System and process for purification of astatine-211 from target materials

Abstract

A new column-based purification system and approach are described for rapid separation and purification of the alpha-emitting therapeutic radioisotope .sup.211At from dissolved cyclotron targets that provide highly reproducible product results with excellent .sup.211At species distributions and high antibody labeling yields compared with prior art manual extraction results of the prior art that can be expected to enable enhanced production of purified .sup.211At isotope products suitable for therapeutic medical applications such as treatment of cancer in human patients.

Claims

1. A method for producing a purified .sup.211At isotope product from dissolved cyclotron targets, the method comprising: dissolving a cyclotron target containing .sup.211At and Bi in a nitric acid solution to form a first solution comprising .sup.211At and Bi-nitrate salts; removing the liquid from the first solution to form a first composition comprising .sup.211At and Bi-nitrate salts; dissolving the first composition in an HCl solution to form a second solution comprising the .sup.211At and Bi in an HCl solution; preparing a separation media with conditioning solution comprising HCl to acidify the separation media; passing the second solution through the separation media to associate .sup.211At isotopes with the media and recover Bi as an eluent; and passing an At elution solution comprising HNO.sub.3 through the separation media to elute .sup.211At isotopes from the separation media and provide .sup.211At isotopes in an HNO.sub.3 solution.

2. The method of claim 1 further comprising the step of washing the column with a wash solution comprising HCl prior to passing the At elution solution through the separation media to elute .sup.211At isotopes.

3. The method of claim 1 wherein the At elution solution has a molarity between 7.5 M and 15.8 M.

4. The method of claim 1 wherein the cyclotron target is a bismuth target.

5. The method of claim 1 wherein the separation media is a non-PEG media.

6. The method of claim 5 wherein the separation media is a macroporous polymer resin.

7. The method of claim 1 wherein the conditioning solution is 8 M HCl.

8. The method of claim 7 further comprising passing the conditioning solution through the separation media for at least one sample column at a flow rate less than or equal to 2 ml/min.

9. The method of claim 1 further comprising providing a first volume of the second solution to the separation media and providing a second volume of the At elution solution to the separation media, wherein the first volume is greater than the second volume.

10. The method of claim 9 wherein the second solution is provided to the separation media at a flow rate less than or equal to 2 mL/min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows one embodiment of a system of the present invention for automated isolation of an .sup.211At isotope product.

(2) FIG. 2 shows a second embodiment of a system of the present invention for the automated isolation of an .sup.211At isotope product.

(3) FIGS. 3(a)-3(c) show column effluent activity fractions for .sup.211At during target load/wash/.sup.211At elute steps, presented as the .sup.211At isolation process performed across three cyclotron bombarded and dissolved Bi targets.

DETAILED DESCRIPTION

(4) The present disclosure provides examples and descriptions of enhanced purification and chemical isolation of .sup.211At for medical and therapeutic applications such as diagnosis and treatment of cancer in patients. In many of these examples purification using a separation column with a small internal volume as low as ˜0.25 cc provides substantially quantitative extraction of .sup.211At from dissolved cyclotron targets at selected flow rates. These separation columns can be packed, for example, with an uncoated material containing a macroporous polymeric resin such as AMBERCHROM® CG-71s that is sandwiched in the column, for example, between two acid-resistant frits.

(5) Various examples and embodiments of specific disclosures are provided hereafter and described in the attached drawings. Referring first to FIG. 1, a separation system and approach for production of a purified radioisotope .sup.211At product from dissolved cyclotron targets for therapeutic applications is shown and described. Referring first to FIG. 1, in this system, a vessel 8 containing a dissolved bismuth target solution 100, for example, in an acid that contains the desired .sup.211At isotope to be obtained is connected by tubing 24 to a fluid distribution valve 14 such as a multiple flow path distribution valve which is also connected by tubing to various other features of the device such as the separation column 10, as well as vessels 8 that contain solutions (100, 200, 300, 400). A syringe pump 12 coupled to distribution valve 14 is configured to deliver solutions (100, 200, 300, 400) at selected flow rates to a separation column 10 filled with a selected packing material 30. From this column 10 solutions are passed by tubing past a detector 16 and on to a fraction collector 18. In other embodiments such as the configuration of FIG. 2, multiple pumps (12, 12′) and valves (14, 14′) can be included. In addition a gate valve 26 that separates product from waste can be included instead of or in addition to the detector 16 and collector 18 shown in FIG. 1. The entire operation can be controlled by a computer 20.

