title: HIF-1alpha modulation by topoisomerase inhibitors in non-small cell lung cancer cell lines.
abstract: OBJECTIVE
  This study was to investigate whether the topoisomerase (Top) I inhibitor topotecan and the Top II inhibitor etoposide could modulate the hypoxia-induced HIF-1alpha expression in non-small cell lung cancer (NSCLC) cell lines.
  
  
  METHODS
  Hypoxic conditions were maintained in a humidified airtight anaerobic incubator flushed with a mixture of gas consisting of 1% O(2), 5% CO(2) and 94% N(2). The expressions of HIF-1alpha and Akt phosphorylation were measured by Western blotting or quantitative reverse transcription-polymerase chain reaction. Small interfering RNA treatment was done to inhibit the expressions of Top I and IIalpha. Constitutively active akt was expressed by transient transfection using pUSEamp(+)/myr Akt.
  
  
  RESULTS
  The HIF-1alpha was increased and this peaked at 9 h in hypoxic conditions. Both topotecan and etoposide in a dose- and time-dependent manner inhibited the accumulation of hypoxia-induced HIF-1alpha protein. Interestingly, the daily addition of these drugs at a lower concentration could inhibit the HIF-1alpha expression more effectively than a single treatment, which shows that their effects are schedule-dependent. This down-regulation of HIF-1alpha was associated with proteosomal degradation and decreased Akt phosphorylation. Top I and Top IIalpha were required for the inhibitory effect of topotecan and etoposide, respectively.
  
  
  CONCLUSIONS
  Both Top I and II inhibitors could suppress the HIF-1alpha expression in a schedule-dependent manner, and this suggests that these drugs might be useful to overcome the therapeutic resistance induced by tumor hypoxia in NSCLC.
authors.affiliation: Department of Internal Medicine, Korea Cancer Center Hospital, Korea Institute of Radiological and Medical Science, 215-4, Gongneung-dong, Nowon-gu, Seoul 139-706, Korea.
authors.forename: Yun Jung
authors.initials: YJ
authors.lastname: Choi
authors.forename: Jin Kyung
authors.initials: JK
authors.lastname: Rho
authors.forename: Sun Joo
authors.initials: SJ
authors.lastname: Lee
authors.forename: Won Seok
authors.initials: WS
authors.lastname: Jang
authors.forename: Seung Sook
authors.initials: SS
authors.lastname: Lee
authors.forename: Cheol Hyeon
authors.initials: CH
authors.lastname: Kim
authors.forename: Jae Cheol
authors.initials: JC
authors.lastname: Lee
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000201:enzymology* / Q000378:metabolism; D045744:Cell Line, Tumor; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D019772:Topotecan / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D005047:Etoposide; D019772:Topotecan; D051057:Proto-Oncogene Proteins c-akt; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II