Angiogenesis and Anti-angiogenic Therapy in Myelofibrosis with Myeloid Metaplasia

The Role of β-Catenin in Bcr/Abl Negative Myeloproliferative Neoplasms: An Immunohistochemical Study

INTRODUCTION

β-Catenin is a multifunctional protein that acts as a central effector molecule in the Wnt signaling pathway. Aberrant activation of the Wnt/β-catenin signaling pathway causes various diseases including cancer. In this study we evaluated β-catenin expression in bcr/abl-negative myeloproliferative neoplasms (MPNs).

MATERIALS AND METHODS

The expression of β-catenin was evaluated in bone marrow using immunohistochemical methods in 66 patients with bcr/abl-negative myeloproliferative neoplasms (MPNs) and in 30 healthy control subjects. Immunreactive score (IRS; staining intensity × percentage of positive stained cells) was used for the evaluation of the cell staining reaction.

RESULTS

IRS of megakaryocytes (IRSmega) was higher in essential thrombocytemia (ET) compared with the control group (P = .022) and primary myelofibrosis (PMF; P = .001). IRS of vascular endothelial cells (IRSvas) was higher in the bcr/abl negative MPN compared with the control group (P = .024). Also, IRSvas was higher in the PMF compared with the control group (P = .001), policythemia vera (PV; P = .005), and ET (P = .006). A positive correlation was detected between IRSmega and platelet counts (P = .019).

CONCLUSION

Results of this study suggest that the Wnt/β-catenin signaling pathway has a role in the angiogenesis of PMF and in the thrombopoiesis of PV and ET. Hence, targeting the Wnt/β-catenin signaling pathway could open new avenues for novel therapeutic approaches in bcr/abl-negative MPNs.

Histone deacetylase: a potential therapeutic target for fibrotic disorders

Histone deacetylases (HDACs) are enzymes that balance the acetylation activities of histone acetyltransferases on chromatin remodeling and play essential roles in regulating gene transcription. In the past several years, the role of HDACs in cancer initiation and progression, as well as the therapeutic effects of HDAC inhibitors in various types of cancer, has been well studied. Recent studies indicated that HDAC activity is also associated with the development and progression of some chronic diseases characterized by fibrosis, including chronic kidney disease, cardiac hypertrophy, and idiopathic pulmonary fibrosis. Here, we review what is known about HDACs in the progression of tissue fibrosis and the potential applications of HDAC inhibitors in the treatment of disorders associated with fibroblast activation and proliferation.

Quantitative investigation of bone microvascularization from 3D synchrotron micro-computed tomography in a rat model

A new method for simultaneous 3D imaging and analysis of microvascularization and bone microstructure in rat bone is developed. The method is based on the use of quantitative synchrotron micro-computed tomography (SR-microCT) coupled to an automatic image analysis procedure. Analysis of bone microvascularization is generally performed from 2D histology. The proposed method enables for the first time the simultaneous 3D analysis of microvascularization and bone microstructure in a rat model. It was applied to investigate the effect of intermittent parathyroid hormone (PTH) administration on angiogenesis and osteogenesis in rats. Rats were posthumously injected with a contrast agent and subsequently imaged. The algorithm allowed the reconstruction and the extraction of 3D quantitative parameters both on bone microstructure and microvascularization. Due to the short acquisition times of SR-microCT and the efficiency of the image analysis algorithm, a large data set was analyzed, which permitted statistical analysis of the measured parameters. Statistical analysis confirmed that treatment with PTH significantly increased bone volume and thickness, but decreased bone mineralization. It was further revealed that treatment with PTH significantly increased average vessel thickness.

Phosphatidylinositol-3-kinase/akt regulates bleomycin-induced fibroblast proliferation and collagen production

