Beta-hydroxyisovalerylshikonin induces apoptosis in human leukemia cells by inhibiting the activity of a polo-like kinase 1 (PLK1)

β-Hydroxyisovalerylshikonin regulates macrophage polarization via the AMPK/Nrf2 pathway and ameliorates sepsis in mice

CONTEXT

The potential anti-inflammatory bioactivities of β-hydroxyisovalerylshikonin (β-HIVS) remain largely unknown.

OBJECTIVE

This study investigated the anti-inflammatory effects and underlying mechanisms of β-HIVS.

MATERIALS AND METHODS

RAW 264.7 cells stimulated with LPS (100 ng/mL) for 24 h were treated with the non-cytotoxic doses of β-HIVS (0.5 or 1 μM, determined by MTT and Trypan blue staining), qRT-PCR and FCM assay were used to examine macrophage polarization transitions. Western blotting was used to evaluate the activation of the AMPK/Nrf2 pathway. In vivo, C57BL/6 mice were randomly divided into vehicle control, LPS (10 mg/kg), and β-HIVS (2.5 mg/kg) combined with LPS (10 mg/kg) groups, blood samples, BALF, and lung tissues of mice were subjected to ELISA, qRT-PCR, FCM, and H&E staining.

RESULTS

β-HIVS (1 μM) inhibited LPS-induced expression of M1 macrophage markers (TNF-α: 0.29-fold, IL-1β: 0.32-fold), promoted the expression of M2 macrophage markers (CD206: 3.14-fold, Arginase-1: 3.98-fold) in RAW 264.7 cells; mechanistic studies showed that β-HIVS increased the expression of nuclear Nrf2 (2.04-fold) and p-AMPK (3.65-fold) compared with LPS group (p < 0.05). In vivo, β-HIVS decreased the levels of pro-inflammatory cytokines (TNF-α: 1130.41 vs. 334.88 pg/mL, IL-1β: 601.89 vs. 258.21 pg/mL in serum; TNF-α: 893.07 vs. 418.21 pg/mL, IL-1β: 475.22 vs. 298.54 pg/mL in BALF), decreased the proportion of M1 macrophages (77.83 vs. 68.53%) and increased the proportion of M2 macrophages (13.55 vs. 19.56%) in BALF, and reduced lung tissue damage and septic mice survival (p < 0.05).

CONCLUSIONS

These results indicate that β-HIVS may be a new potential anti-inflammatory agent.

Targeting Cancer Metabolism and Current Anti-Cancer Drugs

Several studies have exploited the metabolic hallmarks that distinguish between normal and cancer cells, aiming at identifying specific targets of anti-cancer drugs. It has become apparent that metabolic flexibility allows cancer cells to survive during high anabolic demand or the depletion of nutrients and oxygen. Cancers can reprogram their metabolism to the microenvironments by increasing aerobic glycolysis to maximize ATP production, increasing glutaminolysis and anabolic pathways to support bioenergetic and biosynthetic demand during rapid proliferation. The increased key regulatory enzymes that support the relevant pathways allow us to design small molecules which can specifically block activities of these enzymes, preventing growth and metastasis of tumors. In this review, we discuss metabolic adaptation in cancers and highlight the crucial metabolic enzymes involved, specifically those involved in aerobic glycolysis, glutaminolysis, de novo fatty acid synthesis, and bioenergetic pathways. Furthermore, we also review the success and the pitfalls of the current anti-cancer drugs which have been applied in pre-clinical and clinical studies.

Shikonin Inhibits Tumor Growth in Mice by Suppressing Pyruvate Kinase M2-mediated Aerobic Glycolysis

Shift metabolism profile from mitochondrial oxidative phosphorylation to aerobic glycolysis (Warburg effect) is a key for tumor cell growth and metastasis. Therefore, suppressing the tumor aerobic glycolysis shows a great promise in anti-tumor therapy. In the present study, we study the role of shikonin, a naphthoquinone isolated from the traditional Chinese medicine Lithospermum, in inhibiting tumor aerobic glycolysis and thus tumor growth. We found that shikonin dose-dependently inhibited glucose uptake and lactate production in Lewis lung carcinoma (LLC) and B16 melanoma cells, confirming the inhibitory effect of shikonin on tumor aerobic glycolysis. Treatment of shikonin also decreased tumor cell ATP production. Furthermore, pyruvate kinase M2 (PKM2) inhibitor or activator respectively altered the effect of shikonin on tumor cell aerobic glycolysis, suggesting that suppression of cell aerobic glycolysis by shikonin is through decreasing PKM2 activity. Western blot analysis confirmed that shikonin treatment reduced tumor cell PKM2 phosphorylation though did not reduce total cellular PKM2 level. In vitro assay also showed that shikonin treatment significantly promoted tumor cell apoptosis compared to untreated control cells. Finally, when mice implanted with B16 cells were administered with shikonin or control vehicle, only shikonin treatment significantly decreased B16 tumor cell growth. In conclusion, this study demonstrates that shikonin inhibits tumor growth in mice by suppressing PKM2-mediated aerobic glycolysis.

