Isotope preparation method

Abstract

The present invention provides a method for the purification of .sup.227Th from a mixture comprising .sup.227Th and .sup.223Ra, said method comprising: i) preparing a first solution comprising a mixture of .sup.227Th and .sup.223Ra ions dissolved in an aqueous solution of first mineral acid; ii) loading said first solution onto a strong base anion exchange resin; iii) eluting .sup.223Ra from said strong base anion exchange resin using a second mineral acid in an aqueous solution; iv) optionally rinsing said strong base anion exchange resin using a first aqueous medium; v) eluting .sup.227Th from said strong base anion exchange resin using a third mineral acid in an aqueous solution whereby to generate a second solution comprising .sup.227Th. The invention further provides a purified .sup.227Th solution, a corresponding pharmaceutical formulation and methods of treatment of neoplastic disease.

Claims

1. A method for purification of .sup.227Th from a mixture comprising .sup.227Th and .sup.223Ra, said method comprising: i) preparing a first solution comprising a mixture of .sup.227Th and .sup.223Ra ions dissolved in an aqueous solution of a first mineral acid; ii) loading said first solution onto a strong base anion exchange resin; iii) eluting .sup.223Ra from said strong base anion exchange resin using a second mineral acid in an aqueous solution; iv) optionally rinsing said strong base anion exchange resin using a first aqueous medium; v) eluting .sup.227Th from said strong base anion exchange resin using a third mineral acid in an aqueous solution to generate a second solution comprising .sup.227Th, wherein said second solution comprising .sup.227Th has a contamination level of no more than 20 KBq .sup.223Ra per 1 MBq .sup.227Th; and at least one of steps vi)-viii): vi) assaying for .sup.227Th content of said second solution; vii) evaporating the liquid from said second solution; and viii) forming at least one radiopharmaceutical from at least a portion of the .sup.227Th contained in said second solution.

2. The method of claim 1, wherein at least 70% of the .sup.227Th present in said first solution is present in said second solution.

3. The method of claim 1, wherein said method purifies sufficient .sup.227Th for 1 to 20 doses.

4. The method of claim 1, wherein a .sup.227Th radioactivity of at least 1 MBq is employed in step i).

5. The method of claim 1, wherein said strong base anion exchange resin is a polystyrene/divinyl benzene copolymer based resin.

6. The method of claim 1, wherein said strong base anion exchange resin and optionally a second strong base anion exchange resin are independently an RN.sup.+Me.sub.3 (type I) resin or an RN.sup.+Me.sub.2CH.sub.2CH.sub.2OH (type II) resin.

7. The method of claim 1, wherein said first mineral acid is an acid selected from the group consisting of H.sub.2SO.sub.4, HNO.sub.3 and mixtures thereof.

8. The method of claim 1, wherein said first mineral acid is used at a concentration of 1 to 16 M.

9. The method of claim 1, wherein said second mineral acid is an acid selected from the group consisting of H.sub.2SO.sub.4, HNO.sub.3 and mixtures thereof.

10. The method of claim 1, wherein said second mineral acid is used at a concentration of 1 to 16 M.

11. The method of claim 1, wherein said first aqueous medium is water for injections.

12. The method of claim 1, wherein said third mineral acid is an acid selected from the group consisting of H.sub.2SO.sub.4 and HCl.

13. The method of claim 1, wherein said third mineral acid is used at a concentration of 0.1 to 8 M.

14. The method of claim 1, wherein steps ii) to v) provide a separation ratio of .sup.223Th to .sup.223Ra of at least 10:1.

15. The method of claim 1, wherein step vii) comprises evaporation under reduced pressure, at elevated temperature, or under reduced pressure and at elevated temperature.

16. The method of claim 1, wherein step viii) comprises incubating the portion of the .sup.227Th contained in said second solution with a targeting conjugate, wherein said incubating is at a temperature below 50 C. for a period of less than 2 hours.

17. The method of claim 16, wherein said radiopharmaceutical comprises a targeting conjugate formed from a targeting moiety linked to a complexing agent by a covalent linker.

18. The method of claim 17, wherein said complexing agent comprises an octadentate 3,2-HOPO ligand.

19. The method of claim 17, wherein said targeting moiety comprises an antibody, antibody construct or antibody fragment.

