WO1999051276A1

WO1999051276A1 - Tin-free rhenium(v) complexes and methods for their preparation

Info

Publication number: WO1999051276A1
Application number: PCT/AU1998/000223
Authority: WO
Inventors: Ekaterina Dadachova; Janette Evelyn Chapman
Original assignee: Australian Nuclear Science & Technology Organisation
Priority date: 1998-04-01
Filing date: 1998-04-01
Publication date: 1999-10-14
Also published as: AU6712898A

Abstract

There are provided methods for the treatment or diagnosis of cancer in a mammal, including the step of administering to the mammal an effective amount of a substantially tin-free solution of 188Re(V)-2,3-dimercaptosuccinic acid, 186Re(V)-2,3-dimercaptosuccinic acid or mixtures thereof. There is further provided a process for the preparation of substantially tin-free Re(V)-2,3-dimercaptosuccinic acid, including the step of reducing a solution of a rhenium(VII) species in the presence of at least a 105-fold molar excess of 2,3-dimercaptosuccinic acid with at least a 105-fold molar excess of a sulfur dioxide releasing reducing agent at a pH of not greater than 6, wherein the molar excesses are based on the number of moles of the rhenium(VII) species in the solution.

Description

Tin-free Rhenium(V) complexes and methods for their preparation

Technical Field

The invention relates to methods for the treatment or diagnosis of cancer in mammals, to methods for diminishing the renal uptake in a mammal of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid and/or ¹⁸⁶Re(V)-2,3-dimercaptosuccinic acid, to injectable compositions of ¹⁸⁸Re(V 2,3-dimercaptosuccinic acid and/or ¹⁸⁶Re(V)-2,3-dimercaptosuccinic acid and kits for the preparation of such injectable compositions, and to processes for the preparation of a substantially tin-free solution of Re(V)-2,3-dimercaptosuccinic acid.

Background Art Pentavalent ^99mTc-mesø-2,3-dimercaptosuccinic acid (^99mTc(V)-DMSA) is a tumour imaging agent which has been used as an imaging agent for various cancers. Rhenium analogues ^{188 186}Re(V)-2,3-dimercaptosuccinic acid (¹⁸⁸'¹⁸⁶Re(V)-DMSA) have been synthesized and chemically characterized in order to develop a matching pair of radiopharmaceuticals consisting of ^99mTc(V)-DMSA and ^{188 186}Re(V)-DMSA, for diagnosis and therapy of cancer. Both the ^99mTc(V)-DMSA and ^{188 186}Re(V)-DMSA which have been tested in clinical studies have been prepared using 2,3-dimercaptosuccinic acid kits for ^99mTc kidney scintigraphy which are commercially available from Amersham International PLC (Amersham, UK) and contain tin(II) as reducing agent for ^99mTc. The resulting product inevitably contains substantial amounts of tin species. "^mTc(V)-DMSA and ^188,186Re(V)-DMSA show similar tumour-targeting behaviour. However, the rhenium complex as prepared using the commercially available kit exhibits much greater accumulation in the kidney than does the technetium analogue. For this reason, therapeutic or diagnostic applications of ^{188 186}Re(V)-DMSA have been very limited in comparison with "^mTc(V)-DMSA with only a few studies on therapy of the medullary carcinoma of thyroid having being reported. Attempts to modify pharmacologically high renal uptake of ^188,186Re(V)-DMSA have been reported, but this objective has proven to be difficult to achieve.

There remains, therefore, a need for a clinically effective method of treatment of cancers using radiolabelled Re(V)-DMSA. Surprisingly, the present inventors have found that when substantially tin-free radiolabelled Re(V)-DMSA is administered to a mammal, renal uptake of the complex is substantially lower than when radiolabelled Re(V)-DMSA containing tin species is administered, and is in fact diminished to such an extent that the clinical use of radiolabelled Re(V)-DMSA becomes feasible.

