A phase I dose-escalation, safety and pharmacokinetic study of the 2-methoxyestradiol analog ENMD-1198 administered orally to patients with advanced cancer

Modulation of hypoxia-inducible factor-1 signaling pathways in cancer angiogenesis, invasion, and metastasis by natural compounds: a comprehensive and critical review

Tumor cells employ multiple signaling mediators to escape the hypoxic condition and trigger angiogenesis and metastasis. As a critical orchestrate of tumorigenic conditions, hypoxia-inducible factor-1 (HIF-1) is responsible for stimulating several target genes and dysregulated pathways in tumor invasion and migration. Therefore, targeting HIF-1 pathway and cross-talked mediators seems to be a novel strategy in cancer prevention and treatment. In recent decades, tremendous efforts have been made to develop multi-targeted therapies to modulate several dysregulated pathways in cancer angiogenesis, invasion, and metastasis. In this line, natural compounds have shown a bright future in combating angiogenic and metastatic conditions. Among the natural secondary metabolites, we have evaluated the critical potential of phenolic compounds, terpenes/terpenoids, alkaloids, sulfur compounds, marine- and microbe-derived agents in the attenuation of HIF-1, and interconnected pathways in fighting tumor-associated angiogenesis and invasion. This is the first comprehensive review on natural constituents as potential regulators of HIF-1 and interconnected pathways against cancer angiogenesis and metastasis. This review aims to reshape the previous strategies in cancer prevention and treatment.

Inhibition of JAK1/STAT3 pathway by 2-methoxyestradiol ameliorates psoriatic features in vitro and in an imiquimod-induced psoriasis-like mouse model

Psoriasis is characterized by hyperproliferative keratinocytes, dilated capillaries and leukocyte infiltration. 2-Methoxyestradiol (2-ME) has shown significant inhibition on proliferation, angiogenesis and inflammation. To evaluate the anti-psoriatic potential of 2-ME, psoriasis-like dermatitis was induced by topical application of imiquimod (IMQ) on the dorsal skin of C57BL/6 mice for seven consecutive days, followed by treatment of vehicle or 2-ME ointment from Day 4 on. The psoriasis area and severity index (PASI) was assessed daily. On Day 8, skin histology and spleen index were assessed. The effects of 2-ME on the proliferation, apoptosis, cell cycle, vascular endothelial growth factor A (VEGFA), and Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathways of HaCaT cells stimulated by interleukin-17 (IL-17A) were detected, together with its effect on the proliferation, tube formation and VEGF receptor expression of human umbilical vein endothelial cells (HUVECs). We found that topical 2-ME treatment significantly improved IMQ-induced psoriasis-like dermatitis and decreased the PASI scores, the activation of STAT3 in the skin (P < 0.05), and the spleen index in mice (P < 0.01). In vitro, 2-ME inhibited the proliferation of HaCaT cells by inducing apoptosis and G2/M phase arrest (P < 0.01). Moreover, 2-ME suppressed IL-17A-induced VEGFA (2.5 μM: P < 0.05; 5 μM: P < 0.01) and phosphorylation of STAT3 by blocking p-JAK1 in HaCaT cells and prevented tube formation (P < 0.01) and proliferation by targeting VEGF receptors 1 (VEGFR1) and 2 (VEGFR2) in HUVECs. We conclude that 2-ME alleviated psoriasis in vivo and in vitro by inhibiting JAK1/STAT3 pathway and was a promising therapeutic agent for psoriasis.

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.

2-Methoxyestradiol and Its Combination with a Natural Compound, Ferulic Acid, Induces Melanoma Cell Death via Downregulation of Hsp60 and Hsp90

Melanoma is an aggressive type of skin cancer with one of the highest mortality rates. Notably, its incidence in the last few decades has increased faster than any other cancer. Therefore, searching for novel anticancer therapies is of great clinical importance. In the present study, we investigated the anticancer potential of 2-methoxyestradiol, potent chemotherapeutic, in the A375 melanoma cellular model. In order to furthermore evaluate the anticancer efficacy of 2-methoxyestradiol, we have additionally combined the treatment with a naturally occurring polyphenol, ferulic acid. The results were obtained using the melanoma A375 cellular model. In the study, we used MTT assay, flow cytometry, and western blot techniques. Herein, we have evidenced that the molecular mechanism of action of 2-methoxyestradiol and ferulic acid is partly related to the reduction of Hsp60 and Hsp90 levels and the induction of nitric oxide in the A375 melanoma cell model, while no changes were observed in Hsp70 expression after 2-methoxyestradiol and ferulic acid treatment separately or in combination. This is especially important in case of chemoresistance mechanisms because the accumulation of Hsp70 reduces induction of cancer cell death, thus decreasing antitumour efficacy.

