Radiobiological effects of hypoxia-dependent uptake of 64 Cu-ATSM: enhanced DNA damage and cytotoxicity in hypoxic cells

Purpose Hypoxia occurs frequently in cancers and can lead to therapeutic resistance due to poor perfusion and loss of the oxygen enhancement effect. 64 Cu-ATSM has shown promise as a hypoxia diagnostic agent due to its selective uptake and retention in hypoxic cells and its emission of positrons for PET imaging. 64 Cu also emits radiotoxic Auger electrons and β - particles and may therefore exhibit therapeutic potential when concentrated in hypoxic tissue. Methods MCF-7 cells were treated with 0–10 MBq/ml 64 Cu-ATSM under differing oxygen conditions ranging from normoxia to severe hypoxia. Intracellular response to hypoxia was measured using Western blotting for expression of HIF-1α, while cellular accumulation of 64 Cu was measured by gamma counting. DNA damage and cytotoxicity were measured with, respectively, the Comet assay and clonogenic survival. Results 64 Cu-ATSM uptake in MCF-7 cells increased as atmospheric oxygen decreased (up to 5.6 Bq/cell at 20.9% oxygen, 10.4 Bq/cell at 0.1% oxygen and 26.0 Bq/cell at anoxia). Toxicity of 64 Cu-ATSM in MCF-7 cells also increased as atmospheric oxygen decreased, with survival of 9.8, 1.5 and 0% in cells exposed to 10 MBq/ml at 20.9, 0.1 and 0% oxygen. The Comet assay revealed a statistically significant increase in 64 Cu-ATSM-induced DNA damage under hypoxic conditions. Conclusion The results support a model in which hypoxia-enhanced uptake of radiotoxic 64 Cu induces sufficient DNA damage and toxicity to overcome the documented radioresistance in hypoxic MCF-7 cells. This suggests that 64 Cu-ATSM and related complexes have potential for targeted radionuclide therapy of hypoxic tumours.