Lynn McCallum

FKBPL and Peptide Derivatives: Novel Biological Agents That Inhibit Angiogenesis by a CD44-Dependent Mechanism

Purpose: Antiangiogenic therapies can be an important adjunct to the management of many malignancies. Here we investigated a novel protein, FKBPL, and peptide derivative for their antiangiogenic activity and mechanism of action. Experimental Design: Recombinant FKBPL (rFKBPL) and its peptide derivative were assessed in a range of human microvascular endothelial cell (HMEC-1) assays in vitro. Their ability to inhibit proliferation, migration, and Matrigel-dependent tubule formation was determined. They were further evaluated in an ex vivo rat model of neovascularization and in two in vivo mouse models of angiogenesis, that is, the sponge implantation and the intravital microscopy models. Antitumor efficacy was determined in two human tumor xenograft models grown in severe compromised immunodeficient (SCID) mice. Finally, the dependence of peptide on CD44 was determined using a CD44-targeted siRNA approach or in cell lines of differing CD44 status. Results: rFKBPL inhibited endothelial cell migration, tubule formation, and microvessel formation in vitro and in vivo. The region responsible for FKBPLs antiangiogenic activity was identified, and a 24-amino acid peptide (AD-01) spanning this sequence was synthesized. It was potently antiangiogenic and inhibited growth in two human tumor xenograft models (DU145 and MDA-231) when administered systemically, either on its own or in combination with docetaxel. The antiangiogenic activity of FKBPL and AD-01 was dependent on the cell-surface receptor CD44, and signaling downstream of this receptor promoted an antimigratory phenotype. Conclusion: FKBPL and its peptide derivative AD-01 have potent antiangiogenic activity. Thus, these agents offer the potential of an attractive new approach to antiangiogenic therapy. Clin Cancer Res; 17(5); 1044–56. ©2011 AACR.

CCN3 -A key regulator of the hematopoietic compartment

CCN3, a founding member of the CCN family of growth regulators, was linked with hematology in 2003(1) when it was detected in human serum. CCN3 is expressed and secreted by hematopoietic progenitor cells in normal bone marrow. CCN3 acts through the core stem cell signalling pathways including Notch and Bone Morphogenic Protein, connecting CCN3 with the modulation of self-renewal and maturation of a number of cell lineages including hematopoietic, osteogenic and chondrogenic. CCN3 expression is disrupted in Chronic Myeloid Leukemia as a consequence of the BCR-ABL oncogene and allows the leukemic clone to evade growth regulation. In contrast, naïve cord blood progenitors undergo enhanced clonal expansion in response to CCN3. Altered CCN3 expression is associated with numerous solid tumors including glioblastoma, melanoma, adrenocortical tumours, prostate cancer and bone malignancies including osteosarcoma. Mature CCN3 protein has five distinct modules and truncated protein variants with altered function are found in many cancers. Regulation by CCN3 is therefore cell type and isoform specific. CCN3 has emerged as a key player in stem cell regulation, hematopoiesis and a crucial component within the bone marrow microenvironment.

CCN3: a key growth regulator in Chronic Myeloid Leukaemia

Chronic Myeloid Leukaemia (CML) is characterized by expression of the constitutively active Bcr-Abl tyrosine kinase. We have shown previously that the negative growth regulator, CCN3, is down-regulated as a result of Bcr-Abl kinase activity and that CCN3 has a reciprocal relationship of expression with BCR-ABL. We now show that CCN3 confers growth regulation in CML cells by causing growth inhibition and regaining sensitivity to the induction of apoptosis. The mode of CCN3 induced growth regulation was investigated in K562 CML cells using gene transfection and treatment with recombinant CCN3. Both strategies showed CCN3 regulated CML cell growth by reducing colony formation capacity, increasing apoptosis and reducing ERK phosphorylation. K562 cells stably transfected to express CCN3 showed enhanced apoptosis in response to treatment with the tyrosine kinase inhibitor, imatinib. Whilst CCN3 expression was low or undetectable in CML stem cells, primary CD34+ CML progenitors were responsive to treatment with recombinant CCN3. This study shows that CCN3 is an important growth regulator in haematopoiesis, abrogation of CCN3 expression enhances BCR-ABL dependent leukaemogenesis. CCN3 restores growth regulation, regains sensitivity to the induction of apoptosis and enhances imatinib cell kill in CML cells. CCN3 may provide an additional therapeutic strategy in the management of CML.

Proteasome proteolytic profile is linked to Bcr-Abl expression

OBJECTIVE We have previously demonstrated that proteasome activity is higher in bone marrow from patients with chronic myeloid leukemia (CML) than normal controls. This study investigates whether there is any relationship between Bcr-Abl expression and proteasome activity. MATERIALS AND METHODS Fluorogenic substrate assays and an activity-based probe were used to profile proteasome activity in CML cell-line models and the effect of the proteasome inhibitor BzLLLCOCHO on these cell-line models and primary CML cells was investigated. RESULTS We have demonstrated that oncogenic transformation by BCR-ABL is associated with an increase in proteasome proteolytic activity. Furthermore, small interfering RNA targeted against BCR-ABL reduces proteasome activity. In addition, we have found that Bcr-Abl-positive cells are more sensitive than Bcr-Abl-negative cells to induction of apoptosis by the proteasome inhibitor BzLLLCOCHO, and that sequential addition of imatinib followed by BzLLLCOCHO has an additive effect on the induction of apoptosis in Bcr-Abl-positive cells. Finally, we demonstrate that cell lines that become resistant to imatinib remain sensitive to proteasome inhibition. CONCLUSION This is the first time that a direct relationship has been demonstrated between BCR-ABL transformation and the enzymatic activity of the proteasome. Our results suggest that the proteasome might provide a useful therapeutic target in CML, particularly in those patients who have developed resistance to conventional treatment.

