Abstract 2684: The iRGD tumor-penetrating peptide inhibits TGF-β activation mediated by an αvβ5 integrin-rich tumor microenvironment in pancreatic cancer

Abstract αvβ5 integrin is highly expressed in pancreatic ductal adenocarcinoma (PDAC) and predicts poor prognosis in PDAC patients. We previously showed that transforming growth factor-β (TGF-β) produced by cancer-associated fibroblasts and cancer epithelial cells induces the expression of αvβ5 integrin in PDAC, contributing to the αvβ5-rich tumor microenvironment (TME). Here, we show that the αvβ5 integrin is a critical activator of TGF-β in PDAC and that the iRGD tumor-penetrating peptide effectively inhibits the activation cascade causing a dynamic modification of the PDAC TME. TGF-β is secreted as a latent complex (LAP-TGF-β) and activated by various stimuli including receptor-dependent mechanisms. αv integrins potently activate TGF-β by binding to the RGD peptide motif within LAP-TGF-β to mechanically release active TGF-β from the complex. Our results show that the αvβ5 integrin is a major activator of TGF-β in PDAC cells because deleting the integrin significantly reduced TGF-β signaling and target gene expression despite the presence of other αv integrins on the cells. The iRGD peptide, which binds to αv integrins (and neuropilin-1) and delivers drugs deep into the tumor tissue, inhibited the integrin-mediated activation of TGF-β in the PDAC cells in an RGD-dependent manner. iRGD effectively inhibited TGF-β signaling in vivo evidenced by a dramatic suppression of phosphorylated Smad-2 in orthotopic tumors in syngeneic PDAC mice. Various changes in the TME accompanied the effect, such as reduced regulatory T cells, altered distribution of CD8+ T cells, normalization of blood vessels, and reduced stromal fibers. Similar results were obtained in humanized orthotopic PDAC mice that allow proper characterization of human immune response to tumor antigens. Adding an immune checkpoint blockade (ICB) to the iRGD monotherapy led to enhanced anti-tumor effects in both mouse models. Of note, iRGD, even as monotherapy, caused a striking inhibition of liver metastasis formation in humanized PDAC mice. Our findings suggest that PDAC has assembled a mechanism to maintain high levels of active TGF-β and αvβ5 integrin expression that likely contributes to its desmoplastic and drug resistant nature. iRGD interferes with the mechanism to cause dynamic TME modification and sensitization to ICB. The results justify the concept of the ongoing iLSTA clinical trial that studies the effect of iRGD-based immunotherapy in patients with locally advanced PDAC (ACTRN12623000223639). Citation Format: Yukihito Kuroda, Kodai Suzuki, Yuki Kunisada, Hotatka Kawai, Henri Havia, Tero A. Järvinen, Moriya Tsuji, Kazuki N. Sugahara. The iRGD tumor-penetrating peptide inhibits TGF-β activation mediated by an αvβ5 integrin-rich tumor microenvironment in 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 2684.