Capsaicin suppresses metastasis in tongue squamous cell carcinoma by reversing epithelial-mesenchymal transition via the AMPK/HIF-1α/Claudin-1 axis

Abstract Background Tongue squamous cell carcinoma (TSCC) is a highly aggressive malignancy with a strong propensity for early metastasis. Capsaicin (CAP), a major bioactive phytochemical isolated from Capsicum species, possesses significant anti-tumor activity. The present study aimed to elucidate the effects of CAP on epithelial-mesenchymal transition (EMT) and metastasis in TSCC, as well as to decipher the underlying molecular mechanisms. Results Transcriptomic profiling of CAP-treated TSCC cells identified 5,904 DEGs, with GO enrichment in oxidative stress, metabolism and ECM pathways, and KEGG analysis highlighting the AMPK signaling pathway. Network pharmacology further revealed 72 shared targets between CAP and head and neck squamous cell carcinoma (HNSCC), predominantly enriched in the HIF-1 signaling pathway. In exploratory analyses of clinical samples (CPTAC database and 37 paired TSCC specimens), we observed an association of AMPK downregulation and HIF-1α upregulation with advanced tumor stage and poor differentiation. In vitro, CAP activated AMPK, suppressed HIF-1α, and consequently restored the epithelial junction protein Claudin-1, leading to the reversal of key EMT markers by upregulating E-cadherin and downregulating N-cadherin and Vimentin. Functionally, genetic manipulation established an AMPK/HIF-1α/Claudin-1 signaling axis: AMPK knockdown abrogated CAP-mediated effects, whereas HIF-1α overexpression mimicked EMT. Wound healing and Transwell assays verified that Claudin-1 deficiency rescued CAP-induced inhibition of cell migration. In vivo, CAP significantly reduced pulmonary metastatic nodules in nude mice in an AMPK-dependent manner, without inducing detectable hepatic or renal toxicity. Conclusions Our study collectively delineates a novel mechanism wherein CAP constrains EMT and metastasis in TSCC through the AMPK/HIF-1α/Claudin-1 axis. These findings provide a mechanistic basis for understanding how CAP, a natural dietary constituent, interferes with TSCC progression.