P-ERK1/2 Is a Predictive Factor of Response to ESA Treatment in Myelodysplastic Syndromes.

Abstract 294

Endogenous serum erythropoietin (sEPO) less than 500UI/L and a transfusion requirement lower than 2 units per month are the best predictive factors for response to treatment by erythropoiesis-stimulating agents (ESA) in low/int-1 myelodysplastic syndromes (MDS). However, the highest response rate hardly reaches 60% suggesting that other factors may influence the response. To investigate the biological signature of response to ESA, we enrolled 100 low/int-1 MDS patients in a prospective study of erythropoiesis at diagnosis before they were treated with ESA. According to the IWG 2006 criteria, 43 patients were non-responders. These patients had significantly higher serum EPO level, higher number of transfusion per month, and lower number of bone marrow-deriving BFU-E and CFU-E than responders. Analysis of CD34⁺-deriving erythroid progenitors by in vitro liquid culture, demonstrated that all MDS patients (n=54) had an increased apoptosis and a delayed expression of erythroid marker, glycophorin A (GPA). A collapse of EPO-induced DNA synthesis was observed in non-responders, while EPO-dependent erythroid cell differentiation and survival to Fas-induced apoptosis was equivalent in the two groups. Thus, non-responders exhibited an early and isolated default in EPO-induced cell proliferation, suggesting a defect in EPO-R signaling. Immunofluorescence to p-ERK1/2 before and after EPO-R stimulation in immature erythroblasts was negative in 6/8 non-responders, and positive in all 11 responders. Immunohistochemistry to p-ERK1/2 on bone marrow biopsies in 5 non-responders was negative and positive in immature cells in 4 responders. By flow cytometry, p-ERK1/2 expression in the CD71⁺/GPA⁻ bone marrow cell fraction corresponding to immature erythroblasts (n=30) was significantly lower in non-responders (n=16) than in responders (n=14; Wilcoxon-test: p<0.0001). Receiver operator curve (ROC) analysis of the flow cytometry test demonstrated a good predictive value for the response to ESA with a 0.96 area under the curve (AUC) [95%CI: 0.89 – 1.00]. ROC were also constructed for BFU-E number, serum EPO level, and number of transfusion per month and the AUC were computed. p-ERK1/2 was equivalent to BFU-E and superior to serum EPO level or number of transfusion in predicting the response to ESA. Although requiring validation in a larger cohort, these results suggest that p-ERK1/2 is a ready tool available for the prediction of response to ESA in MDS patients.