Erythropoietin-induced reduction of hypoxia before and during fractionated irradiation contributes to improvement of radioresponse in human glioma xenografts.
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.
Pinel
Sophie
S
Laboratoire de Recherche en Oncologie, Centre Alexis Vautrin, Vandoeuvre-lès-Nancy, France.
Barberi-Heyob
Muriel
M
Cohen-Jonathan
Elizabeth
E
Merlin
Jean-Louis
JL
Delmas
Caroline
C
Plenat
François
F
Chastagner
Pascal
P
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
D006454:Hemoglobins; D011994:Recombinant Proteins; D004921:Erythropoietin; D010100:Oxygen