2-Methoxyestradiol Induces Cell Cycle Arrest and Mitotic Cell Apoptosis in Human Vascular Smooth Muscle Cells

2-Methoxyestradiol, an Endogenous 17β-Estradiol Metabolite, Induces Antimitogenic and Apoptotic Actions in Oligodendroglial Precursor Cells and Triggers Endoreduplication via the p53 Pathway

The abnormal growth of oligodendrocyte precursor cells (OPCs) significantly contributes to the progression of glioblastoma tumors. Hence, molecules that block OPC growth may be of therapeutic importance in treating gliomas. 2-Methoxyestradiol (2ME), an endogenous tubulin-interacting metabolite of estradiol, is effective against multiple proliferative disorders. Based on its anti-carcinogenic and anti-angiogenic actions, it is undergoing phase II clinical trials. We hypothesize that 2ME may prevent glioma growth by targeting OPC growth. Here, we tested this hypothesis by assessing the impact of 2ME on the growth of an OPC line, "Oli-neu", and dissected the underlying mechanism(s). Treatment with 2ME inhibited OPC growth in a concentration-dependent manner, accompanied by significant upregulation in the expression of p21 and p27, which are negative cell-cycle regulators. Moreover, treatment with 2ME altered OPC morphology from multi-arm processes to rounded cells. At concentrations of 1uM and greater, 2ME induced apoptosis, with increased expressions of caspase 3, PARP, and caspase-7 fragments, externalized phosphatidylserine staining/APOPercentage, and increased mitochondrial activity. Flow cytometry and microscopic analysis demonstrated that 2ME triggers endoreduplication in a concentration-dependent fashion. Importantly, 2ME induced cyclin E, JNK1/2, and p53 expression, as well as OPC fusion, which are key mechanisms driving endoreduplication and whole-genome duplication. Importantly, the inhibition of p53 with pifithrin-α rescued 2ME-induced endoreduplication. The pro-apoptotic and endoreduplication actions of 2ME were accompanied by the upregulation of survivin, cyclin A, Cyclin B, Cyclin D2, and ppRB. Similar growth inhibitory, apoptotic, and endoreduplication effects of 2ME were observed in CG4 cells. Taken together, our findings provide evidence that 2ME not only inhibits OPC growth and triggers apoptosis, but also activates OPCs into survival (fight or flight) mode, leading to endoreduplication. This inherent survival characteristic of OPCs may, in part, be responsible for drug resistance in gliomas, as observed for many tubulin-interacting drugs. Importantly, the fate of OPCs after 2ME treatment may depend on the cell-cycle status of individual cells. Combining tubulin-interfering molecules with drugs such as pifithrin-α that inhibit endoreduplication may help inhibit OPC/glioma growth and limit drug resistance.

Pharmacological inhibition of MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) induces ferroptosis in vascular smooth muscle cells

MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) is a human paracaspase protein with proteolytic activity via its caspase-like domain. The pharmacological inhibition of MALT1 by MI-2, a specific chemical inhibitor, diminishes the response of endothelial cells to inflammatory stimuli. However, it is largely unknown how MALT1 regulates the functions of vascular smooth muscle cells (SMCs). This study aims to investigate the impact of MALT1 inhibition by MI-2 on the functions of vascular SMCs, both in vitro and in vivo. MI-2 treatment led to concentration- and time-dependent cell death of cultured aortic SMCs, which was rescued by the iron chelator deferoxamine (DFO) or ferrostatin-1 (Fer-1), a specific inhibitor of ferroptosis, but not by inhibitors of apoptosis (Z-VAD-fmk), pyroptosis (Z-YVAD-fmk), or necrosis (Necrostatin-1, Nec-1). MI-2 treatment downregulated the expression of glutathione peroxidase 4 (GPX4) and ferritin heavy polypeptide 1 (FTH1), which was prevented by pre-treatment with DFO or Fer-1. MI-2 treatment also activated autophagy, which was inhibited by Atg7 deficiency or bafilomycin A1 preventing MI-2-induced ferroptosis. MI-2 treatment reduced the cleavage of cylindromatosis (CYLD), a specific substrate of MALT1. Notably, MI-2 treatment led to a rapid loss of contractility in mouse aortas, which was prevented by co-incubation with Fer-1. Moreover, local application of MI-2 significantly reduced carotid neointima lesions and atherosclerosis in C57BL/6J mice and apolipoprotein-E knockout (ApoE-/-) mice, respectively, which were both ameliorated by co-treatment with Fer-1. In conclusion, the present study demonstrated that MALT1 inhibition induces ferroptosis of vascular SMCs, likely contributing to its amelioration of proliferative vascular diseases.

Cellular, Biophysical and in Silico Binding Study of β-Estradiol-6-one 6- (O-carboxy methyl Oxime) with Tubulin in Search of Antimitotic Derivative of 2-Methoxy Estradiol

The tubulin-microtubule system is a major target for a variety of small molecules which can interfere in cell cycle progression. Therefore, it serves as a prospective to control the incessant division of cancer cells. To identify novel inhibitors of the tubulin-microtubule system, a group of estrogen derivatives has been tested with tubulin as a target since literature surveys portray coveted behaviour from the same. Out of them, β-Estradiol-6-one 6- (O-carboxy methyl Oxime) abbreviated as Oxime, disrupts the cytoskeleton network and induces apoptosis with nuclei fragmentation. It has been revealed from the work that Oxime targets the colchicine binding site and binds tubulin in an entropy-driven manner. This suggests that structural variation might play a key role in modulating the anti-mitotic role of estrogen derivatives. Our work reveals that Oxime might serve as a lead molecule to nurture anti-cancer research, having the potential for recovery of the vast cancer population.

