Doubling time

Abstract: A colchicine-resistant clone, CHRE5, has been isolated in a single step from a mutagenized culture of Chinese hamster ovary cells. Its resistance correlates with reduced colchicine permeability. At the same time, CHRE5 cells display a pattern of cross-resistance to unrelated drugs similar to other membrane-altered drug-resistant mutants previously described (Ling and Thompson, 1974). However, CHRE5 cells also express a cold-sensitivity for growth in that at 34° they do not double in number while at 38.5° they grow with a doubling time of about 22 hours. Employing synchronous cultures, the cold sensitive block in CHRE5 cells has been determined to be located prior to S in the G1 phase of the cell cycle. Mutant cells at 33.5° are not able to initiate DNA synthesis, however, cells already synthesizing DNA are able to complete the whole course of S. This cold sensitive block is reversed by shifting cells back to the higher temperature. Additonal clones with the CHRE5 phenotype have been isolated from non-mutagenized cultures of wild-type cells. Moreover, partial revertants of CHRE5 with increased ability to grow at 34° have been isolated and found to display increased colchicine sensitivity. These results are consistent with the hypothesis that the two phenotypes observed in CHRE5, namely, an altered plasma membrane (reduced drug permeability) and an altered ability to initiate DNA synthesis are the result of the same mutation.

Abstract: The effect of delta-9-tetrahydrocannabinol (delta-9-THC) on the growth kinetics and morphology of rat B103 neuroblastoma cells was assessed. Delta-9-THC in doses ranging from 10−4 to 10−7 M inhibited cellular growth in a dose-dependent fashion as evidenced by delay in doubling time, decrease in saturation density, and decrease in efficiency of plating. The inhibition in cellular growth was paralleled by dose-related alterations in cell morphology. Modifications included rounding of cells, retraction of neurites, blebbing of the cell surface, and exfoliation of the plasma membrane. Cytoplasmic alterations included distension of the endoplasmic reticulum, Golgi apparatus, and perinuclear space, and macrovacuolization. Intracytoplasmic laminated inclusions and vesicular clusters were suggestive of membrane repair in drug-treated cells. These morphological changes were accompanied by cytoskeletal rearrangement in the absence of significant alteration in the concentration of total cytoskeletal protein. Autoradiographic examination of the intracellular fate of 3H-delta-9-THC demonstrated that the drug was confined to the cytoplasmic compartment and often associated with macrovacuoles. These results suggest that delta-9-THC interacts with cellular membranes, thereby altering neuroblastoma cell growth and behavior.

Abstract: Clinicians experienced in treating cancer have long been aware of the great variability in growth rates among different types of cancer and even within the same type, but until recently estimates of growth rates were largely limited to measurements of volume doubling times of solid tumors visible externally or roentgenographically (Collins et al., 1956; Collins, 1962; Garland et al., 1963; Spratt and Spratt, 1964; Charbit et al., 1971). These estimates were necessarily rough and gave little insight into the many factors which can influence the doubling time, such as the tumor cells’ intermitotic time and its variability, the relative proportions of actively proliferating and resting tumor cells, changes in the tumor’s proliferative behavior during different stages of growth, rate of cell loss, influence of vascular supply, contribution of stromal tissues, hemorrhage or necrosis to the tumor mass, and perturbations caused by therapy. Information about the comparative proliferative rates of normal tissues was also largely lacking.