a first aspect of the invention concerns fosfestrol ( diethylstilbestrol diphosphate ) for use in a method of curative or palliative treatment of prostate cancer in male mammals , said method comprising orally administering fosfestrol in a daily dosage of at least 1 , 000 mg . the term ‘ fosfestrol ’ as used herein refers to a diethylstilbestrol moiety of which both the hydroxyl groups are phosphated . the term ‘ fosfestrol ’ also encompasses pharmaceutically acceptable salts of fosfestrol . the term ‘ pharmaceutically acceptable salt ’, as used herein , means those salts of compounds of the invention that are safe and effective for use in mammals and that possess the desired biological activity . descriptions of counter ions for pharmaceutically acceptable salts of pharmaceutical compounds can be found in p . heinrich stahl , camille g . wermuth ( eds . ), handbook of pharmaceutical salts , properties , selection and use , wiley vch ( 2002 ). the diethylstilbestrol moiety in the des phosphate of the present invention may be in the trans - form or the cis - form . naturally , also mixtures of the trans - and cis - form may be employed . the term ‘ cancer ’ as used herein refers to a malignant neoplasm involving unregulated cell growth . in cancer , cells divide and grow uncontrollably , forming malignant tumors , and invade nearby parts of the body . the term ‘ curative treatment ’ as used herein refers to a treatment that aims to cure a disease or to improve symptoms associated with a disease . the term ‘ palliative treatment ’ as used herein refers to a treatment or therapy that does not aim at curing a disease but rather at providing relief . the term ‘ oral ’ as used herein , unless indicated otherwise , is synonymous to ‘ per oral ’. the term ‘ dosage ’ as used herein refers to the amount of a pharmaceutically active substance that is administered to a mammal . hence , the term ‘ dosage ’ does not include any carrier or other pharmaceutically acceptable excipient that is part of a ‘ dosage unit ’ to be administered . in this document and in its claims , the verb ‘ to comprise ’ and its conjugations are used in their non - limiting sense to mean that items following the word are included , without excluding items not specifically mentioned . in addition , reference to an element by the indefinite article ‘ a ’ or ‘ an ’ does not exclude the possibility that more than one of the element is present , unless the context clearly requires that there be one and only one of the elements . the indefinite article ‘ a ’ or ‘ an ’ thus usually means ‘ at least one ’. hormone - dependent cancers refer to those types of cancer that grow faster in the presence of particular hormones . this type of cancer is usually treated with hormone therapy . hormone therapy involves blocking in vivo production or action of these hormones . therefore , hormone therapy actually is anti - hormone therapy . cancer of the prostate usually is a hormone - dependent cancer and may be treated by the present method . in the case of hormone - dependent prostate cancer , androgen ablation therapy ( e . g . orchiectomy , treatment with lhrh analogs or lhrh antagonists ) is used as first line treatment to decrease the production of androgens , particularly testosterone , in order to stop or limit the growth of prostate cancer . androgens are key drivers of prostate tumor growth . the androgen ablation therapies reduce the plasma levels of androgen , thereby reducing the growth potential of the prostate tumor . the androgen ablation therapies are successful for a certain period of time , however all prostate tumors eventually become resistant to this treatment approach . after failure of the androgen ablation therapy , secondary hormone treatments with anti - androgens are used to slow the growth of the prostate tumor . after exposure for a certain time to hormone therapy prostate cancer often obtain the ability to grow without hormones and are therefore called ‘ hormone - independent ’. once these cancers become hormone - independent , treatment usually is switched to chemotherapy . hormone - independent prostate cancer is also called hormone - refractory or castration - resistant prostate cancer . these terms are used interchangeably in the following and are considered to have the meaning of ‘ castration - resistant prostate cancer ’. nowadays , the term ‘ castration resistant ’ has replaced ‘ hormone refractory ’ because while these prostate cancers are no longer responsive to castration treatment ( reduction of available androgen / testosterone ), they still show some reliance upon hormones for androgen receptor activation . the present invention encompasses the treatment of hormone - dependent as well as hormone - independent cancers . the present method is particularly suited for treatment of hormone - independent cancers , especially for treatment of hormone - independent cancers that have