Re(V)-DMSA which is substantially tin-free has been synthesised previously, but has not previously been administered to a mammal. It was therefore not known, prior to the present invention, that the presence of tin in a solution of Re(V)-DMSA administered to a mammal is responsible for the high renal uptake which has been observed previously. 2 Tin-free Re(V)-DMSA has been synthesised previously by reduction of Re(VII) species by, for example, triphenyl phosphine. However, this method of synthesis requires the use of organic solvent and/or high concentrations of strong acids or alkali and removal of the solvents and phosphorus-containing byproducts is necessary before the product can be used for therapeutic or diagnostic purposes. It is therefore impractical to synthesise tin-free Re(V)-DMSA for therapeutic or diagnostic use using triphenylphoshine as reductant. Tc(V)-DMSA has been synthesised by the reduction of a Tc(VII) species by a SO₂- releasing reducing agent such as dithionite or metabisulfite under mildly alkaline conditions. Previous studies of attempts to reduce rhenium(VII) using dithionite have utilised similar conditions, including alkaline pH, as have hitherto been used successfully to reduce technetium(VII). However, under these alkaline conditions, yields of rhenium(V) have been poor. In contrast, the present inventors have discovered that excellent yields of Re(V)-DMSA may surprisingly be obtained by reducing Re(VII) with a SO₂-releasing reducing agent under acidic reaction conditions which are quite different to those utilised for the preparation of Tc(V)-DMSA.

Summary of the Invention

According to a first embodiment of the invention there is provided a method for the treatment of cancer in a mammal in need of said treatment, including the step of administering to said mammal an effective amount of a substantially tin-free solution of a therapeutic agent selected from the group consisting of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid, ¹⁸⁶Re(V)-2,3-dimercaptosuccinic acid and mixtures thereof.

According to a second embodiment of the invention there is provided a method for the diagnosis of cancer in a mammal including the step of administering to said mammal a diagnostically effective amount of a substantially tin-free solution of a diagnostic agent selected from the group consisting of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid, ¹⁸⁶Re(V)-2,3- dimercaptosuccinic acid and mixtures thereof.

According to a third embodiment of the invention there is provided a method for diminishing the renal uptake in a mammal of a therapeutic agent selected from the group consisting of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid, ¹⁸⁶Re(V)-2,3-dimercaptosuccinic acid and mixtures thereof, by administering to said mammal a substantially tin-free solution of said therapeutic agent.

According to a fourth embodiment of the invention there is provided a process for the preparation of substantially tin-free Re(V)-2,3-dimercaptosuccinic acid, including the step of reducing a solution of a rhenium(VII) species in the presence of at least a 10⁵-fold molar excess of 2,3-dimercaptosuccinic acid with at least a 10⁵-fold molar excess of a sulfur dioxide releasing reducing agent at a pH of not greater than 6, wherein said molar excesses are based on the number of moles of said rhenium(VII) species in said solution. 3 In a fifth embodiment, the invention also provides Re(V)-2,3-dimercaptosuccinic acid when prepared by the process of the fourth embodiment.

The invention further provides a substantially tin-free injectable composition including a radiolabelled Re(V)-2,3-dimercaptosuccinic acid, together with at least one physiologically acceptable carrier, diluent, excipient or adjuvant. Typically, the radiolabelled Re(V)-2,3- dimercaptosuccinic acid is a radiolabelled Re(V)-2,3-dimercaptosuccinic acid of the fifth embodiment.

The invention yet further provides a kit for preparation of a substantially tin-free injectable composition including a radiolabelled Re(V)-2,3-dimercaptosuccinic acid selected from the group consisting of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid and ¹⁸⁶Re(V)-2,3- dimercaptosuccinic acid, the kit including the radiolabelled Re(V)-2,3-dimercaptosuccinic acid in a suitable container and a physiologically acceptable diluent therefor in a separate container.

The invention still further provides the use of a substantially tin-free therapeutic agent selected from the group consisting of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid, ¹⁸⁶Re(V)-2,3- dimercaptosuccinic acid and mixtures thereof, for the manufacture of a medicament for the treatment or diagnosis of cancer.

Detailed description of the invention

In a process of the fourth embodiment, the sulfur dioxide releasing reducing agent may be a soluble dithionite, such as sodium dithionite, potassium dithionite or ammomum dithionite, a soluble bisulfite or metabisulfite such as sodium bisulfite, potassium bisulfite, lithium bisulfite, ammonium bisulfite, sodium metabisulfite, potassium metabisulfite, lithium metabisulfite or ammomum metabisulfite, or an aqueous solution of sulfur dioxide. Usually, the sulfur dioxide releasing reducing agent is sodium dithionite or sodium metabisulfite.

The pH of the reaction medium is not greater than 6, and is typically in the range of 2-5, more typically from 2.7-4, still more typically from 3.5-4.

