Abstract 3290: Targeting CREB reprograms the tumor immune microenvironment and enhances immunotherapy efficacy in smoking-associated pancreatic cancer

Abstract Background: Smoking, a major risk factor for pancreatic cancer, significantly attenuates the survival benefits of standard therapies, contributing to poor clinical outcomes in this malignancy. Previously, we have identified that hyperactivation of cyclic AMP response element-binding protein (CREB) as driver of immunosuppressive tumor immune microenvironment (TME), which limits the therapeutic potential of immune checkpoint blockade (ICB) therapies. The present study explores the therapeutic strategy of targeting CREB to overcome TME associated immunosuppression and to enhance the efficacy ICB in smoking associated preclinical models of pancreatic cancer. Methods: An in vivo smoking model was developed using syngeneic orthotopic tumor implantation in C57BL/6 mice and genetically engineered mouse model (GEMM) of pancreatic cancer, including Creb deleted (Crebfl/fl, CREBcKO) LSL-KrasG12D/+; Trp53 R172H/+; Pdx1Cre/+ (KPC) mice. CRISPR/Cas9 technology was used to generate Creb knockout (CrebKO) in KPC tumor cells, which were orthotopically implanted into the pancreata of C57BL/6 mice. Mice with established tumors were randomized and treated with CREB inhibitor (CREBi, 666-15) alone or in combination with anti-PD-1 monoclonal antibody. This combination therapy was further evaluated in Ptf1aCre/+; LSL-KrasG12D/+;Tgfbr2flox/flox (PKT) GEMM. Multiplex immunophenotyping was performed on harvested tumors to assess immune subsets changes, along with histological analyses including H&E, immunohistochemistry (IHC) and Sirius red staining. Results: Smoking-exposed KPC GEMM mice showed accelerated PDAC progression, characterized by increased high-grade PanIN lesions and an enhanced fibroinflammatory TME. CREB deletion (CREBcKO) significantly attenuated these effects, highlighting its role in smoking-induced tumorigenesis. Genetic ablation or pharmacological inhibition of CREB using 666-15 attenuated the immunosuppressive TME, promoted effector CD4+ and CD8+ T cell infiltration with elevated PD-1 expression on T cells. In combination with anti-PD-1 therapy, CREB inhibition enhanced the anti-tumor benefits in both PKT GEMMs and in KPC orthotopic models. Similarly, CrebKO tumor cells implanted in smoke-exposed C57BL/6 mice showed significant tumor suppression and modulates TME, with or without anti-PD-1 therapy. Conclusions: This study demonstrates the therapeutic advantage of targeting CREB to reprogram the stromal immune microenvironment and improve the efficacy of immunotherapy in preclinical models of smoking-associated pancreatic cancer. These findings provide a strong rationale of integrating CREB inhibition into immunotherapeutic strategies for pancreatic cancer, particularly in high-risk smoking populations. Citation Format: Varunkumar Krishnamoorthy, Siddharth Mehra, Sudhakar Jinka, Haleh Amirian, Edmond Box, Chen Zheng, Jashodeep Datta, Nipun Merchant, Nagaraj Nagathihalli. Targeting CREB reprograms the tumor immune microenvironment and enhances immunotherapy efficacy in smoking-associated pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3290.