Identification of a novel synthetic thiazolidin compound capable of inducing c-Jun NH2-terminal kinase-dependent apoptosis in human colon cancer cells

High-content microscopy reveals a morphological signature of bortezomib resistance

Drug resistance is a challenge in anticancer therapy. In many cases, cancers can be resistant to the drug prior to exposure, that is, possess intrinsic drug resistance. However, we lack target-independent methods to anticipate resistance in cancer cell lines or characterize intrinsic drug resistance without a priori knowledge of its cause. We hypothesized that cell morphology could provide an unbiased readout of drug resistance. To test this hypothesis, we used HCT116 cells, a mismatch repair-deficient cancer cell line, to isolate clones that were resistant or sensitive to bortezomib, a well-characterized proteasome inhibitor and anticancer drug to which many cancer cells possess intrinsic resistance. We then expanded these clones and measured high-dimensional single-cell morphology profiles using Cell Painting, a high-content microscopy assay. Our imaging- and computation-based profiling pipeline identified morphological features that differed between resistant and sensitive cells. We used these features to generate a morphological signature of bortezomib resistance. We then employed this morphological signature to analyze a set of HCT116 clones (five resistant and five sensitive) that had not been included in the signature training dataset, and correctly predicted sensitivity to bortezomib in seven cases, in the absence of drug treatment. This signature predicted bortezomib resistance better than resistance to other drugs targeting the ubiquitin-proteasome system, indicating specificity for mechanisms of resistance to bortezomib. Our results establish a proof-of-concept framework for the unbiased analysis of drug resistance using high-content microscopy of cancer cells, in the absence of drug treatment.

High-content microscopy reveals a morphological signature of bortezomib resistance

Drug resistance is a challenge in anticancer therapy, particularly with targeted therapeutics and cytotoxic compounds. In many cases, cancers can be resistant to the drug prior to exposure, i.e., possess intrinsic drug resistance. However, we lack target-independent methods to anticipate resistance in cancer cell lines or characterize intrinsic drug resistance without a priori knowledge of its cause. We hypothesized that cell morphology could provide an unbiased readout of drug sensitivity prior to treatment. We therefore isolated clonal cell lines that were either sensitive or resistant to bortezomib, a well-characterized proteasome inhibitor and anticancer drug to which many cancer cells possess intrinsic resistance. We then measured high-dimensional single-cell morphology profiles using Cell Painting, a high-content microscopy assay. Our imaging- and computation-based profiling pipeline identified morphological features typically different between resistant and sensitive clones. These features were compiled to generate a morphological signature of bortezomib resistance, which correctly predicted the bortezomib treatment response in seven of ten cell lines not included in the training dataset. This signature of resistance was specific to bortezomib over other drugs targeting the ubiquitin-proteasome system. Our results provide evidence that intrinsic morphological features of drug resistance exist and establish a framework for their identification.

Drug resistance dependent on allostery: A P-loop rigor Eg5 mutant exhibits resistance to allosteric inhibition by STLC

The mitotic kinesin Eg5 has emerged as a potential anti-mitotic target for the purposes of cancer chemotherapy. Whether clinical resistance to these inhibitors can arise is unclear. We exploited HCT116 cancer cell line to select resistant clones to S-trityl-L-cysteine (STLC), an extensively studied Eg5 loop-L5 binding inhibitor. The STLC resistant clones differed in their resistance to other loop-L5 binding inhibitors but remained sensitive to the ATP class of competitive Eg5 specific inhibitors. Eg5 is still necessary for bipolar spindle formation in the resistant clones since the cells were sensitive to RNAi mediated depletion of Eg5. One clone expressing Eg5(T107N), a dominant point mutation in the P-loop of the ATP binding domain of the motor, appeared to be not only resistant but also dependent on the presence of STLC. Eg5(T107N) expression was associated also with resistance to the clinical relevant loop-L5 Eg5 inhibitors, Arry-520 and ispinesib. Ectopic expression of the Eg5(T107N) mutant in the absence of STLC was associated with strong non-exchangeable binding to microtubules causing them to bundle. Biochemical assays showed that in contrast to the wild type Eg5-STLC complex, the ATP binding site of the Eg5(T107N) is accessible for nucleotide exchange only when the inhibitor is present. We predict that resistance can be overcome by inhibitors that bind to other than the Eg5 loop-L5 binding site having different chemical scaffolds, and that allostery-dependent resistance to Eg5 inhibitors may also occur in cells and may have positive implications in chemotherapy since once diagnosed may be beneficial following cessation of the chemotherapeutic regimen.

