Abstract 5839: Tumor-selective treatment of metastatic pancreatic cancer with an engineered, probiotic living drug

Abstract Treating pancreatic ductal adenocarcinoma (PDAC) with intravenous chemotherapy has remained a challenge, due in part to the hypovascularized and poorly perfused nature of PDAC tumors, thus limiting drug accumulation. However, the features that impede systemic therapy in PDAC may favor bacterial therapies, as bacteria can actively migrate through tissues, thrive in hypoxic microenvironments, and exploit local immune suppression. Once colonized within the tumor niche, live bacteria can provide a stable source of anticancer compounds, rather than relying on repeated systemic doses. Here, we addressed the current drug delivery challenges of PDAC by developing a probiotic-based bacterial therapy. Through 2D monolayer and PDAC tissue-slice screens, we identified the pore-forming Theta toxin (from C. perfringens) as a potent candidate and expressed it in a probiotic strain of E. coli, Nissle 1917 (Nis). Intratumoral injections of live Nis-Theta bacteria into subcutaneous and genetically engineered mouse models of PDAC (KPC - Kras LSL.G12D/+; Tp53 LSL.R172H/+; PdxCre tg/+) resulted in significantly higher rates of complete tumor regression, reduced tumor growth kinetics, and extended median survival to 35.5 days, compared to 12 days for Vehicle or Gemcitabine controls and 16.5 days for non-toxic bacteria, Nis-GFP. We also thoroughly monitored systemic body response to bacterial treatment for safety. Bacterially treated mice did not exhibit any weight loss, body composition changes, or other infection-like symptoms compared to non-bacterial treatment (Gemcitabine) arms. Bacterial spread to healthy tissues (lung, liver, intestine, and diaphragm) was minimal with no increase in cellular damage in non-tumor tissues. Furthermore, mice systemically cleared the bacteria within several weeks of full tumor regression. Strikingly, while there was minimal spread of bacteria to non-tumor tissues, bacteria translocated to distant secondary tumor sites following injection of the primary pancreatic tumor. Histology showed bacterial co-localization with apoptotic tumor cells in both primary and metastatic lesions, suggesting a mechanism for targeting both known and unknown metastases following local administration. Histological and flow cytometry analyses demonstrated modest recruitment of anti-tumor immune populations in Nis-Theta treated tumors, suggesting potential synergy with immunotherapies. Together these data demonstrate potent preclinical activity of cytotoxic bacterial therapy as a novel drug delivery method to circumvent the challenges of systemic treatment of PDAC. These bacteria demonstrated preferred tumor colonization over healthy tissue with no systemic illness, targeted metastatic lesions, and significantly extended survival in a clinically relevant model of PDAC with only a single dose. Citation Format: Amanda R. Decker-Farrell, Stephen A. Sastra, Tetsuhiro Harimoto, Marie C. Hasselluhn, Carmine F. Palermo, Tanner C. Dalton, Llewelyn Levett, Edward R. Ballister, Michael A. Badgley, Tobias Janowitz, Tal Danino, Kenneth P. Olive. Tumor-selective treatment of metastatic pancreatic cancer with an engineered, probiotic living drug abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 5839.