The molar excess of 2,3-dimercaptosuccinic acid, based on the number of moles of the rhenium(VII) species in the solution to be reduced, is typically in the range of from about 10⁵ to about 10⁸, more typically in the range of about 5xl0⁵ to about 5xl0⁷, still more typically in the range of about 5xl0⁵ to about 5xl0⁶. By "molar excess of 2,3- dimercaptosuccinic acid" is meant the ratio of the number of moles of 2,3- dimercaptosuccinic acid in the reaction medium, to the number of moles of rhenium(VII) species initially present. The molar excess of sulfur dioxide releasing reducing agent, based on the number of moles of the rhenium(VII) species in the solution to be reduced, is typically in the range of 4 from about 10⁵ to about 10⁹, more typically in the range of about 5xl0⁵ to about 10⁸, still more typically in the range of about 10⁶ to about 10⁷.

The rhenium (VII) species is typically a ¹⁸⁸Re perrhenate or a ¹⁸⁶Re perrhenate, or a mixture thereof. Sources of radiolabelled perrhenate are known to those of ordinary skill in the art. For instance, ¹⁸⁸Re may be obtained from a ¹⁸⁸W/¹⁸⁸Re generator.

The reaction temperature in a process of the fourth embodiment may be ambient or higher. Typically, the reaction temperature is at least 30°, more typically at least 37°C, still more typically 50°C or above, and up to 90°C or more. It will be appreciated that for given amounts of the reactants, the reaction time required to achieve a maximum yield of the desired product is an inverse function of the reaction temperature. Excessive reaction times at a given temperatures should be avoided, as under some conditions the yield of the desired product first increases with time at a given temperature up to a maximum yield, then begins to decline after the maximum yield has been reached. Usually, the reaction time is not more than two hours, owing to the relatively short half life of ¹⁸⁸Re and ¹⁸⁶Re. Given the teaching herein, persons of ordinary skill in the relevant filed can readily ascertain the approximate maximum yield obtainable with a given set of reaction conditions.

The process of the fourth embodiment may further include the step of separating the substantially tin-free Re(V)-2,3-dimercaptosuccinic acid from unreacted Re(VII) species by contacting the product of the reduction step with a basic anion exchange resin. Optionally, the product obtained from the process of the fourth embodiment may be dried, such as by lyophilisation, or it may be diluted with a suitable diluent such as sterile saline solution.

In the method of the first, second or third embodiments, the ¹⁸⁸Re(V)-2,3- dimercaptosuccinic acid and/ or ¹⁸⁶Re(V)-2,3-dimercaptosuccinic acid administered is usually, but need not be, a product obtained by the process of the fourth embodiment. Other methods for reducing Re(VII), utilising other reducing agents which do not contain tin, are possible and are known to persons of ordinary skill in the relevant field. For example, hydrogen bromide may be utilised as a reducing agent. In general, any soluble reducing agent having a reduction potential sufficiently high to be capable of reducing Re(VII) to Re(V) could be used. Some other reducing agents which may be used include thiocyanate, hypophosphorous acid, hydriodic acid and borohydride or other water-soluble hydride reducing agents. Alternatively, electrochemical reduction may be used. Preferably, the reducing agent is a pharmaceutically acceptable reducing agent. In this respect, the process of the fourth embodiment is advantageous for the synthesis of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid and/or ¹⁸⁶Re(V)-2,3-dimercaptosuccinic acid because the sulfur dioxide releasing reducing agents used are approved for use in foods as preservatives, for example, and thus have low toxicities. 5 In the method of the first embodiment, the therapeutic agent is typically administered in a dose of between about 10 and 500mCi, more typically between about 10 and 200 mCi, still more typically from about 30 to 200 mCi. In the method of the second embodiment, the diagnostic agent is typically administered in an amount of between about 1 and lOmCi. In the method of the third embodiment, the therapeutic agent is typically administered in a dose of between about 1 and 500mCi, more typically between about 1 and 200 mCi. The therapeutic agent may be administered with one or more substances which enhance or modulate uptake of the therapeutic agent. Such substances are known in the art and include meso-2,3-dimercaptosuccinic acid and sodium bicarbonate. The therapeutic agent may be administered in a single dose, or the dose may be repeated once, twice or several times, depending on the stage of the disease being treated, the tumour response, and the degree of any myelotoxicity which is manifested after administration of the therapeutic agent. Appropriate dosages and treatment regimens will depend on the disorder being treated and the stage of the disorder. Given the teaching herein, a physician will readily determine the appropriate dosage and treatment regimen in any given situation.

