Silymarin inhibits melanoma cell growth both in vitro and in vivo by targeting cell cycle regulators, angiogenic biomarkers and induction of apoptosis

Abstract

Cutaneous malignant melanoma is the leading cause of death from skin diseases and is often associated with activating mutations of the proto-oncogene BRAF. To develop more effective strategies for the prevention or treatment of melanoma, we have examined the inhibitory effects of silymarin, a flavanoid from Silybum marianum, on melanoma cells. Using A375 (BRAF-mutated) and Hs294t (non BRAF-mutated but highly metastatic) human melanoma cell lines, we found that in vitro treatment with silymarin resulted in a dose-dependent: (i) reduction in cell viability; (ii) enhancement of either Go/G1 (A375) or G2-M (Hs294t) phase cell cycle arrest with corresponding alterations in cyclins and cyclin-dependent kinases; and (iii) induction of apoptosis. The silymarin-induced apoptosis of human melanoma cells was associated with a reduction in the levels of anti-apoptotic proteins (Bcl-2 and Bcl-xl), an increase in the levels of pro-apoptotic protein (Bax), and activation of caspases. Further, oral administration of silymarin (500 mg/kg body weight/2× a week) significantly inhibited (60%, P < 0.01) the growth of BRAF-mutated A375 melanoma tumor xenografts, and this was associated with: (i) inhibition of cell proliferation; (ii) induction of apoptosis of tumor cells; (iii) alterations in cell cycle regulatory proteins; and (iv) reduced expression of tumor angiogenic biomarkers in tumor xenograft tissues. These results indicate that silymarin may have a chemotherapeutic effect on human melanoma cell growth and warrant its further evaluation.

Estrogen Receptor β in Melanoma: From Molecular Insights to Potential Clinical Utility

“…It was found that this flavonoid prevents UV irradiation-induced apoptosis of these cells, through the activation of the Akt and SIRT1 pathways (197–199). On the other hand, silymarin has been recently shown to inihibit melanoma cell growth both in vitro and in vivo (200, 201) and to induce cell cycle arrest in melanoma cells directly targeting the MEK1/2 pathway (202). Moreover, Vaid and coworkers (203) investigated the effects of silymarin on the metastatic properties of human melanoma cell lines.…”

Silymarin antiproliferative and apoptotic effects: Insights into its clinical impact in various types of cancer

“…In Hs294t cells, silymarin, also in a dose‐dependent manner, reduced cyclin B1, Cdc25B, and Cdc25C expression, which are involved in G2‐M phase regulation of the cell cycle. A study with mice melanoma model exhibited similar results and showed that PCNA, cyclins, and Cdks levels in tumor xenografts lysates were lower, and Cdk inhibitory proteins, including Cip1/p21 and Kip1/p27, were higher, in silymarin‐treated mice when compared with vehicle‐treated control mice (Vaid et al, ).…”

“…Moreover, a significant decrease in S-phase arrest was stated in A375 cells (Vaid, Singh, Prasad, & Katiyar, 2015), but an arrest at G2/M phase and remarkable cell death was also reported in Jurkat cells treated with high silymarin doses (Gharagozloo & Amirghofran, 2007).…”

“…Specifically, silymarin, at a dose‐dependent manner, resulted in an improvement of G0/G1 arrest in A375 cells, as a human melanoma cell lines, and G2‐M arrest in Hs294t cells, as a highly metastatic human melanoma cell lines, as well as in a reduction in cellular viability. Moreover, a significant decrease in S‐phase arrest was stated in A375 cells (Vaid, Singh, Prasad, & Katiyar, ), but an arrest at G2/M phase and remarkable cell death was also reported in Jurkat cells treated with high silymarin doses (Gharagozloo & Amirghofran, ).…”

“…This natural compound, in a dose‐dependent manner, also led to a decrease in cyclins (D1 and D2) and Cdk proteins (Cdk2, Cdk4, and Cdk6) expression. Moreover, the levels of Cdks inhibitory proteins, such as Cip1/p21 and Kip1/p27, were increased (Vaid et al, ). In Hs294t cells, silymarin, also in a dose‐dependent manner, reduced cyclin B1, Cdc25B, and Cdc25C expression, which are involved in G2‐M phase regulation of the cell cycle.…”