Transfusion-associated iron overload as a predictive factor for poor stem cell mobilization in patients with haematological malignancies.

Transfusion-associated iron overload is often observed in patients with haematological malignancies. We analysed the effect of iron overload, indicated by high serum ferritin level, on the mobilization of CD34(+) peripheral blood stem cells (PBSCs). We evaluated the association between the serum ferritin level prior to PBSC collection and the number of CD34(+) cells collected through leukapheresis in 51 patients with various haematological malignancies. Patients with serum ferritin level over 1000 ng mL(-1) were defined as high-ferritin group. Comparing the good (> or =1 x 10(6) per kg CD34(+) cells) and poor (<1 x 10(6) per kg CD34(+) cells) mobilizing groups, there was no difference in disease status, previous chemotherapies and white blood cell count at the first day of apheresis. However, there was a significant difference in the median units of red blood cell transfused between the good and poor mobilizer (2 vs. 8 units; P = 0.012). Serum ferritin level was notably higher in the poor mobilizer (1670 +/- 1320 ng mL(-1)) compared with the good mobilizer (965 +/- 705 ng mL(-1), P = 0.035). The cumulative number of CD34(+) cells per kg collected during the whole procedure was significantly lower in the high-ferritin group (5.5 +/- 4.7 x 10(6) per kg vs. 13.1 +/- 9.1 x 10(6) per kg, P = 0.01). Multivariate analysis revealed that serum ferritin level remained as an independent predictive factor for poor PBSC mobilization. Our study indicated that transfusion-associated iron overload is a predictive factor for poor PBSC mobilization. Iron chelation therapy prior to apheresis may be required to collect sufficient numbers of PBSCs in the iron overload patients.

Constitutive activation of extracellular signal-regulated kinase in human acute leukemias: combined role of activation of MEK, hyperexpression of extracellular signal-regulated kinase, and downregulation of a phosphatase, PAC1.

Extracellular signal-regulated kinase (ERK) is an important intermediate in signal transduction pathways that are initiated by many types of cell surface receptors. It is thought to play a pivotal role in integrating and transmitting transmembrane signals required for growth and differentiation. Constitutive activation of ERK in fibroblasts elicits oncogenic transformation, and recently, constitutive activation of ERK has been observed in some human malignancies, including acute leukemia. However, mechanisms underlying constitutive activation of ERK have not been well characterized. In this study, we examined the activation of ERK in 79 human acute leukemia samples and attempted to find factors contributing to constitutive ERK activation. First, we showed that ERK and MEK were constitutively activated in acute leukemias by in vitro kinase assay and immunoblot analysis. However, in only one half of the studied samples, the pattern of ERK activation was similar to that of MEK activation. Next, by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoblot analysis, we showed hyperexpression of ERK in a majority of acute leukemias. In 17 of 26 cases (65.4%) analyzed by immunoblot, the pattern of ERK expression was similar to that of ERK activation. The fact of constitutive activation of ERK in acute leukemias suggested to us the possibility of an abnormal downregulation mechanism of ERK. Therefore, we examined PAC1, a specific ERK phosphatase predominantly expressed in hematopoietic tissue and known to be upregulated at the transcription level in response to ERK activation. Interestingly, in our study, PAC1 gene expression in acute leukemias showing constitutive ERK activation was significantly lower than that in unstimulated, normal bone marrow (BM) samples showing minimal or no ERK activation (P =.002). Also, a significant correlation was observed between PAC1 downregulation and phosphorylation of ERK in acute leukemias (P =.002). Finally, by further analysis of 26 cases, we showed that a complementary role of MEK activation, ERK hyperexpression, and PAC1 downregulation could contribute to determining the constitutive activation of ERK in acute leukemia. Our results suggest that ERK is constitutively activated in a majority of acute leukemias, and in addition to the activation of MEK, the hyperexpression of ERK and downregulation of PAC1 also contribute to constitutive ERK activation in acute leukemias.