Hinokitiol induces differentiation of teratocarcinoma F9 cells

New therapeutic strategy of hinokitiol in haemorrhagic shock-induced liver injury

Haemorrhagic shock and resuscitation (HS/R) may cause global ischaemia-reperfusion injury, which can result in systemic inflammation, multiorgan failure (particularly liver failure) and high mortality. Hinokitiol, a bioactive tropolone-related compound, exhibits antiplatelet and anti-inflammatory activities. Targeting inflammatory responses is a potential strategy for ameliorating hepatic injury during HS/R. Whether hinokitiol prevents hepatic injury during HS/R remains unclear. In the present study, we determined the role of hinokitiol following HS/R. The in vivo assays revealed that hinokitiol markedly attenuated HS/R-induced hepatic injury. Hinokitiol could inhibited NF-κB activation and IL-6 and TNF-α upregulation in liver tissues. Moreover, hinokitiol reduced caspase-3 activation, upregulated Bax and downregulated Bcl-2. These findings suggest that hinokitiol can ameliorate liver injury following HS/R, partly through suppression of inflammation and apoptosis. Furthermore, the in vitro data revealed that hinokitiol significantly reversed hypoxia/reoxygenation (H/R)-induced cell death and apoptosis in the primary hepatocytes. Hinokitiol prevented H/R-induced caspase-3 activation, PPAR cleavage, Bax overexpression and Bcl-2 downregulation. Moreover, hinokitiol attenuated H/R-stimulated NF-κB activation and reduced the levels of IL-6 and TNF-α mRNAs, suggesting that hinokitiol can protect hepatocytes from H/R injury. Collectively, our data suggest that hinokitiol attenuates liver injury following HS/R, partly through the inhibition of NF-κB activation.

Hinokitiol inhibits vasculogenic mimicry activity of breast cancer stem/progenitor cells through proteasome-mediated degradation of epidermal growth factor receptor

Hinokitiol, alternatively known as β-thujaplicin, is a tropolone-associated natural compound with antimicrobial, anti-inflammatory and antitumor activity. Breast cancer stem/progenitor cells (BCSCs) are a subpopulation of breast cancer cells associated with tumor initiation, chemoresistance and metastatic behavior, and may be enriched by mammosphere cultivation. Previous studies have demonstrated that BCSCs exhibit vasculogenic mimicry (VM) activity via the epidermal growth factor receptor (EGFR) signaling pathway. The present study investigated the anti-VM activity of hinokitiol in BCSCs. At a concentration below the half maximal inhibitory concentration, hinokitiol inhibited VM formation of mammosphere cells derived from two human breast cancer cell lines. Hinokitiol was additionally indicated to downregulate EGFR protein expression in mammosphere-forming BCSCs without affecting the expression of messenger RNA. The protein stability of EGFR in BCSCs was also decreased by hinokitiol. The EGFR protein expression and VM formation capability of hinokitiol-treated BCSCs were restored by co-treatment with MG132, a proteasome inhibitor. In conclusion, the present study indicated that hinokitiol may inhibit the VM activity of BCSCs through stimulating proteasome-mediated EGFR degradation. Hinokitiol may act as an anti-VM agent, and may be useful for the development of novel breast cancer therapeutic agents.

Zn(ii) and Cu(ii) complexes containing bioactive O,O-chelated ligands: homoleptic and heteroleptic metal-based biomolecules

Zn(ii) or Cu(ii) highly stable complexes with chelated O,O-donor ligands from natural extractions give rise to drug delivery systems, new biologically active complexes and potential diagnostic agents due to their intrinsic spectroscopic properties.

