Ind. Eng. Chem. Res. 2000, 39, 3189-3194
3189
Development of a Unique Bismuth (Bi-213) Automated Generator for Use in Cancer Therapy Lane A. Bray,* Joel M. Tingey, Jaquetta R. DesChane, Oleg B. Egorov, and Thomas S. Tenforde Pacific Northwest National Laboratory, Richland, Washington 99352
D. Scott Wilbur, Don K. Hamlin, and P. M. Pathare Department of Radiation Oncology, University of Washington, Seattle, Washington 98195
A unique separations chemistry and an automated “generator” have been developed for application of the R-emitting radionuclide 213Bi to cancer therapy. The generator was developed for separation of the short-lived 213Bi (t1/2 ) 45.6 min) from the parent radionuclide 225Ac (t1/2 ) 10 days), which is separated from 229Th (t1/2 ) 7340 yr) and its daughter isotope 225Ra (t1/2 ) 14.8 days). The generator requires purified 225Ac and uses an organic anion-exchange system capable of isolating 213Bi from a HCl solution of 225Ac. The anion resin is then washed and stripped of the Bi product using a sodium acetate buffer. This allows direct attachment of 213Bi to modified monoclonal antibodies and other targeting agents for use in patient treatment of cancers such as leukemia. To permit safe and rapid isolation of 213Bi in 1 to >20 mCi quantities, an automated system using sequential flow injection was developed. Successful evaluation of the labeling efficiency of proteins was completed using the separated Bi product. Introduction Bismuth-213 is a short-lived (t1/2 ) 45.6 min) R-emitting nuclide generated from the decay of 225Ac. 213Bi emits high-energy (8 MeV) R particles that have a range of 50-80 µm in tissue (total emitted energy ) 8 MeV) and may be ideally suited for the treatment of hematopoietic and carcinoid neoplasms.1 Moreover, there exist low-abundance, low-energy γ emissions associated with 213Bi that are useful for monitoring localization of the isotope in tumors. In 1996, Dr. David Scheinberg and colleagues at Memorial Sloan-Kettering Cancer Center (MSKCC), began administering 213Bi-radiolabeled HuM-195 (humanized monoclonal antibody) to a patient for treatment of acute leukemia.2 The European Transuranium Institute (Karlsruhe, Germany) provided the 225Ac precursor used at MSKCC to obtain the short-lived 213Bi isotope. The generator was developed under the coordination of PharmActinium Inc., Dobbs Ferry, NY. 213Bi is linked to a monoclonal antibody that, when administered to a patient, attaches to the outside of a cancer cell membrane and delivers a lethal radiation dose to the cell upon decay. This initial trial represented the first use of R therapy for human cancer treatment in the U.S. To support future testing with larger quantities of 213Bi, an improved generator concept for the separation and purification of this isotope was required. The present paper summarizes the development and testing of two 213Bi-generator concepts: (1) a Pacific Northwest National Laboratory (PNNL) automated computer-based generator system and (2) a Karlsruhe generator, reengineered and modified by MSKCC.10 The * Corresponding author address: Pacific Northwest National Laboratory, P.O. Box 999 P7-25, Richland, Washington 99352. E-mail:
[email protected]. Phone: (509) 946-2447. Fax: (509) 372-3861.
research was completed as a collaborative project involving MSKCC, PNNL, and University of Washington (UW), Seattle, WA. The advantage to MSKCC included the ability to compare equivalent sources of parent radionuclides and to perform a direct comparison of complementary methods of preparation of 213Bi-labeled radiopharmaceutical reagents. The cooperation of UW in these studies allowed the linking studies to be completed on previously unlabeled proteins and positioned the UW staff for future work using alpha radionuclides.3 Background of Current Bi-Generator Technology The widespread recognition of the effective use of radiation to kill cancer cells has led to increased interest in various radionuclides. Of particular interest are radionuclides such as 213Bi which emit R particles, because this type of radiation does not penetrate deeply into tissue. Bismuth-213 is normally produced as a daughter product of 229Th (t1/2 ) 7340 yr). The radioactive decay chain in which 213Bi is found is well-known (Figure 1): 233U (t1/2 ) 1.62 × 105 yr) f 229Th f 225Ra (t1/2 ) 14.8 days) f 225Ac (t1/2 ) 10 days) f 213Bi (t1/2 ) 45.6 min). Thus, a Bi generator has as the starting material (or “cow”) 225Ac separated from parents or a mixture of 225Ra/225Ac.4 Theoretically, by placing R emitters adjacent to unwanted cell growth, such as a tumor, the DNA of the tumor may be damaged from the R radiation without undue exposure of surrounding healthy tissue. In many such schemes, the R emitter is placed adjacent to the tumor site by binding the R emitter to a chelator, which is in turn bound to a monoclonal antibody to seek out the tumor site within the body. Unfortunately, in many instances the chelator will also bind to cations other
10.1021/ie990068r CCC: $19.00 © 2000 American Chemical Society Published on Web 07/06/2000
3190
Ind. Eng. Chem. Res., Vol. 39, No. 9, 2000
Figure 1.
