Comparison of [125I]I-labeled trastuzumab and pertuzumab for targeted Auger electron therapy of cancers overexpressing HER2 receptors

<b>Objectives:</b> The HER2 receptor is often overexpressed in various cancers, particularly in breast and ovarian cancers, and this overexpression significantly contributes to the growth and spread of these tumors. Trastuzumab (Herceptin) and pertuzumab (Perjeta) are widely used humanized monoclonal antibodies (mAbs) that have shown promise in treating patients with HER2-positive breast cancer. To enhance their effectiveness, mAbs have recently been combined with chemotherapeutic agents and radionuclides. The aim of our studies was to investigate the potential therapeutic use of trastuzumab and pertuzumab labeled with the Auger electron emitter – <sup>125</sup>I. <br><b>Methods:</b> The radioimmunoconjugates synthesized using <sup>125</sup>I and <sup>131</sup>I were tested in various in vitro studies on SKOV-3 cells. These studies included tests for specificity, binding affinity, internalization, cytotoxicity (MTS assay) and confocal imaging. <br><b>Results:</b> The results confirmed that radio-iodinated mAbs have high affinity and internalization properties in an HER2+ cell line. In contrast to trastuzumab, significant localization of iodinated pertuzumab on the cell membrane was observed. MTS assay and spheroid studies demonstrated minor toxic effects from both radio-conjugates resulting from the combination of the mAbs' immuno-toxic effect and the interaction of Auger electrons. However, [<sup>125</sup>I]I-pertuzumab exhibited higher cytotoxicity. <br><b>Conclusions:</b> Despite high internalization, both radio-bioconjugates showed low cytotoxicity due to the lack of radionuclide localization in the cell nucleus. However, [<sup>125</sup>I]I-pertuzumab accumulated in the cell membrane, resulting in slightly higher cytotoxicity. To improve therapeutic efficacy, modifying [<sup>125</sup>I]I-trastuzumab and [<sup>125</sup>I] I-pertuzumab to transport them to the cell nucleus, e.g., using nuclear localization signal (NLS) peptides, is crucial.