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

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First published online May 15, 2007, 10.2967/jnumed.107.040337

Journal of Nuclear Medicine Vol. 48 No. 6 1000-1007

doi: 10.2967/jnumed.107.040337

123I-ITdU-Mediated Nanoirradiation of DNA Efficiently Induces Cell Kill in HL60

Leukemia Cells and in Doxorubicin-, ß-, or -Radiation-Resistant Cell Lines

Sven N. Reske, Deisenhofer, Gerhard Glatting, Boris D. Zlatopolskiy,

Agnieszka Morgenroth, s T. J. Vogg, s K. Buck and Friesen

Nuclear Medicine Clinic, Universität Ulm, Ulm, Germany

Correspondence: For correspondence or reprints contact: Sven N. Reske, MD,

Universität Ulm, Klinik für Nuklearmedizin, -Koch-Strasse 8, D-89081 Ulm,

Germany. E-mail: sven.reske@...

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 5-123I-iodo-4'-thio-2'-deoxyuridine

(123I-ITdU) can induce cell kill and break resistance to doxorubicin, ß-, and

-irradiation in leukemia cells. Methods: 4'-thio-2'-deoxyuridine was

radiolabeled with 123/131I and purified by high-performance liquid

chromatography. Cellular uptake, metabolic stability, DNA incorporation of

123I-ITdU, and the effect of the thymidylate synthase (TS) inhibitor

5-fluoro-2'-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

benzoylcarbonyl-Val-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/µmol for 123I-ITdU and 200

GBq/µmol for 131I-ITdU. An in vitro cell metabolism study of 123I-ITdU with

wild-type HL60 cells demonstrated an uptake of 1.5% of the initial activity/106

cells of 123I-ITdU. Ninety percent of absorbed activity from 123I-ITdU in HL60

cells was specifically incorporated into DNA. 123I-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

123I-ITdU-induced apoptosis from more than 90% to less than 10%, demonstrating

that caspases were central for 123I-ITdU-induced cell death. Inhibition of TS

with FdUrd increased DNA uptake of 123I-ITdU 18-fold and the efficiency of cell

kill about 20-fold. In addition, 123I-ITdU induced comparable apoptotic cell

death (>90%) in sensitive parental leukemia cells and in leukemia cells

resistant to ß-irradiation, -irradiation, or doxorubicin at activities of 1.2,

4.1, 12.4, and 41.3 MBq/mL after 72 h. This finding indicates that 123I-ITdU

breaks resistance to ß-irradiation, -irradiation, and doxorubicin in leukemia

cells. Conclusion: 123I-ITdU-mediated nanoirradiation of DNA efficiently induced

apoptosis in sensitive and resistant leukemia cells against doxorubicin,

ß-irradiation, and -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.