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 eluate obtained directly from a gallium radionuclide generator without additional purification or concentration steps to a chelator composition comprising a pharmaceutically acceptable buffer in amounts sufficient to increase the pH to a level in the range of 3 to 8, and a chelator that is able to chelate radioactive gallium within said pH range and at a temperature of 10 to 30 ? C., said chelator being linked to a biological targeting agent, wherein said chelator is selected from desferrioxamine-B (DFO), bis(2-hydroxybenzyl)ethylenediaminediacetic acid (HBED), 1,4,7-triazacyclononane macrocycle substituted with phosphonic groups at the amines (NOTP), or 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 independently hydrogen or an optionally substituted C.sub.1-7alkyl group; and where Z is hydrogen or a group of formula BH, 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, wherein said chelator, buffer are in lyophilized or freeze-dried form, and wherein said chelator composition does not include agents inhibiting metals other than gallium.

2. The method of claim 1, wherein the gallium radioisotope eluate is at a pH of less than 2.

3. The method of claim 1, wherein the composition further comprises a pharmaceutically acceptable basic reagent selected from sodium hydroxide, potassium hydroxide, a carbonate and bicarbonate.

4. The method of claim 1, wherein the chelator is linked to a biological targeting agent that targets a cancer specific marker.

5. 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, a zwitterionic buffer, a tris(hydroxymethyl)aminomethane (TRIS) buffer, morpholine propanesulphonic acid (MOPS), N-(2-hydroxyethyl) piperazine-N(2- ethanesulfonic acid) (HEPES), tartaric add, arginine or an acetate buffer.

6. The method of claim 4, wherein the cancer specific marker is prostate specific membrane antigen (PSMA).

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be particularly described by way of Example with reference to the accompanying FIGURES in which:

(2) 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.

(3) 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

(4) Preparation of .sup.68Ga Labelled Reagent

(5) 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.

(6) 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.

(7) 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.

(8) 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

(9) 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

(10) Preparation of .sup.68Ga Labelled Reagent

(11) 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.

(12) TABLE-US-00002 TABLE 2 CP256(THP) Concentration ?M % 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

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

Example 3

(14) Comparison of Radiolabelling Using Different Chelators

(15) 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.

(16) 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

(17) Lyophilised Kit

(18) A vial comprising a lyophilised reagent mixture, prepared as described above and comprising CP256(THP)(40 ?g) 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

(19) Alternative Lyophilised Kit

(20) 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.