RESISTANCE-ASSOCIATED FACTORS IN HUMAN SMALL-CELL LUNG-CARCINOMA GLC(4) SUB-LINES WITH INCREASING ADRIAMYCIN RESISTANCE

Previous studies have shown that the in vitro-selected adriamycin-resi stant human small-cell lung-carcinoma cell line GLC(4)A-ADR(150) displ ays multidrug resistance as the result of 3-fold decreased DNA-topoiso merase II (topo II) activity and a 6-fold reduction in adriamycin accu mulation. Not the MDRI gene, but the MRP gene, was over-expressed in t his cell line. The aim of our study was to establish which of these dr ug-resistance-associated factors are already involved in drug resistan ce occurring at early steps of selection with adriamycin. To address t his question, changes in expression of topo II alpha/topo II beta, MRP and drug accumulation were measured along with adriamycin resistance (from 2- to 10- to 150-fold) and in a partial revertant cell line (10- fold resistant). Topo II alpha and II beta mRNA and protein levels wer e decreased in the resistant sub-lines, except in the 10-fold-resistan t cell line. Cellular daunorubicin accumulation was decreased 1.2- to 5-fold with increasing resistance. MRP mRNA was over-expressed in all resistant sub-lines, with a marked increase in the 10-fold-resistant c ells (level of expression as high as in the GLC(4)-ADR(150) cells). Ex pression of an ATP-binding 190-kDa membrane protein and Western-blot a nalysis with anti-MRP anti-serum ASPKE, was in accordance with the exp ression of MRP mRNA in all cell lines. Expression of MRP mRNA and prot ein, however, was not proportional with the decrease in drug accumulat ion in all resistant sub-lines. This study also shows that drug accumu lation, topo II and MRP expression were all changed at the earliest st age of resistance development of GLC(4) cells upon adriamycin selectio n.