Rhein augments ATRA-induced differentiation of acute promyelocytic leukemia cells.

Background: Rhein (4, 5-dihydroxyanthraquinone-2-carboxylic acid), a natural anthraquinone derivative, is a traditional Chinese herb that has been used as a medication in many Asian countries. It has been used as a laxative and stomach drug for a long time in both China and Korea. It is well-known to have many pharmacological activities, such as anti-cancer, anti-bacterial, anti-fungal, anti-oxidant, anti-atherogenic, anti-angiogenic, anti-fibrosis, anti-inflammatory, hepatoprotective, and nephroprotective properties. However, little is known about how rhein may affect the differentiation activities in acute promyelocytic leukemia (APL) cells.

Purpose: The present study was designed to examine the anti-leukemic effects of rhein against APL cells and to explore the underlying mechanism.

Methods: Cell viability was investigated by MTS assay. To examine the differentiation activities in APL cells, the cell surface molecules (CD11b, CD14, CCR1 and CCR2), phagocytosis, reactive oxygen species (ROS) were determined by flow cytometry. Also, induction of caspase-3 activity and reduction of mitochondrial membrane potential (MMP) were determined by flow cytometry. RNA and protein expressions were determined by qRT-PCR and western blotting, respectively.

Results: In this study we assessed the role of rhein in treating APL. Interestingly, rhein potentiated all-trans retinoic acid (ATRA)-induced macrophage differentiation in NB4 cells by inducing changes in morphology, expression of the differentiation markers CD11b and CD14, ROS production, phagocytic activity, and expression of CCR1 and CCR2. Signaling through CD11b was found to be dependent on ERK activation. Additionally, rhein induced APL cell death by activating apoptosis and suppressing the mTOR pathway.

Conclusion: Therefore, we suggest that a combination of rhein and ATRA carries strong therapeutic potential through the beneficial differentiation of APL cells. Moreover, rhein causes cell death via the activation of apoptosis and suppression of survival signals in APL cells. In combination with the ability of rhein to promote functional macrophage differentiation in APL, these properties suggest that a combined treatment of rhein and ATRA has great potential as an anti-leukemic therapy for APL.