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

2-Methoxyestradiol-3,17-O,O-bis-sulfamate (STX140) Inhibits Proliferation and Invasion via Senescence Pathway Induction in Human BRAFi-Resistant Melanoma Cells

The endogenous estradiol derivative 2-Methoxyestradiol (2-ME) has shown good and wide anticancer activity but suffers from poor oral bioavailability and extensive metabolic conjugation. However, its sulfamoylated derivative, 2-methoxyestradiol-3,17-O,O-bis-sulfamate (STX140), has superior potential as a therapeutic agent, acts by disrupting microtubule polymerization, leading to cell cycle arrest and apoptosis in cancer cells and possesses much better pharmaceutical properties. This study investigated the antiproliferative and anti-invasive activities of STX140 in both SKMEL-28 naïve melanoma (SKMEL28-P) cells and resistant melanoma cells (SKMEL-28R). STX140 inhibited cell proliferation in the nanomolar range while having a less pronounced effect on human melanocytes. Additionally, STX140 induced cell cycle arrest in the G2/M phase and sub-G1, reduced migration, and clonogenic potential in monolayer models, and inhibited invasion in a 3D human skin model with melanoma cells. Furthermore, STX140 induced senescence features in melanoma and activated the senescence machinery by upregulating the expression of senescence genes and proteins related to senescence signaling. These findings suggest that STX140 may hold potential as a therapeutic agent for melanoma treatment.

2-Difluoromethoxy-Substituted Estratriene Sulfamates: Synthesis, Antiproliferative SAR, Antitubulin Activity, and Steroid Sulfatase Inhibition

2-Difluoromethoxyestratriene derivatives were designed to improve potency and in vivo stability of the drug candidate 2-methoxyestradiol (2ME2). Compound evaluation in vitro against the proliferation of MCF-7 and MDA MB-231 breast cancer cells, as inhibitors of tubulin polymerisation and also steroid sulfatase (STS) both in cell lysates and in whole cells, showed promising activities. In antiproliferative assays 2-difluoromethoxyestradiol was less potent than 2ME2, but its sulfamates were often more potent than their corresponding non-fluorinated analogues. The fluorinated bis-sulfamate is a promising antiproliferative agent in MCF-7 cells (GI50 0.28 μM) vs the known 2-methoxyestradiol-3,17-O,O-bissulfamate (STX140, GI50 0.52 μM), confirming the utility of our approach. Compounds were also evaluated in the NCI 60-cell line panel and the fluorinated bis-sulfamate derivative displayed very good overall activities with a sub-micromolar average GI50 . It was a very potent STS inhibitor in whole JEG-3 cells (IC50 3.7 nM) similar to STX140 (4.2 nM) and additionally interferes with tubulin assembly in vitro and colchicine binding to tubulin. An X-ray study of 2-difluoromethoxy-3-benzyloxyestra-1,3,5(10)-trien-17-one examined conformational aspects of the fluorinated substituent. The known related derivative 2-difluoromethyl-3-sulfamoyloxyestrone was evaluated for STS inhibition in whole JEG-3 cells and showed an excellent IC50 of 55 pM.

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.

Tetrahydroisoquinoline Sulfamates as Potent Microtubule Disruptors: Synthesis, Antiproliferative and Antitubulin Activity of Dichlorobenzyl-Based Derivatives, and a Tubulin Cocrystal Structure

Tetrahydroisoquinoline (THIQ) 6-O-sulfamate-based anticancer agents, inspired by the endogenous steroid 2-methoxyestradiol and its sulfamate derivatives, are further explored for antiproliferative and microtubule disruptor activity. Based on recently designed C3-methyl C7-methoxy-substituted THIQ derivatives, compounds with mono- and dichloro-substitutions on the pendant N-benzyl ring were synthesized and evaluated. Although improved antiproliferative activity was observed, for example, 4a versus 4b and 4b versus 8c, it was relatively modest. Compound 8c, a 2',5'-dichlorobenzyl derivative was, however, identified as a promising antiproliferative agent with in vitro activities exceeding that of the parent steroid (e.g., GI₅₀ 90 nM in DU-145 cells) and was highly potent against a range of tumor cell lines (e.g., GI₅₀ 26 nM for OVCAR-3). 8c inhibited the polymerization of tubulin in vitro with an IC₅₀ only twofold less potent than combretastatin A-4 and inhibited colchicine binding to tubulin. Tubulin polymerization assays showed the parent THIQ 4a to be only a very weak inhibitor, but a striking potency difference was seen between compounds with C2' methoxy and chloro substituents, whereas this was much smaller when these substituents were positioned at C5'. To confirm the target in atomic detail and because 8c is a racemic mixture, an achiral parent THIQ 6-O-sulfamate derivative 10 was successfully cocrystallized with the αβ-tubulin heterodimer. The derivative 10 binds at the colchicine site on tubulin, the first example of this compound class investigated in such detail, with its sulfamate group interacting with residues beyond the reach of colchicine itself, similar to a recently reported quinazolinone sulfamate derivative, 6a. The structure also suggests that for racemic C3-methyl-substituted THIQ derivatives, such as 8c, the (S)-enantiomer is likely to be preferentially accommodated within the colchicine site for steric reasons. The results further confirm the potential of nonsteroidal THIQ sulfamate derivatives for oncology and suggest that the mechanism of microtubule destabilization for the THIQ compound class is to prevent the curved-to-straight conformational transition of tubulin required for polymerization.

