WO2007109852A1

WO2007109852A1 - Selenium for treatment of cancer

Info

Publication number: WO2007109852A1
Application number: PCT/AU2007/000392
Authority: WO
Inventors: Christopher Hovens; Anthony Costello; Niall Corcoran
Original assignee: Velacor Therapeutics Pty Ltd
Priority date: 2006-03-29
Filing date: 2007-03-29
Publication date: 2007-10-04

Abstract

This invention relates to the use of selenium in biologically available form, in nutritional or supranutritional amounts, in methods of inhibiting the growth or proliferation of tumor cells. In particular, the present invention relates to the use of selenium in biologically available form, in combination with hormone ablation therapy for inhibiting the growth or proliferation of hormone dependent tumor cells. Methods of treating or preventing cancer, especially hormone dependent cancers are also described.

Description

"SELENIUM FOR TREATMENT OF CANCER"

FIELD OF THE INVENTION

[0001] This invention relates generally to the use of selenium in a biologically available form, especially in supranutritional amounts, in methods and compositions for inhibiting the growth or proliferation of tumor cells. In particular, the present invention relates to the use of selenium in a biologically available form, in combination with hormone ablation therapy, and optionally a cytostatic agent or cytotoxic agent or radiotherapy, for inhibiting the growth or proliferation of hormone-dependent tumor cells. In certain embodiments, the methods of the invention are useful for treating or preventing cancers, especially hormone dependent cancers, such as prostate cancer.

BACKGROUND OF THE INVENTION

[0002] There has been much interest in the use of selenium compounds as cancer- preventive agents. Studies spanning the last 20 years have documented their cancer-preventive action in tumors of the mammary gland (Ip, C. 1981, Cancer Res. 41:4386-4390), colon (Reddy et al. 1981, Cancer Res. 47:5901-5904), lung and prostate (Clark et al. 1996, Jama 276:1957- 1963). Both phase II and III clinical trials for prostate cancer prevention using an organic selenomethionine are currently underway (Nelson et al. 1999, Semin. Urol. Oncol. 17(2):91-6).

[0003] Selenium compounds used in chemoprevention studies can broadly be classified into inorganic and organic selenium forms. A typical form of inorganic selenium is sodium selenite, (Na₂SeU₃). The typical organic selenium entity, selenomethionine (SeMet) is relatively non-toxic and non-DNA-damaging (Lu et al. 1995, Biochem. Pharmacol. 50(2):213-9; Sinha ef α/. 1996, Cancer Lett. 107(2):277-84; Stewart et al. 1999, Free Radic. Biol. Med 26(l-2):42-8). [0004] Organic selenomethionine, the major constituent of dietary selenium, is incorporated into cellular selenoproteins, such as thioredoxin reductase and glutathione peroxidase via a series of complex intermediates (Allan et al. 1999, Annu. Rev. Nutr. 19:1-16). Since these selenocysteine-containing selenoenzymes, such as the antioxidant glutathionine peroxidase and the redox-regulatory thioredoxins, are involved in cellular responses to mutagenic oxidative stress, it has long been proposed that supranutritional levels of selenium intake boosts anticarcinogenic cellular activity by promoting a cellular reducing environment (Allan et al. 1999, supra).

[0005] Prostate cancer is a prevalent cancer in human males and treatment of patients with advanced prostate carcinoma growth typically involves medical or surgical castration (Huggins, C. and Hodges, CV. 1941, Cancer Res. 1:293-297). Up to 80% of patients demonstrate a temporary response lasting a median of 12-18 months, before continued tumor growth is evident despite castrate levels of testosterone (Petrylak, D.P. 1999, Urology 54:30- 35). Once androgen-independent growth is established, median life expectancy is 9-12 months. While traditional chemotherapy, such as palliative treatment with prednisolone or mitoxantrone, can improve pain scores and augment quality of life, at the present time, only taxanes such as docetaxel have been shown to extend life expectancy, by approximately 2 months (Tannack et al, 2004, N. Engl. J. Med., 351(15):1502-12, Petrylak et al, 2004, N. Engl. J. Med, 351(15):1513-20). [0006] Interest in the clinical use of selenium-containing compounds as a chemopreventive agent has become widespread following the publication of Clark et al. (1996, supra). These results have spurred a number of human clinical trials using supranutritional selenomethionine as a chemopreventive agent for prostate cancer (Meuillet et al. 2004, J. Cell Biochem. 91 :443-458). However, given the relatively short intervention time compared to the long natural history of prostate cancer, it is possible that rather than preventing the transformation of normal prostate epitheliato neoplasia, selenium more likely inhibits the growth of malignant cells (Corcoran et al. 2004, J. Urol. 171:907-910).

SUMMARY OF THE INVENTION

[0007] The present invention is predicated in part on the discovery that selenium in a biologically available form in combination with hormone ablation therapy has significantly beneficial effects on treatment of hormone-dependent tumor cells, especially when used at high or supranutritional amounts. It has also been found that selenium in a biologically available form, has an inhibitory effect on hormone-dependent tumor cells, especially prostate tumor cells and has a strong synergistic inhibitory effect on tumor cell growth when used in combination with hormone ablation therapy and optionally at least one of a cytostatic agent, a cytotoxic agent and a radiotherapy that is optionally administered with a radiosensitizing agent.

[0008] Accordingly, in one aspect, the present invention provides methods for treating a hormone-dependent cancer in a subject, comprising administering a therapeutically effective amount of selenium in a biologically available form, in combination with a hormone ablation therapy; with the proviso that the selenium in a biologically available form is not selenate or a pharmaceutically acceptable salt thereof. The hormone-dependent cancers are suitably selected from androgen-dependent cancers and estrogen-dependent cancer. In certain embodiments, the hormone-dependent cancer is an androgen-dependent cancer such as prostate cancer. In some embodiments, the hormone-dependent cancer is selected from prostate cancer, breast cancer, ovarian cancer, uterine cancer, endometrial cancer and thyroid cancer. [0009] In a further aspect, the present invention provides a method for inhibiting hormone-dependent growth of tumor cells, comprising exposing the tumor cells to a hormone- dependent tumor cell growth-inhibiting amount of selenium in a biologically available form, and a hormone ablation therapy; with the proviso that the selenium in a biologically available form is not selenate or a pharmaceutically acceptable salt thereof.

[0010] In yet a further aspect, the present invention provides a use of selenium in a biologically available form, in the manufacture of a medicament for treating a hormone- dependent cancer, wherein selenium in a biologically available form is formulated for administration in combination with hormone ablation therapy with the proviso that the selenium in a biologically available form is not selenate or a pharmaceutically acceptable salt thereof.

