Background Despite tremendous effort, the prognosis of patients with pancreatic ductal adenocarcinoma (PDAC) remains poor and therapy options are limited. Recent advances in chemotherapeutic schemes have increased the survival of PDAC patients by a few months only. So far, the success of immunotherapy seen in other cancer types could not be transferred to PDAC. Our group has demonstrated that single agent RIG-I-like helicase (RLH)-targeting immunotherapy induces an anti-tumoral immune response and improves survival in a PDAC mouse model dependent on the induction of immunogenic cell death. In addition, we and others were able to show that tumor cell death induction by RLH ligands is partially dependent on the induction of the pro-apoptotic BH3-only proteins PUMA and NOXA. In the current study we aim at improving therapy response using a combinatorial chemo-immunotherapy (CIT) approach.

Methods Tumor cell death induction by gemcitabine, oxaliplatin and 5-fluoruracil (5-FU) alone or in combination with RLH ligands was evaluated in the murine cell line Panc02. The induction of PUMA and NOXA was measured by real-time PCR. The capability of chemo-immunotherapy -induced tumor cell death to activate splenic CD8a⁺dendritic cells (DC) as well as to induce antigen uptake and cross-presentation was investigated in vitro. Therapeutic efficacy was evaluated in vivo using an orthotopic PDAC mouse model.

Results Gemcitabine, oxaliplatin and 5-FU induced dose-dependent tumor cell death in vitro. however, only gemcitabine lead to an induction of the pro-apoptotic proteins PUMA and NOXA. Simultaneous treatment with gemcitabine and RLH-ligand increased cell death induction without affecting the cytokine secretion substantially. CD8a⁺ DC activation upon RLH-therapy was not affected by chemotherapy. Of note, antigen uptake as well as T cell priming was increased by chemo-immunotherapy. Most importantly, the survival of orthotopic PDAC bearing mice was significantly prolonged in the chemo-immunotherapy group compared to single agent treatment.

Conclusions Gemcitabine treatment of PDAC induces PUMA and NOXA expression which leads to mitochondrial priming and sensitization towards RLH-induced cell death. chemo-immunotherapy increases the cross-presentation capability of DC in vitro and prolongs the survival of PDAC bearing mice. chemo-immunotherapy is therefore an attractive combinatorial therapeutic approach in PDAC.

Funding The project was supported by the Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 179062510 and 329628492 - SFB 1321 as well as the Förderprogramm für Forschung und Lehre (FöFoLe) funded by the Ludwig-Maximilians-Universität München.

Disclosure Information P. Metzger: None. H.T. Bourhis: None. M. Stieg: None. D. Böhmer: None. S. Endres: None. P. Düwell: None. L.M. König: None. M. Schnurr: None.