2-Methoxyestradiol inhibits carotid artery intimal hyperplasia induced by balloon injury via inhibiting JAK/STAT axis in rats

Intimal hyperplasia (IH) is a common complication of vascular interventional procedures that leads to narrowing of the vessel lumen. 2-Methoxyestradiol (2ME), an estrogen metabolite, has numerous pharmacological actions, including vasoprotective and antiproliferative activities. The present study aimed to evaluate the potential of 2ME, prepared as a self-nanoemulsifying drug delivery system (SNEDDS), to inhibit IH induced by balloon injury (BI) in the rat carotid artery. The prepared 2ME SNEDDS had a particle size of 119 ± 2.3 nm and a zeta potential of -7.1 ± 1.4 mV. Animals were divided into 5 groups, namely control, sham, BI, BI + 2ME (100 μg/kg), and BI + 2ME (250 μg/kg). The obtained data indicated that 2ME significantly inhibited IH as indicated by the histological and morphometric assessment of the intima, media and lumen areas. This was associated with enhanced expression of Bax and inhibited expression of Bcl2 mRNA. Furthermore, 2ME exhibited significant antioxidant properties as evidenced by prevention of malondialdehyde accumulation as well as superoxide dismutase and catalase enzymatic exhaustion. In addition, 2ME showed significant anti-inflammatory actions as it significantly inhibited vascular content of interleukin-6, tumor necrosis factor-alpha, and nuclear factor-κB. The observed vasoprotective activities of 2ME were accompanied by inhibition of Janus kinase/signal transducers and activators of transcription (JAK/STAT) protein expression. In conclusion, this study revealed that 2ME ameliorates balloon injury-induced IH in rats via suppressing JAK/STAT axis. This may help to develop new strategies to combat IH.

PCSK9 (Proprotein Convertase Subtilisin/Kexin Type 9) Triggers Vascular Smooth Muscle Cell Senescence and Apoptosis: Implication of Its Direct Role in Degenerative Vascular Disease

OBJECTIVE

PCSK9 (proprotein convertase subtilisin/kexin type 9) plays a critical role in cholesterol metabolism via the PCSK9-LDLR (low-density lipoprotein receptor) axis in the liver; however, evidence indicates that PCSK9 directly contributes to the pathogenesis of various diseases through mechanisms independent of its LDL-cholesterol regulation. The objective of this study was to determine how PCSK9 directly acts on vascular smooth muscle cells (SMCs), contributing to degenerative vascular disease. Approach and Results: We first examined the effects of PCSK9 on cultured human aortic SMCs. Overexpression of PCSK9 downregulated the expression of ApoER2 (apolipoprotein E receptor 2), a known target of PCSK9. Treatment with soluble recombinant human ApoER2 or the DNA synthesis inhibitor, hydroxyurea, inhibited PCSK9-induced polyploidization and other cellular responses of human SMCs. Treatment with antibodies against ApoER2 resulted in similar effects to those observed with PCSK9 overexpression. Inducible, SMC-specific knockout of Pcsk9 accelerated neointima formation in mouse carotid arteries and reduced age-related arterial stiffness. PCSK9 was expressed in SMCs of human atherosclerotic lesions and abundant in the "shoulder" regions of vulnerable atherosclerotic plaques. PCSK9 was also expressed in SMCs of abdominal aortic aneurysm, which was inversely related to the expression of smooth muscle α-actin.

CONCLUSIONS

Our findings demonstrate that PCSK9 inhibits proliferation and induces polyploidization, senescence, and apoptosis, which may be relevant to various degenerative vascular diseases.

2-Methoxyestradiol Reduces Angiotensin II-Induced Hypertension and Renal Dysfunction in Ovariectomized Female and Intact Male Mice

Cytochrome P450 1B1 protects against angiotensin II (Ang II)-induced hypertension and associated cardiovascular changes in female mice, most likely via production of 2-methoxyestradiol. This study was conducted to determine whether 2-methoxyestradiol ameliorates Ang II-induced hypertension, renal dysfunction, and end-organ damage in intact Cyp1b1-/-, ovariectomized female, and Cyp1b1+/+ male mice. Ang II or vehicle was infused for 2 weeks and administered concurrently with 2-methoxyestradiol. Mice were placed in metabolic cages on day 12 of Ang II infusion for urine collection for 24 hours. 2-Methoxyestradiol reduced Ang II-induced increases in systolic blood pressure, water consumption, urine output, and proteinuria in intact female Cyp1b1-/- and ovariectomized mice. 2-Methoxyestradiol also reduced Ang II-induced increase in blood pressure, water intake, urine output, and proteinuria in Cyp1b1+/+ male mice. Treatment with 2-methoxyestradiol attenuated Ang II-induced end-organ damage in intact Cyp1b1-/- and ovariectomized Cyp1b1+/+ and Cyp1b1-/- female mice and Cyp1b1+/+ male mice. 2-Methoxyestradiol mitigated Ang II-induced increase in urinary excretion of angiotensinogen in intact Cyp1b1-/- and ovariectomized Cyp1b1+/+ and Cyp1b1-/- female mice but not in Cyp1b1+/+ male mice. The G protein-coupled estrogen receptor 1 antagonist G-15 failed to alter Ang II-induced increases in blood pressure and renal function in Cyp1b1+/+ female mice. These data suggest that 2-methoxyestradiol reduces Ang II-induced hypertension and associated end-organ damage in intact Cyp1b1-/-, ovariectomized Cyp1b1+/+ and Cyp1b1-/- female mice, and Cyp1b1+/+ male mice independent of G protein-coupled estrogen receptor 1. Therefore, 2-methoxyestradiol could serve as a therapeutic agent for treating hypertension and associated pathogenesis in postmenopausal females, and in males.