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.

Targeted NF1 cancer therapeutics with multiple modes of action: small molecule hormone-like agents resembling the natural anticancer metabolite, 2-methoxyoestradiol

Background:

Both the number and size of tumours in NF1 patients increase in response to the rise in steroid hormones seen at puberty and during pregnancy. The size of tumours decreases after delivery, suggesting that hormone-targeting therapy might provide a viable new NF1 treatment approach. Our earlier studies demonstrated that human NF1 tumour cell lines either went through apoptosis or ceased growth in the presence of 2-methoxyoestradiol (2ME2), a naturally occurring anticancer metabolite of 17-β estradiol. Previous reports of treatment with sulfamoylated steroidal and non-steroidal derivatives of 2ME2 showed promising reductions in tumour burden in hormone-responsive cancers other than NF1. Here we present the first studies indicating that 2ME2 derivatives could also provide an avenue for treating NF1, for which few treatment options are available.

Methods:

STX3451, (2-(3-Bromo-4,5-dimethoxybenzyl)-7-methoxy-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline), a non-steroidal sulphamate analogue of 2ME2, was tested in dose-dependent studies of malignant and benign NF1 human tumour cell lines and cell lines with variable controlled neurofibromin expression. The mechanisms of action of STX3451 were also analysed.

Results:

We found that STX3451-induced apoptosis in human malignant peripheral nerve sheath tumour (MPNST) cell lines, even in the presence of elevated oestrogen and progesterone. It inhibits both PI3 kinase and mTOR signalling pathways. It disrupts actin- and microtubule-based cytoskeletal structures in cell lines derived from human MPNSTs and in cells derived from benign plexiform neurofibromas. STX3451 selectively kills MPNST-derived cells, but also halts growth of other tumour-derived NF1 cell lines.

Conclusion:

STX3451 provides a new approach for inducing cell death and lowering tumour burden in NF1 and other hormone-responsive cancers with limited treatment options.

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.

Synthesis, antitubulin, and antiproliferative SAR of C3/C1-substituted tetrahydroisoquinolines

The syntheses and antiproliferative activities of novel substituted tetrahydroisoquinoline derivatives and their sulfamates are discussed. Biasing of conformational populations through substitution on the tetrahydroisoquinoline core at C1 and C3 has a profound effect on the antiproliferative activity against various cancer cell lines. The C3 methyl-substituted sulfamate (±)-7-methoxy-2-(3-methoxybenzyl)-3-methyl-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline (6 b), for example, was found to be ∼10-fold more potent than the corresponding non-methylated compound 7-methoxy-2-(3-methoxybenzyl)-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline (4 b) against DU-145 prostate cancer cells (GI50 values: 220 nM and 2.1 μM, respectively). Such compounds were also found to be active against a drug-resistant MCF breast cancer cell line. The position and nature of substitution of the N-benzyl group in the C3-substituted series was found to have a significant effect on activity. Whereas C1 methylation has little effect on activity, introduction of C1 phenyl and C3-gem-dimethyl substituents greatly decreases antiproliferative activity. The ability of these compounds to inhibit microtubule polymerisation and to bind tubulin in a competitive manner versus colchicine confirms the mechanism of action. The therapeutic potential of a representative compound was confirmed in an in vivo multiple myeloma xenograft study.

Tetrahydroisoquinolinone-based steroidomimetic and chimeric microtubule disruptors

A structure-activity relationship (SAR) translation strategy was used for the discovery of tetrahydroisoquinoline (THIQ)-based steroidomimetic and chimeric microtubule disruptors based upon a steroidal starting point. A steroid A,B-ring-mimicking THIQ core was connected to methoxyaryl D-ring ring mimics through methylene, carbonyl and sulfonyl linkers to afford a number of steroidomimetic hits (e.g., 7-methoxy-2-(3- methoxybenzyl)-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline (20 c) GI₅₀=2.1 μM). Optimisation and control experiments demonstrate the complementary SAR of this series and the steroid derivatives that inspired its design. Linkage of the THIQ-based A,B-mimic with the trimethoxyaryl motif prevalent in colchicine site binding microtubule disruptors delivered a series of chimeric molecules whose activity (GI₅₀=40 nM) surpasses that of the parent steroid derivatives. Validation of this strategy was obtained from the excellent oral activity of 7-methoxy-6-sulfamoyloxy-2-(3,4,5-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline relative to a benchmark steroidal bis- sulfamate in an in vivo model of multiple myeloma.

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.

