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Enhancement of the loss of multiple drug resistance by hydroxyurea
R D Christen1, D R Shalinsky, S B Howell
1Department of Medicine, University of California, San Diego, La Jolla 92093-0812.
Abstract:
Gene amplification is one mechanism whereby tumor cells can become resistant to antineoplastic agents. Unstably amplified genes occur either on submicroscopic circular pieces of extrachromosomal DNA called episomes or on small acentric chromosomes called double minutes. Double minutes are frequently associated with cells containing amplified drug-resistance genes. Human epidermoid carcinoma KBV1 cells contain unstably amplified mdr1 genes and overexpress P glycoprotein, resulting in decreased intracellular drug accumulation. In this cell line, a nonlethal concentration of hydroxyurea accelerated the rate of loss of vinblastine resistance once vinblastine had been removed from the culture medium. After removal of vinblastine, KBV1 cells exposed to hydroxyurea for the time required to complete 12 cell doublings accumulated more vinblastine than control cells grown in the absence of hydroxyurea. In contrast, hydroxyurea had no effect on vinblastine sensitivity and accumulation in parental drug-sensitive KB-3-1 cells. Hydroxyurea also had no effect on sensitivity to cisplatin in cisplatin-resistant human ovarian carcinoma 2008/C13* cells, indicating that hydroxyurea's effect on drug sensitivity was specific for a drug-resistance phenotype associated with unstably amplified drug-resistance genes. These results indicate that, after removing selective pressure, hydroxyurea accelerates loss of resistance to vinblastine and increases accumulation of vinblastine in KBV1 cells, presumably by accelerating loss of amplified mdr1 genes and thus P glycoprotein.
Insights
Hydroxyurea accelerates the loss of drug resistance in cancer cells with amplified genes. This finding suggests hydroxyurea may help overcome resistance to antineoplastic agents by reducing gene amplification.
Area of Science:
- Molecular Biology
- Cancer Research
- Genetics
Background:
- Gene amplification is a key mechanism for tumor cells developing resistance to antineoplastic agents.
- Unstably amplified genes, often found on double minutes, are linked to drug resistance phenotypes.
- KBV1 cells exhibit unstable mdr1 gene amplification and P-glycoprotein overexpression, leading to reduced intracellular drug accumulation.
Purpose of the Study:
- To investigate the effect of hydroxyurea on drug resistance associated with unstable gene amplification.
- To determine if hydroxyurea can accelerate the loss of drug resistance in cancer cells.
- To explore the potential of hydroxyurea in overcoming antineoplastic agent resistance.
Main Methods:
- Utilized human epidermoid carcinoma KBV1 cells with amplified mdr1 genes and drug resistance.
- Administered a nonlethal concentration of hydroxyurea to KBV1 cells after removal of vinblastine selective pressure.
- Assessed vinblastine resistance, intracellular drug accumulation, and gene amplification markers.
Main Results:
- Hydroxyurea accelerated the rate of loss of vinblastine resistance in KBV1 cells.
- KBV1 cells exposed to hydroxyurea showed increased vinblastine accumulation compared to controls.
- Hydroxyurea's effect was specific to cells with unstably amplified drug-resistance genes, not affecting parental or cisplatin-resistant cells.
Conclusions:
- Hydroxyurea accelerates the loss of vinblastine resistance in cancer cells with unstable gene amplification.
- This effect is likely mediated by accelerated loss of amplified mdr1 genes and P-glycoprotein.
- Hydroxyurea shows potential as a therapeutic agent to overcome drug resistance in certain cancers.