Tiny Meeuwsen-de Boer

Pharmacokinetics of vincristine monotherapy in childhood acute lymphoblastic leukemia.

We studied vincristine pharmacokinetics in 70 children newly diagnosed with acute lymphoblastic leukemia, after a single dose of vincristine as monotherapy. Vincristine plasma concentrations were measured by HPLC analysis. A two-compartment, first-order pharmacokinetic model was fitted to the data by maximum a posteriori parameter estimation. In this group of children pharmacokinetic factors were highly variable: median (25th and 75th percentiles) total body clearance, 228 (128–360) mL·min−1·m−2; elimination half-life, 1001 (737–1325) min; apparent volume of distribution at steady state 262 (158–469) L/m2. Vincristine clearance was substantially slower than has been reported previously for children receiving vincristine in combination with steroids as part of combination chemotherapy (median clearance, 228 mL·min−1·m−2versus mean clearance, 381 and 482 mL· min−1· m−2, respectively). Steroids are known as inducers of vincristine-metabolizing cytochrome P450 3A4 enzymes. The absence of steroids during our study appears to be the most likely explanation for this difference. Furthermore, we found that vincristine clearance was faster in patients with hyperdiploid (>50 chromosomes) than in patients with diploid or hyperdiploid (46–50 chromosomes) leukemic blasts.

Mesenchymal Stem Cells Contribute to Tumor Cell Proliferation by Direct Cell-Cell Contact Interactions

ABSTRACT Bone marrow (BM)-derived mesenchymal stem cells (MSCs) have been implicated in tumor progression, making MSCs important targets for anti-cancer strategies. In this study, we show that MSCs promote tumor growth in vivo in a lymphoma xenograft model. We show that MSCs provide direct cell–cell contact interactions and, to a lesser extend, soluble factors that promote tumor cell proliferation and survival in vitro. PTK787/ZK 222584 reduces tumor growth-promoting effects of MSCs both in vitro and in vivo. Our results address the importance of targeting the MSCs for future anti-cancer strategies.

High acute myeloid leukemia derived VEGFA levels are associated with a specific vascular morphology in the leukemic bone marrow.

BackgroundAcute Myeloid Leukemia (AML) bone marrow biopsies at diagnosis display enhanced angiogenesis and increased VEGFA expression. In a xenograft mouse model it was described that availability of free VEGFA versus bound VEGFA is related to different vascular morphology. In this study we investigate the relationship between vascular morphology within AML bone marrow biopsies and AML derived VEGFA levels.MethodsVessel count and surface area (Chalkley count) were calculated in AML bone marrow biopsies at diagnosis (n = 32), at remission (n = 8) and Normal Bone Marrow (n = 32) using immunohistochemical staining for FVIII, CD31, CTIV, SMA and VEGFA. VEGFA protein levels were measured.ResultsHigh vessel count was associated with an immature vessel status. Combining vessel count and Chalkley count different vessel morphology patterns were quantified within AML bone marrow biopsies. Three different subgroups could be distinguished. The subgroup (37.5% of the samples) exhibiting a high vessel count and vessels with predominantly large lumen (normal Chalkley count) was associated with high secreted VEGFA protein levels.ConclusionDifferent vasculature patterns are seen in AML bone marrow biopsies, defined by combining number and size of vessel. These quantified morphology patterns, combined with VEGFA levels, might be of value in the success of VEGF/VEGFR-signaling interference approaches.

VEGF-A promotes lymphoma tumour growth by activation of STAT proteins and inhibition of p27KIP1 via paracrine mechanisms

Increased levels of circulating VEGF-A have been demonstrated in patients with non-Hodgkin lymphoma (NHL) and are associated with progressive disease and poor clinical outcome. We investigated the role of VEGF-A in lymphoma tumour growth on a molecular level in order to identify the mechanism of VEGF-A-promoted tumour growth and to identify the potential targets for therapy. We used a model in which Daudi (human Burkitt lymphoma) tumour cells were transduced with VEGF-A165 or an empty vector (negative control) and subcutaneously injected in NOD/SCID mice. The weight of tumours overexpressing VEGF-A was increased 4-fold compared to that of control tumours (p<0.0001), whereas no in vitro growth advantage was demonstrated upon VEGF-A overexpression. VEGF-A-tumours were associated with increased microvessel densities (p=0.004) and increased tumour cell proliferation (Ki67; p<0.001) compared to control tumours. VEGF-A-tumours were characterised by upregulation of phosphorylated STAT-4 and STAT-6 and downregulation of phospho-p27(KIP1), a crucial cell cycle inhibitor (p<0.05). This was accompanied by increased levels of phosphorylated receptor tyrosine kinases, including EGFR (ErbB-2 and ErbB-4, p<0.05), an upstream regulator of STAT proteins. We demonstrated that various mouse-derived cytokines produced by mouse-derived tumour stromal cells are upregulated in VEGF-A-tumours compared to control tumours (p<0.05). These results indicate an important role for the tumour microenvironment in paracrine promotion of lymphoma tumour growth in response to tumour-derived VEGF-A. In conclusion, lymphoma-derived VEGF-A promoted lymphoma tumour growth in a paracrine loop by activation of tumour stromal cells. Our study reveals VEGF-A and STAT proteins as potential additional targets in the treatment of lymphoma.

