New insights into 2-methoxyestradiol, a promising antiangiogenic and antitumor agent

Sulfamoylated Estradiol Analogs Targeting the Actin and Microtubule Cytoskeletons Demonstrate Anti-Cancer Properties In Vitro and In Ovo

The microtubule-disrupting agent 2-methoxyestradiol (2-ME) displays anti-tumor and anti-angiogenic properties, but its clinical development is halted due to poor pharmacokinetics. We therefore designed two 2-ME analogs in silico-an ESE-15-one and an ESE-16 one-with improved pharmacological properties. We investigated the effects of these compounds on the cytoskeleton in vitro, and their anti-angiogenic and anti-metastatic properties in ovo. Time-lapse fluorescent microscopy revealed that sub-lethal doses of the compounds disrupted microtubule dynamics. Phalloidin fluorescent staining of treated cervical (HeLa), metastatic breast (MDA-MB-231) cancer, and human umbilical vein endothelial cells (HUVECs) displayed thickened, stabilized actin stress fibers after 2 h, which rearranged into a peripheral radial pattern by 24 h. Cofilin phosphorylation and phosphorylated ezrin/radixin/moesin complexes appeared to regulate this actin response. These signaling pathways overlap with anti-angiogenic, extra-cellular communication and adhesion pathways. Sub-lethal concentrations of the compounds retarded both cellular migration and invasion. Anti-angiogenic and extra-cellular matrix signaling was evident with TIMP2 and P-VEGF receptor-2 upregulation. ESE-15-one and ESE-16 exhibited anti-tumor and anti-metastatic properties in vivo, using the chick chorioallantoic membrane assay. In conclusion, the sulfamoylated 2-ME analogs displayed promising anti-tumor, anti-metastatic, and anti-angiogenic properties. Future studies will assess the compounds for myeloproliferative effects, as seen in clinical applications of other drugs in this class.

Targeting an Old Foe for Cancer: A Molecular Dynamics Perspective to Unravel the Specific Binding Nature of 2-Methoxy Estradiol to Human β-Tubulin Isotypes

Microtubules, composed of α- and β-tubulin subunits are crucial for cell division with their dynamic tissue-specificity which is dictated by expression of isotypes. These isotypes differ in carboxy-terminal tails (CTTs), rich in negatively charged acidic residues in addition to the differences in the composition of active site residues. 2-Methoxy estradiol (2-ME) is the first antimicrotubule agent that showed less affinity toward hemopoietic-specific β1 isotype consequently preventing myelosuppression toxicity. The present study focuses on the MD-directed conformational analysis of 2-ME and estimation of its binding affinity in the colchicine binding pocket of various β-tubulin isotypes combined with the α-tubulin isotype, α1B. AlphaFold 2.0 was used to predict the 3D structure of phylogenetically divergent human β-tubulin isotypes in dimer form with α1B. The dimeric complexes were subjected to induced-fit docking with 2-ME. The statistical analysis of docking showed differences in the binding characteristics of 2-ME with different isotypes. The replicas of atom-based molecular dynamic simulations of the best conformation of 2-ME provided insights into the molecular-level details of its binding pattern across the isotypes. Furthermore, the MM/GBSA analyses revealed the specific binding energy profile of 2-ME in β-tubulin isotypes. It also highlighed, 2-ME exhibits the lowest binding affinity toward the β1 isotype as supported by experimental study. The present study may offer useful information for designing next-generation antimicrotubule agents that are more specific and less toxic.

2-Methoxyestradiol as an Antiproliferative Agent for Long-Term Estrogen-Deprived Breast Cancer Cells

To identify effective treatment modalities for breast cancer with acquired resistance, we first compared the responsiveness of estrogen receptor-positive breast cancer MCF-7 cells and long-term estrogen-deprived (LTED) cells (a cell model of endocrine therapy-resistant breast cancer) derived from MCF-7 cells to G-1 and 2-methoxyestradiol (2-MeO-E2), which are microtubule-destabilizing agents and agonists of the G protein-coupled estrogen receptor 1 (GPER1). The expression of GPER1 in LTED cells was low (~0.44-fold), and LTED cells displayed approximately 1.5-fold faster proliferation than MCF-7 cells. Although G-1 induced comparable antiproliferative effects on both MCF-7 and LTED cells (IC50 values of >10 µM), 2-MeO-E2 exerted antiproliferative effects selective for LTED cells with an IC50 value of 0.93 μM (vs. 6.79 μM for MCF-7 cells) and induced G2/M cell cycle arrest. Moreover, we detected higher amounts of β-tubulin proteins in LTED cells than in MCF-7 cells. Among the β-tubulin (TUBB) isotype genes, the highest expression of TUBB2B (~3.2-fold) was detected in LTED cells compared to that in MCF-7 cells. Additionally, siTUBB2B restores 2-MeO-E2-mediated inhibition of LTED cell proliferation. Other microtubule-targeting agents, i.e., paclitaxel, nocodazole, and colchicine, were not selective for LTED cells. Therefore, 2-MeO-E2 can be an antiproliferative agent to suppress LTED cell proliferation.

Is Estrogen a Missing Culprit in Thyroid Eye Disease? Sex Steroid Hormone Homeostasis Is Key to Other Fibrogenic Autoimmune Diseases - Why Not This One?

Sex bias in autoimmune disease (AID) prevalence is known, but the role of estrogen in disease progression is more complex. Estrogen can even be protective in some AIDs; but in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and systemic sclerosis (SSc), estrogen, its metabolites, and its receptors have been demonstrated to play critical, localized inflammatory roles. Estrogen is instrumental to the fibrosis seen in RA, SLE, SSc and other disease states, including breast cancer and uterine leiomyomas. Fibrotic diseases tend to share a common pattern in which lymphocyte-monocyte interactions generate cytokines which stimulate the deposition of fibrogenic connective tissue. RA, SLE, SSc and thyroid eye disease (TED) have very similar inflammatory and fibrotic patterns-from pathways to tissue type. The thorough investigations that demonstrated estrogen's role in the pathology of RA, SLE, and SSc could, and possibly should, be carried out in TED. One might even expect to find an even greater role for estrogen, and sex steroid homeostasis in TED, given that TED is typically sequalae to Graves' disease (GD), or Hashimoto's disease (HD), and these are endocrine disorders that can create considerable sex steroid hormone dysregulation. This paper highlights the pathophysiology similarities in 4 AIDs, examines the evidence of sex steroid mediated pathology across 3 AIDs and offers a case study and speculation on how this may be germane to TED.

Regulation of Mitochondrial Dynamics in Parkinson's Disease-Is 2-Methoxyestradiol a Missing Piece?

Mitochondria, as "power house of the cell", are crucial players in cell pathophysiology. Beyond adenosine triphosphate (ATP) production, they take part in a generation of reactive oxygen species (ROS), regulation of cell signaling and cell death. Dysregulation of mitochondrial dynamics may lead to cancers and neurodegeneration; however, the fusion/fission cycle allows mitochondria to adapt to metabolic needs of the cell. There are multiple data suggesting that disturbed mitochondrial homeostasis can lead to Parkinson's disease (PD) development. 2-methoxyestradiol (2-ME), metabolite of 17β-estradiol (E2) and potential anticancer agent, was demonstrated to inhibit cell growth of hippocampal HT22 cells by means of nitric oxide synthase (NOS) production and oxidative stress at both pharmacologically and also physiologically relevant concentrations. Moreover, 2-ME was suggested to inhibit mitochondrial biogenesis and to be a dynamic regulator. This review is a comprehensive discussion, from both scientific and clinical point of view, about the influence of 2-ME on mitochondria and its plausible role as a modulator of neuron survival.

