Comparison of 67Ga and 111In plasmid damage Based on the previous section, plasmid incubation was done with 1 MBq of 111In and the same with 67Ga. Damage assessments were made for intervals up to 72 hours to reach roughly 1 half-life of both 67Ga (78 hours) and 111In (67.3 hours). Incubation of plasmid with 67GaCl3 or 111InCl3 showed similar trends (Figure 2-4). At 4 hours of incubation with 67GaCl3, supercoiled plasmid was reduced to 0.62 ± 0.45, lower (p < 0.05) than the untreated group (0.85 ± 0.05). From 24 hours onwards, nearly all plasmid treated with 67GaCl3 changed to circular configuration (SSB). The same trend can be seen with 111InCl3 where at 4 hours of incubation only 0.47 ± 0.05 fraction of plasmid remained in supercoiled configuration. At 4 hours, there was no difference (p > 0.05) in supercoiled plasmid between 67GaCl3 and 111InCl3 treatment. Linear plasmid formations at 72 hours also showed to be no different between (p = 0.08) 67GaCl3 and 111InCl3 treatment (Figure 2-6). To investigate the effects of gamma doses with 1 MBq of 67Ga or 111In, the plasmid was incubated with the same amount of activity while kept separated from the radionuclides by a centrifuge tube. Since the 1 mm thick plastic tube is penetrable by gamma rays but not electrons, the setting should be sufficient to demonstrate the effect of gamma rays on plasmids. Figure 2-4 showed that external irradiation with gamma rays produced by 1 MBq of 67Ga have no effect to the plasmid even up to 72 hours compared to the untreated group (p=0.48 for difference between external irradiation vs untreated group with 2-way Anova). With 111In, the trend is different to 67Ga. Prolonged exposure to gamma rays from 1 MBq of 111In caused an increase in SSB. The fraction of supercoiled plasmid measured at 72 hours of exposure was 0.43 ± 0.06, significantly (p = 0.04) lower than the untreated group (0.66 ± 0.04). Another possible factor that might induce plasmid SSB include the metal itself [140, 141] which might, for example, act via production of reactive oxygen species in the presence of oxygen[142]. It is therefore vital to understand the effect of the metal on SSB. The results showed that with non-radioactive gallium and indium metals, at amounts of 0.7 and 0.6 pmoles respectively (approximately matching their expected concentration in the radionuclide samples), no effect was observed on the plasmid. Figure 2-4 Images of plasmid following treatment with radionuclide preparations at 4, 24, 48 and 72 hours of incubation. ...
