MRP gene overexpression in a human doxorubicin-resistant SCLC cell line: alterations in cellular pharmacokinetics and in pattern of cross-resistance.
The development of non-P-glycoprotein-mediated multi-drug resistance is a frequent event among lung-cancer cell lines. In an attempt to understand the underlying mechanisms of this phenotype, we have selected a multi-drug-resistant subline (POGB/DX) in vitro for doxorubicin resistance. The original cell line (POGB) was established in vitro from a non-treated patient with a small-cell lung cancer. POGB/DX cells were cross-resistant to other drugs, associated with MDR phenotype. In contrast, they were not resistant to taxol, camptothecin or melphalan, but were instead hypersensitive to 5-fluorouracil. Although expression of the mdr-1 gene was not detected in POGB/DX cells, cellular pharmacokinetics showed a reduced drug accumulation and altered intracellular localization in the POGB/DX cell line. This defect in drug accumulation was associated with overexpression and amplification of the MRP gene. Interestingly, verapamil, a known modulator of P-glycoprotein function, was able to reverse drug resistance and to increase drug accumulation. In Northern-blot analysis no differences in expression of topoisomerase I and II (alpha and beta), DNA polymerase beta, or HSP70 and HSP60 genes were observed between POGB and POGB/DX. Coupled to lack of changes in expression of known resistance factors, overexpression of MRP and modulation by verapamil strongly support a role for this gene product in the development of drug resistance in this SCLC cell system. This study provides evidence that (a) altered cellular pharmacokinetics is related to MRP expression; (b) MRP-mediated phenotype is characterized by a specific pattern of cross-resistance, which does not involve taxol; and (c) verapamil may be effective in modulating the function of the MRP gene product.
Binaschi
M
M
Division of Experimental Oncology B, Istituto Nazionale Tumori, Milan, Italy.
Supino
R
R
Gambetta
R A
RA
Giaccone
G
G
Prosperi
E
E
Capranico
G
G
Cataldo
I
I
Zunino
F
F
D018288:Carcinoma, Small Cell / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D004317:Doxorubicin / Q000493:pharmacokinetics* / Q000494:pharmacology*; D018432:Drug Resistance, Multiple / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology
D004317:Doxorubicin; D014700:Verapamil