In the method of the first or second embodiments, the cancer may be any cancer susceptible to treatment by ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid and/or ¹⁸⁶Re(V)-2,3- dimercaptosuccinic acid and includes conditions for which uptake of ^99mTc(V)-2,3- dimercaptosuccinic acid is known. Examples of such cancers have been described in the literature and include medullary and insular carcinoma of the thyroid, head and neck tumours, amyloidosis, osteosarcoma, pancreatic neuroendocrine tumours, soft tissue tumours including lung cancer, brain tumours and hepatic carcinoma, and brain, liver and skeletal metastases, for example from breast carcinoma. In the method of the first, second and third embodiments, the mammal is usually a human.

An injectable composition in accordance with the invention is typically a sterile aqueous solution, such as a solution in sterile saline solution. The concentration of radiolabelled Re(V) in such a solution is typically in the range of from 5xl0^"8molar to 10^"6 molar, and the specific activity of the solution is typically in the range of from 2mCi/mL to lOOOmCi/mL, more typically from 2mCi/mL to 200mCi/mL.

Alternatively, the radiolabelled Re(V)-2,3-dimercaptosuccinic acid may be provided in the form of a kit, consisting of or including the radiolabelled Re(V)-2,3-dimercaptosuccinic acid in a suitable container, in dry form, optionally with one or more solid diluents, adjuvants, carriers or excipients, and a separate container of sterile diluent, such as saline, to be mixed with the radiolabelled Re(V)-2,3-dimercaptosuccinic acid before use. In such a kit, the dry Re(V)-2,3-dimercaptosuccinic acid may conveniently be a lyophilised solution obtained by the process of the fourth embodiment of the present invention. The radiolabelled Re(V)-2, 3 -dimercaptosuccinic acid is usually carrier-free. 6 Best Method and Other Methods for Carrying out the Invention

A preferred process in accordance with the fourth embodiment of the present invention includes the step of reacting ¹⁸⁸Re perrhenate solution with a solution of sodium dithionite in the presence of 2, 3 -dimercaptosuccinic acid at a pH in the range 3.5-4 at a temperature of 37 °C for at least 1 hour, in which the 2, 3 -dimercaptosuccinic acid and sodium dithionite are present in amounts of about l-2mg and 3mg, respectively, per lmCi of ¹⁸⁸Re. An alternative preferred process involves reaction under essentially the same conditions, except that the pH is about 4 and the reaction is at a temperature of about 70 °C for about 15 minutes.

At the end of the reaction time, the pH of the solution is adjusted to 8.5 and the product is separated from any unreacted perrhenate by passing the reaction mixture through a Bond Elut^® (-NH₂) column (Varian Associates) or similar, washing the column with water and eluting the desired product with 0.5M sodium hydroxide solution. The resulting solution may be diluted, if desired, with sterile saline solution, or it may be lyophilised and stored in a suitable container.

A preferred method in accordance with the first embodiment of the invention includes administering to a patient in need of treatment for cancer an amount of from 30-200mCi of a tin-free ¹⁸⁸Re(V)-2, 3 -dimercaptosuccinic acid prepared by a preferred process of the fourth embodiment.

A preferred method in accordance with the second embodiment of the invention includes administering to a patient in need of diagnosis of cancer an amount of from 1-lOmCi of a tin-free ^I88Re(V)-2,3-dimercaptosuccinic acid prepared by a preferred process of the fourth embodiment. The body of the patient, or part of it suspected of including cancerous tissue is then imaged by techniques known in the art, the presence or absence of cancer being indicated by abnormal localisation of radiolabelled rhenium.

The invention will be further described by reference to the following examples, which are not to be construed, however, as limiting the disclosure herein.

Examples

Synthesis of Re(V)-meso-2,3-dimercaptosucάnic acid ( Re(V)-DMSA) using Na₂S₂0₄ or Na₂S₂0₅ as reducing agents

A mixture of l-20mg DMSA and lmg L-ascorbic acid was suspended in lOOμL of water in a first vial. 0.5mL of ¹⁸⁸Re perrhenate solution (about 370 MBq) was added to a second vial containing 5-30 mg Na₂S₂O₄ or Na₂S₂O₅. The mixture was incubated at 25-90°C for 0.25-3 hours. The pH of the mixture was about 3.5-4. In some experiments the pH was altered by addition of appropriate amounts of IM HCl or IM NaOH. On completion of incubation, reaction mixtures were cooled to room temperature and the pH of the solution was adjusted to 8.5 with 1 M NaOH. If necessary, the ¹⁸⁸Re(V)-DMSA product was 7 separated from unreacted perrhenate prior to biodistribution experiments by passing the reaction mixture through a Bond Elut® (-NH₂) column (Varian Associates). The column was first activated by washing with ImL methanol and ImL saline. After the reaction mixture had been passed through the column, it was washed with 1 mL of water and the ¹⁸⁸Re(V)-DMSA was eluted with 0.5mL 0.5M NaOH.

