Technetium-99m labelling of the anti-tumour antibody PR1A3 by photoactivation

We have used the photoactivation method developed by Sykes et al. to label the anti-tumour antibody PR1A3 with 99mTc. The antibody was irradiated at 300 nm using a Rayonet photochemical reactor. The antibody solution was injected into a nitrogen-filled borosilicate gass vial and purged with nitrogen. A degassed solution containing stannous fluoride and methylene diphosphonate was added to the antibody and the vial was irradiated. [99mTc]pertechnetate was injected into the vial and the reaction mixture was incubated for 30 min at room temperature before being analysed by size-exclusion high-pressure liquid chromatography and instant thin-layer chromatography. Labelling yields greater than 95% were obtained using antibody concentrations ranging from 0.5 mg/ml to 5 mg/ml. Irradiation times as short as 5 min and tin to antibody ratios in the range between 11 and 32 μg tin per mg antibody gave high labelling yields. Labelling yields greater than 95% were obtained after storage of the photoactivated antibody at -70 C for several weeks. The stability of the 99mTc-labelled photoactivated PR1A3 was similar to that of 99mTc-labelled photoactivated PR1A3 was similar to that of 99mTc-labelled mercaptoethanol-reduced PR1A3. The mean immunoreactive fraction was 77% for the photoactivation-labelled Pr1A3, compred to 93% for PR1A3 labelled by mercaptoethanol reduction. Biodistribution studies were carried out using 99mTc-photoactivation-labelled PR1A3 or PR1A3 labelled by mercaptoethanol reduction in Balb/c mice and in nude mice with MKN-45 human tumour xenografts. There was no significant difference in tumour uptake between the mice that received photoactivated PR1A3 and those that received mercaptoethanol-reduced PR1A3. There was also no significant difference in uptake in most organs in Balb/c mice. (orig./MG)