Recent Advances in chemistry and pharmacology of 2-methoxyestradiol: An anticancer investigational drug

2-Methoxyestradiol (2ME2), an estrogen hormone metabolite is a potential cancer chemotherapeutic agent. Presently, it is an investigational drug under various phases of clinical trials alone or in combination therapy. Its anticancer activity has been attributed to its antitubulin, antiangiogenic, pro-apoptotic and ROS induction properties. This anticancer drug candidate has been explored extensively in last twenty years for its detailed chemistry and pharmacology. Present review is an update of its chemistry and biological activity. It also extends an assessment of potential of 2ME2 and its analogues as possible anticancer drug in future.

MG132 Induces Expression of Monocyte Chemotactic Protein-Induced Protein 1 in Vascular Smooth Muscle Cells

Monocyte chemoattractant protein-1 (MCP-1) has been reported to induce the expression of monocyte chemotactic protein-induced protein 1 (MCPIP1), which undergoes ubiquitination degradation. Therefore, we predict that in vascular smooth muscle (VSMCs), MCPIP1 may be induced by MCP-1 and undergo degradation, which can be inhibited by the proteasome inhibitor, MG132. Our results showed that treatment of human VSMCs with MCP-1 did not increase the expression of MCPIP1. Treatment with MG132, however, elevated MCPIP1 protein levels through stimulation of the gene transcription, but not through increasing protein stability. MCPIP1 expression induced by MG132 was inhibited by α-amanitin inhibition of gene transcription or cycloheximide inhibition of protein synthesis. Our further studies showed that MCPIP1 expression induced by MG132 was inhibited by the inhibitors of AKT and p38 kinase, suggesting a role of the AKT-p38 pathway in MG132 effects. We also found that treatment with MG132 induces apoptosis, but overexpression of MCPIP1 inhibited bromodeoxyuridine (BrdU) incorporation of human VSMCs without induction of significant apoptosis. In summary, MCPIP1 expression is induced by MG132 likely through activation of the AKT-p38 pathway. MCPIP1 inhibits SMC proliferation without induction of apoptosis. J. Cell. Physiol. 232: 122-128, 2017. © 2016 Wiley Periodicals, Inc.

2-Methoxyestradiol blocks the RhoA/ROCK1 pathway in human aortic smooth muscle cells

2-Methoxyestradiol (2-ME), a metabolite of estradiol with little affinity for estrogen receptors, inhibits proliferation of vascular smooth muscle cells; however, the molecular mechanisms underlying this effect are incompletely understood. Our previous work shows that 2-ME inhibits initiation (blocks phosphorylation of ERK and Akt) and progression (reduces cyclin expression and increases expression of cyclin inhibitors) of the mitogenic pathway and interferes with mitosis (disrupts tubulin organization). Because the RhoA/ROCK1 pathway (RhoA → ROCK1 → myosin phosphatase targeting subunit → myosin light chain) is involved in cytokinesis, herein we tested the concept that 2-ME also blocks the RhoA/ROCK1 pathway. Because of the potential importance of 2-ME for preventing/treating vascular diseases, experiments were conducted in female human aortic vascular smooth muscle cells. Microarray transcriptional profiling suggested an effect of 2-ME on the RhoA/ROCK1 pathway. Indeed, 2-ME blocked mitogen-induced GTP-bound RhoABC expression and membrane-bound RhoA, suggesting interference with the activation of RhoA. 2-ME also reduced ROCK1 expression, suggesting reduced production of the primary downstream signaling kinase of the RhoA pathway. Moreover, 2-ME inhibited RhoA/ROCK1 pathway downstream signaling, including phosphorylated myosin phosphatase targeting subunit and myosin light chain; the ROCK1 inhibitor H-1152 mimicked these effects of 2-ME; both 2-ME and H-1152 blocked cytokinesis. 2-ME also reduced the expression of tissue factor, yet another downstream signaling component of the RhoA/ROCK1 pathway. We conclude that 2-ME inhibits the pathway RhoA → ROCK1 → myosin phosphatase targeting subunit → myosin light chain, and this likely contributes to the reduced cytokinesis in 2-ME treated HASMCs.

The GPER agonist G-1 induces mitotic arrest and apoptosis in human vascular smooth muscle cells independent of GPER

The G protein-coupled estrogen receptor (GPER) has been implicated in the regulation of smooth muscle cell (SMC) proliferation. The GPER selective agonist G-1 has been a useful tool for exploring the biological roles of GPER in a variety of experimental settings, including SMC proliferation. The present study, originally designed to investigate cellular and signaling mechanisms underlying the regulatory role of GPER in vascular SMC proliferation using G-1, unexpectedly revealed off-target effects of G-1. G-1(1-10 μM) inhibited bromodeoxyuridine (BrdU) incorporation of human SMCs and caused G2/M cell accumulation. G-1 treatment also increased mitotic index concurrent with a decrease in phosphorylation of Cdk1 (Tyr 15) and an increase in phosphorylation of the mitotic checkpoint protein BuBR1. Furthermore, G-1 caused microtubule disruption, mitotic spindle damage, and tubulin depolymerization. G-1 induced cell apoptosis as indicated by the appearance of TUNEL-positive and annexin V-positive cells with enhanced cleavage of caspases 3 and 9. However, neither the GPER antagonist G-15 nor the MAPK kinase inhibitor PD98059 prevented these G-1 effects. Down-regulation of GPER or p44/42 MAPK with siRNA transfection also did not affect the G-1-induced apoptosis. We conclude that G-1 inhibits proliferation of SMCs through mechanisms involving mitotic arrest and apoptosis, independent of GPER and the MAPK pathway.