The resurgence of estrogens in the treatment of castration-resistant prostate cancer

Use of exogenous estrogens in manipulating the androgenestrogen equilibrium was one of the earliest therapeutic strategies developed to treat prostate cancer which followed close on heels the discovery of hormone dependence of this tumor. Despite its well-documented benefit, estrogen therapy fell out of favor with the advent of other forms of androgen deprivation therapy (ADT) as the former registered a higher incidence of cardiovascular complications and poorer overall survival. Clearer understanding of the mechanism of action of estrogen coupled with the adoption of alternative routes of administration has triggered a renewed interest in estrogen therapy. Since then, many studies have not only proved the therapeutic benefit of estrogens but also explored the ways and means of minimizing the dreaded side effects deterring its use. Further, the fact that estrogen therapy offered a clear advantage of reduced cost of treatment over other treatments has led many countries to readopt it in the treatment of advanced prostatic cancer. We reviewed the published data on the use of estrogens in CRPC, which may affect its revival as an efficacious treatment option having minimal side effects, with modified dosage and route of administration. Estrogen therapy would be a less expensive option having equivalent or even better therapeutic effect than ADT in advanced carcinoma of prostate.

Discovery of chalcone-modified estradiol analogs as antitumour agents that Inhibit tumour angiogenesis and epithelial to mesenchymal transition

Angiogenesis plays an essential role in tumourigenesis and tumour progression, and anti-angiogenesis therapies have shown promising antitumour effects in solid tumours. 2-Methoxyestradiol (2ME2), an endogenous metabolite of estradiol, has been regarded as a potential antitumour agent mainly targeting angiogenesis. Here we synthesized a novel series of chalcones based on 2-methoxyestradiol and evaluated their potential activities against tumours. Compound 11e was demonstrated to have potent antiangiogenic activity. Further studies showed that 11e suppressed tumour growth in human breast cancer (MCF-7) xenograft models without obvious side effects. Evaluation of the mechanism revealed that 11e targeted the epithelial to mesenchymal transition (EMT) process in MCF-7 cells and inhibited HUVEC migration and then contributed to hindrance of angiogenesis. Thus, 11e may be a promising antitumour agent with excellent efficacy and low toxicity.

Estradiol dimer inhibits tubulin polymerization and microtubule dynamics

Microtubule dynamics is one of the major targets for new chemotherapeutic agents. This communication presents the synthesis and biological profiling of steroidal dimers based on estradiol, testosterone and pregnenolone bridged by 2,6-bis(azidomethyl)pyridine between D rings. The biological profiling revealed unique properties of the estradiol dimer including cytotoxic activities on a panel of 11 human cell lines, ability to arrest in the G2/M phase of the cell cycle accompanied with the attenuation of DNA/RNA synthesis. Thorough investigation precluded a genomic mechanism of action and revealed that the estradiol dimer acts at the cytoskeletal level by inhibiting tubulin polymerization. Further studies showed that estradiol dimer, but none of the other structurally related dimeric steroids, inhibited assembly of purified tubulin (IC₅₀, 3.6 μM). The estradiol dimer was more potent than 2-methoxyestradiol, an endogenous metabolite of 17β-estradiol and well-studied microtubule polymerization inhibitor with antitumor effects that was evaluated in clinical trials. Further, it was equipotent to nocodazole (IC₅₀, 1.5 μM), an antimitotic small molecule of natural origin. Both estradiol dimer and nocodazole completely and reversibly depolymerized microtubules in interphase U2OS cells at 2.5 μM concentration. At lower concentrations (50 nM), estradiol dimer decreased the microtubule dynamics and growth life-time and produced comparable effect to nocodazole on the microtubule dynamicity. In silico modeling predicted that estradiol dimer binds to the colchicine-binding site in the tubulin dimer. Finally, dimerization of the steroids abolished their ability to induce transactivation by estrogen receptor α and androgen receptors. Although other steroids were reported to interact with microtubules, the estradiol dimer represents a new structural type of steroid inhibitor of tubulin polymerization and microtubule dynamics, bearing antimitotic and cytotoxic activity in cancer cell lines.