Characterization of Signalling Pathways That Link Apoptosis and Autophagy to Cell Death Induced by Estrone Analogues Which Reversibly Depolymerize Microtubules

The search for novel anti-cancer compounds which can circumvent chemotherapeutic drug resistance and limit systemic toxicity remains a priority. 2-Ethyl-3-O-sulphamoyl-estra-1,3,5(10)15-tetraene-3-ol-17one (ESE-15-one) and 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) are sulphamoylated 2-methoxyestradiol (2-ME) analogues designed by our research team. Although their cytotoxicity has been demonstrated in vitro, the temporal and mechanistic responses of the initiated intracellular events are yet to be determined. In order to do so, assays investigating the compounds' effects on microtubules, cell cycle progression, signalling cascades, autophagy and apoptosis were conducted using HeLa cervical- and MDA-MB-231 metastatic breast cancer cells. Both compounds reversibly disrupted microtubule dynamics as an early event by binding to the microtubule colchicine site, which blocked progression through the cell cycle at the G₁/S- and G₂/M transitions. This was supported by increased pRB and p27^Kip1 phosphorylation. Induction of apoptosis with time-dependent signalling involving the p-JNK, Erk1/2 and Akt/mTOR pathways and loss of mitochondrial membrane potential was demonstrated. Inhibition of autophagy attenuated the apoptotic response. In conclusion, the 2-ME analogues induced a time-dependent cross-talk between cell cycle checkpoints, apoptotic signalling and autophagic processes, with an increased reactive oxygen species formation and perturbated microtubule functioning appearing to connect the processes. Subtle differences in the responses were observed between the two compounds and the different cell lines.

Molecular mechanisms and clinical management of cancer bone metastasis

As one of the most common metastatic sites of malignancies, bone has a unique microenvironment that allows metastatic tumor cells to grow and flourish. The fenestrated capillaries in the bone, bone matrix, and bone cells, including osteoblasts and osteoclasts, together maintain the homeostasis of the bone microenvironment. In contrast, tumor-derived factors act on bone components, leading to subsequent bone resorption or excessive bone formation. The various pathways involved also provide multiple targets for therapeutic strategies against bone metastases. In this review, we summarize the current understanding of the mechanism of bone metastases. Based on the general process of bone metastases, we specifically highlight the complex crosstalk between tumor cells and the bone microenvironment and the current management of cancer bone metastases.

The Major Heat Shock Proteins, Hsp70 and Hsp90, in 2-Methoxyestradiol-Mediated Osteosarcoma Cell Death Model

2-Methoxyestradiol is one of the natural 17β-estradiol derivatives and a potential novel anticancer agent currently being under evaluation in advanced phases of clinical trials. However, the mechanism of anticancer action of 2-methoxyestradiol has not been yet fully established. In our previous studies we have demonstrated that 2-methoxyestradiol selectively induces the expression and nuclear translocation of neuronal nitric oxide synthase in osteosarcoma 143B cells. Heat shock proteins (Hsps) are factors involved in the regulation of expression and activity of nitric oxide synthases. Herein, we chose osteosarcoma cell lines differed in metastatic potential, metastatic 143B and highly metastatic MG63.2 cells, in order to further investigate the anticancer mechanism of 2-methoxyestradiol. The current study aimed to determine the role of major heat shock proteins, Hsp90 and Hsp70 in 2-methoxyestradiol-induced osteosarcoma cell death. We focused on the implication of Hsp90 and Hsp70 in control under expression of neuronal nitric oxide synthase, localization of the enzyme, and further generation of nitro-oxidative stress. To give the insight into the role of Hsp90 in regulation of anticancer efficacy of 2-methoxyestradiol, we used geldanamycin as a potent Hsp90 inhibitor. Herein, we evidenced that inhibition of Hsp90 controls the protein expression of 2-methoxyestradiol-induced neuronal nitric oxide synthase and inhibits enzyme nuclear translocation. We propose that decreased level of neuronal nitric oxide synthase protein after a combined treatment with 2-methoxyestradiol and geldanamycin is directly associated with the accompanying upregulation of Hsp70 and downregulation of Hsp90. This interaction resulted in abrogation of anticancer efficacy of 2-methoxyestradiol by geldanamycin.

F-Spondin Is the Signal by Which 2-Methoxyestradiol Induces Apoptosis in the Endometrial Cancer Cell Line Ishikawa

The metabolite 2-methoxyestradiol (2ME) is an endogenous estrogen metabolite with potential therapeutic properties in reproductive cancers. However, the molecular mechanisms by which 2ME exerts its anticancer activity are not well elucidated. The purpose of this study was to determine the molecular signals associated with the apoptotic effects of 2ME in a human endometrial cancer cell line. Ishikawa cells were treated with non-apoptotic (0.1 µM) or apoptotic concentrations (5 µM) of 2ME, and 12 hours later mRNA levels for Scd2, Snx6, and Spon1 were determined by real-time PCR. We then investigated by immunofluorescence and Western blot the expression and distribution of F-spondin, encoded by Spon1, in Ishikawa cells treated with 2ME 5 µM at 6, 12, or 24 h after treatment. The role of estrogen receptors (ER) in the effect of 2ME on the Spon1 level was also investigated. Finally, we examined whether 2ME 5 µM induces cell death in Ishikawa cells pre-incubated with a neutralizing F-spondin antibody. Non-apoptotic or apoptotic concentrations of 2ME decreased Scd2 and increased Snx6. However, Spon1 was only increased with the 2ME apoptotic concentration. F-spondin protein was also increased at 12 and 24 h after 2ME treatment, while 2ME-induced Spon1 increase was independent of ER. Neutralization of F-spondin blocked the effect of 2ME on the cell viability. These results show that F-spondin signaling is one of the components in the apoptotic effects of 2ME on Ishikawa cells and provide experimental evidence underlying the mechanism of action of this estrogen metabolite on cancer cells.

The effect of 2-methoxyestradiol liposome on growth inhibition, angiogenesis and expression of VEGF and Ki67 in mice bearing H22 hepatocellular carcinoma

Aims and background

2-methoxyestradiol (2-ME), an endogenous metabolite of estrogen, has very low water solubility. It is currently in phase II clinical trials as both a chemopreventive and chemotherapeutic agent and has been orally administered to cancer patients. However, the poor oral absorption of the compound is one of the major obstacles for 2-ME development. Based on the molecular features of 2-ME, liposome can be considered an attractive formulation approach. Our purpose in this study is to research the antitumor efficacy of 2-methoxyestradiol liposome (2-ME-L) in mice bearing H22 tumors.

Methods

Murine H22 hepatocarcinoma served as an ectopic solid tumor model. The effects of antitumor therapy were evaluated by testing tumor growth, measuring the tumor inhibition rates in terms of weight and volume, and staining the tissues by hematoxylin and eosin. The synergistic mechanism of 2-ME-L therapy was elucidated by detecting changes in the expression of pathognostic factors in the tumor microenvironment.

Results

2-ME-L significantly suppressed tumor growth. The morphological changes in the tumors indicated that the tumors in the treatment groups were effectively confined with little surrounding angiogenesis. Tumor cells of the treatment groups had abundant areas of necrosis with few nuclei in the mitotic phase. It was found that there was less immunohistochemical expression of vascular endothelial growth factor (VEGF), Ki67 and CD31 in the treatment groups and the efficacy of 2-ME-L was better than that of 2-ME solution (2-ME-S). This research demonstrated that 2-ME-L inhibited the growth of H22 tumors in a concentration-dependent manner and was more effective than 2-ME-S.

Conclusions

2-ME-L can suppress the growth of H22 solid tumors and has antiproliferative, proapoptotic and antiangiogenic activity. 2-ME-L could be of potential use in the treatment of hepatocellular carcinoma.

