111In-Labeled Trastuzumab (Herceptin) Modified with Nuclear Localization Sequences (NLS): An Auger Electron-Emitting Radiotherapeutic Agent for HER2/neu-Amplified Breast Cancer

• DOI: 10.2967/jnumed.106.037937
• Publication Date: 2007-07-14T00:43:34Z
• Authors: D. L. Costantini; C. Chan; Z. Cai; K. A. Vallis; R. M. Reilly
• Keywords: HER2/neu; NLS

The cytotoxicity and tumor-targeting properties of the anti-HER2/neu monoclonal antibody trastuzumab modified with peptides (CGYGPKKKRKVGG) harboring nuclear localization sequence ([NLS] italicized) simian virus 40 large T-antigen radiolabeled (111)In were evaluated.Trastuzumab was derivatized sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC) for reaction NLS-peptides labeled using diethylenetriaminepentaacetic acid (DTPA). immunoreactivity (111)In-NLS-trastuzumab determined by its ability to displace binding SK-BR-3 human breast cancer (BC) cells. Cellular uptake evaluated in SK-BR-3, MDA-MB-361, MDA-MB-231 BC cells, expressing high, intermediate, or very low levels HER2/neu, respectively, cell fractionation confocal microscopy. Biodistribution compared athymic mice bearing MDA-MB-361 xenografts. (111)In-trastuzumab studied clonogenic assays, DNA damage assessed probing phosphorylated histone H2AX (gammaH2AX) foci.The dissociation constant cells reduced <3-fold that (111)In-trastuzumab, demonstrating relatively preserved receptor-binding affinity. receptor-mediated internalization increased significantly from 7.2% +/- 0.9%, 1.3% 0.1%, 0.2% 0.05% 14.4% 1.8%, 6.3% 0.2%, 0.9% 6 NLS-peptides, respectively. NLS-trastuzumab localized nuclei whereas unmodified remained surface-bound. Conjugation did not affect tissue biodistribution but promoted specific xenografts (2.4-2.9 %ID/g [percentage injected dose per gram] 1.1 (111)In-trastuzumab). 5- 2-fold more potent at killing than toxicity toward minimal. 6-fold effective unlabeled trastuzumab. Formation gammaH2AX foci occurred a greater proportion after incubation trastuzumab.NLS-peptides routed nucleus HER2/neu-positive rendering radiopharmaceutical lethal through emission nanometer-micrometer range Auger electrons. cytotoxic potency vitro favorable vivo suggest it could be an targeted radiotherapeutic agent HER2/neu-amplified humans.