Synthesis and Pharmacological In Vitro Investigations of Novel Shikonin Derivatives with a Special Focus on Cyclopropane Bearing Derivatives

Abstract

Melanoma is the deadliest form of skin cancer and accounts for about three quarters of all skin cancer deaths. Especially at an advanced stage, its treatment is challenging, and survival rates are very low. In previous studies, we showed that the constituents of the roots of Onosma paniculata as well as a synthetic derivative of the most active constituent showed promising results in metastatic melanoma cell lines. In the current study, we address the question whether we can generate further derivatives with optimized activity by synthesis. Therefore, we prepared 31, mainly novel shikonin derivatives and screened them in different melanoma cell lines (WM9, WM164, and MUG-Mel2 cells) using the XTT viability assay. We identified (R)-1-(1,4-dihydro-5,8-dihydroxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-3-enyl 2-cyclopropyl-2-oxoacetate as a novel derivative with even higher activity. Furthermore, pharmacological investigations including the ApoToxGloTM Triplex assay, LDH assay, and cell cycle measurements revealed that this compound induced apoptosis and reduced cells in the G1 phase accompanied by an increase of cells in the G2/M phase. Moreover, it showed hardly any effects on the cell membrane integrity. However, it also exhibited cytotoxicity against non-tumorigenic cells. Nevertheless, in summary, we could show that shikonin derivatives might be promising drug leads in the treatment of melanoma.

Shikonin Derivatives Inhibit Inflammation Processes and Modulate MAPK Signaling in Human Healthy and Osteoarthritis Chondrocytes

“…Shikonin and acetylshikonin are naturally occurring shikonin derivatives [ 15 , 16 , 17 ]. Cyclopropylshikonin was synthesized in a previous study and found to be the most cytotoxic compound out of a screening of novel shikonin derivatives [ 18 ]. It could be previously shown that the naphthoquinone scaffold, including the hydroxyl groups, is important for the activity of shikonin derivatives.…”

“…It could be previously shown that the naphthoquinone scaffold, including the hydroxyl groups, is important for the activity of shikonin derivatives. Moreover, the side chain was reported to further influence the overall activity [ 18 ]. Both HC and pCH-OA showed a dose-dependent inhibition of cell viability after treatment with shikonin derivatives ( Figure 1 B).…”

“…The IC 50 values of acetylshikonin were 2.4 µM and 2.1 µM, and the values for the novel derivate cyclopropylshikonin were 1.6 µM and 1.8 µM. The values are lower than those determined for melanoma cells and human embryonic kidney (HEK293) cells, indicating that human chondrocytes might be more sensitive to shikonin [ 18 ].…”

“…Furthermore, several attempts have been made to optimize the naturally occurring shikonin derivatives by modulating the structure. One of these novel synthetic derivatives is cyclopropylshikonin, which has already shown promising anti-cancer effects in melanoma cells [ 18 ].…”

SK119, a Novel Shikonin Derivative, Leads to Apoptosis in Melanoma Cell Lines and Exhibits Synergistic Effects with Vemurafenib and Cobimetinib

“…Firstly, among other derivatives, we developed a novel shikonin derivative—cyclopropylacetylshikonin—which was more effective against two metastatic melanoma cell lines than DMAS [ 14 ]. A similar derivative bearing another cyclopropane moiety was also shown by our group to exhibit promising effects in melanoma cell lines [ 15 ]. In the current study, we report on the synthesis and pharmacological effects of another novel shikonin derivative (SK119), which is active in a nano-molar range and exhibited several promising in vitro effects.…”