⁸⁹Zr-Chloride Can Be Used for Immuno-PET Radiochemistry Without Loss of Antigen Reactivity In Vivo

Abstract

⁸⁹Zr immuno-PET continues to be assessed in numerous clinical trials. This report evaluates the use of ⁸⁹Zr-chloride in the radiolabeling of monoclonal antibodies conjugated with desferrioxamine B (DFO), describes its effects on radiopharmaceutical reactivity toward antigen, and offers guidance on how to ensure long-term stability and purity. <b>Methods:</b>⁸⁹Zr-DFO-trastuzumab and ⁸⁹Zr-DFO-cetuximab were prepared using ⁸⁹ZrCl₄ The stability of each was evaluated for 7 d in 20 mM histidine/240 mM sucrose buffer, 0.25 M sodium acetate (NaOAc) buffer containing 5 mg·mL^-1<i>n</i>-acetyl-l-cysteine (NAC), or 0.25 M NaOAc containing 5 mg·mL^-1 l-methionine (L-MET). To assess antigen reactivity, ⁸⁹Zr-DFO-trastuzumab was evaluated using the Lindmo method and tested in PET/CT imaging of mouse models of human epidermal growth factor receptor 2-positive or -negative lung cancer. <b>Results:</b> Using ⁸⁹ZrCl₄, ⁸⁹Zr-DFO-trastuzumab and ⁸⁹Zr-DFO-cetuximab were prepared with increased specific activity and retained purities of 95% after 3 d when formulated in NaOAc buffer containing L-MET. Based on Lindmo analysis and small-animal PET/CT imaging, ⁸⁹Zr-DFO-trastuzumab remained reactive toward antigen after being prepared with ⁸⁹ZrCl₄<b>Conclusion:</b>⁸⁹ZrCl₄ facilitated the radiosynthesis of ⁸⁹Zr immuno-PET agents with increased specific activity. L-MET enhanced long-term solution stability better than all other formulations examined, and ⁸⁹Zr-DFO-trastuzumab remained reactive toward antigen. Although further evaluation is necessary, these initial results suggest that ⁸⁹ZrCl₄ may be useful in immuno-PET radiochemistry as radiolabeled monoclonal antibodies are increasingly integrated into precision medicine strategies.