Introduction: Hypericum perforatum, also known as ‘St. John's wort’, is one of the most studied medicinal plants. Despite its primary use as an anti-depression agent, certain compounds such as hypericin and hyperforin in H. perforatum extract have been shown to inhibit tumor growth by inducing apoptosis/necrosis and inhibiting angiogenesis. Using hypericin in photodynamic cancer therapy is also being studied. Our previous studies have demonstrated that H. perforatum extract and a group of 4 compounds in it, namely pseudohypericin, amentoflavone, quercetin, and chlorogenic acid, decreased lipopolysaccharide (LPS)-stimulated macrophage inflammatory response, and identified the activation of suppressor of cytokine signaling 3 (SOCS3) as a candidate mechanism for this activity. Given that both inflammation and SOCS3 suppression are associated with tumor progression, we studied the role of SOCS3 activation in the anti-inflammatory activity of H. perforatum extract and its components.

Methods: Specific siRNA was used to knockdown the expression of SOCS3 in RAW 264.7 mouse macrophages. Activation of SOCS3 in macrophages was measured at mRNA and protein levels using qRT-PCR and Western blot. H. perforatum extract at 30 µg/mL, the 4 compounds at the same concentrations as in the extract, and the combinations of individual compounds were applied to macrophages with and without SOCS3 knockdown to reveal whether their inhibition of LPS-stimulated prostaglandin E2 (PGE2) and nitric oxide (NO) was dependent on SOCS3.

Results: SOCS3 expression in the mouse macrophages was activated upon LPS stimulation and further potentiated by H. perforatum extract and the 4 compounds studied. SOCS3 siRNA transfection significantly compromised the activation of SOCS3. H. perforatum extract and the 4 compounds reduced LPS-stimulated PGE2 and NO production, but only the inhibitory effect of the 4 compounds was negated by SOCS3 knockdown. Combinations of two or three of the 4 compounds that include pseudohypericin, the most essential component among the four that act synergistically in reducing macrophage inflammatory response, lost their inhibitory effect on PGE2 and NO production in SOCS3 knockdown cells.

Conclusions: SOCS3 activation was critical for pseudohypericin's independent and interactive anti-inflammatory activity with amentoflavone, quercetin, and chlorogenic acid. H. perforatum extract utilized alternative mechanisms that are SOCS3 independent to inhibit macrophage inflammation. In addition to light-activated cytotoxicity and inhibition of angiogenesis, magnification of SOCS3 activation by H. perforatum extract might contribute to its anti-tumor potential.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):A46.