title: Erythropoietin-induced reduction of hypoxia before and during fractionated irradiation contributes to improvement of radioresponse in human glioma xenografts.
abstract: OBJECTIVE
  Our study investigated the influence of recombinant human erythropoietin (rHuEPO) treatment, inducing raised hemoglobin levels in nonanemic mice, on intratumor oxygenation before and during fractionated irradiation. Furthermore, the consequences of rHuEPO administration on tumor response to fractionated radiotherapy (RT) were evaluated.
  
  
  METHODS
  Experiments were performed on two human malignant glioma (GBM Nan1 and U87) xenografted in nude mice. RHuEPO was daily delivered (0.3 IU/g/day, 5 days/week). Tumor hypoxia was assessed before (T1) and during (T6) fractionated irradiation using (1) pO(2)-Histograph (Eppendorf, Hamburg, Germany) and (2) the EF5-binding assay. Vascular density was determined using type IV collagen immunostaining. To assess RT efficacy, the irradiation schedule was 20 fractions of 2 Gy, once daily, 5 days/week over 4 weeks.
  
  
  RESULTS
  At T1, hemoglobin levels in rHuEPO-treated mice were significantly increased. Percentage of pO(2) values <2.5 mm Hg was reduced in rHuEPO-treated tumors as compared with control groups (37.1 +/- 19.1% vs. 58.5 +/- 27.0%; p = 0.009 for GBM Nan1; 81.6 +/- 13.4% vs. 91.5 +/- 8.3%; p = 0.035 for U87). The decrease of viable hypoxic tumor cells fraction after rHuEPO was confirmed by the EF5-binding assay. Vascular density was not altered after rHuEPO treatment. At T6, rHuEPO reduced the hypoxic fraction by about 20% (p = 0.036 and p = 0.171) in GBM Nan1 and U87 irradiated tumors. RHuEPO did not influence tumor growth by itself. RT alone or combined with rHuEPO induced a significant tumor growth delay. Finally, rHuEPO significantly enhanced RT efficacy (p = 0.012 in GBM Nan1 and p = 0.037 in U87), resulting in radiopotentiation ratios of 1.21 and 1.54 for respective models.
  
  
  CONCLUSIONS
  Our results indicate that rHuEPO, by enhancing blood oxygen-carrying capacity, decreases intrinsic tumor hypoxia and maintains its effect during fractionated irradiation in malignant glioma xenografts. Therefore, rHuEPO contributes to radiosensitize these tumors.
authors.affiliation: Laboratoire de Recherche en Oncologie, Centre Alexis Vautrin, Vandoeuvre-lès-Nancy, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Pinel
authors.forename: Muriel
authors.initials: M
authors.lastname: Barberi-Heyob
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Cohen-Jonathan
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Merlin
authors.forename: Caroline
authors.initials: C
authors.lastname: Delmas
authors.forename: François
authors.initials: F
authors.lastname: Plenat
authors.forename: Pascal
authors.initials: P
authors.lastname: Chastagner
mesh_terms: D000818:Animals; D015687:Cell Hypoxia / Q000187:drug effects*; D004921:Erythropoietin / Q000494:pharmacology*; D005910:Glioma / Q000097:blood* / Q000098:blood supply / Q000532:radiotherapy*; D006454:Hemoglobins / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D010100:Oxygen / Q000097:blood; D011836:Radiation Tolerance / Q000187:drug effects; D011994:Recombinant Proteins; D014183:Transplantation, Heterologous
chemical_list: D006454:Hemoglobins; D011994:Recombinant Proteins; D004921:Erythropoietin; D010100:Oxygen