The molecular mechanisms and gene expression profiling for shikonin-induced apoptotic and necroptotic cell death in U937 cells

Acetylshikonin induces necroptosis via the RIPK1/RIPK3-dependent pathway in lung cancer

Despite advances in therapeutic strategies, lung cancer remains the leading cause of cancer-related death worldwide. Acetylshikonin is a derivative of the traditional Chinese medicine Zicao and presents a variety of anticancer properties. However, the effects of acetylshikonin on lung cancer have not been fully understood yet. This study explored the mechanisms underlying acetylshikonin-induced cell death in non-small cell lung cancer (NSCLC). Treating NSCLC cells with acetylshikonin significantly reduced cell viability, as evidenced by chromatin condensation and the appearance of cell debris. Acetylshikonin has also been shown to increase cell membrane permeability and induce cell swelling, leading to an increase in the population of necrotic cells. When investigating the mechanisms underlying acetylshikonin-induced cell death, we discovered that acetylshikonin promoted oxidative stress, decreased mitochondrial membrane potential, and promoted G2/M phase arrest in lung cancer cells. The damage to NSCLC cells induced by acetylshikonin resembled results involving alterations in the cell membrane and mitochondrial morphology. Our analysis of oxidative stress revealed that acetylshikonin induced lipid oxidation and down-regulated the expression of glutathione peroxidase 4 (GPX4), which has been associated with necroptosis. We also determined that acetylshikonin induces the phosphorylation of receptor-interacting serine/threonine-protein kinase 1 (RIPK1)/RIPK3 and mixed lineage kinase domain-like kinase (MLKL). Treatment with RIPK1 inhibitors (necrostatin-1 or 7-Cl-O-Nec-1) significantly reversed acetylshikonin-induced MLKL phosphorylation and NSCLC cell death. These results indicate that acetylshikonin activated the RIPK1/RIPK3/MLKL cascade, leading to necroptosis in NSCLC cells. Our findings indicate that acetylshikonin reduces lung cancer cells by promoting G2/M phase arrest and necroptosis.

Discovery of Sulforaphane as an Inducer of Ferroptosis in U-937 Leukemia Cells: Expanding Its Anticancer Potential

In recent years, natural compounds have emerged as inducers of non-canonical cell death. The isothiocyanate sulforaphane (SFN) is a well-known natural anticancer compound with remarkable pro-apoptotic activity. Its ability to promote non-apoptotic cell-death mechanisms remains poorly investigated. This work aimed to explore the capacity of SFN to induce non-apoptotic cell death modalities. SFN was tested on different acute myeloid leukemia cell lines. The mechanism of cell death was investigated using a multi-parametric approach including fluorescence microscopy, western blotting, and flow cytometry. SFN triggered different cell-death modalities in a dose-dependent manner. At 25 μM, SFN induced caspase-dependent apoptosis and at 50 μM ferroptosis was induced through depletion of glutathione (GSH), decreased GSH peroxidase 4 protein expression, and lipid peroxidation. In contrast, necroptosis was not involved in SFN-induced cell death, as demonstrated by the non-significant increase in phosphorylation of receptor-interacting protein kinase 3 and phosphorylation of the necroptotic effector mixed lineage kinase domain-like pseudokinase. Taken together, our results suggest that the antileukemic activity of SFN can be mediated via both ferroptotic and apoptotic cell death modalities.

Molecular mechanism of shikonin inhibiting tumor growth and potential application in cancer treatment

Shikonin is one of the major bioactive components of Lithospermum erythrorhizon. It has a good killing effect in a variety of tumor cells. Its antitumor effect involves multiple targets and pathways and has received extensive attention and study in recent years. In this review, we systematically review recent progress in determining the antitumor mechanism of shikonin and its derivatives, specifically their induction of reactive oxygen species production, inhibition of EGFR and PI3K/AKT signaling pathway activation, inhibition of angiogenesis and induction of apoptosis and necroptosis. We also discuss the application of nanoparticles loaded with shikonin in the targeted therapy of various cancers. Finally, we suggest new strategies for the clinical application of shikonin and its derivatives.