Yields of ¹⁸⁸Re(V)-DMSA under various conditions are set out in Table 1

Table 1 Preparative conditions and yields for 188 Re(V)-DMSA synthesized by Na₂S₂O₄ or Na₂S₂O₅ reduction

Example DMSA, mg Na₂S₂O₄, mg Na₂S₂O₅, mg pH Time (hrs) Temperature, °C ¹⁸⁸Re(V)DMSA yield, %

ON

1 1 5 - 3.5-4 2 25 16

2 1 12 - 3.5-4 2 25 35

3 1 30 - 4 2 25 25

4 10 30 - 3.5-4 2 25 76

5** 10 30 - 2.7 2 25 30

6 15 30 - 3.2 2 25 82

7 20 30 - 3.2 2 25 83 co

8 10 30 - 3.5-4 1 37 93

9 10 30 - 3.5-4 2 37 96

10 10 30 - 3.5-4 1 50 90

11 10 30 - 3.5-4 2 50 92

12 10 30 - 3.5-4 1 70 89

13 10 30 - 3.5-4 2 70 91 n

14 10 30 - 3.5-4 1 90 49 v©

15 10 30 - 3.5-4 2 90 51

16 10 - 30 4 1 25 50

17 10 - 30 4 1 37 96 v©

*©

18 10 - 30 4 0.25 70 98

19 1 12 - 3.5-4 5 25 39

20 1 12 - 3.5-4 2 60 34

21 1 12 - 3.5-4 5 60 37

22 10 30 - 3.5-4 18 25 96

23 15 30 - 3.2 18 25 100

24 20 30 - 3.2 18 25 100 lO

Comparative Examples ***

1 20 30 - 8.5 2 25 5

2 10 30 - 8.5 2 37 7

** pH adjusted with 40μL IM HCl *** pH adjusted with lOOμL IM NaOH

n H

C \© go

© o

10

Biodistribution of ¹⁸⁸Re(V)-DMSA a) Synthesis of Re V)-DMSA by Sn TT) reduction

0.5 mL of ^I88Re perrhenate solution in normal saline was added to the vial of a kit commercially available from Amersham International PLC, Amersham, UK. The vial was gently shaken for 30 seconds. The pH of the mixture was about 2. The reaction mixture was equilibrated at 90°C for 30 min. In some experiments DMSA (9 mg) was added to the vial before addition of Re perrhenate in order to check the influence of excess of DMSA on biodistribution. b) Synthesis of ^ReCVVDMSA using HBr reduction A mixture of lOmg DMSA and 1 mg L-ascorbic acid was suspended in lOOμL of water in a first vial. 0.5 mL of ¹⁸⁸Re perrhenate solution was added to a second vial containing 200 μL 7M HCl and 200μL 48% HBr. The contents of both vials were combined, and the reaction mixture was incubated at 70°C for 60 min.

On completion of incubation, reaction mixtures obtained according to a) and b) were cooled to room temperature and the pH of the solution was adjusted to 8.5 with 1 M NaOH.

Chromatographically, the product of the reduction using the commercial kit (tin(II) reduction) was essentially indistinguishable from the product of the reduction using dithionite or metabisulfite or HBr. Biodistribution studies in mice

Samples of ¹⁸⁸Re(V)-DMSA synthesised by methods a) and b) above, or by dithionite or metabisulfite reduction as described above were diluted with a sterile solution of 0.84% NaHCO₃ in normal saline and terminally sterilised by filtration through sterile 0.2μ filter. Female BALB/c mice (6-8 weeks old) were injected with lOOμL of the product (activity 10 μCi/lOOμL) and sacrificed at various intervals. 5 animals per time point were sacrificed.

In a second study, to investigate the correlation between bone maturation and bone uptake of ¹⁸⁸Re(V)-DMSA, adult animals (13-15 weeks old) were used.