[0011] In still another aspect, the present invention provides pharmaceutical compositions for treating or preventing cancer. The compositions generally comprise a supranutritional amount of selenium in a biologically available form and an agent suitable for use in hormone ablation therapy and a pharmaceutically acceptable carrier. [0012] In some embodiments of the methods and uses broadly described above, the selenium in a biologically available form and hormone ablation therapy are administered in combination with at least one of a cytostatic agent, a cytotoxic agent or a radiotherapy that is optionally administered with a radiosensitizing agent. In other embodiments, the selenium in a biologically available form is formulated in a composition with an agent for hormone ablation therapy, and/or at least one cytostatic agent or cytotoxic agent. In still other embodiments, the selenium in a biologically available form is formulated in a composition with a radiosensitizing agent for use in combination with radiotherapy.

BRIEF DESCRIPTION OF THE FIGURES [0013] Figure 1 graphically represents the proliferative effect of selenium compounds, sodium selenite (Al and A2), seleno-L-methionine (Bl and B2), Se-(methyl)- selenocysteine (Cl and C2) and seleno-DL-cysteine (Dl and D2), on human prostate tumor cell line LnCaP, measured in the presence of normal serum after 4 days treatment in culture. Graphs A-D(I) show the effect of each compound expressed as the mean of calcein positive cells with standard deviation of six replicates per concentration, at 99% CI (p<0.001, ANOVA). Graphs A-D(2) show the effect of each compound normalized to control (5% NS).

[0014] Figure 2 graphically represents the proliferative effect of selenium compounds, sodium selenite (Al and A2), seleno-L-methionine (Bl and B2), Se-(methyl)- selenocysteine (Cl and C2) and seleno-DL-cysteine (Dl and D2), on human prostate tumor cell line LnCaP, measured in the presence of charcoal strip serum after 4 days treatment in culture. Graphs A-D(I) show the effect of each compound expressed as the mean of calcein positive cells with standard deviation of six replicates per concentration, at 99% CI (p<0.001, ANOVA). Graphs A-D(2) show the effect of each compound normalized to control (5% NS).

[0015] Figure 3 graphically represents the proliferative effect of selenium compounds, sodium selenite (Al and A2), seleno-L-methionine (Bl and B2), Se-(methyl)- selenocysteine (Cl and C2) and seleno-DL-cysteine (Dl and D2), on human breast tumor cell MCF-7, measured in the presence of normal serum after 4 days treatment in culture. Graphs A-D(I) show the effect of each compound expressed as the mean of calcein positive cells with standard deviation of six replicates per concentration, at 99% CI (p<0.001, ANOVA). Graphs A-D(2) show the effect of each compound normalized to control (5% NS).

[0016] Figure 4 graphically represents the proliferative effect of selenium compounds, sodium selenite (Al and A2), seleno-L-methionine (Bl and B2), Se-(methyl)- selenocysteine (Cl and C2) and seleno-DL-cysteine (Dl and D2), on human breast tumor cell MCF-7, measured in the presence of charcoal strip serum after 4 days treatment in culture. Graphs A-D(I) show the effect of each compound expressed as the mean of calcein positive cells with standard deviation of six replicates per concentration, at 99% CI (p<0.001, ANOVA). Graphs A-D(2) show the effect of each compound normalized to control (5% NS).

DETAILED DESCRIPTION OF THE INVENTION

1. Definitions [0017] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred methods and materials are described. For the purposes of the present invention, the following terms are defined below.

[0018] The articles "a" and "an" are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0019] As used herein, the term "about" refers to a quantity, level, value, dimension, size, or amount that varies by as much as 30%, 20%, or 10% to a reference quantity, level, value, dimension, size, or amount.

[0020] By "androgen" is meant a hormone that encourages the development of male sexual characteristics. Non-limiting examples of androgens include testosterone, androstenedione, dihydroepiandrosterone and dihydrotestosterone. [0021] The term "androgen-dependent cancer" or "androgen-dependent tumor cell" refers to a cancer or tumor cell that depends on an androgen for cell survival, growth and/or proliferation. Typically, an "androgen-dependent cancer" results from excessive accumulation of an androgen (e.g., testosterone or other androgenic hormone), increased sensitivity of androgen receptors to androgen, or an increase in androgen-stimulated transcription, and will generally benefit from a decrease in androgen stimulation.

[0022] The term "androgen-independent cancer" or "androgen-independent tumor cell" refers to a cancer or tumor cell which is insensitive to the presence or absence of androgens. [0023] The term "carcinoma" as used herein refers to a form of cancer which develops in epithelial cells covering or lining organs such as the uterus, the breast or the prostate. Carcinomas may, but do not necessarily, directly invade nearby organs or may metastasize to distant sites such as liver, lymph nodes or bones.

[0024] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and

"comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0025] As used herein the term "cytostatic agent" refers to a substance that can inhibit cell proliferation or cell division without necessarily killing the cell. Suitably, the cytostatic agent inhibits the proliferation of cancer cells.

[0026] The term "cytotoxic agent" or "cytotoxic therapy" as used herein refers to a substance or therapy that is harmful to cells and ultimately causes cell death. In some embodiments, the cytotoxic agent harms rapidly dividing cells such as cancer cells and causes cancer cell death, especially cancer cell death while not causing damage to or causing less damage to non-cancer cells. An example of a cytotoxic therapy is radiotherapy.

[0027] As used herein the terms "drug resistant" and "refractory" refer to a cancer or tumor cell which is unresponsive or partially unresponsive to treatments normally used to treat the cancer or kill the tumor cell.

[0028] As used herein, the term "estrogen-dependent cancer" or "estrogen-dependent tumor cell" refers to a cancer or tumor cell that depends on estrogen for survival, growth and/or proliferation. Typically, an "estrogen-dependent cancer" results from excessive accumulation of estrogen, increased sensitivity of estrogen receptors to estrogen or an increase in estrogen-stimulated transcription, and will generally benefit from a decrease in estrogen stimulation. [0029] The terms "hormone ablation" and "hormone ablation therapy" refer to the deprivation of hormones that may be required for the survival and growth of cancer cells. Hormone ablation may be achieved by surgical removal of hormone-producing organs such as testes or ovaries or may be achieved chemically with compounds that interfere with hormone biosynthesis or secretion, compounds that antagonize or block hormone receptors or in some way prevent a hormone exerting its biological effect. For example, the conversion of testosterone to the more active dihydrotestosterone may be blocked by a 5-alpha reductase inhibitor such as finasteride. An "agent for hormone ablation therapy" refers to compounds that interfere with hormone biosynthesis or secretion, antagonize or block hormone receptors or in some way prevent a hormone exerting its biological effect.

