Shikonin, dually functions as a proteasome inhibitor and a necroptosis inducer in multiple myeloma cells

Abstract

Shikonin (SHK), a natural small agent (MW 288.3), reportedly induces cell death in various tumor cells. We have found that SHK also exerts potent cytocidal effects on human multiple myeloma (MM) cells, but its anticancer mechanism in MM cells remains to be elucidated. SHK at 2.5–5 μM induced apoptosis in seven MM cell lines, including the bortezomib-resistant cell line KMS11/BTZ. The IC50 value of SHK against KMS11/BTZ was comparable to that of a parental cell line KMS11 (1.1 and 1.56 μM, respectively). SHK induces accumulation of ubiquitinated proteins and activates XBP-1 in MM cells, suggesting that SHK functions as a proteasome inhibitor, eventually inducing ER stress-associated apoptosis. SHK increases levels of HSP70/72, which protects cells from apoptosis, and exerts greater cytocidal effects in combination with the HSP70/72 inhibitor VER-155008. At higher concentrations (10–20 μM), SHK induced cell death, which was completely inhibited by a necroptosis inhibitor, necrostatin-1 (Nec-1), while the cytocidal activity was unaffected by Z-VAD-FMK, strongly suggesting that cell death is induced by SHK at high concentrations through necroptosis. The present data show for the first time that SHK induces cell death in MM cells. SHK efficiently induces apoptosis and combination of heat shock protein inhibitor with low dose SHK enhances apoptosis, while high dose SHK induces necroptosis in MM cells. These findings together support the use of SHK as a potential therapeutic agent for MM.

Necroptosis promotes autophagy-dependent upregulation of DAMP and results in immunosurveillance

“…18,19 Among these ICD drugs, shikonin (SK) is classified as a type I ICD inducer that promotes either apoptosis or necroptosis depending on the cell types and treatment regimens. [20][21][22][23][24][25][26][27] In this study, we show that SK can induce RIPK1/3-mediated necroptosis in mouse mammary tumor cells, 4T1-luc2 cells. The resultant necroptotic cell death was accompanied by enhanced autophagy, which was in turn generated by an elevated level of reactive oxygen species (ROS).…”

11-Methoxytabersonine Induces Necroptosis with Autophagy through AMPK/mTOR and JNK Pathways in Human Lung Cancer Cells

“…26) Recently, some natural products have been found to induce an alternative non-apoptotic death in cancer cells. For example, shikonin is the first natural compound reported to induce necroptosis in osteosarcoma, 28) glioma 29) and multiple myeloma cells 30) ; Curcumin induces extracellular signal-regulated kinase (ERK) or p38/JNK phosphorylation followed by production of abundant reactive oxygen species (ROS) that promote necroptosis in prostate cancer cells. 31) In this study, 11-MT induced necroptotic cell death in lung cancer cells.…”

Complex Pathologic Roles of RIPK1 and RIPK3: Moving Beyond Necroptosis

“…Furthermore, shikonin retained efficacy in cells expressing high levels of P-glycoprotein, which is one of the central mechanisms in acquiring multi-drug resistance by cancer cells [118]. Subsequent work demonstrated the ability of shikonin to induce necroptosis in cell lines representing a variety of cancer cell types, including glioma, breast cancer, osteosarcoma and multiple myeloma [119-122]. Interestingly, inhibition of necroptosis in various cell types has been shown to promote reversal of cell death phenotype and activation of apoptosis, suggesting that unlike many other in vitro experimental systems where apoptosis is induced first and is reverted to necroptosis in the presence of caspase inhibitors, shikonin preferentially promotes necroptosis even in apoptosis-competent cells.…”