Morphological evidence for a subpopulation selection effect by estrogen and antiestrogen treatments in the heterogeneous MCF-7 cell line

Recently, we developed a method to quantitatively study tumour cell heterog eneity in terms of both nuclear size and estrogen receptor (ER) content by image cytometry. The method, previously used to analyse the proliferation o f the breast cancer cell line MCF-7, was applied here to analyse the growth of this cell line under estradiol (E2), hydroxytamoxifen (OH-TAM), and bot h E2 and OH-TAM treatments. The method extracts characteristic parameters o f single nuclei and features that measure the global and local organisation of the cells in their growing phase. Modifications of the heterogeneity of the cell line are emphasised through phenotypic changes and modifications of the spatial organisation of the cells. The hormone (E2) generates a very fast growth of cells with small nuclei that became ER negative in the long term. The antihormone (OH-TAM) produces a gradual selection of ER negative or poorly positive cells with large nuclei. These modifications are revers ed when E2 and OH-TAM are simultaneously used. Moreover, estradiol induces a permissive context of proliferation, whereas hydroxytamoxifen acts only o n some subpopulations. The combination of cell count, cytomorphology, and c ell organisation revealed the magnitude of the potential of structuration o f hormones or antihormones on in vitro growing cells.