an important aspect of the present invention is that the radioconjugate can be made or quasi be made at the site of therapy . due to the decay sequence which results mainly in α - and / or β - radiation it has become possible that no protection against radiation is necessary . this is extremely useful , because due to the absence of gamma radiation it has become possible that the conjugation can be done at or near the bed side without the necessity to apply radiation shielding or isolation of the patient . this is not only preferable from the point of radiation danger but is also gives advantages for the availability of the short - living isotope . this isotope can be prepared in the neighboorhood of the patient allowing for a rapid administration and prevention of loss of therapeutic action caused by the rapid decay of the isotope . in this way it has become possible to use short lived radioisotopes for therapy . an ion exchange column or another appropriate substrate filled with the long lived isotope can be placed at or near the bedside , for instance , where the short - lived isotope can be eluted by washing the substrate with a suitable solution . after elution the short lived isotope is coupled to the targeting moiety and ( optionally together with an infusion solution ) the conjugate can be administered . this can all be done in a continuous mode with an apparatus according to the invention as shown in fig1 or fig3 or in an intermittent mode by using ordinary laboratory glassware . of course it may also be made possible to add the targeting moiety to the eluting solution so that the coupling takes place in the column . this invention primarily addresses the use of the shortest - lived isotope from the list mentioned above , 213 bi . the invention enables the person skilled in the art to milk this isotope by a continuous or an intermittent extraction - method from one of its precursors , 225 ac , at the bed - side of the patient , or in the nearestby hospital laboratory facility , to link the 213 bi in a continuous or an intermittent manner onto the targeting moiety , to either or not mix the conjugate solution with an infusion liquid and to administer this mixture intravenously to the patient -- for example as is schematically pictured in fig1 . at first sight this procedure might seem extremely wasteful , because 225 ac , itself being an α - emitting isotope , produces three potentially therapeutically useful α - particles before yielding the 213 bi - isotope , as is shown in fig2 . however , the source material for 225 ac , 229 th , and thereby also the 225 ac itself , can be made available at sufficiently low cost to allow it to be used in the proposed manner on economically justifiable terms . the use of 213 bi is not only preferable from a viewpoint of radiation hazards . it is also preferable because no gaseous isotopes occur in the decay sequence of its precursors . this is advantageous over the use of other isotopes which have a decay with a gaseous isotope which necessitates the handling and reaction environment to be air - tight . milking , conjugation and administration of 213 bi are not hampered by the necessity for having air - tight conditions and the reactions can be done under normal conditions . the targeting moiety may preferably be a monoclonal antibody , or a fragment or a derivative thereof . preferably such an antibody is a human or a humanized antibody to prevent immunologic reactions to the antibody . non - human antibodies are mostly of murine origin . these , like all other foreign proteins , are highly immunogenic in man . the phenomenon of hama , human anti mouse antibodies , is well known in the field and severely limits the use of mouse derived antibodies in diagnostic and especially in therapeutic applications in human beings . a single application of a murine antibody is usually sufficient to mount an immune response that will prevent subsequent applications to be effective . of course fragments and / or derivatives of the targeting moieties can also be used , as long as they retain a substantial amount of target specificity . thus , for this invention it should be understood that where a targeting moiety is mentioned one should also consider a fragment or a derivative thereof as part of the invention . preferably antibodies are directed against tumor associated antigens , such as cea ( carcino - embryonic antigen ), afp ( alpha - foetoprotein ), fhap ( fast homoarginine - sensitive alkaline phosphatase ), p97 ( melanome specific ), and el - 1 ( elongation factor 1 ). another preferable targeting moeity is formed by a ligand for a cell surface receptor or a fragment or derivative of such a ligand . examples of such ligands are agonists and / or antagonists of pharmacologically active receptors , but also t cell epitopes which can bind to the t cell receptor are prefered . another aspect of the invention provides a method for treating numerous patients with one ion exchange column loaded with isotope . the amount of isotope loaded depends on the number of patients to be treated . the wanted