Estrogen Metabolite 2-Methoxyestradiol Induces Apoptosis and Inhibits Cell Proliferation and Collagen Production in Rat and Human Leiomyoma Cells: A Potential Medicinal Treatment for Uterine Fibroids

OBJECTIVE

The current study sought to investigate the effect of the estrogen metabolite 2-methoxyestradiol (2-MeOHE(2)) on apoptosis, cell proliferation, and collagen synthesis in human and rat leiomyoma cells.

METHODS

[(3)H] thymidine and [(3)H] proline incorporation studies were conducted. The expression of vascular endothelial growth factor (VEGF), cyclin D1, Bcl-2, and Bax were evaluated by Western blot. Flow cytometry analysis was used to study the effect of 2-MeOHE(2) on apoptosis and the cell cycle.

RESULTS

Compared with untreated controls, treatment of rat leiomyoma (ELT3) cells with 2-MeOHE(2) (0.1, 1, 2, 5, or 10 muM) reduced cell proliferation by 17%, 52%, 61%, 73%, and 79%, respectively (P <.05). Similarly, in human uterine leiomyoma cell line (huLM) cells, proliferation was reduced by 4%, 18%, 37%, 41%, and 51%, respectively. 2-MeOHE(2) also caused a concentration-dependent inhibition of collagen synthesis by 4%, 16%, 23%, 51%, and 70%, respectively, in huLM cells (P <.05). Cell cycle analysis indicated that 2-MeOHE(2) treatment (1 to 5 muM) in huLM cells resulted in G(2)/M cell cycle arrest and a 45% increase in apoptosis compared with untreated control (P <.05). Western immunoblotting analysis indicated that 2-MeOHE(2) induces a concentration-dependent reduction in the expression of cyclin D1, Bcl-2, and VEGF proteins in both rat and human leiomyoma cell lines.

CONCLUSIONS

This study provides the first evidence that 2-MeOHE(2) is a potent antiproliferative/apoptotic and collagen synthesis inhibiting agent in human and rat leiomyoma cells. To the best of our knowledge, this is the first report showing the potential use of 2-methoxyestradiol as a nonsurgical alternative therapy for uterine leiomyomas.

Two faces of the estrogen metabolite 2-methoxyestradiol in vitro and in vivo

2-Methoxyestradiol (2-ME), an endogenous metabolite of 17β-estradiol (E2), interacts with estrogen receptors (ERs) and microtubules, however, 2-ME has a low affinity for ERs. Furthermore, 2‑ME has been identified as a potential novel antitumor agent, combining its anti‑proliferative effects on a variety of tumor cell types with its anti‑angiogenic action. Therefore, 2‑ME is of interest due to its potential anticancer therapeutic effects. In the current study, the estrogenic effect of 2‑ME on CaBP‑9k, ERα, and progesterone receptor (PR) mRNA levels in the absence and presence of E2 and progesterone (P4) in in vivo and in vitro models was examined. In GH3 cells, the mRNA level of CaBP‑9k was induced in the E2 treatment group (concentration, 10‑9 M), and the expression of CaBP‑9k was also upregulated in the 2‑ME‑treated group (concentration, 10‑7 M). Uterine lactoferrin (Ltf) mRNA expression was also increased in the 2‑ME group [dose, 40 mg/kg body weight (BW)], which was comparable to the response with E2 (dose, 40 µg/kg BW) observed in mice. As inhibitors of ER and PR activity, ICI 182,780 and mifepristone (RU486) were observed to reverse the E2 or 2‑ME mediated increase of CaBP‑9k and Ltf mRNA expression. In addition, it was found that 2‑ME significantly decreased the levels of ERα and increased PR transcripts. Consistent with the in vitro results, the mRNA levels revealed decreased ERα and increased PR in in vivo treatment of E2 and 2‑ME. These findings demonstrate that the expression of estrogenic markers, CaBP‑9k and Ltf, is regulated by 2‑ME in in vitro and in vivo models, therefore, estrogenic activi-ties of 2-ME may be increased in females during the estrous cycle via the ER and/or PR-mediated signaling pathway.

Estrogens and Their Genotoxic Metabolites Are Increased in Obese Prepubertal Girls

CONTEXT

Estrogen levels and their metabolites are higher in obese vs lean postmenopausal women, and obesity increases breast cancer risk. Quinone derivatives of 4-hydroxylated estrogen metabolites, independently of the estrogen receptor, cause depurination and impaired DNA repair (genotoxic). 16α-Hydroxy (16α-OH)-estrone (E1), eg, promotes tumor proliferation and 2-methoxy-estradiol (E2) may be chemoprotective. Childhood obesity increases breast cancer death risk in women, but levels of estrogen derivatives had not been previously studied in young children.

OBJECTIVE

The objective of the study was to investigate whether total and genotoxic estrogens are increased in prepubertal obese girls compared with lean controls.

DESIGN

Stored sera from 12 lean and 23 obese prepubertal girls (Tanner stage I breast and pubic hair) studied previously were assayed for E1, E2, and their multiple metabolites (12 steroids total) using highly sensitive liquid chromatography and tandem mass spectrometry.

RESULTS

E2 concentrations were significantly higher in obese [3.45 (0.5, 4.65) pg/ml (median [quartile 1, quartile 3])] vs lean girls [0.5 (0.5, 2.37), P = .04], 57% of values upper quartile or greater (quartile 3) of controls. Concentrations of 16α-OH-E1 were higher in obese [7.17 (0.5, 9.64) pg/mL] vs lean girls [0.5 (0.5, 1.72, P = .007)], 65% of values quartile 3 or greater of controls. 2-Methoxy-E2 concentrations were lower in the obese group (P = .012). 16α-OH-E1 concentrations were positively correlated with body mass index, percentage fat mass, and IL-6 concentrations (P < .001).

CONCLUSIONS

E2 and genotoxic metabolites were higher in obese vs lean prepubertal girls. These data suggest that obesity is associated with an increased extraglandular estrogen production and metabolism before the onset of puberty in girls. Long-term epidemiological studies are needed to assess any potential increase in breast cancer risk.

2ME2 increase radiation-induced apoptosis of keloid fibroblasts by targeting HIF-1α in vitro

BACKGROUND

Radiation therapy is considered to be a treatment for keloid scarring; however, radioresistance has been shown to be a serious impediment to treatment efficacy. There is therefore a need for the discovery of novel critical molecular targets whose inhibition might enhance the radiotherapeutic response. An elevated level of hypoxia inducible factor (HIF)-1α expression after radiation therapy in keloid fibroblasts has been demonstrated in our recent experiments. Therefore, we suggested there was a possible close relationship between HIF-1α and keloid radioresistance. The current study aimed to investigate whether target HIF-1α may enhance the radiotherapeutic efficacy of keloids.

METHODS

2-methoxyestradiol (2ME2) was applied to inhibit HIF-1α expression, and the treatment results were assessed by cell proliferation, apoptosis and radiosensitivity. A lentivirus-mediated small interfering RNA (siRNA) transduction method was used to block the expression of HIF-1α gene.

RESULTS

Both mRNA and protein levels can be effectively inhibited after the knockdown of HIF-1α, leading to a significant increase of radiation-induced apoptosis in keloid fibroblasts. Our experiment also demonstrated that 2ME2 could effectively inhibit the protein expression of HIF-1α, which significantly increased the late stage of radiation-induced apoptosis of keloid fibroblasts.

CONCLUSIONS

The present study indicates that HIF-1α might serve as a therapeutic target for keloids. Furthermore, suppression of HIF-1α by 2ME2 may be a promising therapeutic adjuvant in radiation therapy for keloids.

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.

