Novel derivation of total cell cycle time in malignant cells using two DNA-specific labels

Cell cycle kinetic analysis in vitro has conventionally been accomplished by labeling S-phase cells using two DNA specific labels given sequentially and separated from each other by a certain time interval. By counting the cells labeled by both versus those labeled by either one of the two labels, and using the formulas described by Wimber and Quastler, approximate values for durations of S-phase (Ts) and the total cell cycle (Tc) can be determined. More recently, instead of radio-isotope labeled thymidine, two thymidine analogues have been used to label S-phase cells in vivo in a variety of human tumors based on the same principles. In the present report, new formulas are proposed for the calculation of Ts and Tc which are simpler to apply since only one type of labeled cells (those exiting S-phase as identified by containing only the first label) need to be differentiated from the remaining population for Tc calculations.