229Th
decay scheme.
than the desired R emitter. Thus, it is essential that the R emitter be highly purified from other metal cations. In addition, R emitters such as 213Bi have very short half-lives and must be efficiently separated and purified in a short period of time to maximize the amount of the available R emitter. A more detailed description of the use of such radionuclides is found in numerous papers.2,5 Various methods to separate 213Bi from other radionuclides have been developed over the past few years. However, with the need for increasing amounts of R emitting radionuclides, it has been recognized that a better generator design is required. Recent work to develop 213Bi generators has focused on the use of an actinium-loaded organic cation-exchange resin.5-8 The intent of the PNNL work9 was to develop a new generator system. Goals for this generator include resistance to the intense R bombardment from the 225Ac cow, high recovery of 213Bi with minimal ionexchange column breakthrough of 225Ac, minimization of the steps required to obtain the radiopharmaceutical, and high purity of 213Bi. The major problem with the organic cation-exchange method6,7 is that, with the need for larger amounts of 225Ac (>20 mCi), the generator is limited by radiolytic destruction of the actinium-loaded organic cationexchange resin. Attempts to minimize this destruction have been employed by Drs. Wu and Brechbiel at the National Institutes of Health and by MSKCC.10 Instead of loading 225Ac as a narrow band on the top surface of a cation-exchange column (Karlsruhe approach), the actinium is distributed uniformly on the organic resin in a batch mode to “dilute” the destructive R radiolysis. With this approach, the preparation of the cow, prior to separation of 213Bi from the organic cation-exchange resin, is tedious, is time-consuming, and may not meet ALARA (as low as reasonably achievable) radiation exposure standards for the radiochemists performing the work. In addition, 225Ac remains bound to the organic resin during the lifetime of the generator (>20
Figure 2. PNNL Bi-generator concept.
days), releasing organic ion-exchange resin degradation products into the 213Bi solution each time the cow is milked. Experimental Section PNNL Generator Concept. The PNNL Bi-generator concept for separation of 213Bi from a solution of radionuclides (225Ac/213Bi) has been previously described9 and tested.11 It is based on storing 225Ac as a HCl solution (Figure 2). No organic ion-exchange resin is continually present that could be destroyed during interim 225Ac storage. The method relies on the use of an organic anion-exchange resin “system” which has been prepared in a unique fashion (described below). Instead of placing 225Ac on an organic cation-exchange resin and “milking” 213Bi, 225Ac is contained in a HCl solution. When 213Bi is needed, the “equilibrium radionuclide acid mixture” containing 225Ac and its daughters is passed through the anion-exchange resin, absorbing 213Bi. The Bicontaining anion-exchange “system” is then washed to remove traces of 225Ac along with traces of 0.5 M HCl. The wash solution containing traces of 225Ac is saved as a separate stream, which can be concentrated and added back to the original “cow”. Finally, the anionexchange “system” is stripped of the 213Bi product into a pH 4-5.5 sodium acetate (NaOAc) buffer solution, which will allow final preparation and attachment of the monoclonal antibody for patient treatment. The 213Bi extraction and recovery process requires approximately 6 min to recover 85-93% of 213Bi.
Ind. Eng. Chem. Res., Vol. 39, No. 9, 2000 3191
Figure 3. Dose calculation for 20 mCi 225Ac and daughters, as a function of Ac decay times, daughter ingrowth, and distance from the source.
