Imaging DNA Damage In Vivo Using γH2AX-Targeted Immunoconjugates

DNA damage responses (DDR) occur during oncogenesis and therapeutic responses to DNA damaging cytotoxic drugs. Thus, a real-time method to image DNA damage in vivo would be useful to diagnose cancer and monitor its treatment. Toward this end, we have developed fluorophore-and radioisotope-labeled immunoconjugates to target a DDR signaling protein, phosphorylated histone H2A variant H2AX (gamma H2AX), which forms foci at sites of DNA double-strand breaks. Anti-gamma H2AX antibodies were modified by the addition of diethylenetriaminepentaacetic acid (DTPA) to allow In-111 labeling or the fluorophore Cy3. The cell-penetrating peptide Tat (GRKKRRQRRRPPQGYG) was also added to the immunoconjugate to aid nuclear translocation. In irradiated breast cancer cells, confocal microscopy confirmed the expected colocalization of anti-gamma H2AX-Tat with gamma H2AX foci. In comparison with nonspecific antibody conjugates, In-111-anti-gamma H2AX-Tat was retained longer in cells. Anti-gamma H2AX-Tat probes were also used to track in vivo DNA damage, using a mouse xenograft model of human breast cancer. After local X-ray irradiation or bleomycin treatment, the anti-gamma H2AX-Tat probes produced fluorescent and single photon emission computed tomography signals in the tumors that were proportionate to the delivered radiation dose and the amount of gamma H2AX present. Taken together, our findings establish the use of radioimmunoconjugates that target gamma H2AX as a noninvasive imaging method to monitor DNA damage, with many potential applications in preclinical and clinical settings. Cancer Res; 71(13); 4539-49. (C) 2011 AACR.