Roles and Interaction of the MAPK Signaling Cascade in Aβ25-35-Induced Neurotoxicity Using an Isolated Primary Hippocampal Cell Culture System

Alzheimer's disease (AD) is characterized with increased formation of amyloid-β (Aβ) in the brain. Aβ peptide toxicity is associated with disturbances of several intracellular signaling pathways such as mitogen activated protein kinases (MAPKs). The aim of this study was to investigate the role of MAPKs and their interactions in Aβ-induced neurotoxicity using isolated hippocampal neurons from the rat. Primary hippocampal cells were cultured in neurobasal medium for 4 days. Cells were treated with Aβ25-35 and/or MAPKs inhibitors for 24 h. Cell viability was determined by an MTT assay and phosphorylated levels of P38, JNK, and ERK were measured by Western blots. Aβ treatment (10-40 µM) significantly decreased hippocampal cell viability in a dose-dependent manner. Inhibition of P38 and ERK did not restore cell viability, while JNK inhibition potentiated the Aβ-induced neurotoxicity. Compared to the controls, Aβ treatment increased levels of phosphorylated JNK, ERK, and c-Jun, while it had no effect on levels of phosphorylated P38. In addition, P38 inhibition led to decreased expression levels of phosphorylated ERK; inhibition of JNK resulted in decreased expression of c-Jun; and inhibition of ERK, decreased phosphorylated levels of JNK. These results strongly suggest that P38, ERK, and JNK are not independently involved in Aβ-induced toxicity in the hippocampal cells. In AD, which is a multifactorial disease, inhibiting a single member of the MAPK signaling pathway, does not seem to be sufficient to mitigate Aβ-induced toxicity and thus their interactions with each other or potentially with different signaling pathways should be taken into account.

Heterozygous mutations in valosin-containing protein (VCP) and resistance to VCP inhibitors

In recent years, multiple studies including ours have reported on the mechanism of resistance towards valosin-containing protein (VCP) inhibitors. While all these studies reported target alterations via mutations in VCP as the primary mechanism of resistance, discrepancies persist to date regarding the zygosity of these mutations responsible for the resistance. In addition, the extent to which resistant cells harbor additional mutations in other genes is not well described. In this study, we performed global transcript analysis of the parental and previously reported VCP inhibitor (CB-5083) resistant cells and found additional mutations in the resistant cells. However, our CRISPR-Cas9 gene editing studies indicate that specific mutations in VCP are sufficient to produce resistance to CB-5083 suggesting the importance of on-target mutations in VCP for resistance. Strikingly, our analysis indicates a preexisting heterozygous frameshift mutation at codon 616 (N616fs*) in one of the VCP alleles in HCT116 cells, and we showed that this mutant allele is subjected to the nonsense-mediated decay (NMD). Accordingly, we identified a heterozygous mutation at codon 526 (L526S) in genomic DNA sequencing but a homozygous L526S mutation in complementary DNA sequencing in our independently generated CB-5083 resistant HCT116 cells, implying that the L526S mutation occurs in the allele that does not harbor the frameshift N616fs* mutation. Our results suggest the NMD as a possible mechanism for achieving the homozygosity of VCP mutant responsible for the resistance to VCP inhibitors while resolving the discrepancies among previous studies. Our results also underscore the importance of performing simultaneous genomic and complementary DNA sequencing when attributing mutational effects on the functionality particularly for an oligomer protein like VCP.

