PGP and cancer: Retroviral infection of the MDCK renal cell line with human MDR1 cDNA, encoding the P-gp MDR efflux pump, produces major accumulation of Gb3, sensitivity to Stx and resistance to vinblastine (an antimitotic drug used to treat many kinds of cancer), while P-gp inhibitors prevent Gb3 increase and Stx sensitivity, and concomitantly increase vinblastine sensitivity.