The therapeutic potential of a series of orally bioavailable anti-angiogenic microtubule disruptors as therapy for hormone-independent prostate and breast cancers

2-Methoxyestradiol-3,17-O,O-bis-sulfamate inhibits store-operated Ca2+ entry in T lymphocytes and prevents experimental autoimmune encephalomyelitis

Ca²⁺ signaling is one of the essential signaling systems for T lymphocyte activation, the latter being an essential step in the pathogenesis of autoimmune diseases such as multiple sclerosis (MS). Store-operated Ca²⁺ entry (SOCE) ensures long lasting Ca²⁺ signaling and is of utmost importance for major downstream T lymphocyte activation steps, e.g. nuclear localization of the transcription factor 'nuclear factor of activated T cells' (NFAT). 2-Methoxyestradiol (2ME2), an endogenous metabolite of estradiol (E2), blocks nuclear translocation of NFAT. The likely underlying mechanism is inhibition of SOCE, as shown for its synthetic sulfamate ester analogue 2-ethyl-3-sulfamoyloxy-17β-cyanomethylestra-1,3,5(10)-triene (STX564). Here, we demonstrate that another synthetic bis-sulfamoylated 2ME2 derivative, 2-methoxyestradiol-3,17-O,O-bis-sulfamate (2-MeOE2bisMATE, STX140), an orally bioavailable, multi-targeting anticancer agent and potent steroid sulfatase (STS) inhibitor, antagonized SOCE in T lymphocytes. Downstream events, e.g. secretion of the pro-inflammatory cytokines interferon-γ and interleukin-17, were decreased by STX140 in in vitro experiments. Remarkably, STX140 dosed in vivo completely blocked the clinical disease in both active and transfer experimental autoimmune encephalomyelitis (EAE) in Lewis rats, a T cell-mediated animal model for MS, at a dose of 10 mg/kg/day i.p., whereas neither 2ME2 nor Irosustat, a pure STS inhibitor, showed any effect. The STS inhibitory activity of STX140 is therefore not responsible for its activity in this model. Taken together, inhibition of SOCE by STX140 resulting in full antagonism of clinical symptoms in EAE in the Lewis rat, paired with the known excellent bioavailability and pharmaceutical profile of this drug, open potentially new therapeutic avenues for the treatment of MS.

The in vitro effects of a novel estradiol analog on cell proliferation and morphology in human epithelial cervical carcinoma

Background

The majority of novel chemotherapeutics target the cell cycle, aiming to effect arrest and cause apoptosis. One such agent, 2-methoxyestradiol (2ME), has been shown to possess anticancer properties against numerous cancer types, both in vitro and in vivo. Despite its promise, 2ME has exhibited limitations, including low oral bioavailability and rapid hepatic enzymatic inactivation in vivo. A novel sulphamoylated estrogen analog, 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16), was in silico-designed in our laboratory to overcome these issues. It was then synthesized by a pharmaceutical company and used in an in vitro antiproliferative effect study on a human cervical carcinoma (HeLa) cell line.

Results

Cell proliferation data obtained from the crystal violet assay and real-time cell analysis demonstrated that 0.2 μM of ESE-16 had a significant inhibitory effect on the HeLa cells 24 h post-exposure. Immunofluorescence showed that ESE-16 is a microtubule disruptor that causes cells to undergo a mitotic block. Qualitative morphological studies using polarization-optical transmitted light differential interference contrast (PlasDIC) and light microscopy revealed a decrease in cell density and an increase in the number of cells arrested in metaphase. After ESE-16 exposure, hallmarks of apoptosis were also observed, including membrane blebbing, chromatin condensation and the presence of apoptotic bodies. Flow cytometry provided quantitative results from cell cycle progression analysis, indicating cells undergoing apoptosis and cells in the G₂/M phase of the cell cycle, confirming cell cycle arrest in metaphase after ESE-16 treatment. Quantification of the ESE-16-mediated upregulation of cyclin B in HeLa cells and spectrophotometric and flow cytometric confirmation of cell death via apoptosis further confirmed the substance's impact.