Abnormal repair and dysregulated angiogenesis have been implicated in the pathogenesis of pulmonary fibrosis, but the underlying mechanisms of regulation are not well understood. The present study investigated the role of phosphatidylinositol-3-kinase (PI3K)/Akt in fibrogenesis of human lung fibroblasts and its regulation by reactive oxygen species (ROS). Exposure of lung fibroblasts to bleomycin, a known inducer of fibrosis, resulted in rapid activation of PI3K/Akt and a parallel increase in fibroblast proliferation and collagen production, characteristics of lung fibrosis. Bleomycin had no significant effect on total Akt protein expression but induced phosphorylation of the protein at threonine 308 and serine 473 positions. Inhibition of this phosphorylation by PI3K inhibitors or by dominant-negative Akt (T308A/S473A) expression abrogated the effects of bleomycin on fibroblast proliferation and collagen production, suggesting the role of PI3K/Akt in the fibrogenic process. Activation of PI3K/Akt by bleomycin also led to transcriptional activation and protein expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and vascular endothelial growth factor, which contributed to the fibroproliferative and collagen-inducing effects of bleomycin. The fibrogenic effects of bleomycin were dependent on ROS generation, particularly superoxide anion and hydrogen peroxide, which were induced by bleomycin. Inhibition of ROS generation by antioxidant enzymes, catalase and superoxide dismutase mimetic MnTBAP, abrogated the fibrogenic effects of bleomycin as well as its induction of PI3K/Akt and HIF-1alpha activation. Together, our results indicate a novel role of PI3K/Akt in fibrogenesis of human lung fibroblasts and its regulation by ROS, which could be exploited for the treatment of pulmonary fibrosis and related disorders.

Enhanced histone deacetylase enzyme activity in primary myelofibrosis

We measured histone deacetylase (HDAC) activity in 17 patients with primary myelofibrosis (PMF); 19 with other myeloproliferative neoplasm (MPN) and 16 normal volunteers. Significantly elevated HDAC levels were shown in patients with PMF compared with other MPN patients and normal volunteers (p<0.05). Sixteen patients with PMF were also studied for correlation between JAK2 mutation status and HDAC levels; no significant correlation was found. We further correlated HDAC levels with clinical features in PMF: there was no correlation with WBC, platelet counts, Hb levels or degree of bone marrow fibrosis, but HDAC levels were correlated to the degree of splenomegaly. This suggests that HDAC may be recruited as essential thrombocythemia or polycythemia vera progresses into myelofibrosis or PMF progresses into more advanced stage. We then used the qRT-PCR cycle threshold (CT) method to study which HDACs were elevated in PMF. The results showed that, in general, Class 1 HDACs were elevated (HDAC1,2,8) except HDAC3, Class II HDACs were depressed (HDAC4,5) except HDAC6 and 10, and Class III HDACs were generally elevated. The current study may form the basis for using HDAC inhibitor in the treatment of patients with PMF and may implicate a possible role of HDAC in the association of pathogenesis of PMF.

Role of angiogenesis in chronic lymphocytic leukemia

Angiogenesis is a physiologic process of new blood vessels formation mediated by various cytokines called angiogenic and angiostatic factors. Although its potential pathophysiologic role in solid tumors has been extensively studied for more than 3 decades, enhancement of angiogenesis in chronic lymphocytic leukemia (CLL) and other malignant hematological disorders has been recognized more recently. An increased level of angiogenesis has been documented by various experimental methods both in bone marrow and lymph nodes of patients with CLL. Although the role of angiogenesis in the pathophysiology of this disease remains to be fully elucidated, experimental data suggest that several angiogenic factors play a role in the disease progression. Biologic markers of angiogenesis were also shown to be of prognostic relevance in CLL. The current findings provide the rationale for investigating antiangiogenic agents in CLL. In the current review angiogenesis in CLL is discussed and its potential diagnostic and therapeutic applications.

Angiogenesis inhibitors in the treatment of cancer

The field of cancer research has seen a marked shift in the past decade towards the exploration and development of non-conventional antitumour agents. One of the most widely studied approaches to therapy during this period has been that of antiangiogenesis. The published clinical trials and subsequent FDA approval (in February 2004) of the anti-vascular endothelial growth factor (VEGF) monoclonal antibody bevacizumab (Avastin, Genentech) for the treatment of colorectal cancer marked a milestone for antiangiogenesis therapy. Currently, preclinical and clinical research involving therapeutic targeting of VEGF and other mediators of angiogenesis continues in multiple tumour types. In addition to colorectal cancer, angiogenesis inhibitors are being investigated in the treatment of renal cell carcinoma, head and neck carcinoma, lung cancer, breast cancer, prostate cancer, and a variety of haematological malignancies. This article will discuss the background of antiangiogenesis research, preclinical and clinical data relating to the use of bevacizumab in the treatment of colorectal cancer, other completed clinical trials involving antiangiogenesis agents, and the potential future utility of these agents in the treatment of malignancy.