Autocrine Activation of the MET Receptor Tyrosine Kinase in Acute Myeloid Leukemia

Although the treatment of acute myeloid leukemia (AML) has improved significantly, more than half of all patients develop disease that is refractory to intensive chemotherapy. Functional genomics approaches offer a means to discover specific molecules mediating aberrant growth and survival of cancer cells. Thus, using a loss-of-function RNA interference genomic screen, we identified aberrant expression of the hepatocyte growth factor (HGF) as a critical factor in AML pathogenesis. We found HGF expression leading to autocrine activation of its receptor tyrosine kinase, MET, in nearly half of the AML cell lines and clinical samples studied. Genetic depletion of HGF or MET potently inhibited the growth and survival of HGF-expressing AML cells. However, leukemic cells treated with the specific MET kinase inhibitor crizotinib developed resistance due to compensatory upregulation of HGF expression, leading to restoration of MET signaling. In cases of AML where MET is coactivated with other tyrosine kinases, such as fibroblast growth factor receptor 1 (FGFR1), concomitant inhibition of FGFR1 and MET blocked compensatory HGF upregulation, resulting in sustained logarithmic cell kill both in vitro and in xenograft models in vivo. Our results demonstrate widespread dependence of AML cells on autocrine activation of MET, as well as the importance of compensatory upregulation of HGF expression in maintaining leukemogenic signaling by this receptor. We anticipate that these findings will lead to the design of additional strategies to block adaptive cellular responses that drive compensatory ligand expression as an essential component of the targeted inhibition of oncogenic receptors in human cancers

Donor variation and loss of multipotency during in vitro expansion of human mesenchymal stem cells for bone tissue engineering

The use of multipotent human mesenchymal stem cells (hMSCs) for tissue engineering has been a subject of extensive research. The donor variation in growth, differentiation and in vivo bone forming ability of hMSCs is a bottleneck for standardization of therapeutic protocols. In this study, we isolated and characterized hMSCs from 19 independent donors, aged between 27 and 85 years, and investigated the extent of heterogeneity of the cells and the extent to which hMSCs can be expanded without loosing multipotency. Dexamethasone-induced ALP expression varied between 1.2- and 3.7-fold, but no correlation was found with age, gender, or source of isolation. The cells from donors with a higher percentage of ALP-positive cells in control and dexamethasone-induced groups showed more calcium deposition than cells with lower percentage of ALP positive cells. Despite the variability in osteogenic gene expression among the donors tested, ALP, Collagen type 1, osteocalcin, and S100A4 showed similar trends during the course of osteogenic differentiation. In vitro expansion studies showed that hMSCs can be effectively expanded up to four passages (approximately 10-12 population doublings from a P0 culture) while retaining their multipotency. Our in vivo studies suggest a correlation between in vitro ALP expression and in vivo bone formation. In conclusion, irrespective of age, gender, and source of isolation, cells from all donors showed osteogenic potential. The variability in ALP expression appears to be a result of sampling method and cellular heterogeneity among the donor population

The Effect of a Cyclooxygenase 2 Inhibitor on Early Degenerated Human Nucleus Pulposus Explants

International audienc

Rapportcijfers Voor Voetballers: Zin Of Onzin?

Veel Nederlanders nemen zondagavond en maandagochtend de voetbaluitslagen door. Met collega's worden de verrichtingen van de favoriete teams doorgenomen: de helden van het weekend bejubeld en de scheidsrechters (indien nodig) beschimpt. Het aardige van voetballen is dat iedereen er een mening over heeft, niet noodzakelijkerwijze gebaseerd op kennis van zaken. De voetballers worden overigens niet alleen beoordeeld door het publiek in de stadions en tijdens de gesprekken op maandag, ze krijgen ook rapportcijfers in een landelijk ochtendblad en een weekblad. In deze notitie analyseren we die rapportcijfers; met name gaan we na in hoeverre de beoordelingen tussen beiden bladen overeenstemmen. Die rapportcijfers dienen overigens niet alleen ter vermaak van de lezers: op basis van de rapportcijfers wordt een prestigieuze prijs als 'De voetballer van het jaar' uitgereikt en het gemiddelde rapportcijfer van 5.8 was voor Volendam een van de redenen om Danny den Ouden te ontslaan.