20. The method of claim 1, wherein when step viii) is carried out, said method further comprises: ix) sterile filtering said radiopharmaceutical.

21. The method of claim 5, wherein said polystyrene/divinyl benzene copolymer based resin contains 1-95% DVB.

22. The method of claim 7, wherein said first mineral acid comprises HNO.sub.3.

23. The method of claim 9, wherein said second mineral acid comprises HNO.sub.3.

24. The method of claim 12, wherein said third mineral acid is HCl.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Pharmaceuticals of all types must routinely be produced to a very high standard of purity and a very high confidence that standards (e.g. of purity and sterility) have been met. Administration of an alpha-emitting radionuclide to the body of a subject requires all of these considerations but additionally adds a need for high radiochemical purity. Purification from long-lived precursor isotopes is one key aspect of radiochemical purity but this can typically be accomplished in a specialist radiochemical laboratory or factory where complex methods and handling procedures can be utilised.

(2) A further level of radiochemical purification may be necessary, however, in the event that the radionuclide of interest decays to other radioactive isotopes. The generation of radioactive daughter isotopes may contribute significantly to the toxicity of endo-radionuclide therapy and can be dose-limiting. In the case of .sup.227Th, the daughter isotope is radium, an alkaline earth metal while the parent is a transition metal of the actinide series. This means that any chelation or complexation which may have been suitable for binding thorium will probably not be chemically suitable for retaining the daughter radium. Alpha decay additionally imparts a very significant recoil energy onto the daughter nucleus as a result of conservation of momentum following ejection of an alpha particle at very high speeds. This recoil carries many times more energy than a covalent bond or coordinating interaction and will inevitably shunt the daughter nucleus out of the immediate environment of the original parent isotope. This combination of recoil energy and lack of chelation for the daughter isotope results in uncontrolled release of the daughter isotope following most alpha-decays.

(3) Since the presence of .sup.223Ra and its daughters generated by .sup.227Th decay may be dose limiting, it is important that no unnecessary .sup.223Ra is administered to the subject to further limit the acceptable therapeutic dose of .sup.227Th or to exaggerate the side effects.

(4) The present invention has been developed in view of the inevitable in-growth of .sup.223Ra into a .sup.227Th sample and the desire to minimise that .sup.223Ra delivered to the subject, as far as reasonably possible. Since .sup.223Ra will initially grow in at a rate of around 0.2% of the total activity per hour, the method must be carried out within a few hours before administration (e.g. within 72 hours or within 48 hours) in order to minimise the unnecessary dose. A period of 48 hours between preparation and administration would, for example, result in around 12% decay to radium and thus an additional 1% residual radium would increase the radium administered by around 8%. Correspondingly, if the .sup.227Th can be used within a short time following preparation then the method should preferably provide .sup.227Th with around 99% (e.g. 95% to 99.9%) radiochemical purity with respect to .sup.223Ra (at the time of purification). Higher purity may be inefficient since ingrowth before use will undo any benefits of a more stringent purification method while lower purity (say less than 90% or less than 95% radiochemical purity) is undesirable because the dose of .sup.223Ra (and thus toxicity) could reasonably be further limited while allowing for a realistic administration time.

(5) In one embodiment, the mixtures of .sup.227Th and .sup.223Ra for use in the present invention will contain no significant amount of radioactive isotopes that are not in the decay chain beginning at .sup.227Th. In particular, the mixtures of .sup.227Th and .sup.223Ra for use in any of the aspects of the present invention will preferably comprise less than 20 Bq .sup.227Ac per 100 MBq .sup.227Th, preferably less than 5 Bq .sup.227Ac per 100 MBq .sup.227Th.

(6) The present invention provides a method for the production of .sup.227Th at a purity suitable for use in endo-radionuclide therapy. A number of preferred features of the system are indicated below, each of which may be used in combination with any other feature where technically viable, unless indicated otherwise.

