Observations on the Effects of Residualization and Dehalogenation on the Utility of N-Succinimidyl Ester Acylation Agents for Radioiodination of the Internalizing Antibody Trastuzumab.

Ganesan Vaidyanathan,Satish K. Chitneni,Eftychia Koumarianou,Michael R. Zalutsky

doi:10.3390/molecules24213907

Abstract

Trastuzumab is an antibody used for the treatment of human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancers. Since trastuzumab is an internalizing antibody, two factors could play an important role in achieving high uptake and prolonged retention of radioactivity in HER2-positive tumors after radioiodination—residualizing capacity after receptor-mediated internalization and susceptibility to dehalogenation. To evaluate the contribution of these two factors, trastuzumab was radiolabeled using the residualizing reagent N-succinimidyl 4-guanidinomethyl-3-[*I]iodobenzoate ([*I]SGMIB) and the nonresidualizing reagent N-succinimidyl-3-[*I]iodobenzoate ([*I]SIB), both of which are highly dehalogenation-resistant. Paired-label uptake and intracellular retention of [125I]SGMIB-trastuzumab and [131I]SIB-trastuzumab was compared on HER2-expressing BT474 human breast carcinoma cells. Tumor uptake and normal tissue distribution characteristics for the two labeled conjugates were assessed in mice bearing BT474M1 xenografts. The internalization and intracellular retention of initially-bound radioactivity in BT474 cells was similar for the two labeled conjugates up to 4 h, but were significantly higher for [125I]SGMIB-trastuzumab at 6 and 24 h. Similarly, [*I]SGMIB labeling resulted in significantly higher uptake and retention of radioactivity in BT474M1 xenografts at all studied time points. Moreover, tumor-to-tissue ratios for [125I]SGMIB-trastuzumab were consistently higher than those for [131I]SIB-trastuzumab starting at 12 h postinjection. Thus, optimal targeting of HER2-positive breast cancers with a radioiodinated trastuzumab conjugate requires an acylation agent that imparts residualizing capacity in addition to high stability towards dehalogenation in vivo.

Highlights

Human epidermal growth factor receptor 2 (HER2) is a transmembrane tyrosine kinase receptor that is overexpressed in about 22% of primary breast cancers and in multiple other cancers with varying frequency [1,2]
The significance of HER2 in breast cancer has led to the development of a number of HER2-targeted therapeutic agents including trastuzumab, a humanized monoclonal antibody that binds to the extracellular domain of HER2 [4,5]
With regard to the later, several residualizing agents have been developed for the have been developed for the radioiodination internalizing monoclonal antibody (mAb),catabolites which generate radiolabeled radioiodination of internalizing mAbs, which of generate radiolabeled that are charged at catabolites that are charged at lysosomal pH, thereby minimizingfrom the escape radioactivity from lysosomal pH, thereby minimizing the escape of radioactivity cancerofcells after receptorcancer cellsinternalization after receptor-mediated internalization usedN-succinimidyl of these reagents, mediated

Summary

Introduction

Human epidermal growth factor receptor 2 (HER2) is a transmembrane tyrosine kinase receptor that is overexpressed in about 22% of primary breast cancers and in multiple other cancers with varying frequency [1,2]. The significance of HER2 in breast cancer has led to the development of a number of HER2-targeted therapeutic agents including trastuzumab, a humanized monoclonal antibody (mAb) that binds to the extracellular domain of HER2 [4,5]. Molecules 2019, 24, 3907 expression and fluorescence in situ hybridization (FISH) analysis of HER2 gene amplification of tumor biopsy material [6]. Significant advances have been made toward developing situ hybridization (FISH) analysis of HER2 amplification of tumor biopsy material [6]. Significant radioimmunoconjugates to allowgene noninvasive imaging of HER2-overexpression in tumors advances have been made toward developing radioimmunoconjugates to allowfor noninvasive by radionuclide-based imaging techniques, including PET or SPECT, and targeted imaging of HER2-overexpression in tumors by including PET radiotherapy

Methods

Results

Discussion

Conclusion