Structural dynamics and quantum mechanical aspects of shikonin derivatives as CREBBP bromodomain inhibitors

The Proteins involved in the chemical modification of lysine residues in histone, is currently being excessively focused as the therapeutic target for the treatment of cell related diseases like cancer. Among these proteins, the epigenetic reader, CREB-binding protein (CREBBP) bromodomain is one of the most prominent targets for effective anticancer drug design, which is responsible for the reorganization of acetylated histone lysine residues. Therefore, this study employed an integrative approach of structure based drug design, in combination with Molecular Dynamics (MD) and QM/MM study to identify as well as to describe the binding mechanism of two shikonin derivatives, acetylshikonin and propionylshikonin as inhibitors of CREBBP bromodomain. Here induced fit docking strategy was employed to explore the important intrinsic interactions of ligands with CREBBP bromodomain, consistently molecular dynamics simulation with two different methods and binding energy calculations by MM-GBSA and MM-PBSA were adopted to determine the stability of intermolecular interactions between protein and ligands. The results showed that both these derivatives made direct contacts with the important conserved residues of the active site, where propionylshikonin demonstrated stronger binding and stability than acetylshikonin, according to molecular dynamics simulation and binding free energy calculations. Further, QM/MM energy calculation was employed to study the chemical reactivity of the propionylshikonin and also to describe the mechanism of non bonded interactions between the propionylshikonin and CREBBP bromodomain. Though this study demands in vitro and in vivo experiments to evaluate the efficiency of the compound, these insights would assist to design more potent CREBBP bromodomain inhibitor, guiding the site of modification of propionylshikonin moiety for designing selective inhibitors.

Shikonin Inhibits the Proliferation of Human Breast Cancer Cells by Reducing Tumor-Derived Exosomes

Shikonin is a naphthoquinone isolated from the traditional Chinese medicine Lithospermum. It has been used in the treatment of various tumors. However, the effects of shikonin on such diseases have not been fully elucidated. In the present study, we detected the exosome release of a breast cancer cell line (MCF-7) with shikonin treatment and found a positive relationship between the level of secreted exosomes and cell proliferation. We next analyzed miRNA profiles in MCF-7 cells and exosomes and found that some miRNAs are specifically sorted and abundant in exosomes. Knockdown of the most abundant miRNAs in exosomes and the MCF-7 proliferation assay showed that miR-128 in exosomes negatively regulates the level of Bax in MCF-7 recipient cells and inhibits cell proliferation. These results show that shikonin inhibits the proliferation of MCF-7 cells through reducing tumor-derived exosomal miR-128. The current study suggests that shikonin suppresses MCF-7 growth by the inhibition of exosome release.

Hinesol, a compound isolated from the essential oils of Atractylodes lancea rhizome, inhibits cell growth and induces apoptosis in human leukemia HL-60 cells

Hinesol is a unique sesquiterpenoid isolated from the Chinese traditional medicine, Atractylodes lancea rhizome. In a previous study, we screened various natural products in human leukemia HL-60 cells and identified an essential oil fraction from A. lancea rhizome that exhibited apoptosis-inducing activity in these cells; hinesol was subsequently shown to be the compound responsible for this apoptosis-inducing activity. In this study, we describe the cytotoxic effects and molecular mechanisms of hinesol in HL-60 cells. The antitumor effect of hinesol was associated with apoptosis. When HL-60 cells were treated with hinesol, characteristic features of apoptosis, such as nuclear fragmentation and DNA fragmentation, were observed. These growth-inhibitory and apoptosis-inducing activities of hinesol in leukemia cells were much stronger than those of β-eudesmol, another compound isolated from the essential oil fraction. Furthermore, hinesol induced activation of c-Jun N-terminal kinase (JNK), but not p38, prior to the onset of apoptosis. These results suggested that hinesol induced apoptosis through the JNK signaling pathway in HL-60 cells. Therefore, hinesol may represent a novel medicinal drug having indications in the treatment of various cancers, including leukemia.

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

Shikonin, a natural naphthoquinone isolated from a traditional Chinese medicinal herb, has been reported to promote tumor cell death. However, there are few reports concerning its effect on metastasis-related cell invasion and migration behavior. In the present study, we investigated the effect of shikonin on human breast cancer invasion and migration. We found that shikonin inhibited phorbol 12-myristate 13-acetate (PMA)-induced cell migration and invasion in MCF-7 breast cancer cells, which was correlated with modulation of matrix metalloproteinase-9 (MMP-9) through suppression of both expression and proteolytic and promoter activity. We also found that shikonin inhibited both MMP-9 expression and promoter activity in MDA-MB‑231 cells with high metastatic potential. These results indicated that shikonin induces the suppression of migration and invasion through modulation of MMP-9 in human breast cancer cells. Therefore, shikonin may be a potential anticancer drug for human breast cancer therapy.

Shikonin inhibits the growth of human prostate cancer cells via modulation of the androgen receptor

Shikonin, a natural naphthoquinone isolated from the traditional Chinese medicine Zi Cao (gromwell), has been shown to possess tumor cell killing activity. The human androgen receptor (AR) is a nuclear transcription factor that serves as a major therapeutic target for prostate cancer. However, AR regulation by shikonin has not been reported. We investigated the effects of shikonin on the growth of prostate cancer cells. We observed that shikonin decreased the expression of AR at both the mRNA and the protein levels in LNCaP and 22RV1 human prostate cancer cells. The results from a luciferase assay showed that shikonin decreased the transcriptional activity of AR. Moreover, shikonin treatment inhibited AR target gene expression, PSA and growth inhibition of prostate cancer cells. In conclusion, the present study shows for the first time that shikonin treatment causes transcriptional repression of AR and inhibition of its nuclear localization in human prostate cancer cells. We propose that shikonin, an anticancer drug extracted from natural sources, induces inhibition of cell growth through modulation of AR in androgen-responsive prostate cancer cells and is a candidate for use in cancer chemotherapy for human prostate cancer.

