2-Methoxyestradiol and paclitaxel have similar effects on the cell cycle and induction of apoptosis in prostate cancer cells

The Pros and Cons of Estrogens in Prostate Cancer: An Update with a Focus on Phytoestrogens

The role of estrogens in prostate cancer (PCa) is shrouded in mystery, with its actions going from angelic to devilish. The findings by Huggins and Hodges establishing PCa as a hormone-sensitive cancer have provided the basis for using estrogens in therapy. However, despite the clinical efficacy in suppressing tumor growth and the panoply of experimental evidence describing its anticarcinogenic effects, estrogens were abolished from PCa treatment because of the adverse secondary effects. Notwithstanding, research work over the years has continued investigating the effects of estrogens, reporting their pros and cons in prostate carcinogenesis. In contrast with the beneficial therapeutic effects, many reports have implicated estrogens in the disruption of prostate cell fate and tissue homeostasis. On the other hand, epidemiological data demonstrating the lower incidence of PCa in Eastern countries associated with a higher consumption of phytoestrogens support the beneficial role of estrogens in counteracting cancer development. Many studies have investigated the effects of phytoestrogens and the underlying mechanisms of action, which may contribute to developing safe estrogen-based anti-PCa therapies. This review compiles the existing data on the anti- and protumorigenic actions of estrogens and summarizes the anticancer effects of several phytoestrogens, highlighting their promising features in PCa treatment.

Paclitaxel and docetaxel resistance in prostate cancer: Molecular mechanisms and possible therapeutic strategies

Prostate cancer is among most malignant tumors around the world and this urological tumor can be developed as result of genomic mutations and their accumulation during progression towards advanced stage. Due to lack of specific symptoms in early stages of prostate cancer, most cancer patients are diagnosed in advanced stages that tumor cells display low response to chemotherapy. Furthermore, genomic mutations in prostate cancer enhance the aggressiveness of tumor cells. Docetaxel and paclitaxel are suggested as well-known compounds for chemotherapy of prostate tumor and they possess a similar function in cancer therapy that is based on inhibiting depolymerization of microtubules, impairing balance of microtubules and subsequent delay in cell cycle progression. The aim of current review is to highlight mechanisms of paclitaxel and docetaxel resistance in prostate cancer. When oncogenic factors such as CD133 display upregulation and PTEN as tumor-suppressor shows decrease in expression, malignancy of prostate tumor cells enhances and they can induce drug resistance. Furthermore, phytochemicals as anti-tumor compounds have been utilized in suppressing chemoresistance in prostate cancer. Naringenin and lovastatin are among the anti-tumor compounds that have been used for impairing progression of prostate tumor and enhancing drug sensitivity. Moreover, nanostructures such as polymeric micelles and nanobubbles have been utilized in delivery of anti-tumor compounds and decreasing risk of chemoresistance development. These subjects are highlighted in current review to provide new insight for reversing drug resistance in prostate cancer.

Mechanisms of Taxane Resistance

The taxane family of chemotherapy drugs has been used to treat a variety of mostly epithelial-derived tumors and remain the first-line treatment for some cancers. Despite the improved survival time and reduction of tumor size observed in some patients, many have no response to the drugs or develop resistance over time. Taxane resistance is multi-faceted and involves multiple pathways in proliferation, apoptosis, metabolism, and the transport of foreign substances. In this review, we dive deeper into hypothesized resistance mechanisms from research during the last decade, with a focus on the cancer types that use taxanes as first-line treatment but frequently develop resistance to them. Furthermore, we will discuss current clinical inhibitors and those yet to be approved that target key pathways or proteins and aim to reverse resistance in combination with taxanes or individually. Lastly, we will highlight taxane response biomarkers, specific genes with monitored expression and correlated with response to taxanes, mentioning those currently being used and those that should be adopted. The future directions of taxanes involve more personalized approaches to treatment by tailoring drug-inhibitor combinations or alternatives depending on levels of resistance biomarkers. We hope that this review will identify gaps in knowledge surrounding taxane resistance that future research or clinical trials can overcome.

Targeting antioxidant enzymes enhances the therapeutic efficacy of the BCL-XL inhibitor ABT-263 in KRAS-mutant colorectal cancers

Cancer chemotherapeutic drugs exert cytotoxic effects by modulating intracellular reactive oxygen species (ROS) levels. However, whether ROS modulates the efficacy of targeted therapeutics remains poorly understood. Previously, we reported that upregulation of the anti-apoptotic protein, BCL-X_L, by KRAS activating mutations was a potential target for KRAS-mutant colorectal cancer (CRC) treatment. Here, we demonstrated that the BCL-X_L targeting agent, ABT-263, increased intracellular ROS levels and targeting antioxidant pathways augmented the therapeutic efficacy of this BH3 mimetic. ABT-263 induced expression of genes associated with ROS response and increased intracellular ROS levels by enhancing mitochondrial superoxide generation. The superoxide dismutase inhibitor, 2-methoxyestradiol (2-ME), exhibited synergism with ABT-263 in KRAS-mutant CRC cell lines. This synergistic effect was attributed to the inhibition of mTOR-dependent translation of the anti-apoptotic MCL-1 protein via caspase 3-mediated cleavage of AKT and S6K. In addition, combination treatment of ABT-263 and 2-ME demonstrated a synergistic effect in in vivo patient-derived xenografts harboring KRAS mutations. Our data suggest a novel role for ROS in BH3 mimetic-based targeted therapy and provide a novel strategy for treatment of CRC patients with KRAS mutations.

