METHODS AND KITS FOR PREPARING RADIONUCLIDE COMPLEXES

Abstract

A method for preparing a complex comprising a radioisotope of gallium for use in radiotherapy or in a medical imaging procedure, said method comprising adding a gallium radioisotope solution obtained directly from a gallium radionuclide generator to a composition comprising a pharmaceutically acceptable buffer and optionally also a pharmaceutically acceptable basic reagent, in amounts sufficient to increase the pH to a level in the range of 3 to 8, wherein the composition further comprises a chelator that is able to chelate radioactive gallium within said pH range and at moderate temperature, said chelator being optionally linked to a biological targeting agent. Kits and compositions for use in the method are also described and claimed.

Claims

1. A method for preparing a complex comprising a radioisotope of gallium for use in radiotherapy or in a medical imaging procedure, said method comprising adding a gallium radioisotope solution obtained directly from a gallium radionuclide generator to a composition comprising a pharmaceutically acceptable buffer and optionally also a pharmaceutically acceptable basic reagent, in amounts sufficient to increase the pH to a level in the range of 3 to 8, wherein the composition further comprises a chelator that is able to chelate radioactive gallium within said pH range and at moderate temperature, said chelator being optionally linked to a biological targeting agent.

2. The method of claim 1, wherein the gallium solution is an eluate obtained directly from a gallium-68 radionuclide generator.

3. The method of claim 2, wherein the eluate is at a pH of less than 2.

4. The method of claim 1, wherein the composition comprises the pharmaceutically acceptable basic reagent, the pharmaceutically acceptable basic reagent is chosen from an alkali metal hydroxide, carbonate or bicarbonate, and the alkali metal is sodium or potassium.

5. The method of claim 1, wherein the chelator is linked to the biological targeting agent.

6. The method of claim 1, wherein the chelator is a compound of formula (I) ##STR00012## or a salt thereof; wherein one of X and Y is C=0 and the other is NR; wherein each m and p are independently selected from 0 to 6; wherein R.sup.1 is a chelating group capable of chelating a radionuclide and is selected from: ##STR00013## wherein R, R.sup.2, R.sup.3 and R.sup.4 are independently hydrogen or an optionally substituted C.sub.1-7alkyl group; and where Z is hydrogen or a group of formula —B′—H, —B′-A, or a group —B′-A*-T, where T is a targeting group capable of binding to a target of interest in a subject; A is a reactive group allowing coupling to the group T, A* is a reacted reactive group A; B′ is a linker group for linking the chelating group to a reactive group A, and is represented by the formula: ##STR00014## wherein each Q is independently selected from a group consisting of —NR.sup.5—, —C(O)NR.sup.5—, —C(O)O, —NR.sup.5C(O)NR.sup.5—, —NR.sup.5C(S)NR.sup.5— and —O—, each R.sup.5 is independently hydrogen or an optionally substituted C.sub.1-7 alkyl group, each q and s are independently selected from 0 to 6 and each r is independently selected from 1 to 6.

7. The method of claim 1, wherein the pharmaceutically acceptable buffer is a phosphate buffer, bicarbonate or carbonate buffer, succinate buffer, borate buffer, cacodylate buffer, citrate buffer, sodium chloride, zinc chloride, a zwitterionic buffer, a tris(hydroxymethyl)aminomethane (TRIS) buffer, morpholine propanesulphonic acid (MOPS), N-(2-hydroxyethyl) piperazine-N′(2-ethanesulfonic acid) (HEPES), dextrose, lactose, tartaric acid, arginine, or an acetate buffer.

8. The method of claim 1, wherein the chelator comprises the biological targeting agent, the biological targeting agent is a ligand that targets a cancer specific marker, and the cancer specific marker is prostate specific membrane antigen (PSMA).

9. The method of claim 1, wherein the gallium radioisotope solution is obtained by eluting a .sup.68Ga radionuclide column with an inorganic acid.

10. A kit for use in the method of claim 1, said kit comprising a composition comprising a pharmaceutically acceptable buffer, and a chelator that is able to chelate radioactive gallium within a pH range from 3 to 8 and at moderate temperature, said chelator being optionally linked to a biological targeting agent, the composition optionally comprising a pharmaceutically acceptable basic reagent, wherein the composition produces a solution having a pH in the range of from 3 to 8 when a solution obtained directly from a gallium radionuclide generator is added thereto.