Anti-inflammatory effects of β-hydroxyisovalerylshikonin in BV2 microglia are mediated through suppression of the PI3K/Akt/NF-kB pathway and activation of the Nrf2/HO-1 pathway

In the present study, we investigated whether β-hydroxyisovalerylshikonin (β-HIVS) affects the production of proinflammatory mediators such as nitric oxide (NO) and prostaglandin E2 (PGE2) in BV2 microglial cells. Our data showed that β-HIVS inhibited secretion of NO and PGE2 and downregulated expression of their main regulatory genes, inducible NO synthesis (iNOS) and cyclooxygenase-2 (COX-2). β-HIVS also reduced the LPS-induced DNA-binding activity of nuclear factor-κB (NF-κB) by suppressing nuclear translocation of the NF-κB subunits and inhibiting the degradation and phosphorylation of IκBα. Furthermore, an NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC), attenuated LPS-stimulated iNOS and COX-2 expression, suggesting that NF-κB inhibition is a main effector in the expression of iNOS and COX-2. We also found that LPS-induced NF-κB activation is regulated through inhibition of PI3K/Akt phosphorylation in response to β-HIVS. Additionally, β-HIVS caused the induction of heme oxygenase-1 (HO-1) via upregulation of nuclear factor-erythroid 2-related factor 2 (Nrf2), both of which are involved in the secretion of proinflammatory mediators such as NO and PGE2. Taken together, our data indicate that β-HIVS diminishes the proinflammatory mediators NO and PGE2 and the expression of their regulatory genes, iNOS and COX-2, in LPS-stimulated BV2 microglial cells by inhibiting PI3K/Akt-dependent NF-κB activation and inducing Nrf2-mediated HO-1 expression.

Polo-like kinase 1 (PLK1) is involved in toll-like receptor (TLR)-mediated TNF-α production in monocytic THP-1 cells

Polo-like kinases (PLKs) have been reported to be essential components of anti-viral pathways. However, the role of PLKs in the production of pro-inflammatory cytokines induced by TLR activation is uncertain. We report here that monocytic THP-1 cells expressed PLK1, PLK2, PLK3 and PLK4. When THP-1 cells were treated with GW843682X, an inhibitor of PLK1 and PLK3, the results showed that GW843682X down-regulated Pam3CSK4- and LPS-induced TNF-α at both the gene and protein levels. GW843682X did not impact Pam3CSK4-induced IL-1β and IL-8 or LPS-induced IL-1β, but it down-regulated LPS-induced IL-8 significantly. Moreover, western blot results showed that TLRs activated PLK1, and PLK1 inhibition by RNA interference down-regulated Pam3CSK4-induced TNF-α production, suggesting the involvement of PLK1 in TNF-α up-regulation. In addition, GW843682X treatment for 12 to 24 h induced cell death and down-regulated MyD88, but neither of these roles contributed to the down-regulation of TNF-α, as TNF-α gene expression was up-regulated at 1 h. Furthermore, GW843682X inhibited Pam3CSK4-induced activation of ERK and NF-κB, which contributed to Pam3CSK4-induced up-regulation of TNF-α. GW843682X also inhibited LPS-induced activation of ERK, p38 and NF-κB, which contributed to LPS-induced up-regulation of TNF-α. Taken together, these results suggested that PLK1 is involved in TLR2- and TLR4-induced inflammation, and GW843682X may be valuable for the regulation of the inflammatory response.

Anticancer agent shikonin is an incompetent inducer of cancer drug resistance

PURPOSE

Cancer drug resistance is a major obstacle for the success of chemotherapy. Since most clinical anticancer drugs could induce drug resistance, it is desired to develop candidate drugs that are highly efficacious but incompetent to induce drug resistance. Numerous previous studies have proven that shikonin and its analogs not only are highly tumoricidal but also can bypass drug-transporter and apoptotic defect mediated drug resistance. The purpose of this study is to investigate if or not shikonin is a weak inducer of cancer drug resistance.

EXPERIMENTAL DESIGN

Different cell lines (K562, MCF-7, and a MDR cell line K562/Adr), after repeatedly treated with shikonin for 18 months, were assayed for drug resistance and gene expression profiling.

RESULTS

After 18-month treatment, cells only developed a mere 2-fold resistance to shikonin and a marginal resistance to cisplatin and paclitaxel, without cross resistance to shikonin analogs and other anticancer agents. Gene expression profiles demonstrated that cancer cells did strongly respond to shikonin treatment but failed to effectively mobilize drug resistant machineries. Shikonin-induced weak resistance was associated with the up-regulation of βII-tubulin, which physically interacted with shikonin.

CONCLUSION

Taken together, apart from potent anticancer activity, shikonin and its analogs are weak inducers of cancer drug resistance and can circumvent cancer drug resistance. These merits make shikonin and its analogs potential candidates for cancer therapy with advantages of avoiding induction of drug resistance and bypassing existing drug resistance.

Shikonin and its derivatives: a patent review

INTRODUCTION

Shikonin and its derivatives are the main components of red pigment extracts from Lithospermum erythrorhizon, whose medicinal properties have been confirmed for a long history, and have aroused great interest as the hallmark molecules responsible for their significant biological activities, especially for their striking anticancer effects.

AREAS COVERED

Areas covered in this paper include a review of the total synthesis, biological effects and mechanisms of shikonin and its derivatives for their anticancer activities in the past decade, basing on literature and patents. The current state and problems are also discussed.