Cabazitaxel exhibits more favorable molecular changes compared to other taxanes in androgen-independent prostate cancer cells

Taxane-based chemotherapy drugs (cabazitaxel, docetaxel, and paclitaxel) are microtubule inhibitors, which are effectively and frequently used to treat metastatic prostate cancer (PCa). Among these, cabazitaxel is offered as a new therapeutic option for patients with metastatic castration-resistant PC as that are resistant to other taxanes. Here, we investigated the cellular and molecular changes in response to cabazitaxel in comparison with docetaxel and paclitaxel in androgen-independent human PCas. The androgen-independent human PCa cell lines, PC3 and DU145, were treated with 1 to 5nM cabazitaxel, docetaxel, or paclitaxel, and assessed for cell viability (MTT assay), colony forming ability and migration (scratch assay). The induction of apoptosis was determined through measurement of mitochondrial membrane potential (JC-1 assay) and caspase-3 activity assay. The protein expression changes (caspase-3, caspase-8, Bax, Bcl-2, β-tubulin, nuclear factor-κB [NF-κB/p50, NF-κB/p65], vascular endothelial growth factor, WNT1-inducible signaling pathway protein-1 [WISP1], transforming growth factor β [TGF-β]) in response to drug treatment were screened via western blotting. Under our experimental conditions, all taxanes significantly reduced WISP1 and TGF-β expressions, suggesting an anti-metastatic/antiangiogenic effect for these drugs. On the other hand, cabazitaxel induced more cell death and inhibited colony formation compared to docetaxel or paclitaxel. The highest fold change in caspase-3 activity and Bax/Bcl-2 ratio was also detected in response to cabazitaxel. Furthermore, the induction of β-tubulin expression was lower in cabazitaxel-treated cells relative to the other taxanes. In summary, cabazitaxel shows molecular changes in favor of killing PCa cells compared to other taxanes, at least for the parameters analyzed herein. The differences with other taxanes may be important while designing other studies or in clinical settings.

Inhibiting Multiple Deubiquitinases to Reduce Androgen Receptor Expression in Prostate Cancer Cells

Prostate cancer (PCa), a leading cause of cancer-related death in men, becomes resistant to androgen deprivation therapy by inducing androgen receptor (AR) activity, which is known as castration-resistant PCa (CRPC). Enzalutamide is an approved drug that inhibits AR activity and increases overall survival. However, resistance to enzalutamide develops rapidly often by increasing AR activity, suggesting that new therapies are required for CRPC. We investigated whether betulinic acid (BA), a small molecule from plants that inhibits multiple deubiquitinases (DUBs), reduces AR, and selectively kills PCa cells, can provide an adjuvant strategy for CRPC. Our data indicated that BA reduced AR protein stability and mRNA expression, making it an attractive agent for CRPC. BA decreased AR mRNA possibly by inhibiting a histone 2A DUB thereby increasing ubiquitinated histone 2A, a transcriptional repressor. We identified multiple and specific DUBs inhibited by BA either in PCa cells or using recombinant DUBs. Similar results were obtained using another multi-DUB inhibitor WP1130, suggesting that these DUB inhibitors can decrease AR expression and increase PCa-specific death. Our results also suggest that combining multi-DUB inhibitors BA or WP1130 with enzalutamide may provide a novel strategy for CRPC by further decreasing AR expression and increasing apoptotic cell death.

Suppression of IKK, but not activation of p53 is responsible for cell death mediated by naturally occurring oxidized tetranortriterpenoid

Tetranortriterpenoids (limonoids) obtained from the neem tree (Azadirachta indica) have gained significant attention due to their anti-proliferative properties. Here we are investigating the role of a highly oxidized tetranortriterpenoid, azadirachtin on induction of the cell death. Using various apoptotic assays, we show that azadirachtin induces cell death independent of cell types. Although azadirachtin-treated cells show increased expression of p53, but no phosphorylation of p53 (at Ser15 and Ser46) is detected. In silico analysis reveals that azadirachtin interacts with Mdm2 in the p53 binding site, postulating the mutually exclusive interaction of p53 and azadirachtin with Mdm2. Surprisingly, azadirachtin potentiates cell death efficiently in both p53 wild-type and p53 negative cells. In addition, we find azadirachtin suppresses nuclear transcription factor kappaB (NF-κB) by inhibiting the phosphorylation of upstream inhibitory subunit of NF-κB (IκB) kinase (IKK). Further, azadirachtin is unable to potentiate apoptosis in NF-κB-downregulated (IκB-DN) cells, whereas ectopic expression of p65 rescues azadirachtin-mediated apoptosis, regardless of their p53 status. Hence, our data suggest that azadirachtin mediates cell death through inhibition of NF-κB, but not due to the activation of p53. In conclusion, this study proposes azadirachtin as a potential therapeutic agent where insensitivity toward chemotherapy occurs due to the inactivation or mutations in p53.

Connexins, important players in the dissemination of prostate cancer cells

Over the past 50years, increasing experimental evidences have established that connexins (Cxs) and gap junctional intercellular communication (GJIC) ensure an important role in both the onset and development of cancerous processes. In the present review, we focus on the impact of Cxs and GJIC during the development of prostate cancer (PCa), from the primary growth mainly localized in acinar glands and ducts to the distant metastasis mainly concentrated in bone. As observed in several other types of solid tumours, Cxs and especially Cx43 exhibit an ambivalent role with a tumour suppressor effect in the early stages and, conversely, a rather pro-tumoural profile for most of invasion and dissemination steps to secondary sites. We report here the current knowledge on the function of Cxs during PCa cells migration, cytoskeletal dynamics, proteinases activities and the cross talk with the surrounding stromal cells in the microenvironment of the tumour and the bones. In addition, we discuss the role of Cxs in the bone tropism even if the prostate model is rarely used to study the complete sequence of cancer dissemination compared to breast cancer or melanoma. Even if not yet fully understood, these recent findings on Cxs provide new insights into their molecular mechanisms associated with progression and bone targeted behaviour of PCa. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Core-Cross-Linking Accelerates Antitumor Activities of Paclitaxel-Conjugate Micelles to Prostate Multicellular Tumor Spheroids: A Comparison of 2D and 3D Models