Tables 2 to 4 set out the biodistribution of ¹⁸⁸Re at various time intervals. It will be seen from a comparison of Table 2 with Table 3 or Table 4 that renal uptake of the products which were prepared without a tin-containing reducing agent was very substantially lower than the renal uptake of the product of reduction using the tin(II) reducing agent, although the biodistribution pattern of ¹⁸⁸Re(V)-DMSA in other organs was much less affected. Kidney uptake was decreased from 41.9% for tin(II) reduction to 2.18 - 2.95% injected dose per gram organ at 1 hour post-injection for the other reducing agents. Time dependencies of kidney uptake of ¹⁸⁸Re(V)-DMSA samples using the different reducing agents were also different: in the presence of tin(II), Re(V)-DMSA tended to accumulate 11 in kidneys reaching maximum at 3 h post-injection, while Re(V)-DMSA prepared using other reducing agents was rapidly excreted.

Influence of excess 2.3 -dimercaptosuccinic acid on biodistribution

The data in Table 5 demonstrate that the changed renal uptake of Re(V)-DMSA prepared from tin-free reducing agents was not due to an excess of the ligand, 2,3-

1 oo dimercaptosuccinic acid (DMSA). Biodistribution of Re(V)-DMSA synthesized via tin(II)-reduction in the presence of an additional 9 mg DMSA are presented in Table 5. The concentration of DMSA in the product was 10 times higher than in commercial kit and was equal to that in many of the tin-free preparations. The presence of the DMSA excess lowered to some extent kidney uptake at 1 hour post-injection in comparison with the product obtained using the commercial kit as supplied (25.33 and 41.9% injected dose per gram organ, respectively). By 3 hours post-injection, however, kidney uptake had increased to 42.66% , showing the same trend as uptake of Re(V)-DMSA synthesized via tin(II) reduction without excess DMSA. Bone uptake: influence of bone maturation

Bone uptake of Re(V)-DMSA in young and mature mice is shown in Table 6. The reducing agent used did not substantially affect bone uptake. It will be seen from Table 6 that bone maturation, though incomplete in the 15 week old animals, resulted in about a 50% decrease in bone uptake in the 15 week old mice, compared to the 7 week old animals, whether the ¹⁸⁸Re(V)-DMSA was obtained by tin(II) or Na₂S₂O₄ reduction.

Absence of uptake of tin-free Re(V)-DMSA in normal skeleton is a prerequisite to ensuring that when used in adult patients it will not deliver unnecessary dose to healthy bone, and, simultaneously, will display high tumour uptake according to its ability to accumulate in the sites with increased metabolism.

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Table 2. Biodistribution of 188 R, e(V)-DMSA synthesised by tin(II) reduction (% of injected dose per g of organ/tissue; mean of 5 animals) organ 0.25h 1h 3h 24h 48h 72h liver 4.34(0.36) 4.43(0.44) 5.14(0.79) 5.11 (0.48) 5.26(0.75) 4.64(0.37) kidney 28.6(2.62) 41.91(4.51) 50.3 (5.78) 44.28(4.72) 35.11(5.01) 26.8(4.58) muscle 1.38(0.19) 0.68(0.08) 0.48(0.07) 0.27(0.03) 0.24(0.06) 0.27(0.16) bone 8.52(1.14) 7.85(0.74) 5.4(1.36) 3.27(0.5) 2.3(0.15) 2.17(0.32) lungs 7.92(2.27) 3.91(1.62) 2.75(1.17) 1.58(0.15) 1.77(0.69) 2.0(0.17) blood 9.74(0.58) 4.78(0.6) 2.65(0.46) 0.73(0.06) 0.49(0.07) 0.4(0.11) bladder 6.07(3.18) 1.99(0.49) 1.54(0.17) 1.28(0.86) 0.73(0.36) 3.08(4.61) stomach 2.98(0.23) 1.8(0.18) 1.13(0.31) 0.43(0.1) 0.37(0.05) 0.39(0.06)

GIT 1.98(0.24) 1.64(0.31) 1.47(0.28) 0.64(0.09) 0.71 (0.12) 0.47(0.08) tail 5.0 (0.76) 4.17(0.6) 3.07(0.58) 2.5(1.28) 1.39(0.46) 1.19(0.39) brain 0.32(0.07) 0.18(0.06) 0.13(0.05) 0.04(0.01) 0.04(0.02) 0.03(0.05) thyroid 5.13(1.28) 3.52(1.01) 2.53(0.68) 0.97(0.18) 0.86(0.77) 2.61 (1.99) urine 811(338) 588(218) - 4.87(2.6) 2.69(1.76) -

