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 213 Bi to cancer therapy. The generator was developed for separation of the short-lived 213 Bi (t 1/2 ) 45.6 min) from the parent radionuclide 225 Ac (t 1/2 ) 10 days), which is separated from 229 Th (t 1/2 ) 7340 yr) and its daughter isotope 225 Ra (t 1/2 ) 14.8 days). The generator requires purified 225 Ac and uses an organic anion-exchange system capable of isolating 213 Bi from a HCl solution of 225 Ac. The anion resin is then washed and stripped of the Bi product using a sodium acetate buffer. This allows direct attachment of 213 Bi 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 213 Bi 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 (t 1/2 ) 45.6 min) R-emit- ting nuclide generated from the decay of 225 Ac. 213 Bi 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 hemato- poietic and carcinoid neoplasms. 1 Moreover, there exist low-abundance, low-energy γ emissions associated with 213 Bi 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 213 Bi-radiolabeled HuM-195 (hu- manized monoclonal antibody) to a patient for treatment of acute leukemia. 2 The European Transuranium In- stitute (Karlsruhe, Germany) provided the 225 Ac precur- sor used at MSKCC to obtain the short-lived 213 Bi isotope. The generator was developed under the coor- dination of PharmActinium Inc., Dobbs Ferry, NY. 213 Bi 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 213 Bi, an improved generator concept for the separation and purification of this isotope was required. The present paper summarizes the development and testing of two 213 Bi-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 research was completed as a collaborative project in- volving 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 213 Bi-labeled radiopharmaceutical reagents. The cooperation of UW in these studies allowed the linking studies to be completed on previously unlabeled proteins and posi- tioned the UW staff for future work using alpha radio- nuclides. 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 213 Bi 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 229 Th (t 1/2 ) 7340 yr). The radioac- tive decay chain in which 213 Bi is found is well-known (Figure 1): 233 U(t 1/2 ) 1.62 × 10 5 yr) f 229 Th f 225 Ra (t 1/2 ) 14.8 days) f 225 Ac (t 1/2 ) 10 days) f 213 Bi (t 1/2 ) 45.6 min). Thus, a Bi generator has as the starting material (or “cow”) 225 Ac separated from parents or a mixture of 225 Ra/ 225 Ac. 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 * Corresponding author address: Pacific Northwest Na- tional Laboratory, P.O. Box 999 P7-25, Richland, Washington 99352. E-mail: lane.bray@pnl.gov. Phone: (509) 946-2447. Fax: (509) 372-3861. 3189 Ind. Eng. Chem. Res. 2000, 39, 3189-3194 10.1021/ie990068r CCC: $19.00 © 2000 American Chemical Society Published on Web 07/06/2000