title: Se-methylselenocysteine sensitizes hypoxic tumor cells to irinotecan by targeting hypoxia-inducible factor 1alpha.
abstract: OBJECTIVE
  Hypoxic tumor cells overexpressing hypoxia-inducible factor 1alpha (HIF-1alpha) are generally resistant to chemo/radiotherapy. We have reported that Se-methylselenocysteine (MSC) therapeutically enhances the efficacy and selectivity of irinotecan against human tumor xenografts. The aim of this study was to delineate the mechanism responsible for the observed efficacy targeting on HIF-1alpha and its transcriptionally regulated genes VEGF and CAIX.
  
  
  METHODS
  We investigated the mechanism of HIF-1alpha inhibition by MSC and its critical role in the therapeutic outcome by generating HIF-1alpha stable knockdown (KD) human head and neck squamous cell carcinoma, FaDu by transfecting HIF-1alpha short hairpin RNA.
  
  
  RESULTS
  While cytotoxic efficacy in combination with methylselenic acid (MSA) with SN-38 (active metabolites of MSC and irinotecan) could not be confirmed in vitro against normoxic tumor cells, the hypoxic tumor cells were more sensitive to the combination. Reduction in HIF-1alpha either by MSA or shRNA knockdown resulted in significant increase in cytotoxicity of SN38 in vitro against hypoxic, but not the normoxic tumor cells. Similarly, in vivo, either MSC in combination with irinotecan treatment of parental xenografts or HIF-1alpha KD tumors treated with irinotecan alone resulted in comparable therapeutic response and increase in the long-term survival of mice bearing FaDu xenografts.
  
  
  CONCLUSIONS
  Our results show that HIF-1alpha is a critical target for MSC and its inhibition was associated with enhanced antitumor activity of irinotecan. Inhibition of HIF-1alpha appeared to be mediated through stabilization of PHD2, 3 and downregulation of ROS by MSC. Thus, our findings support the development of MSC as a HIF-1alpha inhibitor in combination chemotherapy.
authors.affiliation: Department of Cancer Biology, Roswell Park Cancer Institute, Buffalo, NY, 14263, USA. sreenivasulu.chintala@roswellpark.org
authors.forename: Sreenivasulu
authors.initials: S
authors.lastname: Chintala
authors.forename: Károly
authors.initials: K
authors.lastname: Tóth
authors.forename: Shousong
authors.initials: S
authors.lastname: Cao
authors.forename: Farukh A
authors.initials: FA
authors.lastname: Durrani
authors.forename: Mary M
authors.initials: MM
authors.lastname: Vaughan
authors.forename: Randy L
authors.initials: RL
authors.lastname: Jensen
authors.forename: Youcef M
authors.initials: YM
authors.lastname: Rustum
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000235:genetics; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000235:genetics; D015687:Cell Hypoxia; D003545:Cysteine / Q000008:administration & dosage / Q000031:analogs & derivatives; D016503:Drug Delivery Systems; D005260:Female; D055785:Gene Knockdown Techniques; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000235:genetics; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors* / Q000235:genetics; D000077146:Irinotecan; D051379:Mice; D008819:Mice, Nude; D016566:Organoselenium Compounds / Q000008:administration & dosage; D034741:RNA, Small Interfering / Q000008:administration & dosage; D017382:Reactive Oxygen Species / Q000378:metabolism; D017279:Selenocysteine / Q000031:analogs & derivatives; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics; D023041:Xenograft Model Antitumor Assays
chemical_list: D000951:Antigens, Neoplasm; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016566:Organoselenium Compounds; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D042461:Vascular Endothelial Growth Factor A; D017279:Selenocysteine; D000077146:Irinotecan; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D003545:Cysteine; C002979:selenomethylselenocysteine; D002166:Camptothecin