Application of lectins to tumor imaging radiopharmaceuticals

We investigated the in vitro binding of 125I-lectins to Ehrlich ascites tumor (EAT) cells and in vivo uptake of 125I-lectins in Ehrlich solid tumor (EST) bearing mice. In in vitro binding assays, phaseolus vulgaris agglutinin (PHA), pisum sativum agglutinin(PSA), and concanavalia agglutinin(Con A) showed a high affinity for EAT cells. The in vivo biodistribution of 125I-lectins showed 125I-I-PSA to be significantly taken up into EST tissues 24 h postinjection. After IV injection of 125I-PSA, uptake of the radioactivity into the tumor tissues reached a maximum at 6 h, and thereafter decreased. Rapid clearance of the radioactivity from blood and its excretion into kidney soon after injection of 125I-PSA were observed. When compared with the biodistribution of 67Ga-citrate in EST bearing mice 24 h postinjection, tumor to liver (T/B), tumor to muscle (T/M), and tumor to blood (T/B) ratios were superior for 125I-PSA. At 6 h postinjection, the T/B-ratio of 125I-PSA was 2.5, and this value may be sufficient to enable discernible diagnostic images. Our results suggest that PSA might be a useful tumor imaging radiopharmaceutical.