The organic anion-absorbing resin “system”, provided by 3M, St. Paul, MN, consists of a paper-thin membrane, which contains an anion-exchange resin and is incorporated into a cartridge. The anion-absorbing resin, Anex, from Sarasep Corp., Santa Clara, CA, is secured in a poly(trifluoroethylene) (PTFE) membrane in accord with the method described by Haugen.12 For our testing, the filter cartridge was 25 mm in diameter. Both the cartridge size and the type of anion-exchange resin used can be varied. The ability to extract bismuth using anion resin is well-known.13 The distribution of the bismuth chloride complex in HCl increases with decreasing acid concentration, while the distribution for contaminants such as iron (Fe) increases with acid concentration. Other chelator-interfering ions of interest, i.e., rare earths, radium (Ra), francium (Fr), thorium (Th), and actinium (Ac), will not extract as chloride anions using a conventional anion-exchange resin. This provides additional radionuclide purification as compared to cation-exchange generators. Automated PNNL 213Bi Generator. The initial generator concept (Figure 2) used a 25 mm 3M filter attached to a syringe, and all operations were completed by hand. The amount of 225Ac used in these tests was 20 mCi), the calculated radiation exposure to the operator required that automation be investigated. Radiation dose calculations for 20 mCi of 225Ac at contact show a value of >10 R/h (Figure 3), after 1 day of Ac daughter ingrowth. The present paper expands on the initial chemistry using an automated closed system, controlled through the use of a personal computer, that automatically performs the same set of functions as the hand-operated generator. The development of the sequential injection (SI) separation system represents a general solutionhandling methodology that combines both automation and chemistry on a microscale and is suitable for remote manipulation with highly radioactive and corrosive solutions. The schematic of the sequential injection generator, designed by O. B. Egorov (PNNL), is shown in the diagram in Figure 4. The automated generator consists
Figure 4. Schematic diagram of the sequential injection closed 213Bi-generator system (flow direction indicated by arrows).
of a high-precision digital syringe pump equipped with a 10 mL syringe, two multiport, multiposition valves (eight-port valve A and six-port valve B), and a fourport, two-position valve. Valve A is used to select solutions for delivery to the membrane filter, and valve B is used to collect the effluents at the desired position or to divert them to waste. A two-position valve provides the possibility of reversing the direction of the flow through the membrane during the elution step. The holding coil is constructed with tubing of 1.6 mm i.d. × 6.25 m length (calculated volume 12.5 mL). The purpose of the holding coil is to accommodate reagent solutions required in the separation process without their introduction into the syringe pump. Using this approach, the pump is never exposed to corrosive or radioactive solutions. The 3M “web” anion-exchange filter (or an anion-exchange column) is placed in-line using Luer adapter fittings. The reagents, 225Ac “cow”, and final 213Bi product are contained in separate bottles or V-vials, positioned at the ports of multiposition valve A or B. 225Ac, received as a dry chloride salt in a glass V-vial, was held in a lead container. To initiate the 213Bi “milking” studies, the cap was removed from the V-vial and 0.5 M HCl was added to dissolve AcCl3 (the lead container was maintained to shield the source). MSKCC Generator. The investigators at MSKCC10 found that the Karlsruhe generator technology8,15 proved inappropriate for clinical studies. A reengineered generator was fabricated to address such factors as radiation damage to the cation resin and column, and to parent radionuclide breakthrough. The original Karlsruhe generator16-18 was designed to load all of 225Ac onto the inlet edge of the AGMP-50 cation-exchange resin support. However, it was evident to MSKCC scientists, because of physical damage to the ion-exchange column and resin, that a refined approach was required. The MSKCC ion-exchange column14 used in PNNL trials consisted of a small plastic tube containing ∼225 mg of an analytical-grade macroporous (AGMP-50) cation-exchange resin. Approximately 200 mg of resin,
3192
Ind. Eng. Chem. Res., Vol. 39, No. 9, 2000
Figure 5. MSKCC tor).