Conclusion

ESE-16 exerts its antiproliferative effects through microtubule disruption, which induces a mitotic block culminating in apoptosis. This research provided information on ESE-16 as a potential antitumor agent and on cellular targets that could aid in the design of prospective microtubule-disrupting compounds. Further in vitro and in vivo investigations of this novel compound are needed.

A molecular understanding of D-homoestrone-induced G2/M cell cycle arrest in HeLa human cervical carcinoma cells

2-Methoxyestradiol (ME), one of the most widely investigated A-ring-modified metabolites of estrone, exerts significant anticancer activity on numerous cancer cell lines. Its pharmacological actions, including cell cycle arrest, microtubule disruption and pro-apoptotic activity, have already been described in detail. The currently tested d-ring-modified analogue of estrone, d-homoestrone, selectively inhibits cervical cancer cell proliferation and induces a G2/M phase cell cycle blockade, resulting in the development of apoptosis. The question arose of whether the difference in the chemical structures of these analogues can influence the mechanism of anticancer action. The aim of the present study was therefore to elucidate the molecular contributors of intracellular processes induced by d-homoestrone in HeLa cells. Apoptosis triggered by d-homoestrone develops through activation of the intrinsic pathway, as demonstrated by determination of the activities of caspase-8 and -9. It was revealed that d-homoestrone-treated HeLa cells are not able to enter mitosis because the cyclin-dependent kinase 1-cyclin B complex loses its activity, resulting in the decreased inactivation of stathmin and a concomitant disturbance of microtubule formation. However, unlike 2-ME, d-homoestrone does not exert a direct effect on tubulin polymerization. These results led to the conclusion that the d-homoestrone-triggered intracellular processes resulting in a cell cycle arrest and apoptosis in HeLa cells differ from those in the case of 2-ME. This may be regarded as an alternative mechanism of action among steroidal anticancer compounds.

In vivo and in vitro properties of STX2484: a novel non-steroidal anti-cancer compound active in taxane-resistant breast cancer

BACKGROUND

STX2484 is a novel non-steroidal compound with potent anti-proliferative activity. These studies aimed to identify STX2484's mechanism of action, in vivo efficacy and activity in taxane-resistant breast cancer models.

METHODS

Effects of STX2484 and paclitaxel on proliferation, cell cycle and apoptosis were assessed in vitro in drug-resistant (MCF-7(DOX)) and non-resistant cells (MCF-7(WT)). STX2484 efficacy in βIII tubulin overexpression in MCF-7 cells was also determined. Anti-angiogenic activity was quantified in vitro by a co-culture model and in vivo using a Matrigel plug assay. An MDA-MB-231 xenograft model was used to determine STX2484 efficacy in vivo.

RESULTS

STX2484 is a tubulin disruptor, which induces p53 expression, Bcl2 phosphorylation, caspase-3 cleavage, cell cycle arrest and apoptosis. In addition, STX2484 is a potent anti-angiogenic agent in vitro and in vivo. In breast cancer xenografts, STX2484 (20 mg kg(-1) p.o.) suppressed tumour growth by 84% after 35 days of daily dosing, with limited toxicity. In contrast to paclitaxel, STX2484 efficacy was unchanged in two clinically relevant drug-resistant models.

CONCLUSIONS

STX2484 is an orally bioavailable microtubule-disrupting agent with in vivo anti-angiogenic activity and excellent in vivo efficacy with no apparent toxicity. Crucially, STX2484 has superior efficacy to paclitaxel in models of clinical drug resistance.

Relaxin receptor antagonist AT-001 synergizes with docetaxel in androgen-independent prostate xenografts

Androgen hormones and the androgen receptor (AR) pathway are the main targets of anti-hormonal therapies for prostate cancer. However, resistance inevitably develops to treatments aimed at the AR pathway resulting in androgen-independent or hormone-refractory prostate cancer (HRPC). Therefore, there is a significant unmet need for new, non-androgen anti-hormonal strategies for the management of prostate cancer. We demonstrate that a relaxin hormone receptor antagonist, AT-001, an analog of human H2 relaxin, represents a first-in-class anti-hormonal candidate treatment designed to significantly curtail the growth of androgen-independent human prostate tumor xenografts. Chemically synthesized AT-001, administered subcutaneously, suppressed PC3 xenograft growth by up to 60%. AT-001 also synergized with docetaxel, standard first-line chemotherapy for HRPC, to suppress tumor growth by more than 98% in PC3 xenografts via a mechanism involving the downregulation of hypoxia-inducible factor 1 alpha and the hypoxia-induced response. Our data support developing AT-001 for clinical use as an anti-relaxin hormonal therapy for advanced prostate cancer.