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.

Estrogen metabolite 2-methoxyestradiol prevents hypertension in deoxycorticosterone acetate-salt rats

PURPOSE

Our early work showed that the estrogen metabolite 2-methoxyestradiol (2ME) inhibits proliferation of vascular smooth muscle cells (SMCs) and vascular contractility through an endothelium-dependent mechanism. The aim of this study was to examine whether 2ME prevents the development of hypertension in rats.

METHODS

A hypertensive model was established in uninephrectomized rats using deoxycorticosterone acetate (DOCA)-salt. Blood pressure in response to 2ME (treatment up to 10 weeks or single bolus) was monitored.

RESULTS

Our results showed that systolic blood pressure, as measured by tail-cuff plethysmography, was significantly increased in conscious rats treated with DOCA-salt for 3-10 weeks. Co-treatment with 2ME (100-300 μg/kg), but not dimethyl sulfoxide (DMSO), completely prevented the increase in blood pressure of DOCA-salt rats. After 10-week treatment, the mean arterial blood pressure (MABP) of anesthetized rats measured using PowerLab Data Acquisition System was: 84 ± 16 mmHg in normotensive control rats and 150 ± 9 mmHg in DOCA-salt rats, which was similar to that of DMSO-treated rats. Treatment with 2ME at low or high doses reduced MABP of DOCA-salt rats close to that of control normotensive rats. In addition, MABP of hypertensive DOCA-salt rats was significantly reduced in response to a single injection of 2ME. Delayed administration of 2ME reduced the further increase of blood pressure in DOCA-salt rats. However, inhibition of 2ME production by entacapone did not significantly affect blood pressure in either control or DOCA-salt rats.

CONCLUSIONS

2ME treatment prevents the development of hypertension in DOCA-salt rats, implicating a therapeutic potential of 2ME in hypertension treatment.

Different effects of epidermal growth factor on smooth muscle cells derived from human myometrium and from leiomyoma

OBJECTIVE

To determine different effects of epidermal growth factor (EGF) on cultured smooth muscle cells (SMCs) derived from human myometrium and leiomyoma.

DESIGN

EGF effects on DNA synthesis and intracellular signal transduction were studied in cultured SMCs from leiomyoma and its matched myometrium.

SETTING

Research laboratories.

PATIENT(S)

Patients 35-50 years old with uterine leiomyomas.

INTERVENTION(S)

Hysterectomy.

MAIN OUTCOME MEASURE(S)

Signal transduction from EGF receptor.

RESULT(S)

As analyzed by laser scanning cytometry (LSC), EGF treatment stimulated DNA synthesis and induced polyploidization of leiomyomal, but not myometrial, SMCs. EGF stimulation was inhibited by AG1478, an EGF receptor (EGFR) inhibitor and PD98059, a mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor. Both leiomyomal and myometrial SMCs had similar expression levels of EGFR, but EGF treatment induced transient phosphorylation activation of EGFR and Akt in leiomyomal SMCs. Consequently, EGF triggered transient phosphorylation activation of p44/42 MAPK in leiomyomal SMCs, followed by down-regulation of p27. In myometrial SMCs, however, EGF induced sustained activation of EGFR, Akt, and p44/42 MAPK with up-regulation of p27.

CONCLUSION(S)

EGF stimulates DNA synthesis and polyploidization in leiomyomal SMCs through transient activation of the EGFR-MAPK pathway. Given that polyploidization plays a role in tumorigenesis, our results shed new light on the pathogenesis of human uterine leiomyoma.

Rapamycin inhibits hydrogen peroxide-induced loss of vascular contractility

Rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR) pathway, has been shown to extend the life span of mice, and oxidative stress plays critical roles in vascular aging involving loss of compliance of arteries. We examined, therefore, whether rapamycin has protective effects on the inhibition of vascular contractility by hydrogen peroxide (H₂O₂). Prolonged (3 h) exposure to H₂O₂ induced complete loss of contraction of mouse aortic rings and mesenteric (resistance) arteries to either KCl or phenylephrine, which was attenuated by pretreatment with rapamycin. H₂O₂-induced loss of contractility was unaffected by treatment with actinomycin D or cycloheximide, inhibitors of gene transcription and protein synthesis, respectively. Western blot analysis showed that there was no increase in phosphorylation of S6 kinase 1 (S6K) or factor 4E binding protein 1 (4EBP1) in response to H₂O₂ treatment, suggesting involvement of the mTOR complex-2 (mTORC2) rather than mTORC1. H₂O₂ treatment inhibited phosphorylation of the 20-kDa regulatory light chains of myosin (LC₂₀), which was partially blocked by rapamycin treatment. Interestingly, the calcineurin inhibitors cyclosporine A and FK506 were found to mimic the rapamycin effect, and rapamycin inhibited calcineurin activation induced by H₂O₂. We conclude that rapamycin inhibits H₂O₂-induced loss of vascular contractility, likely through an mTORC2-calcineurin pathway.

