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

Zr immuno-PET continues to be assessed in numerous clinical trials. This report evaluates the use of Zr-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. Zr-DFO-trastuzumab and Zr-DFO-cetuximab were prepared using ZrCl 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 -acetyl-l-cysteine (NAC), or 0.25 M NaOAc containing 5 mg·mL l-methionine (L-MET). To assess antigen reactivity, Zr-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. Using ZrCl , Zr-DFO-trastuzumab and Zr-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, Zr-DFO-trastuzumab remained reactive toward antigen after being prepared with ZrCl ZrCl facilitated the radiosynthesis of Zr immuno-PET agents with increased specific activity. L-MET enhanced long-term solution stability better than all other formulations examined, and Zr-DFO-trastuzumab remained reactive toward antigen. Although further evaluation is necessary, these initial results suggest that ZrCl may be useful in immuno-PET radiochemistry as radiolabeled monoclonal antibodies are increasingly integrated into precision medicine strategies.