Hinokitiol is a novel glycoprotein VI antagonist on human platelets

Hinokitiol (4-isopropyl-tropolone) is a bioactive compound with various pharmacological activities that is found in the wood of cupressaceous plants. Platelet activation plays an important role in thrombogenesis. In our previous study, hinokitiol specifically inhibited collagen-induced platelet aggregation ex vivo and prolonged thrombogenesis in vivo. The glycoprotein (GP) VI and integrin α2β1 are major collagen receptors that mediate platelet adhesion and aggregation. In our current study, we investigated which of these collagen receptors is involved in the hinokitiol-mediated inhibition of platelet activation. Treatment with 2-100 µM hinokitiol caused a dose-dependent right, parallel shift in the collagen concentration-response curve (0.5-10 µg/ml), with no change in the maximal responses. Furthermore, hinokitiol inhibited platelet aggregation and relative [Ca(2+)]i mobilization stimulated by convulxin, an agonist of GP VI, but not by aggretin, an agonist of integrin α2β1, indicating that hinokitiol mediates the inhibition of platelet activation through GP VI, rather than through integrin α2β1. Hinokitiol also specifically inhibited the convulxin-mediated activation of protein kinase C, phospholipase Cγ2, Akt, mitogen-activated protein kinases, and Lyn. Hinokitiol markedly diminished the co-immunoprecipitation of GP VI-bound Lyn after convulxin stimulation. In conclusion, hinokitiol, an antagonist of collagen GP VI may represent a novel antiplatelet drug for the prevention of thrombi associated with coronary and cerebral artery diseases.

Hinokitiol inhibits platelet activation ex vivo and thrombus formation in vivo

Hinokitiol is a tropolone-related bioactive compound that has been used in hair tonics, cosmetics, and food as an antimicrobial agent. Recently, hinokitiol has attracted considerable interest because of its anticancer activities. Platelet activation plays a crucial role in atherothrombotic processes. We examined the effects of hinokitiol treatment on platelet activation using human platelets. In the present study, hinokitiol (1 and 2 μM) inhibited the collagen-induced aggregation of human platelets, but did not inhibit the activation of platelets by other agonists, including thrombin, arachidonic acid, and ADP. Hinokitiol inhibited the phosphorylation of phospholipase C (PLC)γ2, protein kinase C (PKC), mitogen-activated protein kinases (MAPKs), and Akt in collagen-activated human platelets, and significantly reduced intracellular calcium mobilization and hydroxyl radical (OH·) formation. Hinokitiol also reduced the PKC activation and platelet aggregation stimulated by PDBu. In addition, hinokitiol significantly prolonged thrombogenesis in mice. Hinokitiol did not influence the binding of a fluorescent triflavin probe to the αIIbβ3 integrin on platelet membrane, and neither ODQ nor SQ22536 significantly reversed the hinokitiol-mediated inhibition of platelet aggregation. In conclusion, hinokitiol may inhibit platelet activation by inhibiting the PLCγ2-PKC cascade and hydroxyl radical formation, followed by suppressing the activation of MAPKs and Akt. Our study suggests that hinokitiol may represent a potential therapeutic agent for the prevention or treatment of thromboembolic disorders.

p27-Associated G1 arrest induced by hinokitiol in human malignant melanoma cells is mediated via down-regulation of pRb, Skp2 ubiquitin ligase, and impairment of Cdk2 function

Increasing evidence has confirmed that hinokitiol (beta-thujaplicin), a tropolone-related compound, exhibits anticancer activity in a variety of cancers through inhibition of cell proliferation. The present study indicates that hinokitiol selectively inhibits cell growth and DNA synthesis in FEM human melanoma cells. Hinokitiol-induced growth inhibition was associated with strong G1 cell cycle arrest. Consistent with blocking the G1-S-phase transition, hinokitiol markedly increased p27 protein levels, but caused only a moderate increase in p21, in addition to a decrease in Cdk2, cyclin E, and phosphorylated Rb. In addition, hinokitiol increased the stability of the p27 protein by inhibiting p27 phosphorylation at Thr(187) and by down-regulating Skp2 expression. siRNA knockdown of p27 abrogated hinokitiol-mediated growth inhibition, while knockdown of Skp2 exacerbated the G1 arrest. In addition to increasing Cdk inhibitor levels and decreasing cyclin A expression, hinokitiol also impaired Cdk2 function by inhibiting Cdk2 kinase activity, impeding cyclin E or A/Cdk2 binding, and inducing translocation of the Cdk2 protein complex. Taken together, our data demonstrate that the novel anticancer mechanism of hinokitiol involves accumulation of p27, down-regulation of Skp2, and impairment of Cdk2 function in FEM human melanoma cells. The therapeutic potential of hinokitiol may lead to novel cell-cycle-based anticancer strategies for malignant melanoma.