17-beta-estradiol analog inhibits cell proliferation by induction of apoptosis in breast cell lines

Microtubules are important targets when studying potential anticancer agents since disturbance of these microtubule dynamics results in cell cycle arrest and cell death. 2-Methoxyestradiol is a naturally occurring metabolite that exerts antiproliferative activity and induces apoptosis. Due to limited biological accessibly and rapid metabolic degradation, several analogs were synthesized. This study investigated the antiproliferative influence of an 2-methoxyestradiol analog, (8R, 13S, 14S, 17S)-2-Ethyl-13-methyl-7, 8, 9, 11, 12,13, 14, 15, 16, 17-decahydro-6H-cyclopenta[a]phenanthrane-3, 17-diyl bis(sulfamate) (EMBS) on cell proliferation, morphology and apoptosis induction in a estrogen receptor-positive breast adenocarcinoma cells line (MCF-7), estrogen receptor-negative highly metastatic breast cell line (MDA-MB-231) and a non-tumorigenic breast epithelial cell line (MCF-12A). Spectrophotometry results indicated that EMBS exerted differential antiproliferative activity in the three cell lines. Cell growth of the breast adenocarcinoma and highly metastatic breast cell line reached a plateau effect at 0.4 μM after 24 h of exposure. Light microscopy and polarization-optical transmitted light differential interference contrast demonstrated compromised cell density, cells blocked in metaphase and the presence of apoptotic characteristics after EMBS exposure for 24 h in all three cell lines. Transmission electron microscopy and scanning electron microscopy revealed hallmarks of apoptosis namely the presence of apoptotic bodies, shrunken cells and cell debris in EMBS-exposed cells. This investigation demonstrated that EMBS does exert antimitotic activity and induces apoptosis contributing to elucidating the signal transduction of EMBS in tumorigenic and non-tumorigenic breast cell lines. Findings warrant in-depth analysis of specific targets in vitro and subsequent in vivo investigation for anticancer therapy.

STX140, but not paclitaxel, inhibits mammary tumour initiation and progression in C3(1)/SV40 T/t-antigen transgenic mice

Despite paclitxael's clinical success, treating hormone-refractory breast cancer remains challenging. Paclitaxel has a poor pharmacological profile, characterized by a low therapeutic index (TIX) caused by severe dose limiting toxicities, such as neutropenia and peripheral neuropathy. Consequently, new drugs are urgently required. STX140, a compound previously shown to have excellent efficacy against many tumors, is here compared to paclitaxel in three translational in vivo breast cancer models, a rat model of peripheral neuropathy, and through pharmacological testing. Three different in vivo mouse models of breast cancer were used; the metastatic 4T1 orthotopic model, the C3(1)/SV40 T-Ag model, and the MDA-MB-231 xenograft model. To determine TIX and pharmacological profile of STX140, a comprehensive dosing regime was performed in mice bearing MDA-MD-231 xenografts. Finally, peripheral neuropathy was examined using a rat plantar thermal hyperalgesia model. In the 4T1 metastatic model, STX140 and paclitaxel significantly inhibited primary tumor growth and lung metastases. All C3(1)/SV40 T-Ag mice in the control and paclitaxel treated groups developed palpable mammary cancer. STX140 blocked 47% of tumors developing and significantly inhibited growth of tumors that did develop. STX140 treatment caused a significant (P<0.001) survival advantage for animals in early and late intervention groups. Conversely, in C3(1)/SV40 T-Ag mice, paclitaxel failed to inhibit tumor growth and did not increase survival time. Furthermore, paclitaxel, but not STX140, induced significant peripheral neuropathy and neutropenia. These results show that STX140 has a greater anti-cancer efficacy, TIX, and reduced neurotoxicity compared to paclitaxel in C3(1)/SV40 T-Ag mice and therefore may be of significant benefit to patients with breast cancer.

