Cisplatin (CisPt) is frequently used in the therapy of urothelial carcinoma (UC). Its therapeutic efficacy is limited by inherent or acquired drug resistance. Here, we comparatively investigated the CisPt-induced response of two different parental urothelial carcinoma cell lines (RT-112, J-82) with that of respective drug resistant variants (RT-112R, J-82R) obtained upon month-long CisPt selection. Parental RT-112 cells were ~2.5 fold more resistant to CisPt than J-82 cells and showed a different expression pattern of CisPt-related resistance factors. CisPt resistant RT-112R and J-82R variants revealed a 2-3-fold increased CisPt resistance as compared to their corresponding parental counterparts. Acquired CisPt resistance was accompanied by morphological alterations resembling epithelial mesenchymal transition (EMT). RT-112R cells revealed lower apoptotic frequency and more pronounced G2/M arrest following CisPt exposure than RT-112 cells, whereas no differences in death induction were observed between J-82 and J-82R cells. CisPt resistant J-82R cells however were characterized by a reduced formation of CisPt-induced DNA damage and related DNA damage response (DDR) as compared to J-82 cells. Such difference was not observed between RT-112R and RT-112 cells. J-82R cells showed an enhanced sensitivity to pharmacological inhibition of checkpoint kinase 1 (Chk1) and, moreover, could be re-sensitized to CisPt upon Chk1 inhibition. Based on the data we suggest that mechanisms of acquired CisPt resistance of individual UC cells are substantially different, with apoptosis- and DDR-related mechanisms being of particular relevance. Moreover, the findings indicate that targeting of Chk1 might be useful to overcome acquired CisPt resistance of certain subtypes of UC.
Keywords: DNA damage response; DNA repair; cisplatin; cisplatin resistance; urothelial carcinoma.