EXPERT OPINION

At present, screening for anticancer shikonin derivatives is based on cellular level to find compounds with stronger cytotoxicity. Though several compounds have been discovered with striking cytotoxicity in vitro, however, no selectivity was observed and undoubtedly, the further outcomes have been disappointing because of their great damage to normal cells. Meanwhile, the presumed mechanisms of action are also established in terms of their cytotoxicity. From a pharmacological point of view, most of the shikonin derivatives are at an early stage of their development, and thus it is difficult to determine the exact effectiveness in cancer treatment. With research in this field going deeper, it can be expected that, despite the difficulties, shikonin derivatives as potential anticancer agents will soon follow.

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

We recently reported that shikonin and its analogs were a class of necroptotic inducers that could bypass cancer drug resistance. However, the molecular targets of shikonin are not known. Here, we showed that shikonin and its analogs are inhibitors of tumor-specific pyruvate kinase-M2 (PKM2), among which shikonin and its enantiomeric isomer alkannin were the most potent and showed promising selectivity, that is, shikonin and alkannin at concentrations that resulted in over 50% inhibition of PKM2 activity did not inhibit PKM1 and pyruvate kinase-L (PKL). Shikonin and alkannin significantly inhibited the glycolytic rate, as manifested by cellular lactate production and glucose consumption in drug-sensitive and resistant cancer cell lines (MCF-7, MCF-7/Adr, MCF-7/Bcl-2, MCF-7/Bcl-x(L) and A549) that primarily express PKM2. HeLa cells transfected with PKM1 showed reduced sensitivity to shikonin- or alkannin-induced cell death. To the best of our knowledge, shikonin and alkannin are the most potent and specific inhibitors to PKM2 reported so far. As PKM2 universally expresses in cancer cells and dictates the last rate-limiting step of glycolysis vital for cancer cell proliferation and survival, enantiomeric shikonin and alkannin may have potential in future clinical application.

Polo-like kinase 1 enhances survival and mutagenesis after genotoxic stress in normal cells through cell cycle checkpoint bypass

Polo-like kinase 1 (Plk1) is a key regulator of mitosis. Aberrant Plk1 activity is found in tumors, but little is known regarding its role in the DNA damage response of normal cells and its potential contribution to the early stages of carcinogenesis. Inappropriate survival signaling after DNA damage may facilitate clonal expansion of genetically compromised cells, and it is known that protein tyrosine phosphatase (PTP) inhibitors activate key survival pathways. In this study, we employed hexavalent chromium [Cr(VI)], a well-documented genotoxicant, to investigate the mechanism by which survival pathway activation could lead to loss of checkpoint control via a mechanism involving Plk1. We recently reported that PTP inhibition enhances clonogenic survival and mutagenesis after Cr(VI) exposure by overriding Cr-induced growth arrest. Here, we report that checkpoint bypass, facilitated by PTP inhibition, was associated with decreased Cdk1 Tyr15 phosphorylation, as well as increased Plk1 activity and nuclear localization. Plk1 was necessary for increased survival after PTP inhibition and Cr(VI) exposure in normal human fibroblasts via enhanced mitotic progression. In addition, pharmacological inhibition of Plk1 abolished the PTP inhibitor-induced bypass of the G(2)/M checkpoint. Notably, Plk1 overexpression increased survival and mutagenesis after Cr(VI) exposure in wild-type Saccharomyces cerevisiae. Taken together, our data indicate that Plk1 activation and nuclear localization are necessary for PTP-regulated mitotic progression after DNA damage. Our studies highlight a role for Plk1 in the loss of checkpoint control, increased survival and mutagenesis after genotoxic exposure in normal cells, which in turn may lead to genomic instability and carcinogenesis.

Polo-like kinase 1 (Plk1) as a novel drug target in chronic myeloid leukemia: overriding imatinib resistance with the Plk1 inhibitor BI 2536

In most patients with chronic myeloid leukemia (CML), the disease can be kept under control using the BCR/ABL kinase inhibitor imatinib. Nevertheless, resistance or intolerance to imatinib and other BCR/ABL inhibitors may occur during therapy. Therefore, CML research is focusing on novel targets and targeted drugs. Polo-like kinase 1 (Plk1) is a serine/threonine kinase that plays an essential role in mitosis. In this study, we examined the expression of Plk1 in CML cells and its potential role as a therapeutic target. Plk1 was found to be expressed in phosphorylated form in the CML cell line K562 as well as in primary CML cells in all patients tested. Inhibition of BCR/ABL by imatinib or nilotinib (AMN107) led to decreased expression of the Plk1 protein in CML cells, suggesting that BCR/ABL promotes Plk1 generation. Silencing of Plk1 in CML cells by a small interfering RNA approach was followed by cell cycle arrest and apoptosis. Furthermore, the Plk1-targeting drug BI 2536 was found to inhibit proliferation of imatinib-sensitive and imatinib-resistant CML cells, including leukemic cells, carrying the T315 mutation of BCR/ABL with reasonable IC(50) values (1-50 nmol/L). The growth-inhibitory effects of BI 2536 on CML cells were found to be associated with cell cycle arrest and apoptosis. Moreover, BI 2536 was found to synergize with imatinib and nilotinib in producing growth inhibition in CML cells. In conclusion, Plk1 is expressed in CML cells and may represent a novel, interesting target in imatinib-sensitive and imatinib-resistant CML.

Effects of small interference RNAs targeting Polo-like kinase 1 in human liver cancer cell line HepG2

AIM: To explore the role of PLK1 in carcinogenesis and development of liver cancer and its clinical significance for cancer treatment with the technique of RNA interference (RNAi).

