Studies of the in vivo entry of Ga-67 into normal and malignant tissue

Previous studies of the effect of scandium on the tissue distribution of Ga-67 suggest that Ga-67 makes its initial in vivo entry into normal and malignant tissues by different routes. (Scandium blocking of plasma protein Ga-67 binding increased Ga-67 excretion, decreased its uptake in normal tissues, but had little effect on rodent tumors.) In further studies we have used other methods to alter the plasma binding of Ga-67. Iron saturation of plasma produced effects on Ga-67 tissue distribution similar to those observed with scandium. On the other hand, increasing Ga-67 plasma binding through induction of anemia and administration of apotransferrin produced the reverse of the effects observed with scandium and iron. We conclude that the initial in vivo entry of Ga-67 into tumor tissue involves mainly an unbound or loosely bound form of Ga-67, whereas its uptake by normal soft tissues is strongly promoted by its binding to transferrin.