Novel Natural Product- and Privileged Scaffold-Based Tubulin Inhibitors Targeting the Colchicine Binding Site

Tubulin inhibitors are effective anticancer agents, however, there are many limitations to the use of available tubulin inhibitors in the clinic, such as multidrug resistance, severe side-effects, and generally poor bioavailability. Thus, there is a constant need to search for novel tubulin inhibitors that can overcome these limitations. Natural product and privileged structures targeting tubulin have promoted the discovery and optimization of tubulin inhibitors. This review will focus on novel tubulin inhibitors derived from natural products and privileged structures targeting the colchicine binding site on tubulin.

JNK signaling pathway is involved in piperlongumine-mediated apoptosis in human colorectal cancer HCT116 cells

Piperlongumine (PPLGM), an alkaloid isolated from the long pepper (Piper longum L.), can selectively trigger cancer cell death in colorectal cancer cells. The present study investigated whether the c-Jun NH₂-terminal kinase (JNK) signaling pathway is involved in PPLGM-induced apoptosis in the human colorectal cancer HCT116 cell line. The results demonstrated that PPLGM reduced the cell viability and induced cell apoptosis in a time- and concentration-dependent manner, without a significant effect on cell cycle distribution. Meanwhile, treatment with 10 µM PPLGM resulted in JNK activation within 1 h, and a marked and sustained increase in c-Jun phosphorylation in the HCT116 cells. In addition, SP600125, a general inhibitor of JNK, inhibited PPLGM-induced apoptosis in the HCT116 cells by inhibiting PPLGM-induced c-Jun phosphorylation. Altogether, it can be concluded that the JNK signaling pathway, at least in part, is involved in PPLGM-mediated apoptosis in HCT116 cells.

Vitexin 6, a novel lignan, induces autophagy and apoptosis by activating the Jun N-terminal kinase pathway

Previous studies have reported that vitexins induce cytotoxic effects. In the present study, we investigate a new native lignan vitexin 6 (VB6) in vitro to determine the molecular mechanism underlying its cytotoxicity. We screened and cultured several tumor cell lines and subsequently analyzed VB6 cytotoxicity against 14 different tumor cell lines using a 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. The expression of proteins that regulate apoptosis and autophagy was determined using western blot analysis. VB6 showed an excellent cytotoxic effect against various cancer cell lines in vitro. It induced apoptosis and autophagy of cancer cells. VB6-induced apoptosis showed a time-dependent and concentration-dependent relationship with cleaved poly (ADP-ribose) polymerase, cleaved caspase-3, Bax upregulation, and Bcl-2 downregulation. The levels of Beclin-1 and LC3-II, which are markers for cell autophagy, gradually increased after VB6 treatment. Jun N-terminal kinase (JNK) phosphorylation was increased after VB6 treatment, accompanied by upregulation of P-Bcl-2 and P-C-Jun expression. Cotreatment with a JNK inhibitor significantly decreased VB6-induced cell death and downregulated P-Bcl-2, and cleaved PARP and Beclin-1 expression. The new native lignan VB6 inhibits cancer cell proliferation by activating the JNK pathway. We believe that VB6 could be a valuable chemotherapeutic drug after further evaluation.

2-Aminothiazolones as anti-HIV agents that act as gp120-CD4 inhibitors

We report here the synthesis of 2-aminothiazolones along with their biological properties as novel anti-HIV agents. Such compounds have proven to act through the inhibition of the gp120-CD4 protein-protein interaction that occurs at the very early stage of the HIV-1 entry process. No cytotoxicity was found for these compounds, and broad antiviral activities against laboratory strains and pseudotyped viruses were documented. Docking simulations have also been applied to predict the mechanism, at the molecular level, by which the inhibitors were able to interact within the Phe43 cavity of HIV-1 gp120. Furthermore, a preliminary absorption, distribution, metabolism, and excretion (ADME) evaluation was performed. Overall, this study led the basis for the development of more potent HIV entry inhibitors.

