Improvements of the Bromodeoxyuridine-DNA Flow Cytometry Method for the Study of Cell Proliferation

Potential doubling time (Tpot), DNA synthesis time (TS), and labelling index (LI) are fundamental growth kinetics parameters in clinical and experimental cancer research, which may be of further practical importance regarding prognosis and treatment prediction of cancer. They can be measured by bromodeoxyuridine(BrdUrd)/flow cytometry (FCM) methods, where BrdUrd, an analogue of thymidine, is incorporated into DNA and quantified simultaneously with the DNA content. However, this method requires improvements. Since in many applications only a single sample is available, the method must be reproducible, accurate, and independent of the time of sample collection in relation to BrdUrd pulse-labelling. With the modifications we describe, growth kinetic data could be obtained in response to the demands, both in vitro and in vivo and they were in agreement with those obtained with the [3H]thymidine/autoradiography method. Thus, the BrdUrd/FCM method can replace traditional [3H]thymidine-based methods. The modifications included new mathematic formulas for the calculation of LI and TS. They were compared with various other formulas, in several cell lines and experimental tumours. Our formulas did show sampling time independence in several cell lines studied. The labelling time should be kept as short as possible. The proposed TS formula is used preferable in more slowly growing cell populations. Tpot values based on our formulas did not depend on sampling time. In conclusion, with our modified BrdUrd/FCM method for growth kinetic studies, experimentally and/or clinically, it is possible to obtain reproducible and sampling time independent data from only one sampling, an advantage of great importance when clinical applications are concerned.