Salviolone from Salvia miltiorrhiza Roots Impairs Cell Cycle Progression, Colony Formation, and Metalloproteinase-2 Activity in A375 Melanoma Cells: Involvement of P21(Cip1/Waf1) Expression and STAT3 Phosphorylation

Melanoma is a highly malignant solid tumor characterized by an elevated growth and propagation rate. Since, often, melanoma treatment cannot prevent recurrences and the appearance of metastasis, new anti-melanoma agents need to be discovered. Salvia miltiorrhiza roots are a source of diterpenoid derivatives, natural compounds with several biological activities, including antiproliferative and anticancer effects. Seven diterpenoid derivatives were purified from S. miltiorrhiza roots and identified by NMR and MS analysis. Tanshinone IIA and cryptotanshinone were detected as the main components of S. miltiorrhiza root ethanol extract. Although their antitumor activity is already known, they have been confirmed to induce a reduction in A375 and MeWo melanoma cell growth. Likewise, salviolone has been shown to impair the viability of melanoma cells without affecting the growth of normal melanocytes. The underlying anticancer activity of salviolone has been investigated and compared to that of cryptotanshinone in A375 cells, showing an increased P21 protein expression in a P53-dependent manner. In that way, salviolone, even more than cryptotanshinone, displays a multitarget effect on cell-cycle-related proteins. Besides, it modulates the phosphorylation level of the signal transducer and activator of transcription (STAT)3. Unexpectedly, salviolone and cryptotanshinone induce sustained activation of the extracellular signal-regulated kinases (ERK)1/2 and the protein kinase B (Akt). However, the blockage of ERK1/2 or Akt activities suggests that kinase activation does not hinder their ability to inhibit A375 cell growth. Finally, salviolone and cryptotanshinone inhibit to a comparable extent some crucial malignancy features of A375 melanoma cells, such as colony formation in soft agar and metalloproteinase-2 activity. In conclusion, it has been shown for the first time that salviolone, harboring a different molecular structure than tanshinone IIA and cryptotanshinone, exhibits a pleiotropic effect against melanoma by hampering cell cycle progression, STAT3 signaling, and malignant phenotype of A375 melanoma cells.