PTK787/ZK 222584 inhibits tumor growth promoting mesenchymal stem cells: kinase activity profiling as powerful tool in functional studies.

Bone marrow (BM)-derived mesenchymal stem cells (MSCs) have been shown to favour tumor growth, suggesting the relevance of pharmaceutical inhibition of MSCs for the treatment of malignancies. We tested the effect of PTK787/ZK 222584 (PTK) on the outgrowth of MSCs from human bone marrow-derived mononuclear cells (MNCs) and the migration and tube formation capacity of MSCs in vitro. PTK dose- dependently inhibited the outgrowth of BM-MSCs from BM-MNCs (LC50 1.12 μM PTK), while hematopoietic colony formation (HCF) was only slightly hampered (13 ± 19% at 1 μM PTK, and stable at ~50% at higher concentrations of PTK). Addition of 10 μM PTK inhibited proliferation of MSCs by 74 ± 6.6% compared to control (p

Addition of PTK787/ZK 222584 can lower the dosage of amsacrine to achieve equal amounts of acute myeloid leukemia cell death

Acute myeloid leukemia (AML) is a disease with a poor prognosis. It has been demonstrated that AML cells express the vascular endothelial growth factors, VEGFA and VEGFC, as well as kinase insert domain-containing receptor (VEGFR2), the main receptor for downstream effects, resulting in an autocrine pathway for cell survival. This study investigates the role of the VEGFR inhibitor PTK787/ZK 222584 in leukemic cell death, and the possibility of an additional effect on cell death by a chemotherapeutic drug, amsacrine. In three AML cell lines and 33 pediatric AML patient samples, we performed total cell-kill assays to determine the percentages of cell death achieved by PTK787/ZK 222584 and/or amsacrine. Both drugs induced AML cell death. Using a response surface analysis, we could show that, in cell lines as well as in primary AML blasts, an equal magnitude of leukemic cell death could be obtained when lower doses of the more toxic amsacrine were combined with low dosages of the less toxic VEGFR inhibitor. This study shows that PTK787/ZK 222584 might have more clinical potential in AML when combined with a chemotherapeutic drug such as amsacrine. In future, it will be interesting to study whether the complications and the long-term effects of chemotherapy can be reduced by lowering the dosages of amsacrine, and by replacing it with other drugs with lower toxicity profiles, such as PTK787/ZK 222584.

Kinase activity profiling reveals active signal transduction pathways in pediatric acute lymphoblastic leukemia: A new approach for target discovery

Still about 20% of patients with acute lymphoblastic leukemia (ALL) struggle with relapse, despite intensive chemotherapy. We and others have shown that kinase activity profiling is able to give more insights in active signal transduction pathways and point out interesting signaling hubs as well as new potential druggable targets. With this technique the gap between newly designed drugs and ALL may be bridged. The aim of this study was to perform kinome profiling on 20 pediatric ALL samples (14 BCP‐ALL and six T‐ALL) to identify signaling proteins relevant to ALL. We defined 250 peptides commonly activated in both BCP‐ALL and T‐ALL representing major signal transduction pathways including MAPK, PI3K/Akt, and regulators of the cell cycle/p53 pathway. For 27 peptides, differentially phosphorylation between BCP‐ALL and T‐ALL was observed. Among these, ten peptides were more highly phosphorylated in BCP‐ALL while 17 peptides showed increased phosphorylation in T‐ALL. Furthermore we selected one lead of the list of commonly activated peptides (HGFR_Y1235) in order to test its efficacy as a potential target and provide proof of principle for this approach. In conclusion kinome profiling is an elegant approach to study active signaling and identify interesting potential druggable targets.