Nongenomic inhibition of coronary constriction by 17ß-estradiol, 2-hydroxyestradiol, and 2-methoxyestradiol

The cardioprotective effects of 17beta-estradiol (E2) in women are hypothesized to be partially mediated by the E2 metabolites 2-hydroxyestradiol (2-HOE) and 2-methoxyestradiol (2-MeOH). Therefore, the purpose of our study was to determine the acute effects of E2, 2-HOE, and 2-MeOH on inhibition of coronary arterial constriction. Right coronary arteries obtained from breeding sows were cut into 4 mm rings and suspended in organ baths. Incubation of the rings with E2, 2-HOE, and 2-MeOH (10 micromol/L) for 60 min attenuated a subsequent KCl-induced contraction by approximately 50%. The protein synthesis inhibitor cycloheximide and the estrogen receptor antagonists ICI 182780 and tamoxifen did not affect the attenuation. Moreover, E2, 2-HOE, and 2-MeOH antagonized the contraction induced by the vasospasm agonist endothelin-1 (0.1 micromol/L) by approximately 36%. When the L-type Ca2+ channel blocker nifedipine was added at the conclusion of the experiment, no additional contractile attenuation was present. Our results suggest that E2, 2-HOE, and 2-MeOH demonstrate a similar nongenomic inhibition of agonist-induced extracellular Ca2+-dependent contractions.

New therapies for pulmonary arterial hypertension: an update on current bench to bedside translation

IMPORTANCE OF THE FIELD

Treatments of pulmonary arterial hypertension (PAH) that have so far proven efficacious are all based on the restoration of endothelium control of pulmonary vascular tone and structure, by administration of prostacyclins, endothelin receptor antagonists and phosphodiesterase-5 inhibitors. However, results remain unsatisfactory, with persistent high mortality, insufficient clinical improvement and no convincing report of any reversal of the disease process.

AREAS COVERED IN THIS REVIEW

New antiproliferative approaches that aim to actively limit pulmonary vascular remodeling are being sought. Several such treatments have shown promise in experimental models and in preliminary clinical studies. Noteworthy among these are dichloroacetate, survivin antagonists, nuclear factor of activated T-cell inhibitors, PPAR-gamma agonists, tyrosine kinase inhibitors, Rho-kinase inhibitors, statins, vasoactive intestinal peptide, soluble guanylate cyclase stimulators/activators, adrenomedullin, elastase inhibitors, serotonin reuptake inhibitors, anti-inflammatory agents, and bone marrow-derived progenitor cells.

WHAT THE READER WILL GAIN

Update on various strategies targeting proliferative, inflammatory and regenerating processes currently under evaluation in patients with PAH.

TAKE HOME MESSAGE

In spite of favorable results in experimental models, none of these strategies has achieved the ultimate goal of curing PAH. Further developments will depend on progress made in our pathobiological understanding of the disease and carefully designed randomized, controlled trials.

Estradiol-17beta and its cytochrome P450- and catechol-O-methyltransferase-derived metabolites stimulate proliferation in uterine artery endothelial cells: role of estrogen receptor-alpha versus estrogen receptor-beta

Estradiol-17beta (E(2)beta) and its metabolites, which are sequentially synthesized by cytochrome P450s and catechol-O-methyltransferase to form 2 and 4-hydroxyestradiol (OHE(2)) and 2- and 4-methoxestradiol (ME(2)), are elevated during pregnancy. We investigated whether cytochrome P450s and catechol-O-methyltransferase are expressed in uterine artery endothelial cells (UAECs) and whether E(2)beta and its metabolites modulate cell proliferation via ER-alpha and/or ER-beta and play roles in physiological uterine angiogenesis during pregnancy. Cultured ovine UAECs from pregnant and nonpregnant ewes were treated with 0.1 to 100.0 nmol/L of E(2)beta, 2-OHE(2), 4-OHE(2), 2-ME(2), and 4-ME(2). ER-alpha or ER-beta specificity was tested using ICI 182 780, ER-alpha-specific 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinyleth oxy)phenol]-1H-pyrazole dihydrochloride, ER-beta-specific 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo [1,5-a]pyrim idin-3-yl]phenol antagonists and their respective agonists ER-alpha-specific 4,4',4"-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol and ER-beta-specific 2,3-bis(4-Hydroxyphenyl)-propionitrile. Angiogenesis was evaluated using 5-bromodeoxyuridine proliferation assay. Using confocal microscopy and Western analyses to determine enzyme location and levels, we observed CYP1A1, CYP1A2, CYP1B1, CYP3A4, and catechol-O-methyltransferase expression in UAECs; however, expressions were similar between nonpregnant UAECs and pregnant UAECs. E(2)beta, 2-OHE(2), 4-OHE(2), and 4-ME(2) treatments concentration-dependently stimulated proliferation in pregnant UAECs but not in nonpregnant UAECs; 2-ME(2) did not stimulate proliferation in either cell type. Proliferative responses of pregnant UAECs to E(2)beta were solely mediated by ER-beta, whereas responses to E(2)beta metabolites were neither ER-alpha nor ER-beta mediated. We demonstrate an important vascular role for E(2)beta, its cytochrome P450- and catechol-O-methyltransferase-derived metabolites, and ER-beta in uterine angiogenesis regulation during pregnancy that may be dysfunctional in preeclampsia and other cardiovascular disorders.

