Platelet-derived growth factor (PDGF) in human acute myelogenous leukemia: PDGF receptor expression, endogenous PDGF release and responsiveness to exogenous PDGF isoforms by in vitro cultured acute myelogenous leukemia blasts

Sorafenib maintenance after hematopoietic stem cell transplantation improves outcome of FLT3-ITD-mutated acute myeloid leukemia

In a retrospective analysis, 21 acute myeloid leukemia patients receiving single-agent sorafenib maintenance therapy in complete remission (CR) after hematopoietic stem cell transplantation (HSCT) were compared with a control group of 22 patients without maintenance. Sorafenib was initiated a median of 3 months (IQR: 2.3–3.5) after allogeneic HSCT with a median daily dosage of 400 mg (range: 200–800) orally, and lasted a median of 11.3 months (IQR: 3.3–24.4). No significant increase in graft versus host disease or toxicity was observed. Adverse events were reversible with dose adjustment or temporary discontinuation in 19/19 cases. With a median follow-up of 34.7 months (IQR: 16.9–79.5), sorafenib maintenance significantly improved cumulative incidence of relapse (p = 0.028) as well as overall survival (OS) (p = 0.016), especially in patients undergoing allogeneic HSCT in CR1 (p < 0.001). In conclusion, sorafenib maintenance after allogeneic HSCT is safe and may improve cumulative incidence of relapse and OS in FLT3–ITD-mutated AML.

Connexin expression in human acute myeloid leukemia cells: identification of patient subsets based on protein and global gene expression profiles

Bone marrow stromal cells support both normal and malignant hematopoiesis. Τhis support is mediated through the local cytokine network and by direct cell‑cell interactions mediated via adhesion molecules and the formation of gap junctions by connexins. Previous studies on connexins in human acute myeloid leukemia (AML) have mainly focused on the investigation of leukemia cell lines. In the present study, we therefore investigated the expression of various connexins at the protein (i.e., cell surface expression) and mRNA level in primary human AML cells. The cell surface expression of the connexins, Cx26, Cx32, Cx37, Cx43 and Cx45, varied considerably between patients, and detectable levels were observed only for subsets of patients. On the whole, Cx43 and Cx45 showed the highest cell surface expression. Connexin expression was dependent on AML cell differentiation, but showed no association with cytogenetic abnormalities or mutations of the fms-related tyrosine kinase 3 (FLT3) or nucleophosmin (NPM)‑1 genes. By contrast, only Cx45 showed a significant variation between patients at the mRNA level. A high Cx45 expression was associated with the altered regulation of the mitogen‑activated protein kinase (MAPK) pathway and the release of pro-inflammatory cytokines [interleukin (IL)‑17, tumor necrosis factor (TNF), interferon‑γ], whereas a low Cx45 expression was associated with the altered regulation of protein functions (i.e., ligase activity, protein folding and catabolism). There was no significant correlation observed between the connexin mRNA and protein levels. Thus, differences in connexin expression can be used to subclassify AML patients. Differences in connexin cell surface expression profiles are not reflected at the mRNA level and have to be directly examined, whereas variations in Cx45 mRNA expression are associated with differences in cell signaling and the regulation of protein functions.

STAT3 as a possible therapeutic target in human malignancies: lessons from acute myeloid leukemia

STAT3 is important for transcriptional regulation in human acute myeloid leukemia (AML). STAT3 has thousands of potential DNA binding sites but usually shows cell type specific binding preferences to a limited number of these. Furthermore, AML is a very heterogeneous disease, and studies of the prognostic impact of STAT3 in human AML have also given conflicting results. A more detailed characterization of STAT3 functions and the expression of various isoforms in human AML will therefore be required before it is possible to design clinical studies of STAT3 inhibitors in this disease, and it will be especially important to investigate whether the functions of STAT3 differ between patients. Several other malignancies also show extensive biological heterogeneity, and the present discussion and the suggested scientific approaches may thus be relevant for other cancer patients.

PDGF-C: a new performer in the neurovascular interplay

The importance of neurovascular crosstalk in development, normal physiology, and pathologies is increasingly being recognized. Although vascular endothelial growth factor (VEGF), a prototypic regulator of neurovascular interaction, has been studied intensively, defining other important regulators in this process is warranted. Recent studies have shown that platelet-derived growth factor C (PDGF-C) is both angiogenic and a neuronal survival factor, and it appears to be an important component of neurovascular crosstalk. Importantly, the expression pattern and functional properties of PDGF-C and its receptors differ from those of VEGF, and thus the PDGF-C-mediated neurovascular interaction may represent a new paradigm of neurovascular crosstalk.

Connexin-based signaling in acute myelogenous leukemia (AML)

Normal and malignant hematopoiesis are regulated by intercellular communication in the hematopoietic microenvironments, and both soluble mediators as well as direct cell-cell contact play important functional roles. Gap junctions are complex membrane structures that transfer molecules between neighboring cells and thereby alter intracellular signaling and metabolism. The gap junction building blocks, the connexins, are also involved in gap junction-independent intercellular communication by forming hemichannels that transfer substances between the intra- and extracellular spaces. Connexins are furthermore involved in cell regulation as single molecules by modulating intracellular pathways and possibly gene transcription. The role of connexins in leukemogenesis and leukemic cell functions are not well characterized. In this review, we describe the known effects of gap junctions and connexins in acute myelogenous leukemia and the diverse potential of connexins in acute myelogenous leukemia chemosensitivity, intracellular signaling and cell death regulation.