Hinokitiol, a metal chelator derived from natural plants, suppresses cell growth and disrupts androgen receptor signaling in prostate carcinoma cell lines

Hinokitiol (beta-thujaplicin), a troplone-related compound found in the heartwood of cupressaceous plants, strongly inhibits the proliferation of a broad range of tumor cell lines. This is the first report to demonstrate that hinokitiol, a metal chelator derived from natural plants, suppresses cell growth and disrupts AR signaling in prostate carcinoma cell lines. Our present studies indicate that hinokitiol suppresses androgen/AR-mediated cell growth and androgen-stimulated DNA synthesis by [(3)H]thymidine incorporation in a dose- and time-dependent manner. Hinokitiol simultaneously suppresses the intracellular and secreted PSA levels, a marker for the progression of prostate cancer. Hinokitiol significantly represses the AR mRNA and protein expression in a dose- and time-dependent manner. Additionally, the ligand-binding assay shows that hinokitiol blocks binding of the synthetic androgen [(3)H]R1881 to AR in LNCaP cells. These findings collectively suggest that hinokitiol is potentially effective against prostate cancer in vitro, and thus it might become a novel chemopreventive or chemotherapeutic agent for prostate cancer.

Human metallothionein gene expression is upregulated by beta-thujaplicin: possible involvement of protein kinase C and reactive oxygen species

Recently, we discovered that beta-thujaplicin (BT) induces metallothionein (MT) expression in mouse keratinocytes, both in vivo and in vitro. However, the molecular mechanisms by which BT exerts its biological effects have not been elucidated. The purpose of this study is to explore the signal transduction pathway involved in the MT mRNA induction by BT. Using a HaCaT keratinocyte cell line, Northern blotting was performed for analyzing the human MT-IIA mRNA expression levels in combination with BT and a number of protein kinase (PK) inhibitors including H7, HA1004 and a PKC-specific inhibitor chelerythrin. CAT assays with the MT-IIA gene promorter-CAT construct were conducted for examining the transcriptional regulation by BT of MT. A free radical scavenger N-acetylcysteine (NAC) was used for analyzing a role of oxidative stress for the MT gene induction by BT. BT increased MT-IIA gene transcript levels and CAT activity in a dose-dependent fashion in HaCaT cells. The increase in MT-IIA mRNA levels and CAT activity were completely suppressed by H7 but not by HA1004. In addition, chelerythrin prevented BT-inducible MT-IIA promoter activation. Furthermore, NAC suppressed BT-inducible MT-IIA promoter activation. These results demonstrate that BT is a potent activator of the MT-IIA gene promoter and that PKC activation and reactive oxygen species are implicated in BT-inducible MT-IIA gene expression. BT may be a useful tool for dissecting the signal transduction pathway mediating MT-IIA promoter activation.

