N-Methylcoclaurine Suppresses Hepatocellular Carcinoma by Inhibiting Protein Disulfide Isomerase in vitro and in vivo

Yao Fu, Na Zhao, Shihang Zhang, Yue Liu, Changlong Li, Wanting Jiang, Mojiao Zhao and Yong Yang

Background and Objective: Plumula Nelumbinis (PN) or Lianzixin, is a well-established anti-tumor medicine included by Chinese Pharmacopoeia. Modern pharmacological studies have confirmed that benzylisoquinoline alkaloids are the major anti-tumor components of PN. However, the detailed mechanism remained unclear. This study aimed to evaluate the in vitro and in vivo anti-tumor effects of N-methylcoclaurine (N-MC), a potential natural protein disulfide isomerase (PDI) inhibitor isolated from PN. Materials and Methods: Insulin turbidity assay and molecular docking analysis were conducted for the PDI inhibition study of N-MC. The MTT, scratch assay and transwell assays were performed to evaluate the in vitro effects of N-MC on HepG2 cells. For the in vivo effects of N-MC, the H22-bearing mice model was generated with 40 ICR mice and treated with different doses of N-MC (10, 20 and 40 mg/kg b.wt.). The ANOVA and LSD were performed for the comparisons between groups. Results: The N-MC exhibited a concentration-dependent inhibitory effect on PDI, with an IC₅₀ of 3.91 μM. The N-MC could fit the active pocket of PDI surrounded by Phe 249, Phe 304, Ile 318, Leu 320, Met 324, Lys 436, Val 437 and His 438, with a calculated binding energy of -8.2 kcal/mol. The N-MC effectively inhibited cell migration and invasion of HepG2 cells in a dose-dependent manner. In the H22 tumor-bearing ICR mice model, N-MC also exhibited dose-dependent tumor suppression quantified by tumor inhibition rates and cell number index. Conclusion: The N-MC exhibits the ability to inhibit tumor proliferation, migration and invasion through the inhibition of PDI activity in vitro and effectively suppresses tumor growth in vivo. These findings suggest that N-MC is a promising candidate for anti-tumor drugs through inhibiting PDI.

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