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] The medium-dose combination (LMGL) achieved 89.97% tumor inhibition in H22 mice, significantly reducing tumor mass by 75% vs. lenvatinib alone (0.21±0.18 g vs. 0.84±0.79 g, p < 0.01). H&E staining revealed extensive necrosis in combination groups. Serum TNF-α and IFN-γ levels significantly increased (p < 0.001), while AFP approached baseline. Flow cytometry showed an elevated CD4⁺/CD8⁺ T-cell ratio. Oxidative stress was modulated (reduced MDA and elevated SOD, p < 0.01). Pharmacokinetic studies revealed no significant differences in lenvatinib exposure or steady-state concentrations (p > 0.05) with 1,4-GL co-administration. In vitro, 1,4-GL significantly reduced lenvatinib's IC (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.