Synthesis of New N,N'-Bis(5-arylidene-4-oxo-4,5-dihydrothiazolin-2-yl)piperazine Derivatives Under Microwave Irradiation and Preliminary Biological Evaluation

New N,N’-bis(5-arylidene-4-oxo-4,5-dihydrothiazoline-2-yl)diamine derivatives 5 were prepared in two steps from rhodanine and piperazine, or 1,4-bis(3-amino-propyl)piperazine, under microwave reaction conditions with retention of configuration. Some of these compounds were tested for in vitro antiproliferative activities and for their kinase inhibitory potencies towards six kinases (CDK5/p25, GSK3α/β, DYRK1A, DYRK2, CLK1, and CLK2). The compound 5d showed nanomolar activity towards DYRK1A kinase (IC₅₀ = 0.041 μM).

Resistance to paclitaxel in hepatoma cells is related to static JNK activation and prohibition into entry of mitosis

Hepatocellular carcinoma (HCC) generally shows chemoresistant features to anticancer agents. Paclitaxel has been clinically used in the treatment of various cancers. However, effect of paclitaxel on HCC has not been adequately addressed. Here, we found two categories of hepatoma cells in response to paclitaxel. Paclitaxel effectively decreased the cell viability of SNU475, Hep3B, and SNU387 HCC cells and Chang liver cells (death prone). In contrast, the other five hepatoma cell lines (SNU449, SNU398, SUN368, SNU354, and HepG2 cells) were resistant to paclitaxel (death reluctant). In response to paclitaxel, Bcl-2 was highly phosphorylated in death-prone cells, whereas much less Bcl-2 was phosphorylated in death-reluctant cells. Cotreatment with SP600125, an inhibitor JNK, significantly reduced the phosphorylated Bcl-2 in death-prone cells and caused a significant reduction in cell death. The reduced cell death was due to prohibition into mitotic entry as evidenced by low cyclin B(1)/Cdk1 kinase activity. In death-reluctant cells, inbuild-phospho-JNK levels were high but no longer activated in response to paclitaxel. We found that paclitaxel combined with caffeine or UCN-01, inhibitors of G(2) DNA damage checkpoint, was able to partially overcome resistance to paclitaxel in these cells. Thus our data provide the molecular basis of paclitaxel resistance in hepatoma cells, and appropriate combination therapy may increase treatment efficacy.

Using transcriptome sequencing to identify mechanisms of drug action and resistance

Determining mechanisms of drug action in human cells remains a major challenge. Here we describe an approach in which multiple-drug-resistant clones are isolated and transcriptome sequencing is used to find mutations in each clone. Further analysis of mutations common to more than one clone can identify a drug's physiological target and indirect resistance mechanisms, as indicated by our proof-of-concept studies of the cytotoxic anticancer drugs BI 2536 and bortezomib.

NGX6 inhibits AP-1 and Ets-1 expression and down-regulates cyclin D1 in human colorectal cancer

