The haemotoxicity of mitomycin in a repeat dose study in the female CD-1 mouse

Abstract

Mitomycin (MMC), like many antineoplastic drugs, induces a predictable, dose-related, bone marrow depression in man and laboratory animals; this change is generally reversible. However, there is evidence that MMC may also cause a late-stage or residual bone marrow injury. The present study in female CD-1 mice investigated the haematological and bone marrow changes induced by MMC in a repeat dose study lasting 50 days. Control and MMC-treated mice were dosed intraperitoneally on eight occasions over 18 days with vehicle, or MMC at 2.5 mg/kg, autopsied (n = 6-12) at 1, 7, 14, 28, 42 and 50 days after the final dose and haematological changes investigated. Femoral nucleated bone marrow cell counts and levels of apoptosis were also evaluated and clonogenic assays carried out; serum levels of FLT3 ligand (FL) were assessed. At day 1 post-dosing, MMC induced significant reductions in RBC, Hb and haematocrit (HCT) values, and there were decreases in reticulocyte, platelet, and femoral nucleated cell counts (FNCC); neutrophil, lymphocyte and monocyte values were also significantly reduced. On days 7 and 14 post-dosing, all haematological parameters showed evidence of a return towards normal values, but at these times, and at day 28, values for RBC and FNCC remained significantly reduced in comparison with controls. At days 42 and 50 post-dosing, many haematological parameters in MMC-treated mice had returned to control levels; however, there remained evidence of late-stage effects on RBC, Hb and HCT values, and FNCC also continued to be significantly decreased. Results for granulocyte-macrophage colony-forming units and erythroid colonies showed a profound decrease immediately post-dosing, but a return to normal values was evident at day 50. Serum FL concentrations demonstrated very significant increases in the immediate post-dosing period, but a return to normal was seen at day 50 post-dosing; a relatively similar pattern was seen in the number of apoptotic femoral marrow nucleated cells. The histopathological examination of kidney tissues from MMC animals at day 42 and 50 post-dosing showed evidence of hydronephrosis with cortical glomerular/tubular atrophy and degeneration. It is therefore concluded that MMC administered on eight occasions over 18 days to female CD-1 mice at 2.5 mg/kg induced profound changes in haematological and bone marrow parameters in the immediate post-dosing period with a return to normal levels at day 50 post-dosing; however, there was evidence of mild but significant late-stage/residual effects on RBC and FNCC, and on cells of the erythroid lineage in the bone marrow.

Figure 1

Haematoxylin and eosin-stained sections of the sternum and kidneys from control (vehicle-treated) and mitomycin (MMC)-treated (2.5 mg/kg) mice. (a) Sternum of a mouse, at day 1 after MMC treatment; there is severe depletion of bone marrow cellularity [original magnification (OM) ×40]. (b) Sternum of an MMC-treated mouse at day 14 post-treatment. There is complete recovery of bone marrow cellularity (OM ×40). (c) Kidney from a control (vehicle-treated) mouse, at day 50, showing the normal appearance of cortical and medullary tissues (OM ×10). (d) Kidney from a mouse treated with MMC at 50 days post-treatment; there is severe hydronephrosis with a central cystic space bordered by a thin rim of compressed renal parenchyma (OM ×10). (e) Cortex of the kidney from a control (vehicle-treated) mouse at day 50, showing the normal appearance of tissues (OM ×200). (f) Kidney cortex from a MMC-treated mouse, at day 50 post-dosing. There is cortical atrophy with dilatation of the renal tubules and interstitial fibrosis (OM ×200).