Targeting Drug Chemo-Resistance in Cancer Using Natural Products

Cancer is one of the leading causes of death globally. The development of drug resistance is the main contributor to cancer-related mortality. Cancer cells exploit multiple mechanisms to reduce the therapeutic effects of anticancer drugs, thereby causing chemotherapy failure. Natural products are accessible, inexpensive, and less toxic sources of chemotherapeutic agents. Additionally, they have multiple mechanisms of action to inhibit various targets involved in the development of drug resistance. In this review, we have summarized the basic research and clinical applications of natural products as possible inhibitors for drug resistance in cancer. The molecular targets and the mechanisms of action of each natural product are also explained. Diverse drug resistance biomarkers were sensitive to natural products. P-glycoprotein and breast cancer resistance protein can be targeted by a large number of natural products. On the other hand, protein kinase C and topoisomerases were less sensitive to most of the studied natural products. The studies discussed in this review will provide a solid ground for scientists to explore the possible use of natural products in combination anticancer therapies to overcome drug resistance by targeting multiple drug resistance mechanisms.

The Pro-Apoptotic Effect of Silica Nanoparticles Depends on Their Size and Dose, as Well as the Type of Glioblastoma Cells

Despite intensive investigations, nanoparticle-induced cellular damage is an important problem that has not been fully elucidated yet. Here, we report that silica nanoparticles (SiNPs) demonstrated anticancer influence on glioblastoma cells by the induction of apoptosis or necrosis. These effects are highly cell type-specific, as well as dependent on the size and dose of applied nanoparticles. Exposure of LN-18 and LBC3 cells to different sizes of SiNPs-7 nm, 5-15 nm, or 10-20 nm-at dosages, ranging from 12.5 to 1000 µg/mL, for 24 and 48 h reduced the viability of these cells. Treatment of LN-18 and LBC3 cells with 7 nm or 10-20 nm SiNPs at doses ≥50 µg/mL caused a strong induction of apoptosis, which is connected with an increase of intracellular reactive oxygen species (ROS) production. The 5-15 nm SiNPs exhibited distinct behavior comparing to silica nanoparticles of other studied sizes. In contrast to LBC3, in LN-18 cells exposed to 5-15 nm SiNPs we did not observe any effect on apoptosis. These nanoparticles exerted only strong necrosis, which was connected with a reduction in ROS generation. This suggests that SiNPs can trigger different cellular/molecular effects, depending on the exposure conditions, the size and dose of nanoparticles, and cell type of glioblastoma.

Natural Products as Inducers of Non-Canonical Cell Death: A Weapon against Cancer

Simple Summary

Anticancer therapeutic approaches based solely on apoptosis induction are often unsuccessful due to the activation of resistance mechanisms. The identification and characterization of compounds capable of triggering non-apoptotic, also called non-canonical cell death pathways, could represent an important strategy that may integrate or offer alternative approaches to the current anticancer therapies. In this review, we critically discuss the promotion of ferroptosis, necroptosis, and pyroptosis by natural compounds as a new anticancer strategy.

Abstract

Apoptosis has been considered the main mechanism induced by cancer chemotherapeutic drugs for a long time. This paradigm is currently evolving and changing, as increasing evidence pointed out that antitumor agents could trigger various non-canonical or non-apoptotic cell death types. A considerable number of antitumor drugs derive from natural sources, both in their naturally occurring form or as synthetic derivatives. Therefore, it is not surprising that several natural compounds have been explored for their ability to induce non-canonical cell death. The aim of this review is to highlight the potential antitumor effects of natural products as ferroptosis, necroptosis, or pyroptosis inducers. Natural products have proven to be promising non-canonical cell death inducers, capable of overcoming cancer cells resistance to apoptosis. However, as discussed in this review, they often lack a full characterization of their antitumor activity together with an in-depth investigation of their toxicological profile.

Visualization of Necroptotic Cell Death through Transmission Electron Microscopy

Transmission electron microscopy (TEM) is an all-in-one tool to visualize the complex systems of any specimen that is 1 nm in size or smaller. The current chapter provides detailed guidelines for imaging morphological changes during programmed cell necrosis using TEM as a single-step methodology. In this protocol, a novel aldehyde dehydrogenase inhibitor is used to induce cell programmed necrosis in ovarian cancer cell lines (A2780 and SKOV3). This process is followed by gradient dehydration with ethanol, chemical fixation, sampled grid preparation, and staining with 0.75% uranyl formate. Following fixation and grid preparation, cells are imaged using TEM. The resulting images reveal morphological changes consistent with necrotic morphology, including swelling of cells and organelles, appearance of vacuoles, and plasma membrane rupture followed by leakage of cellular contents. The current approach allows a single-step methodology for characterization of cell-programmed necrosis in cells based on morphology.