The 2D monolayer cell culture model is often the first step in the prediction of the success or failure of a nanoparticle-based drug delivery system. However, there is often poor translation between the 2D monolayer in vitro results and the nanoparticle-drug performance in vivo. One possible way of bridging this gap is the use of multicellular tumor spheroids (MCTSs) as an intermediate in vitro model due to its 3D structure. This paper aims to quantify and compare the results obtained from traditional 2D monolayer cell cultures and 3D MCTS by studying the cytotoxic effects of free paclitaxel (PTX) and paclitaxel, which has been conjugated to a poly(ethylene glycol methyl ether acrylate)-b-poly(carboxyethyl acrylate) (POEGMEA-b-PCEA-PTX) block copolymer and self-assembled to give a micellar delivery system. The core of the micelle was cross-linked with a diamino nondegradable cross-linker to compare the effects of micelle stability on the results. Although the 2D prostate tumor cell culture results indicated that all micellar variants (IC50: 193-271 nM) were significantly less toxic than free paclitaxel (IC50: 15.2 nM), the micelles showed faster and higher cytotoxicity than free PTX in the 3D prostate MCTS. The cross-linking of micelles even showed accelerated antitumor activities to the MCTS compared with un-cross-linked micelles. The results indicate that DAO-cross-linked POEGMEA-b-PCEA-PTX conjugate micelles will be a useful nanodrug carrier for prostate cancer therapy. MCTS offers a very promising method of incorporating 3D structures into in vitro testing.

Dependency of 2-methoxyestradiol-induced mitochondrial apoptosis on mitotic spindle network impairment and prometaphase arrest in human Jurkat T cells

The present study sought to determine the correlation between 2-methoxyestradiol (2-MeO-E2)-induced cell cycle arrest and 2-MeO-E2-induced apoptosis. Exposure of Jurkat T cell clone (JT/Neo) to 2-MeO-E2 (0.5-1.0 μM) caused G2/M arrest, Bak activation, Δψm loss, caspase-9 and -3 activation, PARP cleavage, intracellular ROS accumulation, and apoptotic DNA fragmentation, whereas none of these events except for G2/M arrest were induced in Jurkat T cells overexpressing Bcl-2 (JT/Bcl-2). Under these conditions, Cdk1 phosphorylation at Thr-161 and dephosphorylation at Tyr-15, up-regulation of cyclin B1 expression, histone H1 phosphorylation, Cdc25C phosphorylation at Thr-48, Bcl-2 phosphorylation at Thr-56 and Ser-70, Mcl-1 phosphorylation at Ser-159/Thr-163, and Bim phosphorylation were detected irrespective of Bcl-2 overexpression. Concomitant treatment of JT/Neo cells with 2-MeO-E2 and the G1/S blocking agent aphidicolin resulted in G1/S arrest and abrogation of all apoptotic events, including Cdk1 activation, phosphorylation of Bcl-2, Mcl-1 and Bim, and ROS accumulation. The 2-MeO-E2-induced phosphorylation of Bcl-2 family proteins and mitochondrial apoptotic events were suppressed by a Cdk1 inhibitor, but not by an Aurora A kinase (AURKA), Aurora B kinase (AURKB), JNK, or p38 MAPK inhibitor. Immunofluorescence microscopic analysis revealed that 2-MeO-E2-induced mitotic arrest was caused by mitotic spindle network impairment and prometaphase arrest. Whereas 10-20 μM 2-MeO-E2 reduced the proportion of intracellular polymeric tubulin to monomeric tubulin, 0.5-5.0 μM 2-MeO-E2 increased it. These results demonstrate that the apoptogenic effect of 2-MeO-E2 (0.5-1.0 μM) was attributable to mitotic spindle defect-mediated prometaphase arrest, Cdk1 activation, phosphorylation of Bcl-2, Mcl-1, and Bim, and activation of Bak and mitochondria-dependent caspase cascade.

Prostate cancer cell response to paclitaxel is affected by abnormally expressed securin PTTG1

PTTG1 protein, the human securin, has a central role in sister chromatid separation during mitosis, and its altered expression has been reported in many tumor types. Paclitaxel is a widely used chemotherapeutic drug, whose mechanism of action is related to its ability to arrest cells in mitosis and the subsequent induction of the intrinsic apoptotic pathway. By using two prostate cancer cell lines with different responses to paclitaxel treatment, we have identified two situations in which PTTG1 influences cell fate differentially. In slippage-prone PC3 cells, both PTTG1 downregulation and overexpression induce an increase in mitotic cells that is associated with diminished apoptosis after paclitaxel treatment. In LNCaP cells, however, PTTG1 downregulation prevents mitotic entry and, subsequently, inhibits mitosis-associated, paclitaxel-induced apoptosis. In contrast, PTTG1 overexpression induces an increase in mitotic cells and apoptosis after paclitaxel treatment. We have also identified a role for Mcl-1 protein in preventing apoptosis during mitosis in PC3 cells, as simultaneous PTTG1 and Mcl-1 silencing enhances mitosis-associated apoptosis after paclitaxel treatment. The finding that a more efficient mitotic arrest alone in PC3 cells is not enough to increase apoptosis was also confirmed with the observation that a selected paclitaxel-resistant PC3 cell line showed an apoptosis-resistant phenotype associated with increased mitosis upon paclitaxel treatment. These findings could contribute to identify putative responsive and nonresponsive cells and help us to approach incomplete responses to paclitaxel in the clinical setting.