[0030] The term "hormone-dependent cancer" or "hormone-dependent tumor cell" refers to a cancer or tumor cell which depends on the presence of a hormone for survival, growth and/or proliferation. Hormone-dependent cancers include but are not limited to, prostate cancer, breast cancer, ovarian cancer, uterine cancer, endometrial cancer and thyroid cancer. [0031] As used herein, the term "hormone-dependent tumor cell growth-inhibiting amount" in the context of treating or preventing a cancer or inhibiting the growth of tumor cells is meant the administration of an amount or series of doses of selenium in a biologically available form, which is effective in inhibiting the growth and/or proliferation of cancer or tumor cells or for causing tumor cell death. The amount will vary depending on the health and physical condition of the individual to be treated, the taxonomic group of the individual to be treated, the formulation of the composition, the assessment of the medical situation, and other relevant factors. It is expected that the amount will fall within a relatively broad range that can be determined by routine trials. In some embodiments, a hormone-dependent tumor cell growth- inhibiting amount is a nutritional amount. In some embodiments, the hormone-dependent tumor cell growth-inhibiting amount is a supranutritional amount of selenium in a biologically available form.

[0032] As used herein the term "in combination with" refers to the treatment of cancer or exposure of a tumor cell to at least two therapies such that their effects on the cancer or tumor cell occur, at least in part, over the same time "period. For example, administration of at least two agents may occur simultaneously in a single composition, or each agent may be simultaneously or sequentially administered in separate compositions. The two agents may be the selenium in biologically available form and an agent for hormone ablation therapy. These agents may also be administered in combination with a cytotoxic agent or cytostatic agent. Alternatively, the two therapies may include at least one agent and a second therapy such as surgery, e.g. surgical castration or tumorectomy, or radiotherapy optionally together with a radiosensitizing agent. [0033] The phrase "inhibiting growth of tumor cells" is taken to mean that tumor cell growth is ceased or reduced cell proliferation or cell division is ceased or reduced and the differentiation of normal cells into cancer cells is ceased or reduced. This is also known as cytostasis. The growth of tumor cells can be measured in terms of weight or volume or cell number or cellular metabolic activity, i.e. MTT assay.

[0034] As used herein, the term "nutritional amount" includes an amount that provides an average daily intake. In the US, the average daily intake of selenium is 80-100 μg/kg per day.

[0035] By "pharmaceutically acceptable carrier" it is meant a solid or liquid filler, diluent or encapsulating substance that may be safely used in topical, local or systemic administration.

[0036] The term "pharmaceutically acceptable salt" as used herein in relation to selenium in biologically available form refers to salts which are toxicologically safe for human and animal administration. For example, suitable pharmaceutically acceptable salts include, but are not limited to, salts of pharmaceutically acceptable inorganic acids such as hydrochloric, sulphuric, phosphoric, nitric, carbonic, boric, sulfamic, and hydrobromic acids, or salts of pharmaceutically acceptable organic acids such as acetic, propionic, butyric, tartaric, maleic, hydroxymaleic, fumaric, maleic, citric, lactic, mucic, gluconic, benzoic, succinic, oxalic, phenylacetic, methanesulphonic, toluenesulphonic, benezenesulphonic, salicyclic sulphanilic, aspartic, glutamic, edetic, stearic, palmitic, oleic, lauric, pantothenic, tannic, ascorbic and valeric acids.

[0037] Base salts include, but are not limited to, those formed with pharmaceutically acceptable cations, such as sodium, potassium, lithium, calcium, magnesium, iron, nickel, zinc, ammonium and alkylammonium. [0038] Basic nitrogen-containing groups may be quarternised with such agents as lower alkyl halide, such as methyl, ethyl, propyl and butyl chlorides, bromides and iodides; dialkyl sulfates like dimethyl and diethyl sulfate; and others.

[0039] The term "radiotherapy" as used herein refers to the treatment or exposure of a cancer or cancer cells such as tumor cells to high energy radiation. The effectiveness of radiotherapy may be enhanced by selenium in a biologically available form. Furthermore, radiotherapy may be further enhanced by administration of radiosensitizing agent. Illustrative examples of radiosensitizing agents include but are not limited to efaproxiral, etanidazole, fluosol, misonidazole, nimorazole, temoporfϊn and tirapazamine.

[0040] The term "selenium in biologically available form" refers to forms of selenium that provide selenium that can be absorbed by the tumor cells of a hormone-dependent cancer. The selenium may be in organic or inorganic form. Examples of suitable forms of selenium include selenite and pharmaceutically acceptable salts thereof, selenized yeast and organic selenium compounds selected from selenocysteine, methylselenocysteine, selenomethionine and pharmaceutically acceptable salts thereof. [0041] The terms "subject" or "individual" or "patient", used interchangeably herein, refer to any subject, particularly a vertebrate subject and more particularly a mammalian subject, for whom prophylaxis or treatment is desired. Suitable vertebrate animals that fall within the scope of the invention include, but are not limited to, primates, avians, livestock animals (e.g., pigs, sheep, cows, horses, donkeys), laboratory test animals (e.g., rabbits, mice, rats, guinea pigs, hamsters), companion animals (e.g., cats and dogs) and captive wild animals (e.g., foxes, deer, dingoes). A preferred subject is a human in need of treatment or prophylaxis of a hormone-dependent cancer, especially prostate cancer. However, it will be understood that the aforementioned terms do not imply that symptoms are present.

[0042] The term "supranutritional" as used herein, refers to an amount which is greater than the amount considered as a nutritional requirement. In the US, the average daily intake of selenium is 80-120 μg/day. A supranutritional amount of selenium provides selenium to a subject at above the recommended daily allowance. For example, a supranutritional amount of selenium may be 3.0 μg/kg to 20.0 mg/kg, 0.015 mg/kg to 20.0 mg/kg, 0.15 mg/kg to 20.0 mg/kg, 0.1 mg/kg to 14 mg/kg, 0.1 mg/kg to 13 mg/kg, 0.1 mg/kg to 12 mg/kg, 0.1 mg/kg to 10 mg/kg, 0.1 mg/kg to 9 mg/kg, 0.1 mg/kg to 8 mg/kg, 0.1 mg/kg to 7 mg/kg, 0.1 mg/kg to 6 mg/kg, 0.15 mg/kg to 5 mg/kg, 0.15 mg/kg to 4 mg/kg, 0.15 mg/kg to 3 mg/kg, 0.15 mg/kg to 2 mg/kg, 0.15 mg/kg to 1 mg/kg per day, especially 0.07 mg/kg to 6.5 mg/kg, 0.1 mg/kg to 14 mg/kg or 0.15 mg/kg to 5 mg/kg per day, more especially 0.07 mg/kg to 2 mg/kg per day.