GIT: Gastro-intestinal tract

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Table 3. Biodistribution of 188 R , e(V)-DMSA synthesised by Na₂S₂0₄ reduction (% of injected dose per g of organ/tissue; mean of 5 animals) organ 0.25h 1h 3h 24h 48h 72h liver 1.23(0.06) 0.4(0.05) 0.28(0.02) 0.2(0.02) 0.17(0.02) 0.1 (0.04) kidney 8.62(3.26) 2.18(0.25) 1.63(0.16) 1.24(0.37) 0.78(0.12) 0.12(0.03) muscle 1.71(0.5) 0.18(0.05) 0.06(0.04) 0.02(0.02) 0.08(0.06) 0.97(1.11) bone 12.95(1.77) 10.48(1.28) 7.0(1.01) 3.5(0.53) 3.11 (0.58) 4.5(1.12) lungs 3.53(0.22) 0.53(0.09) 0.21(0.07) 0.05(0.02) 0.07(0.04) 0.01(0.01) blood 4.06(0.42) 0.55(0.1) 0.11 (0.03) 0.02(0.01) 0.03(0.05) 0.01 (0.15) bladder 6.92(4.37) 1.6(1.13) 0.63(0.37) 0.27(0.1) 0.48(0.37) 0.02(0.02) stomach 2.68(0.22) 0.9(0.03) 0.5(0.17) 0.22(0.25) 0.05(0.02) 0.02(0.02)

GIT 1.25(0.08) 0.3(0.07) 0.22(0.05) 0.22(0.12) 0.05(0.02) 0.12(0.03) tail 8.87(4.32) 4.13(0.56) 3.09(1.17) 2.04(1.65) 1.2(0.42) 0.29(0.1) brain 0.16(0.03) 0.06(0) 0.03(0.01) 0.02(0.01) 0.02(0.02) 0 (0) thyroid 14.11 (11.3) 5.65(2.31) 0.92(0.21) 0.34(0.54) 0(0) 0 (0) urine 2460(1189) 500 (120) - - - -

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Table 4. Biodistribution of ^mRe(V)-DMSA synthesised by Na₂S₂0₅ reduction or HBr reduction (% of injected dose per g of organ/tissue; mean of 5 animals)

Na₂S₂0₅- reduction HBr - reduction organ 1h 3h 1h 3h 24h liver 0.51(0.06) 0.33(0.08) 1.15(0.16) 0.78(0.13) 0.22(0.03) kidney 2.32(0.18) 1.64(0.4) 2.95(0.52) 1.72(0.18) 0.88(0.05) muscle 0.16(0.06) 0.06(0.01) 0.4(0.07) 0.14(0.04) 0.02(0.02) bone 10.36(1.7) 7.59(1.06) 12.01(0.99) 8.56(1.56) 2.94(0.5) lungs 0.66(0.07) 0.21 (0.05) 1.34(0.28) 0.65(0.08) 0.06(0.03) blood 0.67(0.08) 0.16(0.04) 0.55(0.1) 0.11(0.03) 0.02(0.01) bladder 3.34(2.38) 0.98(0.89) — — — stomach 1.89(0.26) 1.04(0.41) 12.17(3.56) 6.44(1.2) 0.03(0.01)

GIT 0.49(0.08) 0.27(0.15) 0.65(0.08) 0.56(0.02) 0.04(0.01) tail 4.15(0.72) 2.71 (0.89) 5.8(0.55) 2.92(0.37) 1.7(0.58) brain 0.05(0.01) 0.02(0.01) 0.09(0.04) 0.05(0.02) 0.01(0.01) thyroid 8.59(2.22) 9.37(2.79) 27.68(16.3) 23.97(6.9) 0.22(0.25) urine 812(119) 267(120) 541(278) 285(141) 1.38(0.26)

15

Table 5. Influence of DMSA excess on biodistribution of ¹⁸⁸Re(V)-DMSA synthesized via tin(II)-reduction (commercial kit plus 9 mg DMSA) in 6-8 weeks old BALB/c mice (% injected dose per gram organ/tissue; mean of 5 animals)

organ 1h 3h liver 3.33(0.43) 3.42(0.1) kidney 25.33(4.07) 42.66(4.27) muscle 1.34(0.66) 1.17(0.63) bone 7.33(2.32) 10.89(1.64) lungs 3.79(0.93) 3.45(0.38) blood 5.03(0.25) 3.05(0.26) bladder 3.47(2.62) 3.16(0.74) stomach 1.54(0.38) 1.52(0.47)

GIT 1.41(0.09) 1.55(0.09) heart 1.7(0.55) 1.25(0.22) brain 0.12(0.02) 0.12(0.02)

thyroid 2.34(1.59) 2.46(0.54)

