A method to estimate cell cycle time and growth fraction using bromodeoxyuridine-flow cytometry data from a single sample

BACKGROUND: Presently available flow cytometric methods of bromodeoxyuridine (BrdUrd) labelling do not provide information on the cell cycle time (T(C)) and the growth fraction (GF). In this paper, we describe a novel and simple method to estimate T(C )and GF from flow cytometric analysis of a single tumour sample after BrdUrd labelling. METHODS: The proposed method is based on two assumptions: (1) the number of labelled cells traversing the cell cycle per unit time is constant and (2) the total number of labelled cells is constant throughout the cycle, provided that cells produced after division are excluded. The total numbers of labelled divided G(1 )cells, labelled divided S cells, labelled undivided S cells, and labelled undivided G(2 )cells were obtained for DNA histograms of BrdUrd-positive cells in a collected sample. These cell numbers were used to write equations to determine the durations of cell cycle phases, T(C )and GF. To illustrate the application of the proposed formulae, cell cycle kinetic parameters were analysed in solid SL2 tumours growing in DBA/2 mice and in human T-leukaemia Jurkat cells in culture. RESULTS: The suitability of the proposed method for estimating durations of the cell cycle phases, T(C )and GF was demonstrated. T(C )in SL2 tumours was found to be relatively constant at 4 and 10 days after tumour implantation (20.3 ± 1.1 h and 21.6 ± 0.9 h, respectively). GF in tumours at day 10 was lower than GF at day 4 (54.2 ± 7.7% vs. 79.2 ± 5.9%, p = 0.0003). Approximate values of T(C )and GF of cultured Jurkat cells were 23.9 h and 79.3%, respectively. CONCLUSION: The proposed method is relatively simple and permits estimation of the cell cycle parameters, including T(C )and GF, from a single tumour sample after labelling with BrdUrd. We have shown that this method may be useful in preclinical studies, allowing estimation of changes in GF during growth of murine tumours. Experiments with human Jurkat cells suggest that the proposed method might also prove suitable for measurement of cell kinetics in human tumours. Development of suitable software enabling more objective interpretation of the DNA profile in this method would be desirable.