STX2171, a 17β-hydroxysteroid dehydrogenase type 3 inhibitor, is efficacious in vivo in a novel hormone-dependent prostate cancer model

17β-Hydroxysteroid dehydrogenases (17β-HSDs) catalyse the 17-position reduction/oxidation of steroids. 17β-HSD type 3 (17β-HSD3) catalyses the reduction of the weakly androgenic androstenedione (adione) to testosterone, suggesting that specific inhibitors of 17β-HSD3 may have a role in the treatment of hormone-dependent prostate cancer and benign prostate hyperplasia. STX2171 is a novel selective non-steroidal 17β-HSD3 inhibitor with an IC(50) of ∼200 nM in a whole-cell assay. It inhibits adione-stimulated proliferation of 17β-HSD3-expressing androgen receptor-positive LNCaP(HSD3) prostate cancer cells in vitro. An androgen-stimulated LNCaP(HSD3) xenograft proof-of-concept model was developed to study the efficacies of STX2171 and a more established 17β-HSD3 inhibitor, STX1383 (SCH-451659, Schering-Plough), in vivo. Castrated male MF-1 mice were inoculated s.c. with 1×10(7) cells 24 h after an initial daily dose of testosterone propionate (TP) or vehicle. After 4 weeks, tumours had not developed in vehicle-dosed mice, but were present in 50% of those mice given TP. One week after switching the stimulus to adione, mice were dosed additionally with the vehicle or inhibitor for a further 4 weeks. Both TP and adione efficiently stimulated tumour growth and increased plasma testosterone levels; however, in the presence of either 17β-HSD3 inhibitor, adione-dependent tumour growth was significantly inhibited and plasma testosterone levels reduced. Mouse body weights were unaffected. Both inhibitors also significantly lowered plasma testosterone levels in intact mice. In conclusion, STX2171 and STX1383 significantly lower plasma testosterone levels and inhibit androgen-dependent tumour growth in vivo, indicating that 17β-HSD3 inhibitors may have application in the treatment of hormone-dependent prostate cancer.

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.

Orally bioavailable tubulin antagonists for paclitaxel-refractory cancer

PURPOSE

To evaluate the efficacy and oral activity of two promising indoles, (2-(1H-indol-3-yl)-1H-imidazol-4-yl)(3,4,5-trimethoxyphenyl)methanone [compound II] and (2-(1H-indol-5-ylamino)-thiazol-4-yl)(3,4,5-trimethoxyphenyl)methanone [compound IAT], in paclitaxel- and docetaxel-resistant tumor models in vitro and in vivo.

METHODS

The in vitro drug-like properties, including potency, solubility, metabolic stability, and drug-drug interactions were examined for our two active compounds. An in vivo pharmacokinetic study and antitumor efficacy study were also completed to compare their efficacy with docetaxel.

RESULTS

Both compounds bound to the colchicine-binding site on tubulin, and inhibited tubulin polymerization, resulting in highly potent cytotoxic activity in vitro. While the potency of paclitaxel and docetaxel was compromised in a multidrug-resistant cell line that overexpresses P-glycoprotein, the potency of compounds II and IAT was maintained. Both compounds had favorable drug-like properties, and acceptable oral bioavailability (21-50 %) in mice, rats, and dogs. Tumor growth inhibition of greater than 100 % was achieved when immunodeficient mice with rapidly growing paclitaxel-resistant prostate cancer cells were treated orally at doses of 3-30 mg/kg of II or IAT.

CONCLUSIONS

These studies highlight the potent and broad anticancer activity of two orally bioavailable compounds, offering significant pharmacologic advantage over existing drugs of this class for multidrug resistant or taxane-refractory cancers.

In vitro effects of 2-methoxyestradiol-bis-sulphamate on reactive oxygen species and possible apoptosis induction in a breast adenocarcinoma cell line

Background

In the search for anticancer agents, a promising 17-β-estradiol metabolite, 2-methoxyestradiol (2ME2) was found that exerts antiproliferative in vitro and in vivo activity. Since 2ME2 has limited biological accessibility and rapid metabolic degradation, the purpose of this study was to investigate the in vitro influence exerted by an analogue of 2ME2 namely 2-methoxyestradiol-bis-sulphamate (2MEBM) in a breast adenocarcinoma cell line (MCF-7).

Methods

This was conducted by investigating 2MEBM's in vitro influence on cell cycle progression, mitochondrial membrane potential and possible production of reactive oxygen species (ROS) generation. In vitro effects of 2MEBM on cell cycle progression was demonstrated by means of flow cytometry using propidium iodide. Hydrogen peroxide and superoxide production was investigated using 2,7-dichlorofluorescein diacetate and hydroethidine, respectively. The probable reduction in the mitochondrial membrane potential was demonstrated using a MitoCapture™ kit.

Results

Cell cycle progression revealed the presence of a sub-G₁ apoptotic peak. Reduction of mitochondrial membrane potential after exposure to 2MEBM was demonstrated and an increase in ROS production was also observed.

Conclusion

This study verified that 2MEBM exposure resulted in apoptosis induction, increased ROS production and reduced mitochondrial membrane potential in a tumorigenic breast epithelial cell line. Data obtained from this project contributes to the unravelling of the in vitro signal transduction of 2MEBM in tumorigenic cell lines.

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.