Design, synthesis and antiproliferative effect of 17β-amide derivatives of 2-methoxyestradiol and their studies on pharmacokinetics

A series of 17β-amide-2-methoxyestradiol compounds were synthesized with an aim to enhance the antiproliferative effect of 2-methoxyestradiol. The antiproliferative activity of 2-methoxyestradiol analogs against human cancer cells was investigated. 2-methoxy-3-benzyloxy-17β-chloroacetamide-1,3,5(10)-triene (5e) and 2-methoxy-3-hydroxy-17β-butyramide-1,3,5(10)-triene (6c) had comparable or better antitumor activity than 2-methoxyestradiol. The elimination half-life of 6c (t_1/2β=240.93min) is ten times longer than 2-ME and the area under the curve was seven times (AUC_0-tmin=2068.20±315.74μgmL^-1min) higher than 2-ME, respectively. Whereas 5e had similar pharmacokinetic behavior with 2-ME (t_1/2β=22.28min) with a t_1/2β of 29.5 min. 6c had higher blood concentration, longer actuation duration and better suppression rate against S180 mouse ascites tumor than 2-methoxyestradiol.

2-methoxyestradiol impacts on amino acids-mediated metabolic reprogramming in osteosarcoma cells by its interaction with NMDA receptor

Deregulation of serine and glycine metabolism, have been identified to function as metabolic regulators in supporting tumor cell growth. The role of serine and glycine in regulation of cancer cell proliferation is complicated, dependent on concentrations of amino acids and tissue-specific. D-serine and glycine are coagonists of N-methyl-D-aspartate (NMDA) receptor subunit GRIN1. Importantly, NMDA receptors are widely expressed in cancer cells and play an important role in regulation of cell death, proliferation, and metabolism of numerous malignancies. The aim of the present work was to associate the metabolism of glycine and D-serine with the anticancer activity of 2-methoxyestradiol. 2-methoxyestradiol is a potent anticancer agent but also a physiological 17β- estradiol metabolite. In the study we have chosen two malignant cell lines expressing functional NMDA receptors, that is osteosarcoma 143B and breast cancer MCF7. We used MTS assay, migration assay, flow cytometric analyses, Western blotting and immunoprecipitation techniques as well as molecular modeling studies. We have demonstrated the extensive crosstalk between the deregulated metabolic network and cancer cell signaling. Herein, we observed an anticancer effect of high concentrations of glycine and D-serine in osteosarcoma cells. In contrast, the amino acids when used at low, physiological concentrations induced the proliferation and migration of osteosarcoma cells. Importantly, the pro-cancergogenic effects of both glycine and D-serine where abrogated by the usage of 2-methoxyestradiol at both physiological and pharmacological relevant concentrations. The obtained data confirmed that 2-methoxyestradiol may be a physiological anticancer molecule.

Hypoxia inducible factor down-regulation, cancer and cancer stem cells (CSCs): ongoing success stories

In cancers, hypoxia inducible factor 1 (HIF-1) is an over-expressed transcription factor, which regulates a large set of genes involved in tumour vascularization, metastases, and cancer stem cells (CSCs) formation and self-renewal. This protein has been identified as a relevant target in oncology and several HIF-1 modulators are now marketed or in advanced clinical trials. The purpose of this review is to summarize the advances in the understanding of its regulation and its inhibition, from the medicinal chemist point of view. To this end, we selected in the recent literature relevant examples of "hit" compounds, including small-sized organic molecules, pseudopeptides and nano-drugs, exhibiting in vitro and/or in vivo both anti-HIF-1 and anti-tumour activities. Whenever possible, a particular emphasis has been dedicated to compounds that selectively target CSCs.

Therapeutic targeting of hypoxia and hypoxia-inducible factors in cancer

Insufficient tissue oxygenation, or hypoxia, contributes to tumor aggressiveness and has a profound impact on clinical outcomes in cancer patients. At decreased oxygen tensions, hypoxia-inducible factors (HIFs) 1 and 2 are stabilized and mediate a hypoxic response, primarily by acting as transcription factors. HIFs exert differential effects on tumor growth and affect important cancer hallmarks including cell proliferation, apoptosis, differentiation, vascularization/angiogenesis, genetic instability, tumor metabolism, tumor immune responses, and invasion and metastasis. As a consequence, HIFs mediate resistance to chemo- and radiotherapy and are associated with poor prognosis in cancer patients. Intriguingly, perivascular tumor cells can also express HIF-2α, thereby forming a "pseudohypoxic" phenotype that further contributes to tumor aggressiveness. Therefore, therapeutic targeting of HIFs in cancer has the potential to improve treatment efficacy. Different strategies to target hypoxic cancer cells and/or HIFs include hypoxia-activated prodrugs and inhibition of HIF dimerization, mRNA or protein expression, DNA binding capacity, and transcriptional activity. Here we review the functions of HIFs in the progression and treatment of malignant solid tumors. We also highlight how HIFs may be targeted to improve the management of patients with therapy-resistant and metastatic cancer.