HIF-1α decoy oligodeoxynucleotides inhibit HIF-1α signaling and breast cancer proliferation

Although HIF-1α is considered an attractive target for the development of cancer therapies, like other transcriptional factors, it has been regarded as 'undruggable'. The decoy approach is a new class of antigene strategy that can be used to modulate the function of endogenous transcriptional factors. Here, we designed a decoy oligodeoxynucleotide (ODN) and tested its effect on the function of HIF-1α. We found the HIF-1α decoy ODN could efficiently enter into cells. Furthermore, these decoy ODNs can significantly block the expression of VEGFA, a known targeted gene of HIF-1α suggesting that the HIF-1α decoy ODNs can inhibit the function of HIF-1α. More importantly, the HIF-1α decoy ODN induced apoptosis and cell cycle arrest in MDA-MB-231 breast cancer cells. In summary, HIF-1α decoy ODNs can inhibit the function of HIF-1α and induce cancer cell apoptosis. Therefore, HIF-1α decoy ODNs should be further modified to improve their biological activity in vivo.

Syntheses and antiproliferative effects of D-homo- and D-secoestrones

Substituted and/or heterocyclic d-homoestrone derivatives were synthetized via the intramolecular cyclization of a δ-alkenyl-d-secoaldehyde, -d-secoalcohol or -d-secocarboxylic acid of estrone 3-benzyl ether. The d-secoalcohol was modified at three sites in the molecule. The in vitro antiproliferative activities of the new d-homo- and d-secoestrone derivatives were determined on HeLa, MCF-7, A431 and A2780 cells through use of MTT assay. d-Homoalcohols 3 and 5 displayed cell line-selective cytostatic effects against ovarian and cervical cell lines, respectively. Two d-secoestrones (6 and 12c) proved to be effective, with IC50 values comparable with those of the reference agent cisplatin. A selected compound (6) was tested by tubulin polymerization assay and its cancer specificity was additionally determined by using noncancerous human fibroblast cells.

2-methoxyestradiol plasma levels are associated with clinical severity indices and biomarkers of preeclampsia

We investigated whether clinical severity indices and biomarkers for preeclampsia (PE) are associated with low plasmatic 2-methoxyestradiol (2ME) in the third trimester of gestation. Blood was collected from 53 women with PE and 73 control pregnant women before parturition. The concentration of 2ME was significantly higher in controls than in patients with PE (2906.43 ± 200.69 pg/mL vs 1818.41 ± 189.25 pg/mL). The risk of PE decreased as 2ME levels increased. The 2ME values were negatively correlated with systolic peak arterial pressure and proteinuria in PE. Additionally, those women with PE with lower 2ME had a more serious clinical situation and needed a more aggressive therapy. Finally, 2ME levels (in patients with PE and total population) were significantly correlated with concentrations of soluble fms-like tyrosine kinase 1 and placental growth factor . Summarizing, patients with PE had lower 2ME levels that were correlated with different clinical indices and biomarkers of severity, indicating that 2ME could be taken into account for the clinical management of this syndrome.

2-methoxyestradiol and disorders of female reproductive tissues

2-Methoxyestradiol (2ME) is an endogenous metabolite of 17β-estradiol. Once thought of as a mere degradation product, 2ME has gained attention as an important component of reproductive physiology and as a therapeutic agent in reproductive pathologies such as preeclampsia, endometriosis, infertility, and cancer. In this review, we discuss the involvement of 2ME in reproductive pathophysiology and summarize its known mechanisms of action: microtubule disruption, inhibition of angiogenesis and stimulation of apoptosis. Currently, the clinical uses of 2ME as a single agent are limited due to its poor water solubility and thus low bioavailability; however, 2ME analogs and derivatives have been recently developed and tested as cancer treatments. Despite some isolated success stories and ongoing research, 2ME derivatives have not yet provided the expected results. The adjuvant use of 2ME derivatives with chemotherapeutic agents is hindered by their intrinsic toxicity confounding the unwanted secondary effects of chemotherapy. However, due to the well-tested tolerance of the body to high doses of native 2ME, it may the combination of native 2ME with conventional treatments that will offer novel clinically relevant regimens for cancer and other reproductive disorders.

Upregulation of DR5 receptor by the diaminothiazole DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole] triggers an independent extrinsic pathway of apoptosis in colon cancer cells with compromised pro and antiapoptotic proteins

Mitochondria mediated signalling is the more common way of apoptosis induction exhibited by many chemotherapeutic agents in cancer cells. Death receptor mediated signalling for apoptosis in many cells also requires further amplification from the mitochondrial pathway activation through tBid. Thus the potential of most chemotherapeutic agents in tumours with intrinsic apoptosis resistance due to changes in molecules involved in the mitochondrial pathway is limited. Diaminothiazoles were shown earlier to bind to tubulin thereby exhibiting cytotoxicity towards different cancer cells. We observed that the lead diaminothiazole, DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole] could induce apoptosis in the colon cancer cell line HCT116 by both pathways. However, in contrast to many other chemotherapeutic agents, DAT1 triggered apoptosis where the intrinsic pathway was blocked by changing the pro and antiapoptotic proteins. An independent extrinsic pathway activation triggered by the upregulation of DR5 receptor accounted for that. The induction of DR5 occurred in the transcriptional level and the essential role of DR5 was confirmed by the fact that siRNA downregulation of DR5 significantly reduced DAT1 induced apoptosis. HCT116 cells were earlier shown to have a type II response for apoptosis induction where extrinsic pathway was connected to the intrinsic pathway via the mediator protein tBid. Our finding thus indicates that the signalling events in the manifestation of apoptosis depend not only on the cancer cell type, but also on the inducer. Our results also place diaminothiazoles in a promising position in the treatment of tumours with compromised apoptotic factors.

Reversible action of diaminothiazoles in cancer cells is implicated by the induction of a fast conformational change of tubulin and suppression of microtubule dynamics

Diaminothiazoles are novel cytotoxic compounds that have shown efficacy toward different cancer cell lines. They show potent antimitotic and antiangiogenic activity upon binding to the colchicine-binding site of tubulin. However, the mechanism of action of diaminothiazoles at the molecular level is not known. Here, we show a reversible binding to tubulin with a fast conformational change that allows the lead diaminothiazole DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino)thiazole] to cause a reversible mitotic block. DAT1 also suppresses microtubule dynamic instability at much lower concentration than its IC(50) value in cancer cells. Both growth and shortening events were reduced by DAT1 in a concentration-dependent way. Colchicine, the long-studied tubulin-binding drug, has previously failed in the treatment of cancer due to its toxicity, even though it generates a strong apoptotic response. The toxicity is attributable to its slow removal from the cell due to irreversible tubulin binding caused by a slow conformational change. DAT1 binds to tubulin at an optimal pH lower than colchicine. Tubulin conformational studies showed that the binding environments of DAT1 and colchicine are different. Molecular dynamic simulations showed a difference in the number of H-bonding interactions that accounts for the different pH optima. This study gives an insight of the action of compounds targeting tubulin's colchicine-binding site, as many such compounds have entered into clinical trials recently.

PTEN status mediates 2ME2 anti-tumor efficacy in preclinical glioblastoma models: role of HIF1α suppression

Glioblastoma (GBM) is the most common brain cancer and is highly lethal in both adults and children. 2-methoxyestradiol (2ME2) is a microtubule inhibitor that potently inhibits HIF1α, GBM angiogenesis and tumor growth in preclinical models. In patients, 2ME2 exhibits low toxicity and promising but inconsistent efficacy. Given its preclinical potency and its tolerability in patients, we sought to determine whether 2ME2 therapy could be enhanced by addressing resistance via combination therapy, and with biomarkers to identify responsive glioma subgroups. We demonstrate that the PTEN-PI3K axis regulates HIF1α in glioma models. We utilized isogenic-pairs of glioma cell lines, deficient in PTEN or stably reconstituted with PTEN, to determine the role of PTEN in 2ME2 sensitivity in vitro and in vivo. Chou-Talalay synergy studies reveal significant synergy when a pan-PI3K inhibitor is combined with 2ME2. This synergistic activity was correlated with a synergistic suppression of HIF1α accumulation under hypoxic conditions in glioma models. In vivo, 2ME2 markedly inhibited tumor-induced angiogenesis and significantly reduced tumor growth only in a PTEN reconstituted GBM models in both subcutaneous and orthotopic intracranial mouse models. Collectively, these results: (1) suggest that PTEN status predicts sensitivity to 2ME2 and (2) justify exploration of 2ME2 combined with pan-PI3K inhibitors for the treatment of this intractable brain cancer.

