ABCB1 and breast adenocarcinoma: Moreover, several novel hybrid compounds carrying fused sterane and pyrimidine ring systems, synthesized and tested by ourselves, exhibited strong anticancer activity on a number of different cancerous cells, induced endoplasmic reticulum stress, manifested an impressive potential to inhibit ABCB1, and consequently sensitized ABCB1-overexpressing MCF-7/KCR human breast adenocarcinoma cells to doxorubicin-induced killing [24,25].