¹⁵⁷Gd-Neutron Capture: Potential of ¹⁵⁷Gd-Labelled DNA Ligands for Neutron Capture Therapy

Abstract

The classical feature of BNCT is the limited range of the fission products of the ¹⁰B-NC reaction. Although there are other nuclides with higher thermal neutron capture cross sections than that of ¹⁰B, these have been considered of limited value for NCT because they are all n, gamma reactions. However, ¹⁵⁷Gd, which has the highest thermal neutron capture cross section (250,000 barns) has been reevaluated in recent years ^1,2. We have been particularly interested in the possibility of exploiting the internal conversion and consequent Auger electron emission associated with the n-gamma reaction. Experiments with ¹⁵⁷Gd³⁺ and plasmid DNA demonstrated that DNA-associated ¹⁵⁷Gd-NC induces DNA double-strand breaks¹. DNA-breakage was reduced by sequestering the Gd³⁺ from DNA by addition of EDTA, reflecting the limited range of Auger electrons, which is well-established³ from experiments with Auger-emitting isotopes such as ¹²⁵I. These results demonstrate the potential of ¹⁵⁷Gd-DNA ligands for NCT, by analogy with the radiobiological effectiveness of ¹²⁵I decay in DNA³.