Mafosfamide induces less sister chromatid exchange in Ph-positive cells than in normal bone marrow.

The frequency of induced sister chromatid exchange (SCE) is a sensitive tool for the monitoring of DNA damage and has been shown to indicate chemotherapy resistance. Mafosfamide is presently used for the purging of bone marrow in autologous bone marrow transplantation in the treatment of acute leukemia. We studied the SCE-inducing effect of mafosfamide on leukemic cells of Philadelphia (Ph)-positive chronic myeloid leukemia (CML) as a model for leukemic cells. Corresponding data from normal bone marrow were analyzed for comparison. A positive linear correlation (r = 0.99, P = 0.0005) was found between the dose of mafosfamide and induced SCE in Ph-positive CML and normal bone marrow. The concentration of mafosfamide used was 0.1, 0.2, 0.4, and 0.8 micrograms/ml. Additionally, we analyzed five cases of CML and six cases of normal bone marrow. A significant difference in the frequency of induced SCE/metaphase was found between CML and normal bone marrow even after addition of 0.8 micrograms/ml mafosfamide. Also, spontaneous SCE was significantly lower in CML. Our data indicate a lower sensitivity of the leukemic cells to mafosfamide as shown by the induction of a lower frequency of SCE events.