Transcriptomic Signatures of Auger Electron Radioimmunotherapy Using Nuclear Targeting 111In-Trastuzumab for Potential Combination Therapies

In-111-labeled trastuzumab modified with nuclear localizing signal (NLS) peptides (In-111-trastuzumab-NLS) efficiently delivers an Auger electron (AE) emitter In-111 into the cell nucleus and is thus a promising radiopharmaceutical in AE radioimmunotherapy (AE-RIT) for targeted killing of HER2-positive cancer. However, further improvement of its therapeutic efficacy is required. In this study, the authors show a transcriptomic approach to identify potential targets for enhancing the cytotoxic effects of In-111-trastuzumab-NLS. They generated two types of In-111-trastuzumab-NLS harboring different numbers of NLS peptides, In-111-trastuzumab-NLS-S and -L. These radioimmunoconjugates (230 and 460kBq) showed a significant higher cytotoxicity to SKBR3 human breast cancer cells overexpressing HER2 compared to In-111-trastuzumab. Microarray analysis revealed that NF-kB-related genes (38 genes) were significantly changed in transcription by In-111 trastuzumab-NLS-L (230kBq) treatment. Quantitative reverse transcription polymerase chain reaction confirmed the microarray data by showing transcriptional alternation of selected NF-B target genes in cells treated with In-111-trastuzumab-NLS-L. Interestingly, bortezomib, a drug known as a NF-B modulator, significantly enhanced the cytotoxicity of In-111-trastuzumab-NLS-L in SKBR3 cells. Taken together, the transcriptome data suggest the possibility that the modulation of NF-kB signaling activity is a molecular signature of In-111-trastuzumab-NLS and coadministration of bortezomib may be efficacious in enhancement of AE-RIT with In-111-trastuzumab-NLS.