[3H]thymidine labels less than half of the DNA-synthesizing cells in the mouse tumour, carcinoma NT

Abstract

Carcinoma NT, a transplantable mouse adenocarcinoma of spontaneous origin, was studied. Cells labeled with [3H]thymidine ([3H]TdR) were restricted to a narrow zone around the periphery of this tumor and were found in rings .ltoreq. 50 .mu.m wide around isolated blood vessels in the central necrotic area. Labeling with [3H]deoxyuridine ([3H]UdR), another DNA synthesis precursor, produced a very different pattern. The labeled zone around the periphery was much wider than with [3H]TdR, and [3H]UdR labeled cells were found up to 110 .mu.m from isolated vessels. [3H]iododeoxyuridine ([3H]IUdR) gave the same pattern of labeling as [3H]UdR. In the heavily labeled zone, within 1 mm of the tumor periphery, the labelilng index (LI) was 51% after [3H]UdR or [3H]IUdR injection and only 36% with [3H]TdR. At least half of the DNA-synthesizing cells in this tumor did not incorporate [3H]TdR. Previous workers reported cell loss factors for carcinoma NT of 60% calculated from [3H]TdR labeling data and 30% from the rate of loss of [125I]UdR. Calculations based on [125I]UdR data are more likely to be accurate for carcinoma NT than those using [3H]TdR data.