[0043] As used herein, the term "therapeutically effective amount" in the context of treating or preventing cancer or inhibiting the growth of hormone-dependent tumor cells is meant the administration of an amount of selenium in a biologically available form, either in a single dose or as part of a series of doses, that is effective for inhibiting the growth and/or proliferation of cancer or tumor cells or for causing cancer or tumor cell death. The effective amount will vary depending on the health and physical condition of the individual to be treated, the taxonomic group of the individual to be treated, and the formulation of the composition, the assessment of the medical situations and other relevant factors. It is expected that the amount will fall within a relatively broad range that can be determined through routine trials. In some embodiments, the therapeutic effective amount is a nutritional amount. In specific embodiments, a therapeutically effective amount is a supranutritional amount. 2. Methods for inhibiting tumor cell growth and proliferation and for treating cancer

[0044] The present invention is predicated in part on the determination that selenium in a biologically available form, is effective in inhibiting the growth or proliferation of tumor cells in hormone-dependent cancers when used in combination with hormone ablation therapy. Suitably, the amount of selenium in a biologically available form, is in a nutritional amount or a supranutritional amount. A supranutritional amount is generally from about 0.015 mg/kg to 20.0 mg/kg, usually from about 0.07 mg/kg to 6.5 mg/kg per day, 0.1 m/kg to 14 mg/kg or 0.15 mg/kg to 5 mg/kg, especially 0.07 mg/kg to 2 mg/kg per day.

[0045] The hormone ablation therapy may be any therapy that deprives the cancer or tumor cells of hormones required for cancer or tumor cell survival, growth and/or proliferation. Hormone ablation therapy may be achieved surgically by removal of hormone- producing organs such as testes or ovaries. Alternatively, the hormone ablation therapy may be achieved chemically with compounds that interfere with hormone biosynthesis or secretion, compounds that antagonize or block hormone receptors or in some way prevent the hormone exerting its biological effect. Illustrative agents for chemical hormone ablation therapy include GnRH agonists or antagonists such as Cetrorelix, agents that interfere with the androgen receptor including non-steroidal agents such as Bicalutamide and steroidal agents such as Cyproterone, and agents that interfere with steroid biosynthesis such as Ketoconazole. Chemical agents suitable for use in combination with selenium in biologically available form as hormone ablation therapy for prostate cancer include, but are not limited to, non-steroidal anti-androgens such as Nilutamide, Bicalutamide and flutamide; GnRH agonists such as Goserelin acetate, leuprorelin and triptorelin; 5-alpha reductase inhibitors such as finasteride; and cyproterone acetate. Chemical agents suitable for use in combination with selenium in biologically available form as hormone ablation therapy in breast cancer include but are not limited to aromatase inhibitors such as Anastrozole; Exemestane, Letrozole and Aminoglutethimide; and anti- estrogen compounds such as Tamoxifen, Toremifϊne citrate, Megestrol acetate and Goserelin acetate. Chemical agents suitable for use in combination with selenium in biologically available form as hormone ablation therapy in ovarian and uterine cancers, including endometrial cancer, include but are not limited to, progestins such as Megestrol acetate, levonorgestrol and norgestrol.

[0046] When the hormone ablation therapy is an agent suitable for such therapy, it is administered in an amount capable of depriving the cancer or tumor cell of the effect of the hormone that it depends on. These agents may be administered in amounts normally used for hormone ablation therapy in the absence of selenium. Alternatively, these agents may be administered in lower amounts than normally used when their activity is enhanced by the selenium in biologically available form. In some embodiments, the amount of selenium in biologically available form and the amount of hormone ablation therapy provide a synergistic effect.

[0047] In certain embodiments, the selenium in a biologically available form is administered in combination with a hormone ablation therapy and at least one cytostatic agent or cytotoxic agent. Non-limiting examples of cytostatic agents are selected from: (1) microtubule-stabilizing agents such as but not limited to taxanes, paclitaxel, docetaxel, epothilones and laulimalides; (2) kinase inhibitors, illustrative examples of which include Iressa®, Gleevec, Tarceva™, (Erlotinib HCl), BAY-43-9006, inhibitors of the split kinase domain receptor tyrosine kinase subgroup (e.g., PTK787/ZK 222584 and SUl 1248); (3) receptor kinase targeted antibodies, which include, but are not limited to, Trastuzumab (Herceptin®), Cetuximab (Erbitux®), Bevacizumab (Avastin™), Rituximab (ritusan®), Pertuzumab (Omnitarg™); (4) mTOR pathway inhibitors, illustrative examples of which include rapamycin and CCI-778; (5) Apo2L/Trail, anti-angiogenic agents such as but not limited to endostatin, combrestatin, angiostatin, thrombospondin and vascular endothelial growth inhibitor (VEGI); (6) antineoplastic immunotherapy vaccines, representative examples of which include activated T-cells, non-specific immune boosting agents (i.e., interferons, interleukins); (7) antibiotic cytotoxic agents such as but not limited to doxorubicin, bleomycin, dactinomycin, daunorubicin, epirubicin, mitomycin and mitozantrone; (8) alkylating agents, illustrative examples of which include Melphalan, Carmustine, Lomustine, Cyclophosphamide, Ifosfamide, Chlorambucil, Fotemustine, Busulfan, Temozolomide and Thiotepa; (9) hormonal antineoplastic agents, non-limiting examples of which include Nilutamide, Cyproterone acetate, Anastrozole, Exemestane, Tamoxifen, Raloxifene, Bicalutamide, Aminoglutethimide, Leuprorelin acetate, Toremifene citrate, Letrozole, Flutamide, Megestrol acetate and Goserelin acetate; (10) gonadal hormones such as but not limited to Cyproterone acetate and Medoxyprogesterone acetate; (11) antimetabolites, illustrative examples of which include

Cytarabine, Fluorouracil, Gemcitabine, Topotecan, Hydroxyurea, Thioguanine, Methotrexate, Colaspase, Raltitrexed and Capicitabine; (12) anabolic agents, such as but not limited to, Nandrolone; (13) adrenal steroid hormones, illustrative examples of which include Methylprednisolone acetate, Dexamethasone, Hydrocortisone, Prednisolone and Prednisone; (14) neoplastic agents such as but not limited to Mnotecan, Carboplatin, Cisplatin, Oxaliplatin, Etoposide and Dacarbazine; and (15) topoisomerase inhibitors, illustrative examples of which include topotecan and irinotecan.

[0048] In some embodiments, the cytostatic agent is a nucleic acid molecule, suitably an antisense or siRNA recombinant nucleic acid molecule. In other embodiments, the cytostatic agent is a peptide or polypeptide. In still other embodiments, the cytostatic agent is small molecule. The cytostatic agent may be a cytotoxic agent that is suitably modified to enhance uptake or delivery of the agent. Non-limiting examples of such modified cytotoxic agents include, but are not limited to, pegylated or albumin-labelled cytotoxic drugs.

