Original Paper
Chemosensitivity of prostate cancer cell lines and expression of multidrug resistance-related proteins

https://doi.org/10.1016/S0959-8049(98)00435-3Get rights and content

Abstract

The aim of this study was to obtain insight into the role of the multidrug resistance (MDR) phenomenon in hormone-independent progressive prostate cancer. Using immunocytochemistry and Western blotting we determined the expression of P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP), glutathione-S-transferase-π (GST-π), Bcl-2, Bax, topoisomerase (Topo) I, IIα and IIβ in the human prostate cancer cell lines PC3, TSU-Pr1, DU145 and LNCaP derivatives LNCaP-R, LNCaP-LNO and LNCaP-FGC. Proliferative activity was assessed by immunocytochemistry. MTT assays were used to determine the sensitivity to etoposide, doxorubicin and vinblastin. Pgp was not expressed in any of the cell lines. MRP was variably expressed. GST-π was expressed in TSU-Pr1, PC3 and DU145. The expression of Bcl-2 was restricted to TSU-Pr1, whereas Bax was found in all cell lines. Topo IIα was expressed at the highest level in the rapidly proliferating cell lines TSU-Pr1 and DU145. Topo I and IIβ were equally expressed. Resistance profiles varied among the cell lines, with TSU-Pr1 being the most sensitive and LNCaP-LNO relatively resistant. Multiple MDR proteins were expressed in prostate cancer cell lines and may well influence response to chemotherapy. Future functional studies, using chemo-selected MDR models, may further help to determine the mechanism or combination of mechanisms underlying the resistance of prostate cancer to chemotherapy.

Introduction

Prostate cancer is the most common cancer in men and one of the leading causes of cancer death[1]. Metastatic disease is a major oncological problem and is not curable, but palliation can be achieved by hormone deprivation therapy[2]. However, prostate cancer patients will relapse at some stage in time, the majority within 1–2 years after starting endocrine therapy. After failure of hormone therapy, there are no successful treatment strategies available with respect to prolongation of survival and patients will die of progressive, hormone-independent disease after an average period of 40 weeks following relapse[3].

Hormone-independent prostate cancer is resistant to a broad range of antineoplastic agents[4], which may be caused by the fact that large proportions of prostate cancer cells are in interphase[5]. Also, multidrug resistance (MDR), the resistance of cancer cells to a variety of structurally and functionally distinct cytotoxic agents, may play an important role in progressive therapy resistant prostate cancer. However, the role of MDR in prostate cancer remains to be elucidated. A better understanding of mechanisms underlying the resistance of prostate cancer to chemotherapy may lead to novel approaches to challenge hormone unresponsive prostate cancer more successfully.

We determined the expression of eight MDR-associated proteins in prostate cancer cell lines derived from patients with progressive disease: the drug transporter molecules P-glycoprotein (Pgp)[6]and MDR-associated protein (MRP[7], the detoxifying enzyme glutathione-S-transferase-π (GST-π)[8], modulators of apoptosis Bcl-2[9]and Bax[10]and the enzymes topoisomerase (Topo) I, IIα and IIβ, which are related to one form of MDR: atypical or attenuated MDR[11]. Furthermore, we measured the response of the cell lines to treatment with the cytotoxic agents etoposide, doxorubicin and vinblastin, which are commonly used in the treatment of several malignancies and have been used to challenge prostate cancer in clinical trials.

Section snippets

Cell lines and culture conditions

The human prostate cancer cell lines PC3[12], TSU-Pr1[13], DU145[14]and LNCaP sublines that were established from the original LNCaP line[15]: the androgen-dependent FGC (available through the ATCC, Rockville, Maryland, U.S.A.), the hormone unresponsive R line[16]and the hormone-independent LNO line[17], were maintained at 37°C in a 5% CO2–95% air atmosphere. PC3, TSU-Pr1, DU145, LNCaP-R and LNCaP-FGC were cultured in RPMI 1640 medium, supplemented with 7.5% fetal calf serum (FCS), 1 unit/ml

Chemosensitivity assay

Drug-induced inhibition of human prostate cancer cell growth by the anticancer agents etoposide, doxorubicin and vinblastin was established in vitro. The growth of the cell lines during the assay, defined as the optical density (OD) value after 72 h divided by the OD value after plating of the cells, was 5.4, 2.6, 3.3, 1.5, 3.3 and 3 for TSU-Pr1, LNCaP-FGC, PC3, LNCaP-LNO, LNCaP-R and DU145, respectively. This indicates that drug testing was performed under the condition of cell lines in

Discussion

To gain insight into the mechanisms involved in the resistance of metastatic hormone-independent prostate cancer to chemotherapy we determined the expression of MDR proteins, which may lead to the MDR phenotype, in prostate cancer cell lines. Furthermore, we assessed the resistance profiles to three commonly used antineoplastic agents, etoposide, doxorubicin and vinblastin, whose action is affected by MDR.

We found that the expression of Pgp, the energy-dependent drug transporter molecule, was

Acknowledgements

Supported by Research Grant (9606) from the Dutch Research Foundation (SUWO).

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