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Vol. 302, Issue 3, 963-971, September 2002
Department of Pharmacology, School of Medicine, University of North
Carolina, Chapel Hill, North Carolina
Selective inhibition of the multidrug resistance 1 (MDR1) gene and its
product, the P-glycoprotein, a membrane transporter responsible for
multidrug resistance, could be an important approach for enhancing
cancer therapeutics. An emerging strategy for selective gene regulation
involves designed zinc finger proteins that can recognize specific
sequences in the promoter regions of disease-related genes. Herein, we
investigate the behavior of clones of multidrug-resistant NCI/ADR-RES
breast carcinoma cells displaying ponasterone-inducible expression of a
designed transcriptional repressor targeted to the MDR1 promoter. The
controlled production of this novel repressor resulted in major
reductions in P-glycoprotein levels in these otherwise highly
drug-resistant tumor cells. The regulated reduction of MDR1 expression
in NCI/ADR-RES cells was accompanied by a marked increase in the rate
of uptake of the P-glycoprotein substrate rhodamine 123. In addition,
the cytotoxicity profile of the antitumor drug doxorubicin was
dramatically altered in the induced cells compared with controls. The
expression levels of other genes were examined both by a DNA array
analysis of approximately 2000 genes and by biochemical techniques.
Although some changes were observed in mRNA levels of nontargeted
genes, the most dramatic effect by far was on MDR1, indicating that the
action of the designed transcriptional repressor was quite selective.
This study suggests that designed transcriptional regulators can be
used to strongly and selectively influence expression of cancer-related
genes, even under circumstances of extensive amplification of the
target gene.
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