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Cytogenetic and phenotypic analysis of a human colon carcinoma cell line resistant to mitoxantrone
W S Dalton1, A E Cress, D S Alberts
1Department of Medicine, University of Arizona, Tucson 85724.
Abstract:
A human colon carcinoma cell line selected for a 21-fold resistance to mitoxantrone was cross-resistant to the anthracycline, doxorubicin, but not to the anthracene, bisantrene. A 2-fold resistance was observed with vinblastine, another drug associated with multidrug resistance. Net intracellular mitoxantrone and doxorubicin accumulation were decreased at 1 h for all dose levels in the resistant cell line compared to the sensitive cell line. Although the resistant cells were more resistant to mitoxantrone than doxorubicin, the net accumulation of mitoxantrone was only 19% less than the sensitive cell line; whereas doxorubicin accumulation was decreased by 49%. No significant difference between the sensitive and resistant cell lines was observed in the initial accumulation of mitoxantrone; however, the efflux of mitoxantrone was increased in the resistant cell line. Verapamil did not overcome the resistance to mitoxantrone and did not increase the net accumulation of drug. No alterations in the electrophoretic mobility of membrane proteins were observed. Using immunoblotting techniques, the resistant cell line did not express P-glycoprotein which is frequently observed for cells resistant to anthracycline antibiotics. Cytogenetic analysis showed a putative homogenously staining region on the short arm of chromosome 7 in the resistant cell line. The limited cross-resistant phenotype, lack of verapamil reversal, nondetection of P-glycoprotein, and cytogenetic evidence of gene amplification suggests the involvement of a novel drug-resistant gene associated with resistance to mitoxantrone.
Insights
A novel gene may cause resistance to mitoxantrone in colon cancer cells. This resistance affects doxorubicin accumulation but not P-glycoprotein expression, suggesting a new drug resistance mechanism.
Area of Science:
- * Molecular biology
- * Cancer research
- * Pharmacology
Background:
- * Multidrug resistance (MDR) is a significant challenge in cancer chemotherapy.
- * Mitoxantrone and doxorubicin are anthracycline-based chemotherapy drugs.
- * P-glycoprotein is a common mediator of MDR, but not always involved.
Purpose of the Study:
- * To investigate the mechanism of mitoxantrone resistance in a human colon carcinoma cell line.
- * To determine cross-resistance patterns and drug accumulation in resistant cells.
- * To explore the role of P-glycoprotein and other factors in this resistance phenotype.
Main Methods:
- * Development of a mitoxantrone-resistant human colon carcinoma cell line.
- * Assessment of cross-resistance to doxorubicin, bisantrene, and vinblastine.
- * Measurement of intracellular drug accumulation and efflux.
- * Verapamil reversal studies.
- * Immunoblotting for P-glycoprotein.
- * Cytogenetic analysis.
Main Results:
- * The resistant cell line showed 21-fold resistance to mitoxantrone and cross-resistance to doxorubicin, but not bisantrene or vinblastine.
- * Mitoxantrone and doxorubicin accumulation was reduced in resistant cells, with a greater decrease for doxorubicin.
- * Increased mitoxantrone efflux was observed in resistant cells.
- * Verapamil did not reverse resistance or increase drug accumulation.
- * P-glycoprotein was not detected, and cytogenetic analysis indicated gene amplification on chromosome 7.
Conclusions:
- * The observed resistance to mitoxantrone is mediated by a mechanism distinct from P-glycoprotein.
- * Reduced drug accumulation and increased efflux contribute to the resistance phenotype.
- * Evidence suggests the involvement of a novel drug-resistant gene, potentially through gene amplification.