Bioconjugate chemistry | 14 Nov 2017
M Shah, X Zhang, R Rossin, MS Robillard, D Fisher, T Bueltmann, FJM Hoeben and T Quinn
The pretargeted radioimmunotherapy approach (PRIT) decouples the administration of tumor targeting monoclonal antibodies (mAb) from that of the radiolabeled ligand. This multi-step strategy allows delivery of high doses of radiation to tumor cells while minimizing non-specific normal tissue irradiation. In this study, we evaluated the potential of pretargeted α-particle radioimmunotherapy based on inverse electron demand Diels-Alder reaction (IEDAA) between trans-cyclooctene (TCO) and tetrazine (Tz). Two tetrazine based chelators, DOTA-Tz and TCMC-Tz, were synthesized and compared for their radiolabeling efficiency with 212Pb, radiochemical stability and in-vivo pharmacokinetics. Dosimetry was determined from pretargeted biodistribution studies. The PRIT study was carried out in LS174T tumor bearing mice pretargeted with CC49-TCO mAb. After removing unbound mAbs from the blood using two doses of clearing agent, mice were treated with various doses of (0, 2.78, 4.63, 7.40 and 2 x 2.78 MBq) of 212Pb-DOTA-Tz. 212Pb-DOTA-Tz displayed better in-vivo biodistribution than 212Pb-TCMC-Tz and was selected for PRIT study. All the mouse groups receiving treatment displayed dose dependent reduction in tumor size, while the control groups showed exponential tumor growth. Groups receiving 7.8 MBq of 212Pb-DOTA-Tz and 0.55 MBq of direct labeled CC49 exhibited acute radiation associated toxicity. Treatment with 2.78, 4.63 and 2 x 2.78 MBq of 212Pb-DOTA-Tz resulted in statistically significant improvement in median survival (26, 35 and 39 days respectively). This study successfully demonstrated that pretargeted 212Pb α-particle therapy resulted in reduced tumor growth rates and improved survival with minimal normal tissue toxicity.
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