[ 225 Ac]Ac-FAPI-04 Promotes Anti-tumor Immunity via Synergistic Mediated Pattern by IL-27 Activation and Tnfaip3 Inhibition

Background Accumulating evidence substantiates the capacity of targeted radionuclide therapy (TRT) to potentiate tumor immunotherapy responses. However, combining TRT and immunotherapies exhibits substantial varying efficacy, underscoring the importance of investigating mechanisms through which TRT remodels the tumor microenvironment (TME). Despite recent advancements, the specific signaling molecules mediated by TRT that regulate the functions of cytotoxic T lymphocytes (CTLs) remain unclear. Methods Given the demonstrated potential of α-radionuclides targeting the fibroblast activation protein (FAP) in TRT, this study employed [ 225 Ac]Ac-FAPI-04 to investigate the mechanisms of TRT-induced TME remodeling. The cytotoxic effects were first evaluated in the B16F10 cell line, followed by an assessment of its in vivo therapeutic efficacy in tumor-bearing mice. RNA-sequencing analysis was utilized to elucidate underlying signaling pathways involving immune responses. Results [ 225 Ac]Ac-FAPI-04 significantly induced DNA double-strand breaks, further elevated ROS levels, and apoptosis in tumor cells. Transcriptomic profiling revealed that [ 225 Ac]Ac-FAPI-04 activates the IL-27/JAK-STAT pathway to amplify interferon-mediated responses, indicating IL-27 serves as a critical regulatory signal for CTLs during TRT. A concomitant observation was the downregulation of Tnfaip3 following [ 225 Ac]Ac-FAPI-04 treatment. Tnfaip3 is implicated in modulating CTLs’ behavior and intratumoral infiltration, while its downregulation was associated with the upregulation of cytotoxic effector molecules, as confirmed in this study. Conclusion This study identifies a TRT-induced pattern of synergistic signaling mediated by IL-27 and Tnfaip3 , which collectively enhances CTL recruitment and potentiates their cytotoxic function. These findings provide a detailed mechanistic rationale for strategies aimed at augmenting the therapeutic efficacy of TRT and immunotherapy combinations.