METHODS: HepG2 cells were transfected with small interfering RNAs (siRNAs) targeting against the human PLK1 by chemosynthesis. The PLK1 mRNA levels of the cells transfected with siRNAs were monitored with real time PCR. Cell proliferation was evaluated by direct cell counting with trypan blue staining. Cell cycle and apoptosis were examined by flow cytometry.

RESULTS: The PLK1 mRNA levels of transfected liver cancer cells were greatly lowered as compared with that of the control groups in 48 h after the siRNAs transfection (49.7% ± 3.6%), (P < 0.01). Cell proliferation was reduced from 24 h after transfection. Cell cycle distribution was changed and showed a strong G₂/M arrest in 48 h and 72 h after transfection, and cell apoptosis was increased. There was significant difference as compared with the control group (both P < 0.05).

CONCLUSION: PLK1 plays an important role in the carcinogenesis and development of liver cancer. siRNAs targeting against human PLK1 may specially suppress the expression of PLK1 mRNA in liver cancer cells, inhibit cell proliferation and enhance cell apoptosis. The RNAi targeting PLK1 is expected to be used in gene therapy for human liver cancers.

Theoretical model of treatment strategies for clear cell carcinoma of the ovary: focus on perspectives

OBJECTIVES

Among epithelial ovarian cancer (EOC), clear cell carcinomas (CCC) differ from the other histologic types with respect to their clinical characteristics, carcinogenesis and prognosis. The aim of this review is to summarize the current knowledge and future perspective on the new therapeutic targets and treatment strategies for CCC.

MATERIALS AND METHODS

The present article reviews the English language literature for preclinical and clinical trials and promising molecular targets on CCC of the ovary, based on the gene expression profiling studies.

RESULTS

Here, we show that (1) the expression of the genes involved in transcription, signaling, cell cycle, adhesion, matrix, proteinase, and detoxification was greatly increased in the CCC carcinogenesis; (2) upregulation of hepatocyte nuclear factor-1beta (HNF-1beta) and Polo-like kinase (PLK)-Early mitotic inhibitor-1 (Emi1) as well as their downstream targets are specifically found in most CCC. The promising molecular targeting approach will emerge in the context of HNF-1beta and PLK-Emi1 biology; and 3) several significant common pathways observed in CCC of the ovary overlap the datasets identified in CCC of the kidney. To improve the outcome in CCC therapy, we must learn various adaptive treatment strategies for renal CCC, although it is not supported by any preliminary clinical data.

CONCLUSION

The inhibitors that target HNF-1beta and PLK-Emi1 and their downstream signaling molecules would be evaluated. In addition, the therapy currently used in renal CCC should be considered as an alternative for the present treatments or an attractive therapeutic option for ovarian CCC. The challenges accompanying the recent advance are described in this review article.

Polo-like kinase 1 is overexpressed in acute myeloid leukemia and its inhibition preferentially targets the proliferation of leukemic cells

Polo-like kinase 1 (Plk1) is a major mitotic regulator overexpressed in many solid tumors. Its role in hematopoietic malignancies is still poorly characterized. In this study, we demonstrate that Plk1 is highly expressed in leukemic cell lines, and overexpressed in a majority of samples from patients with acute myeloid leukemia compared with normal progenitors. A pharmacologic inhibitor, BI2536, blocks proliferation in established cell lines, and dramatically inhibits the clonogenic potential of leukemic cells from patients. Plk1 knockdown by small interfering RNA also blocked proliferation of leukemic cell lines and the clonogenic potential of primary cells from patients. Interestingly, normal primary hematopoietic progenitors are less sensitive to Plk1 inhibition than leukemic cells, whose proliferation is dramatically decreased by the inhibitor. These results highlight Plk1 as a potentially interesting therapeutic target for the treatment of acute myeloid leukemia.

Mechanism of inhibition of tumor angiogenesis by beta-hydroxyisovalerylshikonin

Shikonin and beta-hydroxyisovalerylshikonin (beta-HIVS) from Lithospermum erythrorhizon inhibit angiogenesis via inhibition of vascular endothelial growth factor receptors (VEGFR) in an adenosine triphosphate-non-competitive manner, although the underlying molecular mechanism has not been fully understood. In the present study, we found that beta-HIVS inhibited angiogenesis within chicken chorioallantoic membrane approximately threefold more efficiently than shikonin. beta-HIVS also significantly inhibited angiogenesis in two other assays, induced either by Lewis lung carcinoma cells implanted in mouse dorsal skin or by VEGF in s.c. implanted Matrigel plugs and metastasis of Lewis lung carcinoma cells to lung. Therefore, using beta-HIVS as a bioprobe, we investigated the molecular mechanism of shikonin's anti-angiogenic actions. beta-HIVS inhibited the phosphorylation and expression of VEGFR2 and Tie2 without affecting VEGFR1 and fibroblast growth factor receptor 1 levels. beta-HIVS suppressed the phosphorylation but not the expression of extracellular signal-regulated kinase, and an Sp1-dependent transactivation of the VEGFR2 and Tie2 promoters, thereby suppressing the proliferation of vascular endothelial and progenitor cells. This was mimicked by an Sp1 inhibitor mithramycin A and partially rescued by Sp1 overexpression. These results implicate potential use of shikonin and beta-HIVS as leading compounds for clinical application in the future by virtue of their unique properties including: (i) inhibition of VEGFR2 and Tie2 phosphorylation in an adenosine triphosphate-non-competitive manner; (ii) simultaneous inhibition of the phosphorylation and expression of VEGFR2 and Tie2; and (iii) bifunctional inhibition of the growth in endothelial cells and vascular remodeling.

