ABCG2 and prostate cancer: While some variability was noted in relative band intensities of ABCG2, ALDH1A1, and Oct-4 RT-PCR products, there was little variability noted in the relative band intensities of GAPDH and actin RT-PCR products in single side population and single non-side population cells isolated from the CWR-R1 prostate cancer cell line (Figure 4).