P-glycoprotein-mediated Multidrug Resistance Phenotype of L1210/VCR Cells is Associated with Decreases of Oligo- And/or Polysaccharide Contents

Multidrug resistance of murine leukaemic cell line L1210/VCR (obtained by adaptation of parental drug-sensitive L1210 cells to vincristine) is associated with overexpression of mdr1 gene product P-glycoprotein (Pgp)-the ATP-dependent drug efflux pump. 31P-NMR spectra of L1210 and L1210/VCR cells (the latter in the presence of vincristine) revealed, besides the decrease of ATP level, a considerable lower level of UDP-saccharides in L1210/VCR cells. Histochemical staining of negatively charged cell surface binding sites (mostly sialic acid) by ruthenium red (RR) revealed a compact layer of RR bound to the external coat of sensitive cells. In resistant cells cultivated in the absence or presence of vincristine, the RR layer is either reduced or absent. Consistently, resistant cells were found to be less sensitive to Concanavalin A (ConA). Moreover, differences in the amount and spectrum of glycoproteins interacting with ConA-Sepharose were demonstrated between sensitive and resistant cells. Finally, the content of glycogen in resistant cells is lower than in sensitive cells. All the above facts indicate that multidrug resistance of L1210/VCR cells mediated predominantly by drug efflux activity of Pgp is accompanied by a considerable depression of oligo- and/or polysaccharides biosynthesis.