Genistein-induced neuronal apoptosis and G2/M cell cycle arrest is associated with MDC1 up-regulation and PLK1 down-regulation

The aim of the present study is to investigate the effect of genistein on human neuroblastoma SK-N-MC cells. MTT proliferation assay, LDH cytotoxicity assay, flow cytometric analysis, real-time quantitative RT-PCR and western blotting were used to investigate the effect of genistein on cell survival, cellular toxicity, cell cycle progression, and mRNA and protein alterations of selected DNA damage-, cell cycle- and apoptosis-related genes in SK-N-MC cells. Genistein suppressed cell proliferation, increased LDH release and modulated cell cycle distribution through accumulation of cells at G2/M- and S-phase and sub-G0 (cell death) with a concurrent decrease of cells at G0/G1 phase. Genistein increased the MDC1 (Mediator of DNA damage Checkpoint protein 1), p53, p21(waf1/cip1), Cdc2 and Bax mRNA levels in a dose-dependent manner. However, PLK1 (Polo-Like Kinase 1) and Cyclin B1 mRNAs were down-regulated after genistein treatment. Furthermore, Genistein did not alter Chk2 (Checkpoint Kinase 2), Bcl-2 and Cdc25C mRNA levels. On western blotting analyses; genistein increased the protein level of MDC1, p53, p21(waf1/cip1), and Bax in a dose-dependent manner. Genistein also increased the phosphorylation of Chk2 and Cdc25C at Thr-68 and Ser-216, respectively. In addition, consistently with PLK1 down-regulation, the phosphorylation of Cdc25C at Ser-198 was markedly decreased after genistein treatment. Additionally, Chk2, Cdc25C, Cyclin B1, p-Cyclin B1 (Ser-147), and Cdc2 as well as Bcl-2 proteins were down-regulated after genistein treatment. Altogether, these results suggest for the first time the involvement of MDC1 up-regulation after genistein treatment in DNA damage-induced Chk2 activation- and PLK1 down-regulation-mediated apoptosis and cell cycle checkpoint pathways.

A tyrosine kinase inhibitor, beta-hydroxyisovalerylshikonin, induced apoptosis in human lung cancer DMS114 cells through reduction of dUTP nucleotidohydrolase activity

Apoptotic cell death was induced in human lung cancer DMS114 cells by treatment with beta-hydroxyisovalerylshikonin (beta-HIVS), an ATP-noncompetitive inhibitor of protein tyrosine kinases. Changes in phosphoprotein profiles were analyzed by two-dimensional-polyacrylamide gel electrophoresis (2D-PAGE) after the cells were treated with beta-HIVS. One spot on the 2D gel showed a marked decrease in intensity and the corresponding protein was identified by mass spectrometry as dUTP nucleotidohydrolase (dUTPase). The beta-HIVS-induced decrease of dUTPase in the phosphoprotein fraction of DMS114 cells was confirmed using immunoblotting. Treatment of the cells with beta-HIVS-induced rapid reduction of dUTPase activity. An antioxidant N-acetyl-cysteine inhibited both the reduction of phosphorylated dUTPase and the induction of apoptosis by beta-HIVS treatment of DMS114 cells. Introduction of siRNA directed against dUTPase mRNA into DMS114 cells enhanced the susceptibility of beta-HIVS-induced apoptosis. Treatment of DMS114 cells with beta-HIVS and 5-fluorouracil, a specific inhibitor of thymidylate synthase used as a chemotherapeutic drug, revealed the synergistic effects of these drugs on the inhibition of cell growth. These results suggest that dUTPase activity is one of the crucial factors involved in apoptotic cell death in lung cancer cells.

β-Hydroxyisovalerylshikonin induces apoptosis and G0/G1 cell-cycle arrest of endometriotic stromal cells: a preliminary in vitro study

BACKGROUND

Most of the current medical treatments for endometriosis aim to down-regulate the estrogen activity. However, a high recurrence rate after medical treatments has been the most significant problem. Beta-hydroxyisovalerylshikonin (beta-HIVS) is an ATP non-competitive inhibitor of protein-tyrosine kinases and is considered an apoptosis-inducing agent. The aim of this study is to evaluate the effects of beta-HIVS on the proliferation, cell cycle and apoptosis of endometriotic stromal cells.

METHODS

We investigated the effects of beta-HIVS on cultured ovarian endometriotic cyst stromal cells (ECSC) by a modified methylthiazoletetrazolium (MTT) assay, a 5-bromo-2'-deoxyuridine (BrdU) incorporation assay and internucleosomal DNA fragmentation assays. The effect of beta-HIVS on the cell cycle of ECSC was determined by flow cytometry. The expression of apoptosis-related molecules was examined in ECSC using western blot analysis.

RESULTS

Beta-HIVS significantly inhibited the proliferation and DNA synthesis of ECSC and induced apoptosis and G0/G1 phase cell-cycle arrest of these cells. Down-regulation of the B-cell lymphoma/leukaemia-2 (Bcl-2) expression with the activation of caspase-3, caspase-8 and caspase-9 was observed in ECSC after beta-HIVS treatment.

CONCLUSIONS

These results suggest that beta-HIVS induces apoptosis of ECSC by suppressing anti-apoptotic proteins. Although our present findings are preliminary, beta-HIVS could potentially be a therapeutic agent for the treatment of endometriosis.

