THE EFFECTS OF IN-111 DECAY ON PBR322 DNA

We have compared the effectiveness in causing DNA strand breaks of In- 111 bound to DNA or free in aqueous solution with that of gamma rays, Supercoiled DNA from pBR322 plasmid labeled with [H-3]thymidine was pu rified and mixed with (InCl3)-In-111 in the absence or presence of die thylenetriaminepentaacetic dianhydride (DTPA), a metal chelator which prevents the binding of indium to DNA. The reaction mixtures were stor ed at 4 degrees C to accumulate radiation dose from the decay of In-11 1. The DNA was then resolved by gel electrophoresis into supercoiled, nicked circular and linear forms, representing undamaged DNA, single-s trand breaks (SSBs) and double-strand breaks (DSBs), respectively, The D-0 values of pBR322 DNA exposed to gamma radiation from an external Cs-137 source and the decay of In-111 dispersed in solution (+DTPA) ar e 3.1 +/- 0.1 and 2.8 +/- 0.1 Gy, respectively, In terms of accumulate d In-111 disintegrations cm(-3) of plasmid DNA solution, the D-0 value is 15.3 (+/- 0.7) x 10(10) disintegrations in the absence of DTPA and 38.2 (+/- 1.1) x 10(10) disintegrations in its presence, Since only 1 4.6 +/- 5% of the In-111 was bound to DNA in the absence of DTPA, an e ffective D-0 for bound In-111 of 3.4 (+/- 1.1) x 10(10) disintegration s is obtained. The 11-fold (range 9- to 17-fold) increased effectivene ss of this Auger electron emitter when in proximity to DNA appears to be due mainly to the higher yield of SSBs. (C) 1995 by Radiation Resea rch Society