(6) In this approach, the bismuth target is dissolved in nitric acid of a selected molar concentration to form a target solution 100 containing dissolved bismuth ions and dissolved .sup.211At isotope ions. In another step nitric acid in the solution containing the dissolved Bi isotope ions and .sup.211At isotope ions is subsequently removed, for example, by distilling the dissolved target solution that forms stable nitrate salts of both the Bi and .sup.211At isotopes. Next, these Bi and .sup.211At nitrate salts are redissolved in hydrochloric (HCl) acid solution at a selected molar concentration and introduced to the containment vessel 8 filled with prepared dissolved target solution 100 for column separation. The target solution 100 is then passed through the separation column 10 packed with a selected packing material such as, e.g., macroporous CG-71 polymer resin or another suitable material at a preselected flow rate to separate the .sup.211At isotope ions from the dissolved bismuth target solution. Separated .sup.211At isotope ions are retained on the packing material in the separation column 10 and the .sup.211At depleted bismuth target solution passes from the column for subsequent collection as shown in FIG. 1 or waste as shown in FIG. 2.

(7) In one instance, the process operates by conditioning the system by passing an acidic conditioning solution 200 through the system to establish the desired acidity and loading conditions and enhance the loading of the .sup.211At ions in the target solution on to the column. Next, a target solution 100 containing .sup.211At dissolved in a Bi target is added to the system and loaded on to the columns 10. (In some instances a small volume of air can be dispensed into the column influent line to remove the remaining conditioning fluid present in the system prior to loading.) Once loaded on to the columns the materials can be allowed to rest for a period of time and then washed using an acidic wash solution 300. (In some instances the conditioning solution and the wash solution are the same) The .sup.211At is then eluted from the column using a eluent solution 400 from whence the target material can be processed for clinical delivery.

(8) In one example system and process were used in an example wherein conditioning took place by passing 5 mL of 8 M HCl at a flow rate less than or equal to 2 ml/min, followed by passing a small volume of air through the lines. After passing the air through the lines, 15-20 mL of a target solution containing .sup.211At dissolved in a Bi target was added to the system at a low rate less than or equal to 2 mL/min loaded on to the columns.

(9) In this instance the target solution contained a Bi mass between 3.5 and 6 g which had been dissolved using HNO.sub.3, in this process the HNO.sub.3 was then distilled away and the remaining salts re dissolved in 8 M HCl. This bismuth target dissolution can be performed by an automated process such as the one described by O'Hara et al in article entitled “An automated flow system incorporating in-line acid dissolution of bismuth metal from a cyclotron irradiated target assembly for use in the isolation of astatine-211”, Applied Radiation and Isotopes 122 (2017) 202-210. The contents of which are herein incorporated by reference. This system for a distillation assembly and a process for dissolving the resulting bismuth nitrate salt to form the target solution are described therein. Such a system can also be functionally interconnected with the systems such as those shown in FIG. 1 or 2 to form a complete automated system for separations. While these methods and systems are described for forming the target solution it is to be distinctly understood that the implementation is not limited thereto but may be variously alternatively embodied, according to the needs and necessities of a user.

(10) After the loading sequence 8 mL of 8 M HCl was then used as a wash solution and passed through the system at a flow rate of less than or equal to 2 mL/min. An eluent solution consisting of 8 mL of 10 M HNO.sub.3 was then passed through the system at flow rate of 1 mL/min to elute the isolated .sup.211At from the column. A resulting .sup.211At product fraction, examples of which are shown in FIGS. 3(a)-3(c) were isolated in about 1.5 mL.

