Abstract 5102: Gemcitabine and nab-paclitaxel increase immunosuppressive environment in PDAC

Abstract

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) recently became the third-deadliest cancer due to its resistance to effective therapies. The tumor microenvironment (TME) in PDAC is thought to contribute to this resistance, with up to 80% of the tumor bulk consisting of stroma including cancer associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). Gemcitabine (gem) and nab-paclitaxel (nab-p) is standard of care for PDAC with modest efficacy. Immunotherapies, effective in other cancers, are often combined with chemotherapy in an attempt to augment tumor response. We investigated the impact of gem and nab-p on the TME and antigen presentation of PDAC. Methods: A cancer organoid line from KPC (LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre) mice, was used as a murine model of PDAC. The organoids were treated in vitro with 50uM gem and 5.85uM nab-p for 12-24 hrs and subsequently tested for MHC class I expression via flow cytometry. A co-culture in Matrigel was created using KPC organoids, pro-tumor M2-polarized bone-marrow derived macrophages (BMDMs), and pancreatic stellate cells (PSCs). After 48 hrs the co-culture was treated with gem and nab-p for 24 hrs and collected to assess macrophage and fibroblast polarization markers via flow cytometry. KPC organoids were used to generate allografts in wild-type B6 mice randomized to receive 100 mg/kg gem (i.p.) and 30 mg/kg nab-p (i.v.) or control. After 96 hrs, tumors were processed for flow cytometry analyses. Results: The percentage of MHC I expressing KPC cells increased from baseline following 12 hrs of gem/nab-p treatment (32.7% vs 50.4%, p= 0.12 and declined at 24, 48 and 72 hour post-treatment time points (22.5%, p=0.3, 23.2%, p=0.31, and 13.1%, p=0.06, respectively). In the co-culture, gem and gem/nab-p significantly enhanced immunoregulatory inflammatory CAF (iCAF) subtype over control (17.5 vs 17.6 vs 10%, respectively, p<0.001). A decrease in myofibroblastic CAFs (myCAFs) was also observed. M1 macrophages in the co-culture decreased significantly with gem and gem/nab-p compared to controls (6.7% vs 6.9% vs 13.8%, respectively, p=0.02/p=0.004). There was also a subsequent increase in M2 macrophages. KPC allografts demonstrated no significant change in MHC I levels following a 96-hour gem/nab-p treatment compared to vehicle. The CAF subtypes showed trends similar to the in vitro co-culture, with more iCAFs (14.9% vs 26.3%, p=0.32) and less myCAFs (83.5% vs 71.3%, p=0.31). We were also able to identify an MHC II class of antigen-presenting CAFs (apCAFs), within both our in vitro and in vivo studies at levels less than 1% of all CAFs. However, no change was observed with treatment. Conclusion: Here we demonstrate reduced MHC class I expression, increased M2 TAM polarization, and increased iCAFs, all associated with an immunoregulatory phenotype. These finding suggest that further studies on alternative combinations of immunotherapies are warranted. Citation Format: Hanna R. Rainiero, Philip B. Emmerich, Nathaniel Verhagen, Rebecca Destefanis, Cheri A. Pasch, Linda Clipson, Kristina A. Matkowskyj, Dustin A. Deming. Gemcitabine and nab-paclitaxel increase immunosuppressive environment in PDAC [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5102.