Giannoula Klement

Possible mechanisms of acquired resistance to anti-angiogenic drugs: implications for the use of combination therapy approaches.

The ultimate target of anti-angiogenic drugs is the genetically stable, activated endothelial cell of a newly forming tumor blood vessel, rather than the genetically unstable tumor cell population per se. This led to the notion that acquired resistance to such drugs may not develop as readily, if at all. While there is some evidence that this lack of resistance development may be the case for some direct-acting angiogenesis inhibitors, it is becoming apparent that resistance can develop over time to many types of angiogenesis inhibitors including, possibly, some direct inhibitors, especially when used as monotherapies. Possible mechanisms for such acquired or induced resistance include: (i) redundancy of pro-angiogenic growth factors when the drug used targets a single such growth factor or its cognate endothelial cell-associated receptor tyrosine kinase; (ii) the anti-apoptotic/pro-survival function of growth factors such as VEGF, which, in high local concentrations, can antagonize the pro-apoptotic effects of various angiogenesis inhibitors; (iii) epigenetic, transient upregulation, or induction, of various anti-apoptotic effector molecules in host-endothelial cells; and (iv) heterogeneous vascular dependence of tumor cell populations. It is suggested that long-term disease control with anti-angiogenic drugs can be best achieved by judicious combination therapy. In this regard, the great molecular diversity of anti-angiogenic drug targets, in contrast to chemotherapy, makes this a particularly attractive therapeutic option, especially when approved, commercially available drugs considered to have anti-angiogenic effects are used in such combination treatment strategies.

Platelets actively sequester angiogenesis regulators

Clinical trials with antiangiogenic agents have not been able to validate plasma or serum levels of angiogenesis regulators as reliable markers of cancer presence or therapeutic response. We recently reported that platelets contain numerous proteins that regulate angiogenesis. We now show that accumulation of angiogenesis regulators in platelets of animals bearing malignant tumors exceeds significantly their concentration in plasma or serum, as well as their levels in platelets from non-tumor-bearing animals. This process is selective, as platelets do not take up a proportional amount of other plasma proteins (eg, albumin), even though these may be present at higher concentrations. We also find that VEGF-enriched Matrigel pellets implanted subcutaneously into mice or the minute quantities of VEGF secreted by microscopic subcutaneous tumors (0.5-1 mm(3)) result in an elevation of VEGF levels in platelets, without any changes in its plasma levels. The profile of other angiogenesis regulatory proteins (eg, platelet-derived growth factor, basic fibroblast growth factor) sequestered by platelets also reflects the presence of tumors in vivo before they can be macroscopically evident. The ability of platelets to selectively take up angiogenesis regulators in cancer-bearing hosts may have implications for the diagnosis and management of many angiogenesis-related diseases and provide a guide for antiangiogenic therapies.

A feasibility trial of antiangiogenic (metronomic) chemotherapy in pediatric patients with recurrent or progressive cancer.

Standard chemotherapeutic drugs, when modified by the frequency and dose of administration, can target angiogenesis. This approach is referred to as antiangiogenic chemotherapy, low-dose chemotherapy, or metronomic chemotherapy. This study evaluated the feasibility of 6 months of metronomic chemotherapy, its toxicity and tolerability, surrogate markers of activity, and preliminary evidence of activity in children with recurrent or progressive cancer. Twenty consecutive children were enrolled and received continuous oral thalidomide and celecoxib with alternating oral etoposide and cyclophosphamide every 21 days for a planned duration of 6 months using antiangiogenic doses of all four drugs. Surrogate markers including bFGF, VEGF, endostatin, and thrombospondin were also evaluated. Therapy was well tolerated in this heavily pretreated population. Toxicities (predominantly reversible bone marrow suppression) responded to dose modifications. Sixty percent of the patients received less than the prescribed 6 months of therapy due to toxicity (one case of deep vein thrombosis), personal choice (1 patient), or disease progression (10 patients). Forty percent of the patients completed the 6 months of therapy, resulting in prolonged or persistent disease-free status. One quarter of all patients continue to be progression free more than 123 weeks from starting therapy. Sixteen percent of patients showed a radiographic partial response. Only elevated thrombospondin-1 levels appeared to correlate with prolonged response. This oral antiangiogenic chemotherapy regimen was well tolerated in this heavily pretreated pediatric population, which showed prolonged or persistent disease-free status, supporting the continued study of antiangiogenic/metronomic chemotherapy in human clinical trials.