(7) The methods and all corresponding embodiments of the invention will preferably be carried out on a commercial or clinical scale and thus will be capable and suitable for use at this scale while maintaining all of the other characteristics described herein as appropriate (such as radionuclear purity, etc). A commercial scale will typically be a scale greater than that required for the treatment of a single subject, and may be, for example, the purification of more than 2, preferably more than 5 and most preferably more than 20 typical doses of .sup.227Th. Evidently, a typical dose will depend upon the application, but anticipated typical dose may be from 0.1 to 20 MBq, preferably 0.5 to 12 MBq, most preferably around 1 to 10 MBq. Purification may take place in batches of, for example 20 to 500 MBq, preferably 50 to 200 MBq, especially around 100 MBq. Purification of a single dose may, however, be undertaken, particularly where the purification is carried out immediately prior at administration (e.g. within 2 hours, preferably within 1 hour of administration).

(8) Step i) of the method of the invention relates to solution comprising .sup.227Th and .sup.223Ra (and will commonly also comprise .sup.223Ra daughter isotopessee those tabulated above). Such a mixture will inherently form by the gradual decay of a sample of .sup.227Th, but for use in the invention will preferably also have one or more of the following features, either individually or in any viable combination: a) The .sup.227Th radioactivity may be at least 0.1 MBq (e.g. 0.1 MBq to 500 MBq), preferably at least 1.4 MBq, more preferably at least 7 MBq and most preferably at least 20 MBq (e.g. 20 to 200 or around 100 MBq); b) The solution may be formed in an aqueous solution of a first mineral acid; c) The solution may have a volume of no more than 20 ml (e.g. 0.1 to 10 ml), preferably no more than 3 ml, more preferably no more than 2.5 ml. d) The first mineral acid may be an acid selected from H.sub.2SO.sub.4 or HNO.sub.3 preferably HNO.sub.3. e) The first mineral acid may be used at a concentration of 1 to 16 M, such as 3 to 10 M or 5 to 9 M, preferably 7 to 8.5 M (e.g. around 8M), particularly where the first mineral acid is HNO.sub.3. ***

(9) Step ii) of the method of the invention relates to the loading of the first solution onto a strong base anion exchange resin. This step and the entities referred to therein may have the following preferable features, either individually or in any viable combination, and optionally in any viable combination with any of the features of the other steps as described herein: a) The strong base anion exchange resin may be a polystyrene/divinyl benzene copolymer based resin, preferably containing 1-95%; divinyl benzene b) The strong base anion exchange resin may be an RN.sup.+Me.sub.3 type (type I) resin or an RN.sup.+Me.sub.2CH.sub.2CH.sub.2OH (Type II) resin, preferably a type I resin; c) The strong base anion exchange resin may have an exchange capacity of 0.2 to 5 meq/ml, preferably 0.6 to 3 meq/ml, most preferably 0.9 to 1.5 meq/ml (e.g. around 1.0 meq/ml); d) The strong base anion exchange resin may have a particle size grading of 10 to 800 mesh, preferably 50 to 600 mesh, more preferably 100 to 500 mesh (e.g. around 200 to 400 mesh). e) The strong base anion exchange resin may be used in the form of a column. f) The volume of resin used (e.g. when packed in a column) may be 1 ml or less, (e.g. 0.01 to 1 ml), preferably 0.5 ml or less. g) The strong base anion exchange resin may be DOWEX 1X8 (e.g. DOWEX AG 1X8) or equivalent resin with a 200-400 mesh size. h) The strong base anion exchange resin may be pre-equilibrated with a mineral acid. This may be the same as the first mineral acid as described herein.

(10) Step iii) of the method of the invention relates to eluting .sup.223Ra (and preferably also at least one .sup.223Ra daughter product) from the strong base anion exchange resin using a second mineral acid in aqueous solution. This step and the entities referred to therein may have the following preferable features, either individually or in any viable combination, and optionally in any viable combination with any of the features of the other steps as described herein: a) The second mineral acid may be an acid selected from H.sub.2SO.sub.4 or HNO.sub.3 preferably HNO.sub.3. b) The second mineral acid may be used at a concentration of 1 to 16 M, such as 3 to 10 M or 5 to 9 M, preferably 7 to 8.5 M (e.g. around 8M), particularly where the first mineral acid is HNO.sub.3. c) The second mineral acid in aqueous solution may be the same as the first mineral acid in aqueous solution. d) The aqueous solution may be free or substantially free of any alcohol. In particular, the aqueous solution may contain less than 0.1% (e.g. 0 to 0.1%) of any alcohol selected from methanol, ethanol and isopropanol, particularly methanol; e) The .sup.223Ra (and optionally at least one daughter isotope) may be eluted from said strong base anion exchange resin using 1 to 200 column volumes of the second mineral acid in aqueous solution. Preferably the amount will be 5 to 20 column volumes (e.g. around 7 to 11 column volumes).