New molecular bioassays for the estimation of the teratogenic potency of valproic acid derivatives in vitro: activation of the peroxisomal proliferator-activated receptor (PPARdelta)

Therapy with the antiepileptic drug valproic acid (2-propylpentanoic acid, VPA) during early pregnancy can cause teratogenic effects (neural tube defects) in humans and in mice. VPA and a teratogenic derivative specifically induce differentiation of F9 teratocarcinoma cells and activate PPARdelta. We have now studied structure-activity relationships of 11 VPA-related compounds by quantitatively comparing their teratogenic potency with their effects in the two novel in vitro systems. Based on the induction of a Rous sarcoma virus (RSV) promoter-driven reporter gene, which is associated with the differentiation of F9 cells, a system suitable for high-throughput and quantitative screening was established. Structure-activity investigations showed that only teratogenic derivatives of VPA induced the response in F9 cells as well as activated the PPARdelta-dependent reporter system in Chinese hamster ovary (CHO) cells. Increases in the length of the side chain in the VPA-related 2-alkyl-pentynoic acid generate more potent inducers in the cell-culture-based assays, which also show higher teratogenicity and embryonic lethality rates. Activation of PPARdelta correlated well with the effects in the F9 cell assay and with teratogenic potency in vivo (p < 0.007). Evaluation of the effects of the presented set of compounds allows the conclusion that the in vitro systems faithfully reflect teratogenicity of VPA-related compounds. Whether the activation of PPARdelta is causally related to the disruption of proper embryonic development or whether it reflects other yet unknown VPA-induced events remains to be established.

Induction of apoptosis by hinokitiol, a potent iron chelator, in teratocarcinoma F9 cells is mediated through the activation of caspase-3

Hinokitiol, a potent iron chelator, has been reported to induce differentiation in teratocarcinoma F9 cells with a reduction of viable cells. In this study, we examined the steps leading to eventual cell death by hinokitiol during differentiation. Hinokitiol induced DNA fragmentation of F9 cells in a concentration- and time-dependent manner. This effect was also observed in a cell-free system using the nuclei from intact cells and the cytosols from hinokitiol-treated cells. In contrast, hinokitiol methyl ether and hinokitiol-Fe (III) complex, which are deficient in iron-chelating activity, showed no DNA fragmentation activity in both cell culture and cell-free systems. These results suggest that iron deprivation by hinokitiol may be involved in the induction of apoptosis of F9 cells. Caspase-3, one of the key enzymes in the apoptotic cascade, was specifically activated by hinokitiol treatment, but not by the other two derivatives. In addition, its specific inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone, strongly blocked hinokitiol-induced DNA fragmentation. These results indicate that iron deprivation by hinokitiol can induce apoptosis of F9 cells through the activation of caspase-3.

Mechanism of mitochondrial dysfunction and cytotoxicity induced by tropolones in isolated rat hepatocytes

The mechanism of mitochondrial dysfunction and toxicity induced by the tropolones, beta-thujaplicin (4-isopropyl tropolone), tropolone and tropone, has been studied in freshly isolated rat hepatocytes. Incubation of hepatocytes with beta-thujaplicin (1-4 mM) elicited a concentration and time-dependent cell killing. The toxicity was accompanied by losses of cellular ATP, total adenine nucleotides and glutathione, independently of lipid peroxidation and protein thiol oxidation. The beta-thujaplicin-induced cytotoxicity was enhanced by the pretreatment of hepatocyte suspensions with EDTA (4 mM), a hydrophilic chelator, or by incubation in Ca2+ and Mg2+-deficient Krebs-Henseleit buffer. The partition coefficient of beta-thujaplicin, which formed complex with the divalent cations in Krebs-Henseleit buffer, in n-octanol/buffer was increased either in the presence of EDTA or absence of divalent cations. Comparison of toxic effects based on cell viability and adenine nucleotide levels showed that beta-thujaplicin was more toxic than tropolone or tropone in Krebs-Henseleit buffer containing EDTA (4 mM). The addition of beta-thujaplicin to isolated hepatic mitochondria reduced state 3 respiration with NAD+-linked substrate (pyruvate plus malate) and/or with an FAD-linked substrate (succinate plus rotenone), whereas state 3 respiration of ascorbate plus tetramethyl-p-phenylenediamine (cytochrome oxidase-linked respiration) was not significantly affected by beta-thujaplicin. Further, the addition of these tropolones caused a concentration-dependent increase in the rate of state 4 oxygen consumption, indicating an uncoupling effect. These results indicate that beta-thujaplicin- and tropolone-induced cytotoxicity are associated with an acute ATP depletion via mitochondrial dysfunction related to oxidative phosphorylation and that the induction of cytotoxicity is affected by EDTA or divalent cations.