Colorectal cancer (CRC) is a common malignant tumor that is associated with an increased incidence of morbidity and mortality. Nasopharyngeal carcinoma-associated gene 6 (NGX6) is a novel candidate suppressor gene of tumor metastasis, which is down-regulated in CRC. In the present study, we constructed a colorectal tissue microarray to examine the expression profiles of NGX6, phospho-c-Jun N-terminal kinase (p-JNK), and phospho-extracellular signal-regulated kinase (p-ERK ) in CRC tissues. We found that the NGX6 expression was lower in CRC tissues and metastatic lymph nodes, whereas the expressions of p-JNK and p-ERK were higher in CRC tissues, than in normal intestinal mucosa. The expressions of NGX6, p-JNK, and p-ERK were associated with the clinical pathological features of colorectal tissues. NGX6 overexpression inhibited the activation and nuclear translocation of JNK1, which led to an accumulation of p-JNK in the cytoplasm, but did not inhibit the activation and nuclear translocation of ERK1/2. NGX6 also inhibited the expression of the transcription factors AP-1 (c-jun and c-fos) and Ets-1. In addition, NGX6 overexpression decreased the expression of cyclin D1 and dramatically suppressed the transcriptional efficiency of the cyclin D1 promoter. We propose that NGX6 expression is lost in the multistep process of human colorectal carcinogenesis. Its overexpression can inhibit the expression of transcription factors AP-1 and Ets-1, and down-regulate the transcriptional activity of the cyclin D1 promoter in human CRC.

Identification of hematein as a novel inhibitor of protein kinase CK2 from a natural product library

Background

Casein kinase 2 (CK2) is dysregulated in various human cancers and is a promising target for cancer therapy. To date, there is no small molecular CK2 inhibitor in clinical trial yet. With the aim to identify novel CK2 inhibitors, we screened a natural product library.

Methods

We adopted cell-based proliferation and CK2 kinase assays to screen CK2 inhibitors from a natural compound library. Dose-dependent response of CK2 inhibitors in vitro was determined by a radioisotope kinase assay. Western blot analysis was used to evaluate down stream Akt phosphorylation and apoptosis. Apoptosis was also evaluated by annexin-V/propidium iodide (PI) labeling method using flow cytometry. Inhibition effects of CK2 inhibitors on the growth of cancer and normal cells were evaluated by cell proliferation and viability assays.

Results

Hematein was identified as a novel CK2 inhibitor that is highly selective among a panel of kinases. It appears to be an ATP non-competitive and partially reversible CK2 inhibitor with an IC₅₀ value of 0.55 μM. In addition, hematein inhibited cancer cell growth partially through down-regulation of Akt phosphorylation and induced apoptosis in these cells. Furthermore, hematein exerted stronger inhibition effects on the growth of cancer cells than in normal cells.

Conclusion

In this study, we showed that hematein is a novel selective and cell permeable small molecule CK2 inhibitor. Hematein showed stronger growth inhibition effects to cancer cells when compared to normal cells. This compound may represent a promising class of CK2 inhibitors.

Molecular basis of drug resistance in aurora kinases

Aurora kinases have emerged as potential targets in cancer therapy, and several drugs are currently undergoing preclinical and clinical validation. Whether clinical resistance to these drugs can arise is unclear. We exploited a hypermutagenic cancer cell line to select mutations conferring resistance to a well-studied Aurora inhibitor, ZM447439. All resistant clones contained dominant point mutations in Aurora B. Three mutations map to residues in the ATP-binding pocket that are distinct from the "gatekeeper" residue. The mutants retain wild-type catalytic activity and were resistant to all of the Aurora inhibitors tested. Our studies predict that drug-resistant Aurora B mutants are likely to arise during clinical treatment. Furthermore, because the plasticity of the ATP-binding pocket renders Aurora B insensitive to multiple inhibitors, our observations indicate that the drug-resistant Aurora B mutants should be exploited as novel drug targets.

JNK-deficiency enhanced oncolytic vaccinia virus replication and blocked activation of double-stranded RNA-dependent protein kinase

