Chemotherapy induces or increases expression of multidrug resistance-associated protein in malignant melanoma cells.
BACKGROUND
Human malignant melanoma is notoriously resistant to chemotherapeutic agents. Melanoma-derived cell lines are often markedly chemoresistant, suggesting that cellular mechanisms mediate generation of the multidrug resistance (MDR) phenotype. This phenotype is often due to P-glycoprotein (Pgp) and the MDR-associated protein (MRP), which are drug transporter proteins associated with resistance to a broad spectrum of lipophilic drugs.


OBJECTIVE
To determine the relationships between the expression of the MDR gene MDR-1 (the product of which is Pgp) or the MRP gene, and clinical chemoresistance of malignant melanoma.


METHODS
We examined changes in the expression of MDR-1 and MRP genes at the mRNA level before and after chemotherapy by reverse transcription-polymerase chain reaction (RT-PCR) analysis using formalin-fixed, paraffin-embedded sections of 18 specimens taken from eight melanoma patients. mRNA expression of the MDR-1 and MRP gene-specific PCR products was quantitatively determined by densitometry and compared with that of an internal standard (beta-actin).


RESULTS
Five of seven primary melanomas were found to express the MRP gene to a certain extent even before chemotherapy. After first and second courses of chemotherapy, six patients had an increased ratio of MRP mRNA to beta-actin mRNA compared with the prechemotherapy levels in the same patients. None of the cases of melanoma expressed MDR-1.


CONCLUSIONS
These results suggest that a significant mRNA level of MRP gene was intrinsically present in malignant melanoma even before exposure to chemotherapeutic drugs and increased in its expression after chemotherapy, suggesting that MRP plays a part in increasing the chemoresistance of malignant melanoma during chemotherapy.
Ichihashi
N
N
Department of Dermatology, Gifu University School of Medicine, 40 Tukasa-machi, Gifu City 500-8705, Japan. ichihasi@cc.gifu-u.ac.jp
Kitajima
Y
Y
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008545:Melanoma / Q000188:drug therapy / Q000378:metabolism*; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012878:Skin Neoplasms / Q000188:drug therapy / Q000378:metabolism*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm