In vitro binding of 67Ga to Ehrlich ascites tumor cells

The binding of ⁶⁷Ga to Ehrlich ascites tumor cells (ETC) was studied in vitro. Acid mucopolysaccharide (AMPS) present at the cell surface of ETC was identified as heparan sulfate (HS). The extent of ⁶⁷Ga binding to ETC reached a plateau (ca. 10% of the added dose) at 1–2 h after the start of incubation. The binding was higher under neutral or alkaline conditions than under acidic conditions. Heparin and heparitinase treatment both significantly decreased the extent of ⁶⁷Ga binding to ETC. Mild treatment with protease, including trypsin or papain, also decreased the binding. On the contrary, the treatment with trypsin under severe conditions markedly increased the extent of ⁶⁷Ga binding to ETC. These results support the hypothesis that HS plays an important role as a ⁶⁷Ga receptor in the mechanism of gallium binding to ETC.