title: Double-edged sword of chemosensitizer: increase of multidrug resistance protein (MRP) in leukemic cells by an MRP inhibitor probenecid.
abstract: The multidrug resistance protein (MRP) is a drug efflux membrane pump conferring multidrug resistance to tumor cells. Clinical trials have been undertaken to improve the effectiveness of chemotherapy by adding an MRP inhibitor to the treatment regimen. This study attempted not only to determine novel resistance mechanisms in MRP-overexpressing AML cells (AML-2/DX100) by chronic exposure to doxorubicin in the presence of an MRP inhibitor probenecid but also to find out whether probenecid could increase MRP levels. AML-2/DXPBA cultured in the presence of probenecid (600 microM) and doxorubicin (100 ng/ml) showed a higher level of the multidrug resistance (MDR) phenotype when compared to AML-2/DX100. AML-2/DXPBA showed increased levels of MRP compared to those of AML-2/DX100. Probenecid increased the MRP levels without an increase in MRP mRNA in AML-2/WT in both a time- and dose-dependent manner. Of the MRP inhibitors including probenecid, ofloxacin, erythromycin, and rifampicin used in this study, only probenecid showed a marked chemosensitizing effect in AML-2/DX100 but not in HL-60/Adr, suggesting that the chemosensitizing effects of the MRP inhibitors vary according to the type of resistant cells. The maximum noncytotoxic concentrations of these MRP inhibitors increased the MRP levels to various degrees in both AML-2/WT and HL-60/WT. However, the chemosensitizing effects of the MRP inhibitors were not correlated with their MRP-increasing effects. Altogether, MRP inhibitors such as probenecid have been shown to function as a double-edged sword, indicating that they are not only an effective chemosensitizer of MRP-associated MDR tumor cells but also an MRP activator. Therefore caution should be taken whenever using MRP inhibitors to reverse MRP-mediated multidrug resistance in clinical cancer chemotherapy as well as when used to inhibit MRP expression in vitro.
authors.affiliation: Department of Pharmacology, Department of General Surgery, Chosun University Medical School, 375 Seosuk-dong, Dong-gu, Kwangju, 501-759, South Korea.
authors.forename: H S
authors.initials: HS
authors.lastname: Kim
authors.forename: Y D
authors.initials: YD
authors.lastname: Min
authors.forename: C H
authors.initials: CH
authors.lastname: Choi
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004917:Erythromycin / Q000494:pharmacology; D018922:HL-60 Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000378:metabolism*; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D015242:Ofloxacin / Q000494:pharmacology; D011339:Probenecid / Q000494:pharmacology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012293:Rifampin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014528:Uricosuric Agents / Q000494:pharmacology; D014750:Vincristine / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D004317:Doxorubicin; D004791:Enzyme Inhibitors; D004917:Erythromycin; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D015242:Ofloxacin; D011339:Probenecid; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D012293:Rifampin; D014528:Uricosuric Agents; D014750:Vincristine