Similar Lethal Effect in Mammalian Cells for Two Radioisotopes of Copper with Different Decay Schemes, ⁶⁴Cu and ⁶⁷Cu

Summary

The decays of ⁶⁴Cu incorporated in human malignant (A549) or monkey non-malignant (CVI) cells lead to cell death. When plotted as a function of the radioactivity introduced in the growth medium (µCi/ml at t = 0), the residual colony-forming capability decreases exponentially. The slope of the corresponding curve is steeper for A549 than for CV1 cells. Different data show that the cellular lethal event is a consequence of ⁶⁴Cu transmutation and not of the irradiation by the simultaneously emitted β⁻ and β⁺ particles. Liquid holding results show that the lethal event is irreparable. The decays of ⁶⁷Cu, another radioisotope of copper, lead to cell death with the same exponential survival curve and the same lethal efficiency as for ⁶⁴Cu, in spite of their different decay schemes. The lethal efficiency of both copper isotopes is close to that of ¹²⁵I utilized in the form of iododeoxyuridine under the same experimental conditions as ⁶⁴Cu and ⁶⁷Cu. The high lethal efficiency of radioactive copper transmutations raises questions about the role in DNA functioning of copper atoms known to be present in trace amounts in this macromolecule. The lethal consequence of radioactive copper transmutations suggests that the copper atoms bound to DNA are essential for cellular functioning.