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.

2-Hydroxyestradiol slows progression of experimental polycystic kidney disease

Male gender is a risk factor for progression of polycystic kidney disease (PKD). 17β-Estradiol (E2) protects experimentally, but clinical use is limited by adverse effects. Novel E2 metabolites provide many benefits of E2 without stimulating the estrogen receptor, and thus may be safer. We hypothesized that E2 metabolites are protective in a model of PKD. Studies were performed in male control Han:SPRD rats, and in cystic males treated with orchiectomy, 2-methoxyestradiol, 2-hydroxyestradiol (2-OHE), or vehicle, from age 3 to 12 wk. Cystic rats exhibited renal functional impairment (∼50% decrease in glomerular filtration and renal plasma flow rates, P < 0.05) and substantial cyst development (20.5 ± 2.0% of cortex area). 2-OHE was the most effective in limiting cysts (6.0 ± 0.7% of cortex area, P < 0.05 vs. vehicle-treated cystic rats) and preserving function, in association with suppression of proliferation, apoptosis, and angiogenesis markers. Downregulation of p21 expression and increased expression of Akt, the mammalian target of rapamycin (mTOR), and some of its downstream effectors were significantly reversed by 2-OHE. Thus, 2-OHE limits disease progression in a cystic rodent model. Mechanisms include reduced renal cell proliferation, apoptosis, and angiogenesis. These effects may be mediated, at least in part, by preservation of p21 and suppression of Akt and mTOR. Estradiol metabolites may represent a novel, safe intervention to slow progression of PKD.

Involvement of reactive oxygen species in 2-methoxyestradiol-induced apoptosis in human neuroblastoma cells

Neuroblastoma is the most common extra-cranial solid tumor in children. Despite advances in the treatment of childhood cancer, outcomes for children with advanced-stage neuroblastoma remain poor. Here we reported that 2-methoxyestradiol (2-ME) inhibited the proliferation and induced apoptosis in human neuroblastoma SK-N-SH and SH-SY5Y cells. 2-ME treatment also resulted in the generation of ROS and the loss of mitochondrial membrane potential in SK-N-SH and SH-SY5Y, indicating that 2-ME-induced apoptosis is mediated by ROS. This is supported by the results that have shown that co-treatment with antioxidants, VC, L-GSH and MitoQ(10), decreased 2-ME-induced generation of ROS and the loss of the mitochondrial membrane potential, increased the Bcl-2/Bax ratio, decreased 2-ME-induced activation of caspase-9 and caspase-3 and the up-regulation of apoptosis-inducing factor (AIF), and prevented 2-ME-induced apoptosis in SK-N-SH and SH-SY5Y cells. These results suggested that oxidative stress plays an important role in 2-ME-induced apoptotic death of human neuroblastoma cells.

Effect of magnetic Fe3O4 nanoparticles with 2-methoxyestradiol on the cell-cycle progression and apoptosis of myelodysplastic syndrome cells

This study aims to evaluate the potential benefit of combination therapy of 2-methoxyestradiol (2ME) and magnetic nanoparticles of Fe₃O₄ (MNPs-Fe₃O₄) on myelodysplastic syndrome (MDS) SKM-1 cells and its underlying mechanisms. The effect of the unique properties of tetraheptylammonium-capped MNPs-Fe₃O₄ with 2ME on cytotoxicity was tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Cell-cycle distribution and apoptosis were assessed by flow cytometry. The expression of cell-cycle marker protein was measured by Western blotting. Growth inhibition rate of SKM-1 cells treated with the 2ME-loaded MNPs-Fe₃O₄ was enhanced when compared with 2ME alone. 2ME led to an increase of caspase-3 expression, followed by apoptosis, which was significantly increased when combined with an MNPs-Fe₃O₄ carrier. Moreover, the copolymer of 2ME with MNPs- Fe₃O₄ blocked a nearly two-fold increase in SKM-1 cells located in G₂/M phase than in 2ME alone, which may be associated with an accompanying increase of p21 as well as a decrease in cyclin B1 and cdc2 expression, but there was no obvious difference between the MNPs-Fe₃O₄ and control group. These findings suggest that the unique properties of MNPs-Fe₃O₄ as a carrier for 2ME, a new anticancer agent currently in clinical trials, may be a logical strategy to enhance the therapeutic activity of MDS.

2-methoxyestradiol analogue ENMD-1198 reduces breast cancer-induced osteolysis and tumor burden both in vitro and in vivo

It has been estimated that 70% of advanced breast cancer patients will face the complication of bone metastases. Three processes are pivotal during bone metastatic growth of breast cancer, namely, tumor cell proliferation, angiogenesis, and osteolysis. During tumor-induced osteolysis, a number of cytokines and growth factors are released from the degraded bone matrix. These factors stimulate further tumor growth, tumor angiogenesis, and tumor-induced osteolysis. New therapies should target all relevant processes to halt this powerful feedback loop. Here, we characterized the new 2-methoxyestradiol analogue ENMD-1198 and showed that it is cytotoxic to tumor cells. Moreover, ENMD-1198 showed both antiangiogenic and vascular disruptive properties and was capable of protecting the bone against tumor-induced osteolysis. We confirmed the in vitro data with a series of in vivo experiments showing the beneficial effects of ENMD-1198 and ENMD-1198-based combination treatments of metastatic breast cancer in bone both on tumor progression and on survival with long-term ENMD-1198 treatment. We confirmed the in vivo relevance of the ENMD-1198 protective effect on bone both with X-ray radiographs and microcomputed tomography. In addition, we combined ENMD-1198 treatment with low-dose metronomic cyclophosphamide and the bisphosphonate risedronic acid, leading to a mild increase in treatment efficacy.

In vitro effects of 2-methoxyestradiol-bis-sulphamate on the non-tumorigenic MCF-12A cell line

A priority in recent anti-cancer drug development has been attaining better side-effect profiles for potential compounds. To produce highly specific cancer therapies it is necessary to understand both the effects of the proposed compound on cancer and on normal cells comprising the rest of the human body. Thus in vitro evaluation of these compounds against non-carcinogenic cell lines is of critical importance. One of the most recent developments in experimental anti-cancer agents is 2-methoxyestradiol-bis-sulphamate (2ME-BM), a sulphamoylated derivative of 2-methoxyestradiol. The aim of this study was to evaluate the in vitro effects of 2ME-BM on cell proliferation, morphology and mechanisms of cell death in the non-carcinogenic MCF-12A breast epithelial cell line. The study revealed changes in proliferative capacity, morphology and cell death induction in response to 2ME-BM exposure (24 h at 0.4 microM). Microscopy showed decreased cell density and cell death-associated morphology (increased apoptotic characteristics), a slight increase in acidic intracellular vesicles and insignificant ultra-structural aberrations. Mitotic indices revealed a G(2)M-phase cell cycle block. This was confirmed by flow cytometry, where an increased fraction of abnormal cells and a decrease in cyclin B1 levels were observed. These results evidently demonstrate that the non-carcinogenic MCF-12A cell line is less susceptible when compared to 2ME-BM-exposed cancer cell lines previously tested. Further in vitro research into the mechanism of this potentially useful compound is warranted.