The matricellular protein CCN3 regulates NOTCH1 signalling in chronic myeloid leukaemia.

Deregulated NOTCH1 has been reported in lymphoid leukaemia, although its role in chronic myeloid leukaemia (CML) is not well established. We previously reported BCR‐ABL down‐regulation of a novel haematopoietic regulator, CCN3, in CML; CCN3 is a non‐canonical NOTCH1 ligand. This study characterizes the NOTCH1–CCN3 signalling axis in CML. In K562 cells, BCR‐ABL silencing reduced full‐length NOTCH1 (NOTCH1‐FL) and inhibited the cleavage of NOTCH1 intracellular domain (NOTCH1‐ICD), resulting in decreased expression of the NOTCH1 targets c‐MYC and HES1. K562 cells stably overexpressing CCN3 (K562/CCN3) or treated with recombinant CCN3 (rCCN3) showed a significant reduction in NOTCH1 signalling (> 50% reduction in NOTCH1‐ICD, p < 0.05). Gamma secretase inhibitor (GSI), which blocks NOTCH1 signalling, reduced K562/CCN3 colony formation but increased that of K562/control cells. GSI combined with either rCCN3 or imatinib reduced K562 colony formation with enhanced reduction of NOTCH1 signalling observed with combination treatments. We demonstrate an oncogenic role for NOTCH1 in CML and suggest that BCR‐ABL disruption of NOTCH1–CCN3 signalling contributes to the pathogenesis of CML.

A rapid and sensitive method for measuring cell adhesion

We have adapted the CyQuant® assay to provide a simple, rapid, sensitive and highly reproducible method for measuring cell adhesion. The modified CyQuant® assay eliminates the requirement for labour intensive fluorescent labelling protocols prior to experimentation and has the sensitivity to measure small numbers (>1000) of adherent cells.

FKBPL: a novel prognostic and predictive biomarker?

Approximately 40% of patients with oestrogen receptor (ER)-positive breast cancers do not respond to endocrine therapies; furthermore, most responsive tumours eventually become resistant. We have identified a novel oestrogen-responsive Hsp90 co-chaperone and immunophilin, FKBPL, which affects the stability and signalling of ER with implications for breast cancer growth and sensitivity to endocrine therapies. MCF7 cells stably overexpressing FKBPL demonstrate a slower rate of proliferation and become highly dependent on oestrogen for their growth. This dependence on oestrogen renders these cells dramatically more sensitive to tamoxifen and fulvestrant. FKBPL overexpressing cells also exhibit decreased levels of ER and an oestrogen-responsive gene, cathepsin D, critical for breast cancer growth, survival and invasion. Moreover, knockdown of FKBPL using a targeted siRNA approach dramatically increases both ER and cathepsin D protein levels and cell resistance to tamoxifen. FKBPL has been previously implicated in the stabilisation of the cyclin-dependent kinase inhibitor, p21 [1]. Loss of p21 has been associated with a tamoxifen growth-inducing phenotype and hyperphosphorylation of ER at Ser118, with increased expression of ER-regulated genes. Following FKBPL knockdown, we have observed a fall in p21 levels and subsequent increase in Ser118 phosphorylation following treatment with 17β-estradiol or tamoxifen while FKBPL overexpressing cells exhibit the reverse effects. Our in vitro data support a model in which high levels of FKBPL would stabilise p21, decrease ER phosphorylation and abrogate tamoxifen-induced agonist potency, thereby increasing drug sensitivity, and suggest that FKBPL may have prognostic value that might impact upon tumour proliferative capacity and improve patient outcome. In addition, analysis of two publically available breast cancer microarray patient cohorts demonstrated that high FKBPL expression was correlated with increased overall and distant metastasis-free survival.

CCN3: A NOVel Growth Factor in Leukaemia

The Leukaemias are a group of cancers affecting the white blood cell system. Chronic myeloid leukaemia (CML) is characterised by a reciprocal translocation between chromosomes 9 and 22 resulting in the production of the BCR-ABL protein tyrosine kinase. Expression of BCR-ABL in stem cells of the myeloid blood cell population has been shown to be directly responsible for malignant transformation. We identified down-regulation of the negative growth regulator, CCN3, as a consequence of BCR-ABL expression. Investigations have shown CCN3 functions to inhibit cell growth and survival whilst promoting apoptosis; our findings suggest that BCR-ABL utilises CCN3 down-regulation to escape growth control. Further understanding of CCN3 mechanisms are required to develop new therapeutic strategies targeting this pathway.