Absorption of iodofolic acids by the cells of malignant tumors

The uptake of our synthesized 125-iodine labeled 3′-iodofolic acid (*IF) and 3′-iodo-5-formyltetrahyrofolic acid (*IFT) by the HeLa, EVC, L-41, human glioma, and rat glioma cells has been studied. The Human Embryonic Lung Fibroblasts (HELFs) were used as healthy control cells for comparison. It was shown for the quantity of *IF absorbed at its long-term uptake phase by the L-41 and ECV cells is hundreds of times higher than that of the HELF cells. The short-term *IFT uptake phase by the cells was studied. For the HeLa cells, the dissociation constant was determined for the *IFT complex with an acceptor, which is supposed to be responsible for *IFT accumulation in the cells. Using competitive sorption approach, the dissociation constants of folic, 3′-iodofolic, and 3′,5′-diiodofolic acid complexes with this acceptor were assessed. The distribution ratio of *IF and *IFT in tissues of different organs of healthy mice and rats and also in rats with sarcoma grafted on their thigh and glioma grafted into the brain was studied. A considerable differences were shown in the concentrations of *IF and *IFT in the tumor and in the healthy tissue, i.e., *IF in the healthy thigh muscle is five times lower than in the tumor grafted to the thigh, and *IFT concentration is 10 times lower in the healthy brain compared to the brain tumor.