title: Rapamycin sensitizes multiple myeloma cells to apoptosis induced by dexamethasone.
abstract: Circumvention of chemoresistance in the B-cell neoplasm multiple myeloma (MM) might be achieved by targeting certain intracellular signaling pathways crucial for survival of the malignant clone. The use of the macrolide rapamycin, selectively inhibiting the phosphoprotein mammalian target of rapamycin (mTOR) downstream of, for example, insulin-like growth factor-I receptor (IGF-IR), possibly represents such a molecular mode of therapy. By using a panel of MM cell lines we showed that rapamycin induced G0/G1 arrest, an effect being associated with an increase of the cyclin-dependent kinase inhibitor p27 and a decrease of cyclins D2 and D3. Interestingly, in primary, mainly noncycling MM cells, rapamycin, at clinically achievable concentrations, induced apoptosis. More important, rapamycin sensitized both MM cell lines and primary MM cells to dexamethasone-induced apoptosis. This effect was associated with a decreased expression of cyclin D2 and survivin. The phosphorylation of the serine/threonine kinase p70S6K at Thr389 and Thr421/Ser424 was down-regulated by rapamycin and/or dexamethasone. Strikingly, the combinatorial treatment with rapamycin and dexamethasone suppressed the antiapoptotic effects of exogenously added IGF-I and interleukin 6 (IL-6) as well as their stimulation of p70S6K phosphorylation. The induction of apoptosis by rapamycin and dexamethasone despite the presence of survival factors was also demonstrated in primary MM cells, thus suggesting this drug combination to be active also in vivo.
authors.affiliation: Department of Genetics and Pathology, Rudbeck Laboratory, Uppsala, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Strömberg
authors.forename: Anna
authors.initials: A
authors.lastname: Dimberg
authors.forename: Anna
authors.initials: A
authors.lastname: Hammarberg
authors.forename: Kristina
authors.initials: K
authors.lastname: Carlson
authors.forename: Anders
authors.initials: A
authors.lastname: Osterborg
authors.forename: Kenneth
authors.initials: K
authors.lastname: Nilsson
authors.forename: Helena
authors.initials: H
authors.lastname: Jernberg-Wiklund
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D056742:Cyclin D2; D056743:Cyclin D3; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000378:metabolism; D003907:Dexamethasone / Q000008:administration & dosage / Q000494:pharmacology*; D004347:Drug Interactions; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology*; D010766:Phosphorylation; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000737:chemistry / Q000378:metabolism; D020123:Sirolimus / Q000008:administration & dosage / Q000494:pharmacology*; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: C080336:CCND2 protein, human; C534696:CCND3 protein, human; D018797:Cell Cycle Proteins; D056742:Cyclin D2; D056743:Cyclin D3; D016213:Cyclins; D015850:Interleukin-6; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus