Anticancer effect of aloe-emodin on cervical cancer cells involves G2/M arrest and induction of differentiation

Aim: The aim of this study was to investigate the effects of aloe-emodin, a natural compound from the root and rhizome of Rheum palmatum, on the growth of human cervical cancer cells, HeLa. Methods: HeLa cells were treated with various concentrations of aloe-emodin for 1-5 d, and cell growth was measured by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide assay. The long-term growth effect was investigated by crystal violet assay. The distributions of the cell cycle and apoptosis were analyzed by flow cytometry. The alkaline phos-phatase (ALP) activity was analyzed by a chemical analyzer. Finally, Western blotting was used to indicate the abundant changes of protein kinase C (PKC), c-myc, cyclins, cyclin-dependent kinases (CDK), and proliferating cell nuclear antigen (PCNA). Results: Aloe-emodin inhibited the growth of HeLa cells in a dose-dependent manner at concentrations ranging between 2.5 and 40 mu mol/L. The flow cytometric analysis showed that HeLa cells were arrested at the G(2)/M phase. This effect was associated with the decrease in cyclin A and CDK2, and the increase in cyclin B1 and CDK1. More importantly, the ALP activity was found to be increased by aloe-emodin treatment, and accompanied by the inhibition of PCNA expression. In addition, aloe-emodin suppressed the expression of PKC alpha and c-myc. Conclusion: These findings provide a possible mechanistic explanation for the growth inhibitory effect of aloe-emodin on HeLa, which includes cell cycle arrest and inducing differentiation.