Growth-Factor-Driven Rescue to Receptor Tyrosine Kinase (RTK) Inhibitors through Akt and Erk Phosphorylation in Pediatric Low Grade Astrocytoma and Ependymoma

Up to now, several clinical studies have been started investigating the relevance of receptor tyrosine kinase (RTK) inhibitors upon progression free survival in various pediatric brain tumors. However, single targeted kinase inhibition failed, possibly due to tumor resistance mechanisms. The present study will extend our previous observations that vascular endothelial growth factor receptor (VEGFR)-2, platelet derived growth factor receptor (PDGFR)β, Src, the epidermal growth factor receptor (ErbB) family, and hepatocyte growth factor receptor (HGFR/cMet) are potentially drugable targets in pediatric low grade astrocytoma and ependymoma with investigations concerning growth-factor-driven rescue. This was investigated in pediatric low grade astrocytoma and ependymoma cell lines treated with receptor tyrosine kinase (RTK) inhibitors e.g. sorafenib, dasatinib, canertinib and crizotinib. Flow cytometry analyses showed high percentage of cells expressing VEGFR-1, fibroblast growth factor receptor (FGFR)-1, ErbB1/EGFR, HGFR and recepteur d’origine nantais (RON) (respectively 52-77%, 34-51%, 63-90%, 83-98%, 65-95%). Their respective inhibitors induced decrease of cell viability, measured with WST-1 cell viability assays. At least this was partially due to increased apoptotic levels measured by Annexin V/Propidium Iodide apoptosis assays. EGF, HGF and FGF, which are normally expressed in brain (tumor) tissue, showed to be effective rescue inducing growth factors resulting in increased cell survival especially during treatment with dasatinib (complete rescue) or sorafenib (partial rescue). Growth-factor-driven rescue was less prominent when canertinib or crizotinib were used. Rescue was underscored by significantly activating downstream Akt and/or Erk phosphorylation and increased tumor cell migration. Combination treatment showed to be able to overcome the growth-factor-driven rescue. In conclusion, our study highlights the extensive importance of environmentally present growth factors in developing tumor escape towards RTK inhibitors in pediatric low grade astrocytoma and ependymoma. It is of great interest to anticipate upon these results for the design of new therapeutic trials with RTK inhibitors in these pediatric brain tumors.

Impaired Long-Term Expansion and Self-Renewal Potential of Pediatric Acute Myeloid Leukemia Initiating Cells by PTK787/ZK 222584

Although most children with acute myeloid leukemia (AML) achieve complete remission, the relapse rate is 30% to 40%. Because it is thought that leukemia-initiating cells (LIC) are responsible for AML relapses, targeting these cells might improve outcome. Treatment of pediatric AML blasts with the receptor tyrosine kinase (RTK) inhibitor PTK787/ZK 222584 (PTK/ZK) induces cell death in vitro. However, the role of PTK/ZK inhibition on outgrowth of (pediatric) LICs is unknown. In this study, we cultured CD34+ cells from pediatric patients with AML on MS5 stromal cells in long-term cocultures. In analogy to adult AML, long-term expansion of leukemic cells up to 10 weeks could be generated in 9 of 13 pediatric AMLs. Addition of PTK/ZK to long-term cocultures significantly inhibited leukemic expansion in all samples, ranging from 4% to 80% growth inhibition at week 5 compared with untreated samples. In 75% of the samples, the inhibitory effect was more pronounced at week 10. Proteome profiler array analysis of downstream kinases revealed that PTK/ZK reduced activation of PI3K/Akt kinase signaling. Although main targets of PTK/ZK are VEGF receptors (VEGFR), no effect was seen on outgrowth of LICs when cultured with bevacizumab (monoclonal VEGFA-antibody), specific antibodies against VEGFR2 or VEGFR3, or exposed to stroma-derived VEGFA. These data suggest that the effect of PTK/ZK on LICs is not only dependent on inhibition of VEGFA/VEGFR signaling. Taken together, our data elucidated antileukemic properties of PTK/ZK in long-term expansion cultures, and suggest that targeting multiple RTKs by PTK/ZK might be a potential effective approach in eradicating (pediatric) LICs. Mol Cancer Res; 11(4); 339–48. ©2013 AACR.

DNA copy number alterations mark disease progression in paediatric chronic myeloid leukaemia

Early recognition of children with chronic phase chronic myeloid leukaemia (CML‐CP) at risk for developing a lymphoid blast crisis (LyBC) is desirable, because therapy options in CML‐LyBC are limited. We used Multiplex Ligation‐dependent Probe Amplification to determine whether B‐cell lymphoid leukaemia‐specific copy number alterations (CNAs) (e.g. IKZF1, PAX5, CDKN2A deletions) could be detected in CML‐CP and may be used to predict disease progression to LyBC. CNAs were detected in all patients with CML‐LyBC, but in none of the 77 patients with CML‐CP. Based on this study we conclude that CNAs remain a hallmark of disease progression.