Melatonin reverses lenvatinib resistance in HCC by regulating the ATF4-NRF1 pathway mediated by ceramide synthase 6

The tyrosine kinase inhibitor lenvatinib is a first-line drug for the treatment of advanced hepatocellular carcinoma (HCC). However, its efficacy is significantly compromised by the development of drug resistance. Gaining insights into the molecular mechanisms underlying lenvatinib resistance could offer novel strategies to enhance and prolong therapeutic responses. In this study, we established lenvatinib-resistant HCC cells and identified melatonin as a potential therapeutic agent to reverse lenvatinib resistance. We found that the key lipid metabolism gene CERS6 was significantly upregulated in lenvatinib-resistant cells, suggesting its involvement in mediating resistance to lenvatinib in HCC. Notably, the combination of lenvatinib and melatonin treatment, along with CERS6 knockdown, effectively overcame resistance by suppressing HCC cell proliferation and promoting cell death. Further investigations revealed pronounced endoplasmic reticulum (ER) stress in HCC cells treated with melatonin. Mechanistically, melatonin treatment reduced the expression levels of p-PERK, p-eIF2α, and ATF4, proteins associated with the activation of the ER stress response pathway. Additionally, the mitochondrial biogenesis-related PGC1α-NRF1-TFAM signaling cascade was altered, along with changes in mitochondrial morphology. Our findings demonstrate that the combination of lenvatinib and melatonin effectively mitigates lenvatinib resistance in HCC cells, offering a promising strategy to address drug resistance in clinical HCC management.