Oestrogens and oestrogen receptors in prostate cancer

The role of androgens in prostate cancer is obvious due to the fact that androgen signalling is the main regulator of prostate growth and function. Androgen deprivation therapy is a mainstay treatment for advanced prostate cancer. However, prostate cancer often becomes androgen-independent, which in consequence leads to lethal and incurable disease. In addition, oestrogens play a crucial role in prostate cancer, especially in elder men in whom the overall ratio of oestrogens to androgens is increasing. This review summarizes the current knowledge on molecular mechanisms through which oestrogens are involved in prostate cancer development. We focused on commonly alternated molecular signalling pathways contributing to tumourgenesis in prostate cancer.

Neuronal Nitric Oxide Synthase-Mediated Genotoxicity of 2-Methoxyestradiol in Hippocampal HT22 Cell Line

2-methoxyestradiol, metabolite of 17β-estradiol, is considered a potential anticancer agent, currently investigated in several clinical trials. This natural compound was found to be effective towards great number of cancers, including colon, breast, lung, and osteosarcoma and has been reported to be relatively non-toxic towards non-malignant cells. The aim of the study was to determine the potential neurotoxicity and genotoxicity of 2-methoxyestradiol at physiological and pharmacological relevant concentrations in hippocampal HT22 cell line. Herein, we determined influence of 2-methoxyestradiol on proliferation, inhibition of cell cycle, induction of apoptosis, and DNA damage in the HT22 cells. The study was performed using imaging cytometry and comet assay techniques. Herein, we demonstrated that 2-methoxyestradiol, at pharmacologically and also physiologically relevant concentrations, increases nuclear localization of neuronal nitric oxide synthase. It potentially results in DNA strand breaks and increases in genomic instability in hippocampal HT22 cell line. Thus, we are postulating that naturally occurring 2-methoxyestradiol may be considered a physiological modulator of neuron survival.

Mcl-1 protects prostate cancer cells from cell death mediated by chemotherapy-induced DNA damage

The anti-apoptotic protein Mcl-1 is highly expressed in castration-resistant prostate cancer (CRPC), resulting in resistance to apoptosis and association with poor prognosis. Although predominantly localized in the cytoplasm, there is evidence that Mcl-1 exhibits nuclear localization where it is thought to protect against DNA damage-induced cell death. The role of Mcl-1 in mediating resistance to chemotherapy-induced DNA damage in prostate cancer (PCa) is not known. We show in human PCa cell lines and in TRAMP, a transgenic mouse model of PCa, that the combination of the antimitotic agent ENMD-1198 (analog of 2-methoxyestradiol) with betulinic acid (BA, increases proteotoxic stress) targets Mcl-1 by increasing its proteasomal degradation, resulting in increased γH2AX (DNA damage) and apoptotic/necrotic cell death. Knockdown of Mcl-1 in CRPC cells leads to elevated γH2AX, DNA strand breaks, and cell death after treatment with 1198 + BA- or doxorubicin. Additional knockdowns in PC3 cells suggests that cytoplasmic Mcl-1 protects against DNA damage by blocking the mitochondrial release of apoptosis-inducing factor and thereby preventing its nuclear translocation and subsequent interaction with the cyclophilin A endonuclease. Overall, our results suggest that chemotherapeutic agents that target Mcl-1 will promote cell death in response to DNA damage, particularly in CRPC.

DNA strand breaks induced by nuclear hijacking of neuronal NOS as an anti-cancer effect of 2-methoxyestradiol

2-Methoxyestradiol (2-ME) is a physiological metabolite of 17β-estradiol. At pharmacological concentrations, 2-ME inhibits colon, breast and lung cancer in tumor models. Here we investigated the effect of physiologically relevant concentrations of 2-ME in osteosarcoma cell model. We demonstrated that 2-ME increased nuclear localization of neuronal nitric oxide synthase, resulting in nitro-oxidative DNA damage. This in turn caused cell cycle arrest and apoptosis in osteosarcoma cells. We suggest that 2-ME is a naturally occurring hormone with potential anti-cancer properties.

