Imaging DNA Damage Repair in vivo Following 177 Lu-DOTATATE Therapy.

Molecular radiotherapy using Lu-177-DOTATATE is a most effective treatment for somatostatin receptor-expressing neuroendocrine tumors. Despite its frequent and successful use in the clinic, little or no radiobiologic considerations are made at the time of treatment planning or delivery. On positive uptake on octreotide-based PET/ SPECT imaging, treatment is usually administered as a standard dose and number of cycles without adjustment for peptide uptake, dosimetry, or radiobiologic and DNA damage effects in the tumor. Here, we visualized and quantified the extent of DNA damage response after Lu-177-DOTATATE therapy using SPECT imaging with In-111-anti-gamma H2AX-TAT. This work was a proof-of-principle study of this in vivo noninvasive biodosimeter with p-emitting therapeutic radiopharmaceuticals. Methods: Six cell lines were exposed to external-beam radiotherapy (EBRT) or Lu-177-DOTATATE, after which the number of gamma H2AX foci and the clonogenic survival were measured. Mice bearing CA20948 somatostatin receptor-positive tumor xenografts were treated with Lu-177-DOTATATE or sham-treated and coinjected with In-111-anti-gamma H2AX-TAT, In-111-IgG-TAT control, or vehicle. Results: Clonogenic survival after external-beam radiotherapy was cell-line-specific, indicating varying levels of intrinsic radiosensitivity. Regarding in vitro cell lines treated with Lu-177-DOTATATE, clonogenic survival decreased and gamma H2AX foci increased for cells expressing high levels of somatostatin receptor subtype 2. Ex vivo measurements revealed a partial correlation between Lu-177-DOTATATE uptake and gamma H2AX focus induction between different regions of CA20948 xenograft tumors, suggesting that different parts of the tumor may react differentially to Lu-177-DOTATATE irradiation. Conclusion: In-111-anti-gamma H2AX-TAT allows monitoring of DNA damage after Lu-177-DOTATATE therapy and reveals heterogeneous damage responses.