Analysis of the effect of hydroxyurea on stem cell (CFU-s) kinetics

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Abstract
Hydroxyurea [an antineoplastic drug] induces profound changes in the [mouse] pluripotential hemopoietic stem cell (CFU-s) kinetics. The main feature of these changes is a synchronous entry of resting [cell cycle phase] G0 CFU-s into the cell cycle. The analysis of the passage of the CFU-s cohort through the cell cycle has been largely based on the examination of the fraction of CFU-s which synthesize DNA in the S phase of the cell cycle. This analysis has been hampered by the fact that both the sensitivity of the S phase CFU-s to hydroxyurea and their sensitivity in the [3H]-thymidine suicide technique vary as the cells pass through the S phase. Methods which overcome these difficulties have been used. Hydroxyurea kills only .apprx. 80% of the S phase CFU-s. The sensitivity to hydroxyurea gradually decreases as the cells approach the middle part of the S phase and increases again as the cells enter the late portions of the S phase. The degree of CFU-s synchrony at the point of entry into and exit from the S phase was established. Mathematical analysis of the available data suggests that CFU-s pass through the S phase with a mean transit time of 4.79 h (SD 1.45 h). Hydroxyurea administered in vivo blocks CFU-s in the late G1 phase. The duration of this G1-S block, induced by a dose of 100 mg of hydroxyurea/kg body wt, is .apprx. 2 h. The CFU-s in the middle of the S phase, which survive hydroxyurea administration, are also blocked in their passage through the S phase. These cells seem to finish the S phase with a delay of .apprx. 2 h.