Investigational cancer drugs targeting cell metabolism in clinical development

Introduction: Malignant cell transformation and tumor progression are associated with alterations in glycolysis, fatty acid synthesis, amino acid delivery and production of reactive oxygen species. With increased understanding of the role of metabolism in tumors, there has been interest in developing agents that target tumor specific metabolic pathways. Numerous promising agents targeting altered metabolic pathways are currently in Phase I - III clinical trials. Areas covered: This paper reviews the early phase clinical trial development of these agents and provides perspective on the future direction of this emerging field. Specifically, the authors describe novel and repurposed therapies, focusing on the effects of each agent on tumor metabolism and results from relevant Phase I and II clinical trials. Expert opinion: Metabolism modulating agents, alone and in combinations with other classes of agents, have shown efficacy in the treatment of neoplasm, which, the authors believe, will bear positive results in future studies. Because of the significant crosstalk between metabolic pathways and oncogenic signaling pathways, the authors also believe that combining metabolic modifiers with targeted agents will be an important strategy. An increased understanding of cancer metabolism, in addition to the continued study of metabolic modulators, should lead to further advances in this nascent therapeutic field in the future.

Proteomic signatures associated with p53 mutational status in lung adenocarcinoma

p53 is commonly mutated in lung adenocarcinoma. Mutant p53 loses wild-type function and some missense mutations further acquire oncogenic functions, while p53 wild-type may also induce pro-survival signaling. Therefore identification of signatures based on p53 mutational status has relevance to our understanding of p53 signaling pathways in cancer and identification of new therapeutic targets. To this end, we compared proteomic profiles of three cellular compartments (whole-cell extract, cell surface, and media) from 28 human lung adenocarcinoma cell lines that differ based on p53 mutational status. In total, 11,598, 11,569, and 9090 protein forms were identified in whole-cell extract, cell surface, and media, respectively. Bioinformatic analysis revealed that representative pathways associated with epithelial adhesion, immune and stromal cells, and mitochondrial function were highly significant in p53 missense mutations, p53 loss and wild-type p53 cell lines, respectively. Of note, mRNA levels of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α), a transcription coactivator that promotes mitochondrial oxidative phosphorylation and mitochondrial biogenesis, was substantially higher in p53 wild-type cell lines compared to either cell lines with p53 loss or with missense mutation. Small interfering RNA targeting PGC1-α inhibited cell proliferation in p53 wild-type cell lines, indicative of PGC1-α and its downstream molecules as potential therapeutic targets in p53 wild-type lung adenocarcinoma.

An estrogen analogue and promising anticancer agent refrains from inducing morphological damage and reactive oxygen species generation in erythrocytes, fibrin and platelets: a pilot study

Background

2-Methoxyestradiol is known to have antitumour and antiproliferative action in vitro and in vivo. However, when 2-methoxyestradiol is orally administered, it is rapidly oxidized by the enzyme 17β-hydroxysteriod dehydrogenase in the gastrointestinal tract. Therefore, 2-methoxyestradiol never reaches high enough concentrations in the tissue to be able to exert these antitumour properties. This resulted in the in silico-design of 2-methoxyestradiol analogues in collaboration with the Bioinformatics and Computational Biology Unit (UP) and subsequent synthesis by iThemba Pharmaceuticals (Pty) Ltd (Modderfontein, Midrand, South Africa). One such a novelty-designed analogue is 2-ethyl-3-O-sulphamoyl-estra-1, 3, 5(10)16-tetraene (ESE-16).

Methods

This pilot study aimed to determine the morphological effect and possible generation of reactive oxygen species by ESE-16 on erythrocytes and platelet samples (with and without added thrombin) by means of scanning electron microscopy, transmission electron microscopy and flow cytometry.

Results

Erythrocytes and platelets were exposed to ESE-16 at a concentration of 180nM for 24Â hours. Scanning- and transmission electron microscopy indicated that ESE-16 did not cause changes to erythrocytes, platelets or fibrin networks. Flow cytometry measurements of hydrogen peroxide and superoxide indicated that ESE-16 does not cause an increase in the generation of reactive oxygen species in these blood samples.

Conclusion

Further in vivo research is warranted to determine whether this novel in silico-designed analogue may impact on development of future chemotherapeutic agents and whether it could be considered as an antitumour agent.

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.

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

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

Recent agents targeting HIF-1α for cancer therapy

The discovery of hypoxia-inducible factor-1 (HIF-1) has led to an increasing understanding of the mechanism of tumor hypoxia in the past two decades. As a key transcriptional regulator, HIF-1 plays a central role in the adaptation of tumor cells to hypoxia by activating the transcription of targeting genes, which regulate several biological processes including angiogenesis, cell proliferation, survival, glucose metabolism and migration. The inhibitors of HIF-1 in cancer have provided us a new clue for the targeting cancer therapy. This review will introduce the general knowledge of the biology characteristic of HIF-1 and mechanism of O(2)-dependent regulation. Moreover, a number of chemical inhibitors plus protein and nucleic acid inhibitors are included and classified mainly based on their different mechanism of inhibiting action. We also prefer to discuss the advantages of protein and nucleic acid inhibitors compared with chemical inhibitors.