Molecular alterations after Polo-like kinase 1 mRNA suppression versus pharmacologic inhibition in cancer cells

Multiple roles within mitosis have been assigned to Polo-like kinase 1 (Plk1), making it an attractive candidate for mitotic targeting of cancer cells. We have employed chimeric antisense oligonucleotides to investigate the molecular alterations after targeted interference with Plk1 in RKO human colon adenocarcinoma and PC3 prostate cancer cells. Suppression of Plk1 mRNA resulted in a dramatic increase of the mitotic index followed by the onset of apoptosis. Mitotically arrested cells displayed randomly separated condensed chromosomes and the occurrence of multiple spindle poles with well-formed asters. Induction of apoptosis was strictly dependent on cell cycle progression: Genetically engineered RKO cells with inducible expression of the cyclin-dependent kinase inhibitor p27(Kip1) were completely refractory to Plk1 depletion-induced apoptosis when they were arrested in the G1 phase of the cell cycle. Various mitotic markers, including MPM-2, cdc25c, cyclin B1, or phosphorylated histone H3, were investigated to explore the molecular consequences of Plk1 depletion. Whereas most marker proteins showed similar alterations compared with treatment with paclitaxel, cdc25c was fully phosphorylated solely in paclitaxel-treated cells but only partially phosphorylated in Plk1-depleted cells, although both treatments caused a profound mitotic arrest. This differential phosphorylation of cdc25c was used to test whether a pharmacologic inhibitor of Plk1 would exert the same cellular effects as interference with Plk1 on a mRNA level. It was found that the differential electrophoretic mobility of cdc25c can serve as a reliable molecular marker to track inhibition of Plk1 by small-molecule inhibitors within a cell.

SAK, a new polo-like kinase, is transcriptionally repressed by p53 and induces apoptosis upon RNAi silencing

Chip profiling of a p53 temperature-sensitive tumor model identified SAK (Snk/Plk-akin kinase), encoding a new member of polo-like kinases (PLKs), as a gene strongly repressed by wild-type p53. Further characterization revealed that SAK expression was downregulated by wild-type p53 in several tumor cell models. Computer search of a 1.7-kb SAK promoter sequence revealed three putative p53 binding sites, but p53 failed to bind to any of these sites, indicating that SAK repression by p53 was not through a direct p53 binding to the promoter. Transcriptional analysis with luciferase reporters driven by SAK promoter deletion fragments identified SP-1 and CREB binding sites, which together conferred a two-fold SAK repression by p53. However, the repression was not reversed by cotransfection of SP-1 or CREB, suggesting a lack of interference between p53 and SP-1 or CREB. Significantly, p53-mediated SAK repression was largely reversed in a dose-dependent manner by Trichostatin A, a potent histone deacetylase (HDAC) inhibitor, suggesting an involvement of HDAC transcription repressors in SAK repression by p53. Biologically, SAK RNA interference (RNAi) silencing induced apoptosis, whereas SAK overexpression attenuated p53-induced apoptosis. Thus, SAK repression by p53 is likely mediated through the recruitment of HDAC repressors, and SAK repression contributes to p53-induced apoptosis.

Molecular dissection of a medicinal herb with anti-tumor activity by oligonucleotide microarray

It is difficult to understand precisely the physiological actions of herbs because they contain a complex array of constituent molecules. In the present study we used DNA microarray data for 12600 genes to examine the anti-proliferative activity of the herb Coptidis rhizoma and eight constituent molecules against eight human pancreatic cancer cell lines. We identified 27 genes showing strong correlation with the 50% inhibitory dose (ID50) of C. rhizoma after 72-h exposure. Hierarchical cluster analysis with correlation coefficients between expression levels of these 27 C. rhizoma-related genes and the ID50 of each constituent molecule classified these test molecules into two clusters, one consisting of C. rhizoma and berberine and the other consisting of the remaining seven molecules. Our results suggest that one molecule, berberine, can account for the majority of the anti-proliferative activity of C. rhizoma and that DNA microarray analyses can be used to improve our understanding of the actions of an intact herb.

Silencing of polo-like kinase (Plk) 1 via siRNA causes induction of apoptosis and impairment of mitosis machinery in human prostate cancer cells: implications for the treatment of prostate cancer

Prostate cancer (PCa) is one of the most common cancers in men. Each year approximately 543,000 new cases are reported worldwide, and the disease kills 200,000 (mostly older men) in developed countries. The existing treatment approaches and surgical intervention have not been able to effectively manage this dreaded cancer and, therefore, continuing efforts are ongoing to explore novel targets and strategies for the management of PCa. The activity of polo-like kinase 1 (Plk1) is elevated in tissues and cells with a high mitotic index, including cancer cells. An increasing body of evidence suggests that the level of Plk1 expression has prognostic value for predicting outcomes in patients with some cancers. A close correlation between Plk1 expression and carcinogenesis has been documented. However, the role of Plk1 in PCa is not known. We propagated a hypothesis that Plk1 inhibition will result in elimination of human PCa cells via a mitotic arrest followed by apoptosis (1). To define the role of Plk1 in PCa, we used the technique of RNA silencing via small interfering RNA (siRNA). First, using a series of human prostate carcinoma cells and normal human prostate epithelial (PrEC) cells, we assessed Plk1 levels in PCa. Immunoblot analyses clearly showed a significant expression of Plk1 in LNCaP, DU145, and PC3 human PCa cells. Interestingly, Plk1 was not detectable in normal PrEC cells. Next, we transfected the PCa cells with Plk 1 siRNA, which resulted in a significant inhibition in Plk1 protein in all PCa cells. Plk1 depletion resulted in a decrease in cell viability and induction of apoptosis in PCa cells but had no appreciable effect in normal PrEC cells. Our data also demonstrated that Plk1 siRNA transfection of PCa cells resulted in 1) a mitotic cell cycle arrest, 2) failure of cytokinesis, and 3) defects in centrosome integrity and maturation. Thus, our study suggested that 1) Plk1 plays a critical role in the process of PCa development and 2) gene therapeutic approaches aimed at Plk1 or the pharmacological inhibitors of Plk1 may be developed for the management of PCa.

