Identification of drug‐resistant myeloid leukemic cells by measurement of DNA content, nuclear area, and detection of P‐glycoprotein

BACKGROUND This study was designed to evaluate the significance of aneuploidy in DNA ploidy, nuclear area, and expression of P‐glycoprotein (P‐GP) in differentiating drug‐resistant myeloid leukemic cells (DRMLC) from drug‐sensitive myeloid leukemic cells. METHODS Bone marrow aspirates from 28 myeloid leukemic patients were fixed in 95% ethanol solution and stained using the Papanicolaou method. The nuclear area and DNA content were measured. An immunohistochemical study was performed using monoclonal antibody (JSB‐1) directed against P‐GP. RESULTS Leukemic cell morphology changed once or twice after the diagnosis of acute myeloid leukemia (AML), blastic crisis (BC) of chronic myeloid leukemia, or chronic neutrophilic leukemia. DRMLC showed severe atypia and were morphologically distinguishable from normal myeloblasts, promyelocytes, and drug‐sensitive leukemic cells at the diagnosis of AML or BC. The mean nuclear index (NI) and DNA index (DI) of DRMLC were significantly larger than those of drug‐sensitive leukemic cells of AML or BC. The frequency of aneuploidy and P‐GP expression was 9.1% and 4.5%, respectively, at the diagnosis of AML or BC, and 92.8% and 28.5%, respectively, for resistant disease. The incidence of heterogeneity in DNA ploidy was 86.3%. CONCLUSIONS DI and NI values larger than 1.2 and the expression of P‐GP are significant indications of DRMLC. Cancer 1996;77:878‐87.