ABT-737, a small molecule Bcl-2/Bcl-xL antagonist, increases antimitotic-mediated apoptosis in human prostate cancer cells

Castration-resistant prostate cancer (CRPC) expresses high levels of the anti-apoptotic proteins Bcl-2, Bcl-xL and Mcl-1, resulting in resistance to apoptosis and association with poor prognosis. Docetaxel, an antimitotic drug that is the first-line treatment strategy for CRPC, is known to provide a small survival benefit. However, docetaxel chemotherapy alone is not enough to counteract the high levels of Bcl-2/Bcl-xL/Mcl-1 present in CRPC. ABT-737 is a small molecule that binds to Bcl-2/Bcl-xL (but not Mcl-1) with high affinity and disrupts their interaction with pro-apoptotic Bax/Bak, thus enhancing apoptosis. Our results indicate that ABT-737 can sensitize androgen-dependent LNCaP and CRPC PC3 cells to docetaxel- and to the novel antimitotic ENMD-1198-mediated caspase-dependent apoptosis. CRPC DU145 cells, however, are more resistant to ABT-737 because they are Bax null and not because they express the highest levels of anti-apoptotic Mcl-1 (associated with ABT-737 resistance). Knockdown of Bax or Bak in LNCaP indicates that ABT-737-induced antimitotic enhancement of apoptosis is more dependent on the levels of Bax than Bak. Furthermore, we find that the ability of docetaxel to increase cyclin B1/Cdk1-mediated phosphorylation of Bcl-2/Bcl-xL and decrease Mcl-1 is required for ABT-737 to enhance apoptosis in PC3 cells, as determined by addition of Cdk1 inhibitor purvalanol A and expression of shRNA specific for cyclin B1. Overall, our data suggests that the high levels of anti-apoptotic proteins in Bax-expressing CRPC cells can be overcome by targeting Bcl-2/Bcl-xL with ABT-737 and Mcl-1 with antimitotics.

Hrk mediates 2-methoxyestradiol-induced mitochondrial apoptotic signaling in prostate cancer cells

Prostate cancer is one of the most prevalent cancers in males and ranks as the second most common cause of cancer-related deaths. 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite, is a promising anticancer agent for various types of cancers. Although 2-ME has been shown to activate c-Jun-NH2-kinase (JNK) and mitochondrial-dependent apoptotic signaling pathways, the underlying mechanisms, including downstream effectors, remain unclear. Here, we report that the human Bcl-2 homology 3 (BH3)-only protein harakiri (Hrk) is a critical effector of 2-ME-induced JNK/mitochondria-dependent apoptosis in prostate cancer cells. Hrk mRNA and protein are preferentially upregulated by 2-ME, and Hrk induction is dependent on the JNK activation of c-Jun. Hrk knockdown prevents 2-ME-mediated apoptosis by attenuating the decrease in mitochondrial membrane potential, subsequent cytochrome c (cyt c) release, and caspase activation. Involvement of the proapoptotic protein Bak in this process suggested the possible interaction between Hrk and Bak. Thus, Hrk activation by 2-ME or its overexpression displaced Bak from the complex with antiapoptotic protein Bcl-xL, whereas deletion of the Hrk BH3 domain abolished its interaction with Bcl-xL, reducing the proapoptotic function of Hrk. Finally, Hrk is also involved in the 2-ME-mediated reduction of X-linked inhibitor of apoptosis through Bak activation in prostate cancer cells. Together, our findings suggest that induction of the BH3-only protein Hrk is a critical step in 2-ME activation of the JNK-induced apoptotic pathway, targeting mitochondria by liberating proapoptotic protein Bak.

Betulinic acid selectively increases protein degradation and enhances prostate cancer-specific apoptosis: possible role for inhibition of deubiquitinase activity

Inhibition of the ubiquitin-proteasome system (UPS) of protein degradation is a valid anti-cancer strategy and has led to the approval of bortezomib for the treatment of multiple myeloma. However, the alternative approach of enhancing the degradation of oncoproteins that are frequently overexpressed in cancers is less developed. Betulinic acid (BA) is a plant-derived small molecule that can increase apoptosis specifically in cancer but not in normal cells, making it an attractive anti-cancer agent. Our results in prostate cancer suggested that BA inhibited multiple deubiquitinases (DUBs), which resulted in the accumulation of poly-ubiquitinated proteins, decreased levels of oncoproteins, and increased apoptotic cell death. In normal fibroblasts, however, BA did not inhibit DUB activity nor increased total poly-ubiquitinated proteins, which was associated with a lack of effect on cell death. In the TRAMP transgenic mouse model of prostate cancer, treatment with BA (10 mg/kg) inhibited primary tumors, increased apoptosis, decreased angiogenesis and proliferation, and lowered androgen receptor and cyclin D1 protein. BA treatment also inhibited DUB activity and increased ubiquitinated proteins in TRAMP prostate cancer but had no effect on apoptosis or ubiquitination in normal mouse tissues. Overall, our data suggests that BA-mediated inhibition of DUBs and induction of apoptotic cell death specifically in prostate cancer but not in normal cells and tissues may provide an effective non-toxic and clinically selective agent for chemotherapy.

Platelets increase survival of adenocarcinoma cells challenged with anticancer drugs: mechanisms and implications for chemoresistance

BACKGROUND AND PURPOSE

Cancer cells grow without the restraints of feedback control mechanisms, leading to increased cancer cell survival. The treatment of cancer is often complicated by the lack of response to chemotherapy leading to chemoresistance and persistent survival of tumour cells. In this work we studied the role of platelets in chemotherapy-induced cancer cell death and survival.