developed after treatment of hormone dependent cancers with hormone therapy . the present method of treatment is advantageously applied to treat a prostate cancer that does not respond to treatment with anti - androgen or an inhibitor of 17α hydroxylase / c17 , 20 lyase ( cyp17a1 ), especially a prostate cancer that does not respond to treatment with an inhibitor of 17α hydroxylase / c17 , 20 lyase ( cyp17a1 ), more particularly to treatment with abiraterone . the present method is particularly suited for treatment of hormone - independent prostate cancer that has developed after treatment of hormone - dependent prostate cancer with anti - androgen or an inhibitor of 17α hydroxylase / c17 , 20 lyase ( cyp17a1 ), notably abiraterone . as explained herein before , fosfestrol in the context of the present invention also encompasses pharmaceutically acceptable salts of fosfestrol . pharmaceutically acceptable salts include those formed from cations of alkali metals such as sodium , lithium , potassium , and earth alkali metals such as calcium and magnesium . in a preferred embodiment the fosfestrol is an alkali metal salt , notably a sodium and / or a potassium salt . more preferably , the fosfestrol is in the potassium salt form . the present method of treatment may be used to treat several kinds of mammals , e . g . humans , horses , cattle etc . the present method is particularly suited for the treatment of humans . the fosfestrol dosage may vary depending upon the specific conditions and patients undergoing treatment . the therapeutically effective dosage of the compound can be provided as repeated doses within a prolonged treatment regimen that will yield clinically significant results . the actual dosage of the compound will vary according to factors such as the disease indication and particular status of the subject such as for example , age , size , fitness , extent of symptoms , susceptibility factors and the like , and other factors such as time and route of administration , other drugs or treatments being administered concurrently . dosage regimens can be adjusted to provide an optimum therapeutic response . typically , the present method comprises administering fosfestrol in a daily oral amount of at least 1 , 000 mg , more preferably of 1 , 000 - 4 , 500 mg and most preferably of 1 , 000 - 2 , 000 mg . expressed differently , it is preferred to administer fosfestrol orally in a daily amount of at least 12 . 5 mg per kg of bodyweight , more preferably of 12 . 5 - 60 mg per kg of bodyweight and most preferably of 12 . 5 - 27 mg per kg of bodyweight . the duration of the present method of treatment typically exceeds 7 days . more particularly , the present method has a duration of at least 14 days , especially of at least 28 days . the aforementioned daily amount may be administered once daily of it may be administered in the form of two or more separate doses at more or less regular intervals . according to a particularly preferred embodiment , the present method of treatment comprises orally administering at least two doses per day , more preferably two doses of each at least 200 mg fosfestrol per day , even more preferably it comprises orally administering at least 3 doses of at least 200 mg fosfestrol per day . another aspect of the invention relates to an oral dosage unit comprising at least 500 mg , preferably at least 800 mg and most preferably at least 1 , 000 mg , of fosfestrol . the oral dosage unit of the present invention can advantageously be applied in the curative or palliative treatment of prostate cancer as defined herein before . the oral dosage units is preferably selected from the group consisting of tablets , granulates , capsules and powders and liquids . even more preferably , the oral dosage unit is a tablet or capsule . the oral dosage units typically have a weight of between 0 . 5 and 2 . 0 g , more preferably of 0 . 75 - 1 . 5 g and most preferably of 0 . 8 - 1 . 2 g . in another embodiment , the oral dosage units comprise between 20 and 80 wt . % of pharmaceutically acceptable excipient . the pharmaceutically acceptable excipient is suitably selected from coloring agents , flavoring or taste masking agents , diluents , binders , lubricants , disintegrants , stabilizers , surfactants , glidants , plasticizers , preservatives , sweeteners and combinations thereof . the disintegrants are advantageously chosen from the group consisting of lactose , anhydrous lactose , crospovidone , croscarmellose sodium , sodium starch glycolate , hydroxypropyl cellulose , polacrilin potassium , pregelatinized starch , microcrystalline cellulose and combinations thereof . in a preferred embodiment the oral dosage units comprise up to 7 wt . %, preferably 2 - 5 wt . % of disintegrants . the dosage unit of the present invention may suitably take the shape of a compressed tablet . such a tablet may suitably comprise two or more layers of different composition , for example a core comprising fosfestrol as defined herein before encased in a coating . the dosage units of the present inventions are conveniently produced in a tabletting machine . in order to enable easy removal of the tablets from the moulds , the dosage unit typically contains between 0 . 