The anticancer activities and SARs of estradiol-17-O-sulfamates and estradiol 3,17-O,O-bis-sulfamates (E2bisMATEs) as steroid sulfatase (STS) inhibitors and antiproliferative agents are discussed. Estradiol 3,17-O,O-bis-sulfamates 20 and 21, in contrast to the 17-O-monosulfamate 11, proved to be excellent STS inhibitors. 2-Substituted E2bisMATEs 21 and 23 additionally exhibited potent antiproliferative activity with mean graph midpoint values of 18-87 nM in the NCI 60-cell-line panel. 21 Exhibited antiangiogenic in vitro and in vivo activity in an early-stage Lewis lung model, and 23 dosed p.o. caused marked growth inhibition in a nude mouse xenograft tumor model. Modeling studies suggest that the E2bisMATEs and 2-MeOE2 share a common mode of binding to tubulin, though COMPARE analysis of activity profiles was negative. 21 was cocrystallized with carbonic anhydrase II, and X-ray crystallography revealed unexpected coordination of the 17-O-sulfamate of 21 to the active site zinc and a probable additional lower affinity binding site. 2-Substituted E2bisMATEs are attractive candidates for further development as multitargeted anticancer agents.

2-Methoxyoestradiol (2-MeOE2) is an endogenous oestrogen metabolite that inhibits the proliferation of cancer cells in vitro, and it is also antiangiogenic. In vivo 2-MeOE2, when administered at relatively high doses, inhibits the growth of tumours derived from breast cancer cells, sarcomas and melanomas. Sulphamoylated derivatives of 2-MeOE2 are more potent inhibitors of in vitro breast cancer cell growth than 2-MeOE2. In the present study, we have compared the pharmacokinetic profiles and metabolism of 2-MeOE2 and its sulphamoylated derivative, 2-methoxyoestradiol-bis-sulphamate (2-MeOE2bisMATE), in adult female rats. Their ability to inhibit tumour growth was compared in nude mice bearing xenografts derived from MDA-MB-435 (oestrogen receptor negative) melanoma cancer cells. After a single oral 10 mg kg À1 dose of 2-MeOE2bisMATE, significant concentrations of this compound were still detectable at 24 h. In contrast, no 2-MeOE2 or metabolites were detected in plasma at any time after a 10 mg kg À1 oral dose. Thus, the bioavailability of 2-MeOE2 is very low, whereas for 2-MeOE2bisMATE it was 85%. No significant metabolites of 2-MeOE2bisMATE were detected in plasma after oral or intravenous dosing, showing that this drug is resistant to metabolism. In the tumour efficacy model, oral administration of 2-MeOE2bisMATE, at 20 mg kg À1 day À1 daily for 28 days, almost completely inhibited tumour growth. Inhibition of tumour growth was maintained for a further 28 days after the cessation of dosing. At this dose level, 2-MeOE2 did not inhibit tumour growth. The resistance to metabolism shown by 2-MeOE2bisMATE and its ability to inhibit tumour growth in vivo suggest that this compound should have considerable potential for development as a novel anticancer drug.

Efficient and flexible syntheses of 2-substituted estrone, estradiol and their 3-O-sulfamate (EMATE) derivatives have been developed using directed ortho-lithiation methodology. 2-Substituted EMATEs display a similar antiproliferative activity profile to the corresponding estradiols against a range of human cancer cell lines. 2-Methoxy (3, 4), 2-methylsulfanyl (20, 21) and 2-ethyl EMATEs (32, 33) proved the most active compounds with 2-ethylestradiol-3-O-sulfamate (33), displaying a mean activity over the NCI 55 cell line panel 80-fold greater than the established anticancer agent 2-methoxyestradiol (2). 2-Ethylestradiol-3-O-sulfamate (33) was also an effective inhibitor of angiogenesis using three in vitro markers, and various 2-substituted EMATEs also proved to be inhibitors of steroid sulfatase (STS), a therapeutic target for the treatment of hormone-dependent breast cancer. The potential of this novel class of multimechanism anticancer agents was confirmed in vivo with good activity observed in the NCI hollow fiber assay and in a MDA-MB-435 xenograft mouse model.

BACKGROUND: Class III b-tubulin overexpression is a marker of resistance to microtubule disruptors in vitro, in vivo and in the clinic for many cancers, including breast cancer. The aims of this study were to develop a new model of class III b-tubulin expression, avoiding the toxicity associated with chronic overexpression of class III b-tubulin, and study the efficacy of a panel of clinical and pre-clinical drugs in this model. METHODS: MCF-7 (ER þ ve) and MDA-MB-231 (ERÀve) were either transfected with pALTER-TUBB3 or siRNA-tubb3 and 24 h later exposed to test compounds for a further 96 h for proliferation studies. RT -PCR and immunoblotting were used to monitor the changes in class III b-tubulin mRNA and protein expression. RESULTS: The model allowed for subtle changes in class III b-tubulin expression to be achieved, which had no direct effect on the viability of the cells. Class III b-tubulin overexpression conferred resistance to paclitaxel and vinorelbine, whereas downregulation of class III b-tubulin rendered cells more sensitive to these two drugs. The efficacy of the colchicine-site binding agents, 2-MeOE2, colchicine, STX140, ENMD1198 and STX243 was unaffected by the changes in class III b-tubulin expression. CONCLUSION: These data indicate that the effect of class III b-tubulin overexpression may depend on where the drug's binding site is located on the tubulin. Therefore, this study highlights for the first time the potential key role of targeting the colchicine-binding site, to develop new treatment modalities for taxane-refractory breast cancer.