isotope can be eluted from the column intermittently , with suitable intervals depending on the half - lifes in the decay chain . with related tumours or infectious organisms the same targeting moiety ( or mix of targeting moieties ) may be used for various patients . for unrelated diseases there must be a means for changing the targetting moiety preparation . the coupling of the isotope to the targeting moiety can be done in any suitable way , as long as the targeting specificity of the targeting moiety is not hampered to a substantial amount . preferably the coupling will be done through one of the now many known chelating agents . as already disclosed , it may be advantageous to couple the isotopes to a carrier , such as hsa , which of course can also be done through chelating agents . the advantage of a carrier is that a large number of radioisotopes can be brought to the target cell . since it is assumed that several α - particles are necessary for the destruction of one target cell an increase in the number of isotopes in the direct neighbourhood of the target cell is preferable . the invention also provides a conjugate as produced by the method of the invention , as well as a pharmaceutical formulation comprising such a conjugate . a method is provided for producing the conjugate of a targeting moiety and a radioisotope and administering it to the patient without delay or any necessary actions of the therapist . another aspect of the invention provides an apparatus for carrying out site directed therapy or imaging . the simplest way to describe the method and apparatus , subject of this invention , with reference to fig1 is as follows : a capillary column contains , by means of example , twice the amount of precursor - 225 ac needed for a single patient dose of 213 bi . example : in a case the patient dose corresponds with 30 mci ( equals 2 . 10 - 9 g ) of 213 bi over a 10 day period , the capillary column ( 3 ) will contain 200 μci of 225 ac ( equals 4 . 10 - 9 g ). the 225 ac is present in a 3 + form on a suitable ionexchange substrate . upon its ( continuously occurring ) decay it is stripped from the column by a certain overdose of the eluent in flask ( 1 ) containing the appropriate targetting moiety capable of binding the isotope . the binding part of the targetting moiety and other chemical equilibrium conditions of the eluent - ionexchange system are chosen such that the 213 bi , for all practical purposes , quantitatively binds to the targetting moiety . the immediate daughter of 225 ac , 221 fr has a radioactive decay halflife of 4 . 8 minutes . it is this isotope which acts via the very short - lived 217 at as the direct precursor of 113 bi . in case the 221 fr is not retained by itself or in the ion exchange substrate , the delaying effect of the 221 fr - halflife causes the need of a certain period of time between the decay of 225 ac at and its stripping from the capillary column and the binding of the 213 bi onto the targetting moieties . the optimum value for such a delay is somewhere between the halflife of the 221 fr and the halflife of the 213 bi isotopes . this delay can be effected by the length of tubing between the capillary ( 3 ) and the patient ( 4 ), if necessary enhanced by an extra length of intermediate tubing , as indicated in fig1 as ( 5 ). the infusion liquid from flask ( 2 ) enters the patient , it is mixed with the isotope - containing eluate from column ( 3 ), as indicated as junction ( 6 ) in fig1 . in order to obtain optimal stripping and conjugation conditions in the capillary column ( 3 ), it may be that the composition of the eluent in flask ( 1 ) is not optimal ( for example its ph - value ) for administration to the patient . presuming that the volume rate of infusion liquid is an order of magnitude higher than of the eluate liquid , this can easily be countered for by a compensating off - balance ( buffered ) ph - value of the infusion liquid . it is also possible that the binding of the targeting moiety is hampered by the physico - chemical properties of the eluent . therefore , an other embodiment of the invention is represented in fig3 where an eluens is lead from a vessel ( 7 ) through an ion exchange column ( 3 ) so that a radioisotope is stripped from that column . the eluens containing the isotope is mixed with a liquid from a vessel ( 1 ) containing a targeting moiety , so that the isotope is bound to the targeting moiety . the resulting fluid is mixed with infusion liquid from vessel ( 2 ) at junction ( 6 ) and administered to the patient ( 4 ). optionally the eluens containing the isotope may be lead through an additional length of tubing ( 5 ) to correct for the half - life of intermediate daughter isotopes . what the invention enables in terms of the development and the clinical use of α - radioimmunotherapy , in this case using 213 bi as the active cell - killing agent is : &# 34 ; single patient kits &# 34 ; in the form of precursor with a halflife that is logistically managable regarding : minimization of active material loss by radioactive decay during operations