Imaging DNA Damage Repair In Vivo After ¹⁷⁷Lu-DOTATATE Therapy

Abstract

Purpose. Molecular Radiotherapy (MRT) using 177 Lu-DOTATATE is a most effective therapy for the treatment of somatostatin receptor expressing neuroendocrine tumors (NETs). Despite its frequent and successful use in the clinic, little or no radiobiological considerations are taken into account at the time of treatment planning or delivery, and upon positive uptake of octreotide-based PET/SPECT imaging, treatment is usually administered as a standard dose and number of cycles without adjustment for peptide uptake, dosimetry, or radiobiological and DNA damage effects in the tumor. Here, we visualize and quantify the extent of DNA damage response following 177 Lu-DOTATATE therapy using SPECT imaging with 111 In-anti-γH2AX-TAT. This work is a proof-of-principle study of this in vivo non-invasive biodosimeter with beta-emitting therapeutic radiopharmaceuticals. Methods. Six cell lines were exposed to external beam radiotherapy (EBRT) or 177 Lu-DOTATATE, after which the number of γH2AX foci and clonogenic survival were measured. Mice bearing CA20948 somatostatin receptor positive tumor xenografts were treated with 177 Lu-DOTATATE or sham-treated, and co-injected with 111 In-anti-γH2AX-TAT, 111 In-IgG-TAT control, or vehicle. Results. Clonogenic survival following EBRT was cell line specific, indicating varying levels of intrinsic radiosensitivity. In vitro, cell lines treated with 177 Lu-DOTATATE, clonogenic survival decreased and γH2AX foci increased in cells expressing high levels of somatostatin receptor subtype 2 (SST2). Ex vivo measurements revealed a partial correlation between 177 Lu-DOTATATE uptake and γH2AX foci induction between different regions of CA20948 xenograft tumors, suggesting different parts of the tumor may react differentially to 177 Lu-DOTATATE irradiation. Conclusion. 111 In-anti-γH2AX-TAT allows monitoring of DNA damage following 177 Lu-DOTATATE therapy, and reveals heterogeneous damage responses.

Assessment of γ-H2AX and 53BP1 Foci in Peripheral Blood Lymphocytes to Predict Subclinical Hematotoxicity and Response in Somatostatin Receptor-Targeted Radionuclide Therapy for Advanced Gastroenteropancreatic Neuroendocrine Tumors

“…In line with the experimental data in LCLs and healthy donor PBLs, we observed similar DDR patterns. Indeed, γ-H2AX and 53BP1 foci disappear with progression of DSB repair [ 12 ]. Our observations in PBLs of PRRT patients are consistent with results of previous studies with respect to foci kinetics [ 13 , 14 ], although some variability in absolute number of detected foci is present.…”

“…The tumor suppressor p53-binding protein 1 (53BP1) also occurs at DSBs, signaling chromatin damage and facilitating ataxia-telangiectasia mutated (ATM)-dependent DSB repair [ 9 , 10 , 11 ]. Due to the direct response to radiation and the sensitivity of these assays, both markers have emerged for biological dosimetry by measuring DDR signaling [ 12 ].…”

Does the proteasome inhibitor bortezomib sensitize to DNA-damaging therapy in gastroenteropancreatic neuroendocrine neoplasms? – A preclinical assessment in vitro and in vivo

“…In contrast, predictive markers or broad mechanistic knowledge of DDR upon PRRT is rare (reviewed in [71] ). PRRT using Lu-177 as beta emitter has been shown to induce mainly SSBs and, to a lower extent, DSBs [11 , 72 , 73] . SSBs are primarily repaired by components of base excision repair (BER), nucleotide excision repair (NER) and mismatch repair (MMR) whereas DSB are cleared predominantly by non-homologous end joining (NHEJ) or homologous recombination (HR), depending on the availablilty of homologous DNA material and genetic background.…”

DNA Damage-Inducing Anticancer Therapies: From Global to Precision Damage

“…Research on differences in DNA damage induction and relevant DDR pathways between MRT and EBRT is currently ongoing, with a major factor being the dose rate: while EBRT is applied as an acute high dose, local IR delivery by radionuclides can last for several days to weeks, depending on radionuclide half-life [66]. These features give important implications for our understanding of MRT radiobiology and future research directions.…”