[0049] In specific embodiments, the cytostatic agent is a microtubule stabilizing agent, especially a taxane and preferably paclitaxel. [0050] In some embodiments, the cytotoxic agent is selected from the anthracyclines such as idarubicin, doxorubicin, epirubicin, daunorubicin and mitozantrone, CMF agents such as cyclophosphamide, methotrexate and 5-fluorouracil or other cytotoxic agents such as cisplatin, carboplatin, bleomycin, topotecan, irinotecan, melphalan, chlorambucil, vincristine, vinblastine and mitomycin-C. [0051] Therapeutically effective amounts of cytostatic agents and cytotoxic agents may be those that would normally be used in the absence of selenium. Alternatively, the therapeutically effective amount of the cytotoxic agent or cytostatic agent is lower than used in the absence of the combination of selenium and hormone ablation therapy.

[0052] In some embodiments, the hormone-dependent cancer is selected from prostate cancer, breast cancer, ovarian cancer, endometrial cancer, uterine cancer or thyroid cancer, especially prostate cancer or breast cancer.

[0053] Certain embodiments of the present invention are directed to methods for treating hormone-dependent cancer in a subject, which methods generally comprise administering to the subject a therapeutically effective amount of selenium in a biologically available form together with a hormone ablation therapy. To practice these methods, the person managing the subject can determine the effective dosage form of selenium in a biologically available form for the particular condition and circumstances of the subject. A therapeutically effective amount of selenium in a biologically available form is one that is effective for the treatment or prevention of the hormone-dependent cancer, including the prevention of incurring a symptom (e.g., proliferation of cancer cells), holding in check such symptoms, and/or treating existing symptoms associated with the cancer (e.g., pain, fluid build-up, urinary retention, nausea, indigestion, gas, appetite, changes in bowel habits and weight loss). In some embodiments, the therapeutically effective amount is a supranutritional amount of selenium in a biologically available form. [0054] Modes of administration, amounts of selenium in a biologically available form administered, and selenium formulations, for use in the methods of the present invention, are discussed below. Whether the cancer has been treated is determined by measuring one or more diagnostic parameters indicative of the course of the disease, compared to a suitable control. In the case of a human subject, a "suitable control" may be the individual before treatment, or may be a human (e.g., an age-matched or similar control) treated with a placebo. In accordance with the present invention, the treatment of cancer includes and encompasses without limitation: (i) preventing cancer in a subject who may be predisposed to the cancer but has not yet been diagnosed with the cancer and, accordingly, the treatment constitutes prophylactic treatment for the cancer; (ii) inhibiting tumorigenesis, i.e., arresting the development of hormone-dependent cancer; or (iii) relieving symptoms resulting from the hormone-dependent cancer.

[0055] The methods of the present invention are suitable for treating an individual who has been diagnosed with a hormone-dependent cancer, who is suspected of having a cancer, who is known to be susceptible and who is considered likely to develop a cancer, or who is considered likely to develop a recurrence of a previously treated cancer.

[0056] In preferred embodiments, the hormone-dependent cancer is prostate cancer and the hormone ablation therapy is selected from surgical castration, fϊnesteride, Nilutamide, Cyproterone acetate, Bicolutamide, Leuprorelin acetate, Flutamide and Goserelin acetate. In other preferred embodiments, the hormone-dependent cancer is breast cancer and the hormone ablation therapy is selected from Anastrozole; Exemestane, Tamoxifen, Aminoglutethimide, Toremifene citrate, Letrozole, Megestrol acetate and Goserelin acetate. In still other preferred embodiments, the hormone-dependent cancer is ovarian, uterine or endometrial cancer and the hormone ablation therapy is selected from progestins such as megestrol acetate, levinorgestrol and norgestrol. In some embodiments, the therapy further comprises a cytostatic agent, particularly a microtubule stabilizing agent, especially a taxane, more especially paclitaxel.

[0057] Exemplary subjects for treatment with the methods of the invention are vertebrates, especially mammals. In certain embodiments, the subject is selected from the group consisting of humans, sheep, cattle, horses, bovine, pigs, dogs and cats. A preferred subject is a human. [0058] The selenium in a biologically available form may be formulated by following any number of techniques known in the art of anticancer drug delivery. Selenium in a biologically available form may of course be administered by a number of means keeping in mind that all formulations are not suitable for every route of administration. Selenium in a biologically available form can be administered in solid or liquid form. The application may be oral, rectal, nasal, topical (including buccal and sublingual), or by inhalation. Selenium in a biologically available form may be administered together with conventional pharmaceutical acceptable adjuvant, carriers and/or diluents.

[0059] The solid forms of application comprise tablets, capsules, powders, pills, pastilles, suppositories and granular forms of administration. They may also include carriers or additives, such as flavors, dyes, diluents, softeners, binders, preservatives, lasting agents and/or enclosing materials. Liquid forms of administration include solutions, suspensions and emulsions. These may also be offered together with the above-mentioned additives.

[0060] Solutions and suspensions of selenium in a biologically available form, assuming a suitable viscosity for ease of use, may be injected. Suspensions too viscous for injection may be implanted using devices designed for such purposes, if necessary. Sustained release forms are generally administered via parenteral or enteric means. Parenteral administration is another route of administration of the selenate or a pharmaceutically acceptable salt thereof used to practice the invention. "Parenteral" includes formulations suitable for injection and for nasal, vaginal, rectal, and buccal administration. [0061] The administration of selenium in a biologically available form may involve an oral prolonged dose formulation. Oral dose formulations are preferably administered once daily to three times daily in the form of a sustained release capsule or tablet, or alternatively as an aqueous based solution. Selenium in a biologically available form may be administered intravenously either daily, continuously, once a week or three times a week. [0062] The administration of selenium in a biologically available form may include daily administration, preferably once daily in the form of a sustained release capsule or tablet, or once daily as an aqueous solution.

[0063] Combinations of selenium in a biologically available form, an agent for hormone ablation therapy and/or at least one cytostatic agent or a cytotoxic agent may be administered in solid or liquid form in a single formulation or composition or in separate formulations or compositions. In some embodiments, the selenium in a biologically available form, the agent for hormone ablation therapy and/or the cytostatic agent(s) or cytotoxic agent(s) are administered orally as a single tablet or capsule or separate tablets or capsules. In other embodiments, the selenium in a biologically available form, the agent for hormone ablation therapy and/or the cytostatic agent(s) or cytotoxic agent(s), are administered intravenously in a single composition or separate compositions.

