The characterisation of ovarian cancer stem cells and the effects of Chinese herbal medicines

The resistance of ovarian cancer to chemotherapy and the recurrence may be due to the existence of cancer stem cells (CSCs) which are capable of self-renewal, proliferation, differentiation and initiation of tumours. Recent studies have showed that a distinct subpopulation within cancer cells known as the side population (SP) is enriched with putative CSCs.This study documents the presence of SP in SK-OV-3 and OVCAR3 ovarian cancer cell lines. It is the first report on the upregulated genes in the SP cells of SK-OV-3 and OVCAR3. SP cells are smaller than non-SP population (NSP) cells and SP cells have fewer organelles inside the cytoplasm than do NSP cells. SK-OV-3 SP cells were able to regenerate both SP and NSP cells more effectively at an earlier time point than NSP cells. The analysis of growth rate and the clone forming efficiency suggested that in SK-OV-3 the SP phenotype was related to cell quiescence which might result from the resting nature of stem cell.This study revealed that SP yield was not only affected by the Hoechst concentration, staining cell density, staining cell viability, staining duration, staining temperature, staining medium, FCM setting and SP gating strategy, but also by the cell passage number in SK-OV-3.The results showed that both short time exposure and long time co-culture of SK-OV-3 with berberine or the Chinese Herbal Medicine (CHM) Coptis chinensis extract inhibited the drug efflux of SP cells. Berberine and Coptis diminished the SP in SK-OV-3 cells treated for 24h or less in a dose-dependent manner. Berberine had a long term inhibitory effect on SP cells, with 72h treatment and 17 days of normal culture thereafter. Extracts from CHMs and berberine possess anticancer properties such as antiproliferation, apoptosis induction, cell cycle arrestment, suggesting that the anticancer mechanism of CHMs is multi-targeting.This study suggests that some CHM extracts may be potential SP inhibitors targeting CSCs, thereby enhancing the effects of chemotherapy. The study may have a profound impact on treatment strategies of ovarian cancer and the design of new chemotherapy regimes that include CHM extracts