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Quantitative analysis of MDR1 (multidrug resistance) gene expression in human tumors by polymerase chain reaction
K E Noonan1, C Beck, T A Holzmayer
1Department of Genetics, University of Illinois, Chicago 60612.
Abstract:
The resistance of tumor cells to chemotherapeutic drugs is a major obstacle to successful cancer chemotherapy. In human cells, expression of the MDR1 gene, encoding a transmembrane efflux pump (P-glycoprotein), leads to decreased intracellular accumulation and resistance to a variety of lipophilic drugs (multidrug resistance; MDR). The levels of MDR in cell lines selected in vitro have been shown to correlate with the steady-state levels of MDR1 mRNA and P-glycoprotein. In cells with a severalfold increase in cellular drug resistance, MDR1 expression levels are close to the limits of detection by conventional assays. MDR1 expression has been frequently observed in human tumors after chemotherapy and in some but not all types of clinically refractory tumors untreated with chemotherapeutic drugs. We have devised a highly sensitive, specific, and quantitative protocol for measuring the levels of MDR1 mRNA in clinical samples, based on the polymerase chain reaction. We have used this assay to measure MDR1 gene expression in MDR cell lines and greater than 300 normal tissues, tumor-derived cell lines, and clinical specimens of untreated tumors of the types in which MDR1 expression was rarely observed by standard assays. Low levels of MDR1 expression were found by polymerase chain reaction in most solid tumors and leukemias tested. The frequency of samples without detectable MDR1 expression varied among different types of tumors; MDR1-negative samples were most common among tumor types known to be relatively responsive to chemotherapy.
Insights
Multidrug resistance (MDR) in cancer is a major challenge. A new, sensitive assay detects low levels of MDR1 gene expression in tumors, aiding in understanding drug resistance.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Tumor cell resistance to chemotherapy, known as multidrug resistance (MDR), is a significant clinical problem.
- The MDR1 gene encodes P-glycoprotein, a transporter that reduces intracellular drug accumulation, leading to MDR.
- MDR1 expression is often observed in tumors post-chemotherapy and in some drug-refractory tumors.
Purpose of the Study:
- To develop a highly sensitive and quantitative method for measuring MDR1 mRNA levels in clinical samples.
- To assess MDR1 gene expression in various human tissues, cell lines, and untreated tumors.
Main Methods:
- Development of a sensitive, specific, and quantitative polymerase chain reaction (PCR)-based assay for MDR1 mRNA.
- Application of the PCR assay to analyze MDR1 expression in over 300 normal tissues, tumor cell lines, and clinical tumor specimens.
Main Results:
- The PCR assay successfully detected low levels of MDR1 mRNA in most solid tumors and leukemias tested.
- MDR1 expression was rarely detectable by conventional assays in certain tumor types.
- The frequency of MDR1-negative samples varied by tumor type, being highest in chemotherapy-responsive tumors.
Conclusions:
- The developed PCR assay provides a sensitive tool for quantifying MDR1 mRNA in clinical samples.
- Low-level MDR1 expression is present in a majority of solid tumors and leukemias.
- MDR1 expression patterns may correlate with tumor chemosensitivity.