(11) Testing of the eluted .sup.211At demonstrated that while chemical yields were high, preferably greater than or equal to about 70%, more particularly greater than or equal to about 90%, and yet more particularly greater than or equal to about 95%. The present invention also recovers .sup.211At ions from the column at recovery yields greater than or equal to about 95%. The present invention also reduces process complexity enabling significantly shorter processing times as low as 20 minutes or better compared with the generally longer processing times (up to 3× greater) of the prior art solvent extraction process. Automated processing provided by the present invention also reduces radiation doses to personnel stemming from sample contact and handling that is not addressed in the manual solvent extraction process described above.

(12) In other alternative embodiments and configurations such as the example, shown in FIG. 2 a pair of syringe pumps and distribution valves are used with one pump and valve utilized, for example, for column conditioning, washing, and eluting with the other pump and valve utilized, for example, for handling the dissolved target. Packing material in the separation column recovers and retains the .sup.211At isotope from the dissolved target solution on the column packing material until the .sup.211At isotope is eluted from the column. In the preferred embodiment, packing material utilized for separation, recovery, and purification of the .sup.211At isotope from the dissolved bismuth target is a macroporous polymeric resin such as AMBERCHROM CG-71s or another suitable packing material. An optional detector, such as a radiochromatography detector capable of monitoring .sup.211At activity in column effluents, can be coupled to the separation column.

(13) In some embodiments the radiochromatography detector is a NaI(TI) scintillation detector. Other detectors may also be utilized. An optional fraction collector is shown coupled to the detector for collection of column effluents. In this embodiment the system also includes a control computer for automated control of system components as well as separation process parameters such as, for example, distribution valve flow channel and syringe pump delivery volumes as well as dissolved target and eluent flow rates. Control of other system components and processing parameters are also envisioned.

(14) As described above exemplary tests utilized a flow rate ≤2.0 mL/min but faster or slower flow rates may be utilized and are thus not intended to be limited. The separation column can also be pre-conditioned in a preparatory step with a small volume(s) of hydrochloric acid (HCl). In addition, clean HCl solution can be introduced to the column to wash any residual traces of target solution from the column yielding a highly purified .sup.211At product prior to the elution step. .sup.211At product elution profiles are controlled in part utilizing higher or lower HNO.sub.3 concentrations and are thus not intended to be limited. In one example, 10 M HNO.sub.3 was utilized to efficiently remove sorbed .sup.211At isotope ions from the column. Eluted .sup.211At product solutions can then be neutralized with a small quantity of strong base (NaOH) to create a solution having a desired pH, preferably a nearly neutral or neutral solution.

(15) In one set of tests, one embodiment of the automated fluidic system described above was utilized and operated to process a full-scale Bi target containing ˜14 mCi .sup.211At. The column utilized a resin bed of dimensions ˜5.7 mm dia.ט11.3 mm tall. Packing material in the separation column was a macroporous, polymeric resin (e.g., AMBERCHROM CG-71 ROHM and HAAS utilized conventionally to separate biomolecules including proteins, peptides, and nucleic acids) of a generally small particle size, preferably at or below about 120 microns (μm), more preferably at or below about 75 μm, and most preferably at or below about 35 μm. Other packing materials are also envisioned. The packing material for separation and purification of the .sup.211At isotope was positioned within the column sandwiched between two acid-resistant frits such as glass fiber frits or polymer (e.g., polyethylene) frits. .sup.211At activity in all column effluents was monitored utilizing a NaI(TI) scintillation radiochromatography detector. Column effluents were collected as fractions of known volume in a fraction collector. Table 1 shows the information related to various Bi target masses and the activity of the .sup.211At in each of the outlined cyclotron bombarded targets.

