Abstract 5392: Angiocidin induces differentiation of acute myeloid leukemia (AML) cells

Acute myeloid leukemia (AML) is a malignant proliferative disorder where blast stage cells fail to terminally differentiate and accumulate in the blood and bone marrow. AML represents a very significant health risk in the general population with rising incidence in aging adults. From 2004-2008 the median age at diagnosis was 67.8 years and it is estimated 12,950 adults will be diagnosed with 9,050 deaths from AML leukemia in 2011 (http://seer.cancer.gov/statfacts/html/amyl.html, accessed November 2011). Standard AML therapy requires intensive combination chemotherapy with a low rate of durable remissions often requiring stem cell transplantation and associated with significant treatment-related toxicity, especially in elderly patients. Due to this toxicity, the majority of elderly patients are not eligible for therapy. Therefore, new therapeutic options for the treatment of AML are urgently needed. In this study, we present evidence that the human protein angiocidin, discovered in our laboratory, has the potential to be used as a novel, non-toxic therapy for AML. We found that angiocidin can induce both AML cell lines and primary patient cells to increase expression of surface markers characteristic of a more normal differentiated phenotype. We evaluated expression of CD14, a major receptor for the innate immune system in macrophages, CD54 or ICAM-1, the major adhesion receptor used by macrophages for endothelial transmigration, and CD15, a neutrophil phagocytosis receptor. Expression of these receptors was measured by flow cytometry after cells were cultured for 24 hours in media alone or media containing 10 μg/ml angiocidin. Angiocidin up-regulated these receptors by more than 10 fold in 50% of the AML cells tested. The AML cells included the cell line THP-1 and 11 primary AML patient cells. Angiocidin up-regulated CD14 and CD54 in THP-1 cells and in 3 out of 5 M5 phenotype AML patient cells tested and 1 M4 AML phenotype out of 6 M4 samples tested. Angiocidin also up-regulated CD15 in 1 M4 AML patient phenotype out of 6 M4 patient cells tested. These results suggest that angiocidin can differentiate AML cells and therefore has the potential to be developed as differentiation therapy for AML.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5392. doi:1538-7445.AM2012-5392

Antibody-directed targeting of angiostatin's receptor annexin II inhibits Lewis Lung Carcinoma tumor growth via blocking of plasminogen activation: Possible biochemical mechanism of angiostatin's action

Angiostatin, the N-terminal four kringles (K1-4) of parent molecule plasminogen, is reported to block Lewis Lung Carcinoma (LLC) tumor growth and metastasis. However, angiostatin's mechanism of action is unclear. We earlier reported that angiostatin binds to cell surface annexin II through the lysine-binding domain (kringles 1-4) [Tuszynski, G.P., Sharma, M., Rothman, V.L., Sharma, M.C., 2002. Angiostatin binds to tyrosine kinase substrate annexin II through the lysine-binding domain in endothelial cells. Microvasc. Res. 64:448-462.]). We now show that annexin II on the cell surface of LLC cells regulates conversion of plasminogen to plasmin. Activation of plasminogen to plasmin is time-dependent, with the linear activation lasting up to 120 min. Monoclonal antibodies to annexin II reduced plasminogen activation by 92.6%, suggesting a specific role of annexin II in plasmin generation. Angiostatin also reduced plasmin generation by 81.6%, suggesting that angiostatin may be competing with plasminogen through lysine-binding domain. epsilon-Aminocaproic acid, a lysine analogue, effectively blocked plasminogen activation indicating that, indeed, the lysine-binding site of the kringles domain is required for activation. These data suggest that annexin II may be a receptor target for angiostatin's action. Therefore, we tested the effect of high affinity monoclonal antibody to annexin II in mouse model of LLC. A single dose of antibody treatment inhibited LLC tumor growth almost 70% with concomitant inhibition of circulating plasmin generation and its proteolytic activity. Taken together, it is possible that inhibition of LLC tumor growth and metastasis reported by angiostatin therapy may be due to blocking of annexin-II-dependent plasmin generation. Plasmin is known to influence angiogenic, invasive and metastatic capability of tumors.

Thrombospondin-1 and transforming growth factor-beta l promote breast tumor cell invasion through up-regulation of the plasminogen/plasmin system

BACKGROUND

Pericellular proteolysis is crucial in tumor cell invasion. The plasminogen/plasmin system is one of the main protease systems involved in cancer progression. Thrombospondin-1 (TSP-1), through activation of transforming growth factor-beta 1 (TGF-beta 1), up-regulates the main plasminogen activator, the urokinase-type plasminogen activator (uPA). The objectives of this study were to determine the role of TSP-1 and TGF-beta 1 in the localization of the plasminogen/plasmin system to the tumor cell surface by the uPA receptor (uPAR) and to determine its effect in breast tumor cell invasion.

METHODS

The effect of TSP-1 and TGF-beta 1 in uPAR expression was determined in MDA-MB-231 human breast cancer cells by enzyme-linked immunosorbent assay and Western blot analysis. Their effect and the role of the plasminogen/plasmin system in breast tumor cell invasion were studied with a Boyden Chamber assay.

