Mechanism of d-Glucaro-1,4-lactone enhancing the anticancer efficacy of lenvatinib via the IFN-γ-STAT3-PD-L1 signaling pathway in hepatocellular carcinoma

OBJECTIVE: Hepatocellular carcinoma (HCC) remains a leading cause of cancer mortality. Targeted therapies like lenvatinib face limitations due to resistance and immunosuppression. d-Glucaro-1,4-lactone (1,4-GL), a bioactive natural compound with anti-HCC activity, holds unexplored synergistic potential with lenvatinib. This study investigates the combinatorial efficacy of 1,4-GL and lenvatinib against HCC and elucidates the underlying mechanisms. METHODS: Efficacy was evaluated in H22 tumor-bearing mice treated with lenvatinib (20 mg/kg/day) ± 1,4-GL (25, 50, 100 mg/kg/day). Tumor inhibition, serum cytokines (TNF-α, IFN-γ, AFP), oxidative stress markers (MDA, SOD), liver enzymes (ALT, AST), and splenic T-cell subsets (flow cytometry) were assessed. Histopathology was analyzed via H&E staining. Lenvatinib pharmacokinetics (serum, liver, tumor) with/without 1,4-GL was determined in mice and SD rats using UPLC-MS/MS. In vitro, combinatorial effects on proliferation (CCK-8), migration (scratch assay), and clonogenicity (colony formation) were tested in Huh7 and HepG2 cells. STAT3 phosphorylation and PD-L1 expression (protein: Western blot; mRNA: RT-qPCR) were analyzed. PD-L1 induction was achieved using IFN-γ (20 ng/ml). RESULTS: (Huh7: 18.54 μmol/l; HepG2: 30.34 μmol/l). Combinatorial treatment markedly downregulated PD-L1 protein/mRNA and inhibited STAT3 phosphorylation (p < 0.05). Scratch and colony formation assays indicated synergy stemmed from immunomodulation and signaling inhibition, not enhanced anti-migration/proliferation. CONCLUSION: 1,4-GL potently synergizes with lenvatinib against HCC by enhancing oxidative stress, reconstituting antitumor immunity, and suppressing the STAT3/PD-L1 signaling axis, without perturbing lenvatinib pharmacokinetics. This defines a novel phytochemical-based combinatorial strategy with significant clinical translation potential for HCC therapy.