Relevance of drug uptake and efflux for cisplatin sensitivity of tumor cells

Platinum sensitivity and platinum resistance may involve altered activity of transport proteins. In order to assess the role of drug uptake and efflux in this phenomenon, we compared the expression of three copper transporters, intracellular platinum accumulation, DNA platination and cytotoxicity of cisplatin in two cisplatin-sensitive and -resistant tumor cell line pairs (ovarian A2780/A2780cis and cervical HeLa/HeLaCK cells). Gene expression of importer CTR1, and ATP7A and ATP7B efflux transporters (with and without cisplatin treatment) was investigated using quantitative real-time PCR and platinum concentrations were determined by flameless atomic absorption spectrometry. After incubation with cisplatin, DNA platination was significantly lower in the resistant variants compared to the respective sensitive cell lines, whereas no obvious difference in DNA repair was found. Accordingly, the resistant variants exhibited lower intracellular platinum concentrations than their respective parental cells (2.5- and 2.9-fold lower in A2780cis and HeLaCK cells, respectively). No differences in efflux were observed. Resistant cells expressed lower levels of CTR1 (1.5-1.8-fold) than their sensitive counterparts. Expression differences of ATP7A and ATP7B between resistant and sensitive cells were cell type-specific. The results highlight the relevance of CTR1 for cisplatin sensitivity as there is a clear relationship between lower CTR1 expression, intracellular concentration, DNA platination and cytotoxicity of cisplatin in both resistant cell lines. Our data provide the basis for a quantitative understanding of alterations in uptake and efflux processes leading to cisplatin resistance and might hence facilitate the development of ex vivo assays that can predict cisplatin sensitivity in tumor specimens of patients.