Dual Targeting of HIF-1α and DLL4 by Isoxanthohumol Potentiates Immune Checkpoint Blockade

Tumor angiogenesis is a critical driver of cancer progression; however, current anti-angiogenic therapies remain limited by resistance and toxicity. Hypoxia within the tumor microenvironment induces hypoxia-inducible factor-1α (HIF-1α), which promotes aberrant angiogenesis by upregulating vascular endothelial growth factor (VEGF) and, subsequently, delta-like ligand 4 (DLL4) in endothelial cells. A systematic screening of flavanone derivatives was performed to identify compounds capable of dual inhibition of HIF-1α and DLL4. Among 16 natural compounds evaluated, isoxanthohumol (IXN), a prenylated flavanone, emerged as the most potent, suppressing both hypoxia-induced HIF-1α accumulation in tumor cells and VEGF-induced DLL4 expression in endothelial cells. IXN markedly inhibited endothelial proliferation, migration, and tube formation in vitro. In a Lewis lung carcinoma (LLC) mouse syngeneic model, IXN monotherapy reduced tumor growth and vessel density. Notably, combination treatment with IXN and anti-PD-1 immunotherapy produced greater anti-tumor effects than either monotherapy. This combination enhanced cytotoxic T cell infiltration into the tumor core, increased granzyme B expression, and induced widespread tumor cell apoptosis, consistent with improved vascular normalization. These findings identify IXN as a promising dual-targeting agent that inhibits both HIF-1α and DLL4 and demonstrate its potential to enhance immune checkpoint blockade. Simultaneous targeting of hypoxia-driven and VEGF-DLL4-mediated angiogenic pathways represents a compelling therapeutic strategy to overcome the limitations of current anti-angiogenic and immunotherapeutic approaches.