Reutilization of Thymidine and Iododeoxyuridine by Mouse Mammary Carcinoma Strain MTG-B 1

Summary

The incorporation of ³H-TdR and ¹²⁵I-UdR into MTG-B tumor tissue and DNA, and the persistence of radioactivity from these precursors in the small intestine, were studied in mice treated with these drugs before tumor grafting. The results confirm the results of others that DNA synthesizing cells can reutilize precursors released by dying cells, and that TdR is more readily reutilized than IUdR. Neither the administration of drinking water containing 2.5 mg unlabeled TdR/ml, nor the inclusion of lethally irradiated cells in the tumor inocula, significantly affected reutilization of either precursor. When the drugs were injected into the intestinal lumen rather than the peritoneal cavity of tumor-bearing animals, the incorporation of ³H-TdR was reduced to 50%, and of ¹²⁵I-UdR, to 14-20%, in both small intestinal and tumor DNA. These findings suggest that labeled precursors from sluffing intestinal epithelium entered the general circulation before reutilization by either intestinal or tumor cells. In accord with the conclusions of others, radiolabeled IUdR appears to be the DNA precursor of choice in studies of tumor cell population kinetics, with the reservation that cell population growth and cell loss rates will be moderately underestimated as a result of reutilization of the labeled compound.