Subchronic intravenous toxicity of the antineoplastic drug, amsacrine, in male Wistar rats.

Amsacrine, a DNA intercalator and topoisomerase II inhibitor, is efficacious as an antileukemogenic agent. This study was conducted to assess the subchronic toxicity of amsacrine in rats following a cyclic clinical dosing regimen and as a range-finding experiment for a subsequent carcinogenicity bioassay. Groups of 30 male Wistar rats were administered drug intravenously at doses of 0, 0.25, 1.0, and 3.0 mg/kg daily for 5 days followed by 23 days without treatment. This cycle of dosing and recovery was repeated six times to simulate human clinical usage of the drug. Assessments of hematology, clinical chemistry, and gross and microscopic pathology were conducted 3 and 21 days following completion of dosing in the first, third, and sixth cycles. There were no deaths during the study. Hair loss, diarrhea, tail injuries, chromodacryorrhea, and rhinorrhea were observed primarily in animals administered 3 mg/kg. Hair loss and diarrhea occurred during periods of dosing and generally resolved during the recovery phase of each cycle. Both of these signs became progressively more severe during the latter half of the study. Body weight loss and reduced food consumption also occurred in the 3 mg/kg group during each week of dosing. At study termination, mean body weight and food consumption of the 3 mg/kg group were significantly less than those of controls by approximately 20 and 50%, respectively. Marked, reversible leukopenia associated with reductions in both neutrophil and lymphocyte counts occurred in cycles one and three in animals administered 1 and 3 mg/kg, respectively. Reversible neutropenia was also observed in the 3 mg/kg group in cycle 6. Similar effects on platelet counts were seen in the 3 mg/kg group in all three cycles analyzed. Absolute and relative testes weights of the 3 mg/kg group were significantly less than the vehicle controls at all time points in the third and sixth cycles. Relative testes weights were also decreased in the 1 mg/kg group in cycle 6. Reversible decreases in absolute relative spleen weights occurred in all drug-treated groups in cycle 1 and for the 3 mg/kg group in cycle 3. Lymphoid depletion (spleen, thymus, lymph node), marked hypocellularity of bone marrow, segmental degeneration of seminiferous tubules, and intestinal epithelial cell degeneration were observed at 3 mg/kg. With the exception of testicular changes which remained evident at the end of cycle 6, pathologic lesions were reversible during the 23-day recovery period of each cycle. The results show that the subchronic toxicity of amsacrine is consistent with a cytotoxic mechanism and that target organs are generally tissues with the highest rates of cell turnover. The doses administered in this study induced a range of effects which were minimal at 0.25 mg/kg and dose-limiting at 3 mg/kg and therefore were considered appropriate for use in the subsequent carcinogenicity bioassay.