ABCG2 and cancer: In addition, coordinated induction of the MDR transporter P‐gp and the detoxifying enzyme were observed in drug‐resistant cancer cells; for instance, the P‐gp and GST‐π isoenzyme were co‐overexpressed in MCF/ADR cells, leading to an increased peroxidase activity.30 In addition to GST, glutathione (GSH) also plays a major role in MDR cancer cells by reacting with exogenous substrates and then removing them from milieu through ABC transporters, as elevated GSH levels have been investigated in many MDR cancer cells.31, 32