L. Amable, S. Smith, C. Stephan
Keywords: cisplatin, single cell ICP-MS
Summary:Cisplatin, carboplatin, and oxaliplatin are the most widely used class of cancer chemotherapy drugs in the Western world. Many cancers are initially sensitive to platinum treatment but often the cancer reoccurs, exhibiting drug resistance. Cellular uptake of cisplatin is related to tumor burden and how much damage can occur, thus lower intracellular cisplatin levels are associated with a decreased tumor response. Traditional methods to assess cisplatin uptake in cells involves digesting a cell population and measuring the total platinum content. The downfall of this approach is it does not reflect the distribution and individual cellular variation of cisplatin uptake. Here, we present a new method, single cell inductively coupled plasma-mass spectrometry (SC-ICP-MS) to quantitate the platinum concentration within individual cells. Experiments were performed using the A2780 cisplatin-sensitive and the corresponding cisplatin-resistant A2780-CP70 ovarian cancer cell lines. Time course experiments were performed to measure the change of cisplatin uptake over time. Serum starvation experiments were also performed to examine if differences in cisplatin uptake were dependent on the cell cycle. SC-ICP-MS was performed by injecting cell suspensions and analyzing the platinum 195 isotope. Individual cellular cisplatin levels were collected and a histogram representing the cell population was generated using the instrument software (Syngistix Nano Application). Other metals, such as zinc, iron, and copper, were analyzed to measure the variation between cell lines after treatment. We observed a heterogeneous distribution of cisplatin concentration within the sample reflecting that cisplatin uptake differs from cell to cell. Serum starvation affected the uptake of cisplatin within cells, changing the cisplatin distribution curve. SC-ICP-MS was also effective in measuring other metals within individual cells and differences were observed between the A2780 and A2780-CP70 cell lines. In conclusion, single cell ICP-MS analysis allows for the quantitation of cisplatin within individual cells. The heterogeneous distribution of cisplatin uptake reflects more of what is observed within tumors. SC-ICP-MS allows for the development of strategies to increase cisplatin uptake, translating to a better response in the clinic.