Thujaplicin-copper chelates inhibit replication of human influenza viruses

The effects of alpha-, beta- and gamma-thujaplicins and six of their metal chelates on human influenza virus-induced apoptosis in Madin-Darby canine kidney (MDCK) cells were examined by DNA fragmentation and flow cytometry. Among the compounds tested, thujaplicin copper chelates inhibited apoptosis induced in the infected MDCK cells with influenza A/PR/8/34(H1N1), A/Shingapol/1/57(H2N2), A/Aichi/2/68(H3N2) and B/Lee/40 viruses, at concentrations of more than 5 microM. These results indicate that the copper chelates inhibit influenza virus-induced apoptosis and that the inhibitory effects may be independent of influenza virus subtype or types. Furthermore, the copper chelates also inhibited the release of the viruses from the infected MDCK cells during apoptosis. The anti-apoptotic effects of the copper chelates may occur 2 4 h postinfection, suggesting that the copper chelates affect MDCK cells directly in the early stage of influenza virus-induced apoptosis. In this study, we demonstrated that thujaplicin-copper chelates inhibit influenza virus-induced apoptosis of MDCK cells and also inhibit virus replication and release from the infected cells.

Induction of differentiation and apoptosis by dithizone in human myeloid leukemia cell lines

We investigated the effect of diphenylthiocarbazone (dithizone) and its structurally related compounds on the differentiation and apoptosis of two human myeloid leukemia cell lines. Dithizone caused a time- and concentration-dependent induction of differentiation in both the promyelocytic leukemia cell line HL-60 cells and the myeloblastic leukemia cell line ML-1 cells, as measured by nitroblue tetrazolium (NBT) reducing activity. Morphological changes and esterase activities confirmed that this differentiation took place. The induction of differentiation required the addition of dithizone to the culture medium for at least 12 h. The differentiation inducing activity was inhibited by the preincubation of dithizone with various metal ions such as Pb2+, Zn2+, Cu2+ and Mn2+ ions, but not with Fe3+ and Mg2+ ions. In addition, the DNA extracted from dithizone-treated HL-60 cells showed a typical ladder pattern characteristic of apoptosis in agarose gel electrophoresis. A quantitative analysis of DNA fragmentation revealed that this apoptosis was concentration- and time-dependent in both the HL-60 and ML-1 cells. Dithizone-induced apoptosis was also inhibited by preincubation with Mn2+ ions, but not with Mg2+ ions. These results indicate that dithizone induces both differentiation and apoptosis in HL-60 and ML-1 cells through a unique mechanism including metal chelation.

Induction of embryonal carcinoma cell differentiation by deferoxamine, a potent therapeutic iron chelator

We investigated the effects of deferoxamine on the differentiation of embryonal carcinoma F9 cells. Deferoxamine, a widely used therapeutic agent for thalassemia and iron overload, was found to induce F9 cell differentiation and to have some unique characteristics compared with other chelators, hinokitiol and dithizone, which were previously reported to induce differentiation of these cells. This hydrophilic agent induced reversible differentiation as did sodium butyrate, whereas other chelators did not. However, morphological features of the cells after deferoxamine-induced differentiation were similar to those of cells incubated with the other chelators. The differentiation-inducing activity of deferoxamine was abolished by preincubation with Fe3+ ions, similarly to the other chelators examined. Moreover, cell proliferation was inhibited by treatment with this agent, and the numbers of cells in the colonies were reduced by apoptosis. Based on these results, we conclude that deferoxamine induces differentiation and apoptosis of F9 cells via chelation of extracellular and/or intracellular Fe3+ ions.