Shikonin Causes Non-apoptotic Cell Death in B16F10 Melanoma

Melanoma treatment is highly resistant to current chemotherapeutic agents. Due to its resistance towards apoptotic cell death, non-apoptotic cell death pathways are sought after.

We investigated a Chinese herbal medicine, shikonin, and its effect on B16F10 melanoma cells in vitro.

Cell growth of B16F10 melanoma cells treated with shikonin was analyzed using an MTT assay. Shikonin was combined with necrostatin, an inhibitor of necroptosis; caspase inhibitor; 3-methyladenine, an inhibitor of autophagy; or N-acetyl cysteine, an inhibitor of reactive oxygen species. Flow cytometry was used to assess types of cell death resulting from treatment with shikonin. Cell proliferation was also analyzed utilizing a BrdU labeling assay. Monodansylcadaverine staining was performed on live cells to gauge levels of autophagy. Western blot analysis was conducted to identify specific protein markers of necroptosis including CHOP, RIP1, and pRIP1. MitoTracker staining was utilized to identify differences in mitochondrial density in cells treated with shikonin.

Analysis of MTT assays revealed a large decrease in cellular growth with increasing shikonin concentrations. The MTT assays with necrostatin, 3-methyladenine, and N-acetyl cysteine involvement, suggested that necroptosis, autophagy, and reactive oxygen species are a part of shikonin's mechanism of action. Cellular proliferation with shikonin treatment was also decreased. Western blotting confirmed that shikonin-treated melanoma cells increase levels of stress-related proteins, e.g., CHOP, RIP, pRIP.

Our findings suggest that mainly necroptosis is induced by the shikonin treatment of B16F10 melanoma cells. Induction of ROS production and autophagy are also involved.