title: The mechanism of cross-resistance to proteasome inhibitor bortezomib and overcoming resistance in Ewing's family tumor cells.
abstract: EWS-Fli1 plays important roles in oncogenesis of Ewing's family tumors (EFTs). We have reported that EWS-Fli1 inhibits p21(waf1/cip1) and p27(kip1) expressions, which are degraded by the ubiquitin-proteasome pathway. Bortezomib efficiently up-regulated p21(waf1/cip1) and p27(kip1) expression, and induced apoptosis accompanied by the expression of cleaved-PARP, DR4 and activated caspase-8 in EFT cells. Since most EFTs deaths result from the tumor being resistant to chemotherapeutic drugs, the effects of novel anti-tumor reagents on drug-resistant tumors were next investigated. The results demonstrated that the drug-resistant EFT clones were cross-resistant to bortezomib probably due to the over-expression of the efflux pumps, P-glycoprotein and MRP1. We further investigated whether the efflux pump inhibitors would modulate the effects of bortezomib. The combination of P-gp-specific or MRP1-specific inhibitors could enhance the anti-tumor effects of bortezomib on the drug-resistant clones. These data suggest that bortezomib might be a substrate of P-gp and MRP1. Although bortezomib would be effective on the primary EFTs, it is necessary to pay attention to the resistance to bortezomib in clinical trials for the advanced cases. The combination of bortezomib and the efflux pump inhibitors might be a promising method as a novel molecular target therapy for advanced EFTs.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, Maidashi, Fukuoka 812-8582, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nakamura
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Tanaka
authors.forename: Tomoya
authors.initials: T
authors.lastname: Matsunobu
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Okada
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Nakatani
authors.forename: Riku
authors.initials: R
authors.lastname: Sakimura
authors.forename: Masuo
authors.initials: M
authors.lastname: Hanada
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D002453:Cell Cycle; D049109:Cell Proliferation / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D019008:Drug Resistance, Neoplasm; D006655:Histone Deacetylases; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012512:Sarcoma, Ewing / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured / Q000187:drug effects