[0064] The methods of the present invention may be employed in combination with other known treatments for cancer, for instance but not limited to, surgery, chemotherapy and radiotherapy. In some embodiments, the selenium in a biologically available form is used in combination with radiotherapies, such as but not limited to, conformal external beam radiotherapy (50-100 Grey given as fractions over 4-8 weeks), either single shot or fractionated, high dose rate brachytherapy, permanent interstitial brachytherapy, systemic radio-isotopes (e.g., Strontium 89). In some embodiments the radiotherapy may be administered in combination with a radiosensitizing agent. Illustrative examples of radiosensitizing agents include but are not limited to efaproxiral, etanidazole, fluosol, misonidazole, nimorazole, temoporfin and tirapazamine. In other embodiments, selenium in a biologically available form and hormone ablation therapy are used in combination with a tumorectomy, for example as an adjuvant therapy.

[0065] The present invention also provides pharmaceutical compositions for treating or preventing hormone dependent cancer, generally comprising a supranutritional amount, suitably from about 0.5 mg to about 1.0 g or 5 mg to 450 mg of selenium in a biologically available form and a pharmaceutically acceptable carrier. In some embodiments, the selenium in a biologically available form is in an amount of about 5.0 mg to about 700 mg, especially 5 mg to 450 mg. In illustrative examples, the selenium in a biologically available form is an amount of about 1.6 mg to 450 mg, 5 mg to 450 mg or 7.5 mg to 250 mg, especially 50 mg to 200 mg, for example, 50 to 100 mg or 100 to 150 mg for a single or divided daily dose.

[0066] In some embodiments, the pharmaceutical compositions further comprise at least one cytostatic agent or cytotoxic agent. In other embodiments, the pharmaceutical compositions further comprise a chemical hormone ablation agent. In still other embodiments, the pharmaceutical compositions further comprise at least one cytostatic agent and/or a cytotoxic agent and a chemical hormone ablation agent. In still other embodiments, the pharmaceutical compositions may further comprise a radiosensitizing agent for use with radiotherapy.

[0067] The pharmaceutical composition of the present invention may include any additional components that are non-immunogenic and biocompatible with selenium, as well as capable of bioabsorption, biodegradation, elimination as an intact molecule. The formulation may be supplied in a ready-to-use form or may be supplied as a sterile powder or liquid requiring vehicle addition prior to administration. If sterility is desired, the formulation may be made under sterile conditions, the individual components of the mixture may be sterile, or the formulation may be sterile filtered prior to use. Such a solution can also contain appropriate pharmaceutically acceptable carriers, such as but not limited to buffers, salts, excipients, preservatives, etc.

[0068] In some embodiments, sustained release oral formulations are used for administering selenium in a biologically available form in the methods of the invention. These formulations generally comprise selenium in a biologically available form having decreased solubility in order to delay absorption into the bloodstream. In addition, these formulations may include other components, agents, carriers, etc., which may also serve to delay absorption of the selenium in a biologically available form. Microencapsulation, polymeric entrapment systems, and osmotic pumps, which may or may not be bioerodible, may also be used to allow delayed or controlled diffusion of the selenium in a biologically available form from a capsule or matrix. [0069] The selenium in a biologically available form can be used solus or as part of another agent. Accordingly, the present invention also contemplates an agent that comprises selenium in a biologically available form for the treatment of a hormone-dependent cancer in which the agent is formulated for administration in combination with hormone ablation therapy.

[0070] In order that the nature of the present invention may be more clearly understood and put into practical effect, particular preferred embodiments thereof will now be described with reference to the following non-limited examples.

EXAMPLES

EXAMPLE 1

[0071] 5x10⁴ human prostate cancer androgen sensitive LNCaP cells are seeded in a 6-weIl dish and 8 hours later are treated with 50μM sodium selenite, seleno-L-methionine, seleno-DL-cysteine, Se-(methyl)-selenocysteine, selenized yeast or not (control). Cells are harvested at 72 hours following addition of the compounds and cell counts of viable cells as assessed by Trypan Blue staining are determined.

EXAMPLE 2

[0072] 1 x 10⁵ human prostate cancer androgen sensitive NS LNCaP cells are seeded in a 6- well dish and 8 hours later are treated with either 5 μM sodium selenite, seleno-L- methionine, seleno-DL-cysteine, Se-(methyl)-selenocysteine, selenized yeast or lOuM LY294002. Cells are harvested at 72 hours following addition of the selenium compounds or Ly294002 and cell counts of viable cells as assessed by Trypan Blue staining are determined.

Materials And Methods

Cell Culture

[0073] The parental androgen-sensitive LNCaP cell line is obtained from the American Type Culture Collection (Manassas, Virginia, USA) and routinely cultured in RPMI 1641 (Invitrogen) supplemented with 10% foetal calf serum and 1% antibiotic/antimycotic mixture (Invitrogen). Cells are maintained at 37⁰C in 5% CO₂.

Selenium compounds

[0074] Selenium compounds are made up as 10 mM stock solutions in distilled water and filter sterilized before dilution in media for in vitro experiments. The PI3K inhibitor, LY294002 is dissolved in DMSO at 5OmM stock solution and diluted in cell culture media for in vitro experiments.

Cell growth curve

[0075] Between 5x10⁴ and 1 xl O⁵ LNCaP are allowed to attach overnight. After some hours the media is changed to include a selenium compound or LY294002 in the presence of normal serum and allowed to grow. Supernatants and cells are then harvested, combined and viable cells assessed by Trypan Blue exclusion assay. Experiments are performed in triplicate. Statistical analysis

[0076] Data may be presented as mean + SE. Differences between treatments and the control group are analyzed using pairwise t test with significance assumed at p < 0.05. Asterisks represent values significantly different from the corresponding control value. Statistical analysis is performed using SPSS 9.05 for Windows (SPSS, Chicago, Illinois) software.

EXAMPLE 3

Selenium compounds and hormone ablation therapy in LnCaP cells, a human hormone sensitive prostate cancer cell line

Materials and Methods

[0077] Cell Culture. Human prostate cancer cell line, LnCaP was obtained from American Type Tissue Collection (ATCC, Manassas, VA, USA) and was routinely cultured in growth medium containing phenol red RPMI 1640 (Invitrogen, Auckland, New Zealand) supplemented with 10% fetal bovine serum (FBS, GIBCO) and 1% antibiotic/antimycotic mixture (Invitrogen, Auckland, New Zealand). Cells were maintained at 37⁰C in 5% CO₂. Sodium selenite (S-5261), seleno-L-methionine (-3132), Se-(Methyl) selenocysteine (M-6680) and seleno-DL-cysteine (S-1650) were all purchased from Sigma (St Louis, MO, USA) were made up as 100 μM stock solutions in phenol-red RPMI 1640 (Invitrogen, Auckland, New Zealand) and serial dilutions were made for each selenium compound in either 5% FBS or 5% charcoal strip serum (CSS) (HyClone, South Logan, UT, USA) for in vitro experiments.