like packaging , transport , etc ., applicability in practice on a large scale in many hospitals without need for special precautions , regarding : the handling of the material and the application procedures regarding the treatment of patients , all without complicated monitoring equipment , maximal ( and in case of continous extraction , almost total ) use of the 213 bi after it is generated from the precursor isotope , maximum flexibility in dose administration by the possibility of changing treatment time , allowing for a minimum range of single patient kit precursor concentration standards . all these aspects then pertain precisely to fields where the short - range α - particles are most suited for their potential therapeutic uses like : also , certain kinds of very localized autoimmune diseases , all of which can essentially be directly addressed either by the blood - circulation system or locally without the need for slow diffusion processes of the antibody - ligand - isotope complexes through intercellular space in order to find their ultimate destination . a special advantage of intermittent administration of the therapeutic radioconjugates is the advantage which occurs by dose fractionation . statistically it is possible to calculate the dose needed to kill 99 . 9 % of the tumor cells with a dose of radioconjugate : assuming that a leukemic ( monocellular , blood and marrow bone ) tumor load of 1 kg exisits , which is roughly equal to 10 12 cells , and that 10 α - particles are needed to kill a cell ( 6 mev ), then 10 13 α - particles would be needed , which corresponds with 50 mci 213 bi . thus for a single dose , which would kill 99 . 9 % of the tumor cells 50 mci 213 bi would be needed . the &# 34 ; dose versus survival &# 34 ; relation for this cell morphology with 6 mev α - particles can be derived from the formula d / d 0 =- ln s , in which s = survival fraction , d = dose administered and d 0 = reference dose for 37 % survival . from this formula the following table of values can be calculated : table 1______________________________________dose versus kill ratio for tumor cells . the numbers are thenumber of α - particles necessary to kill the given % of tumorcells . in case a 600 rad are necessary to obtain a 99 % kill ratio . in caseb 2000 rad is assumed necessary for the same effect . cell kill in % case a case b______________________________________0 0 01 0 . 015 0 . 0510 0 . 15 0 . 540 0 . 7 250 1 360 1 . 3 470 1 . 5 590 3 1099 6 2099 . 9 9 3099 . 99 12 4099 . 999 15 50______________________________________ from this table the effects of an intermittent , dose fractioned , administration can be read : the effect of cell survival of successive doses of 5 mci 213 bi in case a is as follows : the first dose of 5 mci equals 1 α - particle per cell , which gives 50 % survival , which means that 0 . 5 · 10 12 cells remain ; the second dose of 5 mci equals 2 α - particles per cell , which gives 20 % survival , which means that 0 . 1 · 10 12 cells remain ; the third dose of 5 mci equals 10 α - particles per cell , which gives 0 . 1 % survival , which means that 0 . 1 · 10 9 cells remain ; the fourth dose of 5 mci equals 10 , 000 α - particles per cell , which means a total kill . thus it can be shown that by intermittent dosing a total dose of 4 times 5 = 20 mci 213 bi is sufficient to give a total kill of the tumor cells . for clarity the effects of intermediate tumor growth and maximization of the number of targeting moieties on the tumor cells have been omitted . nevertheless , it is clear that by intermittent administration the total load of radioactive material can be kept smaller . even in case b , which has a more unfavourable dose versus survival rate , and advantageous effect is realized : there are two ways presently known to obtain 229 th as a precursor for the 225 ac - source - isotope : from stockpiled 233 u , by its natural α - decay . batches of 233 u were made in nuclear breeder reactors about 30 years ago , but never used as nuclear fuel . some of the 233 u was separated from the bulk - 233 th , from which it was made , so that the now available 229 th can be obtained in highly pure form . by high neutron flux irradiation from natural 226 ra , with 227 ac as an intermediate product . futher irradiation of this 227 ac yields roughly equal amounts of 229 th and 228 th , the latter with much shorter halflife ( 2 years ) than the 229 th . on the one hand this complicates the extraction of 225 ac considerably , but in properly equipped installations it may on the other hand yield 224 ra , an α - emitter with a 3 . 7 day halflife . when the ra is properly isolated , it may be used as a source for 212 pb . the 10 . 5 hour halflife of 212 pb will cause considerable complications in handling . however , when these are properly taken care of , one may envisage to use the 212 pb - isotope in the same manner as the 225 ac in this invention as a bed - side source of 212 bi , which for al practicle purposes acts as an α - emitter with a halflife of 1 . 