Effects of WR-2721 and cyclophosphamide on the cell cycle phase specificity of apoptosis in mouse bone marrow

Elucidation of the mechanisms of action of the thiol and alkylating agents on normal cells requires the knowledge of their cell cycle phase specificity in terms of their ability to induce apoptosis. The effects of S-2-/3-aminopropylamino/ethyl phosphorothioic acid (WR-2721, Amifostine) and cyclophosphamide (CP) on apoptosis and cell cycle progression were assessed in the mouse bone marrow. Adult male Swiss mice were treated with WR-2721, at a dose of 400 mg/kg body weight, and/or CP, at a dose of 200 mg/kg body weight. Application of the laser scanning cytometry APO-BRDU assay, a two-color staining method for labeling of DNA breaks and cellular DNA, allowed an identification of apoptotic and non-apoptotic cells, and their position with respect to their cell cycle phase. Temporary alterations in the number of apoptotic cells and also all bone marrow cells, including apoptotic and non-apoptotic ones, were determined throughout the 240-h period after treatment of mice with WR-2721 and/or CP. These drugs, given alone, affected apoptotic cell death and caused deregulation of the cell cycle in the bone marrow. WR-2721, applied 30 min prior to CP administration, resulted in a suppressing effect on apoptosis and the cell cycle perturbation triggered in normal bone marrow cells by the alkylating drug. The patterns of changes in the frequency of apoptotic cells and the number of apoptotic and non-apoptotic bone marrow cells, observed in all phases of the cell cycle, were dependent on the agent(s) given and the time interval after WR-2721 and/or CP administration.