Introduction:
This study was undertaken to examine the anticancer effects of the natural product rhein on human leukaemia cells.

Material and methods:
Cell viability was determined by MTT assay. Immunofluorescence staining, DAPI, AO/EB, and annexin V/PI staining were used for the detection of apoptosis. qRT-PCR analysis was used to examine protein expression. Western blot analysis was used to determine protein expression.

Results:
The results revealed that rhein caused a significant (p < 0.05) and dose-dependent decrease in the viability of AML-193 leukaemia cells. It was also revealed that rhein caused morphological changes such as cell rounding in rhein-treated AML-193 cells. The DAPI and AO/EB staining showed that rhein caused remarkable changes in the nuclear morphology of the AML-193 cells, characteristic of apoptosis. The percentage of apoptosis was found to be 3.12%, 14.80%, 30.31%, and 60.85% at the concentrations of 0, 3.5, 7, and 14 µM of rhein, respectively. The expression of Bax, cleaved caspase-3, 9, and cleaved PARP increased concentration dependently, while the expression of Bcl-2 decreased. The effects of rhein were also examined on 11 different miRs, and it was found that rhein specifically and significantly (p < 0.05) inhibited the expression of miR-27. Additionally, inhibition of miR-27 resulted in the decrease of AML-193 viability and upregulation of Cullin 5 (CUL5).

Conclusions:
Taken together, rhein triggers apoptosis in leukaemia cells and modulates the miR-27/CUL5 axis. As such, rhein may prove to be beneficial in the treatment of leukaemia.