mdr1/P-glycoprotein gene segments analyzed from various human leukemic cell lines exhibiting different multidrug resistance profiles.

Three high-level multidrug-resistant sublines of the human T-lymphoblastoid cell line CCRF-CEM were selected independently with either actinomycin D, vincristine or adriamycin. They exhibited distinct quantitative differences of cross-resistance profiles, and showed amplification and marked expression of the mdrl/P-glycoprotein gene. DNA and RNA were prepared from the cell lines, and additionally from three cell samples of patients suffering from acute lymphatic leukemia. Applying the polymerase chain reaction (PCR) for amplification, we cloned and sequenced from these sources segments of the mdrl/P-glycoprotein gene around the codon 185 which codes for an amino acid residue possibly influencing the drug binding function of the P-glycoprotein. Altogether, only 2 single nucleotide differences in an intron were found in 2 out of 40 recombinants each harboring a 209 bp genomic or a 269 bp cDNA fragment of the mdrl/P-glycoprotein gene. Our result does not support the idea of clustered point mutations in this segment of the P-glycoprotein gene as a cause of different multidrug resistance profiles. We additionally examined another segment of the P-glycoprotein gene in its second half, essentially delivering the same negative result, though.