Candidate genes and mechanisms for 2-methoxyestradiol-mediated vasoprotection

2-Methoxyestradiol (2-ME; estradiol metabolite) inhibits vascular smooth muscle cell (VSMC) growth and protects against atherosclerosis and vascular injury; however, the mechanisms by which 2-ME induces these actions remain obscure. To assess the impact of 2-ME on biochemical pathways regulating VSMC biology, we used high-density oligonucleotide microarrays to identify differentially expressed genes in cultured human female aortic VSMCs treated with 2-ME acutely (4 hours) or long term (30 hours). Both single gene analysis and Gene Set Enrichment Analysis revealed 2-ME-induced downregulation of genes involved in mitotic spindle assembly and function in VSMCs. Also, Gene Set Enrichment Analysis identified effects of 2-ME on genes regulating cell-cycle progression, cell migration/adhesion, vasorelaxation, inflammation, and cholesterol metabolism. Transcriptional changes were associated with changes in protein expression, including inhibition of cyclin D1, cyclin B1, cyclin-dependent kinase 6, cyclin-dependent kinase 4, tubulin polymerization, cholesterol and steroid synthesis, and upregulation of cyclooxygenase 2 and matrix metalloproteinase 1. Microarray data suggested that 2-ME may activate peroxisome proliferator-activated receptors (PPARs) in VSMCs, and 2-ME has structural similarities with rosiglitazone (PPARγ agonist). However, our finding of weak activation and lack of binding of 2-ME to PPARs suggests that 2-ME may modulate PPAR-associated genes via indirect mechanisms, potentially involving cyclooxygenase 2. Indeed, the antimitogenic effects of 2-ME at concentrations that do not inhibit tubulin polymerization were blocked by the PPAR antagonist GW9662 and the cyclooxygenase 2 inhibitor NS398. Finally, we demonstrated that 2-ME inhibited hypoxia-inducible factor 1α. Identification of candidate genes that are positively or negatively regulated by 2-ME provides important leads to investigate and better understand the mechanisms by which 2-ME induces its vasoprotective actions.

2-Methoxyestradiol blocks cell-cycle progression at the G2/M phase and induces apoptosis in human acute T lymphoblastic leukemia CEM cells

2-Methoxyestradiol (2-ME2) is an endogenous metabolite of 17beta-estradiol (E2) with estrogen receptor-independent anti-cancer activity. The current study sought to determine the mechanism of anti-cancer activity of 2-ME2 in human acute T lymphoblastic leukemia CEM cells. Results showed that 2-ME2 markedly suppressed proliferation of CEM cells in a time- and dose-dependent manner. 2-ME2-treated CEM cells underwent typical apoptotic changes. Exposure to 2-ME2 led to G(2)/M phase cell-cycle arrest, which preceded apoptosis characterized by the appearance of a sub-G(1) cell population. In addition, cytosolic cytochrome c release, increased procaspase-9 and -3 expressions, poly(ADP-ribose) polymerase (PARP) cleavage, and induced expression of caspase-8 were detected, suggesting that both the intrinsic apoptotic pathway and extrinsic apoptotic pathway were involved in 2-ME2-induced apoptosis. Moreover, the expression level of p21 protein was upregulated, whereas Bcl-2 and dysfunctional p53 protein were downregulated, which also contributed to 2-ME2-induced apoptosis. Our findings revealed that 2-ME2 might be a potent natural candidate for chemotherapeutic treatment of human acute T lymphoblastic leukemia when the precise effects of 2-ME2 were investigated further in other T leukemia cell lines and in primary T-cell leukemias.

Correlation of 2-methoxyestradiol levels in cord blood and complications of prematurity

2-methoxyestradiol (2ME2) is a potent antiangiogenic molecule that inhibits the expression of hypoxia-inducible factor (HIF)-1alpha and, consequently, of VEGF and other HIF-1alpha target genes. Although 2ME2 is elevated during pregnancy in maternal serum, its presence in fetal fluids and its impact in neonatal health are unknown. In this study, we 1) described normal levels of 2ME2 in maternal blood, cord blood, breast milk, and amniotic fluid, and 2) compared a composite measure of perinatal outcome between infants born with high and low levels of 2ME2. We found that 2ME2 was significantly decreased in all fluids compared with prepartum maternal serum. After stratifying babies by 2ME2 exposure levels, we observed no differences in the vulnerability to impaired lung development or to complications involving aberrant angiogenesis or vascular leak, such as necrotizing enterocolitis (NEC), intraventricular hemorrhage (IVH), posthemorrhagic hydrocephalus (PHH), and retinopathy of prematurity (ROP). In summary, fetal 2ME2 concentrations do not appear to affect neonatal outcome.

Analysis of estrogens in serum and plasma from postmenopausal women: past present, and future

Previous studies have shown that the selection of women who are at high breast cancer risk for treatment with chemoprevention agents leads to an enhanced benefit/risk ratio. However, further efforts to implement this strategy will require the development of new models to predict the breast cancer risk of particular individuals. Postmenopausal women with elevated plasma or serum estrogens are at increased risk for breast cancer. Therefore, the roles of various enzymes involved in the biosynthesis of estrogens in postmenopausal women have been reviewed in detail. In addition, the potential genotoxic and/or proliferative effects of the different estrogen metabolites as risk factors in the etiology of breast cancer have been examined. Unfortunately, much of the current bioanalytical methodology employed for the analysis of plasma and serum estrogens has proved to be problematic. Major advances in risk assessment would be possible if reliable methodology were available to quantify estradiol and its major metabolites in the plasma or serum of postmenopausal women. High performance liquid chromatography (HPLC) coupled with radioimmunoassay (RIA) currently provides the most sensitive and best validated immunoassay method for the analysis of estrone and estradiol in serum samples from postmenopausal women. However, inter-individual differences in specificity observed with many other immunoassays have caused significant problems when interpreting epidemiologic studies of breast cancer. It is almost impossible to overcome the inherent assay problems involved in using RIA-based methodology, particularly for multiple estrogens. For reliable measurements of multiple estrogens in plasma or serum, it will be necessary to employ stable isotope dilution methodology in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Extremely high sensitivity can be obtained with pre-ionized estrogen derivatives when employed in combination with a modern triple quadrupole mass spectrometer and nanoflow LC. Using [(13)C(6)]-estrone as the internal standard it has proved possible to analyze estrone as its pre-ionized Girard T (GT) derivative in sub-fg (low amol) amounts on column. This suggests that in the future it will be possible to routinely conduct LC-MS assays of multiple estrogen metabolites in serum and plasma at even lower concentrations than the current lower limit of quantitation of 0.4pg/mL (1.6pmol/L). The ease with which the pre-ionization derivatization strategy can be implemented will make it possible to readily introduce high sensitivity stable isotope dilution methodology in laboratories that are currently employing LC-MS/MS methodology. This will help conserve important plasma and serum samples as it will be possible to conduct high sensitivity analyses using low sample volumes.

Structure activity analysis of 2-methoxyestradiol analogues reveals targeting of microtubules as the major mechanism of antiproliferative and proapoptotic activity

2-Methoxyestradiol (2ME2) is an anticancer agent with antiproliferative, antiangiogenic, and proapoptotic effects. A major proposed mechanism of drug action is the disruption of the microtubule skeleton, leading to the induction of cell cycle arrest and apoptosis. In addition, other mechanisms of action have been proposed, including the generation of reactive oxygen species (ROS), inhibition of hypoxia-inducible factor (HIF), and interference with mitochondrial function. In this study, we used a selection of 2ME2 analogues to conduct structure activity analysis and correlated the antiproliferative and proapoptotic activity of the various analogues with their effects on different drug targets. A good correlation was observed between drug activity and effects on microtubule function. In contrast, our results indicate that effects on ROS, HIF, and mitochondria are unlikely to contribute significantly to the cellular activity of 2ME2. Thus, our data indicate that the structural requirements for inducing ROS and inhibition of complex I of the mitochondrial electron transport chain were different from those required for proapoptotic drug activity. Furthermore, antioxidant treatment or overexpression of catalase did not inhibit the cellular activity of 2ME2 in epithelial cancer cells. Inhibition of HIF required much higher concentrations of 2ME2 analogues compared with concentrations that inhibited cell proliferation and induced apoptosis. Our results thus provide a better insight into the mechanism of action of 2ME2 and reveal structural requirements that confer high cellular activity, which may aid future drug development.

