Abstract B015: Toxin-producing bacterial therapy limits tumor growth in autochthonous mouse models of pancreatic ductal adenocarcinoma
Authors: Decker-Farrell Amanda R. , Sastra Stephen A. , Harimoto Tetsuhiro , Hasselluhn Marie C. , Li Fangda , Vincent Rosa , Palermo Carmine F. , Ballister Edward R. , Danino Tal , Olive Kenneth P. 
Published: January 2024

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, impeding the accumulation of systemically delivered drugs. Several clinical trials aimed at improving drug delivery in PDAC, through targeting of ECM components (HALO-301) or stromal angiogenic signaling (IPI-926-03) have unfortunately not been effective. However, the features that have interfered with systemic therapy in PDAC are potential advantages for the use of bacterial therapies, as bacteria can actively migrate through tissues, thrive in hypoxic microenvironments, and benefit from local immune suppression. Recent developments in the field of synthetic biology have made it possible to engineer complex logic circuits into bacteria, enabling the production of anticancer therapies directly within the tumor parenchyma. Furthermore, live bacteria, once colonized within the tumor niche, are capable of providing a stable source of anticancer compounds directly, rather than relying on repeated systemic doses. We have therefore worked to develop novel bacterial strains and demonstrate preclinical efficacy of a novel strain of therapeutic bacteria for targeting PDAC. We began by testing a range of bacteria-produced toxins and identified the pore-forming protein theta toxin as having the greatest effect in both 2D cell culture and PDAC explant (tissue slice) models. We then engineered a non-toxic probiotic bacteria, E. coli Nissle 1917, to produce either theta toxin or GFP. To assess preclinical efficacy, we performed intratumoral injections of live GFP- and theta-expressing bacteria into the “KPC” genetically engineered mouse model (Kras LSL.G12D/+; Tp53 LSL.R172H/+; PdxCre tg/+). While GFP-producing bacteria did not induce a change in tumor growth kinetics, treatment with theta toxin-producing bacteria demonstrated prolonged stabilization of tumor growth, increasing the median survival to 34 days compared to ~12 days for vehicle- or gemcitabine-treated controls and 18.5 days for GFP-producing bacteria without additional therapy. Strikingly, while there was minimal spread of bacteria to non-tumor tissues, we observed translocation of the bacteria to macro- and micro- metastatic lesions and distant papillomas following injection of the primary pancreatic tumor, indicating a mechanism for targeting both known and unknown metastases following local administration. Histological analyses demonstrated that diffuse populations of bacteria co-localized with regions of cell death, but that bacterial presence and evidence of increased cell death was not observed in healthy tissues, such as the lung, liver, intestine, and diaphragm. Additionally, bacterial treatment, independent of the payload, led to a modest influx of anti-tumor immune populations, suggesting potential synergy with immunotherapies. Together these data demonstrate potent preclinical activity of cytotoxic bacterial therapy as a novel strategy to circumvent the challenges of systemic treatment of PDAC.
Citation Format: Amanda R. Decker-Farrell, Stephen A. Sastra, Tetsuhiro Harimoto, Marie C. Hasselluhn, Fangda Li, Rosa Vincent, Carmine F. Palermo, Edward R. Ballister, Tal Danino, Kenneth P. Olive. Toxin-producing bacterial therapy limits tumor growth in autochthonous mouse models of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr B015.