In addition, the σ2 receptor ligands exhibited promising anti-tumor proliferative activity against breast cancer MCF-7/ADR cells and could inhibit the activity of ABCB1, suggesting that σ2 receptor ligands may be potential therapeutic agent in anti-tumor MDR (Azzariti et al., 2006; Abate et al., 2011). Here, ABCB1 is linked to breast cancer.