(11) Step iv) of the method of the invention relates to the optional step of rinsing said strong base anion exchange resin using a first aqueous medium. This step and the entities referred to therein may have the following preferable features, either individually or in any viable combination, and optionally in any viable combination with any of the features of the other steps as described herein: a) The first aqueous medium may be water, such as distilled water, deionised water or water for injections. b) The first aqueous medium may contain said second mineral acid, preferably at a concentration lower than used in step v). c) The first aqueous medium may be used in an amount of 1 to 200 column volumes.

(12) Step v) of the method of the invention relates to eluting .sup.227Th from said strong base anion exchange resin using a third mineral acid in an aqueous solution whereby to generate a second solution comprising .sup.227Th. This step and the entities referred to therein may have the following preferable features, either individually or in any viable combination, and optionally in any viable combination with any of the features of the other steps as described herein: a) The third mineral acid may be an acid selected from H.sub.2SO.sub.4 and HCl, preferably HCl. b) The third mineral acid may be used at a concentration of 0.1 to 12M, preferably 0.5 to 6M, more preferably 2 to 4M, most preferably around 3M. This applies particularly where the second mineral acid is HCl. c) The second .sup.227Th solution may be eluted from said strong base anion exchange resin using 1 to 200 column volumes of the second mineral acid in aqueous solution. Preferably the amount will be 5 to 20 column volumes (e.g. around 7 to 11 column volumes). d) The aqueous solution may be free or substantially free of other solvents such as alcoholic solvents. e) The second .sup.227Th solution will preferably have a contamination level of no more than 10 (e.g. 1 to 10) kBq .sup.223Ra per 1 MBq .sup.227Th, more preferably no more than 5 kBq .sup.223Ra per 1 MBq 227Th.

(13) The steps ii) to iv) of loading the .sup.227Th and .sup.223Ra mixture onto the base anion exchange resin, eluting a mixture of said .sup.227Th and .sup.223Ra solution may provide a separation ratio of .sup.227Th to .sup.223Ra of at least 50:1 (e.g. 50:1 to 500:1), preferably at least 100:1, more preferably at least 200:1. g) The .sup.227Th may be eluted from said strong base anion exchange resin in uncomplexed form, such as in the form of a sample salt in solution (e.g. as the salt of the third mineral acid). h) Optionally, the use of complexing agents such as DTPA may be avoided, and in one embodiment all solutions used in steps ii to iv) are substantially free of complexing agents, such as DTPA.

(14) The methods of the present invention may comprise a number of optional steps, each of which may be present or absent independently so far as technically possible.

(15) Step vi) of the method of the invention relates to optionally assaying for the .sup.227Th content of the second solution. This step and the entities referred to therein may have the following preferable features, either individually or in any viable combination, and optionally in any viable combination with any of the features of the other steps as described herein: a) The assay calculation of thorium-227 may be performed using a dose calibrator, preferably a dose calibrator with an established dial setting for thorium-227.

(16) Step vii) of the method of the invention relates to the optional step of evaporating the liquid from said second solution. This step may be desirable where the final pharmaceutical composition has a low volume or does not comprise as much of the third mineral acid or its salts as is present in the second solution. Typically this method will be most effective when the third mineral acid is an acid that can be removed by evaporation, such as a hydrohalic acid (e.g. HCl). This step and the entities referred to therein may have the following preferable features, either individually or in any viable combination, and optionally in any viable combination with any of the features of the other steps as described herein: a) The third mineral acid may be an acid selected from H.sub.2SO.sub.4 and HCl, preferably HCl. b) The evaporation may be conducted under reduced pressure (e.g. 1 to 500 mbar). c) The evaporation may be conducted at elevated temperature (e.g. 50 to 200 C., preferably 80 to 110 C.);