Vaccinia virus has recently been used as an expression vector for gene delivery and an oncolytic agent for cancer therapy. Although it has been established that interferon-induced double-stranded RNA (dsRNA)-activated protein kinase (PKR) and RNase L interfere with viral replication, little else is known about the other host factors that might affect viral replication and virus-mediated host cell killing. In this study, we evaluated the roles of c-Jun NH2-terminal kinase (JNK) in oncolytic vaccinia virus replication and vaccinia virus-mediated host cell killing. We found that JNK knockout mouse embryonic fibroblasts (MEFs) were more susceptible to oncolytic vaccinia virus infection than wild-type MEFs. Moreover, viral replication and the production of infectious viral progeny were up to 100-fold greater in JNK-deficient MEFs than in wild-type MEFs. A similar result was observed for wild-type vaccinia virus. The increased killing of infected cells and the production of viral progeny was also observed in wild-type MEFs that had been treated with JNK inhibitors and in human colon cancer cells that had been transfected with dominant-negative JNK constructs. Moreover, testing on several human lung cancer cell lines and HeLa cells showed an inverse correlation between levels of JNK expression and susceptibility to oncolytic vaccinia virus. Our study also revealed that oncolytic virus infection-mediated PKR activation was blocked or diminished in JNK-deficient MEFs. The adenovirus-mediated ectopic expression of human PKR in JNK-deficient MEFs reduced vaccinia virus replication to the levels observed in wild-type MEFs, indicating that JNK is required for vaccinia virus to efficiently activate PKR. Our results demonstrated that the cellular status of JNK function can dramatically affect oncolytic vaccinia virus replication and vaccinia virus-mediated host cell killing. This finding may enable further improvements in oncolytic virotherapy using vaccinia virus.

The novel Akt inhibitor, perifosine, induces caspase-dependent apoptosis and downregulates P-glycoprotein expression in multidrug-resistant human T-acute leukemia cells by a JNK-dependent mechanism

A significant impediment to the success of cancer chemotherapy is the occurrence of multidrug resistance, which, in many cases, is attributable to overexpression of membrane transport proteins, such as the 170-kDa P-glycoprotein (P-gp). Also, upregulation of the phosphatidylinositol 3-kinase (PI3K)/Akt-signaling pathway is known to play an important role in drug resistance, and has been implicated in the aggressiveness of a number of different cancers, including T-acute lymphoblastic leukemia (T-ALL). We have investigated the therapeutic potential of the novel Akt inhibitor, perifosine (a synthetic alkylphospholipid), on human T-ALL CEM cells (CEM-R), characterized by both overexpression of P-gp and constitutive upregulation of the PI3K/Akt network. Perifosine treatment induced death by apoptosis in CEM-R cells. Apoptosis was characterized by caspase activation, Bid cleavage and cytochrome c release from mitochondria. The proapoptotic effect of perifosine was in part dependent on the Fas/FasL interactions and c-Jun NH(2)-terminal kinase (JNK) activation, as well as on the integrity of lipid rafts. Perifosine downregulated the expression of P-gp mRNA and protein and this effect required JNK activity. Our findings indicate that perifosine is a promising therapeutic agent for treatment of T-ALL cases characterized by both upregulation of the PI3K/Akt survival pathway and overexpression of P-gp.

Spontaneous regression of colorectal cancer: a review of cases from 1900 to 2005

INTRODUCTION

Spontaneous regression of cancer is an exceptional but well-documented biological event. Further understanding of this phenomenon and harnessing of the mechanisms involved will have significant preventative and therapeutic implications.

DISCUSSION

In this review, the literature of spontaneous regression of colon or rectal cancer is reviewed from 1965 to 2005 to update reviews by Everson et al., Boyd and Challis et al. By adding to these, the author reports the entire series of colorectal cancer, which underwent documented spontaneous regression from 1900 to 2005. The demographic and pathologic characteristics, the details of regression and the outcome of reported cases are presented and discussed. Special emphasis is placed on identifying possible causes hypothesized by authors for occurrence of regression. Possible mechanisms operating to affect these regressions are also discussed.

