Cardiac glycosides activate non-canonical STAT1 signaling to reprogram antigen-presenting cells 2310011

Introduction Effective activation of antigen-presenting cells (APCs) is essential for durable vaccine responses and successful cancer immunotherapy, yet pharmacologic strategies to achieve it remain limited. Methods Approximately 1000 compounds of Library of Pharmacologically Active Compounds (LOPAC) were screened to identify inducers of innate immune responses in activation of monocyte-derived dendritic cells (MDDCs). Results We identify cardiac glycosides (CGs) as a class of small-molecule immunopotentiators that trigger a non-canonical STAT1 pathway through the Na+/K+-ATPase-Src-p38 axis. In primary human dendritic cells, the CGs Bufalin and ouabain induce serine STAT1 phosphorylation (S727) independent of interferon signaling, driving a distinct proinflammatory and antigen-presentation program. Bufalin enhances CD8+ T-cell priming in response to mRNA vaccination and, in combination with an oncolytic Newcastle disease virus, promotes myeloid remodeling and enhances tumor regression in vivo. Conclusion These findings reveal a previously unrecognized mechanism linking Na+/K+-ATPase signaling to immune activation through non-canonical STAT1 pathway activation. Identification of non-toxic agonists of this pathway may lead to a next-generation of small-molecule adjuvants and immunotherapy co-agents.