title: Proteasome inhibition with bortezomib enhances activity of topoisomerase I-targeting drugs by NF-kappaB-independent mechanisms.
abstract: OBJECTIVE
  The potentiation of topoisomerase (topo)-I-induced apoptosis by proteasome inhibitors is dependent on the treatment sequence, but not on NF-kappaB. In this study, alternate mechanisms modulating apoptosis induced with the topo I-targeting drug, SN-38, when followed by the proteasome inhibitor bortezomib (PS-341) were investigated.
  
  
  METHODS
  Human non-small cell lung carcinoma (NSCLC-3) cells transfected with a control vector (NSCLC-3/neo) or a vector containing dominant negative IkappaBalpha (NSCLC-3/mIkappaBalpha) were treated with SN-38 for 1 h followed by PS-341 for 4 h (SN-38 --> PS-341), or with either drug alone. The functional role of the anti-apoptotic protein survivin was tested using NSCLC-3 transfected with myc-tagged wild-type (NSCLC-3/myc-survivin), or dominant negative mutant T34A survivin (NSCLC-3/myc-T34A).
  
  
  RESULTS
  In NSCLC-3/neo or NSCLC-3/mIkappaBalpha cells, treatment with SN-38 --> PS-341 led to down-regulation of the survivin transcript and protein, enhanced apoptosis and reduced (> 3-fold) survival compared to SN-38 or PS-341 alone. In contrast to the cells transfected with wild-type survivin, or the control NSCLC-3/neo, those cells transfected with mutant survivin and treated with SN-38 --> PS-341 exhibited enhanced caspase 9 activity (> 2-fold), caspase 3 (> 2- to 3-fold) activity and cytotoxicity compared to the NSCLC-3/neo cells.
  
  
  CONCLUSIONS
  In contrast to inhibition of NF-kappaB activity, down-regulation of the anti-apoptotic survivin was correlated with modulation of the sequence-dependent synergistic effects of PS-341 in SN-38-induced apoptosis.
authors.affiliation: Experimental Therapeutics, Taussig Cancer Center, Cleveland Clinic Foundation, Ohio 44195, USA.
authors.forename: Nagio
authors.initials: N
authors.lastname: Takigawa
authors.forename: Susan A J
authors.initials: SA
authors.lastname: Vaziri
authors.forename: Dale R
authors.initials: DR
authors.lastname: Grabowski
authors.forename: Kenichi
authors.initials: K
authors.lastname: Chikamori
authors.forename: Lisa R
authors.initials: LR
authors.lastname: Rybicki
authors.forename: Ronald M
authors.initials: RM
authors.lastname: Bukowski
authors.forename: Mahrukh K
authors.initials: MK
authors.lastname: Ganapathi
authors.forename: Ram
authors.initials: R
authors.lastname: Ganapathi
authors.forename: Tarek
authors.initials: T
authors.lastname: Mekhail
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001897:Boronic Acids / Q000008:administration & dosage / Q000494:pharmacology*; D000069286:Bortezomib; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D045744:Cell Line, Tumor; D004249:DNA Damage; D015536:Down-Regulation / Q000187:drug effects*; D004357:Drug Synergism; D006801:Humans; D020672:I-kappa B Proteins / Q000235:genetics; D051034:Inhibitor of Apoptosis Proteins; D000077146:Irinotecan; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009154:Mutation; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000008:administration & dosage / Q000494:pharmacology*; D000077022:Survivin; D059004:Topoisomerase I Inhibitors; D014162:Transfection
chemical_list: C107489:BIRC5 protein, human; D001897:Boronic Acids; D020672:I-kappa B Proteins; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D009363:Neoplasm Proteins; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D000077022:Survivin; D059004:Topoisomerase I Inhibitors; D000072000:NF-KappaB Inhibitor alpha; D000069286:Bortezomib; D000077146:Irinotecan; D002166:Camptothecin