Journal of Steroid Biochemistry & Molecular Biology 84 (2003) 269–278 Growth inhibition of multi-drug-resistant breast cancer cells by 2-methoxyoestradiol-bis-sulphamate and 2-ethyloestradiol-bis-sulphamate  R.N. Suzuki a , S.P. Newman a , A. Purohit a , M.P. Leese b , B.V.L. Potter b , M.J. Reed a,∗ a Endocrinology and Metabolic Medicine and Sterix Ltd., Faculty of Medicine, Imperial College, St. Mary’s Hospital, London W2 1NY, UK b Department of Pharmacy and Pharmacology and Sterix Ltd., University of Bath, Bath BA7 2AY, UK Abstract There is currently considerable interest in the use of the endogenous oestrogen metabolite, 2-methoxyoestradiol (2-MeOE2) for the treatment and prevention of breast cancer. We have previously shown that sulphamoylation of 2-MeOE2 and related derivatives greatly enhances their ability to inhibit the proliferation of ER+ and ER- breast cancer cells. In this study, we have compared the abilities of 2-methoxyoestradiol-bis-sulphamate (2-MeOE2bisMATE) and 2-ethyloestradiol-bis-sulphamate (2-EtE2bisMATE) with that of 2-MeOE2 to inhibit the proliferation of breast cancer cells when grown on three different substrata: plastic, collagen I and Matrigel. The human breast cell line MCF-7 was utilised for these studies together with its doxorubicin resistant variant, MCF-7 DOX40 and mitoxantrone resistant variant, MCF-7 MR, as a longitudinal model of in vitro drug resistance. On a plastic substratum all three cell lines were sensitive to the effects of 2-MeOE2bisMATE and 2-EtE2bisMATE whereas MCF-7 cells and the MCF-MR variant cells were resistant to the effects of 2-MeOE2 at 1 M. The sensitivity of the cell lines to those compounds also remained significant when grown on more physiological substrata. All of the drugs tested arrested cells in the G2/M phase of the cell cycle. The finding that breast cancer cells that are resistant to conventional chemotherapeutic agents remain sensitive to 2-substituted oestrogen sulphamates offers considerable potential for the treatment of women with drug-resistant breast cancer. © 2003 Elsevier Science Ltd. All rights reserved. Keywords: Breast cancer; Oestrogens; Multi-drug resistance; 2-Methoxyoestradiol; Oestrogen sulphamates 1. Introduction Breast cancer is reported to be one of the commonest cancers, accounting for almost 20% of all malignancies world-wide, and over half a million women develop breast cancer every year [1]. For advanced breast cancer (recur- rence and metastasis), the aim of drug treatments is to shrink the existing breast cancers, or to decrease the rate at which they grow or spread. For metastasis affecting the liver or lungs, chemotherapy is used as the first line of treatment. It is also applied if patients do not respond to hormone therapy. Many patients with metastatic breast cancer, however, de- velop recurrences after an initial response to chemotherapy. In such patients, drug resistance is a common phenomenon.  Poster paper presented at the 15th International Symposium of the Journal of Steroid Biochemistry and Molecular Biology, “Recent Advances in Steroid Biochemistry and Molecular Biology”, Munich, Germany, 17–20 May 2002. ∗ Corresponding author. Tel.: +44-207-886-1738; fax: +44-207-886-1790. E-mail address: m.reed@ic.ac.uk (M.J. Reed). When they no longer respond to chemotherapeutic cytotoxic agents, there is currently little therapeutic alternative avail- able. More than three quarters of patients with metastatic breast cancers die within 5 years of diagnosis [2]. Discovery of new therapeutic regimens for such patients is, therefore, most urgently required. In order to identify novel therapeutic candidates for ad- vanced breast cancer, 2-methoxyoestradiol-bis-sulphamate (2-MeOE2bisMATE) and 2-ethyloestradiol-bis-sulphamate (2-EtE2bisMATE) were investigated in comparison with the human endogenous metabolite 2-methoxyoestradiol (2-MeOE2) (Fig. 1). Previously, 2-MeOE2 has been shown to inhibit the growth of breast cancer cell lines in vitro [3,4] and it has been suggested that this metabolite may be an endogenous inhibitor of breast cancer [5]. The sulphamoylated oestrogen derivatives were initially de- veloped as steroid sulphatase inhibitors but it became apparent that they also inhibited cell proliferation. They induce a mitotic arrest and apoptosis in cells which is thought to result from their anti-microtubule activity [4]. 0960-0760/03/$ – see front matter © 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0960-0760(03)00035-9