Analysis of DNA double-strand breaks in gastric cancer cells after treatment with 213Bi-immunoconjugates

Objectives To facilitate dosimetric calculations in α-emitter therapy, new concepts, preferably based on biological models, are needed. Since cytotoxicity of α-particles is due to induction of DNA double-strand breaks (DSBs), detection of DSBs should be a straightforward concept. At sites of DSBs histones H2AX are phosphorylated, resulting in γ-H2AX. Using an antibody that specifically binds to γ-H2AX, the numbers of DSBs can be correlated to the α-emitter activity applied. The aim of this study was to quantify DNA-DSBs in gastric cancer cells after incubation with ²¹³Bi-immunoconjugates.

Methods The monoclonal antibody d9MAb specifically binds to HSC45-M2 gastric cancer cells expressing mutant d9-E-cadherin. HSC45-M2 cells were incubated with different activity concentrations of tumor-specific ²¹³Bi-d9MAb conjugates for 3 h (t½ = 46 min). At different time points after incubation γ-H2AX was detected using immunofluorescence and Western blotting.

Results Incubation of HSC45-M2 cells seeded in chamber slides with 1.48 GBq/ml caused massive formation of γ-H2AX foci in the nuclei of treated cells that were not observed in the neighboring chamber incubated with PBS only. Thus, γ-emission during ²¹³Bi decay is unable to induce DSBs while α-particles triggered massive DSBs. Phosphorylation of histone H2AX in HSC45-M2 cells could also be demonstrated via Western blotting. Induction of γ-H2AX foci was dependent on ²¹³Bi-d9MAb activity concentration.

Conclusions Detection of DSBs via γ-H2AX foci is a promising concept to evaluate cytotoxicity and to estimate doses in ²¹³Bi-immunotherapy.