Abstract PO-033: Bacterial cytotoxin therapy limits tumor growth for pancreatic ductal adenocarcinoma
Authors: Decker Amanda R. , Harimoto Tetsuhiro , Sastra Steve A. , Danino Tal , Olive Kenneth P. 
Published: November 2021

Abstract
Treating pancreatic ductal adenocarcinoma (PDAC) with systemic chemotherapeutic drugs has remained a challenge, due in part to the hypovascularized and poorly perfused nature of PDAC tumors. Limited blood flow within the tumor tissue creates an extremely hypoxic microenvironment and impedes the accumulation of drugs. Moreover, local immunosuppression in PDAC has so far limited the efficacy of immunotherapy approaches. However, these very features that have interfered with systemic therapy in PDAC (hypoperfusion, hypoxia, and immunosuppression) are potential advantages for the use of bacterial therapies. Bacteria have been used as a directed cancer therapy for over 100 years, starting with Dr. William Coley’s use of heat killed bacteria (Coley’s Toxin) against sarcomas in 1893. Recent developments in the field of synthetic biology have made it possible to engineer complex logical circuits into bacteria, enabling the manufacture of anticancer therapies directly within the tumor parenchyma. Bacteria can actively migrate through tissues, they can thrive in hypoxic microenvironments, and they benefit from the local immune suppression. We have therefore worked to develop novel bacterial strains for targeting PDAC. We began by testing a range of bacteria-derived toxins that could be used as a payload to target PDAC. These toxins were produced by an engineered strain of a non-toxic, probiotic E. coli Nissle 1917. We identified four pore-forming toxins that significantly reduced viability of the cells compared to bacterially produced GFP: hemolysin E, heat stable enterotoxin, magainin, and theta toxin. We then performed a secondary screen using a novel PDAC explant model system developed in our lab, in which thick slices of murine or human PDAC are culture intact for up to 7 days. Consistent with the monolayer screen, two of the candidate compounds, heat stable enterotoxin and theta toxin, significantly increased tissue death compared to non-toxic GFP-producing bacteria. Finally, we delivered live bacteria producing either toxins or GFP into KPC mouse tumors through intratumoral injection. While GFP-producing strains did not induce a change in tumor growth kinetics, theta toxin treatment demonstrated an immediate, prolonged stabilization of tumor volume for more than a month. Histological analyses of treated tumors demonstrated that diffuse populations of bacteria co-localized with regions of tumor necrosis and cell death. Most interestingly, while there was minimal spread of bacteria to healthy non-target tissues, translocation of the bacteria did occur to regions of liver metastases and secondary papilloma tumors, suggesting a mechanism for diffuse treatment of known and unknown metastases following the initial treatment of the primary tumor. Together these studies demonstrate that cytotoxic bacterial therapy is an effective candidate strategy to circumvent the difficulties in systemic treatment of PDAC.
Citation Format: Amanda R. Decker, Tetsuhiro Harimoto, Steve A. Sastra, Tal Danino, Kenneth P. Olive. Bacterial cytotoxin therapy limits tumor growth for pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-033.