The Role of IL-33 in Promoting Tumor Growth in Pancreatic Cancer Tissue and its Potential as a Therapeutic Target

Background Introduction

Pancreatic Cancer (PDA) is one of the most lethal malignancies worldwide, characterized by rapid clinical progression and poor treatment responses, with a five-year survival rate of only 13%. In the United States, PDA is currently the third leading cause of cancer-related death. Over 95% of PDA cases carry driver mutations of the small GTPase KRAS, with KRAS^G12D being the most common. KRAS^G12D can drive the transformation of pancreatic tissue into precancerous lesions such as Pancreatic Intraepithelial Neoplasia (PanIN) in mouse models, ultimately progressing to invasive PDA.

A profuse fibroinflammatory microenvironment exists in pancreatic cancer, containing not only stromal cells but also immunosuppressive immune cells and abundant Extracellular Matrix (ECM). Cancer-Associated Fibroblasts (CAFs) are an important component of this microenvironment, primarily derived from the transformation of normal fibroblasts and Pancreatic Stellate Cells (PSCs).

Source and Publication of the Study

This paper was completed by a research team from the Rogel Cancer Center at the University of Michigan and other institutions, with leading researchers including Katelyn L Donahue, Hannah R Watkoske, Padma Kadiyala, etc. The paper was published in the 2024 edition of the journal “Cancer Discovery,” focusing on the role of IL-33 in the KRAS-driven pancreatic cancer microenvironment.

Research Process and Methods

Overall Research Process

The research was divided into several steps: 1. Sample Collection and Analysis: Using Immunohistochemistry (IHC) to stain IL-33 in human pancreatic cancer and normal adjacent tissues, and employing Single Cell RNA Sequencing (scRNASeq) to analyze cancer tissue samples from 16 patients. 2. Animal Experiments: Generating mouse models with specific genetic deletions of IL-33, inducing gene deletion with Tamoxifen treatment. Orthotopic injection of pancreatic cancer cells was performed on model mice to observe tumor growth. 3. Study of Molecular Mechanisms: Exploring the signaling mechanisms of IL-33 in fibroblasts through various experiments, such as confocal immunofluorescence and blockade experiments for MEK-ERK signaling pathways.

Research Details

1. Expression and Distribution of IL-33 in Pancreatic Cancer Patients and Mouse Models:

   • In patient tumor tissues, IL-33 is significantly expressed in both tumor cells and disease-associated stromal regions, while it is low in normal tissues.
   • scRNASeq data show that IL33 gene transcription levels are significantly higher in tumor tissues compared to adjacent normal tissues, mainly expressed in fibroblasts, pericytes, and endothelial cells.

2. Animal Model Experiments:

   • CreER;IL33^f/f mouse models were created, and the IL-33 gene was specifically knocked out in fibroblasts through Tamoxifen treatment, resulting in a significant reduction of tumor volume by about 40%.
   • Immunostaining results indicate a decrease in proliferation of tumor cells and CAFs and a significant increase in apoptotic markers.
   • scRNASeq data reveal a significant decrease in IL-33 transcription levels in the stromal cells of IL-33 knockout mice and identify a unique subgroup of epithelial-mesenchymal transition (EMT) cells.

Experimental Results

1. CAF IL-33 Promotes Pancreatic Cancer Growth:

   • The maintenance of IL-33 in fibroblasts depends on the KRAS^G12D and JAK1/2-STAT3 signaling pathways.
   • By conditionally deleting the IL-33 gene in PDGFRA-marked fibroblasts, a change in tumor hormone secretion was observed, including reduced production of immunosuppressive cytokines such as CXCL12, and increased production of pro-inflammatory factors.

2. Reprogramming of the Immune Microenvironment:

   • Following IL-33 knockout, CD8+ T cell infiltration and activation significantly increased, and tumor growth slowed.
   • Neutrophils and macrophages expressed increased pro-inflammatory markers such as IL1A and TNF, while immunosuppressive markers like ARG1 and MRC1 decreased.

3. Study of Molecular Signaling Mechanisms:

   • The maintenance of IL-33 in PAFs and CAFs depends on the expression of epithelial KRAS^G12D, activated through the JAK1/2-STAT3 signaling pathway.
   • Tumor cell-mediated RAS-dependent autocrine signaling activates IL-33 in fibroblasts, verified using tumor cell-conditioned culture fluid.

Research Conclusions and Significance

This paper thoroughly delineates the role of IL-33 in the pancreatic cancer microenvironment and posits IL-33 as a potential therapeutic target through various biological experimental methods. The results indicate that IL-33 secreted by KRAS^G12D-driven fibroblasts promotes tumor growth by altering the immune microenvironment. The deletion of IL-33 not only reduces tumor proliferation but also changes the differentiation state of CAFs and increases the production of pro-inflammatory factors, making the pancreatic cancer microenvironment more conducive to CD8+ T cell infiltration and activation.

Highlights of the Study

1. Innovative Experimental Design: By utilizing diverse mouse models and cutting-edge molecular biology techniques, the study accurately assesses the role of IL-33 in the pancreatic cancer microenvironment and reveals its potential as a therapeutic target.
2. Detailed Mechanism Elucidation: The signal transduction pathways of IL-33 in fibroblasts are thoroughly investigated, especially activation through the JAK1/2-STAT3 pathway, demonstrating its importance in maintaining the tumor environment.
3. Broad Application Prospects: The study suggests that inhibiting IL-33 or its related signaling pathways could serve as a new strategy for treating pancreatic cancer, potentially bringing new treatment methods to clinical practice.

The authors have not only proposed a new tumor therapeutic target but also deepened our understanding of the role of CAFs in the pancreatic cancer microenvironment, providing important insights for future research and treatment.