Sulphamoylated 2-methoxyestradiol analogues induce apoptosis in adenocarcinoma cell lines

2-Methoxyestradiol (2ME2) is a naturally occurring estradiol metabolite which possesses antiproliferative, antiangiogenic and antitumor properties. However, due to its limited biological accessibility, synthetic analogues have been synthesized and tested in attempt to develop drugs with improved oral bioavailability and efficacy. The aim of this study was to evaluate the antiproliferative effects of three novel in silico-designed sulphamoylated 2ME2 analogues on the HeLa cervical adenocarcinoma cell line and estrogen receptor-negative breast adenocarcinoma MDA-MB-231 cells. A dose-dependent study (0.1–25 μM) was conducted with an exposure time of 24 hours. Results obtained from crystal violet staining indicated that 0.5 μM of all 3 compounds reduced the number of cells to 50%. Lactate dehydrogenase assay was used to assess cytotoxicity, while the mitotracker mitochondrial assay and caspase-6 and -8 activity assays were used to investigate the possible occurrence of apoptosis. Tubulin polymerization assays were conducted to evaluate the influence of these sulphamoylated 2ME2 analogues on tubulin dynamics. Double immunofluorescence microscopy using labeled antibodies specific to tyrosinate and detyrosinated tubulin was conducted to assess the effect of the 2ME2 analogues on tubulin dynamics. An insignificant increase in the level of lactate dehydrogenase release was observed in the compounds-treated cells. These sulphamoylated compounds caused a reduction in mitochondrial membrane potential, cytochrome c release and caspase 3 activation indicating apoptosis induction by means of the intrinsic pathway in HeLa and MDA-MB-231 cells. Microtubule depolymerization was observed after exposure to these three sulphamoylated analogues.

Preclinical analysis of resistance and cross-resistance to low-dose metronomic chemotherapy

Low-dose metronomic chemotherapy is an emerging form of chemotherapy with distinct mechanisms of action from conventional chemotherapy (e.g., antiangiogenesis). Although developed to overcome resistance to conventional chemotherapy, metronomic chemotherapy is subject to resistance on its own. However, there is a paucity of information on mechanisms of resistance, on cross-resistance between metronomic regimens using different cytotoxic drugs, and on cross-resistance between metronomic versus conventional chemotherapy, or versus targeted antiangiogenic therapy. Herein we show that PC-3 human prostate cancer xenografts were sensitive to both metronomic cyclophosphamide and metronomic docetaxel, but resistant to metronomic topotecan. Conventional docetaxel was only moderately active in parental PC-3 and in metronomic cyclophosphamide resistant PC-3 tumors. However, in metronomic cyclophosphamide resistant PC-3 tumors combining conventional docetaxel or bolus cyclophosphamide therapy with continued metronomic cyclophosphamide was superior to each treatment alone. Furthermore, bevacizumab had single-agent activity against metronomic cyclophosphamide resistant PC-3 tumors. Microarray analyses identified altered regulation of protein translation as a potential mechanism of resistance to metronomic cyclophosphamide. Our results suggest that sensitivity to metronomic chemotherapy regimens using different cytotoxic drugs not only depends on shared mechanisms of action such as antiangiogenesis, but also on as yet unknown additional antitumor effects that appear to be drug-specific. As clinically observed with targeted antiangiogenic agents, the continued use of metronomic chemotherapy beyond progression may amplify the effects of added second-line therapies or vice versa. However, metronomic chemotherapy is no different from other systemic therapies in that predictive biomarkers will be essential to fully exploit this novel use of conventional chemotherapeutics.