0 hour . the separation chemistry of the various radioactive elements mentioned in the text before has been sorted out decades ago and is well - documented in the public literature . examples are references ( 3 ) and ( 4 ). 225 ac can be separated from 229 th on a dowex 50 ionexchanger by stripping with 4n hno 3 . after evaporation of the acid , the 225 ac can be dissolved again in 0 . 5n hno 3 in a fixed concentration and absorbed in the appropriate amount on dowex 50 , which then becomes the material in the mini - column ( 3 ) of fig3 . 0 . 68 ± 0 . 07 mci of 225 ac was obtained from the european joint research centre . this was loaded on a mp - 50 cation exchange resin ( bio - rad ). the formed 213 bi was eluted with a mixture of 50 : 50 10 % nh 4 ac : meoh with a ph of 6 . 75 . an autoburet was used to deliver 35 μl of eluant per minute ; alternatively , manual elution was done at 50 μl amounts of eluant per minute . in a few experiments it was necessary to purify the 213 bi . this was accomplished by heating the eluant to dryness in a 10 ml beaker containing 0 . 5 ml of conc . hno 3 . after evaporation under an ir lamp , the bismuth activity was transferred to a column of mp - 50 resin ( 2 × 30 cm , pre - equilibrated with 0 . 1m hno 3 ). the resin was washed with 0 . 2 ml h 2 o . then the 213 bi was eluted with 0 . 5 ml of hcl and hi . various concentrations of hcl and hi have been tried . fig4 shows the elution patterns for 213 bi . in all cases the elution is rapid and quantitative . all of the isotope can be obtained within 5 to 10 minutes after the start of the elution . radiolabeling was done by adding enough 3m nh 4 ac to the 213 bi stock to achieve ph 4 . 0 - 5 . 0 . then 53 μl or 106 μl of a 4 . 7 mg / ml solution of monoclonal antibody b3 coupled with the chelator chx - dtpa ( cyclohexyldiethylenetriaminepenta acetic acid ) according to the method described in ( 5 ) were gently mixed into the solution . after a fifteen minute reaction time , 1 . 5 μl of 0 . 1m edta were added . the solution was transferred to a 1 ml syringe with 0 . 2 ml wash . the solution was then injected into the hplc ( high pressure liquid chromatography ) having a tsk 3000 column . the buffer was 0 . 02m mes / cl - ( mes = morpholino ethane sulfonic acid ), 0 . 15m nacl , ph 6 . 5 . elution of the b3 antibody occurred at 7 . 5 minutes . the amount of 213 bi incorporated into the antibody was monitored with an in - line radiochemical detector ( beckman ). all activity measurements of 213 bi were corrected for decay ( t 1 / 2 = 45 . 6 min ). results are depicted in table 2 . activities of 225 ac , 221 fr or 217 at were not detectable in any of the 213 bi elution products . table 2______________________________________results of radiolabeling experiments incorporating . sup . 213 bi into mab b3 - chx - dtpa . . sup . 213 biacid vol . acid μl μg mab recovered in mab (%) ______________________________________2m hcl 210 250 43 . 4 ( 37 %) 2m hcl 210 500 45 . 0 ( 25 %) 0 . 1m hcl 500 500 3 . 4 ( 7 %) 0 . 1m hi______________________________________ in the same way as described in example 2 and 3 , 213 bi was eluted from 225 ac and coupled to a targeting moiety . for this experiment a conjugate of monoclonal antibody m195 and the chelator chx - dtpa was used . table 3 summarizes the results . table 3______________________________________results of radiolabeling experiments incorporating . sup . 213 bi into mab m195 - chx - dtpa . μg antibody . sup . 213 bi recovered (%) ______________________________________50 198 ( 53 %) 25 107 ( 39 %) ______________________________________ ( 1 ) d . r . fisher : &# 34 ; α - particle emmitters in medicine &# 34 ;, proceedings of a symposium held at loews l &# 39 ; enfant plaze hotel , washington , d . c ., september 21 and 22 , 1989 , pages 194 - 214 , published by the american college of nuclear physicians . ( 2 ) d . s . wilbur : &# 34 ; potential use of α - emitting radionuclides in the treatment of cancer &# 34 ;, antibody , immunoconjugates , and radiopharmaceuticals , volume 4 , number 1 , 1991 , pages 85 - 97 , published by mary ann liebert , inc . ( 3 ) t . mitsugashira : &# 34 ; preparation of traces for actinium , thorium , protactinium and uranium &# 34 ;, spey , min . educ . sci . & amp ; cult ., tokyo , 9 , 1984 , pages 111 - 116 . ( 4 ) s . suzuki : &# 34 ; solution chemistry of light actinide elements &# 34 ;, japan - us seminar on thorium fuel reactors -- proceedings , nara , japan , 18 - 22 october 1982 ( tokyo , 1985 ) pages 137 - 143 . ( 5 ) mirzadeh , s ., brechbiel , m . w ., atcher , r . w ., gansow , o . a ., bioconjugate chem ., volume 1 , 1990 , 59 - 65 .
the present invention relates to the field of site directed therapy . more specifically it relates to site directed radio therapy . it provides a method for production of radioimmuno conjugates and an apparatus for radioimmuno therapy . the method , conjugates and apparatus can be practicalized without the need for radioactive shielding and / or airtight facilities . without these restrictions the invention provides a simple and efficient means of therapy at the bed - side of the patient .