Shikonin exerts antitumor activity via proteasome inhibition and cell death induction in vitro and in vivo

Abstract

Dysregulation of the ubiquitin-proteasome pathway plays an essential role in tumor growth and development. Shikonin, a natural naphthoquinone isolated from the traditional Chinese medicine Zi Cao (gromwell), has been reported to possess tumor cellkilling activity, and results from a clinical study using a shikonincontaining mixture demonstrated its safety and efficacy for the treatment of late-stage lung cancer. In this study, we reported that shikonin is an inhibitor of tumor proteasome activity in vitro and in vivo. Our computational modeling predicts that the carbonyl carbons C 1 and C 4 of shikonin potentially interact with the catalytic site of b5 chymotryptic subunit of the proteasome. Indeed, shikonin potently inhibits the chymotrypsin-like activity of purified 20S proteasome (IC 50 12.5 lmol/L) and tumor cellular 26S proteasome (IC 50 between 2-16 lmol/L). Inhibition of the proteasome by shikonin in murine hepatoma H22, leukemia P388 and human prostate cancer PC-3 cultures resulted in accumulation of ubiquitinated proteins and several proteasome target proapoptotic proteins (IjB-a, Bax and p27), followed by induction of cell death. Shikonin treatment resulted in tumor growth inhibition in both H22 allografts and PC-3 xenografts, associated with suppression of the proteasomal activity and induction of cell death in vivo. Finally, shikonin treatment significantly prolonged the survival period of mice bearing P388 leukemia. Our results indicate that the tumor proteasome is one of the cellular targets of shikonin and inhibition of the proteasome activity by shikonin contributes to its antitumor property.

Sanggenon C decreases tumor cell viability associated with proteasome inhibition

“…Cell death was quantified using an AnnexinV-FITC/PI kit and FACSCalibur flow cytometry as described previously (17). Cells were plated at a density of 2×10 5 cells per well in sixwell plates and incubated overnight, and were then treated with either vehicle or Sanggenon C as indicated.…”

Shikonin and its analogs inhibit cancer cell glycolysis by targeting tumor pyruvate kinase-M2

“…In the last four decades, shikonin, alkannin and their derivatives have been investigated as potential anticancer drugs for various aspects of cancer treatment (Ahn et al, 1995;Papageorgiou VP et al, 1999;Bailly, 2000;Kim et al, 2001;Masuda et al, 2003Masuda et al, , 2004Nakaya and Miyasaka, 2003;Han et al, 2007;Hu and Xuan, 2008;Xuan and Hu, 2009;Yang et al, 2009), including a clinical study (Guo et al, 1991), which indicated that a shikonin mixture was effective in treating 19 patients of later-stage lung cancer who were not suitable for operation, radiotherapy and chemotherapy. We previously reported that shikonin and its analogs induced cell death with characteristics of necroptosis, a basic cell death defined by Degterev et al and further studied in depth by the same group of scientists (Degterev et al, 2005Hitomi et al, 2008).…”

Shikonin blocks migration and invasion of human breast cancer cells through inhibition of matrix metalloproteinase-9 activation

“…Shikonin and its analogues can kill cancer cells through a number of mechanisms, including inhibition of topoisomerase-I (11), polo-like kinase 1 (PLK1) and protein tyrosine kinase (PTK) (12); regulation of phosphorylation-dependent activities of extracellular-regulated protein kinase (pERK), c-Jun N-terminal kinase (JNK) and protein kinase Ca (PKCa) (13); suppression of tumor necrosis factor receptor-associated protein 1 (TRAP1) expression (14); activation of caspases (15) and inhibition of proteasome activity (16). In previous studies, shikonin and its derivatives were shown to exert antiproliferative and pro-apoptotic effects against a number of tumor cells, including sarcoma 180 (S-180) ascites cells, gastric cancer, colon adenocarcinoma and oral cancer (17).…”