Table 6. Bone uptake of • 188 R, e(V)-DMSA synthesized via tin(H)- and Na₂S₂θ₅- reduction in young (6-8 weeks old) and mature (13-15 weeks) BALB/c mice (% injected dose per gram bone; mean of 5 animals)

tin(ll)-reduct ion Na₂S₂0₅- reduc tion

Animal age, weeks 3 h 24 h 48 h 3 h 24 h 48 h

7 5.4(1.36) 3.27(0.5) 2.3(0.15) 7(1.01) 3.5(0.53) 3.11(0.58)

15 3.13(0.27) 1.81 (0.19) 1.77(0.28) 3.57(0.85) 1.82(0.79) 1.3(0.18)

Claims

16Claims

1. A method for the treatment of cancer in a mammal in need of said treatment including the step of administering to said mammal an effective amount of a substantially tin-free solution of a therapeutic agent selected from the group consisting of ¹⁸⁸Re(V)-2,3- dimercaptosuccinic acid, ¹⁸⁶Re(V)-2, 3 -dimercaptosuccinic acid and mixtures thereof.

2. A method for the diagnosis of cancer in a mammal including the step of administering to said mammal a diagnostically effective amount of a substantially tin-free solution of a diagnostic agent selected from the group consisting of ¹⁸⁸Re(V)-2,3- dimercaptosuccinic acid, ¹⁸⁶Re(V)-2,3-dimercaptosuccinic acid and mixtures thereof. 3. A method for diminishing the renal uptake in a mammal of a therapeutic agent selected from the group consisting of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid, ¹⁸⁶Re(V)-2,

3- dimercaptosuccinic acid and mixtures thereof, by administering to said mammal a substantially tin-free solution of said therapeutic agent.

4. The method of any one of claims 1, 2 or 3, wherein said therapeutic or diagnostic agent is ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid.

5. The method of any one of claims 1, 2 or 3, wherein said therapeutic or diagnostic agent is substantially carrier-free.

6. A process for the preparation of substantially tin-free Re(V)-2, 3 -dimercaptosuccinic acid, including the step of reducing a solution of a rhenium(VII) species in the presence of at least a 10⁵-fold molar excess of 2, 3 -dimercaptosuccinic acid with at least a 10⁵-fold molar excess of a sulfur dioxide releasing reducing agent at a pH of not greater than 6, wherein said molar excesses are based on the number of moles of said rhenium(VII) species in said solution.

7. A process according to claim 6, wherein the molar excess of 2,3-dimercaptosuccininc acid is from about 5xl0⁵ to about 5xl0⁷.

8. A process according to claim 6, wherein the molar excess of 2,3-dimercaptosuccininc acid is from about 5xl0⁵ to about 5xl0⁶.

9. A process according to claim 6, wherein the pH of said solution is in the range 3.5 to 4.

10. A process according to claim 6, wherein said sulfur dioxide releasing reducing agent is a dithionite.

11. Substantially tin-free Re(V)-2, 3 -dimercaptosuccinic acid when prepared by the process of any one of claims 6-10.

12. A substantially tin-free injectable composition including a radiolabelled Re(V)-2,3- dimercaptosuccinic acid selected from the group consisting of ¹⁸⁸Re(V)-2,3- 17 dimercaptosuccinic acid, ¹⁸⁶Re(V)-2, 3 -dimercaptosuccinic acid and mixtures thereof, together with at least one physiologically acceptable carrier, diluent, excipient or adjuvant.

13. A composition according to claim 12, wherein the radiolabelled Re(V)-2,3- dimercaptosuccinic acid is a radiolabelled Re(V)-2,3-dimercaptosuccinic acid when prepared by the process of any one of claims 6-10.

14. Use of a substantially tin-free therapeutic or diagnostic agent selected from the group consisting of ¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid, ¹⁸⁶Re(V)-2,3- dimercaptosuccinic acid and mixtures thereof, for the manufacture of a medicament for the treatment or diagnosis of cancer.

15. Use according to claim 14, wherein said therapeutic or diagnostic agent is the product of any one of claims 6-10.

16. A kit for preparing a substantially tin-free injectable composition including a radiolabelled Re(V)-2,3-dimercaptosuccinic acid selected from the group consisting of

¹⁸⁸Re(V)-2,3-dimercaptosuccinic acid, ¹⁸⁶Re(V)-2,3-dimercaptosuccinic acid, and mixtures thereof, said kit including said radiolabelled Re(V)-2,3-dimercaptosuccinic acid in a suitable container and a physiologically acceptable diluent therefor in a separate container.