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Multidrug resistance in androgen-independent growing rat prostate carcinoma cells is mediated by P-glycoprotein
M J Siegsmund1, C Kreukler, A Steidler
1Department of Urology, Faculty of Clinical Medicine Mannheim, University of Heidelberg, Germany.
Abstract:
Prostate carcinomas are in general resistant against virtually all cytotoxic drugs. Up to now it has not been thoroughly evaluated whether specific resistance factors, such as the expression of the MDR1 gene, play a role in this multi-agent resistance and whether there is a link between drug resistance and hormone-independent growth. We investigated the resistance patterns of a hormone-sensitive and four hormone-independent Dunning rat carcinoma sublines against four drugs which are substrates of P-glycoprotein (vinblastine, taxol, doxorubicin, and etoposide) and two agents (methotrexate and cis-platinum) which are not transported by this efflux pump. All hormone-insensitive sublines, AT.1, AT. 3.1., MatLu and Mat LyLu, continuously showed a clearly enhanced resistance (3- to 26-fold) against the P-glycoprotein substrates, compared to the hormone-sensitive subline G. Only two of the androgen-independent sublines displayed enhanced resistance against methotrexate, whereas all of them were more sensitive against cisplatin than the androgen-sensitive G cells. By addition of verapamil the resistance against vinblastine (9- to 10-fold) and taxol (6.7- to 26.7-fold) in the hormone-insensitive cells could be almost totally reversed. Furthermore, the fluorescent P-glycoprotein substrate rhodamine-123 was effectively pumped out of the four tested hormone-independent cell lines, whereas the hormone-sensitive G cells were unable to extrude the dye. By reverse transcriptase polymerase chain reaction (RT-PCR) with primers specific for the rat mdr1b gene, the homologue to the human MDR1 gene, we could easily detect mdr1b expression in the androgen independent cell lines, but not in the G cells. Our results suggest that the product of the rat mdr1b gene is involved in the multidrug resistance of androgen-independent Dunning prostate carcinoma cells.
Insights
Prostate cancer cells resistant to chemotherapy show increased expression of the multidrug resistance gene 1b (mdr1b). This gene is linked to hormone-independent growth and drug resistance in Dunning rat prostate carcinoma.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Prostate carcinomas often exhibit resistance to cytotoxic drugs.
- The role of specific resistance factors like the MDR1 gene in this multi-agent resistance and its link to hormone-independent growth remains unclear.
Purpose of the Study:
- To investigate the drug resistance patterns of hormone-sensitive and hormone-independent Dunning rat prostate carcinoma sublines.
- To determine the involvement of the multidrug resistance gene 1b (mdr1b) in acquired drug resistance.
Main Methods:
- Assessed resistance of Dunning rat prostate carcinoma sublines to P-glycoprotein substrates (vinblastine, taxol, doxorubicin, etoposide) and non-substrates (methotrexate, cis-platinum).
- Evaluated drug resistance reversal using verapamil.
- Measured rhodamine-123 efflux as an indicator of P-glycoprotein activity.
- Analyzed mdr1b gene expression using reverse transcriptase polymerase chain reaction (RT-PCR).
Main Results:
- Hormone-insensitive sublines displayed significantly higher resistance (3- to 26-fold) to P-glycoprotein substrates compared to hormone-sensitive cells.
- Verapamil treatment nearly abolished resistance to vinblastine and taxol in hormone-insensitive cells.
- Hormone-independent cells effectively extruded rhodamine-123, unlike hormone-sensitive cells.
- Expression of the rat mdr1b gene was detected in hormone-independent sublines but not in the hormone-sensitive subline.
Conclusions:
- The rat mdr1b gene, homologous to human MDR1, is involved in multidrug resistance in androgen-independent Dunning prostate carcinoma cells.
- Increased mdr1b expression contributes to the resistance of hormone-independent prostate cancer to various chemotherapeutic agents.