MicroCT scanner performance and considerations for vascular specimen imaging

Obtaining three-dimensional geometrical data of vascular systems is of major importance to a number of research areas in medicine and biology. Examples are the characterization of tumor vasculature, modeling blood flow, or genetic effects on vascular development. The performance of the General Electric Medical Systems MS8 microCT scanner is examined in the context of these applications. The system is designed to acquire high-resolution images of specimens up to 5 cm in diameter. A maximum resolution of 38 lp/mm at the 10% modulation transfer function level or 22 microm full width at half maximum of the plane spread function can be achieved with 8.5 microm voxels and a 17 mm field of view. Three different contrast agents are discussed and applied for imaging of small animal vasculature: corrosion casting material Batsons No. 17 with an added lead pigment, silicon rubber MICROFIL MV122, and a suspension of barium sulfate (Baritop) in gelatin. Contrast for all of these agents was highly variable in different vessels as well as within the same vessel. Imaging of PMMA tubing filled with MICROFIL shows that even vessels below 20 microm in diameter are detectable and that diameter estimation of vessels based on thresholding is possible with a precision of 2-3 pixels.

Normal ranges of angiogenesis regulatory proteins in human platelets

Platelets sequester angiogenesis regulatory proteins early in tumor growth, which suggests a new avenue for monitoring disease. To date, there are no clinically relevant reference ranges for markers of early angiogenesis. We introduce a new ELISA‐based method for accurate and reproducible measurement of vascular endothelial growth factor (VEGF), platelet‐derived growth factor (PDGF), platelet factor 4 (PF4), thrombospondin‐1 (TSP‐1), fibroblast growth factor, basic (bFGF), and endostatin in platelets. To facilitate clinical applicability, the platelet levels in isolated samples were determined utilizing a new actin ELISA method. Platelets from healthy donors at single and repetitive time points were used for the assessment of normal ranges of these proteins. The physiological levels in platelets were: VEGF (0.74 ± 0.37 pg/106 platelets); PDGF (23 ± 6 pg/106); PF4 (12 ± 5 ng/106); TSP‐1 (31 ± 12 ng/106); bFGF (0.44 ± 0.15 pg/106); and endostatin (5.6 ± 3.0 pg/106). There was an excellent correlation (R2 = 0.7) between the platelet levels calculated with the actin ELISA and complete blood count. The levels of the platelets were higher than those in platelet‐poor plasma by factors of: VEGF (215‐fold); PDGF (914‐fold); PF‐4 (516‐fold); TSP‐1 (813‐fold); and bFGF (17‐fold). The endostatin levels were nearly equivalent. The biovariability of the platelet proteins in eight healthy subjects over a 5‐week period was found to be minimal. We describe accurate and direct measurements of the concentrations of VEGF, bFGF, PDGF, TSP‐1, endostatin, and PF4 in platelets of healthy human subjects. In contrast to the highly variable levels in plasma and serum, the platelet‐derived measurements were accurate and reproducible with minimal biovariability. Am. J. Hematol., 2010.

Cell Therapy, a New Standard in Management of Chronic Critical Limb Ischemia and Foot Ulcer