(17) Step viii) of the method of the invention relates to the optional step of forming at least one radiopharmaceutical from at least a portion of the .sup.227Th purified by means of steps i) to v). This step and the entities referred to therein may have the following preferable features, either individually or in any viable combination, and optionally in any viable combination with any of the features of the other steps as described herein. Furthermore, all of the features of the radiopharmaceutical indicated herein form preferred features of the pharmaceutical aspect of the present invention, particularly where that pharmaceutical is formed or formable by a method of the invention: a) The portion of the .sup.227Th contained in said second sample (purified by means of steps i) to v)) may be 0.1 MBq to 100 MBq, preferably 1 to 10 MBq. b) The radiopharmaceutical may comprise at least one complexing agent. c) The complexing agent may be an octadentate ligand. d) The complexing agent may be a hydroxypyridinone such as 3,2-hydroxypyridinone (2.3-HOPO) ligand, preferably an octadentate 3,2-HOPO. e) The radiopharmaceutical may comprise a targeting moiety. f) The targeting moiety may be an anntibody, antibody construct, antibody fragment (e.g. FAB or F(AB)2 fragment) or any fragment comprising at least one antigen binding region(s). g) The targeting moiety may be a small organic molecule binder, a receptor or receptor binder (e.g. a hormone, vitamin, folate or a folate analogue) a bisphosphonate or nano-particle. h) The targeting moiety may have specificity for at least on disease-associated antigen such as a cluster of differentiation (CD) cell surface molecule (e.g. CD22, CD33, CD34, CD44, CD45, CD166 etc). i) The targeting moiety may be linked to the complexing agent by a covalent linker whereby to form a targeting conjugate. j) The method of formation may comprise incubating the portion of the .sup.227Th contained in said second sample with the targeting conjugate. Such incubation may be at a temperature below 50 C., preferably 20 to 40 C. Such incubation may be for a period of less than 2 hours, such as 1 minute to 60 minutes, most preferably 45 minuttes.

(18) The radiopharmaceutical formed or formable in the various aspects of the present invention may be used in the treatment of any suitable disease, such as a neoplastic or hyperplastic disease including cancer (e.g. a carcinoma, sarcoma, melanoma, lymphoma, or leukemia). Such a use and the corresponding methods of treatment of a subject form further aspects of the invention. The invention will further provide for a method of administration of a radiopharmaceutical to a subject (e.g. one in need thereof) comprising forming said radiopharmaceutical by steps i) to v), viii) and optionally steps vi), vii) and ix) and injecting said radiopharmaceutical (e.g. by intravenous injection or injection directly to a specific tissue or site).

(19) Step ix) of the method of the invention is an optional step comprising sterile filtering the pharmaceutical (especially that formed in step viii)). This step and the entities referred to therein may have the following preferable features, either individually or in any viable combination, and optionally in any viable combination with any of the features of the other steps as described herein: a) The filtration may be through a suitable membrane, such as a 0.22 m (or smaller) membrane. b) The filtration may be by syringe through a suitable syringe filter.

(20) In addition to the above steps, the methods of the invention and all corresponding aspects may comprise additional steps, for example to validate the purity of the .sup.227Th for pharmaceutical purposes, to exchange counter-ions, concentrate or dilute the solution or to control factors such as pH and ionic strengths. Each of these steps thus forms an optional but preferable additional step in the various aspects of the present invention.

(21) It is preferable that the methods of the present invention provide for a high yield of the .sup.227Th product. This is not only because of the desire to avoid wastage or a valuable product but also because all lost radioactive material forms radioactive waste which must then be disposed of safely. Thus, in one embodiment, at least 50% (e.g. 50 to 90%) of the .sup.227Th loaded in step ii) is eluted in step v). This will preferably be at least 60%, more preferably at least 65% and most preferably at least 68% yield or at least 70% yield.

(22) In a corresponding aspect of the present invention, there is additionally provided pharmaceutical composition comprising the .sup.227Th and optionally at least one pharmaceutically acceptable diluent. Such a pharmaceutical composition may comprise .sup.227Th of a purity indicated herein (preferably complexed as described herein and conjugated to a targeting molecule as described herein), optionally formed or formable by the methods of the present invention. Suitable carriers and diluents including water for injection, pH adjusters and buffers, salts (e.g. NaCl) and other suitable materials will be well known to those of skill in the art.

