A dose titration of each compound compared to the positive controls DEAB and WIN18446 demonstrated that MBE1 and MBE1.5 potently reduced atRA formation in MDA-MB-468 cells while MBE1.5B exhibited a higher IC50 (Figure 3I), thus confirming that MBE1 and related compounds block ALDH1A3 in cells and that ALDH1A3 produces atRA in retinoid-insensitive human cancer cells. Here, ALDH1A3 is linked to cancer.