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Updated: Jul 29, 2026
Implementation of In Vitro Drug Resistance Assays: Maximizing the Potential for Uncovering Clinically Relevant Resistance Mechanisms
Published on: December 9, 2015
Intermittent exposure to doxorubicin in vitro selects for multifactorial non-P-glycoprotein-associated multidrug
1Department C of Internal Medicine, Kantonsspital St Gallen, Switzerland.
Abstract:
The purpose of the present study was to evaluate whether intermittent exposure to a constant dose of doxorubicin selects for multidrug resistance (MDR) in RPMI 8226 human myeloma cells and, if so, to determine the molecular mechanism. In an attempt to approximate clinical doxorubicin treatment in vitro, cells were exposed to a fixed dose of doxorubicin for 4 d alternating with growth in drug-free medium for 17 d. An MDR subline emerged, termed 8226/DOXint5, which was 3-4-fold resistant to doxorubicin, etoposide and m-AMSA, and 1.6-fold resistant to vincristine. Sensitivity to docetaxel, melphalan and cisplatin was normal. Verapamil normalized vincristine sensitivity but had little effect on resistance to the other agents. Cellular uptake and retention of daunorubicin and vincristine were reduced by approximately 10%. The 8226/DOXint5 cells showed diminished DNA topoisomerase IIalpha expression and increased expression of the multidrug resistance protein MRP. Expression of MDR1/P-glycoprotein was not detected. Immunostaining showed 70% of the cells to over-express the lung-resistance protein LRP. This new MDR myeloma cell line may prove to be a useful model for the development of strategies to overcome low-level, multifactorial MDR, which might be a common phenomenon in clinical myeloma treated with doxorubicin.
Insights
Intermittent doxorubicin exposure selected for multidrug resistance (MDR) in human myeloma cells. This new MDR model reveals molecular mechanisms contributing to drug resistance in cancer therapy.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Multidrug resistance (MDR) is a significant challenge in cancer chemotherapy.
- Understanding the mechanisms of MDR is crucial for developing effective treatment strategies.
Purpose of the Study:
- To investigate if intermittent doxorubicin exposure induces MDR in RPMI 8226 human myeloma cells.
- To elucidate the molecular mechanisms underlying the acquired doxorubicin resistance.
Main Methods:
- RPMI 8226 cells were exposed to doxorubicin intermittently (4 days on, 17 days off).
- Drug resistance profiles were assessed against various chemotherapeutic agents.
- Expression levels of key drug resistance proteins (e.g., MRP, P-glycoprotein, LRP) and DNA topoisomerase IIalpha were analyzed.
Main Results:
- An MDR subline (8226/DOXint5) emerged, exhibiting 3-4 fold resistance to doxorubicin, etoposide, and m-AMSA.
- Reduced cellular uptake and retention of daunorubicin and vincristine were observed.
- Diminished DNA topoisomerase IIalpha expression and increased multidrug resistance-associated protein (MRP) expression were key findings.
- Overexpression of the lung-resistance protein (LRP) was detected in 70% of the cells, while MDR1/P-glycoprotein was not detected.
Conclusions:
- Intermittent doxorubicin treatment can select for MDR in human myeloma cells.
- The acquired MDR phenotype is multifactorial, involving decreased topoisomerase IIalpha and increased MRP and LRP expression.
- The 8226/DOXint5 cell line serves as a valuable model for studying and overcoming low-level MDR in clinical settings.
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