(16) TABLE-US-00001 TABLE 1 Run .sup.211At Activity, Date Bi Target Mass, g mCi (EOB) Dec. 8, 2016 4.54 13.2 Feb. 1, 2017 5.54 26.8 Apr. 5, 2017 3.29 24.0

(17) In another set of experiments a Bi target irradiated in a cyclotron containing ˜25-30 mCi .sup.211At was dissolved in 10 M HNO.sub.3 for a total volume of 15.5 mL. 50% (7.75 mL) of the solution was removed as a duplicate sample and replaced with 7.75 mL of 2.2 g non-irradiated Bi metal separately dissolved in 10 M HNO.sub.3 so as to provide ˜100% of the original Bi and original volume of HNO.sub.3 found in the originally dissolved target. HNO.sub.3 was distilled from the solution in a distillation chamber leaving a salt cake of Bi nitrate salts. These salts were redissolved in 8 M HCl to yield a final solution volume of 18.75 mL (0.242 g Bi/mL). The sample container containing the final solution (4.54 g dissolved Bi and ˜3.2 mCi.sup.211At) was connected to the fluid delivery system and processed. A second cyclotron target sample with 5.54 g Bi metal containing ˜27 mCi .sup.211At was also dissolved and processed. A third sample containing 3.29 g Bi metal containing about 24 mCi .sup.211At was also dissolved and processed.

(18) FIGS. 3A-3C show column separation profiles for .sup.211At products resulting from replicate purification runs obtained from separate cyclotron irradiated Bi targets. Asterisks (*) in these figures represent volumes of the .sup.211At product fractions of between 1.5 and 2.0 mL selected for subsequent species distribution and antibody labelling tests. These volumes are not intended to be limiting.

(19) Column effluent volumes are shown (FIGS. 3A-3C) during which the dissolved target loading, column washing, and column eluting steps were performed. During column elution, .sup.211At elution profiles were traced with the radiochromatography detector so that the fraction collector could collect the purified .sup.211At isotopes in a minimum volume. Single peaks in these figures correspond to .sup.211At product fractions recovered for subsequent speciation distribution and antibody labeling tests. Volumes of individual .sup.211At fractions were analyzed by dose calibrator. Percent activity for each fraction was calculated by taking each fraction volume and dividing by the total activity recovered in the process (column effluent fractions+ activity remaining on the column+ activity remaining in the vessel that originally contained the dissolved target+ activity in waste vessels). Table 2 lists results for the purification approach and .sup.211At activity results obtained in each step of the purification process for the 13 mCi, 27 mCi, and 24 mCi .sup.211At target samples, respectively.

(20) TABLE-US-00002 TABLE 2 Dec. 8, 2016 Column Feb. 1, 2017 Column Apr. 5, 2017 Column Effluent Recoveries Effluent Recoveries Effluent Recoveries Activity, Activity Activity, Activity Activity, Activity Step mCi Distribution, % mCi Distribution, % mCi Distribution, % Col. Condition — — — — Dissolved Target 0.144 1.1 0.062 0.2 0.040 0.2 Load Col. Wash 0.0283 0.2 0.011 0.0 0.010 0.0 Elute 12.601 95.5.sup.b 25.7 96.1.sup.c 22.950 95.6.sup.d Residue on 0.420 3.2 0.622 2.3 0.564 2.3 Column Misc. waste 0.728 2.7 0.439 1.8 streams Target Total 13.2 100 26.8 102 24.0 101 a. Activities reported for end-of-bombardment (EOB) .sup.bActivity in all elute fractions; the isolated .sup.211At fraction used for antibody labeling contained 88.4% of the target activity in 1.56 mL .sup.cActivity in all elute fractions; the isolated .sup.211At fraction used for antibody labeling contained 88.5% of the target activity in 1.96 mL .sup.dActivity in all elute fractions; the isolated .sup.211At fraction used for antibody labeling contained 84.4% of the target activity in 1.64 mL

(21) Results in Table 2 show that of the total 13.2 mCi, 27 mCi, and 24 mCi .sup.211At obtained from the three targets and loaded onto the columns (at end-of-bombardment, EOB), ˜96% of the total activity was collected during column elution. Isolated product fractions were also collected in a small volume (1.56 mL, 1.96 mL, and 1.64 mL) with two containing ˜88% and one containing about 84% of the total .sup.211At activity. Only 1.1% activity was lost to the column during the loading and washing steps. And only ˜2-3% activity remained in the column resin bed or frits after .sup.211At elution. In this exemplary approach, the column-based method invention yields highly purified .sup.211At that is released in a low volume acidic product fraction (e.g., 10 M HNO.sub.3). By comparison, the prior art manual extraction method as set out in the Balking publication has a general yield distribution of 78±11%.