Isobutyrylshikonin has a potentially stronger cytotoxic effect in oral cancer cells than its analogue shikonin in vitro

OBJECTIVES

The aim of the present study was to identify the anticancer effects and the mechanisms of action of shikonin and its analogue isobutyrylshikonin in oral squamous carcinoma cells.

DESIGNS

The cytotoxic effects of isobutyrylshikonin and shikonin in Ca9-22 and SCC-25 cells were analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry analysis of Annexin V/Propidium Iodide (PI) staining, western blot analysis and immunohistochemistry.

RESULTS

Treatment with both isobutyrylshikonin and shikonin induced dose- and time-dependent apoptotic cell death in Ca9-22 cells, although the IC₅₀ of isobutyrylshikonin was less than that of shikonin. The induction of apoptosis by both isobutyrylshikonin and shikonin was accompanied by activation of caspase-8, -9, -3, and PARP, loss of mitochondrial trans-membrane potential, and release of cytochrome c from the mitochondria. ROS mediated the apoptosis induced by isobutyrylshikonin and shikonin, indicating that ROS may play a critical role in the distinctive cytotoxic effects of isobutyrylshikonin and shikonin in Ca9-22. Isobutyrylshikonin showed a similar cytotoxic effect in SCC-25 cells at concentrations showing the effects in Ca9 cells, but not in human normal keratinocyte cells. Although there is no biological difference between isobutyrylshikonin and shikonin, isobutyrylshikonin exerts the same cytotoxic effect at a concentration 6 times lower than shikonin.

CONCLUSIONS

The present study suggest that isobutyrylshikonin may be a more potent chemotherapeutic agent against oral cancer cells than shikonin. In addition, our data exhibit that both isobutyrylshikonin and shikonin induce caspase-dependent apoptosis via the mitochondrial pathway through accumulation of ROS in oral squamous carcinoma cells.

Cutting off the fuel supply to calcium pumps in pancreatic cancer cells: role of pyruvate kinase-M2 (PKM2)

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) has poor survival and treatment options. PDAC cells shift their metabolism towards glycolysis, which fuels the plasma membrane calcium pump (PMCA), thereby preventing Ca2+-dependent cell death. The ATP-generating pyruvate kinase-M2 (PKM2) is oncogenic and overexpressed in PDAC. This study investigated the PKM2-derived ATP supply to the PMCA as a potential therapeutic locus.

METHODS

PDAC cell growth, migration and death were assessed by using sulforhodamine-B/tetrazolium-based assays, gap closure assay and poly-ADP ribose polymerase (PARP1) cleavage, respectively. Cellular ATP and metabolism were assessed using luciferase/fluorescent-based assays and the Seahorse XFe96 analyzer, respectively. Cell surface biotinylation identified membrane-associated proteins. Fura-2 imaging was used to assess cytosolic Ca2+ overload and in situ Ca2+ clearance. PKM2 knockdown was achieved using siRNA.

RESULTS

The PKM2 inhibitor (shikonin) reduced PDAC cell proliferation, cell migration and induced cell death. This was due to inhibition of glycolysis, ATP depletion, inhibition of PMCA and cytotoxic Ca2+ overload. PKM2 associates with plasma membrane proteins providing a privileged ATP supply to the PMCA. PKM2 knockdown reduced PMCA activity and reduced the sensitivity of shikonin-induced cell death.

CONCLUSIONS

Cutting off the PKM2-derived ATP supply to the PMCA represents a novel therapeutic strategy for the treatment of PDAC.

Pharmacological properties and derivatives of shikonin-A review in recent years

Shikonin is the major bioactive component extracted from the roots of Lithospermum erythrorhizon which is also known as "Zicao" in Traditional Chinese Medicine (TCM). Recent studies have shown that shikonin demonstrates various bioactivities related to the treatment of cancer, inflammation, and wound healing. This review aimed to provide an updated summary of recent studies on shikonin. Firstly, many studies have demonstrated that shikonin exerts strong anticancer effects on various types of cancer by inhibiting cell proliferation and migration, inducing apoptosis, autophagy, and necroptosis. Shikonin also triggers Reactive Oxygen Species (ROS) generation, suppressing exosome release, and activate anti-tumor immunity in multiple molecular mechanisms. Examples of these effects include modulating the PI3K/AKT/mTOR and MAPKs signaling; inhibiting the activation of TrxR1, PKM2, RIP1/3, Src, and FAK; and regulating the expression of ERP57, MMPs, ATF2, C-MYC, miR-128, and GRP78 (Bip). Next, the anti-inflammatory and wound-healing properties of shikonin were also reviewed. Furthermore, several studies focusing on shikonin derivatives were reviewed, and these showed that, with modification to the naphthazarin ring or side chain, some shikonin derivatives display stronger anticancer activity and lower toxicity than shikonin itself. Our findings suggest that shikonin and its derivatives could serve as potential novel drug for the treatment of cancer and inflammation.

