Cancer Mol. 3: 91-94, 2007
Interference against MDR1 but not MRP1 Reverses Drug Resistance in Human
Small-Cell Lung Cancer Cells
David Sadava1 and Wendy Hamman
Science Center, Claremont, CA, USA
Human small-cell lung carcinoma (SCLC) cells can express two drug efflux
pumps, MDR1 and MRP1, possibly involved in drug resistance. The aim of
this study was to investigate the ex vivo significance of these
We transfected small interfering RNA (siRNA) directed against the mRNAs
of these two genes into drug-sensitive (H69) and drug-resistant (H69VP)
SCLC cells and tested down-regulation of gene expression, cytotoxicity,
and drug accumulation by calcein efflux.
After 24 h, RT-PCR showed down-regulation of the targeted mRNAs. The
3-day cytotoxicities of etoposide, doxorubicin and vincristine were
unchanged in H69 cells compared to mock-transfected controls. For the
H69VP cells, drug resistance was reversed by anti-MDR1 siRNA but not
anti-MRP1 siRNA. These data were supported by experiments measuring
reduced accumulation of the fluorescent dye, calcein acetoxymethyl
ester. Compared to H69 cells, accumulation after 15 min was reduced by
80% in H69VP cells. This was reversed by concurrent administration of
cyclosporin A or pretreatment with siRNA against MDR1, but not by siRNA
The pump expressed by MDR1 but not MRP1 is important in drug resistance
in these cells.
lung cancer; drug resistance; MDR1; MRP1; siRNA)
Received 4/25/07; Revised 5/21/07; Accepted 5/25/07.
Dr. David Sadava,
Keck Science Center, 925 North Mills Ave., Claremont, CA 91711, USA.
Fax: 1-909-6218588. E-mail:
SCLC, small-cell lung carcinoma; MDR, multidrug resistance; MRP, MDR-associated
protein; siRNA, small interfering RNA; PGK, phosphoglycerate kinase;
calcein AM, calcein acetoxymethyl ester.
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