Sulphamoylated estradiol analogue induces antiproliferative activity and apoptosis in breast cell lines

Research into potential anticancer agents has shown that 2-methoxyestradiol exerts antiproliferative activity in vitro and in vivo in an estrogen receptor-independent manner. Due to its limited biological accessibility and rapid metabolic degradation, several new analogues have been developed in recent years. This study investigated the in vitro effects of a novel in silicodesigned compound (C16) in an estrogen receptor-positive breast adenocarcinoma epithelial cell line (MCF-7), an estrogen receptor-negative breast adenocarcinoma epithelial cell line (MDA-MB-231) and a nontumorigenic breast cell line (MCF-12A). Light microscopy revealed decreased cell density, cells blocked in metaphase and the presence of apoptotic characteristics in all three cell lines after exposure to C16 for 24 h. Polarizationoptical transmitted light differential interference contrast revealed the presence of several rounded cells and decreased cell density. The xCELLigence real-time label-independent approach revealed that C16 exerted antiproliferative activity. Significant inhibition of cell growth was demonstrated after 24 h of exposure to 0.2 μM C16 in all three cell lines. However, the non-tumorigenic MCF-12A cell line recovered extremely well after 48 h when compared to the tumorigenic cell lines. This indicates that C16 acts as an antiproliferative agent, possesses antimitotic activity and induces apoptosis in vitro. These features warrant further investigation.

2-Methoxyestradiol-bis-sulphamate refrains from inducing apoptosis and autophagy in a non-tumorigenic breast cell line

Background

Anticancer research resulted in the discovery of a promising antimitotic metabolite, 2-methoxyestradiol. 2-Methoxyestradiol-bis-sulphamate, a bis-sulphamoylated analogue exerts antiproliferative- and antimitotic activity. Investigating the anticancer potential of 2-methoxyestradiol-bis-sulphamate requires demonstrating the influence of 2-methoxyestradiol-bis-sulphamate on non-tumorigenic cells. This project focused on the in vitro effects of 2-methoxyestradiol-bis-sulphamate on the non-tumorigenic MCF-12A breast epithelial cell line.

Methods

The in vitro influence of 2-methoxyestradiol-bis-sulphamate was investigated on cell cycle progression, possible induction of apoptosis and autophagy and reactive oxygen species generation. Cell cycle progression was done using flow cytometry in conjunction with ethanol fixation and propidium iodide staining. Displaying effects on the mitochondrial membrane potential was achieved utilizing flow cytometry and the MitoCapture ^TM Mitochondrial apoptosis detection kit. Autophagy detection was done by means of flow cytometry and anti-LC3B conjugated to DyLight 488. Reactive oxygen species generation was conducted employing flow cytometry and 2,7-dichlorofluorescein diacetate and hydroethidine.

Results

This study demonstrated that 2-methoxyestradiol-bis-sulphamate did not affect cell cycle progression or reactive oxygen species in a statistically significant manner in the non-tumorigenic MCF-12A cell line. In addition, 2-methoxyestradiol-bis-sulphamate did not statistically significantly induce apoptosis or autophagy.

Conclusion

Reports indicate that 2-methoxyestradiol-bis-sulphamate induces apoptosis and autophagy in several tumorigenic cell lines. The anticancer ability of 2-methoxyestradiol-bis-sulphamate is due to its antimitotic activity. However, this study demonstrates the promising notion that 2-methoxyestradiol-bis-sulphamate does not affect the non-tumorigenic MCF-12A cells. This project contributes to the embedded scientific knowledge regarding the differential death mechanisms used by 2-methoxyestradiol-bis-sulphamate on tumorigenic and non-tumorigenic cell lines.

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.

Structure-activity relationships of C-17-substituted estratriene-3-O-sulfamates as anticancer agents

The synthesis and antiproliferative activities of analogues of 2-substituted estradiol-3,17-O,O-bis-sulfamates (E2bisMATEs) are discussed. Modifications of the C-17 substituent confirm that an H-bond acceptor is essential for high activity; its optimal linkage to C-17 and the local environment in which it resides are defined. In the non-sulfamoylated series 17β-acyl substitution delivers 48b, the most potent compound identified to date. In the sulfamate series a number of permutations of linker and H-bond acceptor deliver excellent activity, with 55, 61, 65, 49a, and 49b proving especially promising. The in vivo potential of these compounds was explored in the NCI hollow fiber assay and also in a mouse Matrigel model of antiangiogenesis in which 49 and 55 show significant inhibitory activity.