Shikonin derivatives for cancer prevention and therapy

Phytochemicals gained considerable interest during the past years as source to develop new treatment options for chemoprevention and cancer therapy. Motivated by the fact that a majority of established anticancer drugs are derived in one way or another from natural resources, we focused on shikonin, a naphthoquinone with high potentials to be further developed as preventive or therapeutic drug to fight cancer. Shikonin is the major chemical component of Lithospermum erythrorhizon (Purple Cromwell) roots. Traditionally, the root extract has been applied to cure dermatitis, burns, and wounds. Over the past three decades, the anti-inflammatory and anticancer effects of root extracts, isolated shikonin as well as semi-synthetic and synthetic derivatives and nanoformulations have been described. In vitro and in vivo experiments were conducted to understand the effect of shikonin at cellular and molecular levels. Preliminary clinical trials indicate the potential of shikonin for translation into clinical oncology. Shikonin exerts additive and synergistic interactions in combination with established chemotherapeutics, immunotherapeutic approaches, radiotherapy and other treatment modalities, which further underscores the potential of this phytochemical to be integrated into standard treatment regimens.

Redox biology of regulated cell death in cancer: A focus on necroptosis and ferroptosis

Redox changes and generation of reactive oxygen species (ROS) are part of normal cell metabolism. While low ROS levels are implicated in cellular signaling pathways necessary for survival, higher levels play major roles in cancer development as well as cell death signaling and execution. A role for redox changes in apoptosis has been long established; however, several new modalities of regulated cell death have been brought to light, for which the importance of ROS production as well as ROS source and targets are being actively investigated. In this review, we summarize recent findings on the role of ROS and redox changes in the activation and execution of two major forms of regulated cell death, necroptosis and ferroptosis. We also discuss the potential of using modulators of these two forms of cell death to exacerbate ROS as a promising anticancer therapy.

Transcriptomic Profiling of MDA-MB-231 Cells Exposed to Boswellia Serrata and 3-O-Acetyl-B-Boswellic Acid; ER/UPR Mediated Programmed Cell Death

BACKGROUND/AIM

Triple-negative breast cancer (TNBC) is characterized by the absence of hormone receptors (estrogen, progesterone and human epidermal growth factor receptor-2) and a relatively poor prognosis due to inefficacy of hormone receptor-based chemotherapies. It is imperative that we continue to explore natural products with potential to impede growth and metastasis of TNBC. In this study, we screened over 1,000 natural products for capacity to induce cell death in TNBC (MDA-MB -231) cells.

MATERIALS AND METHODS

Frankincense (Boswellia serrata extract (BSE)) and 3-O-Acetyl-β-boswellic acid (3-OAβBA) were relatively potent, findings that corroborate the body of existing literature. The effects of BSE and 3-OAβBA on genetic parameters in MDA-MB-231 cells were evaluated by examining whole-transcriptomic influence on mRNAs, long intergenic non-coding RNA transcripts (lincRNA) and non-coding miRNAs.