[0078] In Vitro - growth proliferation study. 5 x 10³ LnCaP cells were plated per well in a Falcon 96-well plate and were allowed to attach overnight at 5%CO₂/ 37⁰C in growth medium (as indicated above). The medium was replaced with fresh complete growth medium containing various concentrations (5, 20, 50 and 100 μM) of different selenium compounds (as indicated above) in RPMI medium supplemented either with 5%FBS (normal serum, NS) or 5%CSS. After 96 hours in culture, cells were washed once with PBS and labelled with calcein (C 1430, Molecular Probes, Oregon, USA) at 1 mM final concentration in PBS. Calcein positive cells were detected at 498 nm by using FLUOstar OPTIMA plate reader (BMG Labtech, Victoria, Australia). Experiments were performed in 6 replicates per compound concentrations for each concentration of selenium compound used in serum (containing NS) and serum-free (containing charcoal strip serum). [0079] Statistical analysis. Data are presented as mean + SD. unless otherwise indicated. Differences between treatment groups were analyzed using Fisher's least significant difference test with significance assumed at 99% confidence interval, for p<0.01, One- Way ANOVA. All statistical analysis was performed using STATGRAPFflCS statistical software (Virginia, USA). The proliferative effect of different selenium compounds in combination with either normal serum or charcoal strip serum were calculated according to the method of Romanelli S et al {Cancer Chemother. Pharmacol. 1998, 41(5):385-90).

[0080] Figure 1 graphically represents the effect of selenium compounds, sodium selenite (Al and A2), seleno-L-methionine (Bl and B2), Se-(methyl)-selenocysteine (Cl and C2) and seleno-DL-cysteine (Dl and D2) on the proliferation of androgen sensitive LnCaP cells grown in normal serum.

[0081] Figure 2 graphically represents the effect of selenium compounds, sodium selenite (Al and A2), seleno-L-methionine (Bl and B2), Se-(methyl)-selenocysteine (Cl and C2) and seleno-DL-cysteine (Dl and D2) on the proliferation of androgen sensitive LnCaP cells grown in charcoal stripped serum.

[0082] The results indicate that for hormone-sensitive prostate cancer LNCaP cells, the selenium co-treatment with hormone ablation therapy is able to synergistically reduce prostate cancer cell proliferation over either treatment alone. A synergy index value, known as the R index value, was calculated for each treatment using expected versus observed treatment responses, according to the method of Romanelli S et al {supra), enabling a quantitative analysis of potential synergistic combinations. The results are shown in Table 1.

Table 1. Proliferative effect of different selenium compounds in normal serum and charcoal strip serum on Lncap cell, after 4 days in culture.

C CO

m

C/)

I m , m s

Ti m

IO σ>

Ti O

(fi

C CO

(f)

m (ft m m O

Ti c r~ m

IO

O

Observed values: average of each compound/ control (normal serum) x 100% Expected values: product of each observed compound in NS with 5%CSS/ 100 Synergy: R>1 [0083] With this method R index values greater than or equal to one indicate that synergy has been observed.

[0084] Sodium selenite was able to synergize with hormone ablation therapy to reduce prostate cancer proliferation at all dose levels tested as assessed by the R index value, with R index values greater than one in all cases (sodium selenite 5 μM R=I .71 ; 20 μM 1.06; 50μM 6.41; lOOμM 1.78).

[0085] Selenomethionine was similarly able to synergize with hormone ablation therapy to reduce prostate cancer proliferation at most dose levels tested, as assessed by the R index value (selenomethionine 5 μM R=1.07; 50μM 1.17 and lOOμM 2.38).

[0086] Se-(methyl)-selenocysteine was able to synergize with hormone ablation therapy to reduce prostate cancer proliferation at a number of dose levels tested, as assessed by the R index value (Se-(methyl)-selenocysteine 20 μM R=I.79; 50μM 1.20).

EXAMPLE 4

Selenium compounds and hormone ablation therapy in MCF-7 cells, a human hormone sensitive breast cancer cell line

Materials and Methods

[0087] Cell Culture. Human breast adenocarcinoma (MCF-7) cell line was obtained from Dr Waltham (St Vincent Hospital, Victoria, Australia) and was routinely cultured in growth medium containing phenol red RPMI 1640 (Invitrogen, Auckland, New Zealand) supplemented with 10% fetal bovine serum (FBS, GIBCO) and 1% antibiotic/antimycotic mixture (Invitrogen, Auckland, New Zealand). Cells were maintained at 37⁰C in 5% CO₂. Sodium selenite (S-5261), seleno-L-methionine (-3132), Se-(Methyl) selenocysteine (M-6680) and seleno-DL-cysteine (S-1650) were all purchased from Sigma (St Louis, MO, USA) were made up as 100 μM stock solutions in phenol-red free RPMI 1640 (Invitrogen, Auckland, New Zealand) and serial dilutions were made for each selenium compound in either 5% FBS or 5% charcoal strip serum (CSS) (HyClone, South Logan, UT, USA) for in vitro experiments. [0088] In Vitro - growth proliferation study. 5 x 10³ MCF-7 cells were plated per well in a Falcon 96-well plate and were allowed to attach overnight at 5%CO₂/ 37⁰C in growth medium (as indicated above). The medium was replaced with fresh complete growth medium containing various concentrations (5, 20, 50 and 100 μM) of different selenium compounds (as indicated above) in either phenol-red or phenol-red free RPMI media supplemented either with 5%FBS or 5%CSS. Cells were washed once in PBS and labelled with calcein (C1430, Molecular Probes, Oregon, USA) after 4 days and 7 days in culture. Calcein was diluted in PBS to final concentration of 1 mM. Calcein positive cells were detected at 498 nm by using FLUOstar OPTIMA plate reader (BMG Labtech, Victoria, Australia). Phenol-red free RPMI was required to mimic hormone therapy for 'non-estrogen' condition. Experiments were performed in 6 replicates per compound concentrations for each concentration of selenium compound were used in normal serum and charcoal strip serum. The cells grown in normal serum (NS) mimic estrogen conditions and those grown in CSS mimic non-estrogen conditions (hormone ablation therapy). [0089] Statistical analysis. Data are presented as mean + SD. unless otherwise indicated. Differences between treatment groups were analyzed using Fisher's least significant difference test with significance assumed at 99% confidence interval, for p<0.01, One- Way ANOVA. All statistical analysis was performed using STATGRAPHICS statistical software (Virginia, USA). The proliferative effect of different selenium compounds in combination with either normal serum or charcoal strip serum were calculated according to the method of Romanelli S et al., {supra).