EXPERIMENTAL APPROACH

Human adenocarcinoma cells, colonic (Caco-2) and ovarian (59 M) cells, were incubated with 5-fluorouracil (1-300 µg·mL(-1) ) or paclitaxel (1-200 µg·mL(-1) ) in the presence or absence of platelets (1.5 × 10(8) mL(-1) ) for 1, 24 or 72 h. Following incubation, cancer cells were harvested and cell survival/death was assayed using flow cytometry, Western blotting, real-time PCR, TaqMan® Gene Expression Assays and proteomics.

KEY RESULTS

Human platelets increased the survival of colonic and ovarian adenocarcinoma cells treated with two standard anticancer drugs, 5-fluorouracil and paclitaxel. In the presence of platelets, cancer cells up-regulated anti-apoptotic and down-regulated pro-apoptotic genes, increased the number of cells in the synthesis of DNA and decreased the number in the quiescent phase, increased expression of cyclins, DNA repair proteins and MAPKs. The analysis of platelet-Caco-2 secretome demonstrated the release of the chemokine RANTES, thrombospondin-1, TGF-β and clusterin. Finally, human recombinant RANTES and thrombospondin-1 improved survival of Caco-2 cells challenged with paclitaxel.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate that platelets increase adenocarcinoma cells survival, proliferation and chemoresistance to standard anticancer drugs. Modulating cancer cell-platelet interactions may offer a new strategy to improve the efficacy of chemotherapy.

Critical role of cyclin B1/Cdc2 up-regulation in the induction of mitotic prometaphase arrest in human breast cancer cells treated with 2-methoxyestradiol

Earlier studies showed that 2-methoxyestradiol (2ME(2)), an endogenous nonpolar metabolite of estradiol-17β, is a strong inducer of G(2)/M cell cycle arrest (based on analysis of cellular DNA content) in human cancer cell lines. The present study sought to investigate the molecular mechanism underlying 2ME(2)-induced cell cycle arrest. We found that 2ME(2) can selectively induce mitotic prometaphase arrest, but not G(2) phase arrest, in cultured MDA-MB-435s and MCF-7 human breast cancer cells. During the induction of prometaphase arrest, there is a time-dependent initial up-regulation of cyclin B1 and Cdc2 proteins, occurring around 12-24h. The strong initial up-regulation of cyclin B1 and Cdc2 matches in timing the 2ME(2)-induced prometaphase arrest. The 2ME(2)-induced prometaphase arrest is abrogated by selective knockdown of cyclin B1 and Cdc2, or by pre-treatment of cells with roscovitine, an inhibitor of cyclin-dependent kinases, or by co-treatment of cells with cycloheximide, a protein synthesis inhibitor that was found to suppress the early up-regulation of cyclin B1 and Cdc2. In addition, we provided evidence showing that MAD2 and JNK1 are important upstream mediators of 2ME(2)-induced up-regulation of cyclin B1 and Cdc2 as well as the subsequent induction of mitotic prometaphase arrest. In conclusion, treatment of human cancer cells with 2ME(2) causes up-regulation of cyclin B1 and Cdc2, which then mediate the induction of mitotic prometaphase arrest.

NF-kappaB activation enhances cell death by antimitotic drugs in human prostate cancer cells

Background

NF-κB is a transcription factor that promotes inhibition of apoptosis and resistance to chemotherapy. It is commonly believed that inhibition of NF-κB activity can increase sensitivity of cancer cells to chemotherapy. However, there is evidence that NF-κB activation can sensitize cells to apoptosis and that inhibition of NF-κB results in resistance to chemotherapy. In prostate cancer, it is not clear in the different cell types (androgen-dependent and castration-resistant) if activation or inhibition of NF-κB is required for stimulation of apoptosis by chemotherapy.

Results

Our data indicate that the response of prostate cancer (PC) cells to the antimitotic drugs docetaxel (Doc) and 2-methoxyestradiol (2ME2) is dependent on the levels of NF-κB activity. In androgen-dependent LNCaP cells, Doc and 2ME2 treatment increased the low basal NF-κB activity, as determined by Western blot analysis of phospho-IκBα/p65, NF-κB promoter reporter assays, and p65 localization. Treatment of LNCaP cells with parthenolide, a pharmacologic inhibitor of NF-κB, or introduction of dominant-negative IκBα, or an shRNA specific for p65, a component of the NF-κB heterodimer, blocked apoptosis induced by Doc and 2ME2. In castration-resistant DU145 and PC3 cells, Doc and 2ME2 had little effect on the high basal NF-κB activity and addition of parthenolide did not enhance cell death. However, the combination of Doc or 2ME2 with betulinic acid (BA), a triterpenoid that activates NF-κB, stimulated apoptosis in LNCaP and non-apoptotic cell death in DU145 and PC3 cells. Increased sensitivity to cell death mediated by the Doc or 2ME2 + BA combination is likely due to increased NF-κB activity.

Conclusions

Our data suggest that the combination of antimitotic drugs with NF-κB inhibitors will have antagonistic effects in a common type of PC cell typical of LNCaP. However, combination strategies utilizing antimitotic drugs with BA, an activator of NF-κB, will universally enhance cell death in PC cells, notably in the aggressive, castration-resistant variety that does not respond to conventional therapies.