(22) Two characteristic astatine peaks appear in the HPLC chromatograms from HPLC assays which are labeled as peak 1 and peak 2. Astatine Peak 1 behaves like iodate and is thus referred to as “astatate”. Astatine Peak 2 behaves like iodide and is thus referred to as “astatide”. Maximum tolerance for Peak 1 in the prior art approach is 15%. Peak 2 is a preferred species for establishing antibody labeling efficacy. Minimum threshold quantity of this species obtained in any purified .sup.211At product fraction in the prior art approach generally must be greater than or equal to 85%. Table 3 shows that purified .sup.211At product fractions of the present invention are substantially comprised of the preferred efficacious “astatide” species easily surpassing threshold quality metrics established for the prior art L/L extraction approach.

(23) TABLE-US-00003 TABLE 3 Peak 1 Peak 2 Processing UW .sup.211At (“astatate”), % (“astatide”), % Date Product Criteria ≤15 ≥85 Dec. 8, 2016 Column Product 6 94 (pH ~13) Feb. 1, 2017 Column Product 8 92 (pH ~13) Column Product 2 98 (pH ~6.5, after acid swing) Column Product 0.1 99.9 (after taken to salts and brought to pH ~6.5).sup.a Apr. 5, 2017 Column Product 4.5 95.5 (pH ~14) Column Product 12.7 87.3 (after taken to salts and brought to pH ~6.5) (solution reconstituted in 50% the original vol.).sup.a *.sup.211At solution reconstituted in phosphate buffered saline; has twice the dissolved solids concentration as it had originally

(24) In another set of tests, labeling efficiency of purified .sup.211At isotopes obtained by the present invention to boron-10 (B-10) conjugated CA10 antibodies was determined. .sup.211At nitrate salts generated by the present invention were dissolved in a phosphate buffered saline (PBS) solution. .sup.211At labeling measurements onto the B-10 conjugated CA10 antibodies were collected for each of the two separate column-generated .sup.211At product fractions in duplicate using two 0.5 mL aliquots or 1.0 mL aliquots of phosphate buffered saline (PBS)-dissolved .sup.211At solution. Table 4 lists antibody labeling results for each of the 13.2 mCi, 27 mCi, and 24 mCi .sup.211At column-generated samples performed in at least duplicate.

(25) TABLE-US-00004 TABLE 4 Product Vol. Mass of Processing Labeled, Antibody, Date Sample mL Mg Labeling Yield, % Dec. 8, 2016 A.sup.a 0.5 0.5 76.3 B.sup.a 0.5 0.5 73.4 Feb. 1, 2017 A.sup.b 1.0 1.0 83.8 B.sup.c 1.0 1.0 80.7 Apr. 5, 2017 A.sup.b 0.5 1.0 82.6 B.sup.b 0.5 0.2 79.5 C.sup.c 0.5 1.0 77.3 .sup.aReplicate labeling experiments occurred the next day; performed on post-neutralized .sup.211At product .sup.bPost-neutralization of .sup.211At product .sup.cPost-neutralization, evaporation to dryness, and reconstituted in phosphate buffered saline

(26) Slightly lower labeling yields were obtained for the 13 mCi samples as they were performed a day following .sup.211At isolation. Yet, results were still comparable to fresh .sup.211At product results obtained utilizing the prior art manual extraction method. Results demonstrate that purified .sup.211At products of the present invention exhibit comparable to better labeling efficiencies compared to the prior manual extraction method. In addition to the sample examples provided in additional embodiments the use of a PD-10 size exclusion column served as an effective means to remove nitrate salts from the labeling fluid during the step wherein protein is separated prior to patient injection. FIG. 3 shows column effluent activity fractions for .sup.211At during target load/wash/.sup.211At elute steps. Asterisks indicate single .sup.211At product fraction that was isolated for .sup.211At speciation monitoring by HPLC, .sup.211At antibody labeling, and Bi metal contamination. Table 5 shows results from PD-10 size exclusion separation of .sup.211At labeled CA10-B10 antibody from labeling solvent for labeling experiments A and C from the final Apr. 5, 2017 run which contained about 24 mCi of .sup.211At. Table 6 shows the Residual Bi contamination in column-generated .sup.211At product fractions as determined by inductively coupled plasma—mass spectrometry analysis of .sup.211At product fraction. The 2/1 run was not as good as the 4/5 run. This is because the 2/1 run used the single pump set-up from FIG. 1 and the 4/5 run used the dual pump set-up from FIG. 2.