213Bi
generator (modified Karlsruhe genera-
placed in a 10 mL syringe, was batch mixed with a 1.5 M HCl solution containing ∼16 mCi of 225Ac. The rest of the resin served as an 225Ac “catch plug” in each end of the column and is separated from the active resin using a glass wool plug (Figure 5). Using a three-way stopcock, the manipulation of the syringes is as follows: The 225Ac solution (following dissolution in the V-vial) is pulled into the syringe containing the acidwashed AGMP-50 cation resin. The third port on the stopcock is attached to one end of the unloaded column. The other end of the column is attached to a 60 mL syringe, which is used to apply a negative pressure while filling the cation column with the 225Ac-loaded resin. Loading is accomplished by gentle agitation and a slight negative pressure from the 60 mL syringe. This allows the resin to pack uniformly into the column. After the syringe and column are washed with 1.5 M HCl, the column is disconnected from the stopcock and a small plug of acid-washed glass wool is applied on top of the 225Ac-loaded resin followed by ∼25 mg of clean resin. A barbed reducing fitting is then attached, and the generator is ready for production of 213Bi. The generator is eluted upflow in the vertical position such that the catch resin portion is always on top, thus allowing any fine particulate to settle out and not clog the resin bed retaining frits. The MSKCC generator is washed with 0.001 M HCl and dried by passage of an air purge via a syringe several hours prior to use. The ends of the tubing attached to the column are connected to maintain a closed system when not in use. After 213Bi ingrowth, the MSKCC generator is eluted upflow using a solution of 0.1 M HCl + 0.1 M NaI. Protein-Labeling Procedure. Chemicals and proteins, provided by investigators from UW, were used to complete 213Bi-labeling experiments with each generator concept (PNNL and MSKCC). The two proteins labeled included a canine monoclonal antibody, CA12.10C12, which is reactive with the CD45 antigen on hematopoietic cells, and recombinant streptavidin (r-SAv). For each of the labeling experiments, the following general conditions were employed. The r-SAv used was modified with the “B” isomer of cyclohexyldiethylenetriaminepentaacetic acid (1.5 CHX-B DTPA chelates/molecule).
In each labeling reaction, a 200 µg quantity of r-SAv in 120 µL of a phosphate-buffered saline solution (PBS) was used. The anti-CD45 canine monoclonal antibody (mAb) was modified with 3.6 CHX-B DTPA chelates/ molecule. In each labeling reaction, a 100 µg quantity of mAb in 120 µL of PBS was used. The 120 µL of a protein solution was mixed with 100 µL of 1 M NaOAc, pH 5, and ∼300 µL of 213Bi from the first fraction of eluant from either the PNNL or MSKCC generators. An initial determination of the amount of radioactivity in the labeling was made using a Capintec CRC-7 dose calibrator. After 10 min of reaction time, the mixture was placed on the top of a NAP-10 (G-25) size-exclusion column and eluted. Elution fractions (200 µL of PBS each) were collected in separate microcentrifuge tubes and counted. The empty reaction vial and the eluted NAP-10 column were also counted. Considering the 45.6 min half-life of 213Bi, it was necessary to determine the fraction of 213Bi available at the end of each milking and protein-labeling procedure by a rapid method. In addition to the use of the Capintec CRC-7 dose calibrator, a portable γ energy analysis instrument was used to provide rapid counting results without transporting samples to an analytical laboratory. Recoveries were based on a standard solution of 225Ac/213Bi in radioactive equilibrium as compared to separated 213Bi fractions corrected for decay back to the start of the milking step. Dose Calculations. During loading/elution of the generators, the dose to the operator will become more of an issue as the size of the “cow” is increased from the current level of 1-20 mCi to >50 mCi of 225Ac. Dose calculations for 20 mCi of 225Ac were made using the computer software program MicroShield 3.12 (Figure 3). The majority of the dose (>80%) can be attributed to 213Bi and 209Tl. The source was assumed to be a glass cylinder containing water, 2.3 cm high with a radius of 0.4 cm, and the wall clad of the glass (density 2.9 g/cm3) was 0.397 cm. The initial 225Ac was free from all daughter products at time 0. The dose was determined as a function of ingrowth of daughter products, 225Ac decay (60 s to 1 month), and distance from the source (contact to 12 cm). Results and Discussion Two major objectives were sought during the collaborative research effort. First, the PNNL automated computer-based closed anion-exchange system was evaluated against the MSKCC cation-exchange column for the separation and purification of 213Bi from 225Ac. Oak Ridge National Laboratory (Dr. Saed Mirzadeh) and the United States Department of Energy (U.S. DOE) provided ∼16 mCi of 225Ac for the trials. MSKCC (Drs. Ron Finn and Michael McDevitt) collaborated with the PNNL staff in preparing the generators and provided additional guidance relative to their use in a clinical radiopharmacy setting. Second, the advantages and disadvantages of each generator system were compared through controlled 213Bi radiolabeling experiments, directed by scientists from UW. 225Ac Feed Analysis. Approximately 16 mCi of 225Ac was received from ORNL as a dried chloride salt in a V-vial. 225Ac was dissolved in 3.1 mL of 0.5 M HCl, sampled, and determined to be 16.35 mCi. The 225Ac to 225Ra millicurie ratio at the time of receipt was 391, and the 225Ac to 229Th ratio was 2.54 × 104. The ICP-AES (inductively coupled plasma-atomic emission spectroscopy) cation analysis showed a contamination level of 0.07 mg of Al and 0.005 mg of Cr/mCi of 225Ac.
