| Popis: |
The growth curve of monolayer cultures of ARH-77 cells, a human myeloma cell line propagated in vitro, is represented by an everbending curve on a semilogarithmic plot; however, the curve can be fitted by a straight line on a linear-linear plot. This unusual growth pattern suggests that, instead of a fixed proportion of the population, a fixed number of ARH-77 cells divide per unit time. The following are cell cycle transit time parameters calculated from percent labeled mitosis experiments: TG1, 10.0 +/- 3.5 hours; Ts, 14.3 +/- 2.3 hours; TG2, 4.3 hours; TM, 1.4 +/- 1.3 hours; and Tc, 30.0 +/- 6.1 hours. For cells exposed continuously to 3H-thymidine the values are: growth fraction, 67%; TG1, 6.5 hours; Ts, 13.0 hours; and TG2 + M, 3.0 hours. The average doubling time is 4.6 days (range, 3.8-4.7 days); after about 10 to 15 days in culture, the growth rate of freshly passaged cells declines markedly, as reflected by a growth curve with a much shallower slope. The changes are accompanied by a marked decline in the labeling index from 41.3% (range, 28.9%-53.7%) during the first 3 days of culture to less than 5% measured on day 21. Flow cytometry for DNA content-dependent cell cycle compartment distribution demonstrates an obvious decline in the proportion of S-phase cells and a marked accumulation of G2 phase cells as the cultures age. When the supernatant medium of ARH-77 cells grown for 10 days is replaced by fresh medium, a new burst of vigorous cellular growth is observed with a curve slope similar to that observed during the first 5 days of culture. If the 10-day-old supernatant medium is used to set up cultures with freshly harvested ARH-77 cells, their growth curve resembles that of 10-day-old cultures. However, this supernatant medium induces no decrease in the growth rate of other human tumor cells, suggesting that inhibition of cellular growth does not result from exhaustion of nutrients, but that ARH-77 cells produce a molecular mediator that specifically inhibits the growth of these cells. ARH-77 cells could be synchronized with a single treatment of 3 or 5 mM thymidine; (dThd) and cloning efficiency was 2% to 4% in a double-layer soft agar assay. Treatment for 1 hour with increasing concentrations of melphalan produced a threshold exponential survival curve (Dq = 0.45 microgram/ml and D0 = 0.35 microgram/ml, 1 hour).(ABSTRACT TRUNCATED AT 400 WORDS) |
Plný text