Quantitative subcellular study of transferrin receptor-targeted doxorubicin and its metabolite in human breast cancer cells

The extended use of doxorubicin (DOX) could be limited due to the emergence of drug resistance and cardiotoxicity associated with its treatment. Conjugates of DOX with transferrin (DOX–TRF) can effectively alleviate these side effects, thereby leading to a better treatment. The effectiveness of DOX–TRF could result from the enhancement of transferrin receptor (TfR)-mediated transportation. However, detailed TfR-mediated DOX delivery has not been fully elucidated thus far, which may rely on the quantitative subcellular study of DOX distribution and metabolism. In this study, an immunoisolation assay was developed to isolate the organelles with high purity, yield and integrity. Using this immunoisolation assay together with liquid chromatography–tandem mass spectrometry (LC/MS/MS), the subcellular distribution profiles of DOX and its main metabolite doxorubicinol (DOXol) in human breast cancer cells MCF-7/WT and MCF-7/ADR were determined and compared after the treatment of DOX and DOX–TRF. As expected, DOX–TRF treated cells have a higher drug accumulation compared to DOX treated cells. DOX–TRF was predominantly cytoplasmic. In addition, TfR-mediated transportation had a significant impact on the transformation of DOX to DOXol in the cells. This study provided the evidence that immunoisolation together with LC/MS/MS is an effective technique in subcellular investigations.