Microarray Expression Profiling of ABC Transporters in Human Breast Cancer

The ATP-binding cassette (ABC) transporters are highly conserved genes involved in the translocation of molecules through biological membranes. Several of them are involved in tumor drug resistance, and it is thought that many others may contribute to the development of the tumor phenotype in a still unknown way. A low-density DNA microarray was recently developed for the analysis of 38 ABC-transporter genes and 3 other transporters. In the present pilot study, clinical samples from 16 breast cancer patients were tested. Of the 41 transporters analyzed, 10 were not or very seldom expressed, while 23 were found to be expressed, sometimes at very high levels, in the majority of the tumors. Comparison of the treated and untreated tumors showed an unexpected similarity of results. The signal obtained on the capture probes for ABCC6/8/9 was, however, found to be higher in the treated samples. The microarray data were validated on 15 ABC-transporter genes by real-time PCR. The present results showed that the expression of the majority of the ABC transporters was a clear feature of breast tumors, whether treated or not.