Polo-like kinases (Plks) and cancer

Deregulated centrosome duplication or maturation often results in increased centrosome size and/or centrosome number, both of which show a positive and significant correlation with aneuploidy and chromosomal instability, thus contributing to cancer formation. Given the role of Polo-like kinases (Plks) in the centrosome cycle, it is not unexpected that deregulated expression of Plks is detected in many types of cancer and is associated with oncogenesis. Extensive studies have shown that Plk1 expression is elevated in non-small-cell lung cancer, head and neck cancer, esophageal cancer, gastric cancer, melanomas, breast cancer, ovarian cancer, endometrial cancer, colorectal cancer, gliomas, and thyroid cancer. Plk1 gene and protein expression has been proposed as a new prognostic marker for many types of malignancies, and Plk1 is a potential target for cancer therapy. In contrast to Plk1, several studies have observed that Plk3 expression is negatively correlated with the development of certain cancers.

Involvement of tumor necrosis factor receptor-associated protein 1 (TRAP1) in apoptosis induced by beta-hydroxyisovalerylshikonin

beta-Hydroxyisovalerylshikonin (beta-HIVS), a compound isolated from the traditional oriental medicinal herb Lithospermum radix, is an ATP non-competitive inhibitor of protein-tyrosine kinases, such as v-Src and EGFR, and it induces apoptosis in various lines of human tumor cells. However, the way in which beta-HIVS induces apoptosis remains to be clarified. In this study, we performed cDNA array analysis and found that beta-HIVS suppressed the expression of the gene for tumor necrosis factor receptor-associated protein 1 (TRAP1), which is a member of the heat-shock family of proteins. When human leukemia HL60 cells and human lung cancer DMS114 cells were treated with beta-HIVS, the amount of TRAP1 in mitochondria decreased in a time-dependent manner during apoptosis. A similar reduction in the level of TRAP1 was also observed upon exposure of cells to VP16. Treatment of DMS114 cells with TRAP1-specific siRNA sensitized the cells to beta-HIVS-induced apoptosis. Moreover, the reduction in the level of expression of TRAP1 by TRAP1-specific siRNA enhanced the release of cytochrome c from mitochondria when DMS114 cells were treated with either beta-HIVS or VP16. The suppression of the level of TRAP1 by either beta-HIVS or VP16 was blocked by N-acetyl-cysteine, indicating the involvement of reactive oxygen species (ROS) in the regulation of the expression of TRAP1. These results suggest that suppression of the expression of TRAP1 in mitochondria might play an important role in the induction of apoptosis caused via formation of ROS.

[Basic studies for the development of anticancer, antidementia, and taste modifier drugs]

We developed various types of differentiation- and apoptosis-inducing agents against tumor cells and also studied the function and structure of synucleins and taste modifiers. Differentiation- and apoptosis-inducing agents are classified into DNA-damaging agents, Na(+), K(+)-ATPase inhibitors, agents affecting the redox states of tumor cells, agents affecting signal transduction pathways, isoprenoid compounds, and ATP-noncompetitive tyrosine kinase inhibitors. These include camptothecin, etoposide, cisplatin, transplantin, bufalin, arsenic trioxide, costunolide, C(2)- ceramide, daidzein, geranylgeranylacetone, geranylgeraniol, vitamin K(2), sophoranone, and beta-hydroxyisovalerylshikonin. The mechanisms of action of these differentiation- and apoptosis-inducing agents are described. The structure and function of synucleins are also reviewed for the development of potential antidementia agents. In addition, the structures of three purified taste modifiers are described.

Identification of common or distinct genes related to antitumor activities of a medicinal herb and its major component by oligonucleotide microarray

Although the physiological actions of many herbs are gradually being elucidated at the molecular level, it remains unclear how individual components of herbs contribute to their biological activities. In the present study, the antiproliferative activity of Coptidis rhizoma, a medicinal herb, and the major component berberine was investigated in 8 human pancreatic cancer cell lines. Gene expression patterns associated with sensitivities to each agent were analyzed with oligonucleotide arrays that comprised approximately 11,000 genes. We used a tetrazolium dye (MTT) assay to determine ID(50) values after the 8 cell lines were exposed to the 2 agents for 72 hr. The ID(50) value for berberine was correlated positively with that for C. rhizoma (r=0.725, p=0.0401). C. rhizoma killed tumor cells more effectively than purified berberine when normalized to the level of berberine present in the herb. From the oligonucleotide array data, we selected 20 and 13 genes with strong correlations (r(2)>0.81) to ID(50) values for berberine and C. rhizoma, respectively. Among these 33 genes, the levels of expression of 12 were correlated with the ID(50) values of both agents, suggesting that these genes are associated with tumor-killing activity of berberine in C. rhizoma. Expression of the remaining 21 genes was correlated with the ID(50) value of either purified berberine or C. rhizoma. Thus, we identified common and distinct genes responsible for anti-proliferative activities of purified berberine and C. rhizoma. This strategy may improve our understanding of the actions of herbs with antitumor activities.