PGP and cancer: A number of studies have shown that Gom A, Gom C, SCH, Sch A, and Sch B could reverse P-gp-mediated multidrug resistance (MDR) and decrease the efflux of P-gp substrate in cancer cells (Wan et al., 2006; Fong et al., 2007; Li et al., 2007; Yoo et al., 2007; Qin et al., 2010b).