An etoposide-resistant lung cancer subline overexpresses the multidrug resistance-associated protein.
We have characterised an etoposide-resistant subline of the small-cell lung cancer cell line, UMCC-1, derived at our centre. Subline UMCC-1/VP was developed by culturing the parent line in increasing concentrations of etoposide over 16 months. UMCC-1/VP is 20-fold resistant to etoposide by MTT assays, relative to the parent line, and is cross-resistant to doxorubicin, vincristine and actinomycin D, but not to taxol, cisplatin, melphalan, thiotepa or idarubicin. Topoisomerase II immunoblotting demonstrates a 50% reduction of the protein in the resistant subline. The UMCC-1/VP subline demonstrates a marked decrease in the accumulation of [3H]etoposide relative to the parent line, as well as a modest reduction in the accumulation of daunorubicin. Reverse transcription-polymerase chain reaction assays demonstrate no detectable mdr1 expression but marked expression of the multidrug resistance-associated protein (MRP) gene in the resistant subline. Northern blotting with an MRP cDNA probe confirms marked overexpression of the MRP gene only in the UMCC-1/VP subline. Western blotting with antisera against MRP peptide confirms a 195 kDa protein band in the UMCC-1/VP subline. Southern blotting experiments demonstrate a 10-fold amplification of the MRP gene in the resistant subline. Depletion of glutathione with buthionine sulphoximine sensitised UMCC-1/VP cells to daunorubicin and etoposide. Our studies indicate that MRP gene expression may be induced by etoposide and may lead to reduced accumulation of the drug.
Doyle
L A
LA
Department of Medicine, University of Maryland School of Medicine, Baltimore, USA.
Ross
D D
DD
Ordonez
J V
JV
Yang
W
W
Gao
Y
Y
Tong
Y
Y
Belani
C P
CP
Gutheil
J C
JC
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology; D018288:Carcinoma, Small Cell / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004351:Drug Resistance; D018432:Drug Resistance, Multiple / Q000235:genetics / Q000502:physiology; D005047:Etoposide / Q000493:pharmacokinetics / Q000494:pharmacology*; D015870:Gene Expression; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism; D008875:Middle Aged; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D010641:Phenotype; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D004250:DNA Topoisomerases, Type II; D005047:Etoposide; D008565:Membrane Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D059005:Topoisomerase II Inhibitors