ABCG2 and cancer: Among 48 identified human transporters, breast cancer resistance protein (BCRP) (encoded by ABCG2), P-glycoprotein (P-gp) (encoded by ABCB1), and multidrug resistance-associated protein 1 (MRP1) (encoded by ABCC1) are known to transport a structurally diverse array of cytotoxic compounds including anti-cancer agents and photosensitizers[33-35].