Inhibition of Histone Acetylation as a Tool in Bone Tissue Engineering

Our approach to bone tissue engineering is the in vitro expansion and osteogenic differentiation of bone marrow–derived human mesenchymal stem cells (hMSCs) and their subsequent implantation on porous ceramic materials. Current osteogenic differentiation protocols use dexamethasone to initiate the osteogenic process, thus ignoring the multiple signaling pathways that control osteogenesis in vivo. Supporting osteogenesis at multiple stages might further enhance the bone-forming capacity of hMSCs. As reported previously, inhibition of so-called histone deacetylases (HDACs) stimulates osteoblast maturation, and in this report, we investigated whether trichostatin A (TSA), a widely used HDAC inhibitor, can be implemented in bone tissue engineering. We confirmed that TSA treatment of hMSCs results in increased expression of alkaline phosphatase (ALP) with concomitant increase in mineralization. Flow cytometry demonstrated that TSA increases the percentage of ALP-positive hMSCs as well as their average ALP expression level, but the robustness of the response differs between donors. Unfortunately, TSA has a profound negative effect on cell proliferation, so we investigated whether hMSCs respond to TSA after reaching confluence. Confluent hMSCs on tissue culture plastic displayed enhanced ALP expression. Therefore, we seeded TSA-treated hMSCs onto ceramic particles and analyzed ectopic bone formation upon implantation in immune-deficient mice. Unfortunately, TSA-treated hMSCs did not display better bone formation in vivo than control cells. Finally, we observed that TSA treatment strongly enhanced bone formation of ex vivo cultured mouse calvaria, which warrants further exploration of TSA in bone tissue engineering

Applicability of a newly developed bioassay for determining bioactivity of anti-inflammatory compounds in release studies--celecoxib and triamcinolone acetonide released from novel PLGA-based microspheres

PURPOSE: To develop a bio-assay for measuring long-term bioactivity of released anti-inflammatory compounds and to test the bioactivity of celecoxib (CXB) and triamcinolone acetonide (TA) released from a new PLGA-based microsphere platform. METHODS: Human osteoarthritic chondrocytes were plated according to standardized procedures after batch-wise harvest and cultured for 3 days to prevent cell confluency and changes in cell behaviour. Prostaglandin E2 (PGE2) production stimulated by TNFα was used as a parameter of inflammation. A novel microsphere platform based on PTE-functionalised PLGA was used to incorporate CXB and TA. Loaded microspheres were added to transwells overlying the cells, with transfer of the wells to new cell cultures every 3 days. Inhibition of PGE2 production was determined over a period of 21 days. RESULTS: PLGA(75:25)-PTE microspheres were prepared and loaded with CXB and TA at 86 and 97% loading efficiency, respectively. In the bioactivity assay, PGE2 levels induced by TNFα were reduced to an average of 30% using microspheres loaded with 0.1 nmol CXB per transwell; with microspheres loaded with 0.1 nmol TA, PGE2 production was initially reduced to 3% and gradually recovered to 30% reduction. At 1 nmol loading, PGE2 was inhibited to 0-7% for CXB-loaded microspheres, and 0-28% for TA-loaded microspheres. CONCLUSIONS: We present a novel sustained release bioactivity assay which provides an essential link between in vitro buffer-based release kinetics and in vivo application. Novel PLGA-based microspheres loaded with TA and CXB showed efficient anti-inflammatory effects over time

Predicting the therapeutic efficacy of MSC in bone tissue engineering using the molecular marker CADM1