1,1-Bis(3'-indolyl)-1-(p-substituted phenyl)methanes inhibit ovarian cancer cell growth through peroxisome proliferator-activated receptor-dependent and independent pathways

1,1-Bis(3'-indolyl)-1-(p-t-butylphenyl)methane (DIM-C-pPhtBu) is a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, and treatment of SKOV3 ovarian cancer cells with this compound (5 micromol/L) inhibits cell proliferation, whereas up to 15 micromol/L rosiglitazone had no effect on cell growth. DIM-C-pPhtBu also inhibits G0-G1 to S phase cell cycle progression and this is linked, in part, to PPARgamma-dependent induction of the cyclin-dependent kinase inhibitor p21. DIM-C-pPhtBu induces PPARgamma-independent down-regulation of cyclin D1 and we therefore further investigated activation of receptor-independent pathways. DIM-C-pPhtBu also induced apoptosis in SKOV3 cells and this was related to induction of glucose-related protein 78, which is typically up-regulated as part of the unfolded protein response during endoplasmic reticulum (ER) stress. Activation of ER stress was also observed in other ovarian cancer cell lines treated with DIM-C-pPhtBu. In addition, DIM-C-pPhtBu induced CCAAT/enhancer binding protein homologous protein through both ER stress and c-jun NH2-terminal kinase-dependent pathways, and CCAAT/enhancer binding protein homologous protein activated death receptor 5 and the extrinsic pathway of apoptosis. These results show that DIM-C-pPhtBu inhibits growth and induces apoptosis in ovarian cancer cells through both PPARgamma-dependent and PPARgamma-independent pathways, and this complex mechanism of action will be advantageous for future clinical development of these compounds for treatment of ovarian cancer.

Activation of sterile20-like kinase 1 in proteasome inhibitor bortezomib-induced apoptosis in oncogenic K-ras-transformed cells

Bortezomib (PS-341), a specific proteasome inhibitor, exhibits antitumor activity against a wide range of malignancies. However, the molecular mechanisms by which bortezomib causes apoptosis selectively in cancer cells still remain unclear. Ras signaling is involved in multiple cellular processes, including cell cycle progression, differentiation, and apoptosis, and can either promote or inhibit apoptosis depending on the type of apoptotic stimuli and the cell model. Here, we investigated the role of K-ras signaling in bortezomib-induced apoptosis. We found that K-ras-transformed cells were more susceptible to bortezomib-induced apoptosis than were nontransformed cells and that bortezomib-induced apoptosis was mainly caspase dependent in K-ras-transformed cells. We also found that mammalian sterile20-like kinase 1 (MST1) was activated by bortezomib in K-ras-transformed cells and K-ras-mutated cancer cells. Treatment of K-ras-transformed cells with bortezomib resulted in translocation of MST1 from cytoplasm into the nucleus and an increase of phosphorylated histone H2B and histone H2AX. Moreover, pretreatment with leptomycin B, an inhibitor of the nuclear export signal receptor, dramatically enhanced bortezomib-mediated MST1 activation, phosphorylation of histones H2B and H2AX, and apoptosis induction in K-ras-transformed cells. Knockdown of MST1 expression by small interfering RNA diminished bortezomib-induced apoptosis or caspase-3 activation. Our data suggested that bortezomib may be useful for treatment of K-ras-mutated cancer cells, and MST1 is one of the mediators for bortezomib-induced apoptosis in K-ras-transformed cells.

Acetylcholinesterase expression mediated by c-Jun-NH2-terminal kinase pathway during anticancer drug-induced apoptosis

It has been shown that acetylcholinesterase (AChE) expression was induced during apoptosis and the anti-sense oligonucleotides and siRNA of AChE may prevent apoptosis in various cell types. However, the mechanisms underlying AChE upregulation remain elusive. We demonstrated here that c-Jun NH2-terminal kinase (JNK) could mediate AChE expression. In this study, both etoposide and excisanin A, two anticancer agents, induced apoptosis in colon cancer cell line SW620 as determined by Annexin V staining, the cleavage of caspase-3 and the proteolytic degradation of poly (ADP-ribose) polymerase (PARP). The results showed that both the agents upregulated AChE in SW620 cells. In the meantime, JNK was also activated and the expression and phosphorylation of c-Jun increased in SW620 cells exposed to the two agents. The induced AChE mRNA and protein expression could be blocked by SP600125, a specific inhibitor of SAPK/JNK, and small interfering RNA directed against JNK1/2. Transfection with adenovirus-mediated dominant negative c-Jun also blocked the upregulation of AChE expression. Together, these results suggest that AChE expression may be mediated by the activation of JNK pathway during apoptosis through a c-Jun-dependent mechanism.