RESULTS

Bio-statistical analysis demarcates the primary effect of both BSE/3-OAβBA on the up-regulation of PERK (protein kinase RNA-like endoplasmic reticulum kinase)- endoplasmic reticulum (ER)/unfolded protein response (UPR) pathways that are closely tied to activated programmed cell death (APCD). Global profiling confirms concomitant effects of BSE/3-OAβBA on upwardly expressed ER/URP APCD key components PERK (EIF2AK3), XBP1, C/EBP homologous protein transcription factor (CHOP), ATF3 and DDIT3,4/DNA-damage-inducible transcript 3,4 (GADD34). Further, BSE and/or 3-OAβBA significantly down-regulated oncogenes (OG) which, heretofore, lack functional pathway mapping, but are capable of driving epithelial-mesenchymal transition (EMT), cell survival, proliferation, metastasis and drug resistance. Among these are cell migration-inducing protein hyaluronan binding (CEMIP) [-7.22]; transglutaminase 2 [-4.96], SRY box 9 (SOX9) [-4.09], inhibitor of DNA binding 1, dominant negative helix-loop-helix protein (ID1) [-6.56]; and endothelin 1 (EDN1, [-5.06]). Likewise, in the opposite manner, BSE and/or 3-OAβBA induced the robust overexpression of tumor suppressor genes (TSGs), including: glutathione-depleting ChaC glutathione-specific gamma-glutamylcyclotransferase 1 (CHAC1) [+21.67]; the mTOR inhibitors - sestrin 2 (SESN2) [+16.4] Tribbles homolog 3 (TRIB3) [+6.2], homocysteine-inducible, endoplasmic reticulum stress-inducible, ubiquitin-like domain member 1 (HERPUD1) [+12.01]; and cystathionine gamma-lyase (CTH) [+11.12].

CONCLUSION

The anti-cancer effects of the historically used frankincense sap (BSE) appear to involve major impact on the ER/UPR response, concomitant to effecting multiple targets counter to the growth, proliferation and metastasis of TNBC cancer cells. The microarray data are available at Expression Omnibus GEO Series accession number GSE102891.

Metabolic profiling study of shikonin's cytotoxic activity in the Huh7 human hepatoma cell line

Shikonin and its enantiomer alkannin, which are natural products, have been extensively studied in vitro and in vivo for, among others, their antitumor activity. The investigation of the molecular pathways involved in their action is of interest, since they are not yet clearly defined. Metabolic profiling in cells can provide a picture of a cell's phenotype upon intervention, assisting in the elucidation of the mechanism of action. In this study, the cytotoxic effect of shikonin on a human hepatocarcinoma cell line was studied. Huh7 cells were treated with shikonin at 5 μM, and it was found that shikonin markedly inhibited cell growth. Metabolic profiling indicated alterations in the metabolic content of the cells and the culture media upon treatment, detecting the metabolic response of the cells. This study demonstrates the potential of metabolomics to improve knowledge on the mechanisms involved in shikonin's antitumor action.

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

Programmed necrosis, necroptosis, is considered to be a highly immunogenic activity, often mediated via the release of damage-associated molecular patterns (DAMPs). Interestingly, enhanced macroautophagic/autophagic activity is often found to be accompanied by necroptosis. However, the possible role of autophagy in the immunogenicity of necroptotic death remains largely obscure. In this study, we investigated the possible mechanistic correlation between phytochemical shikonin-induced autophagy and the shikonin-induced necroptosis for tumor immunogenicity. We show that shikonin can instigate RIPK1 (receptor [TNFRSF]-interacting serine-threonine kinase 1)- and RIPK3 (receptor-interacting serine-threonine kinase 3)-dependent necroptosis that is accompanied by enhanced autophagy. Shikonin-induced autophagy can directly contribute to DAMP upregulation. Counterintuitively, among the released and ectoDAMPs, only the latter were shown to be able to activate the cocultured dendritic cells (DCs). Interruption of autophagic flux via chloroquine further upregulated ectoDAMP activity and resultant DC activation. For potential clinical application, DC vaccine preparations treated with tumor cells that were already pretreated with chloroquine and shikonin further enhanced the antimetastatic activity of 4T1 tumors and reduced the effective dosage of doxorubicin. The enhanced immunogenicity and vaccine efficacy obtained via shikonin and chloroquine cotreatment of tumor cells may thus constitute a compelling strategy for developing cancer vaccines via the use of a combinational drug treatment.

Shikonin induces ROS-based mitochondria-mediated apoptosis in colon cancer

Colon cancer is the third most common malignancy worldwide, and chemotherapy is a widely used strategy in clinical therapy. Chemotherapy-resistant of colon cancer is the main cause of recurrence and progression. Novel drugs with efficacy and safety in treating colon cancer are urgently needed. Shikonin, a naphthoquinone derived from the roots of the herbal plant Lithospermum erythrorhizon, has been determined to be a potent anti-tumor agent. The aim of the present study was to detect the underlying anti-tumor mechanism of shikonin in colon cancer. We found that shikonin suppressed the growth of colon cancer cells in a dose-dependent manner in vitro and in vivo. Shikonin induced mitochondria-mediated apoptosis, which was regulated by Bcl-2 family proteins. Shikonin increased the generation of intracellular ROS, which played an upstream role in shikonin-induced apoptosis. Our data indicated that generation of ROS, down-regulated expression of Bcl-2 and Bcl-xL, depolarization of the mitochondrial membrane potential and activation of the caspase cascade were components of the programmed event of shikonin-induced apoptosis in colon cancer cells. In addition, shikonin presented minimal toxicity to non-neoplastic colon cells and no liver injury in xenograft models, showing safety in the control of colon cancer cell growth in vitro and in vivo. Taken together, our findings suggest that shikonin might serve as a potential novel therapeutic drug in the treatment of human colon cancer.