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Sulfamoylation of 2-methoxyestrone (2-MeOE1) was shown previously to enhance its potency as an anti-proliferative agent against breast cancer cells. We have examined the ability of a series of 2-methoxyestradiol (2-MeOE2) and 2-ethylestradiol (2-EtE2) sulfamates to inhibit angiogenesis in vitro. 2-MeOE2 bis-sulfamate and 2-EtE2 sulfamate were potent inhibitors of human umbilical vein endothelial cell (HUVEC) proliferation with IC 50 values of 0.05 M and 0.01 M, respectively. A novel co-culture system, in which endothelial cells were cultured in a matrix of human dermal fibroblasts, was also used to assess the anti-angiogenic potential of these drugs. In this system endothelial cells proliferate and migrate through the culture matrix to form tubule structures. Key words: angiogenesis; breast cancer; estrogens; estrogen sulfamates; microtubulesEstrogens can be metabolised via either a 2-hydroxylase or 16␣-hydroxylase pathway and there is a growing awareness that the route of estrogen metabolism may influence the development of breast tumors. 2-Hydroxyestrogens and their 2-methoxy derivatives are non-estrogenic whereas 16␣-hydroxy metabolites are estrogenic due, in part, to their ability to form adducts with proteins. 1,2 Research carried out by Bradlow and others 3,4 has indicated that although the 2-hydroxylase pathway is associated with a reduced risk of breast cancer, increased formation of 16␣-hydroxy metabolites may increase breast cancer risk. It was suggested recently that the major derivative of 2-hydroxyestrogens, 2-methoxyestradiol (2-MeOE2, Fig. 1) may in fact be the endogenous estrogen metabolite that inhibits breast carcinogenesis. 5 2-MeOE2 is currently undergoing Phase I/II trials as a novel agent for breast cancer therapy. 6 Its selection for development as an anti-cancer agent was based on its ability to inhibit the proliferation of a wide range of cancer cells including estrogen receptor positive (ERϩ) and negative (ERϪ) breast cancer cells. 7,8 In vivo oral administration of 2-MeOE2 inhibited the growth of Meth-A sarcoma, B16 melanoma and human MDA-MB-435 breast carcinomas. 8,9 Relatively high doses of 2-MeOE2 (75-100 mg/kg/day) were administered to produce the reductions in tumor growth. In addition to its anti-proliferation effects 2-MeOE2 was also identified as the active ingredient of urine extracts that was able to inhibit angiogenesis. 9 Using brain-derived capillary endothelial cells 2-MeOE2 was found to be a specific inhibitor of the proliferation of these cells being 90ϫ more potent than 2-methoxyestrone (2-MeOE1) and 250ϫ more potent than estradiol. Several subsequent investigations have confirmed the potency of 2-MeOE2 as an inhibitor of endothelial cell growth and angiogenesis in vitro and in vivo. 8,10 The mechanism(s) by which 2-MeOE2 inhibits endothelial cell growth and angiogenesis remains to be elucidated.The estrogen sulfamate, estrone-3-O-sulfamate (EMATE) was initially identified as a potent steroid sulfatase inhibitor. 11,12 Unexpectedly, EMATE proved to be a potent estroge...

Estradiol-3,17-O,O-bis-sulfamates inhibit steroid sulfatase (STS), carbonic anhydrase (CA), and, when substituted at C-2, cancer cell proliferation and angiogenesis. C-2 Substitution and 17-sulfamate replacement of the estradiol-3,17-O,O-bis-sulfamates were explored with efficient and practical syntheses developed. Evaluation against human cancer cell lines revealed the 2-methyl derivative 27 (DU145 GI(50) = 0.38 microM) as the most active novel bis-sulfamate, while 2-ethyl-17-carbamate derivative 52 (GI(50) = 0.22 microM) proved most active of its series (cf. 2-ethylestradiol-3,17-O,O-bis-sulfamate 4 GI(50) = 0.21 microM). Larger C-2 substituents were deleterious to activity. 2-Methoxy-17-carbamate 50 was studied by X-ray crystallography and was surprisingly 13-fold weaker as an STS inhibitor compared to parent bis-sulfamate 3. The potential of 4 as an orally dosed anti-tumor agent is confirmed using breast and prostate cancer xenografts. In the MDA-MB-231 model, dramatic reduction in tumor growth or regression was observed, with effects sustained after cessation of treatment. 3-O-Sulfamoylated 2-alkylestradiol-17-O-carbamates and sulfamates have considerable potential as anticancer agents.

Quinazolinone-based anticancer agents were designed, decorated with functional groups from a 2-methoxyestradiol-based microtubule disruptor series, incorporating the aryl sulfamate motif of steroid sulfatase (STS) inhibitors. The steroidal AB-ring system was mimicked, favoring conformations with an N-2 substituent occupying D-ring space. Evaluation against breast and prostate tumor cell lines identified 7b with DU-145 antiproliferative activity (GI 300 nM). A preliminary structure-activity relationship afforded compounds (e.g., 7j GI 50 nM) with activity exceeding that of the parent. Both 7b and 7j inhibit tubulin assembly in vitro and colchicine binding, and 7j was successfully co-crystallized with the αβ-tubulin heterodimer as the first of its class, its sulfamate group interacting positively at the colchicine binding site. Microtubule destabilization by 7j is likely achieved by preventing the curved-to-straight conformational transition in αβ-tubulin. Quinazolinone sulfamates surprisingly showed weak STS inhibition. Preliminary in vivo studies in a multiple myeloma xenograft model for 7b showed oral activity, confirming the promise of this template.