(23) The pharmaceutical composition will comprise the .sup.227Th as described here, typically as an ion, such as the Th.sup.4+ ion. Such compositions may comprise a simple salt of the .sup.227Th of the invention but will more preferably comprise a complex of the .sup.227Th of the invention with at least one ligand, such as an octadentate 3,2-hydroxypyridinone (3,2-HOPO) ligand. Suitable ligands are disclosed in WO2011/098611, which is hereby incorporated by reference, particularly with reference to formulae I to IX disclosed therein, which represent typical suitable HOPO ligands. Such ligands may be used in themselves or conjugated to at least one targeting moiety, such as an antibody. Antibodies, antibody constructs, fragments of antibodies (e.g. FAB or F(AB)2 fragments or any fragment comprising at least one antigen binding region(s)), constructs of fragments (e.g. single chain antibodies) or a mixture thereof are particularly preferred. The pharmaceutical compositions of the invention may thus comprise Th.sup.4+ ion of .sup.227Th of pharmaceutical purity as disclosed herein, complexed to a conjugate of a 3,2-hydroxypyridinone (3,2-HOPO) ligand and at least one antibody, antibody fragment or antibody construct, plus optionally pharmaceutically acceptable carriers and/or diluents. The embodiments described herein with respect to the pharmaceutical composition will also form embodiments of the corresponding method where practicable and vice versa.

(24) In one embodiment, the kit of the invention may comprise components needed for any of the methods of the present invention, optionally including any optional steps, such as steps vi) to ix) as described herein. Such components will have the features set out herein with respect to the corresponding steps, such as step viii).

(25) Where the kit of the invention is suitable for carrying out the method of the present invention including optional step viii) (forming at least one radiopharmaceutical), the kit may include at least one of the following optional components: a) A complexing agent, such as an octadentate ligand. b) A hydroxypyridinone complexing agent such as 3,2-hydroxypyridinone (2.3-HOPO) ligand, preferably an octadentate 3,2-HOPO. c) A targeting moiety, optionally and preferably conjugated or conjugatable to the complexing agent. d) A targeting moiety selected from an anntibody, antibody construct, antibody fragment (e.g. FAB or F(AB)2 fragment) or any fragment comprising at least one antigen binding region(s). e) A targeting moiety selected from a small organic molecule binder, a receptor or receptor binder (e.g. a hormone, vitamin, folate or a folate analogue) a bisphosphonate or nano-particle. f) A targeting moiety having specificity for at least one disease-associated antigen such as a cluster of differentiation (CD) cell surface molecule (e.g. CD22, CD33, CD34, CD44, CD45, CD166 etc).

(26) As used herein, the term comprising is given an open meaning such that additional components may optionally be present (thus disclosing both open and closed forms). In contrast the term consisting of is given a closed meaning only, such that (to an effective, measurable and/or absolute degree), only those substances indicated (including any optional substances as appropriate) will be present. Correspondingly, a mixture or substance described as consisting essentially of will in essence consist of the stated components such that any additional components do not affect the essential behaviour to any significant extent. Such mixtures may, for example, contain less than 5% (e.g. 0 to 5%) of other components, preferably less than 1% and more preferably less than 0.25% of other components. Similarly, where a term is given as substantially, around, about or approximately a given value, this allows for the exact value given, and independently allows for a small variability, particularly where this does not affect the substance of the property described. Such variability may be, for example 5% (e.g. 0.001% to 5%), preferably 1%, more preferably 0.25%.

(27) The invention will now be illustrated further by reference to the following non-limiting examples and the attached figures, in which:

(28) FIG. 1 Shows the decay of .sup.227Th over time and the corresponding in-growth of .sup.223Ra and daughter isotopes over 28 days.

(29) FIG. 2 Shows a typical manufacturing process and control, comprising an embodiment of the method of the present invention including several optional steps.

(30) FIG. 3 Shows the decay chain for .sup.227Ac.

EXAMPLES

Example 1Batch Purification

(31) Purification was carried out by the method indicated in FIG. 2.

(32) TABLE-US-00002 Batch no. Batch no. Technical Technical batch 12 batch 14 Test SUS SUS Date of purification Sep. 9th Nov. 2015 11th 2015 Radionuclidic purity (RNP) 99.8% 99.8% Thorium-227 Thorium-227 content in vial prior 100 MBq 100 MBq to purification Separation ratio of .sup.227Th to .sup.223Ra 500:1 500:1