PDGF-BB is a novel prognostic factor in colorectal cancer

PURPOSE

Human platelet-derived growth factor BB (PDGF-BB) is thought to be involved in human malignancies. Its overexpression has been reported in some human tumors. However, its expression in colorectal cancer has not been studied. We thus investigated the clinicopathological and biological significance of PDGF-BB gene expression in human colorectal cancer.

EXPERIMENTAL DESIGN

Using real-time reverse transcription-PCR, we evaluated PDGF-BB expression status and correlated data with clinicopathological parameters in 60 patients with colorectal cancer. Additionally, we established a colorectal cancer cell line expressing PDGF-BB and investigated its effects on cell invasion and proliferation.

RESULTS

The incidence of vascular invasion was significantly greater in patients expressing PDGF-BB at a high level than in those at a low level (P < .05). Patients with high PDGF-BB expression had a significantly poorer survival rate than those with low PDGF-BB expression (P < .05). A multivariate analysis demonstrated that PDGF-BB expression was an independent prognostic factor. We demonstrated in vitro that cells transduced with PDGF-BB showed greater invasiveness (P < .05) and migration (P < .001) than did mock transduced cells. In a xenograft study, cells transduced with PDGF-BB had higher proliferation rates than mock transfected cells.

CONCLUSION

PDGF-BB expression may be a new prognostic indicator for patients with colorectal cancer.

Autocrine expression of platelet-derived growth factor B in B cell chronic lymphocytic leukemia

Platelet-derived growth factor (PDGF) regulates clonal proliferation of malignant pre-B cell lines, but little is known about its role in normal B lymphocyte differentiation and malignant transformation. To understand the expression of PDGF-A, PDGF-B and the beta-receptor (PDGF-Rbeta) in B cell lymphoproliferative disorders, we used an immunohistochemical method to stain formalin-fixed, paraffin-embedded tissues in 5 patients with reactive lymphoid hyperplasia, 15 with non-Hodgkin's lymphoma and 23 with B cell chronic lymphocytic leukemia (B-CLL). Abundant PDGF-A, rather than PDGF-B, was expressed in normal B cell differentiation. There was no difference in the expression of PDGF-A and PDGF-B between patients with reactive lymphoid hyperplasia and patients with malignant lymphoproliferative disorders. Among the patients with B-CLL, the expression of PDGF-B was much stronger than the expression of PDGF-A, and 18 of the patients had coexpression of PDGF-B and PDGF-Rbeta. A larger proportion of patients with B-CLL than with non-Hodgkin's lymphoma had expression of PDGF-B and PDGF-Rbeta. In conclusion, PDGF-A expression in all stages of B lymphocyte differentiation suggests that it is important in B cell differentiation and proliferation. Expression of PDGF-B and PDGF-Rbeta suggests that autocrine signaling of PDGF may be important in malignant transformation of B-CLL. However, further studies are necessary to confirm these conclusions.

Tyrosine kinase oncogenes in normal hematopoiesis and hematological disease

Tyrosine kinase oncogenes are formed as a result of mutations that induce constitutive kinase activity. Many of these tyrosine kinase oncogenes that are derived from genes, such as c-Abl, c-Fes, Flt3, c-Fms, c-Kit and PDGFRbeta, that are normally involved in the regulation of hematopoiesis or hematopoietic cell function. Despite differences in structure, normal function, and subcellular location, many of the tyrosine kinase oncogenes signal through the same pathways, and typically enhance proliferation and prolong viability. They represent excellent potential drug targets, and it is likely that additional mutations will be identified in other kinases, their immediate downstream targets, or in proteins regulating their function.

Effects of cytarabine and various anthracyclins on platelet activation: characterization of in vitro effects and their possible clinical relevance in acute myelogenous leukemia

Previous in vitro studies have demonstrated that normal platelets and platelet-released mediators can alter in vitro characteristics of human acute myelogenous leukemia (AML) blasts. To further investigate whether platelets can be expected to adhere to and thereby affect AML blasts through their release of soluble mediators into a common microenvironment, we investigated (i) the effects on platelet activation by cytotoxic drugs commonly used in AML therapy; (ii) the occurrence of circulating activated platelets in acute leukemia patients; and (iii) the in vivo and in vitro adherence of platelets to AML blasts. The anthracyclins daunorubicin and idarubicin increased the expression of activation-associated membrane molecules (GPIIb/IIIa, CD62P, CD63) by normal platelets, daunorubicin then having the strongest effect. In contrast, cytarabine, epirubicin, doxorubicin and mitoxantrone had no significant effects. Although AML patients did not show increased levels of activated platelets in the circulation, adhesion of platelets to AML blasts was demonstrated both in vivo and in vitro. These results suggest that platelets and AML blasts may locate to common in vivo microenvironments, and platelet-derived soluble mediators may thereby affect the functional characteristics of the leukemia cells.