Abstract B047: CXCR4 synergizes with multi-RAS inhibition by overcoming T cell exclusion to enhance immunogenic cancer cell death in human pancreatic cancer slice culture
Sheela R. Damle, Nancy Liu, Xiuyun Jiang, Heidi L. Kenerson, Kristin E. Goodsell, Jason A. Carter, Andrew Brane, Kimberly S. Smythe, Eric A. Collisson, Venu G. PillarisettyAbstract
Background:
The multi-RAS inhibitor, daraxonrasib, has demonstrated a remarkable improvement in outcomes for patients with metastatic PDAC. Pre-clinical murine studies have shown that the durable effects of the pre-clinical multi-RAS inhibitor, RMC-7977, require an intact immune system including CD8+ T cells and cross-presenting dendritic cells. We sought to characterize changes in the immune microenvironment in human PDAC after daraxonrasib treatment and to identify opportunities for enhanced tumor control.
Methods:
Under an IRB-approved protocol, we treated resected PDAC (n=3) in our well-established tumor slice culture system with the indicated agents for 3 days. We measured tumor cell death with cleaved-caspase 3 immunohistochemistry (CC3 IHC) in fixed slices and caspase-cleaved cytokeratin 18 (ccCK18) ELISA of culture supernatant. We used spatial proteomics (Akoya ImmunoOncology 60 panel) to assess changes in the tumor microenvironment. We analyzed existing single-cell RNA sequencing (scRNAseq) from RMC-7977-treated KPC tumor-bearing mice by custom python scripts with standard scRNAseq packages. Generative artificial intelligence (AI) was used to assist with code development for spatial proteomics analysis.
Results:
Human PDAC tumor slices treated with daraxonrasib exhibited a 1.75-fold increase in tumor cell apoptosis by CC3 IHC and 2-fold increase in ccCK18 compared to control. Using high-plex spatial proteomics, we found similar overall proportions of immune cells between treatment groups; however, there were more cytotoxic CD8+ T cells and an increase in M1/M2 macrophage ratio with daraxonrasib treatment versus control. Interestingly, despite the increase in cytotoxic T cells within the tumor slices, daraxonrasib exacerbated T cell exclusion, a known feature of the PDAC microenvironment, with the observed-to-predicted nearest-neighbor distance ratio between CD8+ T cells and tumor cells increasing from 2.7 to 7.8 (p=0.001). In the scRNAseq dataset, RMC-7977-treated tumors had higher expression of the chemokine CXCL12 by cancer-associated fibroblasts compared to vehicle controls (p=0.001). We tested whether increased CXCL12 drives T cell exclusion after daraxonrasib treatment by blocking the CXCL12 receptor, CXCR4 with AMD3100. In PDAC slice culture, combination treatment with daraxonrasib and AMD3100 led to significantly increased tumor cell apoptosis compared to individual agents (3.5 vs 2 (daraxonrasib) and 1.25-fold (AMD3100 alone) or control, p=0.027). Further, T cell exclusion was reduced to below control levels after combination treatment (1.4 vs 2.7 (control) and 7.8 (daraxonrasib alone), p=0.001).
Conclusions:
Daraxonrasib treatment of human PDAC slice cultures drives an expansion of cytotoxic CD8+ T cells and a shift towards more inflammatory macrophages but also exacerbates immune exclusion. Addition of CXCR4 blockade overcomes this immune exclusion and enhances tumor cell death by pan-RAS inhibition, supporting further clinical investigation. Generative AI was used to assist in editing the language of this abstract.
Citation Format:
Sheela R. Damle, Nancy Liu, Xiuyun Jiang, Heidi L. Kenerson, Kristin E. Goodsell, Jason A. Carter, Andrew Brane, Kimberly S. Smythe, Eric A. Collisson, Venu G. Pillarisetty. CXCR4 synergizes with multi-RAS inhibition by overcoming T cell exclusion to enhance immunogenic cancer cell death in human pancreatic cancer slice culture [abstract]. In: Proceedings of the AACR Conference on Pancreatic Cancer: New Frontiers in Biology and Therapeutic Development; 2026 Sep 25-28; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(18_Suppl_2):Abstract nr B047.