salmonella Selectively Trigger Protein Expression Upon Colonization within Tumors

Engineered salmonella possess unique capabilities that make them ideal drug delivery vectors for tumors.  Current cancer chemotherapeutic regimes have limited efficacy due to therapeutic resistance, which decreases the success rate for treatment of late-stage cancer and metastases.  This therapeutic resistance can be explained by a number of factors including 1) intra-tumoral transport limitations, 2) reduced susceptibility of quiescent cancer cells, and 3) protein pumps that expel therapeutics from cells.  Bacteria are capable of overcoming these therapeutic limitations because they preferentially accumulate in tumors, actively penetrate tumor tissue, and can be engineered to produce anti-cancer drugs in situ.  Due to systemic toxicity, however, bacteria that constitutively express an anti-cancer drug would not be an ideal alternative to standard chemotherapy.  Therefore, we have engineered salmonella to secrete anti-cancer drugs after tumoral colonization has occurred through the use of the lux quorum sensing system.  Quorum sensing is the ability for bacteria to change their gene expression based on changes in population density.  Because salmonella preferentially accumulate in tumors, a quorum sensing genetic circuit, coupled with an anti-cancer agent, creates a robust expression switch that only turns on in bacterial tumor colonies.  This unique bacterial drug delivery vector will allow for targeted delivery of a powerful anti-cancer drug to therapeutically resistant tumors and metastases while minimizing the risk of systemic toxicity. Salmonella transformed with the quorum-sensing system induce expression upon reaching a threshold bacterial density of 10⁸ cfu/mL (OD = 0.5).  Furthermore, in a tumor-on-a-chip device, quorum-sensing bacteria induce expression once colonies have formed within the tissue.  These colonies have formed deep within the therapeutically resistant regions of tumors where most standard chemotherapeutic drugs cannot reach due to diffusion limitations.  Additionally, 4T1 murine tumor models injected with the quorum-sensing system show co-localization of GFP and salmonella within tumor tissue while healthy tissue shows low-counts of salmonella without any GFP expression.  Finally, quorum-sensing salmonella secrete therapeutic proteins that reduce tumor burden and enhance mouse survival.  The culmination of this data demonstrates that salmonella integrated with a quorum-sensing expression vector can sense colonization within tumors and induce protein expression once a critical density has been reached. Bacteria transformed with a quorum-sensing system will also form colonies deeper into the therapeutically resistant regions of tumors allowing for treatment of tumor tissue previously unreachable by standard chemotherapeutic regiments.  Overall, this system creates a robust on/off switch that will allow for targeted bacterial drug delivery to tumors and metastases while minimizing the risk of potentially harmful drugs reaching healthy tissue.