Differential inhibition of Hedyotis diffusa (HD) and Scutellaria barbata (SB) on human nasopharyngeal carcinoma cells

Abstract

There are increasing interests and growing opportunities for different investigations to verify Traditional Chinese medicines (TCM) as a complementary therapy for cancers. TCM has a growing popularity as a less intensive and more natural approach to achieve health or improve quality of life. Hedyotis diffusa (HD) and Scutellaria barbata (SB) are two popularly used TCM with documented lethal activities on hepatoma, cervical, gastric and intestinal carcinoma. In this study, we aimed to explore the inhibitory mechanism of the HD and SB extracts on Nasopharyngeal Carcinoma Cells (NPC/CNE2), which is a prevalent cancer in Hong Kong and Southern China. We determined the Chinese Medicine formula with restrict pharmaceutical procedures and performed the chemical fingerprint with HPLC for assessing the quality consistency of SB and HD. At 2-hour drug incubation, the CNE2 cells were well-responsive to both extracts and a lethal dose of 50 (LD50) was achieved with HD (276 µg/mL) and SB (65µg/mL) using trypan blue exclusion assay. At LD10, early apoptotic cell death was triggered by both extracts (HD: 28µg/mL; SB: 3µg/mL); and at LD30, late apoptotic/necrotic cells were significantly increased to 80% (HD: 276µg/mL; SB: 13µg/mL) by Annexin-V-FLOUS staining under fluorescent microscopy. The cytotoxic effect of HD and SB on CNE2 cells was predominantly mediated by H2O2 released by both extracts demonstrated by PerXOquantTM Quantitative Peroxide Assay. DNA damage was evident at half hour post treatment for both extracts using comet assay. In order to verify H2O2 was the toxic species that induced DNA damage, catalase was used to scavenge the H2O2 upon co-incubation with the herb extracts on the CNE2 cells. In conclusion, both HD and SB extracts exhibited a potent growth inhibition on NPC/CNE2 cells due to the induction of DNA damage and apoptosis via the generation of H2O2; hence both herbs can be potential therapeutic interventions for nasopharyngeal carcinoma.