Antitumor properties of aloe-emodin and induction of transglutaminase 2 activity in B16-F10 melanoma cells.

Aloe-emodin (AE), a natural hydroxyanthraquinone compound, has been reported as a potential anticancer agent. We studied the antineoplastic properties of AE on highly metastatic B16-F10 melanoma murine cells. Cell proliferation was assessed by cell counting and viability was investigated using MTT and Trypan Bleu exclusion tests. As a growth marker, we determined intracellular polyamine levels by high performance liquid chromatography. Then, we evaluated transglutaminase 2 (TG2) activity, protoporphyrin IX accumulation and melanin content as differentiative markers. Tyrosinase activity was checked by DOPA-staining assay. The antimetastatic effect of AE was evaluated by means of a series of in vitro metastatic assays, including aggregation, wound healing migration, adhesion, 3D-invasion, circular invasion and the Boyden chamber invasion assays. Gelatin zymography was performed to evaluate metalloproteinase activities. Our results demonstrated inhibitory effects of AE on melanoma cell proliferation and invasion power, accompanied by the stimulation of cell differentiation parameters. Cell differentiation correlated with a remarkable increase of the activity of the transamidating form of TG2, with a significative enhancement of cell adhesion and aggregation. Impaired invasion was paralleled by the decrease of the secretion of matrix metalloproteinase-9. The overall data confirm a remarkable antiproliferative, antimetastatic and differentiative capability of this anthraquinone. Results suggest that AE appears particularly promising for its potential application in the newborn differentiation therapy of cancer.