Novel derivative of benzofuran induces cell death mostly by G2/M cell cycle arrest through p53-dependent pathway but partially by inhibition of NF-kappaB

The Dracaena resin is widely used in traditional medicine as an anticancer agent, and benzofuran lignan is the active component. In this report, we provide evidence that the synthetic derivative of benzofuran lignan (Benfur) showed antitumor activities. It induced apoptosis in p53-positive cells. Though it inhibited endotoxin-induced nuclear factor kappaB (NF-kappaB) activation in both p53-positive and -negative cells, the activation of caspase 3 was observed in p53-positive cells. It showed partial cell death effect in both p53-positive and -negative cells through inhibition of NF-kappaB. Cell cycle analysis using flow cytometry showed that treatment with this novel benozofuran lignan derivative to Jurkat T-cells, but not U-937 cells, resulted in a G2/M arrest in a dose- and time-dependent manner. It increased amounts of p21, p27, and cyclin B, but not phospho-Rb through p53 nuclear translocation in Jurkat T-cells, but not in U-937 cells. It inhibited amounts of MDM2 (murine double minute 2) by repressing the transcription factor Sp1, which was also proved in silico. It induced cell death in tumor cells, but not in primary T-cells. Overall, our data suggest that Benfur-mediated cell death is partially dependent upon NF-kappaB, but predominantly dependent on p53. Thus, this novel benzofuran lignan derivative can be effective chemopreventive or chemotherapeutic agent against malignant T-cells.

2-methoxyestradiol inhibits Barrett's esophageal adenocarcinoma growth and differentiation through differential regulation of the beta-catenin-E-cadherin axis

The purpose of this study was to evaluate whether 2-methoxyestradiol (2-ME(2)), a promising anticancer agent, modulates Barrett's esophageal adenocarcinoma (BEAC) cell growth and behavior through a cellular pathway involving beta-catenin in partnership with E-cadherin, which seems to play a critical role in the induction of antitumor responses in cancer cells. We found that 2-ME(2) markedly reduced the BEAC cell proliferation through regulating apoptotic machinery such as Bcl-2 and Bax. It may nullify the aggressive behavior of the cells by reducing the migratory behavior. Expressions of beta-catenin and E-cadherin and binding of these two proteins is activated in a 2-ME(2)-dependent fashion in Bic-1 cells. Moreover, overexpressions of these two proteins may be due to the stabilization of these proteins by 2-ME(2). We found that 2-ME(2)-induced antimigratory effects are mediated through the beta-catenin-E-cadherin signaling pathways. In view of these results, we determined whether 2-ME(2) reduces BEAC tumor growth. Administration of 2-ME2 significantly decreased the growth of BEAC cells xenografted on the flank of nude mice. The evidence presented points out that the effect of 2-ME(2) on beta-catenin-orchestrated signal transduction plausibly plays a multifaceted functional role to inhibit the proliferation and cell migration of 2-ME(2)-treated malignant cells and it could be a potential candidate in novel treatment strategies for Barrett's esophageal adenocarcinoma.

In vitro effects of 2-methoxyestradiol on cell numbers, morphology, cell cycle progression, and apoptosis induction in oesophageal carcinoma cells

The influence of 2-methoxyestradiol (2-ME) was investigated on cell numbers, morphology, cell cycle progression, and apoptosis induction in an oesophageal carcinoma cell line (WHCO3). Dose-dependent studies (1 x 10(-9)M-1 x 10(-6)M) revealed that 2-ME significantly reduced cell numbers to 60% in WHCO3 after 72 h of exposure at a concentration of 1 x 10(-6)M compared to vehicle-treated cells. Morphological studies entailing light-, fluorescent-, as well as transmission electron microscopy (TEM) confirmed 2-ME's antimitotic effects. These results indicated hallmarks of apoptosis including cell shrinkage, hypercondensation of chromatin, cell membrane blebbing, and apoptotic bodies in treated cells. Flow cytometric analyses demonstrated an increase in the G(2)/M-phase after 2-ME exposure; thus preventing cells from proceeding through the cell cycle. beta-tubulin immunofluorescence revealed that 2-ME caused spindle disruption. In addition, increased expression of death receptor 5 protein was observed further supporting the proposed mechanism of apoptosis induction via the extrinsic pathway in 2-ME-exposed oesophageal carcinoma cells.

Activity of 2 methoxyestradiol (Panzem NCD) in advanced, platinum-resistant ovarian cancer and primary peritoneal carcinomatosis: a Hoosier Oncology Group trial

BACKGROUND

2-Methoxyestradiol (Panzem, 2ME2) is an endogenous metabolite of estradiol that destabilizes microtubules and exerts anti-angiogenic properties. This study was conducted to determine the activity and safety of 2ME2 administered as a NanoCrystal dispersion (NCD) formulation in patients with recurrent, platinum-resistant epithelial ovarian cancer (EOC).

METHODS

Eligible patients had relapsed, platinum-resistant or refractory EOC with measurable or detectable disease. There was no limit on the number of prior treatment regimens. 2ME2 NCD 1000 mg orally four times daily (q.i.d.) was administered continuously during 4 week cycles. The primary endpoint was objective response rate (ORR). Secondary endpoints were assessment of toxicity, rate of clinical benefit defined as the number of patients experiencing an objective response, a CA125 response or stable disease (SD) >3 months, mean change in CA-125, progression-free survival (PFS), and pharmacokinetic analyses of 2ME2.

RESULTS

Eighteen patients were enrolled. Median age was 65.5 (range 40-73). Patients had received a median of five prior treatments. The most common adverse events were fatigue (78%), nausea (78%), diarrhea (39%), neuropathy (50%), edema (39%), and dyspnea (44%), the majority being grade 1-2. There were no objective responses, but seven patients had SD as best response. Of those, two patients had SD for greater than 12 months. The rate of clinical benefit was 31.3%. Fairly stable plasma levels of 2ME2 ranging within the predicted therapeutic window were observed.

