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Isolation of human mdr DNA sequences amplified in multidrug-resistant KB carcinoma cells
Abstract:
The ability of tumor cells to develop simultaneous resistance to structurally different cytotoxic drugs constitutes a major problem in cancer chemotherapy. It was previously demonstrated that multidrug-resistant Chinese hamster cell lines contain an amplified, transcriptionally active DNA sequence designated mdr. This report presents evidence that multidrug-resistant sublines of human KB carcinoma cells, selected for resistance to either colchicine, vinblastine, or Adriamycin (doxorubicin), display amplification of two different DNA sequences homologous to the hamster mdr gene. Segments of the human mdr DNA sequences, designated mdr1 and mdr2, have been cloned. mdr1 sequences were amplified in all of the highly drug-resistant sublines and were expressed as a poly(A)+ RNA species of 4.5 kilobases that was detected in the resistant cells but not in the parental cell line. No expression of mdr2 sequences was detected. mdr2 sequences were coamplified with mdr1 in some of the multidrug-resistant sublines and, in two independently derived cell lines, underwent very similar rearrangements. The data suggest that the mdr1 gene is involved in multidrug resistance in human cells.
Insights
Multidrug resistance in cancer chemotherapy is a major challenge. This study found that human cancer cells resistant to multiple drugs show amplification of specific DNA sequences, suggesting a key gene involved in this resistance.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Simultaneous resistance to diverse cytotoxic drugs in tumor cells is a significant obstacle in cancer chemotherapy.
- Multidrug resistance (MDR) in cancer cells can arise from genetic alterations.
- Previous studies identified an amplified DNA sequence (mdr) in multidrug-resistant Chinese hamster cells.
Purpose of the Study:
- To investigate the genetic basis of multidrug resistance in human cancer cells.
- To identify and characterize DNA sequences homologous to the hamster mdr gene in drug-resistant human cell lines.
Main Methods:
- Selection of human KB carcinoma cell sublines resistant to colchicine, vinblastine, or Adriamycin (doxorubicin).
- Analysis of DNA amplification using techniques to detect sequences homologous to the hamster mdr gene.
- Cloning of human mdr DNA sequences (mdr1 and mdr2).
- Detection of RNA expression using Northern blotting for a 4.5 kilobase poly(A)+ RNA species.
Main Results:
- Multidrug-resistant human KB cell sublines exhibited amplification of two DNA sequences (mdr1 and mdr2) homologous to the hamster mdr gene.
- The mdr1 sequence was amplified in all resistant sublines and expressed as a 4.5 kb poly(A)+ RNA in resistant cells but not parental cells.
- mdr2 sequences were coamplified with mdr1 in some sublines and showed similar rearrangements in independently derived resistant lines.
- No expression of mdr2 was detected in the studied cell lines.
Conclusions:
- The mdr1 gene is likely involved in mediating multidrug resistance in human cancer cells.
- Amplification and expression of the mdr1 gene correlate with resistance to structurally different cytotoxic drugs.
- The findings provide insights into the molecular mechanisms underlying multidrug resistance in human cancers.