PGP and hepatocellular carcinoma: All the in vitro tests identified that Pi starvation irreversibly increased the cellular influx of DOX as the expression of three common MDR plasma membrane proteins driving the efflux of drugs (P-gp, BCRP, and MRP1) was effectively impaired as Pi stress led to downregulated expression levels of ABC transporter genes, which has been reported to influence the efficacy of chemotherapy in patients with HCC (Korita et al., 2010).