2-Methoxyestradiol-bis-sulfamate induces apoptosis and autophagy in a tumorigenic breast epithelial cell line

In anticancer research where the focus is on finding agents that induces cell death while leaving non-tumorigenic cells less affected, a novel 2-methoxyestradiol derivative has come forth. 2-Methoxyestradiol-bis-sulfamate (2-MeOE2bisMATE) is a 2-methoxyestradiol derivative produced by bis-sulphamoylation, which possesses increased antiproliferative activity and biological availability. Several questions remain regarding the type of cell death mechanisms and possible induction of autophagy by 2-MeOE2bisMATE. The aim of this in vitro study was to investigate the cell death mechanisms exerted by 2-MeOE2bisMATE in an adenocarcinoma cell line (MCF-7) by analyzing its influence on cell growth, morphology, and possible induction of cell death. Spectrophotometry (crystal violet staining), transmission electron microscopy (TEM), light microscopy (hematoxylin and eosin staining), and fluorescent microscopy (Hoechst 33342, propidium iodide and acridine orange) were employed. Spectrophotometrical studies indicated that 2-MeOE2bisMATE decreased cell numbers to 75% in MCF-7 cells after 24 h and to 47% after 48 h of exposure. TEM demonstrated membrane blebbing, nuclear fragmentation, and chromatin condensation indicating the hallmarks of apoptosis. Light microscopy revealed the presence of several cells blocked in metaphase, and apoptotic cells were also observed. Fluorescent microscopy demonstrated increased lysosomal staining; suggesting the induction of autophagy. 2-MeOE2bisMATE shows therapeutic potential, as an, anticancer agent, and the investigation of the cell death mechanisms used by 2-MeOE2bisMATE, thus, warrants further investigation.

Ezrin, radixin, and moesin are phosphorylated in response to 2-methoxyestradiol and modulate endothelial hyperpermeability

We showed previously that microtubule disruptor 2-methoxyestradiol (2ME) induces hyperpermeability of the endothelial monolayer via mechanisms that include the activation of p38 and Rho kinase (ROCK) and rearrangement of the actin cytoskeleton. Using the protein kinase C (PKC) inhibitors Ro-31-7549 and Ro-32-0432, we show in vitro and in vivo that 2ME-induced barrier dysfunction is also PKC-dependent. The known PKC substrates ezrin, radixin, and moesin (ERM) were recently implicated in the regulation of endothelial permeability. This study tested the hypotheses that ERM proteins are phosphorylated in response to 2ME, and that this phosphorylation is involved in 2ME-induced barrier dysfunction. We show that the application of 2ME leads to a dramatic increase in the level of ERM phosphorylation. This increase is attenuated in cells pretreated with the microtubule stabilizer taxol. In human pulmonary artery endothelial cells (HPAECs), the phosphorylation of ERM occurs in a p38-dependent and PKC-dependent manner. The activation of p38 appears to occur upstream from the activation of PKC, in response to 2ME. Phosphorylated ERM are localized at the cell periphery during the early phase of response to 2ME (15 minutes), and colocalize with F-actin branching points during the later phase of response (60 minutes). Using the short interfering RNA approach, we also showed that individual ERM depletion significantly attenuates 2ME-induced hyperpermeability. HPAEC monolayers, depleted of ERM proteins and monolayers, overexpressing phosphorylation-deficient ERM mutants, exhibit less attenuation of 2ME-induced barrier disruption in response to the PKC inhibitor Ro-31-7549. These results suggest a critical role of PKC activation in response to microtubule-disrupting agents, and implicate the phosphorylation of ERM in the barrier dysfunction induced by 2ME.

