The Biological Effects of Auger Electrons Compared to α-Particles and Li Ions

Abstract

The present study reports the results of V-79 Chinese hamster cell survival studies in which Auger electron emission was stimulated in gadolinium (Gd) after thermal neutron capture. When a porphyrin that had previously been labeled with boron (¹⁰BOPP) was also labeled with Gd (Gd-¹⁰BOPP), the cells were incubated with Gd-¹⁰BOPP to assess the compound's ability to physiologically transport the Gd into the cell, and localize the Gd atoms in or near the cell's critical target, presumably the DNA. It was anticipated that Auger electron emission, stimulated during the ¹⁵7Gd (n, °)¹⁵⁸Gd interaction, would impart additional high LET damage to that observed from the α-particle and Li ion during the ¹⁰B(n, α) ⁷Li reaction. Following irradiation with thermal neutrons from the Brookhaven Medical Research Reactor, the effectiveness of the Auger electrons was determined by comparing the response of cells incubated with ¹⁰BOPP, where damage was imparted by the boron neutron capture (BNC) products, to that from Gd-¹⁰BOPP, with equal concentration of ¹⁰B in both solutions. An Auger effectiveness factor of ∼2 was found for the Gd-¹⁰BOPP cells. The Auger effectiveness observed with Gd strongly suggested that the ¹⁰BOPP molecule physiologically transported the Gd³⁺ ion intracellularly where it probably bound to DNA. Others have reported that Gd³⁺ does, in fact, complex with DNA. While depositing less energy per interaction than the high LET BNC reaction by-products, Auger electron ionization was more effective.