2-methoxyestradiol inhibits atorvastatin-induced rounding of human vascular smooth muscle cells

The cardiovascular benefits of statins, including atorvastatin (ATV), have been reported to be gender-dependent, but the underlying mechanism is unclear. In this study we examine whether estrogen and its metabolite, 2-methoxyestradiol (2ME), affect the rounding response of human vascular smooth muscle cells (SMCs) induced by ATV. Twenty-four hour treatment with ATV (10-100 microM) induced rounding of cultured human SMCs. Addition of 2ME (1-20 microM), but not 17beta-estradiol, for 2 h induced re-spreading of rounded cells. Our further studies showed that the effects of 2ME were mimicked by microtubule-disrupting drugs and inhibited by taxol. Inhibition of RhoA and ROCK (Rho-kinase) by C3-toxin and H-1152, respectively, blocked 2ME effects. 2ME effects were also blocked by treatment with either actin-interfering drugs, such as cytochalasin D and jasplakinolide, or myosin inhibitor blebbistatin. ML-7 and -9, the inhibitors for myosin light chain kinase, inhibited 2ME effect as well. ATV treatment induced a decrease of F-actin content and Thr18/Ser19 dual phosphorylation of myosin regulatory light chain (MRLC), which was rescued by 2ME or mevalonate. The rescue effects of 2ME on F-actin content and MRLC dual phosphorylation were abolished by taxol or H-1152. In addition, kinesin Eg5 inhibitor monastrol and dynein inhibitor erythro-9-3-(2-hydroxynonyl) adenine (EHNA) significantly blocked 2ME effects. Finally, our results revealed that 2ME inhibited the migration of SMCs induced by ATV (0.1 microM) in wound healing assay and Boyden chamber assay. In summary, our data show that 2ME, but not estrogen, inhibits ATV-induced rounding of human SMCs through induction of microtubule disassembly and activation of the Rho-ROCK-actinomyosin pathway.

Potential vascular actions of 2-methoxyestradiol

2-Methoxyestradiol (2-ME) is a biologically active metabolite of 17beta-estradiol that appears to inhibit key processes associated with cell replication in vitro. The molecule has been suggested to have potent growth-inhibitory effects on proliferating cells, including smooth muscle cells and endothelial cells, and may be antiangiogenic. Because of these potential roles for 2-ME, its lack of cytotoxicity and low estrogenic activity, we hypothesize that 2-ME could be a valuable therapeutic molecule for prevention and treatment of cardiovascular diseases. Whether 2-ME is as effective in vivo as it is in vitro at modulating vascular processes remains controversial. Here we discuss recent developments regarding mechanisms by which 2-ME might regulate vascular activity and angiogenesis and speculate on the therapeutic implications of these developments.

Therapeutic targets in pulmonary arterial hypertension

Pulmonary arterial hypertension is a progressive, fatal disease. Current treatments including prostanoids, endothelin-1 (ET-1) antagonists, and phosphodiesterase (PDE) inhibitors, have sought to address the pulmonary vascular endothelial dysfunction and vasoconstriction associated with the condition. These treatments may slow the progression of the disease but do not afford a cure. Future treatments must target more directly the structural vascular changes that impair blood flow through the pulmonary circulation. Several novel therapeutic targets have been proposed and are under active investigation, including soluble guanylyl cyclase, phosphodiesterases, tetrahydrobiopterin, 5-HT2B receptors, vasoactive intestinal peptide, receptor tyrosine kinases, adrenomedullin, Rho kinase, elastases, endogenous steroids, endothelial progenitor cells, immune cells, bone morphogenetic protein and its receptors, potassium channels, metabolic pathways, and nuclear factor of activated T cells. Tyrosine kinase inhibitors, statins, 5-HT2B receptor antagonists, EPCs and soluble guanylyl cyclase activators are among the most advanced, having produced encouraging results in animal models, and human trials are underway. This review summarises the current research in this area and speculates on their likely success.

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.

Inhibition of rat aortic smooth muscle contraction by 2-methoxyestradiol

Recent studies suggest that 2-methoxyestradiol (2-ME), an estrogen metabolite, has a similar inhibitory effect as 17beta-estradiol (E2) on vascular tone. However, it is not known whether 2-ME mediates the effects of E2 or by what mechanism 2-ME regulates smooth muscle contraction. Therefore, we compared the effects of 2-ME and E2 on rat aortic smooth muscle contraction. A preincubation with 2-ME (10 microM) for 1 h inhibited phenylephrine (PE)-induced tension in endothelium-intact, but not -denuded, tissues, whereas E2 inhibited PE-induced contraction in both preparations. The effects of 2-ME and E2 on endothelium-intact preparations were prevented by L-NAME hydrochloride (a nitric oxide synthase inhibitor). The 2-ME treatment reduced PE-induced phosphorylation of the 20-kDa myosin regulatory light chain. The inhibitory effects of 2-ME and E2 were not affected by ICI-182780 (an estrogen receptor antagonist) or actinomycin D (a gene transcription inhibitor); however, the effect of 2-ME, but not E2, was prevented by cycloheximide (a protein synthesis inhibitor). Furthermore, the effect of E2 was not blocked by 1-aminobenzotriazole (a cytochrome P-450 inhibitor) or Ro 41-0960 (a catechol-O-methyltransferase inhibitor). The effect of 2-ME was not mimicked by microtubule-interfering agents (nocodazole or Taxol). We conclude that 2-ME inhibits smooth muscle contractility through an endothelium- and nitric oxide-dependent mechanism, which does not involve estrogen receptors or microtubule disruption. The effect of 2-ME, but not E2, involves de novo protein synthesis. 2-ME does not mediate the inhibitory effect of E2 on smooth muscle contraction. These results support a potentially important role of 2-ME in the regulation of smooth muscle tone in the vasculature.