BCRP expression does not result in resistance to STX140 in vivo, despite the increased expression of BCRP in A2780 cells in vitro after long-term STX140 exposure

The anti-proliferative and anti-angiogenic properties of the endogenous oestrogen metabolite, 2-methoxyoestradiol (2-MeOE2), are enhanced in a series of sulphamoylated derivatives of 2-MeOE2. To investigate possible mechanisms of resistance to these compounds, a cell line, A2780.140, eightfold less sensitive to the 3,17-O,O-bis-sulphamoylated derivative, STX140, was derived from the A2780 ovarian cancer cell line by dose escalation. Other cell lines tested did not develop STX140 resistance. RT-PCR and immunoblot analysis demonstrated that breast cancer resistance protein (BCRP) expression is dramatically increased in A2780.140 cells. The cells are cross-resistant to the most structurally similar bis-sulphamates, and to BCRP substrates, mitoxantrone and doxorubicin; but they remain sensitive to taxol, an MDR1 substrate, and to all other sulphamates tested. Sensitivity can be restored using a BCRP inhibitor, and this pattern of resistance is also seen in a BCRP-expressing MCF-7-derived cell line, MCF-7.MR. In mice bearing wild-type (wt) and BCRP-expressing tumours on either flank, both STX140 and mitoxantrone inhibited the growth of the MCF-7wt xenografts, but only STX140 inhibited growth of the MCF-7.MR tumours. In conclusion, STX140, a promising orally bioavailable anti-cancer agent in pre-clinical development, is highly efficacious in BCRP-expressing xenografts. This is despite an increase in BCRP expression in A2780 cells in vitro after chronic dosing with STX140.

2-Methoxyoestradiol-3,17-O,O-bis-sulphamate and 2-deoxy-D-glucose in combination: a potential treatment for breast and prostate cancer

Drug combination therapy is a key strategy to improve treatment efficacy and survival of cancer patients. In this study the effects of combining 2-methoxyoestradiol-3,17-O,O-bis-sulphamate (STX140), a microtubule disruptor, with 2-deoxy-D-glucose (2DG) were assessed in MCF-7 (breast) and LNCaP (prostate) xenograft models in vivo. In mice bearing MCF-7 xenografts, daily p.o. administration of STX140 (5 mg kg⁻¹) resulted in a 46% (P<0.05) reduction of tumour volume. However, the combination of STX140 (5 mg kg⁻¹ p.o.) and 2DG (2 g kg⁻¹ i.p.) reduced tumour volume by 76% (P<0.001). 2-Methoxyoestradiol-3,17-O,O-bis-sulphamate also reduced tumour vessel density. 2-Deoxy-D-glucose alone had no significant effect on tumour volume or vessel density. A similar benefit of the combination treatment was observed in the LNCaP prostate xenograft model. In vitro the degree of inhibition of cell proliferation by STX140 was unaffected by oxygen concentrations. In contrast, the inhibition of proliferation by 2DG was enhanced under hypoxia by 20 and 25% in MCF-7 and LNCaP cells, respectively. The combination of STX140 and 2DG in LNCaP cells under normoxia or hypoxia inhibited proliferation to a greater extent than either compound alone. These results suggest that the antiangiogenic and microtubule disruption activities of STX140 may make tumours more susceptible to inhibition of glycolysis by 2DG. This is the first study to show the benefit of combining a microtubule disruptor with 2DG in the two most common solid tumours.

Structure-activity relationships of C-17 cyano-substituted estratrienes as anticancer agents

The synthesis, SAR, and preclinical evaluation of 17-cyanated 2-substituted estra-1,3,5(10)-trienes as anticancer agents are discussed. 2-Methoxy-17beta-cyanomethylestra-1,3,5(10)-trien-3-ol ( 14), but not the related 2-ethyl derivative 7, and the related 3- O-sulfamates 8 and 15 display potent antiproliferative effects (MCF-7 GI 50 300, 60 and 70 nM, respectively) against human cancer cells in vitro. Investigation of the SAR reveals that a sterically unhindered hydrogen bond acceptor attached to C-17 is most likely key to the enhanced activity. Compound 8 displayed significant in vitro antiangiogenic activity, and its ability to act as a microtubule disruptor was confirmed. Inhibitory activity of the sulfamate derivatives against steroid sulfatase and carbonic anhydrase II (hCAII) was also observed, and the interaction between 15 and hCAII was investigated by protein crystallography. The potential of these multimechanism anticancer agents was confirmed in vivo, with promising activity observed for both 14 and 15 in an athymic nude mouse MDA-MB-231 human breast cancer xenograft model.