11. The kit of claim 10, wherein the composition is in liquid form.

12. The kit of claim 10, wherein components of the kit are in lyophilized or freeze-dried form.

13. The kit of claim 10, wherein the chelator is a compound of formula (I) ##STR00015## or a salt thereof; wherein one of X and Y is C=0 and the other is NR; wherein each m and p are independently selected from 0 to 6; wherein R.sup.1 is a chelating group capable of chelating a radionuclide and is selected from: ##STR00016## wherein R, R.sup.2, R.sup.3 and R.sup.4 are independently hydrogen or an optionally substituted C.sub.1-7alkyl group; and where Z is hydrogen or a group of formula —B′—H, —B′-A, or a group —B′-A*-T, where T is a targeting group capable of binding to a target of interest in a subject; A is a reactive group allowing coupling to the group T, A* is a reacted reactive group A; B′ is a linker group for linking the chelating group to a reactive group A, and is represented by the formula: ##STR00017## wherein each Q is independently selected from a group consisting of —NR.sup.5—, —C(O)NR.sup.5—, —C(O)O, —NR.sup.5C(O)NR.sup.5—, —NR.sup.5C(S)NR.sup.5— and —O—, each R.sup.5 is independently hydrogen or an optionally substituted C.sub.1-7 alkyl group, each q and s are independently selected from 0 to 6 and each r is independently selected from 1 to 6.

14. A composition for use in the method of claim 1, said composition comprising (i) a chelator which is able to chelate with a gallium radionuclide at pH 3 to 8 and at moderate temperature, optionally linked to a biological targeting agent, (ii) a pharmaceutically acceptable buffer and optionally also (iii) a pharmaceutically acceptable basic reagent, wherein (ii) and (iii) are present in the composition in amounts sufficient to result in a pH from 3 to 8 when a solution obtained directly from a gallium radionuclide generator is added thereto.

15. The composition of claim 14, wherein the gallium radionuclide chelator is a compound of formula (I) ##STR00018## or a salt thereof; wherein one of X and Y is C=0 and the other is NR; wherein each m and p are independently selected from 0 to 6; wherein R.sup.1 is a chelating group capable of chelating a radionuclide and is selected from: ##STR00019## wherein R, R.sup.2, R.sup.3 and R.sup.4 are independently hydrogen or an optionally substituted C.sub.1-7alkyl group; and where Z is hydrogen or a group of formula —B′—H, —B′-A, or a group —B′-A*-T, where T is a targeting group capable of binding to a target of interest in a subject; A is a reactive group allowing coupling to the group T, A* is a reacted reactive group A; B′ is a linker group for linking the chelating group to a reactive group A, and is represented by the formula: ##STR00020## wherein each Q is independently selected from a group consisting of —NR.sup.5—, —C(O)NR.sup.5—, —C(O)O, —NR.sup.5C(O)NR.sup.5—, —NR.sup.5C(S)NR.sup.5— and —O—, each R.sup.5 is independently hydrogen or an optionally substituted C.sub.1-7 alkyl group, each q and s are independently selected from 0 to 6 and each r is independently selected from 1 to 6.

16. The composition of claim 14, which is in a lyophilized or freeze-dried form.

17. The composition of claim 14, which in solution, has a pH from 3 to 8.

18. The composition of claim 14, which includes the pharmaceutically acceptable basic reagent, the pharmaceutically acceptable basic reagent is chosen from an alkali metal hydroxide, carbonate or bicarbonate, and the alkali metal is sodium or potassium.

19. The composition of claim 14, wherein the pharmaceutically acceptable buffer is a phosphate buffer, bicarbonate or carbonate buffer, succinate buffer, borate buffer, cacodylate buffer, citrate buffer, sodium chloride, zinc chloride, a zwitterionic buffer, a tris(hydroxymethyl)aminomethane (TRIS) buffer, morpholine propanesulphonic acid (MOPS), N-(2-hydroxyethyl) piperazine-N′(2-ethanesulfonic acid) (HEPES), dextrose, lactose, tartaric acid, arginine, or an acetate buffer.

20. The composition of claim 14, wherein the biological targeting agent is a ligand that targets a cancer specific marker, and the cancer specific marker is prostate specific membrane antigen (PSMA).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] The invention will now be particularly described by way of Example with reference to the accompanying FIGURES in which:

[0092] FIG. 1 is a graph showing the results of a comparison of chelation efficiency of a range of chelators using the method of the invention.