Antitumor activity and downregulation of pro-angiogenic molecules in human prostate cancer cells by a novel thiazolidione compound

BACKGROUND

Current treatments for prostate cancer are effective in many patients with locally advanced disease, but many of these patients eventually have recurrence. It is therefore important to develop alternative therapeutic agents with improved efficacy and tolerability. We recently identified a synthetic thiazolidin compound, 5-(2,4-dihydroxybenzylidene)-2-(phenylimino)-1,3-thiazolidione (DBPT), that induces apoptosis in human colon cancer cells, independent of p53 and P-glycoprotein status. Here, we investigated the antitumor properties and mechanisms of action of this compound in human prostate cancer cell lines.

METHODS

The effect of DBPT on cell-cycle progression and apoptosis in LNCaP and DU145 cells was examined by flow cytometry and Western blotting. The effect of DBPT on pro-angiogenic molecules was analyzed by Western blotting and by an enzyme-linked immunosorbent assay.

RESULTS

DBPT inhibited the growth of LNCaP and DU145 cells with 50% inhibitory concentrations ranging from 1.6 to 5.9 microM. Treating LNCaP and DU145 cells with DBPT led to a time-dependent cell-cycle arrest in the G(2)/M phase and increased levels of G(2)/M checkpoint proteins, such as cyclin B1, cdc25C, phosphorylated histone H(3), and MPM-2. DBPT induced the phosphorylation of Bcl-xL and Bim, and induced apoptosis, as evidenced by cleavage of caspase and poly (ADP-ribose) polymerase. DBPT also effectively induced apoptosis in Bcl-2-overexpressing DU145 cells. Furthermore, DBPT decreased hypoxia-inducible factor 1 alpha and vascular endothelial growth factor expression in LNCaP cells under both normoxia and hypoxia.

CONCLUSIONS

DBPT can suppress proliferation, induce apoptosis, and down regulate pro-angiogenic molecules in prostate cancer cells, and might be useful in treating prostate cancer.

JNK1-dependent antimitotic activity of thiazolidin compounds in human non-small-cell lung and colon cancer cells

We recently identified two thiazolidin compounds, 5-[(4-methylphenyl)methylene]-2-(phenylamino)-4(5H)-thiazolone (MMPT) and 5-(2,4-dihydroxybenzylidene)-2-(phenylimino)-1,3-thiazolidin (DBPT), that inhibit the growth of human non-small-cell lung and colon cancer cells independent of P-glycoprotein and p53 status. Here we further investigated the mechanism by which these thiazolidin compounds mediate their anticancer effects. Treatment of cancer cells with MMPT and DBPT led to a time-dependent accumulation of cells arrested in the G2/M phase with modulation of the expression of proteins such as cyclin B1, cdc25C, and phosphorylated histone H3. Moreover, treatment with MMPT and DBPT increased M-phase arrest with abnormal spindle formation. DBPT-mediated G2/M phase arrest and phosphorylation of cdc25C and histone H3 were abrogated when JNK activation was blocked either with SP600125, a specific JNK inhibitor, or a dominant-negative JNK1 gene. Moreover, DBPT-mediated microtubule disruption was also blocked by SP600125 treatment. Our results demonstrate that thiazolidin compounds can effectively induce G2/M arrest in cancer cells and that this G2/M arrest requires JNK activation.