DNA Condensation with a Boron-Containing Cationic Peptide for Modeling Boron Neutron Capture Therapy.

The amino acid derivative 4-borono--phenylalanine (BPA) has been used in the radiation medicine technique boron neutron capture therapy (BNCT). Here we have characterized its interaction with DNA when incorporated into a positively charged hexa--arginine peptide. This ligand binds strongly to DNA and induces its condensation, an effect which is attenuated at higher ionic strengths. The use of an additional tetra--arginine ligand enables the preparation of a DNA condensate in the presence of a negligible concentration of unbound boron. Under these conditions, Monte Carlo simulation indicates that >85% of energy deposition events resulting from thermal neutron irradiation derive from boron fission. The combination of experimental model systems and simulations that we describe here provides a valuable tool for accurate track structure modeling of the DNA damage produced by the high LET particles involved in BNCT.