Radioactive triiodothyronine as a tumor cell label for kinetic studies.

Triiodothyronine tagged with 131Ihas been used as a label for Walker 256 tumor cells. This hormone attaches rapidly to the surface of tumor cells, and after 60 min less than 5% of the radio activity was removed by each washing. Radioactive iodine administered as triiodothyronine remained in the hormone during experiments several hr in duration. A considerable portion of the hormone penetrated into cells within 1 hr as indicated by radioautographs made by tritiated triiodothyronine. The use of this technic for labeling tumor cells permits studies of the kinetics of embolie tumor cell passage through the pul monary blood vessels of rats.