Monitoring cancer treatment in live melanoma cells using FLIM

Anticancer therapies with cisplatin and volasertib (BI 6727) were monitored by fluorescence lifetime imaging microscopy (FLIM) in live SK-Mel-2 melanoma cells. A CdSe/ZnS quantum dot functionalized with a peptide containing D-penicillamine and histidine (CdSe/ZnS-PH) was used as intracellular pH fluorescent probe. A faster cytosol acidification was observed for cells treated with cisplatin when compared to volasertib. The first changes in the intracellular pH were found after 2 h of treatment with cisplatin and 8 h with volasertib. Additionally, the apoptosis of SK-Mel-2 cells was also monitored by FLIM for both cancer treatments. Similar low percentages of apoptotic cells were observed after short incubation periods (2–8 h) with both drugs. In contrast, late apoptosis and death were found for a large fraction of cells during 24-hour incubation with cisplatin but not volasertib. There is not a clear correlation between the onset of apoptosis and the cytosol acidification, but the early acidification observed in cisplatin treatment could accelerate apoptosis and cell death. For longer periods, MMT assays showed a similar inhibitory effect for treatments after 72 hours of incubation, but with a significantly lower IC50 for volasertib. This study proves the potential of FLIM technique in the study of the mechanism of action of antitumor drugs.