The importance of the chemical state of 99mTc radiopharmaceuticals: an effective tumor imaging form of 99mTc bleomycin

Pingyangmycin as a 99mTc carrier in tumor localization

A simple method of preparation of 99mTc-pingyangmycin (PYM) for clinical use has been established using super-micro-amounts of SnCl2 as a reductant under dark conditions. The labeling efficiency was higher than 96%, and further purification was not necessary. The effect of ascorbic acid on the distribution of 99mTc-PYM had been investigated. Ascorbic acid increased uptake of 99mTc-PYM in the tumor. Tumor uptake increased with increasing concentration of ascorbic acid. Tumor-blood, tumor-liver, tumor-lung ratios at 1.5 h after 99mTc-PYM administration were 5.19 +/- 1.64, 2.71 +/- 0.51 and 4.15 +/- 0.57, respectively. Preliminary clinical trials in nine patients showed that 99mTc-PYM is a potentially useful tracer for tumor detection with good sensitivity and specificity (true positive 7/7, true negative 1/1, and false positive 1/1).

Mononuclear and dinuclear complexes of 99mTc

In the labeling of penicillamine (Pen) with 99mTc, various complexes were detected. Studies of the conditions for differentiating the product formed in order to understand the chemical and biological behavior were carried out. Marked roles of pH and SnCl2 concentration were observed. Controlled delivery of Sn2+ ion was obtained with the tin-adsorbed resin (Sn-resin) developed. Radiopharmaceutical and biological characterization of mononuclear and dinuclear complexes of Tc-Pen, under given sets of labeling condition, were established. Those studies provided a good basis in technetium chemistry which facilitated the development of new Tc-radiopharmaceuticals. Selection of the appropriate ligand offered a stable mononuclear complex of Tc-bleomycin for tumor detection, Tc-Pen-ethyl-ester for blood-element labeling and, above all, development of a bis-thiosemicarbazone derivative as a new bifunctional chelating agent to be coupled to proteins, fatty acids, glucose etc. On the other hand, various cholescintigraphic agents were better conceived of as dinuclear complexes and this created the possibility of generating a new agent, a phthalein derivative, Tc-PC, containing the required coordination environment for the technetium to be bridged in a dinuclear state.