DISTRIBUTION OF GA-67 IN NORMAL AND HYPOTRANSFERRINEMIC TUMOR-BEARINGMICE

The mechanism by which Ga-67 accumulates in tumors is controversial. T he most popular theory is that Ga-67 binds to transferrin and gains ac cess to cells by the transferrin receptor. However, substantial eviden ce suggests that uptake of Ga-67 may not be universally mediated by tr ansferrin in tumors. To determine whether transferrin is required for uptake of Ga-67 in vivo, we compared the uptake of Ga-67 by two types of implanted tumors and by normal tissues in normal and severely hypot ransferrinemic strains of Balb/C mice. One type of tumor was strongly gallium-avid in normal mice; the other was not. Uptake of Ga-67 by nor mal soft tissues was markedly less in hypotransferrinemic than in norm al mice. Uptake of Ga-67 by bone was equivalent in the two types of mi ce. For the more gallium-avid tumor, uptake of Ga-67 was similar and t he ratio of tumor-to-background activity was substantially higher in t he hypotransferrinemic than in the normal mice. For the less gallium-a vid tumor, uptake was significantly less in hypotransferrinemic than i n normal mice. These data suggest that uptake of Ga-67 by bone and by some tumors may be a transferrin-independent process.