Morphological differentiation of human choriocarcinoma cells induced by methotrexate.

BeWo is a malignant human choniocarcinoma line derived from a methotmexate-nesistantumor. Under normal conditions, two BeWo phenotypes coexist in culture. The predominant form, 96 to 99% of the total population, consists of cytotro phoblast-like (CTL) cells that are proliferative, mononucleate, and moderate in size. The remaining cells are syncytiotropho blast-like (STL), being giant, nonproliferative, and multinucle ated. Treatment of BeWo cultures with 1 @.tMmethotnexate causes a total inhibition of cell division but does not stop nuclear division or DNA or protein synthesis. Consequently, there arises a population of giant, multinucleated, nonprolifer ative cells that is momphologically indistinguishable from the naturally occurring STL cells. CTL BeWo cells possess promi nent surface muffles,contain moderate numbers of microvilli and filopodia, contain a prominent network of interlacing fila ment bundles, and are connected by fascia adherens and desmosomes. STL BeWo cells are 3 to 10 times larger than CTL's; have reduced ruffles, filopodia, cytoplasmic filament bundles, and desmosome and fascia adhemensjunctions; but possess increased microvilli, Golgi apparatus, smooth and dilated endoplasmic reticulum, and a variety of vesicles and granules. The methotrexate induction of STL cells is reversible upon drug removal. A comparison of our observations with literature data for the normal in utero trophoblast indicates that CTL BeWo cells are ultrastructurally similar to cells of the cytotrophoblast, while STL BeWo cells are ultrastructurally similar to the normal syncytiotrophoblast. Our findings indicate that the BeWo line provides an excellent culture model system for investigating the nontoxic, cytodifferentiative changes that chemotherapeutic agents induce in human tumor cells and raise the possibility that the BeWo line may also prove a valuable culture model system for the investigation of mam malian trophoblast development.