Mesenchymal stromal cells (hMSCs) are advancing into the clinic but the therapeutic efficacy of hMSCs faces the problem of donor variability. In bone tissue engineering, no reliable markers have been identified which are able to predict the bone-forming capacity of hMSCs prior to implantation. To this end, we isolated hMSCs from 62 donors and characterized systematically their in vitro lineage differentiation capacity, gene expression signature and in vivo capacity for ectopic bone formation. Our data confirms the large variability of in vitro differentiation capacity which did not correlate with in vivo ectopic bone formation. Using DNA microarray analysis of early passage hMSCs we identified a diagnostic bone-forming classifier. In fact, a single gene, CADM1, strongly correlated with the bone-forming capacity of hMSCs and could be used as a reliable in vitro diagnostic marker. Furthermore, data mining of genes expressed correlating with in vivo bone formation represented involvement in neurogenic processes and Wnt signaling. We will apply our data set to predict therapeutic efficacy of hMSCs and to gain novel insight in the process of bone regeneration. Our bio-informatics driven approach may be used in other fields of cell therapy to establish diagnostic markers for clinical efficacy

Predicting the therapeutic efficacy of MSC in bone tissue engineering using the molecular marker CADM1

Mesenchymal stromal cells (hMSCs) are advancing into the clinic but the therapeutic efficacy of hMSCs faces the problem of donor variability. In bone tissue engineering, no reliable markers have been identified which are able to predict the bone-forming capacity of hMSCs prior to implantation. To this end, we isolated hMSCs from 62 donors and characterized systematically their in vitro lineage differentiation capacity, gene expression signature and in vivo capacity for ectopic bone formation. Our data confirms the large variability of in vitro differentiation capacity which did not correlate with in vivo ectopic bone formation. Using DNA microarray analysis of early passage hMSCs we identified a diagnostic bone-forming classifier. In fact, a single gene, CADM1, strongly correlated with the bone-forming capacity of hMSCs and could be used as a reliable in vitro diagnostic marker. Furthermore, data mining of genes expressed correlating with in vivo bone formation represented involvement in neurogenic processes and Wnt signaling. We will apply our data set to predict therapeutic efficacy of hMSCs and to gain novel insight in the process of bone regeneration. Our bio-informatics driven approach may be used in other fields of cell therapy to establish diagnostic markers for clinical efficacy

Cell type and transfection reagent-dependent effects on viability, cell content, cell cycle and inflammation of RNAi in human primary mesenchymal cells

The application of RNA interference (RNAi) has great therapeutic potential for degenerative diseases of cartilaginous tissues by means of fine tuning the phenotype of cells used for regeneration. However, possible non-specific effects of transfection per se might be relevant for future clinical application. In the current study, we selected two synthetic transfection reagents, a cationic lipid-based commercial reagent Lipofectamine RNAiMAX and polyethylenimine (PEI), and two naturally-derived transfection reagents, namely the polysaccharides chitosan (98% deacetylation) and hyaluronic acid (20% amidation), for siRNA delivery into primary mesenchymal cells including nucleus pulposus cells, articular chondrocytes and mesenchymal stem cells (MSCs). Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used as an endogenous model gene to evaluate the extent of silencing by 20 nM or 200 nM siRNA at day 3 and day 6 post-transfection. In addition to silencing efficiency, non-specific effects such as cytotoxicity, change in DNA content and differentiation potential of cells were evaluated. Among the four transfection reagents, the commercial liposome-based agent was the most efficient reagent for siRNA delivery at 20 nM siRNA, followed by chitosan. Transfection using cationic liposomes, chitosan and PEI showed some decrease in viability and DNA content to varying degrees that was dependent on the siRNA dose and cell type evaluated, but independent of GAPDH knockdown. Some effects on DNA content were not accompanied by concomitant changes in viability. However, changes in expression of marker genes for cell cycle inhibition or progression, such as p21 and PCNA, could not explain the changes in DNA content. Interestingly, aspecific upregulation of GAPDH activity was found, which was limited to cartilaginous cells. In conclusion, non-specific effects should not be overlooked in the application of RNAi for mesenchymal cell transfection and may need to be overcome for its effective therapeutic application