Shikonin induces glioma cell necroptosis in vitro by ROS overproduction and promoting RIP1/RIP3 necrosome formation

Necroptosis is a type of programmed necrosis regulated by receptor interacting protein kinase 1 (RIP1) and RIP3. Necroptosis is found to be accompanied by an overproduction of reactive oxygen species (ROS), but the role of ROS in regulation of necroptosis remains elusive. In this study, we investigated how shikonin, a necroptosis inducer for cancer cells, regulated the signaling leading to necroptosis in glinoma cells in vitro. Treatment with shikonin (2-10 μmol/L) dose-dependently triggered necrosis and induced overproduction of intracellular ROS in rat C6 and human SHG-44, U87 and U251 glioma cell lines. Moreover, shikonin treatment dose-dependently upregulated the levels of RIP1 and RIP3 and reinforced their interaction in the glioma cells. Pretreatment with the specific RIP1 inhibitor Nec-1 (100 μmol/L) or the specific RIP3 inhibitor GSK-872 (5 μmol/L) not only prevented shikonin-induced glioma cell necrosis but also significantly mitigated the levels of intracellular ROS and mitochondrial superoxide. Mitigation of ROS with MnTBAP (40 μmol/L), which was a cleaner of mitochondrial superoxide, attenuated shikonin-induced glioma cell necrosis, whereas increasing ROS levels with rotenone, which improved the mitochondrial generation of superoxide, significantly augmented shikonin-caused glioma cell necrosis. Furthermore, pretreatment with MnTBAP prevented the shikonin-induced upregulation of RIP1 and RIP3 expression and their interaction while pretreatment with rotenone reinforced these effects. These findings suggest that ROS is not only an executioner of shikonin-induced glioma cell necrosis but also a regulator of RIP1 and RIP3 expression and necrosome assembly.

3-O-trans-p-coumaroyl-alphitolic acid, a triterpenoid from Zizyphus jujuba, leads to apoptotic cell death in human leukemia cells through reactive oxygen species production and activation of the unfolded protein response

3-O-trans-p-coumaroyl-alphitolic acid (3OTPCA), a triterpenoid isolated from the plant Zizyphus jujuba (ZJ), is known to be cytotoxic to cancer cells; however, the molecular mechanism underlying 3OTPCA-induced cell death remains unknown. Here, we provide novel evidence that 3OTPCA induces apoptotic cell death in human leukemia cells. We found that 3OPTCA induces DNA fragmentation within 24 h after treatment in U937 cells, which was also observed in other leukemia cell lines, including Molt-4 and Jurkat cells. We then investigated other parameters involved in apoptosis, including phosphatidylserine externalization and caspase-3 cleavage in U937 cells treated with 3OTPCA. 3OTPCA caused significant DNA fragmentation, annexin-V binding, and caspase-3 cleavage, indicating that 3OTPCA exerts cytotoxicity through apoptosis induction. RNA-seq analysis revealed that the expression of transcripts associated with the unfolded protein response (UPR), such as spliced XBP-1 and CHOP, were up-regulated by 3OTPCA treatment. 3OTPCA-induced UPR activation may be due to endoplasmic reticulum (ER) stress because both 3OTPCA and thapsigargin, an endoplasmic Ca²⁺ transport ATPase inhibitor, increased intracellular calcium levels. 3OTPCA down-regulated the expression of Bcl-2, a target of CHOP, and led to the loss of the mitochondrial membrane, indicating that the intrinsic (mitochondrial) apoptotic pathway was triggered by 3OTPCA, likely through UPR activation. Furthermore, we found that 3OTPCA induced superoxide anion generation and, following p38 MAPK phosphorylation, caspase-8 cleavage without affecting Fas expression. It also induced subsequent Bid cleavage, which may enhance the apoptosis triggered by the intrinsic pathway. These findings reveal for the first time that 3OTPCA induces apoptotic cell death through the generation of reactive oxygen species and activation of UPR.

