[Absorption of iodofolic acids by the cells of malignant tumors]

The uptake of 125-iodine labeled 3' iodofolic acid (I*F) and 3' iodo, 5 formyl tetrahydrofolic acid (I*FT) by the cells HeLa, ECV, L-41, human glioma, and rat glioma was studied. Human Embrionic Lung Fibroblasts (HELF) were taken for comparison as healthy cells. It was shown for *IF that its long-term uptake by cells L-41 and ECV is hundreds oftimes higher than those of HELF cells. The short-term uptake phase was studied for *IFT uptake. The dissociation constant was determined for a complex formed by *IFT and an acceptor in the HeLa cells, which is supposed to cause concentrative uptake of *IFT in cells. The dissociation constants of this acceptor complexes with folic acid, 3' iodofolic acid and 3',5'-diiodofolic acid were determined by competition with I*FT. The distribution ratio of *IF and *IFT in tissues of different organs of healthy mice and rats and rats with a sarcoma grafted on his thigh and glioma grafted into the brain was studied. As was shown there are large differences in the concentration of *IF and *IFT in the tumor and in the healthy tissue, *IF concentration in thigh muscle of healthy being 5 times lower than those in tumor grafted to the thigh, and *IFT concentration in healthy brain being 10 times lower than in brain tumor.