Wet harvesting of no-carrier-added 211At from an irradiated 209Bi target for radiopharmaceutical applications

Development of a preclinical 211Rn/211At generator system for targeted alpha therapy research with 211At

INTRODUCTION

The availability of ²¹¹At for targeted alpha therapy research can be increased by the ²¹¹Rn/²¹¹At generator system, whereby ²¹¹At is produced by ²¹¹Rn electron capture decay. This study demonstrated the feasibility of using generator-produced ²¹¹At to label monoclonal antibody (BC8, anti-human CD45) for preclinical use, following isolation from the ²⁰⁷Po contamination also produced by these generators (by ²¹¹Rn α-decay).

METHODS

²¹¹Rn was produced by ²¹¹Fr electron capture decay following mass separated ion beam implantation and chemically isolated in liquid alkane hydrocarbon (dodecane). ²¹¹At produced by the resulting ²¹¹Rn source was extracted in strong base (2N NaOH) and purified by granular Te columns. BC8-B10 (antibody conjugated with closo-decaborate(2-)) was labeled with generator-produced ²¹¹At and purified by PD-10 columns.

RESULTS

Aqueous solutions extracted from the generator were found to contain ²¹¹At and ²⁰⁷Po, isolated from ²¹¹Rn. High radionuclidic purity was obtained for ²¹¹At eluted from Te columns, from which BC8-B10 monoclonal antibody was successfully labeled. If not removed, ²⁰⁷Po was found to significantly contaminate the final ²¹¹At-BC8-B10 product. High yield efficiencies (decay-corrected, n=3) were achieved for ²¹¹At extraction from the generator (86%±7%), Te column purification (70%±10%), and antibody labeling (76%±2%).

CONCLUSIONS

The experimental ²¹¹Rn/²¹¹At generator was shown to be well-suited for preclinical ²¹¹At-based research.

ADVANCES IN KNOWLEDGE

We believe that these experiments have furthered the knowledge-base for expanding accessibility to ²¹¹At using the ²¹¹Rn/²¹¹At generator system.

IMPLICATIONS FOR PATIENT CARE

As established by this work, the ²¹¹Rn/²¹¹At generator has the capability of facilitating preclinical evaluations of ²¹¹At-based therapies.

Production of [(211)At]-astatinated radiopharmaceuticals and applications in targeted α-particle therapy

(211)At is a promising radionuclide for α-particle therapy of cancers. Its physical characteristics make this radionuclide particularly interesting to consider when bound to cancer-targeting biomolecules for the treatment of microscopic tumors. (211)At is produced by cyclotron irradiation of (209)Bi with α-particles accelerated at ~28 MeV and can be obtained in high radionuclidic purity after isolation from the target. Its chemistry resembles iodine, but there is also a tendency to behave as a metalloid. However, the chemical behavior of astatine has not yet been clearly established, primarily due to the lack of any stable isotopes of this element, which precludes the use of conventional analytical techniques for its characterization. There are also only a limited number of research centers that have been able to produce this element in sufficient amounts to carry out extensive investigations. Despite these difficulties, chemical reactions typically used with iodine can be performed, and a number of biomolecules of interest have been labeled with (211)At. However, most of these compounds exhibit unacceptable instability in vivo due to the weakness of the astatine-biomolecule bond. Nonetheless, several compounds have shown high potential for the treatment of cancers in vitro and in several animal models, thus providing a promising basis that has allowed initiation of the first two clinical studies.