CAF-mediated cancer immunotherapy resistance can be overcome via selective inhibition of NOX1, 2 and 4

Cancer-associated fibroblasts (CAFs) represent a functionally heterogeneous population forming a major component of the tumor stroma. CAFs interact with cancer cells and immune cells via cytokine secretion, contributing to extracellular matrix (ECM) remodeling and immune suppression in the tumor microenvironment (TME). Through these mechanisms, CAFs promote tumor progression and induce resistance to chemotherapy and immunotherapy, driving tumor aggressiveness and correlating with poor prognosis in various types of cancers. The primary function of NADPH oxidases (NOXs) is to generate reactive oxygen species (ROS). NOXs are key drivers of CAF activation, thereby facilitating tumor progression and resistance to anticancer therapies. In particular, NOX1, NOX2, and NOX4 are highly expressed in CAFs and contribute to regulation of CAF functions. Herein, we demonstrate for the first time that NOX1 and NOX2, in addition to NOX4, play critical roles in promoting fibrotic and immunosuppressive responses in CAFs. These findings indicate that selective inhibition of NOX1, NOX2, and NOX4 may prevent CAF activation, suppress tumor growth, enhance antitumor immunity, and represent a promising approach to overcome resistance. As a result, we found that NOX1, 2, and 4 are markedly elevated in human pancreatic CAFs (pCAFs) compared with human pancreatic fibroblasts (PFs). Moreover, knockdown of NOX1, 2, or 4 effectively decreased fibrosis-related markers and immune cytokines/chemokines in pCAFs, respectively. Furthermore, treatment of Compound-19 (Com-19), a selective NOX inhibitor, significantly reduced the expression of fibrosis-related factors and immune cytokines/chemokines in pCAFs and also inhibited tumor fibrosis and immune cytokines via NOX inhibition in CAF-rich colorectal cancer mouse model. Importantly, Com-19 increased the intratumoral infiltration of CD8+ T cells, resulting in synergistic anti-cancer efficacy when co-administered with immune check inhibitors (ICIs) in the model which poorly responses to ICIs. Collectively, the results indicate that NOX1, 2, and 4 play a crucial role in CAF-mediated resistance to ICIs in cancers and NOX inhibition can be an effective strategy to overcome the resistance. Notably, Com-19 effectively modulated the fibrotic and immune-suppressive properties of CAF-rich tumors via NOX inhibition, thereby resensitizing tumors to ICI therapy. Therefore, Com-19 has the potential to enhance the efficacy of cancer immunotherapy by overcoming CAF-mediated ICI resistance. Phase 1 clinical trials are underway, with administration beginning in 4Q 2025. This open-label, dose-escalation study is designed to evaluate the safety, tolerability, PK, and preliminary efficacy of Com-19 as monotherapy (Part A) and in combination with pembrolizumab (Part B) in patients with advanced solid tumors. The study aims to identify the MTD and/or RP2D of Com-19.