[Use of photoactivation in the preparation of radiopharmaceuticals. I. Human immunoglobulin labelled with technetium (99mTc)].

The aim of the study was to evaluate the photochemical effects of ultraviolet (UV) light on biologically active substances usable in radionuclide diagnosis. Human immunoglobulin (IgG) was irradiated with UV light at 254 nm and labelled with technetium(99mTc) by reducing pertechnetate(99mTc) with stannous chloride, or by use of redox polymer (RP SP-C25). Radiochemical purity was evaluated using paper chromatography. The biodistribution of labelled IgG in rats with experimentally induced inflammation was determined by counting the 99mTc activity of isolated organs or by planar gamma camera imaging 4 and 26 hours after administration. Irradiated IgG shows a higher efficacy of 99mTc labelling (98%) compared with non-irradiated IgG (95%) and photoactivation raises the number of free SH groups. UV light has a beneficial effect on 99mTc-IgG stability. The stability of a kit prepared using redox polymer is significantly higher (by 20%) compared with that of a kit prepared using stannous chloride (by 10%). Human IgG irradiation more than triples 99mTc deposition into inflammatory lesions. Photoactivation can be used in formulating protein-based radiopharmaceuticals in an effort to improve their biodistribution in nuclear medicine diagnostic imaging.