Identification of an ABCB1 (P-glycoprotein)-positive carfilzomib-resistant myeloma subpopulation by the pluripotent stem cell fluorescent dye CDy1

Multiple myeloma (MM) is characterized by the malignant expansion of differentiated plasma cells. Although many chemotherapeutic agents display cytotoxic activity toward MM cells, patients inevitably succumb to their disease because the tumor cells become resistant to the anticancer drugs. The cancer stem cell hypothesis postulates that a small subpopulation of chemotherapy-resistant cancer cells is responsible for propagation of the tumor. Herein we report that efflux of the pluripotent stem cell dye CDy1 identifies a subpopulation in MM cell lines characterized by increased expression of P-glycoprotein, a member of the ABC (ATP-binding cassette) superfamily of transporters encoded by ABCB1. We also demonstrate that ABCB1-overexpressing MM cells are resistant to the second-generation proteasome inhibitor carfilzomib that recently received accelerated approval for the treatment of therapy-refractive MM by the U.S. Food and Drug Administration. Moreover, increased resistance to carfilzomib in sensitive MM cells following drug selection was associated with upregulation of ABCB1 cell-surface expression which correlated with increased transporter activity as measured by CDy1 efflux. We further show that chemosensitization of MM cells to carfilzomib could be achieved in vitro by cotreatment with vismodegib, a hedgehog pathway antagonist which is currently in MM clinical trials. CDy1 efflux may therefore be a useful assay to determine whether high expression of ABCB1 is predictive of poor clinical responses in MM patients treated with carfilzomib. Our data also suggest that inclusion of vismodegib might be a potential strategy to reverse ABCB1-mediated drug resistance should it occur.

Signaling pathways of ESE-16, an antimitotic and anticarbonic anhydrase estradiol analog, in breast cancer cells

The aim of this study was to characterize the in vitro action of 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) on non-tumorigenic MCF-12A, tumorigenic MCF-7 and metastatic MDA-MB-231 breast cancer cells. ESE-16 is able to inhibit the activity of a carbonic anhydrase II and a mimic of carbonic anhydrase IX in the nanomolar range. Gene and protein expression studies using various techniques including gene and antibody microarrays and various flow cytometry assays yielded valuable information about the mechanism of action of ESE-16. The JNK pathway was identified as an important pathway mediating the effects of ESE-16 while the p38 stress-induced pathway is more important in MDA-MB-231 cells exposed to ESE-16. Lysosomal rupture and iron metabolism was identified as important mediators of mitochondrial membrane depolarization. Abrogation of Bcl-2 phosphorylation status as a result of ESE-16 also plays a role in inducing mitochondrial membrane depolarization. The study provides a basis for future research projects to develop the newly synthesized compound into a clinically usable anticancer agent either alone or in combination with other agents.

Keywords: Antimitotic, anticarbonic anhydrase IX, apoptosis, autophagy, cell cycle arrest, Bcl-2, JNK, p38, mitochondrial membrane depolarization, flow cytometry, gene expression and protein microarray, anticancer.

In vitro changes in mitochondrial potential, aggresome formation and caspase activity by a novel 17-β-estradiol analogue in breast adenocarcinoma cells

2-Methoxyestradiol, a natural metabolite of estradiol, exerts antiproliferative and antitumour properties in vitro and in vivo. Because of its low oral bioavailability, several promising analogues of 2-methoxyestradiol have been developed. In this study, the in vitro influence of the compound, 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (C19), a non-commercially available 17-β-estradiol analogue, was tested on the breast adenocarcinoma MCF-7 cell line. The in vitro influence of 24 h exposure to 0.18 μM of C19 on MCF-7 cells was evaluated on cell morphology, cell cycle progression and possible induction of apoptosis and autophagy. Polarization-optical transmitted light differential interference contrast and fluorescence microscopy revealed the presence of cells blocked in metaphase, occurrence of apoptotic bodies and compromised cell density in C19-treated cells. Hallmarks of autophagy, namely an increase in the number of acidic vacuoles and lysosomes, were also observed in C19-treated samples. An increase in the number of cells present in the sub-G1 fraction, as well as a reduction in mitochondrial membrane potential was observed. No significant alterations in caspase 8 activity were observed. A twofold increase in aggresome formation was observed in C19-treated cells. C19 induced both apoptosis and autophagy in MCF-7 cells.

