We examined the genetic and biochemical bases for drug resistance and the order of appearance of different mechanisms underlying the increasingly more resistant @entity19 @entity6007 cell lines established in @entity632 (ADR). In the first-step low-level resistant cell line PC4-A5 (able to grow in 5 ng/mL ADR), there was a 2-fold reduction in topoisomerase IIalpha and topoisomerase IIbeta mRNA levels, as well as topoisomerase IIalpha protein and activity levels as compared with the parental cell line. The topoisomerase IIalpha activity levels remained reduced as the cells became increasingly more resistant. In contrast, the topoisomerase II mRNA and protein levels returned to approximately the parental levels in resistant cells growing in higher drug concentrations (40-160 ng/mL). Parental cells expressed the multidrug resistance protein (MRP), but beginning with PC4-A5 MRP expression decreased and remained reduced in increasingly resistant cell lines. At high levels of ADR resistance, the cells expressed the @entity678 gene concomitant with the appearance of @entity1891 resistance and energy-dependent @entity5699 and @entity1891 efflux. @entity2041 levels, internal pH, and expression of the major vault protein (MVP) remained unchanged in all cell lines. Fluorescence microscopy revealed no alterations in @entity5699 distribution or vesicle numbers between the parental and resistant cell lines. Different resistance mechanisms emerge sequentially as cells become more resistant to ADR; the mechanisms are retained during the development of multidrug resistance (MDR). In intermediate-level MDR cell lines (PC4-A10 and PC4-A20), resistance involves an as yet undetermined mechanism(s).

Emergence of different mechanisms of resistance in the evolution of multidrug resistance in @entity19 XXXX cell lines.

@entity632 :: ('MESH:D004317', 'Chemical') :: ['Adriamycin'] @entity5699 :: ('MESH:D003630', 'Chemical') :: ['daunomycin'] @entity19 :: ('10090', 'Species') :: ['murine'] @entity2041 :: ('MESH:D005978', 'Chemical') :: ['Glutathione'] @entity6007 :: ('MESH:D004915', 'Disease') :: ['erythroleukemia'] @entity1891 :: ('MESH:D014750', 'Chemical') :: ['vincristine'] @entity678 :: ('18671(Tax:10090)', 'Gene') :: ['mdr3']
@entity6007 :: (MESH:D004915,Disease) :: ['erythroleukemia']