Targeting human 8-oxoguanine DNA glycosylase to mitochondria protects cells from 2-methoxyestradiol-induced-mitochondria-dependent apoptosis

2-Methoxyestradiol (2-ME), an endogenous estrogen metabolite of 17beta-estradiol, is known to induce mitochondria-mediated apoptosis through several mechanisms. We sought to study the effect of mitochondrialy targeted hOGG1 (MTS-hOGG1) on HeLa cells exposed to 2-ME. MTS-hOGG1-expressing cells exposed to 2-ME showed increased cellular survival and had significantly less G(2)/M cell cycle arrest compared to vector-only-transfected cells. In addition, 2-ME exposure resulted in an increase in mitochondrial membrane potential, increased apoptosis, accompanied by higher activation of caspase-3, -9, cleavage of Bid to tBid and protein poly(ADP-ribose) polymerase (PARP) cleavage in HeLa cells lacking MTS-hOGG1. Fas inhibitors cerulenin or C75 inhibited 2-ME-induced caspase activation, PARP cleavage, apoptosis and reversed mitochondrial membrane hyperpolarization, thereby recapitulating the increased expression of MTS-hOGG1. Hence, MTS-hOGG1 plays an important protective role against 2-ME-mediated mitochondrial damage by blocking apoptosis induced through the Fas pathway.

Emerging therapies for pulmonary arterial hypertension

Pulmonary arterial hypertension is characterised by increased pulmonary vascular resistance due to increased vascular tone and structural remodelling of pulmonary vessels. The therapies that are in use so far have been developed to correct endothelial dysfunction and reduce vasomotor tone. These treatments have a limited effect on the remodelling process and, increasingly, the focus is turning to potent strategies for inhibiting vascular proliferation and promoting vascular apoptosis. Multiple novel targets have been uncovered over the last 5 years and several are now in early clinical trials. At present, it is clear that there is no single treatment for the condition. Although this is the case, studies are investigating the role of combining therapies that are already established.

Predisposition to tetraploidy in pulmonary vascular smooth muscle cells derived from the Eker rats

Somatic mutations in the tuberous sclerosis complex-2 (TSC2) gene are associated with pulmonary lymphangioleiomyomatosis (LAM), a disorder characterized by benign lesions of smooth muscle and/or smooth muscle-like cells in the lung. However, the cellular mechanisms underlying LAM disease are largely unknown. Given that the TSC2 gene product tuberin is involved in the regulation of cell growth and proliferation, the present study was designed to investigate the potential roles of TSC2 in regulation of the cell cycle. We studied cell cycle profiles of pulmonary vascular smooth muscle cells (SMCs) derived from Eker rats (Tsc2(+/EK)), a genetic model carrying a germline insertional deletion in one copy of the Tsc2 gene, and the wild-type rats (Tsc2(+/+)), a noncarrier counterpart. We found that Tsc2(+/EK), but not Tsc2(+/+), SMCs displayed increases in cells with > or =4N DNA content (> or =4N cells) and in the bromodeoxyuridine (BrdU) incorporation of > or =4N cells. Centrosome number was also increased in Tsc2(+/EK) SMCs, but the mitotic index was comparable between Tsc2(+/+) and Tsc2(+/EK) SMCs. Furthermore, Tsc2(+/EK) SMCs showed elevated phosphorylation of p70S6K and increased expression of cell cycle regulatory proteins Cdk1, cyclin B, Cdk2, and cyclin E. Inhibition of the mammalian target of rapamycin (mTOR) pathway by rapamycin not only inhibited the phosphorylation of p70(S6K) and the expression of cell cycle regulatory proteins but also reduced accumulation of > or =4N cells and BrdU incorporation of >4N cells. Therefore, our results demonstrate that Tsc2(+/EK) SMCs are predisposed to undergo tetraploidization, involving activation of the mTOR pathway. These findings suggest an important role of Tsc2 in regulation of the cell cycle.

The oestrogen metabolite 2-methoxyoestradiol alone or in combination with tumour necrosis factor-related apoptosis-inducing ligand mediates apoptosis in cancerous but not healthy cells of the human endometrium

Cancers of the reproductive tract account for 12% of all malignancies in women. As previous studies have shown that oestrogen metabolites can cause apoptosis, we characterised the effect of oestrogen and oestrogen metabolites on non-cancerous and cancerous human endometrial cells. Herein, we demonstrate that 2-methoxyoestradiol (2ME), but not 17beta-oestradiol, induces apoptosis in cancer cell lines and primary cultured tumours of endometrial origin. In contrast, 2ME had no effect on cell viability of corresponding normal tissue. This ability of 2ME to induce apoptosis does not require oestrogen receptor activation, but is associated with increased entry into the G2/M phases of the cell cycle and the activation of both the intrinsic and the extrinsic apoptotic pathways. The selective behaviour of 2ME on cancerous as opposed to normal tissue may be due to a reduction in 17beta-hydroxysteroid dehydrogenase type II levels in cancer cells and to a differential down-regulation of superoxide dismutase. Furthermore, we demonstrate that pre-treatment with 2ME enhances the sensitivity of reproductive tract cancer cells to the apoptotic drug tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), without the loss in cell viability to normal cells incurred by currently chemotherapeutic drugs. In conclusion, 2ME, alone or in combination with TRAIL, may be an effective treatment for cancers of uterine origin with minimal toxicity to corresponding healthy female reproductive tissue.