Ind. Eng. Chem. Res., Vol. 39, No. 9, 2000 3193
Figure 6. Elution profiles for the PNNL automated and MSKCC 213Bi generators.
PNNL Automated Generator. The automated Bi generator was tested using the 16 mCi of 225Ac to recover 213Bi. The feed was dissolved in 3 mL of 0.5 M HCl and remained in the V-vial. The 3M disk was preconditioned with 5 mL of 0.5 M HCl at 10 mL/min. The 225Ac solution (3 mL of 0.5 M HCl) was fed through the anion-exchange disk at 4 mL/min to extract 213Bi. Following the flush step using 10 mL of air, the disk was washed with 4 mL of 0.005 M HCl at 6 mL/min to remove the residual 225Ac and 0.5 M acid. The absorbed 213Bi chloro-complexed anion was then eluted using 4 mL of 0.1 M NaOAc, pH 5.5, at 1 mL/min and collected in 1 mL increments. The anion-exchange disk (after elution), the 4 mL of wash solution, and each of the 1 mL effluent fractions were sampled and counted using a portable γ energy analysis (GEA) system to obtain a material balance. A sample (10 µL) of the first 1 mL of effluent was sent to the analytical laboratory for complete analysis, and the remainder was used for linking studies. The above test was repeated after approximately 3 h of 213Bi ingrowth. Approximately 88% of 213Bi was recovered in 4 mL of 0.1 M NaOAc, pH 5.5 (Figure 6). The 25 mm anionexchange disk retained a portion of 225Ac in the interstitial space (wash effluent, 2-3% Ac). A smaller disk size (∼13 mm) may reduce this loss. The 13 mm disk became available for testing after the conclusion of these experiments. MSKCC Generator. At the completion of the PNNL generator studies, the ∼3 mL of 225Ac (∼16 mCi) was
placed in a syringe containing ∼200 mg of AGMP-50 cation-exchange resin. After batch extraction (Experimental Section), the 225Ac-loaded resin was placed in the MSKCC ion-exchange column and washed with 0.001 M HCl. After ∼16 h of equilibration, the MSKCC column was eluted using 0.1 M HCl + 0.1 M NaI at ∼1 mL/min. Aliquots of the effluent (∼13 drops/mL) were placed in separate vials for analysis. The eluted column was then washed with 0.001 M HCl, the interstitial liquid removed from the column with air, and the column stored. The above test was repeated five times, each time after >3 h of 213Bi ingrowth. The initial feed and each aliquot were sampled (50 µL). A sample of the first aliquot was sent to the analytical laboratory for complete analysis, and the remaining fraction of the first aliquot was used for linking studies. Approximately 100% of 213Bi was found in the first four fractions (Figure 6). Bismuth Product Analysis. The first 1 mL of “product” from the PNNL generator and the first “product” from the MSKCC test were analyzed for comparison of radiochemical purity. The 213Bi values are estimates based on GEA obtained within minutes of separation. The other values were determined after 213Bi had decayed to determine 225Ac in the “product”. The results show that the 213Bi to 225Ac (mCi) ratios in the PNNL and MSKCC product samples were 1400 and 22 000, respectively, at the time of separation. Except for Na+ from the NaOAc eluant, no other cation impurity was detected in the first 1 mL of PNNL 213Bi product. The ICP-AES results for three MSKCC elution tests show aluminum (Al) contamination, resulting from Al in the initial ORNL feed. Al appears to have loaded