In Vivo DNA Cross-Linking by Cyclophosphamide: Comparison of Human Chronic Lymphatic Leukemia Cells with Mouse LI 210 Leukemia and Normal Bone Marrow Cells1

Alkaline elution was done on a variety of cells following cyclophosphamide (CY) treatment in vivo.Cells used were 1.1210 leukemia, normal mouse bone marrow, and peripheral blood cells obtained from a patient with chronic lymphatic leukemia (d.i.). Endpoints used were determi nation of single strand breaks, DNA-DNA interstrand and DNA-protein cross-links. After treatment of mice with CY (4 mg/mouse), low levels of single strand breaks were observed in both I 1210 leukemia and ( 1)1, normal bone marrow. When a patient with CLL was treated with CY (750 mg/ m '), no evidence of single strand breaks could be demonstrated. Maximum levels of DNA-DNA interstrand cross-links were observed in mice 2 h after injection of CY for the L1210 leukemia cells |175 ±25 rad-equivalents (req)| and at 4 h for the (1)1, normal bone marrow cells (47 ±9 req). In human CLL, maximum levels were observed 12 h after injection of CY. Peak levels of DNA-DNA interstrand cross-links were approximately 4-fold lower in (1)1, normal bone marrow cells than in 11210 leukemia. The frequencies measured in human CLL cells were relatively low at any timepoint (mean at 12 h = 36 req). Maximum levels of DNA-protein cross-links were observed 4 h after injection of CY (4 mg/mouse) for both I 1210 leukemia (123 req (mean)] and normal bone marrow cells [50 req (mean)]. DNA-protein cross-links were measurable in CLL at timepoints later than 4 h after the start of injection of CY. In order to obtain equitoxicity between LI 210 leukemia and CDFi normal bone marrow cells, about 18-fold higher doses of CY had to be given than in the case of the normal bone marrow cells. In contrast, only 4-fold higher doses had to be given to the normal bone marrow to obtain equivalent peak levels of DNA-DNA interstrand cross links.