Incorporation of lododeoxyuridine-12 51 into the DNA of LI210 Leukemia Cells during Tumor Development1

bearing L1210 or L1210/MTX leukemia to study DNA synthesis in vivo. In mice bearing a large population of leukemia cells, most of the retained radioactivity could be recovered from the DNA of these cells. Total body retention and the anatomical distribution of radioactivity in leukemic mice were highly dependent upon the route of iododeoxyuridine administration. Intraperitoneal injections into mice bearing a peritoneal tumor resulted in three times as much retention of radioactivity by the whole mouse as intravenous or subcutaneous injections, and this route was 15 times more effective in labeling the peritoneal leukemia population. In control mice the total body retention of radioactivity was the same with all three routes of injection, although uptake of radioactivity by spleen and intestine was slightly enhanced by intraperitoneal administration. The organ distribution of radioactivity indicated extensive migration of tumor cells from the peritoneal cavity within the first few days after their inoculation. The incorporation of radioactivity into peritoneal LI 210 cells initially appeared to increase as fast as the number of tumor cells, possibly even faster. After Day 3 of tumor growth peritoneal uptake of iododeoxyuridine gradually leveled off and reached a maximum of 20 to 30% of the inoculated dose on Day 5. The number of LI 210 cells present in the peritoneal cavity however continued to rise until the mice died. I2SI