Comparison of the growth-inhibitory effect of Hypericum perforatum L. extracts, differing in the concentration of phloroglucinols and flavonoids, on leukaemia cells

ABSTRACT In this study we compared, simultaneously, the growth‐inhibitory effect of Hypericum perforatum L. extracts, containing various amounts of hyperforin (A 3.25%; B 2.21%; C 0.21% w/w) and flavonoids (A and B 5.3%; C 10% w/w), but closely same amounts of naphthodiantrones (0.3%) on two leukaemic cell lines K562 and U937 in the WST‐1 assay. The GI50 (concentration of extracts which caused 50% of cell growth inhibition) for H. perforatum extracts analysed and characterized by HPLC for their biologically active constituents was 248.3–621.3 μg mL−1 in K562 and 378.2–911.7 μg mL−1 in U937 cells. The corresponding values of the three main groups were 1.6–3.9 μm naphthodianthrones, 1.0–40.7 μm phloroglucinols and 30.5–68.5 μm flavonoids. The results of this study supported the hypothesis that, apart from hyperforin and flavonoids, other components of the extract could be involved in its growth‐inhibitory effect that it exerts without light activation.