Abstract
The development of resistance to chemotherapy is one of the main problems for effective cancer treatment. Drug resistance may result from disturbances in two important physiological processes-cell proliferation and cell death. Importantly, both processes characterize alterations in cell metabolism, the level of which is often measured using MTT/MTS assays. To examine resistance to chemotherapy, different cancer cell lines are usually used for the in vitro modulation of developing resistance. However, after the creation of resistant cell lines, researchers often have difficulty in starting investigations of the mechanisms of insensitivity. In the first stage, researchers should address the question of whether the drug resistance results from a depression of cell proliferation or an inhibition of cell death. To simplify the choice of research strategy, we have suggested a combination of different approaches which reveal the actual mechanism. This combination includes rapid and high-throughput methods such as the MTS test, the LIVE/DEAD assay, real-time cell metabolic analysis, and Western blotting. To create chemoresistant tumor cells, we used four different cancer cell lines of various origins and utilized the most clinically relevant pulse-selection approach. Applying a set of methodological approaches, we demonstrated that three of them were more capable of modulating proliferation to avoid the cytostatic effects of anti-cancer drugs. At the same time, one of the studied cell lines developed resistance to cell death, overcoming the cytotoxic action.