(A) Expression of mdr1 mRNA in K562/ADM cells after random or MDR1-AS treatment (5 μmol/L) by RT-PCR analysis. The ratio of mdr1/β2-microglobulin in random- and MDR1-AS–treated groups by scanning densitometry were 5.26 and 1.89, respectively. (B) Expression of mdr1 mRNA of cells from pooled colonies produced by K562/ADM cells treated with random or MDR1-AS oligonucleotide (5 μmol/L) by RT-PCR analysis. The ratio ofmdr1/β2-microglobulin in random- and MDR1-AS–treated groups by scanning densitometry were 1.94 and 0.49, respectively.