Natural Compounds As Modulators of Non-apoptotic Cell Death in Cancer Cells

Cell death is an innate capability of cells to be removed from microenvironment, if and when they are damaged by multiple stresses. Cell death is often regulated by multiple molecular pathways and mechanism, including apoptosis, autophagy, and necroptosis. The molecular network underlying these processes is often intertwined and one pathway can dynamically shift to another one acquiring certain protein components, in particular upon treatment with various drugs. The strategy to treat human cancer ultimately relies on the ability of anticancer therapeutics to induce tumor-specific cell death, while leaving normal adjacent cells undamaged. However, tumor cells often develop the resistance to the drug-induced cell death, thus representing a great challenge for the anticancer approaches. Numerous compounds originated from the natural sources and biopharmaceutical industries are applied today in clinics showing advantageous results. However, some exhibit serious toxic side effects. Thus, novel effective therapeutic approaches in treating cancers are continued to be developed. Natural compounds with anticancer activity have gained a great interest among researchers and clinicians alike since they have shown more favorable safety and efficacy then the synthetic marketed drugs. Numerous studies in vitro and in vivo have found that several natural compounds display promising anticancer potentials. This review underlines certain information regarding the role of natural compounds from plants, microorganisms and sea life forms, which are able to induce non-apoptotic cell death in tumor cells, namely autophagy and necroptosis.

Shikonin induces mitochondria-mediated apoptosis and enhances chemotherapeutic sensitivity of gastric cancer through reactive oxygen species

The prognosis of gastric cancer remains poor due to clinical drug resistance. Novel drugs are urgently needed. Shikonin (SHK), a natural naphthoquinone, has been reported to trigger cell death and overcome drug resistance in anti-tumour therapy. In this study, we investigated the effectiveness and molecular mechanisms of SHK in treatment with gastric cancer. In vitro, SHK suppresses proliferation and triggers cell death of gastric cancer cells but leads minor damage to gastric epithelial cells. SHK induces the generation of intracellular reactive oxygen species (ROS), depolarizes the mitochondrial membrane potential (MMP) and ultimately triggers mitochondria-mediated apoptosis. We confirmed that SHK induces apoptosis of gastric cancer cells not only in a caspase-dependent manner which releases Cytochrome C and triggers the caspase cascade, but also in a caspase-independent manner which mediates the nuclear translocation of apoptosis-inducing factor and Endonuclease G. Furthermore, we demonstrated that SHK enhanced the chemotherapeutic sensitivity of 5-fluorouracil and oxaliplatin in vitro and in vivo. Taken together, our data show that SHK may be a novel therapeutic agent in the clinical treatment of gastric cancer.

Inhibition of c-MYC with involvement of ERK/JNK/MAPK and AKT pathways as a novel mechanism for shikonin and its derivatives in killing leukemia cells

Leukemia remains life-threatening despite remarkable advances in chemotherapy. The poor prognosis and drug resistance are challenging treatment. Novel drugs are urgently needed. Shikonin, a natural naphthoquinone, has been previously shown by us to be particularly effective towards various leukemia cell lines compared to solid tumors. However, the underlying mechanisms are still poorly understood. Here, we investigated shikonin and 14 derivatives on U937 leukemia cells. Four derivatives (isobutyrylshikonin, 2-methylbutyrylshikonin, isovalerylshikonin and β,β-dimethylacrylshikonin) were more active than shikonin. AnnexinV-PI analysis revealed that shikonins induced apoptosis. Cell cycle G1/S check point regulation and the transcription factor c-MYC, which plays a vital role in cell cycle regulation and proliferation, were identified as the most commonly down-regulated mechanisms upon treatment with shikonins in mRNA microarray hybridizations. Western blotting and DNA-binding assays confirmed the inhibition of c-MYC expression and transcriptional activity by shikonins. Reduction of c-MYC expression was closely associated with deregulated ERK, JNK MAPK and AKT activity, indicating their involvement in shikonin-triggered c-MYC inactivation. Molecular docking studies revealed that shikonin and its derivatives bind to the same DNA-binding domain of c-MYC as the known c-MYC inhibitors 10058-F4 and 10074-G5. This finding indicates that shikonins bind to c-MYC. The effect of shikonin on U937 cells was confirmed in other leukemia cell lines (Jurkat, Molt4, CCRF-CEM, and multidrug-resistant CEM/ADR5000), where shikonin also inhibited c-MYC expression and influenced phosphorylation of AKT, ERK1/2, and SAPK/JNK. In summary, inhibition of c-MYC and related pathways represents a novel mechanism of shikonin and its derivatives to explain their anti-leukemic activity.