[0093] However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. The following descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive of or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments are shown and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

EXAMPLE 1

Preparation of .SUP.68.Ga Labelled Reagent

[0094] A range of compositions comprising the chelator CP256 were prepared containing various concentrations of pharmaceutically acceptable buffer (sodium phosphate buffer) and pharmaceutically acceptable basic reagent (sodium hydroxide) as set out in Table 1 below. The mixtures were lyophilised under vacuum overnight.

[0095] An Eckert and Zeigler .sup.68Ga generator was eluted with 0.1M HCl, to produce 5 ml eluents of 300 MBq per elution. Portions (1 ml) of the eluent were added each of the compositions at room temperature.

[0096] The pH of the resultant solutions was measured. The % radiolabelling of the CP256 (THP) was investigated using TLC. The results are also shown in Table 1 below.

TABLE-US-00001 TABLE 1 Reagent(amounts) CP256 NaOH Phosphate buffer Radiolabelling % (nmoles) (mmoles) mmoles) pH TLC 13.5 0.15 0.10 7 >47 13.5 0.10 0.10 7 >74 13.5 0.15 0.25 7 >76 13.5 0.00 0.50 4 >85 13.5 0.10 0.25 7 >89 13.5 0.05 0.25 5-6 >90 13.5 0 0.25 4 >90 13.5 0.05 0.10 5-6 >90 13.5 0 0.10 3-4 >90

[0097] The results show that radiolabelled CP256 was obtained with high levels of efficiency in 2 minutes. The high level of purity in some instances would mean that there is no need to further purify the gallium before administration to patients.

EXAMPLE 2

Preparation of .SUP.68.Ga Labelled Reagent

[0098] The methodology of Example 1 was repeated using a range of formulations comprising 0.13M sodium bicarbonate, 0.1M phosphate buffer (PBS) and a range of CP256 concentrations as listed in the following Table. Highly efficient labelling was achieved in relation to the concentration of the chelator as illustrated in Tables 2 and 2a.

TABLE-US-00002 TABLE 2 CP256 (THP) Concentration μM % Labelling Standard Dev 1000 97.55 1.45 100 95.76 4.84 10 91.52 2.36 1 62.62 7.99 0.1 31.29 4.47 0.001 0.00 1.63

TABLE-US-00003 TABLE 2A CP256 (THP) Concentration % Labelling Standard Dev 1 mM 97 0.15 500 μM 9695.76 1.42 50 μM 9791.52 0.97 5 μM 9762.62 0.06 500 nM 981.29 0.14 50 nM 150.00 3.10

EXAMPLE 3

Comparison of Radiolabelling Using Different Chelators

[0099] The method of Example 1 was repeated using a range of different chelators (DOTA, NOTA, TRAP, NOTP, HBED, DFO and THP) at various concentrations. The amounts of phosphate buffer and sodium hydroxide was adjusted to provide a pH of either 4 or 7 on addition of the 0.1M eluate. Solutions were incubated at room temperature for 10 minutes.

[0100] The results at pH 7 are shown in FIG. 1. Acceptable labelling efficiencies in excess of 95% were only found with with THP and DFO. All other chelators did not label >95% at pH 7.0. In addition the concentration of most the other chelators had to be quite high to achieve >90% labelling

EXAMPLE 4

Lyophilised Kit

[0101] A vial comprising a lyophilised reagent mixture, prepared as described above and comprising CP256(THP)(40 μg) linked to a PSMA targeting agent (30 nmoles), sodium bicarbonate (42 mg), sodium phosphate monobasic anhydrous (8.2 mg) and sodium phosphate dibasic heptahydrate (8.5 mg) is prepared. It could be reconstituted using a 0.1M HCl eluate (5 ml) obtained from an Eckert and Zeigler .sup.68Ga generator to produce a solution of pH 6.5 to 7.0, which may be used in therapy or in molecular imaging.

EXAMPLE 5

Alternative Lyophilised Kit

[0102] A vial comprising a lyophilised reagent mixture as described in Example 4 but also containing from 1 to 2 mg ascorbic acid may also be prepared. This kit also can be reconstituted using a 0.1M HCl eluate (5 ml) obtained from an Eckert and Zeigler .sup.68Ga generator to produce a solution of pH 6.5 to 7.0, which may be used in therapy or in molecular imaging.