on the initial cation column and slowly eluted during the first three tests. Sulfur (S) was found in three MSKCC elution products. The S values vary as a function of the time elapsed between elutions and are assumed to represent degradation of the sulfonic acid cation functionalities due to radiolysis by 225Ac. The chemical form of S is not known, but the species did not appear to compete with radiolabeling or affect the radiopharmaceutical quality of the product. The advantage of the PNNL generator concept is that anion resin only absorbs 213Bi and other metal ions if they form anionic chloride complexes. This eliminates most metal contaminants with the exception of Cr(VI). In addition, 213Bi remains on the anion resin only a few minutes compared to >20 days for 225Ac stored on the cation resin (MSKCC). Labeling. Labeling experiments were successfully completed using the 213Bi products from the two Bi generators. After purification on NAP-10 columns, 72% (1.7 mCi) of the PNNL 213Bi was labeled with r-SAv and 69% (1.31 mCi) was labeled with anti-CD45 canine mAb, 12.10C12. Linking experiments were completed using the first fraction of 213Bi from three of the five MSKCC generator elutions. The first test showed only partial linking, caused by insufficient NaOAc buffer to adjust 0.1 M HCl + 0.1 M NaI to a pH of ∼4. The problem was resolved after the pH of several test solutions was checked. Increasing the buffer to 5 M NaOAc appeared to bring the pH up to >4. However, for the remaining two tests, the buffer and 213Bi solutions were premixed, the resulting solution was adjusted to pH > 5 with NaOH, and the linker was then added. After purification on a NAP-10 column, 82% (3.6 mCi) of 213Bi was labeled with
3194
Ind. Eng. Chem. Res., Vol. 39, No. 9, 2000
r-SAv and 78% (4.33 mCi) of the 213Bi was labeled with anti-CD-45 canine mAb, 12.10C12. Summary and Conclusions A unique generator has been developed by PNNL for the separation of 213Bi from 225Ac. This automated system minimizes the exposure to the intense R bombardment from the 225Ac “cow”, provides high-purity recovery of 213Bi, minimizes the time required to obtain the radiopharmaceutical, and provides 213Bi, which can be directly linked to monoclonal antibodies with minimum handling by personnel. The PNNL system was demonstrated for the separation and purification of 213Bi using a ∼16 mCi 225Ac “cow”. A Karlsruhe cation-exchange column generator, modified by MSKCC, was also demonstrated. Although there are differences between the two generator systems, both performed with excellent product recovery. The labeling efficiencies of proteins (UW) using the resulting 213Bi products from each generator system were essentially equivalent in radiochemical yield and purity. Acknowledgment This work was supported by the U.S. Department of Energy under Contract DE-AC06-76RLO-1830. The authors acknowledge the MSKCC radiochemistry team for their assistance in the preparation of the generator used in this work and the assistance from Dr. Tom Kafka, 3M New Products Research and Development, St. Paul, MN. Literature Cited (1) McDevitt, M. R.; Sgouros, G.; Finn, R. D.; Humm, J. L.; Jurcic, J. G.; Larson, S. M.; Scheinberg, D. A. Radioimmunotherapy with Alpha-emitting Nuclides. Eur. J. Nucl. Med. 1998, 9, 1341-1351. (2) Scheinberg, D. A. Alpha-emitting