Targeting γH2AX during oncogenesis with Auger electron therapy delays tumor onset

Objectives During the early stages of tumorigenesis, genetic and signaling stresses cause DNA damage, causing tissue to activate DNA damage response (DDR) signaling. A main event during DDR is the phosphorylation of histone H2AX to γH2AX. We used γH2AX as a target for the antibody-based theranostic agent ¹¹¹In-anti-γH2AX-Tat, for SPECT imaging¹ and Auger electron therapy ^2,3.

Methods Balb-neuT mice express mutated neuT under mmtv promoter control. Mice develop DCIS-like tumors in mammary fat pads. Mice underwent weekly SPECT imaging using ¹¹¹In-anti-γH2AX-Tat or ¹¹¹In-rabbitIgG-Tat; or monthly treatment at higher specific activity with ¹¹¹In-anti-γH2AX-Tat, ¹¹¹In-rabbitIgG-Tat or PBS.

Results Expression of γH2AX in dysplastic, hyperplastic and invasive ductal tissue was shown by immunohistochemistry. Microautoradiography showed ¹¹¹In-anti-γH2AX-Tat in hyperplastic ducts. SPECT imaging using ¹¹¹In-anti-γH2AX-Tat showed significantly increased signal in mammary fat pads, correlating to precancerous stages, but not ¹¹¹In-rabbitIgG-Tat (5.1±0.7%ID/g vs. 1.3±0.5%ID/g, respectively; P<0.001). Tumor tissue showed less γH2AX foci, and did't take up ¹¹¹In-anti-γH2AX-Tat significantly more than ¹¹¹In-rabbitIgG-Tat (P<0.05). SPECT imaging using ¹¹¹In-anti-γH2AX-Tat could detect tumorous tissue in mice of 96 days old. This was 18% faster than anatomical imaging using DCE-MRI (median=117 days), and 28% faster than clinical detection by palpation (median=130 days). After therapy, tumor-free survival as monitored by palpation was significantly increased in mice treated with ¹¹¹In-anti-γH2AX-Tat, compared to ¹¹¹In-rabbitIgG-Tat or PBS (tumor onset after start of therapy was 32.5 vs. 12.5 or 12 days, respectively; P=0.008). Humane endpoints were reached significantly later (48 vs. 27 days; P=0.003). Compared to PBS-treated mice, there was an additional benefit of survival of 22 vs. -4 days, respectively (P=0.013).

Conclusions ¹¹¹In-anti-γH2AX-Tat delays tumorigenesis by targeting DDR activation in cancer precursor lesions in a genetically engineered mouse model of neuT-overexpressing breast cancer.