FTY720 induces autophagy-related apoptosis and necroptosis in human glioblastoma cells

FTY720 is a potent immunosuppressant which has preclinical antitumor efficacy in various cancer models. However, its role in glioblastoma remains unclear. In the present study, we found that FTY720 induced extrinsic apoptosis, necroptosis and autophagy in human glioblastoma cells. Inhibition of autophagy by either RNA interference or chemical inhibitors attenuated FTY720-induced apoptosis and necrosis. Furthermore, autophagy, apoptosis and necrosis induction were dependent on reactive oxygen species-c-Jun N-terminal kinase-protein 53 (ROS-JNK-p53) loop mediated phosphatidylinositide 3-kinases/protein kinase B/mammalian target of rapamycin/p70S6 kinase (PI3K/AKT/mTOR/p70S6K) pathway. In addition, receptor-interacting protein 1 and 3 (RIP1 and RIP3) served as an upstream of ROS-JNK-p53 loop. However, the phosphorylation form of FTY720 induced autophagy but not apoptosis and necroptosis. Finally, the in vitro results were validated in vivo in xenograft mouse of glioblastoma cells. In conclusion, the current study provided novel insights into understanding the mechanisms and functions of FTY720-induced apoptosis, necroptosis and autophagy in human glioblastoma cells.

Shikonin Induces Apoptosis, Necrosis, and Premature Senescence of Human A549 Lung Cancer Cells through Upregulation of p53 Expression

Shikonin, a natural naphthoquinone pigment isolated from Lithospermum erythrorhizon, has been reported to suppress growth of various cancer cells. This study was aimed to investigate whether this chemical could also inhibit cell growth of lung cancer cells and, if so, works via what molecular mechanism. To fulfill this, A549 lung cancer cells were treated with shikonin and then subjected to microscopic, biochemical, flow cytometric, and molecular analyses. Compared with the controls, shikonin significantly induced cell apoptosis and reduced proliferation in a dose-dependent manner. Specially, lower concentrations of shikonin (1-2.5 μg/mL) cause viability reduction; apoptosis and cellular senescence induction is associated with upregulated expressions of cell cycle- and apoptotic signaling-regulatory proteins, while higher concentrations (5-10 μg/mL) precipitate both apoptosis and necrosis. Treatment of cells with pifithrin-α, a specific inhibitor of p53, suppressed shikonin-induced apoptosis and premature senescence, suggesting the role of p53 in mediating the actions of shikonin on regulation of lung cancer cell proliferation. These results indicate the potential and dose-related cytotoxic actions of shikonin on A549 lung cancer cells via p53-mediated cell fate pathways and raise shikonin a promising adjuvant chemotherapeutic agent for treatment of lung cancer in clinical practice.

In vitro induction of erythrocyte phosphatidylserine translocation by the natural naphthoquinone shikonin

Shikonin, the most important component of Lithospermum erythrorhizon, has previously been shown to exert antioxidant, anti-inflammatory, antithrombotic, antiviral, antimicrobial and anticancer effects. The anticancer effect has been attributed to the stimulation of suicidal cell death or apoptosis. Similar to the apoptosis of nucleated cells, erythrocytes may experience eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and by phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include the increase of cytosolic Ca²⁺-activity ([Ca²⁺]_i) and ceramide formation. The present study explored whether Shikonin stimulates eryptosis. To this end, Fluo 3 fluorescence was measured to quantify [Ca²⁺]_i, forward scatter to estimate cell volume, annexin V binding to identify phosphatidylserine-exposing erythrocytes, hemoglobin release to determine hemolysis and antibodies to quantify ceramide abundance. As a result, a 48 h exposure of human erythrocytes to Shikonin (1 µM) significantly increased [Ca²⁺]_i, increased ceramide abundance, decreased forward scatter and increased annexin V binding. The effect of Shikonin (1 µM) on annexin V binding was significantly blunted, but not abolished by the removal of extracellular Ca²⁺. In conclusion, Shikonin stimulates suicidal erythrocyte death or eryptosis, an effect at least partially due to the stimulation of Ca²⁺ entry and ceramide formation.