Comparison of LC-MS/MS-based targeted proteomics and conventional analytical methods for monitoring breast cancer resistance protein expression.

Multidrug resistance is a major obstacle in chemotherapy, which is mainly caused by the overexpression of ATP-binding cassette (ABC) transporters. Breast cancer resistance protein (BCRP) is one of the ABC transporters and is strongly associated with multidrug resistance. Results of studies on BCRP and multidrug resistance are always uncomparable and contradictory, which may be stem from the disadvantages of qualitative and semi-quantitative techniques. In addition, there are few literatures studying at low resistance level which is more similar to the clinical situation. Thus, it is imperative to develop a quantitative method to quantitate the expression of BCRP accurately and reveal its relationship with multidrug resistance. SMMC-7721, MCF-7 and HepG-2 were induced by different concentrations of mitoxantrone, doxorubicin and methotrexate respectively to establish resistance cells. An advanced liquid chromatography linked to tandem mass spectrometry (LC-MS/MS) based method with surrogate peptide was developed and validated for determining BCRP at low resistant cells. The amount of BCRP was also evaluated by real-time-polymerase chain reaction (RT-PCR) and Western Blot (WB). The LC-MS/MS-based method we developed is more sensitive and stable than the similar methods and can monitor the slight variation of BCRP expression accurately and sensitively, while RT-PCR and WB cannot. This study provides a solid foundation for understanding the development of drug resistance in cells and can be used to explain the conflicting results of published studies. Moreover, clinical multidrug resistances are mostly at low levels, which have not been discussed in current quantitative studies of BCRP.