Direct-Time Resolved Measurement of DNA Strand Scission Reactions from 225ac
Abstract
Purpose
We present advancements of single-molecule biodosimetry to measure radiation-induced DNA damage from α-emitting 225Ac. These results will be compared to β-emitting radionuclides to assess relative biological effectiveness (RBE) for radionuclide therapies.
Methods
A solution of 225Ac in 0.04 mol/L HCl was received and diluted gravimetrically to prepare sources for calibration and for addition to DNA-containing reservoirs. The massic activity of the solution was determined by ionization chamber measurement with direct traceability to primary standards and combined standard uncertainty <0.4%. Conical quartz nanopipettes pulled to ≈15 nm were filled with 3 mol/L LiCl at pH 8.0 with 10 mmol/L TRIS and immersed in the same with 3 nmol/L φX174 supercoiled DNA. Aliquots of 225Ac (18 kBq to 111 kBq at the time of addition) were added to the DNA-containing buffer and the pH was titrated to ≈pH 8 with 1 mol/L LiOH. The sample was evaluated for DNA lesions by applying an electric field to drive the DNA into the nanocapillary. Resistive pulses were then recorded for each molecule, and evaluated to extract the DNA secondary structure (i.e., coiled state) and length by decoding the shape and duration of the pulses.
Results
These results demonstrate that supercoiled DNA can serve as an in situ radiation dosimeter for single-molecule biodosimetry. Improvements in nanocapillary capabilities allow us to observe DNA damage in the low dose regime (i.e., <2 Gy) in real time. Preliminary assessment suggests that DNA damage by a emitters is greater than b emitters for similar dose absorbed.
Conclusion
DNA damage from a emitters can be assessed by resistive pulse sensors and compared directly to b emitters with quantitative nanopore-based single molecule sensors. These measurement will allow the development of precise quantification of dose delivered in radiopharmaceutical therapy and provide a framework for developing RBE values for emerging treatments.