Differential effects of drugs upon hematopoiesis can be assessed in long-term bone marrow cultures established on nylon screens.

Hematotoxicity is associated with exposure to chemotherapeutic drugs and numerous other agents. Most measurements of the hematopoietic effects of prospective therapeutic drugs and environmental agents have been made in animal models. We tested the influence of various drugs on hematopoiesis in long-term cultures of Long-Evans rat bone marrow cells. These cultures were established on nylon screen-bone marrow stromal cell templates that were suspended in liquid medium. Previous phenotypic analyses of adherent zone cells of suspended nylon screen bone marrow cultures (NSBMC) using monoclonal antibodies and flow cytometry indicated that they maintain a multilineage character for extended periods in culture and display continuous proliferation of hematopoietic progenitors (colony-forming unit culture [CFU-C]). NSBMC of various ages were incubated for 21 hr with several concentrations of beta-D-cytosine arabinofuranoside, 5-fluorouracil, cyclophosphamide, or methotrexate. Adherent zone cells were dissociated enzymatically, phenotyped by flow cytometry, and assayed for colony-forming unit culture content. beta-D-cytosine arabinofuranoside, 5-fluorouracil, and methotrexate treatment of bone marrow cultures resulted in a dose-related diminution in colony-forming unit culture numbers in the adherent zones of NSBMC. Phenotypic analyses revealed similar trends but certain of these drugs manifested lineage specificities. Toxicity was also related to cyclophosphamide dose, but the presence of bone marrow stroma was necessary to demonstrate this effect in vitro. A subpopulation of these cells was found to metabolize ethoxyfluorescein ethyl ester to fluorescein after induction with 2,3,7,8-tetrachlorodibenzo-p-dioxin, an effect which was quantified by flow cytometry. NSBMC may be used to ascertain lineage-specific toxicities and evaluate the effects of drugs on the proliferation of hematopoietic progenitor cells.