AHH-1 tk +/cells were exposed to the chemotherapeutic agent, momsa, both in complete medium and in medium without serum, subcultured in complete medium, and the effect on the traverse of the cell cycle determined by flow cytometric analysis of bromodeoxyuridine (BrdUrd)-labeled DNA. After exposure to mamsa (day 0), the percentage of S phase cells increased significantly (P < 0.001 7) with increasing concentration. Cells also accumulated in G2/M as evidenced by the significant (P < 0.0026), concentrationdependent increase in the percentage of cells detected within this phase. Serum deprivation during exposure resulted in significantly (P = 0.024) more cells in Sphase than in cultures exposed to momsa in complete medium.
After three days in culture, a significant (P = 0.0001) accumulation of cells in G2/M was present; the percentage of cells in G2/M did not differ significantly (P = 0.148) in cultures exposed to m amsa in complete medium or in serum-free medium.
However, a significant (P < 0.001) loss of Sphase cells was found in cultures exposed without serum.
At day 7, no significant concentration effects were detected (GO/Gl, P = 0.6026; Sphase, P = 0.9773; G2/M, P = 0.8401). These resultsdemonstrate that exposure to momsa perturbs the traverse of the cell cycle, initially by inhibiting the completion of Sphase and followed by an accumulation of cells in G2/M. In addition, exposure to momso under conditions of serum deprivation results in an increased percentage of cells in the initial S-phase after exposure, the loss of S-phase cells from the culture after three days, and the appearance of a subdiploid peak, consistent with cells undergoing apoptosis.