title: Synergistic interactions between the synthetic  retinoid tamibarotene and glucocorticoids in human  myeloma cells.
abstract: Tamibarotene (TM411) is a synthetic retinoic acid receptor-alpha/-beta selective retinoid that is chemically more stable than all-trans retinoic acid. This study was designed to evaluate the activity of TM411 in multiple myeloma (MM) and the effects of TM411 combined with a glucocorticoid (GC). In vitro, five human myeloma cells were treated with TM411 alone, GC alone, or TM411 + GC. Cell survival was analyzed by the tetrazolium dye assay and the Hoechst 33342/propidium iodide double-staining method. The effect of TM411 + GC was assessed by the isobologram method. In vivo, the growth-inhibitory effects of the drugs on RPMI-8226 cell xenografts established in SCID mice were examined. The effects of the agents on IL-6-mediated signaling pathways were also analyzed by Western blotting. TM411 was 2- to 10-fold more potent, in terms of its growth-inhibitory effect, than all-trans retinoic acid. The combination of TM411 and GC was found to show a markedly synergistic interaction. While increased expressions of the IL-6 receptor, phosphorylated MAPK, and Akt were observed after exposure to GC, TM411 attenuated this increase in the expressions, suggesting that such modification of the effect of GC by TM411 might be the possible mechanism underlying the synergistic interaction. Furthermore, TM411 + GC showed a supra-additive inhibitory effect in a xenograft model as compared with TM411 or GC alone. These results imply that the combination of TM411 + GC might be highly effective against MM, and suggest the need for clinical evaluation of TM411 + GC for the treatment of MM.
authors.affiliation: Shien-Lab and Support Facility of Project Ward, National Cancer Center Hospital, 5-1-1 Tsukiji, Tokyo 104-0045, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Fukui
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kodera
authors.forename: Kazuto
authors.initials: K
authors.lastname: Nishio
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Masuda
authors.forename: Tomohide
authors.initials: T
authors.lastname: Tamura
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Koizumi
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001565:Benzoates / Q000627:therapeutic use*; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004357:Drug Synergism; D005260:Female; D005938:Glucocorticoids / Q000627:therapeutic use*; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000473:pathology; D012176:Retinoids / Q000627:therapeutic use*; D013764:Tetrahydronaphthalenes / Q000627:therapeutic use*; D014212:Tretinoin / Q000627:therapeutic use*
chemical_list: D000970:Antineoplastic Agents; D001565:Benzoates; D005938:Glucocorticoids; D012176:Retinoids; D013764:Tetrahydronaphthalenes; C061133:tamibarotene; D014212:Tretinoin