Phenotype-specific inhibition of the vascular smooth muscle cell cycle by high glucose treatment

AIMS/HYPOTHESIS

Diabetes accelerates the development of atherosclerosis, which critically involves the proliferation of vascular smooth muscle cells (SMCs). However, how high glucose treatment regulates SMC proliferation is controversial. Considering the established SMC heterogeneity, we hypothesised that glucose treatment may have distinct effects on proliferation of the various phenotypic SMCs.

MATERIALS AND METHODS

We tested this possibility using cloned spindle-shaped and epithelioid SMCs and laser scanning cytometry.

RESULTS

Our results showed that glucose treatment significantly inhibited the serum-independent proliferation of epithelioid SMCs, but had no effect on the proliferation of spindle-shaped cells either with or without serum stimulation. Furthermore, glucose treatment inhibited DNA synthesis, as detected by bromodeoxyuridine (BrdU) incorporation, and increased the production of reactive oxygen species in epithelioid SMCs. The inhibition of BrdU incorporation by glucose treatment was mimicked by glucosamine and phorbol 2,13-dibutyrate, a protein kinase C (PKC) activator, and reversed by azaserine, an inhibitor of the hexosamine pathway. In addition, the inhibitory effects of glucose treatment were blocked by GF 109203X (a PKC inhibitor) and PD98058 (a MAPK/ERK kinase, MEK inhibitor), and by knockdown of MEK1 by small interfering RNA (siRNA). The addition of either GF 109203X or PD98058 also reduced the phosphorylation of MAP kinase induced by glucose treatment.

CONCLUSIONS/INTERPRETATION

Glucose treatment inhibits the proliferation of epithelioid, but not spindle-shaped, vascular SMCs through the activation of PKC and the MAP kinase pathway, suggesting that the effects of hyperglycaemia on vascular disease depend on the phenotype of SMCs involved.

Endoreduplication of human smooth muscle cells induced by 2-methoxyestradiol: a role for cyclin-dependent kinase 2

Endoreduplication has been suggested to contribute to the development of hypertrophy of smooth muscle cells (SMCs) in hypertension. However, endoreduplication in vascular SMCs and the underlying molecular mechanisms are not clear. Treatment of human SMCs with 10 μM 2-methoxyestradiol (2-ME) for 24 h induces accumulation of cells with ≥4N DNA content, and some polyploid/aneuploid cells actively synthesize their DNA, suggesting the occurrence of endoreduplication. In addition, 2-ME treatment upregulates the expression of cyclin-dependent kinase 2 (Cdk2). The present study was designed to characterize endoreduplication of human SMCs and explore the potential roles of Cdk2 in endoreduplication induced by 2-ME. Treatment with 2-ME (10 μM) for 2–4 days not only caused increases in >4N cells and their reentry into S phase but also induced overduplication of chromosomes. Furthermore, 2-ME increased the kinase activity of Cdk2 and its interaction with cyclin E. Inducible overexpression of dominant-negative Cdk2 in human SMCs inhibited both DNA synthesis of >4N cells and the accumulation of >4N cells induced by 2-ME. We conclude that 2-ME induces endoreduplication of human SMCs and Cdk2 plays an important role in endoreduplication in response to 2-ME.

2-Methoxyestradiol, an estradiol metabolite, inhibits neointima formation and smooth muscle cell growth via double blockade of the cell cycle

2-Methoxyestradiol (2-ME), an endogenous metabolite of estradiol with no affinity for estrogen receptors, is a potent anticarcinogenic agent (in phase II clinical trials) and mediates the inhibitory effects of estradiol on smooth muscle cell (SMC) growth. Here we studied the intracellular mechanisms by which 2-ME inhibits SMC growth and whether 2-ME prevents injury-induced neointima formation. 2-ME concentrations that inhibit proliferation of cycling human aortic SMCs by >or=50% blocked cell-cycle progression in G(0)/G(1) and in G(2)/M phase, as determined by flow cytometry. Consistent with the cell-cycle effects, at a molecular level (Western blots), 2-ME inhibited cyclin D(1) and cyclin B(1) expression; cyclin-dependent kinase (cdk)-1 and cdk-2 activity; and retinoblastoma protein (pRb), extracellular signal-regulated kinase (ERK) 1/2, and Akt phosphorylation. 2-ME also upregulated the Cdk inhibitor p27 and interfered with tubulin polymerization. Moreover, 2-ME augmented COX-2 expression, suggesting that it may also inhibit SMC growth via prostaglandin formation. In rats, treatment with 2-ME abrogated injury-induced neointima formation; decreased proliferating SMCs; downregulated expression of proliferating-cell nuclear antigen (PCNA), c-myc, cyclin D(1), cyclin B(1), phosphorylated Akt, phosphorylated ERK1/2, p21, and pRb; inhibited cdk-1 and cdk-4 activity; and upregulated expression of cyclooxygenase (COX)-2 and p27. Caspase-3 cleavage assay and fluorescence-activated cell-sorting (FACS) analysis showed no evidence of apoptosis in 2-ME-treated SMCs, and TUNEL staining in carotid segments showed no evidence of 2-ME-induced apoptosis in vivo. The antimitotic effects of 2-ME on SMCs are mediated by the inhibition of key cell-cycle regulatory proteins and effects on tubulin polymerization and COX-2 upregulation. These effects of 2-ME most likely contribute to the antivasoocclusive actions of this endogenous compound.