Fluorescent taxoid probes for microtubule research

The use of the antitumor drug taxol as an experimental microtubule-stabilizing agent is widespread. Fluorescent taxol conjugates, although less employed, are very useful tools for several purposes in microtubule research. These include easily visualizing microtubule cytoskeletons in a variety of cells as well as in vitro assembled microtubules, studying the molecular recognition processes of taxoids by microtubules and investigating new microtubule-stabilizing agents. This chapter describes both the methods for working with fluorescent taxol conjugates and several applications employing the active fluorescent taxoids Flutax-1, Flutax-2, Hexaflutax, Rotax, and FChitax-3. These methods include visualizing microtubules in native and mildly fixed cytoskeletons from cultured cells, ciliate and flagellate protozoans and in living tumor cells, purification of tubulin from tumor cell lines and measurement of its taxoid binding capacity. The applications discussed include a homogeneous assay to screen for compounds binding the taxol site, the determination of the pathway of taxol entry into microtubules and the design of high affinity microtubule-stabilizing agents.

Regulation of aryl hydrocarbon receptor function by selective estrogen receptor modulators

Selective estrogen receptor modulators (SERMs), such as tamoxifen (TAM), have been used extensively for the treatment and prevention of breast cancer and other pathologies associated with aberrant estrogen receptor (ER) signaling. These compounds exhibit cell-selective agonist/antagonist activities as a consequence of their ability to induce different conformational changes in ER, thereby enabling it to recruit functionally distinct transcriptional coregulators. However, the observation that SERMs can also regulate aspects of calcium signaling and apoptosis in an ER-independent manner in some systems suggests that some of the activity of drugs within this class may also arise as a consequence of their ability to interact with targets other than ER. In this study, we demonstrate that 4-hydroxy-TAM (4OHT), an active metabolite of TAM, directly binds to and modulates the transcriptional activity of the aryl hydrocarbon receptor (AHR). Of specific interest was the observation, that in the absence of ER, 4OHT can induce the expression of AHR target genes involved in estradiol metabolism, cellular proliferation, and metastasis in cellular models of breast cancer. The potential role for AHR in SERM pharmacology was further underscored by the ability of 4OHT to suppress osteoclast differentiation in vitro in part through AHR. Cumulatively, these findings provide evidence that it is necessary to reevaluate the relative roles of ER and AHR in manifesting the pharmacological actions and therapeutic efficacy of TAM and other SERMs.

Hypoxia and TGF-beta drive breast cancer bone metastases through parallel signaling pathways in tumor cells and the bone microenvironment

Background

Most patients with advanced breast cancer develop bone metastases, which cause pain, hypercalcemia, fractures, nerve compression and paralysis. Chemotherapy causes further bone loss, and bone-specific treatments are only palliative. Multiple tumor-secreted factors act on the bone microenvironment to drive a feed-forward cycle of tumor growth. Effective treatment requires inhibiting upstream regulators of groups of prometastatic factors. Two central regulators are hypoxia and transforming growth factor (TGF)- β. We asked whether hypoxia (via HIF-1α) and TGF-β signaling promote bone metastases independently or synergistically, and we tested molecular versus pharmacological inhibition strategies in an animal model.

Methodology/Principal Findings

We analyzed interactions between HIF-1α and TGF-β pathways in MDA-MB-231 breast cancer cells. Only vascular endothelial growth factor (VEGF) and the CXC chemokine receptor 4 (CXCR4), of 16 genes tested, were additively increased by both TGF-β and hypoxia, with effects on the proximal promoters. We inhibited HIF-1α and TGF-β pathways in tumor cells by shRNA and dominant negative receptor approaches. Inhibition of either pathway decreased bone metastasis, with no further effect of double blockade. We tested pharmacologic inhibitors of the pathways, which target both the tumor and the bone microenvironment. Unlike molecular blockade, combined drug treatment decreased bone metastases more than either alone, with effects on bone to decrease osteoclastic bone resorption and increase osteoblast activity, in addition to actions on tumor cells.

Conclusions/Significance

Hypoxia and TGF-β signaling in parallel drive tumor bone metastases and regulate a common set of tumor genes. In contrast, small molecule inhibitors, by acting on both tumor cells and the bone microenvironment, additively decrease tumor burden, while improving skeletal quality. Our studies suggest that inhibitors of HIF-1α and TGF-β may improve treatment of bone metastases and increase survival.

c-Jun NH2-terminal kinase activation is essential for DRAM-dependent induction of autophagy and apoptosis in 2-methoxyestradiol-treated Ewing sarcoma cells

Ewing sarcoma and osteosarcoma are two aggressive cancers that affect bones and soft tissues in children and adolescents. Despite multimodal therapy, patients with metastatic sarcoma have a poor prognosis, emphasizing a need for more effective treatment. We have shown previously that 2-methoxyestradiol (2-ME), an antitumoral compound, induces apoptosis in Ewing sarcoma cells through c-Jun NH(2)-terminal kinase (JNK) activation. In the present study, we provide evidence that 2-ME elicits macroautophagy, a process that participates in apoptotic responses, in a JNK-dependent manner, in Ewing sarcoma and osteosarcoma cells. We also found that the enhanced activation of JNK by 2-ME is partially regulated by p53, highlighting the relationship of JNK and autophagy to p53 signaling pathway. Furthermore, we showed that 2-ME up-regulates damage-regulated autophagy modulator (DRAM), a p53 target gene, in Ewing sarcoma cells through a mechanism that involves JNK activation. The silencing of DRAM expression reduced both apoptosis and autophagy triggered by 2-ME in Ewing sarcoma and osteosarcoma cells. Our results therefore identify JNK as a novel mediator of DRAM regulation. These findings suggest that 2-ME or other anticancer therapies that increase DRAM expression or function could be used to effectively treat sarcoma patients.

Interference with endothelial cell function by JG-03-14, an agent that binds to the colchicine site on microtubules

JG-03-14, a novel tetrasubstituted pyrrole with microtubule-depolymerizing and anti-proliferative activities, was tested for its effect on endothelial cell (EC) functions in vitro. JG-03-14 was a potent inhibitor of EC vessel-like tube formation on extracellular matrix (IC(50) of 40nM) and caused the involution of established vessels, potential anti-angiogenic and vascular-disrupting activities, respectively. These actions were not due to the inhibition of EC proliferation or to the induction of apoptosis by JG-03-14. While similar effects were observed with the microtubule-depolymerizing and vascular-disrupting drug combretastatin-A4 (CoA4), JG-03-14 had a more selective effect on tube formation, relative to its cytotoxic actions, than did CoA4. Potential molecular mechanisms for JG-03-14's anti-vascular actions were explored. In contrast to the taxanes, which also have anti-vascular actions, JG-03-14 did not disrupt focal adhesion formation or block VEGF-induced phosphorylation of focal adhesion kinase. It did, however, inhibit VEGF-induced phosphorylation of VE-cadherin and reduce the association of beta-catenin with VE-cadherin. It caused cell retraction, intercellular gaps, and abnormally elongated adherens junctions at low concentrations, and prominent, but reversible, plasma membrane blebbing at higher concentrations. These results suggest that JG-03-14 may affect vascular morphogenesis by disrupting the interaction of adjacent endothelial cells, possibly as a consequence of effects on VE-cadherin, beta-catenin, and/or actin. They also provide the first report of anti-vascular activity for this class of compounds.

