PGP and cancer: Furthermore, among the many factors and causes of acquired drug resistance, Wnt/β-catenin signaling induced chemo-resistance was reported to be related to the up-regulated expression of P-glycoprotein (P-gp/ABCB1), which is encoded by the multidrug resistance 1 (MDR1) gene and plays a significant role in drug resistance due to the increased energy-dependent efflux of cytotoxic drugs from cancer cells [47].