Cell viability assays demonstrated that ASR490 effectively inhibited the viability of all three cell types, though its effects on Notch1-positive BCSCs (ALDH+: IC50: 770 nM at 24 h, and 443 nM at 48 h; and CD44+/CD24−: IC50: 800 nM at 24 h, and 541 nM at 48 h) was more profound than its effect on ALDH− BC cells (IC50: 1.6 μM at 24 h and 836 nM at 48 h) (Figures 1A, B). Here, CD44 is linked to breast cancer.