BT20, MCF7 (human breast cancer cell line), SUM190 (human breast cancer cell line), BxPC3 (human pancreatic adenocarcinoma cell line), HEK‐293 (human embryonic kidney cell line), and HCT‐116 xenografts.444, 445, 446, 447 Probe visualizes tumors and is not a substrate for P‐gp (P‐glycoprotein) or MRP‐1 (multidrug resistance‐associated protein 1). The gene discussed is PGP; the disease is breast cancer.