COMPARISON OF DIFFERENT LABELING INDEX FORMULAS USED ON BROMODEOXYURIDINE-FLOW CYTOMETRY DATA

The essence of the bromodeoxyuridine (BrdUrd)-flow cytometry (FCM) tec hnique is that cells are labelled with the thymidine analogue BrdUrd. They are then allowed to progress through the cell cycle in a BrdUrd-f ree environment during the postlabelling time period. At a postlabelli ng time shorter than the length of the S phase (T-s), cells are fixed and prepared for FCM-mediated analysis of BrdUrd and DNA contents. Fro m FCM-derived data, cell cycle kinetic parameters such as labelling in dex (LI), T-s, and potential doubling time (T-pot) can be calculated. T-pot is believed to be important in the evaluation of tumor aggressiv eness and therapy response. Since LI is most commonly used together wi th T-s to calculate T-pot, it is important that both LI and T-s are in dependent of the time when cells are sampled. Several formulae to calc ulate LI and T-s have been presented. In the present paper, we deal wi th various formulae to calculate LI, These formulae differ in how they take into account unlabelled and BrdUrd-labelled cells in various fra ctions of the cell cycle. We present a new formula, which takes into c onsideration cells in the different fractions and thus makes LT theore tically independent of postlabelling time. Our results show that diffe rent LI values are obtained when different formulae are used to calcul ate LI. In addition, we show that the BrdUrd labelling period should b e kept as short as possible. (C) 1998 Wiley-Liss, Inc.