(27) TABLE-US-00005 TABLE 5 Antibody- .sup.211At Nitrate Antibody- .sup.211At Nitrate bearing Activity, conc., bearing Activity, conc., Fraction μCi.sup.a μg/mL.sup.b Fraction μCi.sup.a μg/mL.sup.b A5 181 <0.2 C5 313 <0.2 A6 850 <0.2 C6 995 <0.2 A7 1077 <0.2 C7 1088 <0.2 A8 561 <0.2 C8 369 <0.2 A9 78 <0.2 C9 40 <0.2 A10 18 <0.2 C10 12 <0.2 .sup.aAt end of beam (EOB) .sup.bValues are below the reported limit of quantification (LOQ) of the instrument

(28) TABLE-US-00006 TABLE 6 .sup.211At Total Bi in Product Bi Product Bi Processing Fraction contamination, Fraction, Decontamination Date Vol, mL.sup.b μg/mL μg Factor.sup.e Feb. 1, 2017 1.96 42.1.sup.c 65.7 8.43 × 10.sup.4 Apr. 5, 2017 1.64 9.6.sup.d 15.7 2.10 × 10.sup.5 .sup.aAs determined by ICP-MS analysis of .sup.211At product fraction .sup.bFrom Table 4 .sup.cResults obtained on process that utilized only a single syringe pump to deliver dissolved Bi target and perform column condition/wash/elute steps (FIG. 1) .sup.dResults obtained on a process that utilized a separate syringe pump to deliver dissolved Bi target, and one to perform column condition/wash/elute steps (FIG. 2) .sup.eBased on ratio of initial Bi mass in bombarded target (see Table 3) to the Bi mass in the .sup.211At product fraction (column 4, this table)

(29) This data shows that despite the fact that the .sup.211At/antibody labeling solution contained multi-molar nitrate concentration (originally from the 10 M HNO3 .sup.211At column eluent that required neutralization with NaOH (thereby creating a solution of 10 M NaNO3), the size exclusion separation process prevented the high nitrate levels from passing through the PD-10 column and into the final isolated .sup.211At-labeled protein fractions.

(30) In some embodiments, purified .sup.211At isotopes in the nearly neutral or neutral product solutions are directly labeled with the selected antibody. In some embodiments, liquid from the solution is removed, for example, in a centrifugal evaporator system to create a .sup.211At product salt (e.g., nitrate salt) that stabilizes the .sup.211At isotopes for transport for end use in clinical and medical applications. In another embodiment, nitrate in the solution can first be decomposed to form an alternate salt such as a chloride salt or a hydroxide salt for transport.

(31) The present application makes clear that the system and method of the present invention provides several advantages over the prior art. The present invention (1) has a lower processing complexity compared to the prior art with fewer and simpler process steps; (2) reduces preparation time for purified .sup.211At product fractions for clinical uses and applications compared to the prior art extraction approach; (3) is automated allowing remote handling and processing in shielded environments thus reducing radiation doses to personnel stemming from handling and contact; (4) provides purified product fractions in a low elution volume enabling rapid removal of the liquid volume for transport of the purified .sup.211At product, for example, as a salt; (5) provides a .sup.211At product of superior purity and consistent quality; (6) provides a purified .sup.211At product with a superior distribution of a preferred species of isotope; and (7) provides a purified product with a comparable or better antibody labeling efficiency that can be expected to be advantageous for medical and therapeutic applications.

(32) While a number of embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications that fall within the scope of the invention.