Lucidin 3-methyl ether from Rubia philippinensis suppresses the proliferation of multiple myeloma cells through the promotion of β-catenin degradation.

BACKGROUND

Constitutive accumulation of β-catenin has been frequently observed in multiple myeloma. Extracts from genus Rubia plants exhibit cytotoxic activity against several types of cancer cells; however, little is known about their chemopreventive mechanisms and bioactive metabolites.

PURPOSE

Purpose: The study aimed to identify the underlying antiproliferative mechanisms of Rubia philippinensis extract in multiple myeloma cells and the major active metabolites responsible for cytotoxic activity of R. philippinensis.

METHODS

The effects of R. philippinensis extracts and lucidin 3-methyl ether on the Wnt/β-catenin pathway were determined by cell-based reporter assay, Western blot analysis, and RT-PCR. The antiproliferative activity was evaluated by cell viability assay and apoptosis analysis in RPMI8226 and MM.1S multiple myeloma cells.

RESULTS

R. philippinensis extracts inhibited Wnt/β-catenin signaling and lucidin 3-methyl ether, an anthraquinone derivative, was identified as the major active metabolite responsible for the inhibition of Wnt/β-catenin signaling. Lucidin 3-methyl ether induced β-catenin phosphorylation at Ser33/Ser37/Thr41 residues and promoted proteasomal degradation of β-catenin via a GSK-3β-independent mechanism, thereby downregulating Wnt3a-induced β-catenin response transcription (CRT). Moreover, lucidin 3-methyl ether repressed the expression of β-catenin/T-cell factor (TCF)-dependent genes, such as cyclin D1, c-myc, and axin-2, thus inhibiting MM cell proliferation. Apoptosis was also elicited by lucidin 3-methyl ether, as indicated by the increase in the population of annexin V-FITC positive cells and caspase-3/7 activity in MM cells.

CONCLUSION

These findings indicate that R. philippinensis and its active metabolite lucidin 3-methyl ether prevent cell proliferation through the suppression of the Wnt/β-catenin pathway and exhibit potential as chemopreventive agents for the treatment of MM.