Brain tumor hypoxia: tumorigenesis, angiogenesis, imaging, pseudoprogression, and as a therapeutic target

Hypoxia is implicated in many aspects of tumor development, angiogenesis, and growth in many different tumors. Brain tumors, particularly the highly aggressive glioblastoma multiforme (GBM) with its necrotic tissues, are likely affected similarly by hypoxia, although this involvement has not been closely studied. Invasion, apoptosis, chemoresistance, resistance to antiangiogenic therapy, and radiation resistance may all have hypoxic mechanisms. The extent of the influence of hypoxia in these processes makes it an attractive therapeutic target for GBM. Because of their relationship to glioma and meningioma growth and angiogenesis, hypoxia-regulated molecules, including hypoxia inducible factor-1, carbonic anhydrase IX, glucose transporter 1, and vascular endothelial growth factor, may be suitable subjects for therapies. Furthermore, other novel hypoxia-regulated molecules that may play a role in GBM may provide further options. Emerging imaging techniques may allow for improved determination of hypoxia in human brain tumors to better focus therapeutic treatments; however, tumor pseudoprogression, which may be prompted by hypoxia, poses further challenges. An understanding of the role of hypoxia in tumor development and growth is important for physicians involved in the care of patients with brain tumors.

Antivascular actions of microtubule-binding drugs

Microtubule-binding drugs (MBD) are widely used in cancer chemotherapy and also have clinically relevant antiangiogenic and vascular-disrupting properties. These antivascular actions are due in part to direct effects on endothelial cells, and all MBDs (both microtubule-stabilizing and microtubule-destabilizing) inhibit endothelial cell proliferation, migration, and tube formation in vitro, actions that are thought to correspond to therapeutic antiangiogenic actions. In addition, the microtubule-destabilizing agents cause prominent changes in endothelial cell morphology, an action associated with rapid vascular collapse in vivo. The effects on endothelial cells occur in vitro at low drug concentrations, which do not affect microtubule gross morphology, do not cause microtubule bundling or microtubule loss and do not induce cell cycle arrest, apoptosis, or cell death. Rather, it has been hypothesized that, at low concentrations, MBDs produce more subtle effects on microtubule dynamics, block critical cell signaling pathways, and prevent the microtubules from properly interacting with transient subcellular assemblies (focal adhesions and adherens junctions) whose subsequent stabilization and/or maturation are required for cell motility and cell-cell interactions. This review will focus on recent studies to define the molecular mechanisms for the antivascular actions of the MBDs, information that could be useful in the identification or design of agents whose actions more selectively target the tumor vasculature.

Bcl-2 blocks 2-methoxyestradiol induced leukemia cell apoptosis by a p27(Kip1)-dependent G1/S cell cycle arrest in conjunction with NF-kappaB activation

2-Methoxyestradiol (2-ME2) induces leukemia cells to undergo apoptosis in association with Bcl-2 inactivation but the mechanisms whereby Bcl-2 contributes to protection against programmed cell death in this context remain unclear. Here we showed that 2-ME2 inhibited the proliferation of Jurkat leukemia cells by markedly suppressing the levels of cyclins D3 and E, E2F1 and p21(Cip1/Waf1) and up-regulating p16(INK4A). Further, 2-ME2 induced apoptosis of Jurkat cells in association with down-regulation and phosphorylation of Bcl-2 (as mediated by JNK), up-regulation of Bak, activation of caspases-9 and -3 and PARP-1 cleavage. To determine the importance and mechanistic role of Bcl-2 in this process, we enforced its expression in Jurkat cells by retroviral transduction. Enforcing Bcl-2 expression in Jurkat cells abolished 2-ME2-induced apoptosis and instead produced a G1/S phase cell cycle arrest in association with markedly increased levels of p27(Kip1). Bcl-2 and p27(Kip1) were localized mainly in the nucleus in these apoptotic resistant cells. Interestingly, NF-kappaB activity and p50 levels were increased by 2-ME2 and suppression of NF-kappaB signaling reduced p27(Kip1) expression and sensitized cells to 2-ME2-induced apoptosis. Importantly, knocking-down p27(Kip1) in Jurkat Bcl-2 cells sensitized them to spontaneous and 2-ME2-induced apoptosis. Thus, Bcl-2 prevented the 2-ME2-induced apoptotic response by orchestrating a p27(Kip1)-dependent G1/S phase arrest in conjunction with activating NF-kappaB. Thus, we achieved a much better understanding of the penetrance and mechanistic complexity of Bcl-2 dependent anti-apoptotic pathways in cancer cells and why Bcl-2 inactivation is so critical for the efficacy of apoptosis and anti-proliferative inducing drugs like 2-ME2.

Cancer and the tumor microenvironment: a review of an essential relationship

PURPOSE

The role of the microenvironment during the initiation and progression of carcinogenesis is now realized to be of critical importance, both for enhanced understanding of fundamental cancer biology, as well as exploiting this source of relatively new knowledge for improved molecular diagnostics and therapeutics.

METHODS

This review focuses on: (1) the approaches of preparing and analyzing secreted proteins, (2) the contribution of tumor microenvironment elements in cancer, and (3) the potential molecular targets for cancer therapy.

RESULTS

The microenvironment of a tumor is an integral part of its physiology, structure, and function. It is an essential aspect of the tumor proper, since it supplies a nurturing environment for the malignant process. A fundamental deranged relationship between tumor and stromal cells is essential for tumor cell growth, progression, and development of life threatening metastasis. Improved understanding of this interaction may provide new and valuable clinical targets for cancer management, as well as risk assessment and prevention. Non-malignant cells and secreted proteins from tumor and stromal cells are active participants in cancer progression.

CONCLUSIONS

Monitoring the change in the tumor microenvironment via molecular and cellular profiles as tumor progresses would be vital for identifying cell or protein targets for cancer prevention and therapy.

In vitro effects of 2-methoxyestradiol on MCF-12A and MCF-7 cell growth, morphology and mitotic spindle formation

The influence of 2-methoxyestradiol (2ME) was investigated on cell growth, morphology and spindle formation in a tumorigenic (MCF-7) and non-tumorigenic (MCF-12A) epithelial breast cell line. Inhibition of cell growth was more pronounced in the MCF-7 cells compared to the MCF-12A cells following 2ME treatment. Dose-dependent studies (10(-5)-10(-9) M) revealed that 10(-6) M 2ME inhibited cell growth by 44% in MCF-12A cells and by 84% in MCF-7 cells (p-value < 0.05). 2ME-treated MCF-7 cells showed abnormal metaphase cells, membrane blebbing, apoptotic cells and disrupted spindle formation. These observations were either absent or less prominent in MCF-12A cells. 2ME had no effect on the length of the cell cycle between S-phase and the time a mitotic peak was reached in either cell line but MCF-7 cells were blocked in mitosis with no statistically significant alterations in the phosphorylation status of Cdc25C. Nevertheless, Cdc2 activity was significantly increased in MCF-7 cells compared to MCF-12A cells (p-value < 0.05). The results indicate that 2ME disrupts mitotic spindle formation and enhances Cdc2 kinase activity, leading to persistence of the spindle checkpoint and thus prolonged metaphase arrest that may result in the induction of apoptosis. The tumorigenic MCF-7 cells were especially sensitive to 2ME treatment compared to the normal MCF-12A cells. Therefore, differential mechanism(s) of growth inhibition are evident between the normal and tumorigenic cells.