ECTO-5'-NUCLEOTIDASE (CD73) IN MULTIDRUG-RESISTANT CELL-LINES GENERATED BY DOXORUBICIN

Cytochemical screening for a panel of enzymes revealed increased 5'nuc leotidase (5'NT) expression in 3 of 3 P-glycoprotein 170 (Pgp170)-posi tive multidrug-resistant (MDR) variants of the murine EL4 T-lymphoma c ell line (EL4/ADM, ER2 and ER13). Electron microscopic localization es tablished the presence of the membrane-bound ecto-form of the enzyme. Nine other murine, human and Chinese hamster cell lines and their MDR variants were tested for ecto-5'NT. Of these, 4 MDR variants (human ce ll lines MCF7A6, MCF7A2, HelaJ2C and the murine cell line L1210A) show ed increased expression of ecto-5'NT, when compared with their parenta l cell lines. The findings with cells of human origin were confirmed b y immunofluorescent localization with a specific monoclonal antibody ( MAb) (27.2) against the human ecto-5'NT. All MDR cell lines with eleva ted ecto-5'NT expression were generated by doxorubicin treatment. Thes e cells were more sensitive than their parental cell lines to AMP at c oncentrations of 1.5-3.0 mM, confirming that the expressed ecto-5'NT w as biologically active. The parental and MDR cells did not differ, in general, in their sensitivity to adenosine. An inhibitor of ecto-5'NT, alpha,beta-methyleneadenosine 5'-diphosphate, completely reversed the resistance of the EL4/ADM cell line to doxorubicin. The possibility e xists of a functional relationship between the ecto-5'NT molecule and the members of the ATE-binding cassette transporter superfamily, impor tant components of MDR, in some cell types. (C) 1994 Wiley-Liss, Inc.