Targeting the αvβ5 Integrin Modifies the TGFβ-Rich Tumor Microenvironment of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is notorious for its aggressive, therapy-resistant nature that is in part driven by the desmoplastic, hypoperfused, and immunosuppressive tumor microenvironment (TME). In this study, we demonstrated that the αv integrin and neuropilin-1 (NRP-1) dual targeting iRGD peptide reverses some of these TME features by inhibiting transforming growth factor β (TGFβ) activation in the tumor, a process mediated by the αvβ5 integrin. In addition to PDAC epithelial cells and fibroblasts, regulatory T cells (Treg) in PDAC tumors also expressed the αvβ5 integrin and NRP-1. The αvβ5+ Tregs potently inhibited T-cell proliferation, and systemic iRGD therapy not only depleted αvβ5+ Tregs from PDAC tumors but also reduced their αvβ5- counterparts. Mechanistically, iRGD inhibited the activation of TGFβ mediated by the αvβ5-rich TME, thereby depriving Tregs of the cytokine essential for their development and maintenance. NRP-1-dependent tumor penetration was required for this effect because a traditional RGD peptide without an NRP-1-binding motif failed to inhibit TGFβ signaling or deplete Tregs in vivo. Treatment with iRGD induced a series of additional TME changes, such as improved vascular patency and perfusion, reduced stromal fibers, and increased CD8+ T-cell entry into the core of the tumors. Combining iRGD with immune checkpoint blockade led to an enhanced antitumor effect. Together, these findings support targeting the αvβ5 integrin with affinity ligands such as iRGD as a potential approach to enhance immunotherapy efficacy against PDAC and other desmoplastic tumors with high TGFβ and αvβ5 expression. SIGNIFICANCE: The iRGD tumor penetrating peptide inhibits αvβ5 integrin-dependent TGF-β activation in pancreatic cancer to normalize the desmoplastic and immunosuppressive tumor microenvironment.