Abstract
Objective: Clear-cell renal cell carcinoma (ccRCC) is an immune-desert tumor. This study investigates the role of ectonucleotide pyrophosphatase/phosphodiesterase 3 (ENPP3) as a potential therapeutic target and immune-checkpoint enzyme in ccRCC. Methods: ENPP3 expression and its link to hypoxia and prognosis were analyzed in ccRCC. Functional roles were tested using gain/loss-of-function studies in vitro and in xenograft models, followed by therapeutic anti-ENPP3 antibody administration, alone or with anti-PD-L1. Mechanisms were explored via promoter analysis, cGAMP measurement, flow cytometry, cytokine profiling, and in vivo neutralization with STING- or interferon-α/β receptor-1 (IFNAR1) blocking antibodies. Results: ENPP3 is hypoxia-inducible via HIF-1α, upregulated in ccRCC, and predicts poor prognosis. ENPP3 overexpression accelerated tumor growth, while its knockdown or antibody blockade inhibited progression and synergized with anti-PD-L1. Mechanistically, ENPP3 hydrolyzes extracellular cGAMP. Its depletion elevated extracellular cGAMP, expanded anti-tumor immune cells (M1 macrophages, cDC1s, and cytotoxic T cells), reduced Tregs, and induced a STING- and IFNAR1-dependent type I interferon signature in macrophages. The anti-tumor efficacy of ENPP3 blockade was abrogated by IFNAR1 inhibition. Conclusion: ENPP3 is a hypoxia-driven, cGAMP-targeting innate immune checkpoint in ccRCC. Its inhibition reactivates STING-dependent anti-tumor immunity, providing a strong preclinical rationale for targeting ENPP3 therapeutically.