To study the expression levels of ferroportin (Fpn) in lymphoblastic leukemia cells in children with precursor B-cell acute lymphoblastic leukemia (BCP-ALL), and to explore the possible correlations with various clinical features and treatment outcomes.

Sixty-four children with newly diagnosed BCP-ALL in West China Second Hospital from February 2011 to June 2014 were enrolled into this study as study group, and were risk-stratified and treated according to the Chinese Children Leukemia Group ALL 2008 (CCLG-ALL 2008) protocol. Twenty-one healthy children for health check-up in our hospital during the same period were chosen by random number table as control group. Levels of Fpn relative media expression levels in bone marrow and peripheral mononuclear cells isolated from leukemic and control group children were determined respectively by fluorescence real-time reverse transcription polymerase chain reaction (RT-PCR). Level of Fpn relative media expression 0.18 was set as the threshold of Fpn relative media expression levels, patients with level of Fpn relative expression >0.18 in study group were enrolled into Fpn high expression levels subgroup (n=32), while patients with level of Fpn relative expression ≤0.18 in study group were enrolled into Fpn low expression levels subgroup (n=32). Prognosis in terms of relapse-free survival (RFS) rate, event-free survival (EFS) rate and overall survival (OS) rate were calculated by Kaplan-Meier method. Correlations between relative median Fpn expression levels and various clinical features, immunophenotype, ALL related fused gene, early treatment response, clinical risk degree and prognosis were analyzed by statistical methods. The study protocol was approved by the Ethical Review Board of Investigation in Human Being of West China Second University Hospital, Sichuan University.

①There were no statistical differences among the gender ratio and age distribution between study group and control group, Fpn high expression levels subgroup and Fpn low expression levels subgroup in study group, respectively (P>0.05). ②The relative median Fpn expression level in study group (0.18) was significantly lower than that in control group (2.19) (U=1 415.0, P<0.001). ③ The relative median Fpn expression levels in patients with initial white blood cell count <50×10⁹/L (47 cases) and those with white blood cell count ≥50×10⁹/L (17 cases) were 0.23 and 0.04 respectively, relative relative and there was statistical difference between them (U=399.0, P=0.02). With the median initial white blood cell count (21.1×10⁹/L) and median absolute blast count (14.1×10⁹/L) as the cutoff points respectively, relative median Fpn expression levels in patient with high and low cell counts were 0.09 and 0.28, respectively (U=870.0, P=0.02), 0.09 and 0.28 (U=878.0, P=0.03), respectively. Similarly, with relative median Fpn expression as the cutoff point, the median white blood cell count and median absolute blast count in Fpn high expression levels subgroup and Fpn low expression levels subgroup were 15.4×10⁹/L and 29.3×10⁹/L (U=863.5, P=0.018), 8.2×10⁹/L and 21.3×10⁹/L (U=866.0, P=0.019) respectively. In addition, Spearman rank correlation analysis showed that Fpn expression level was negatively correlated to both initial white blood cell count and absolute blast counts (r_s=-0.357, -0.366; P=0.004, 0.003). ④No correlations were documented between Fpn expression levels and age at diagnosis, gender, leukemia immunophenotyping, fusion genes, glucocorticoid resistance, risk assignment and early chemotherapy response (P>0.05). No significant differences were disclosed between Fpn high and low expression levels subgroups , in terms of patient proportions with different clinical features (P>0.05). ⑤The median follow-up time was 13 months (2-50 months) in study group. Up to the follow-up endpoint, the rates of 3-year RFS, EFS and OS were 74.4% and 61.7% (χ²=0.975, P=0.323), 68.0% and 62.4% (χ²=0.102, P=0.749), 85.0% and 74.4% (χ²=0.576, P=0.448) in Fpn high and low expression levels subgroups respectively.

Our research findings that Fpn expression level is remarkably down-regulated as compared to normal children, and is negatively correlated to both initial white blood cell count and absolute blast cell count in peripheral blood, which strongly suggest that decreased Fpn expression level in highly proliferating lymphoblastic leukemia cells plays key role in sequestering iron within cells, in order to meet iron demand for enhanced cellular metabolism and proliferation. The dysregulated Hepcidin (Hepc)-Fpn axis might turn out to be an important underlying mechanism of cellular iron modulation in lymphoblastic leukemia cells, as revealed by recent studies in breast cancer cell lines and patients.