2 and 4 . 0 wt . % of a lubricant or gliding agent . preferably , the lubricant or gliding agent is selected from the group consisting of talc , sodium stearyl fumarate , magnesium stearate , calcium stearate , hydrogenated castor oil , hydrogenated soybean oil , polyethylene glycol , starches , anhydrous colloidal silica and combinations thereof . the following examples are meant to further illustrate the invention and some of its preferred embodiments without intending to limit its scope . the in vitro direct cytotoxicity of des and fosfestrol in hormone - dependent ( lncap ) and hormone - independent ( du - 145 ) prostate cancer cell lines was tested . cells were maintained in vitro in rpmi 1640 containing 10 % ( v / v ) heat inactivated fetal bovine serum ( fbs ) and 2 mm l - glutamine ( growth media ) at 37 ° c . in 5 % co 2 and humidified conditions . cells were harvested , washed , re - suspended into growth medium and counted . the cells were re - suspended into assay media ( rpmi 1640 + 1 % ( v / v ) heat inactivated fbs + and 2 mm l - glutamine ) at 0 . 5 × 10 5 cells / ml for du - 145 cells and 1 × 10 5 for lncap cells , and plated into 96 - well assay plates ( corning , black - wall plates ) and 50 μl / well aliquots . plates were incubated o / n at 37 ° c . in 5 % humidified co 2 prior to addition of the compounds . des was dissolved in 100 % dmso at stock concentration of 60 mm . fosfestrol was dissolved in sterile water at stock concentration of 60 mm . stocks of all compounds were then serially diluted . final concentrations to which cells were exposed were : 300 , 150 , 75 , 37 . 5 , 18 . 75 , 9 . 4 , 4 . 7 , 2 . 3 , 1 . 2 and 0 . 6 μm . positive control was taxotere . taxotere was diluted in 100 % dsmo to give a stock concentration of 1 mm . stock was serial diluted and final concentration to which cells were exposed was : 1000 , 333 . 3 , 111 . 1 , 37 . 0 , 12 . 3 , 4 . 1 , 1 . 4 , 0 . 5 , and 0 . 2 nm . plates were incubated for 72 hrs at 37 ° c . in 5 % humidified co - 2 after addition of the compounds . viability of the cells was assessed with the cell titer blue ® ( promega ) assay . 10 μl of cell titer blue ™ reagents was added to each test / blank well . plates were incubated for 3 hrs at 37 ° c . in 5 % humidified co 2 prior to analysis . fluorescence was measured with a flex ii station plate reader . excitation wavelength was 570 nm , emission wave length was 600 nm , cut off was 590 nm . raw data was processed by graphpad prism to calculate mean , standard deviation and ic 50 values . fosfestrol and excipients were first passed over a 0 . 85 mm sieve . next , 500 gram of fosfestrol tetrasodium was blended with 435 gram of silicified microcrystalline cellulose ( prosolv smcc 90 ™) and 50 gram of croscarmellose sodium ( ac - di - sol ™) for 20 minutes in a v - blender . added to the mixture was 15 grams of magnesium stearate and blending was continued for 5 minutes . tablets of 1 , 000 mg each were prepared on a korsch eko , using oval punches . a patient study was conducted in chemo and hormone resistant prostate cancer patients to explore the effects of high dose oral fosfestrol treatment . 11 patients were included into the study and all had undergone at least 2 prior treatments ( mostly taxotere and estramustine ) with a maximum of prior 4 treatments . patients were treated with three times 360 mg / d oral fosfestrol for 4 weeks . total fosfestrol dose per day was 1 , 080 mg . all other treatments were stopped during high dose oral fosfestrol therapy . psa decline was used to measure objective response . 72 % of the patients showed a psa decline of & gt ; 50 % during high dose oral fosfestrol treatment . in addition , 54 % of the patients experienced a & gt ; 80 % psa decline . treatment was accompanied by minor toxicities and no thromboembolic side effects were detected . this study showed that high dose oral fosfestrol is effective and safe to use in heavily pretreated chemo and hormone resistant prostate cancer patients .
the present invention relates to the use of fosfestrol in a method of curative or palliative treatment of prostate cancer in male mammals , said method comprising orally administering fosfestrol in a daily dosage of at least 1 , 000 mg . the inventors have discovered that fosfestrol when administered in very high oral dosages is effective in the treatment of prostate cancer , especially hormone resistant prostate cancer , without giving rise to serious side effects , such as thromboembolic toxicity or mortality . the invention further provides an oral dosage unit comprising at least 500 mg , of fosfestrol .