Quantitative comparison of MRP3 mRNA levels in glioblastoma cell lines. After normalization to β-actin, which had minimal variation in all normal and malignant samples that we tested, relative MRP3 mRNA transcript levels were expressed as compared to normal whole brain (NWB), which was set equal to 1. Results are expressed as the mean ± SD of four independent real-time PCR experiments, including a six-NWB sample average as the baseline standard. Inset: Incidence of MRP3 mRNA expression in GBM patient samples. Relative MRP3 mRNA expression was measured by quantitative RT-PCR in GBM tumor samples (n = 67) over NWB (n = 6). Results are the mean of triplicate measurements repeated twice. Positive cases were defined as those with MRP3 RNA levels 3-fold higher than normal brain; >10-fold: MRP3 RNA levels >10-fold those of normal brain.