Bullet Targets Leukemia Cells. Nucl. News 1996, June, 47-48. (3) Wilbur, D. S.; Hamlin, D. K.; Pathare, P. M. (UW); Bray, L. A.; Tingey, J. M.; Egorov, O. B. (PNNL); Brechbiel, M. W.; Sandmaier, B. M. (Fred Hutchinson Cancer Research Center, Seattle, WA). Studies of Labeling Proteins with the AlphaEmitting Radionuclide Bi-213. J. Nucl. Med. 1998, 39, 91. (4) Ryan, J. L.; Bray, L. A. U.S. Patent 5 809 394, 1998. (5) Pippin, C. G.; Gansow, O. A.; Brechbiel, M. W.; Koch, L.; Molinet, R.; van Geel, J.; Apostolidis, C.; Geerlings, M. W.; Scheinberg, D. A. Recovery of Bi-213 from an Ac-225 Cow:
Application to the Radiolabeling of Antibodies with Bi-213. Chemists’ Views of Imaging Centers; Emran, A. M., Ed.; Plenum Press: New York, 1995. (6) Wu, C.; Brechbiel, M. W.; Gansow, O. A. An Improved Generator for the Production of Bi-213 from Ac-225. Radiochim. Acta 1997, 79, 141-144. (7) Mirzadeh, S.; Kennel, S. J.; Boll, R. A. Optimization of Radiolabeling of Immunoproteins with Bi-213. Radiochim. Acta 1997, 79, 145-149. (8) Geerlings, M. W.; Kaspersen, F. M.; Apostilidis, C.; Van Der Hout, R. The Feasibility of 225Ac as a Source of R-particles in Radioimmunotherapy. Nucl. Med. Commun. 1993, 14, 121-125. (9) Bray, L. A.; DesChane, J. R. U.S. Patent 5 749 042, 1998. (10) Finn, R. D.; McDevitt, M. R.; Scheinberg, D. A.; Jurcic, J.; Larson, S.; Sgouros, G.; Humm, J.; Curcio, M. (MSKCC); Brechbiel, M. W.; Gansow, O. A. (NIH); Geerlings, M. W. (Pharmactinium Inc., Wilmington, DE); Apostolidis, C.; Molinet, R. (European Commission, Joint Research Centre, Institute for Transuranium Elements, Karlsruhe, Germany). Refinements and Improvements for Bismuth-213 Production and Use as a Targeted Therapeutic Radiopharmaceutical. J. Labelled Compd. Radiopharm. 1997, XL, 293. (11) Pathare, P. M.; Hamlin, D. K.; Wilbur, D. S.; Brechbiel, M. W.; Bray, L. A. Synthesis and Radiolabeling of a Biotin CHX-B Chelate for Bi-213. J. Labelled Compd. Radiopharm. 1998, XLI, 595-603. (12) Haugen, D. F.; Markell, C. G.; Balsimo, W. V.; Errede, L. A. U.S. Patent 5 071 610, 1991. (13) Kraus, K. A.; Nelson, F. Adsorption of the Elements from Hydrochloric Acid, Figure 1. Proc. Int. Conf. Peaceful Uses Atomic Energy, Nucl. Chem. Effect Irradiat. 1955, VII, P/837. (14) McDevitt, M. R.; Finn, R. D.; Sgouros, G.; Ma, D. An Ac225/Bi-213 Generator System for Therapeutic Clinical Applications: Construction and Operation. Appl. Radiat. Isot. 1999, 505, 895. (15) Kaspersen, F. M.; Bos, E.; Doornmalen, A. V.; Geerlings, M. W.; Apostolidis, C.; Molinet, R. Cytotoxicity of 213Bi and 225Acimmunoconjugates. Nucl. Med. Commun. 1995, 16, 468-476. (16) Koch, L.; Apostolidis, C.; Molinet, R.; Nicolaou, G.; Janssens, W.; Schweikert, H. Production of Bi-213 and Ac-225. Joint Research Centre, European Commission, Institute for Transuranium Elements ITU, Karlsruhe, Germany, 1996. (17) Institute for Transuranium Elements (ITU), Karlsruhe, Germany. Methods for the Production of 225Ac and 213Bi for Alpha Immunotherapy. ITU Annu. Rep. Basic Actinide Res. 1995, EUR 16368. (18) Institute for Transuranium Elements (ITU), Karlsruhe, Germany. Radioimmunotherapy. ITU Annu. Rep. Basic Actinide Res. 1996, 1.7, EUR 17296.
Received for review January 28, 1999 Revised manuscript received November 15, 1999 Accepted November 21, 1999 IE990068R
