Drug sensitivity of granulocyte-macrophage precursors (GM-CFU) from fresh murine bone marrow and from long- term bone marrow cultures

The granulocyte-macrophage colony forming unit (GM-CFU) assay has been widely used to investigate the pathogenic mechanism of drug-induced blood disorders and for screening the potential myelotoxicity of antineoplastics. Considering the wide use of this technique, there is a need for a more standardized protocol, particularly with respect to the exposure conditions. The sensitivity of granulocyte-macrophage progenitors to three antineoplastic drugs; Etoposide (ETO), Doxorubicin (DOX) and Camptothecin (CAM), measured by the GM-CFU agar assay, is described. Continuous drug treatment has been compared with short-term drug pretreatments (1, 6 and 24 hr of exposure) using granulocyte-macrophage progenitors from both fresh bone marrow (FBM) and from long-term bone marrow culture (LTBMC). The continuous exposure of fresh bone marrow cells to the drugs resulted in a dose-dependent inhibition of progenitor growth. The IC10, IC50, IC90 and NOEL values calculated for each drug did not show any differences irrespective of whether FBM or LTBM was used as the cell source. Drug pretreatment of FBM and LTBMC cells for 1 hr did not affect the clonogenic capacity of GM-CFU while, following treatment for 6 and 24 hr, a different degree of GM-CFU inhibition and a higher susceptibility of GM-CFU from LTBMC was observed. This different susceptibility may be due to the different sensitive of cycling progenitors in LTBMC and FBM, or to some alteration of the metabolism process dependent on the different cell populations present in FBM and LTBMC. The results obtained indicate that the continuous presence of drugs during culture is important for the expression of their toxic effects on the proliferation and differentiation of myeloid progenitors (GM-CFU), and that this guarantees a better correlation between the IC50 values determined for FBM and LTBMC progenitor cells.