Hydroxyurea (HU) in experimental hematology. II. Similarities and dissimilarities between HU and 3H-thymidine killing.

The lethal effects of hydroxyurea (HU) and 3H-thymidine (3H-dT) on mouse hematopoietic cells were compared after various experimental procedures. The aim was to explore the relative efficiency of these two methods in analyzing the kinetic properties of progenitor cells. Both methods indicated that 40-50% of progenitor cells assayed with diffusion chamber culture (DCPC) were in S phase 3 days after cyclophosphamide treatment. Effects of HU, but not 3H-dT, were altered by neostigmine triggering of normal DCPC into cell cycle. On the other hand, cooling marrow cells before exposure to HU or 3H-dT largely abrogated the effect of HU, but not of 3H-dT. Blood-borne DCPC were not in cycle according to the HU effect. Separated blood DCPC were apparently in cycle, as judged with 3H-dT, but the Isopaque-Ficoll separation procedure rendered normal marrow DCPC susceptible to 3H-dT killing. When marrow cells were cultured in DC the HU technique appeared to be suitable for evaluation of modulation of progenitor cell (CFU-S or CFU-C) proliferation, whereas our previous experiments have shown that the 3H-dT technique is a convenient method to assess the initial triggering of CFU-S into cycle in DC culture.