Measuring the doxorubicin content of single nuclei by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection

Individual nuclei isolated from the human leukemia CCRF-CEM and CEM-C2 cells treated with doxorubicin (DOX) were in-column lysed with a sodium dodecyl sulfate (SDS) containing buffer, their contents were then separated by micellar electrokinetic capillary chromatography using the same lysing buffer, and the DOX content was detected by laser-induced fluorescence. Use of a microscope for the selection of one nucleus from the nuclear preparation decreases the possibility of introduction of other subcellular components that are commonly found as impurities in subcellular fractions. The presence of SDS in the running buffer made negligible the DNA's quenching effect on DOX fluorescence, which often compromises quantification of DOX by direct imaging, making it possible to carry out the first direct measurement of the doxorubicin content of isolated nuclei. On average, nuclei from CCRF-CEM and CEM/C2 cell lines contained 85 +/-64 (n = 6) and 91 +/- 51 (n =7) amol of DOX, respectively. These values correspond to 74 and 65% of the average total cellular content as determined by single-cell analysis of the corresponding cell types. It is envisioned that this approach could become an important bioanalytical tool to investigate the effect of treatments with fluorescent drugs targeting the nucleus.