This bachelor's thesis deals with the development and basic characterization of cell lines resistant to nucleoside cytostatics, cultivated in vitro. The theoretical part of the work is devoted to general facts associated with the development of cancer and mechanisms of resistance to cytostatic drugs, focusing on nucleoside derivatives that are used in clinical practice for the treatment of leukaemia and solid tumours. The literature review also highlights the importance of in vitro models in drug development. The beginning of the experimental part of the work is focused on the selection of resistant cells. Resistance was verified using the MTS cytotoxicity test, furthermore, the screening of new potential drugs is involved. The second part is dedicated to their basic characterization using standardized procedures for this laboratory. The expression of P-glycoprotein and MRP1 was analyzed by flow cytometry. The presence of proteins associated with the mTOR pathway was determined by western blotting.This bachelor's thesis deals with the development and basic characterization of cell lines resistant to nucleoside cytostatics, cultivated in vitro. The theoretical part of the work is devoted to general facts associated with the development of cancer and mechanisms of resistance to cytostatic drugs, focusing on nucleoside derivatives that are used in clinical practice for the treatment of leukaemia and solid tumours. The literature review also highlights the importance of in vitro models in drug development. The beginning of the experimental part of the work is focused on the selection of resistant cells. Resistance was verified using the MTS cytotoxicity test, furthermore, the screening of new potential drugs is involved. The second part is dedicated to their basic characterization using standardized procedures for this laboratory. The expression of P-glycoprotein and MRP1 was analyzed by flow cytometry. The presence of proteins associated with the mTOR pathway was determined by western blotting.