CONCLUSIONS

The NCD formulation of 2ME2 is well tolerated in patients with heavily pretreated EOC. Few of these heavily pretreated patients had sustained stable disease.

Mana-Hox displays anticancer activity against prostate cancer cells through tubulin depolymerization and DNA damage stress

Tubulin and deoxyribonucleic acid (DNA) are two potential targets for the development of cancer chemotherapeutic agents. Mana-Hox is a synthetic derivative of beta-carboline, a structure relevant to marine sponge component, manzamine. In this study, Mana-Hox induced an inhibition of cell proliferation in several types of human cancer cell lines, including androgen-independent prostate cancer PC-3 and DU-145, hepatocellular carcinoma Hep3B and HepG2, and colorectal cancer HT-29 cells. The p53-null PC-3 cells were used for to anticancer mechanisms. Mana-Hox stimulated an increase of ataxia telangiectasia mutated (ATM) phosphorylation on Ser-1981, indicating the induction of DNA double-strand breaks. It also displayed an inhibitory effect on tubulin polymerization using tubulin turbidity assay and immunofluorescence identification. However, it only showed a minor inhibition on the activity of Aurora kinase and histone deacetylase. Mana-Hox induced mitotic arrest of the cell cycle identified by downregulation of cyclin E, cyclin A, and cyclin-dependent kinase 2 (Cdk2) and an increase of MPM-2 expression. Next, it caused Bcl-2 phosphorylation on Ser-70, downregulation of Mcl-1 expression, and activation of caspase-3, leading to apoptotic cell death. Notably, Mana-Hox was not a P-glycoprotein (P-gp) substrate and showed equipotent activity against P-gp-rich cancer cells. We conclude that Mana-Hox induces dual effects on DNA damage and tubulin depolymerization, leading to mitotic arrest and activation of mitochondria-mediated apoptotic pathways. Data provide evidence that the anticancer strategy of dual-action targets could be a potential anticancer approach.

Zinc deficiency reduces paclitaxel efficacy in LNCaP prostate cancer cells

Chemotherapeutics used to treat prostate cancer are often from a class of drugs that target microtubule networks, such as paclitaxel. A previous report indicated that supplemental zinc sensitized prostate cancer cells to paclitaxel-induced apoptosis, suggesting that increased zinc levels might enhance paclitaxel efficacy. The effect of zinc deficiency on paclitaxel activity is not known though, so we tested this in two prostate cancer cell lines maintained under moderately zinc-deficient conditions. LNCaP and PC3 cell lines were used as models of early and late-stage prostate cancer, respectively. Cells cultured in reduced zinc levels did not demonstrate altered cell viability, growth rates, or intracellular zinc content. Additionally, zinc deficiency alone had no apparent effect on cell cycle kinetics or apoptosis levels. However, the IC(50) for paclitaxel-induced cell cycle arrest increased in LNCaP cells from zinc-deficient compared to zinc-replete conditions. Consequently, paclitaxel-induced apoptosis was reduced in LNCaP cells from zinc-deficient compared to zinc-replete conditions. In PC3 cells, the effects of paclitaxel were independent of zinc status. Reduced extracellular zinc levels were shown to affect paclitaxel activity in a prostate cancer cell line. Given the prevalence of zinc deficiency, determining how chemotherapeutic action is modulated by zinc adequacy may have clinical importance.

Increased expression of cyclin B1 sensitizes prostate cancer cells to apoptosis induced by chemotherapy

Chemotherapeutic drugs ideally should take advantage of the differences between transformed and normal cells and induce apoptosis only in cancer cells. One such difference may be the overexpression of cyclin B1 protein in cancer cells, which is required for the proper progression through mitosis. Previously, we showed that treatment of human prostate cancer cells with 2-methoxyestradiol (2-ME) or docetaxel results in an accumulation of cyclin B1 protein and an increase in cyclin B1 kinase activity, followed by induction of apoptotic cell death. Inhibition of cyclin B1 kinase lowers apoptosis induced by 2-ME and docetaxel. In this study, we established a positive correlation between cyclin B1 protein and apoptosis induced by chemotherapy in prostate cancer cells. There is minimal cyclin B1 and induction of apoptosis by chemotherapy in nontransformed cells. LNCaP and PC-3 prostate cancer cells stably overexpressing cyclin B1 are more sensitive to apoptosis induced by chemotherapy. LNCaP cells expressing cyclin B1 small interfering RNA to lower cyclin B1 protein or dominant negative cyclin-dependent kinase 1 to inhibit cyclin B1 kinase show a decrease in apoptosis. Increased sensitivity to apoptosis by overexpression of cyclin B1 may be due to lower Bcl-2, higher p53, and decreased neuroendocrine differentiation. We suggest that a cancer-specific mechanism whereby 2-ME and docetaxel may exert anti-prostate cancer activity is the deregulated activation of cyclin B1 kinase, leading to the induction of apoptotic cell death. Our results also suggest that higher levels of cyclin B1 in prostate cancer cells may be a good prognostic marker for chemotherapy.

Overload of the heat-shock protein H11/HspB8 triggers melanoma cell apoptosis through activation of transforming growth factor-beta-activated kinase 1

Molecular therapeutics is a recognized promising approach for melanoma, but relevant target genes remain elusive. We report that overload of the recently cloned H11/HspB8 induces apoptosis in 55% of examined melanoma cultures. Apoptosis was determined by activation of caspases-9 and -3 and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL), and was not seen in normal melanocytes. It was associated with H11/HspB8 complexation with transforming growth factor-beta-activated kinase (TAK) 1 and activation of TAK1 and p38 mitogen activated protein 3 kinases. TAK1 was not bound, nor activated by the H11/HspB8 mutant W51C, which has dominant antiapoptotic activity. beta-Catenin was phosphorylated by activated TAK1, inhibiting its nuclear accumulation and mictophthalmia-associated transcription factor and cyclin dependent kinase 2 expression. The dominant-negative TAK1 mutant K63W inhibited beta-catenin phosphorylation and caspase activation. The data indicate that H11/HspB8 overload causes melanoma growth arrest and apoptosis through TAK1 activation and suggest that H11/HspB8 is a promising molecular therapy target.