Antiproliferative effect of normal and 13-epi-D-homoestrone and their 3-methyl ethers on human reproductive cancer cell lines

The possibility of the therapeutic use of estrogens emerged following the recognition that certain estradiol analogs, and particularly metabolites (e.g. the A-ring metabolite 2-hydroxyestrone, etc.) inhibit the differentiation of diverse tumor cell lines. Until recently, despite the investigation of numerous synthetic d-ring-substituted estrone derivatives, no analysis had been published on the effects of D-ring expansion of estrone on its tumor-suppressing activity. The aim of the present study was to characterize the antiproliferative effects of normal and 13-epi-D-homoestrone and their 3-methyl ethers (1-4) on human reproductive cancer cell lines. The antitumor activities of the two epimer pairs on HeLa, MCF-7 and Ishikawa cells were determined. Normal D-homoestrone exerted the greatest cytostatic effect on HeLa cells (IC(50)=5.5 μM) and was subjected to further investigations to elucidate its mechanism of action on apoptosis induction. Morphological changes detected by Hoechst 33258-propidium iodide double staining, the cell cycle arrest at phase G2/M and the subsequent increase in the proportion of the subG1 fraction determined by flow cytometric analysis and the significant increase in the activity of caspase-3 confirmed the induction of apoptosis in HeLa cells treated with D-homoestrone. D-Homoestrone was also tested on a non-cancerous human lung fibroblast cell line (MRC-5) to determine its selective toxicity. The concentration in which it inhibited cell proliferation by 50% was at least six times higher for the fibroblast cells than for cervical cancer cells. No significant in vivo estrogenic activity was observed as concerns the uterus weight of gonadectomized rats after a 7-day treatment with normal D-homoestrone. These results led to the conclusion that normal D-homoestrone is a novel antitumor compound with a similar activity on HeLa cells as that of the reference agent cisplatin, but its selectivity toward non-cancerous cells is significantly higher than that of cisplatin. It may be considered to be a basic lead molecule for the preclinical development of potential anticancer agents.

Small-molecule inhibitors of the HIF pathway and synthetic lethal interactions

INTRODUCTION

Activation of the hypoxia response pathway is a feature of many tumours and is one of the key mechanisms associated with tumour growth, chemoresistance and radioresistance. The major component of the hypoxia response pathway is the heterodimeric transcription factor, hypoxia-inducible factor (HIF), which is upregulated in many human cancers. Therefore, HIF is an attractive therapeutic target and several strategies have been developed to target it.

AREAS COVERED

Approaches used in targeting the hypoxia response pathway are discussed. Reviewed are agents that target upstream, directly and downstream of HIF, as well as some of the challenges in HIF-targeted therapy.

EXPERT OPINION

Many of the therapeutic agents that are in clinical use inhibit downstream HIF target genes, but ideally a molecule specific to HIF will have a more potent effect in inhibiting multiple HIF pathways. However, many anti-HIF molecules have multiple targets, which may increase non-specific cytotoxicity. In addition, many anti-HIF agents cannot discriminate between the different isoforms of HIF-α. So, it is important to assess whether targeting both HIF-1α and HIF-2α or each subunit selectively will provide better therapeutic effects.

A phase II study of 2-methoxyestradiol nanocrystal colloidal dispersion alone and in combination with sunitinib malate in patients with metastatic renal cell carcinoma progressing on sunitinib malate

BACKGROUND

Current treatment for metastatic renal cell cancer with vascular endothelial growth factor (VEGF) tyrosine kinase inhibitors (TKI) have provided improved overall survival, but complete responses are rare. We conducted a multicenter phase II study to evaluate the objective response rate of 2-methoxyestradiol (2ME2 NCD) alone and in combination with sunitinib for patients with metastatic renal cell carcinoma who have progressed on sunitinib alone.

METHODS

Adults with metastatic kidney cancer were stratified depending on whether they were still taking sunitinib or had discontinued sunitinib therapy at the time of registration. Patients were treated with 2ME2 NCD alone or in combination with sunitinib. The primary endpoint was objective response rate.

RESULTS

In total, 17 patients were enrolled, and 12 were evaluable for response (arm A, n = 7; arm b, n = 5). In arm A, four patients had the best response of stable disease, and three patients developed disease progression. In arm B, three patients had a best response of stable disease, and two patients had disease progression. One patient continued to receive treatment for a total of 14 cycles before developing disease progression. Fatigue was the most common observed toxicities. Thirty five percent of patients required discontinuation of therapy secondary to toxicities.

CONCLUSIONS

2ME2 NCD had minimal anti-tumor activity, with no observed objective responses. The study was terminated because 2ME2 NCD was not found to be tolerable at the recommended phase 2 dose in this patient population. A newer 2ME2 analog is in development with a more favorable toxicity profile and increased potency.