[0090] Figure 3 graphically represents the effect of selenium compounds, sodium selenite (Al and A2), seleno-L-methionine (Bl and B2), Se-(methyl)-selenocysteine (Cl an C2) and seleno-DL-cysteine (Dl and D2), on the proliferation of MCF-7 cells after 4 days treatment in the presence of normal serum (estrogenic conditions).

[0091] Figure 4 graphically represents the effect of selenium compounds, sodium selenite (Al and A2), seleno-L-methionine (Bl and B2), Se-(methyl)-selenocysteine (Cl an C2) and seleno-DL-cysteine (Dl and D2), on the proliferation of MCF-7 cells after 4 days treatment in the presence of CCS (non-estrogenic conditions). [0092] The results indicate that for human hormone-sensitive breast cancer MCF-7 cells, the selenium co-treatment with hormone ablation therapy is able to synergistically reduce breast cancer cell proliferation over either treatment alone. The synergy index value, known as the R index value, was calculated for each treatment using expected versus observed treatment responses, enabling a quantitative analysis of potential synergistic combinations. The results are shown in Table 2. Table 2. Proliferative effect of different selenium compounds in normal serum and charcoal strip serum on human breast tumour cell line (MCF- T), after 4 days in culture.

C OD (fi

m

C/)

I m m

Ti m

IO σ>

Ti O

m (ft m £ m ^■

Observed values: average of each compound/ control (normal serum) x 100% Expected values: product of each observed compound in NS with 5%CSS/ 100 Synergy: R>1 [0093] Sodium selenite was able to synergize with hormone ablation therapy to reduce breast cancer proliferation as assessed by the R index value, (sodium selenite 50μM 12.31).

[0094] Selenomethionine was similarly able to synergize with hormone ablation therapy to reduce breast cancer proliferation at most dose levels tested, as assessed by the R index value (selenomethionine 5 μM R=71.84; 20μM 9.44 and 50μM 26.55).

[0095] Se-(methyl)-selenocysteine was able to synergize with hormone ablation therapy to reduce breast cancer proliferation at a number of dose levels tested, as assessed by the R index value (Se-(methyl)-selenocysteine 5 μM R=I 5.68; 20 μM R=8.41; 50μM 15.01; 100 μM R=5.20). [0096] Seleno-DL-cysteine was able to synergize with hormone ablation therapy to reduce breast cancer proliferation at a number of dose levels tested, as assessed by the R index value (seleno-DL-cysteine 50μM 1.30; 100 μM R=2.13).

[0097] These results confirm that the tested selenium species are able to combine synergistically with hormone ablation therapy to reduce prostate and breast cancer cell growth. [0098] The disclosure of every patent, patent application, and publication cited herein is hereby incorporated herein by reference in its entirety.

[0099] The citation of any reference herein should not be construed as an admission that such reference is available as "Prior Art" to the instant application.

[0100] Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. Those of skill in the art will therefore appreciate that, in light of the instant disclosure, various modifications and changes can be made in the particular embodiments exemplified without departing from the scope of the present invention. All such modifications and changes are intended to be included within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method for treating a hormone-dependent cancer in a subject, the method comprising administering to the subject a therapeutically effective amount of selenium in a biologically available form in combination with hormone ablation therapy, with the proviso that the selenium in a biologically available form is not selenate or a pharmaceutically acceptable salt thereof.

2. A method according to claim 1, wherein the selenium in a biologically available form is selected from sodium selenite, selenomethionine, selenocysteine, methylselenocysteine and selenized yeast.

3. A method according to claim 1, wherein the therapeutically effective amount of selenium in a biologically available form is a nutritional amount or a supranutritional amount.

4. A method according to claim 1, wherein the therapeutically effective amount of selenium in a biologically available form is from about 0.015 mg/kg to about 20 mg/kg.

5. A method according to claim 1, wherein the hormone-dependent cancer is selected from an androgen-dependent cancer or an estrogen-dependent cancer.

6. A method according to claim 1, wherein the hormone-dependent cancer is selected from prostate cancer, breast cancer, ovarian cancer, uterine cancer, endometrial cancer or thyroid cancer.

7. A method according to claim 1, wherein the hormone-dependent cancer is an androgen-dependent prostate cancer or an estrogen-dependent breast cancer.

8. A method according to claim 1, wherein the hormone ablation therapy is selected from agents that interfere with the androgen receptor, agents that interfere with steroid biosynthesis, GnRH agonists or antagonists, non-steroidal anti-androgens, 5-alpha-reductase inhibitors, aromatase inhibitors, anti-estrogen compounds and progestins, or surgical removal of hormone producing organs.

9. A method according to claim 1, further comprising administration of a cytostatic agent or a cytotoxic agent.

10. A method according to claim 9, wherein the cytostatic agent is a microtubule stabilizing agent.

11. A method according to claim 10, wherein the microtubule stabilizing agent is paclitaxel.

12. A method according to claim 1, further comprising administration of radiotherapy, optionally together with a radiosensitizing agent.

13. Use of selenium in a biologically available form in the manufacture of a medicament for treating a hormone-dependent cancer, wherein the medicament is formulated for use with hormone ablation therapy; with the proviso that the selenium in biologically available form is not selenate or a pharmaceutically acceptable salt thereof.

14. A method for inhibiting hormone-dependent growth of tumor cells, comprising exposing the tumor cells to a hormone-dependent tumor cell growth-inhibiting amount of selenium in a biologically available form, and a hormone ablation therapy, with the proviso that the selenium in biologically available form is not selenate or a pharmaceutically acceptable salt thereof.

15. A pharmaceutical composition comprising selenium in a biologically available form and a chemical hormone ablation agent and a pharmaceutically acceptable carrier, with the proviso that the selenium in biologically available form is not selenate or a pharmaceutically acceptable salt thereof.

16. A pharmaceutical composition according to claim 15, wherein the selenium in a biologically available form is selected from sodium selenite, selenomethionine, selenocysteine, methylselenocysteine and selenized yeast.

17. A pharmaceutical composition according to claim 16, wherein the hormone ablation therapy is selected from agents that interfere with the androgen receptor, agents that interfere with steroid biosynthesis, GnRH agonists or antagonists, non-steroidal anti-androgens, 5-alpha-reductase inhibitors, aromatase inhibitors, anti-estrogen compounds and progestins.

18. A pharmaceutical composition according to claim 16, further comprising at least one cytostatic agent or cytotoxic agent or a radiosensitising agent.

19. A pharmaceutical composition comprising selenium in a biologically available form and at least one cytostatic or cytotoxic agent and a pharmaceutically acceptable carrier, with the proviso that the selenium in biologically available form is not selenate or a pharmaceutically acceptable salt thereof.