Mitogenic action of the androgen receptor sensitizes prostate cancer cells to taxane-based cytotoxic insult

Prostate cancer cells are dependent on androgen for growth and survival; as such, inhibition of androgen receptor (AR) activity is the first line of intervention for disseminated disease. Recently, specific cytotoxic agents have been shown to extend survival times in patients with advanced disease. Given the established ability of androgen to modify cell survival in prostate cancer cells, it is imperative to determine the effect of the hormonal environment on cytotoxic response. Here, we show that the response of prostate cancer cells to taxane-induced cell death is significantly enhanced by androgen stimulation in AR-positive, androgen-dependent prostate cancer cells. Similar results were observed on androgen-independent AR activation. By contrast, AR-positive yet androgen-independent or AR-negative cells were refractory to androgen influence on taxane function. The ability of androgen to potentiate taxane activity was dependent on its mitogenic capacity and was separable from overall AR activity, as coadministration of AR antagonists, G(1) cyclin-dependent kinase inhibitors, or high-dose (growth inhibitory) androgen nullified the proapoptotic function of androgen. Observed induction of cell death was attributed to caspase-dependent apoptosis and correlated with p53 activation. Combined, these data indicate that the cytotoxic effects of taxanes are substantially influenced by the hormonal environment and/or status of AR activity in prostate cancer cells and provide the foundation for refinement and optimization of cytotoxic intervention in prostate cancer.

2-methoxyestradiol induces spindle aberrations, chromosome congression failure, and nondisjunction in mouse oocytes

2-Methoxyestradiol (2-ME) is a metabolite of 17beta-estradiol and a natural component of follicular fluid. Local concentrations of 2-ME may be increased by exposure to environmental pollutants that activate the expression of enzymes in the metabolic pathway from 17beta-estradiol to 2-ME. It has been suspected that this may have adverse effects on spindle formation in maturing oocytes, which would affect embryo quality. To study the dose-response patterns, we exposed denuded mouse oocytes to 2-ME during in vitro maturation. Meiotic progression, spindle morphology, centrosome integrity, and chromosome congression were examined by immunofluorescence and noninvasive polarizing microscopy (PolScope). Chromosomal constituents were assessed after spreading and C-banding. 2-ME sustained MAD2L1 expression at the centromeres and increased the number of meiosis I-blocked oocytes in a dose-dependent manner. 2-ME also caused dramatic dose-dependent increases in the hyperploidy of metaphase II oocytes. Some of these meiosis II oocytes contained anaphase I-like chromosomes, which suggests that high concentrations of the catecholestradiol interfere with the physical separation of chromosomes. Noninvasive PolScope analysis and tubulin immunofluorescence revealed that perturbations in spindle organization, which resulted in severe disturbances of the chromosome alignment at the spindle equator (congression failure), were caused by 2-ME at meiosis I and II. Pericentrin-positive centrosomes failed to align at the spindle poles, and multipolar spindles and prominent arrays of cytoplasmic microtubule asters were induced in 2-ME-exposed metaphase II oocytes. In conclusion, a micromolar level of 2-ME is aneugenic for mammalian oocytes. Therefore, exposure to 2-ME and conditions that increase the intrinsic local concentration of 2-ME in the ovary may affect fertility and increase risks for chromosomal aberrations in the oocyte and embryo.

Sequential combination of flavopiridol and docetaxel reduces the levels of X-linked inhibitor of apoptosis and AKT proteins and stimulates apoptosis in human LNCaP prostate cancer cells

Clinical trials have shown that chemotherapy with docetaxel combined with prednisone can improve survival of patients with androgen-independent prostate cancer. It is likely that the combination of docetaxel with other novel chemotherapeutic agents would also improve the survival of androgen-independent prostate cancer patients. We investigated whether the combination of docetaxel and flavopiridol, a broad cyclin-dependent kinase inhibitor, can increase apoptotic cell death in prostate cancer cells. Treatment of DU 145 prostate cancer cells with 500 nmol/L flavopiridol and 10 nmol/L docetaxel inhibited apoptosis probably because of their opposing effects on cyclin B1-dependent kinase activity. In contrast, when LNCaP prostate cancer cells were treated with flavopiridol for 24 hours followed by docetaxel for another 24 hours (FD), there was a maximal induction of apoptosis. However, there was greater induction of apoptosis in DU 145 cells when docetaxel was followed by flavopiridol or docetaxel. These findings indicate a heterogeneous response depending on the type of prostate cancer cell. Substantial decreases in X-linked inhibitor of apoptosis (XIAP) protein but not survivin, both being members of the IAP family, were required for FD enhanced apoptosis in LNCaP cells. Androgen ablation in androgen-independent LNCaP cells increased activated AKT and chemoresistance to apoptosis after treatment with FD. The proteasome inhibitor MG-132 blocked FD-mediated reduction of XIAP and AKT and antagonized apoptosis, suggesting that the activation of the proteasome pathway is one of the mechanisms involved. Overall, our data suggest that the docetaxel and flavopiridol combination requires a maximal effect on cyclin B1-dependent kinase activity and a reduction of XIAP and AKT prosurvival proteins for augmentation of apoptosis in LNCaP cells.