CELL-CYCLE KINETICS IN AN INVITRO TUMOR MODEL

Cell cycle kinetic parameters of multicell spheroids in vitro were estimated using thymidine labeling techniques and autoradiography. The mitotic index and thymidine labeling index decreased in larger spheroids, whereas the duration of the cell cycle, as determined by 2 independent methods utilizing labeled mitoses or labeled cells, was essentially independent of spheroid size or age. The tumor-like growth exhibited by Chinese hamster V79-171 cell spheroids is the result of a decreasing growth fraction and a large apparent cell loss, rather than a general elongation of the cell cycle.