In vitro effects of an in silico-modelled 17β-estradiol derivative in combination with dichloroacetic acid on MCF-7 and MCF-12A cells

OBJECTIVES

  To investigate anti-proliferative properties of a novel in silico-modelled 17β-oestradiol derivative (C9), in combination with dichloroacetic acid (DCA), on MCF-7 and MCF-12A cells.

MATERIALS AND METHODS

  xCELLigence system was employed to determine optimal seeding number for cells, and crystal violet assay was used to assess cell number and to determine IC(50) value (24 h) for combination treatment. Light and fluorescent microscopy techniques were used to morphologically detect types of cell death. Flow cytometry was used to analyse cell cycle and apoptosis.

RESULTS

  Optimal seeding number for 96-well plates was determined to be 5000-10 000 cells/well for both MCF-7 and MCF-12A cells. IC(50) for MCF-7 cells of the combination treatment after 24 h was 130 nm of C9 in conjunction with 7.5 mm of DCA (P < 0.05). In contrast, the same concentration inhibited cell population growth by only 29.3% for MCF-12As after 24-h treatment (P < 0.05). Morphological studies revealed lower cell density of both types of combination-treated cells. Flow cytometric analyses demonstrated increase in sub-G(1) phase in combination-treated MCF-7 cells.

CONCLUSIONS

  These results demonstrate that the novel 17β-oestradiol derivative C9, in combination with DCA is a potent anti-proliferation treatment, with properties of selectivity towards tumourigenic cells. Thus, this warrants further studies as a potential combination chemotherapeutic agent for further cancer cell lines.

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.

Docking, synthesis, and in vitro evaluation of antimitotic estrone analogs

In the present study, Autodock 4.0 was employed to discover potential carbonic anhydrase IX inhibitors that are able to interfere with microtubule dynamics by binding to the Colchicine binding site of tubulin. Modifications at position 2' of estrone were made to include moieties that are known to improve the antimitotic activity of estradiol analogs. 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10),15-tetraen-3-ol-17-one estronem (C9) and 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (C12) were synthesized and tested in vitro. Growth studies were conducted utilizing spectrophotometrical analysis with crystal violet as DNA stain. Compounds C9 and C12 were cytotoxic in MCF-7 and MDA-MB-231 tumorigenic and metastatic breast cancer cells, SNO non-keratinizing squamous epithelium cancer cells and HeLa cells after 48 h exposure. Compounds C9 inhibited cell proliferation to 50% of the vehicle-treated controls from 110 to 160 nm and C12 at concentrations ranging from 180 to 220 nm. Confocal microscopy revealed abnormal spindle morphology in mitotic cells. Cell cycle analysis showed an increase in the number of cells in the G(2) /M fraction after 24 h and an increase in the number of cell in the sub-G(1) fraction after 48 h, indicating that the compounds are antimitotic and able to induce apoptosis.

A phase II study of 2-methoxyestradiol (2ME2) NanoCrystal® dispersion (NCD) in patients with taxane-refractory, metastatic castrate-resistant prostate cancer (CRPC)

PURPOSE

2ME2 (Panzem®) is a non-estrogenic derivative of estradiol with antiproliferative and antiangiogenic activity. Preclinical data support antitumor activity in prostate cancer. This trial evaluated the efficacy of 2ME2 NCD in patients with taxane-refractory, metastatic CRPC.

EXPERIMENTAL DESIGN

Patients with metastatic CRPC who had progressed on only one prior taxane-based regimen were eligible. All patients received 2ME2 NCD at 1,500 mg orally four times daily, repeated in 28 day cycles. The primary endpoint was progression-free survival at month 6, with a secondary endpoint of PSA response. An exploratory endpoint was metabolic response on FDG-PET imaging.

RESULTS

A total of 50 pts was planned. The study was terminated after 21 pts when a futility analysis showed the primary endpoint was unlikely to be reached. The median number of cycles on study was 2 (range <1 to 12). Adverse events (AE) of grade ≥3 related to the study drug occurred in 7 unique patients (33%): elevations in liver function tests, fatigue or weakness, gastrointestinal hemorrhage, and hyponatremia. Paired FDG-PET scans were obtained for 11 pts. No metabolic responses were observed.

CONCLUSIONS

2ME2 NCD did not appear to have clinically significant activity in this study. 2ME2 NCD was well-tolerated and showed some evidence of biologic activity. Given the aggressive biology in this taxane-refractory population, the potential benefit from a cytostatic agent like 2ME2 might better be realized in the pre-chemotherapy (or rising PSA only) stage of CRPC.