Background: A Chinese folk medicine plant Pleurospermum lindleyanum possesses pharmacological
activities of heat-clearing, detoxifying and preventing from hepatopathy, coronary heart disease, hypertension,
and high altitude sickness. We isolated and characterized its constituents to investigate its synergistic effects
against human hepatoma SMMC-7721 cells.
Objective: The aim of this study was to explore the synergistic anti-cancer activities of isolates from P. lindleyanum
with 5-FU on hepatoma SMMC-7721 cells in vitro and their primary mechanisms.
Methods: Sequential chromatographic techniques were conducted for the isolation studies. The isolate's structures
were established by spectroscopic analysis as well as X-ray crystallographic diffraction. Growth inhibition
was detected by MTT assay. The isobologram method was used to assess the effect of drug combinations. Flow
cytometry and western blot were used to examine apoptosis and protein expression.
Results: A new coumarin (16), along with sixteen known compounds, were isolated from the whole plant of P.
lindleyanum and their structures were elucidated by spectroscopic methods. Four coumarins (2, 3, 5, and 16),
two flavonoids (8 and 9) and three phytosterols and triterpenes (12-14) were found to synergistically enhance
the inhibitory effect of 5-FU against SMMC-7721 cells. Among them, compounds 3 and 16 exhibited the best
synergistic effects with IC50 of 5-FU reduced by 16-fold and 22-fold possessing the minimum Combination
Index (CI) 0.34 and 0.27. The mechanism of action of combinations might be through synergistic arresting for
the cell cycle at G1 phases and the induction of apoptosis. Moreover, western blotting and molecular docking
revealed that compounds 3 or 5 might promote 5-FU-induced apoptosis by regulating the expression of Caspase
9 and PARP.
Conclusion: Constituents from P. lindleyanum may improve the treatment effectiveness of 5-FU against hepatocellular