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Molecular analysis of two human doxorubicin-resistant cell lines: evidence for differing multidrug resistance
M L Slovak1, M Coccia, P S Meltzer
1Department of Cytogenetics, City of Hope National Medical Center, Duarte, CA 91010.
Abstract:
The molecular characteristics of two human doxorubicin-resistant cell lines were examined specifically for MDR1 gene amplification by Southern analysis and for overexpression of its messenger RNA. The 285-fold doxorubicin-resistant colon adenocarcinoma subline, LoVo/DR5, was found to overexpress the mRNA for P-glycoprotein without the concomitant requirement of MDR1 gene amplification, suggesting that relatively high levels of P-glycoprotein mediated multiple drug resistance may occur by transcriptional activation of the gene. Despite a similar in vitro selection strategy and in contrast to LoVo/DR cells, the 220-fold doxorubicin-resistant fibrosarcoma subline, HT1080/DR4, did not overexpress P-glycoprotein mRNA nor was the MDR1 gene amplified. In-gel renaturation studies were performed to determine the nature of a putative HSR-bearing chromosome 7 found in HT1080/DR4 cells; however, at a level of sensitivity nearing 20 copies of an amplified DNA fragment per haploid genome, no amplified sequences could be detected. These results suggest that doxorubicin resistance is multifactorial and alternative mechanisms of multiple drug resistance remain to be determined. LoVo/DR5 cells should prove to be a useful model for investigating transcriptional activation of the MDR1 gene; HT1080/DR4 cells should be an excellent model for the study of non-P-glycoprotein mediated multiple drug resistance.
Insights
Two doxorubicin-resistant cell lines show distinct mechanisms of drug resistance. One line exhibits P-glycoprotein overexpression via gene activation, while the other displays non-P-glycoprotein mediated resistance.
Area of Science:
- Molecular biology
- Cancer research
- Genetics
Background:
- Doxorubicin resistance is a major challenge in cancer chemotherapy.
- Multiple drug resistance (MDR) mechanisms, including P-glycoprotein overexpression, are critical to understand.
- Investigating resistant cell lines provides insights into MDR pathways.
Purpose of the Study:
- To characterize the molecular basis of doxorubicin resistance in two distinct human cell lines.
- To determine if MDR1 gene amplification or mRNA overexpression drives resistance.
- To identify alternative mechanisms of multiple drug resistance.
Main Methods:
- Southern analysis to detect MDR1 gene amplification.
- Messenger RNA expression analysis for P-glycoprotein.
- In-gel renaturation studies to identify amplified DNA sequences.
Main Results:
- The LoVo/DR5 cell line showed high P-glycoprotein mRNA levels without MDR1 gene amplification, suggesting transcriptional activation.
- The HT1080/DR4 cell line did not overexpress P-glycoprotein mRNA or show MDR1 gene amplification.
- No amplified sequences were detected in HT1080/DR4 cells, even at high sensitivity.
Conclusions:
- Doxorubicin resistance is multifactorial, involving both P-glycoprotein and other mechanisms.
- LoVo/DR5 cells are a valuable model for studying MDR1 transcriptional activation.
- HT1080/DR4 cells offer a model for investigating non-P-glycoprotein mediated drug resistance.