RESULTS

uPAR expression was up-regulated more than twofold by both TSP-1 and TGF-beta 1. The effect of TSP-1 involved its receptor and the activation of TGF-beta 1 by TSP-1. Breast tumor cell invasion was up-regulated sevenfold to eightfold by both TSP-1 and TGF-beta 1 compared with the control group. Antibodies against uPA or uPAR neutralized the TSP-1- and TGF-beta 1-promoted breast tumor cell invasion.

CONCLUSIONS

TSP-1, through the activation of endogenous TGF-beta 1, up-regulates the plasminogen/plasmin system and promotes tumor cell invasion in breast cancer cells.

Thrombospondin promotes cell-substratum adhesion

The physiological role of the platelet-secreted protein thrombospondin (TSP) is poorly understood, although it has been postulated to be involved in platelet aggregation and cellular adhesion. In this report, TSP isolated from human platelets was found to promote, in vitro, the cell-substratum adhesion of a variety of cells, including platelets, melanoma cells, muscle cells, endothelial cells, fibroblasts, and epithelial cells. The adhesion-promoting activity of TSP was species independent, specific, and not due to contamination by fibronectin, vitronectin, laminin, or platelet factor 4. The cell surface receptor for TSP is protein in nature and appears distinct from that for fibronectin.

Evidence that cholesteryl ester hydrolase and triglyceride lipase are different enzymes in rat liver

Studies on intracellular cholesteryl ester hydrolase (CEH) and triglyceride lipase (TGL) from rat adipose tissue and adrenal cortex have suggested that a single protein is responsible for both activities. To determine whether one hepatic protein catalyzes both reactions, we studied several properties of CEH and TGL in rat liver. During liver perfusion with heparin, perfusate peaks of TGL and CEH did not consistently coincide, and TGL activity was considerably higher and less heat-stable than that of CEH. Significant TGL, but not CEH, activity was released during incubation of isolated hepatocytes. Although microsomes isolated from hepatocytes contained both activities, the specific activities of CEH and TGL in cytosol from hepatocytes were 95% and 3%, respectively, of those found in cytosol from whole liver. Preincubation of liver cytosol with 5 mM Mg2+ decreased CEH, but not TGL, activity. Intracellular CEH and TGL activities were completely separated by prep-disc gel electrophoresis. Finally, both cytosolic and microsomal TGL, but not CEH, activities were inhibited by antiserum against rat hepatic TGL. We conclude that extracellular TGL does not have CEH activity and intracellular CEH differs from TGL.

Immobilized E. coli alkaline phosphatase. Its properties, stability, and utility in studying the dephosphorylation of proteins

We have immobilized E. coli alkaline phosphatase (EC 3.1.3.1) by linking it covalently to sepharose 4B. This preparation has several advantages over the soluble enzyme. The immobilized enzyme is easily separable from other constituents in incubation mixtures. The immobilized enzyme can be reused repeatedly and is more stable than the soluble enzyme to heat treatment in the presence of 10 mM Mg2+. The insoluble and soluble phosphatases removed 75 and 77%, respectively, of the inorganic phosphorus from casein. The immobilized enzyme inactivated two enzymes believed to be active in the phosphorylated state, acyl-CoA:cholesterol acyltransferase (ACAT) by 39% and NADPH-cytochrome P-450 reductase by 89%. The utility of immobilized alkaline phosphatase for studying the phosphorylation and dephosphorylation of soluble or membrane-bound enzymes and proteins is discussed.

Stimulation of bile acid synthesis by dibutyryl cyclic AMP in isolated rat hepatocytes

Freshly isolated rat hepatocytes were used to examine the effects of dibutyryl cyclic AMP on the incorporation of 14C-acetate and 14C-cholesterol into bile acids. After an initial lag period, both precursors were incorporated into cholic and chenodeoxycholic acids at a linear rate for the subsequent 60 min. An apparent stimulation of bile acid formation from 14C-acetate by dibutyryl cyclic AMP was complicated by the concomitant inhibition of cholesterol synthesis. In experiments with 14C-cholesterol, dibutyryl cyclic AMP (1 mM) increased the labeled cholic and chenodeoxycholic acids in the medium by 83 and 224%, respectively, but cellular levels of labeled bile acids were unchanged. As a result, the nucleotide stimulated the overall incorporation of 14C-cholesterol into cholic acid by 39% and into chenodeoxycholic acid by 123%. The mean ratio of labeled cholic to chenodeoxycholic acid declined from 55:45 in control cells to 41:59 in cells incubated with dibutyryl cyclic AMP. The results demonstrate that label incorporation can be used to study the regulation of bile acid synthesis in isolated hepatocytes. We propose that dibutyryl cyclic AMP enhanced bile acid production by phosphorylating, and thus stimulating the activity of, cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in bile acid synthesis.