123I-ITdU-Mediated Nanoirradiation of DNA Efficiently Induces Cell Kill in HL60 Leukemia Cells and in Doxorubicin-,  -, or  -Radiation-Resistant Cell Lines

Abstract

Resistance to radiotherapy or chemotherapy is a common cause of treatment failure in high-risk leukemias. We evaluated whether selective nanoirradiation of DNA with Auger electrons emitted by 5-123 I-iodo-49-thio-29-deoxyuridine ( 123 I-ITdU) can induce cell kill and break resistance to doxorubicin, b-, and g-irradiation in leukemia cells. Methods: 49-thio-29-deoxyuridine was radiolabeled with 123/131 I and purified by high-performance liquid chromatography. Cellular uptake, metabolic stability, DNA incorporation of 123 I-ITdU, and the effect of the thymidylate synthase (TS) inhibitor 5-fluoro-29-deoxyuridine (FdUrd) were determined in HL60 leukemia cells. DNA damage was assessed with the comet assay and quantified by the olive tail moment. Apoptosis induction and irradiation-induced apoptosis inhibition by benzoylcarbonylVal-Ala-Asp-fluoromethyl ketone (z-VAD.fmk) were analyzed in leukemia cells using flow cytometry analysis. Results: The radiochemical purity of ITdU was 95%. Specific activities were 900 GBq/mmol for 123 I-ITdU and 200 GBq/mmol for 131 I-ITdU. An in vitro cell metabolism study of 123 I-ITdU with wild-type HL60 cells demonstrated an uptake of 1.5% of the initial activity/10 6 cells of 123 I-ITdU. Ninety percent of absorbed activity from 123 I-ITdU in HL60 cells was specifically incorporated into DNA. 123 I-ITdU caused extensive DNA damage (olive tail moment . 12) and induced more than 90% apoptosis in wild-type HL60 cells. The broad-spectrum inhibitor of caspases zVAD-fmk reduced 123 IITdU-induced apoptosis from more than 90% to less than 10%, demonstrating that caspases were central for 123 I-ITdU-induced cell death. Inhibition of TS with FdUrd increased DNA uptake of 123 I-ITdU 18-fold and the efficiency of cell kill about 20-fold. In addition, 123 I-ITdU induced comparable apoptotic cell death (.90%) in sensitive parental leukemia cells and in leukemia cells resistant to b-irradiation, g-irradiation, or doxorubicin at activities of 1.2, 4.1, 12.4, and 41.3 MBq/mL after 72 h. This finding indicates that 123 I-ITdU breaks resistance to b-irradiation, g-irradiation, and doxorubicin in leukemia cells. Conclusion: 123 I-ITdU-mediated nanoirradiation of DNA efficiently induced apoptosis in sensitive and resistant leukemia cells against doxorubicin, b-irradiation, and g-irradiation and may provide a novel treatment strategy for overcoming resistance to conventional radiotherapy or chemotherapy in leukemia. Cellular uptake and cell kill are highly amplified by inhibiting TS with FdUrd.

First Demonstration of Leukemia Imaging with the Proliferation Marker 18F-Fluorodeoxythymidine

“…Coupling Auger-electron-emitting isotopes may be appropriate for nanoirradiation of DNA and entire leukemic cell kill. Recently, our group demonstrated specific induction of apoptosis and leukemic cell kill with the Auger-electron-emitting radionucleoside 123 I-ITdU (17). These in vitro results are encouraging and will be recapitulated in animal models and potentially in the human disease.…”

“…The significantly higher uptake of 18 F-FLT in bone marrow and spleen observed in patients with relapsed, refractory, or untreated leukemia than in controls is presumably related to deregulated cell cycle progression of leukemic blasts. Recently, our group demonstrated rapid uptake of 18 F-FLT in an aggressive lymphoma cell line (DoHH2) (23) and of the related nucleoside 123 I-ITdU in HL60 leukemia cells (17). Leukemic blasts exhibit a more than 10-fold overexpression of thymidine kinase 1, which is a key enzyme for intracellular trapping of nucleosides such as 18 F-FLT (25,26).…”

“…Because of physiologically increased uptake of 18 F-FLT in the bone marrow, 18 F-FLT PET has also been suggested for bone marrow imaging (16). More recently, our group has shown that radiolabeled thymidine analogs such as 5-123 I-iodo-49-thio-29-deoxyuridine ( 123 I-ITdU) can be used for induction of leukemia cell kill by mediating nanoirradiation to DNA (17).…”

Synthesis and Biologic Study of IV-14, a New Ribonucleoside Radiotracer for Tumor Visualization

“…It was reported (20,21) that pretreatment with nontoxic concentrations of the thymidylate synthase inhibitor such as 5-fluoro-29-deoxyuridine increased cellular uptake of 29-deoxynucleosides such as ITdU and IdU in tumor cells. In contrast, uptake of 131 I-IV-14 in HL60 and Mia-PaCa-2 cells (Fig.…”

Radioisotopes and Nanomedicine

“…To date, In-111, I-123 and I-125 have been studied as potential agents for this purpose (Chow et al 2008;Liu et al 2010;Liu et al 2009;Mamede et al 2003;Reske et al 2007). …”