Fifty percent of diabetics (7% of general population) suffer from peripheral arterial occlusive disease, which may lead to amputation due to critical limb ischemia (CLI). The aim of our study was to prevent major limb amputation (MLA) in this group of patients using a local application of autologous bone marrow stem cells (ABMSC) concentrate. A total of 96 patients with CLI and foot ulcer (FU) were randomized into groups I and II. Patients in group I (n = 42, 36 males, 6 females, 66.2 ± 10.6 years) underwent local treatment with ABMSC while those in group II (n = 54, control, 42 males, 12 females, 64.1 ± 8.6 years) received standard medical care. The frequency of major limb amputation in groups I and II was 21% and 44% within the 120 days of follow up, respectively (p < 0.05). Only in salvaged limbs of group I both toe pressure and toe brachial index increased (from 22.66 ± 5.32 to 25.63 ± 4.75 mmHg and from 0.14 ± 0.03 to 0.17 ± 0.03, respectively, mean ± SEM). The CD34+ cell counts in bone marrow concentrate (BMC) decreased (correlation, p = 0.024) with age, even though there was no correlation between age and healing. An unexpected finding was made of relative, bone marrow lymphopenia in the initial bone marrow concentrates in patients who failed ABMSC therapy (21% of MLA). This difference was statistically significant (p < 0.040). We conclude ABMSC therapy results in 79% limb salvage in patients suffering from CLI and FU. In the remaining 21% lymphopenia and thrombocytopenia were identified as potential causative factors, suggesting that at least a partial correction with platelet supplementation may be beneficial.

A Cyclosporine-Sensitive Psoriasis-Like Disease Produced in Tie2 Transgenic Mice

Psoriasis is a common, persistent skin disorder characterized by recurrent erythematous lesions thought to arise as a result of inflammatory cell infiltration and activation of keratinocyte proliferation. Unscheduled angiogenic growth has also been proposed to mediate the pathogenesis of psoriasis although the cellular and molecular basis for this response remains unclear. Recently, a role for the angiopoietin signaling system in psoriasis has been suggested by studies that demonstrate an up-regulation of the tyrosine kinase receptor Tie2 (also known as Tek) as well as angiopoietin-1 and angiopoietin-2 in human psoriatic lesions. To examine temporal expression of Tie2, we have developed a binary transgenic approach whereby expression of Tie2 can be conditionally regulated by the presence of tetracycline analogs in double-transgenic mice. A psoriasis-like phenotype developed in double-transgenic animals within 5 days of birth and persisted throughout adulthood. The skin of affected mice exhibited many cardinal features of human psoriasis including epidermal hyperplasia, inflammatory cell accumulation, and altered dermal angiogenesis. These skin abnormalities resolved completely with tetracycline-mediated suppression of transgene expression, thereby illustrating a complete dependence on Tie2 signaling for disease maintenance and progression. Furthermore, the skin lesions in double-transgenic mice markedly improved after administration of the immunosuppressive anti-psoriatic agent cyclosporine, thus demonstrating the clinical significance of this new model.

Serum proteome profiling detects myelodysplastic syndromes and identifies CXC chemokine ligands 4 and 7 as markers for advanced disease

Myelodysplastic syndromes (MDS) are among the most frequent hematologic malignancies. Patients have a short survival and often progress to acute myeloid leukemia. The diagnosis of MDS can be difficult; there is a paucity of molecular markers, and the pathophysiology is largely unknown. Therefore, we conducted a multicenter study investigating whether serum proteome profiling may serve as a noninvasive platform to discover novel molecular markers for MDS. We generated serum proteome profiles from 218 individuals by MS and identified a profile that distinguishes MDS from non-MDS cytopenias in a learning sample set. This profile was validated by testing its ability to predict MDS in a first independent validation set and a second, prospectively collected, independent validation set run 5 months apart. Accuracy was 80.5% in the first and 79.0% in the second validation set. Peptide mass fingerprinting and quadrupole TOF MS identified two differential proteins: CXC chemokine ligands 4 (CXCL4) and 7 (CXCL7), both of which had significantly decreased serum levels in MDS, as confirmed with independent antibody assays. Western blot analyses of platelet lysates for these two platelet-derived molecules revealed a lack of CXCL4 and CXCL7 in MDS. Subtype analyses revealed that these two proteins have decreased serum levels in advanced MDS, suggesting the possibility of a concerted disturbance of transcription or translation of these chemokines in advanced MDS.

Impact of Oncogenes and Tumor Suppressor Genes on Deregulation of Hemostasis and Angiogenesis in Cancer

We postulate that oncogenes and tumor suppressor genes may influence tumor angiogenesis not only directly (e.g. by upregulating vascular endothelial growth factor) but also through their impact on expression (and/or function) of tissue factor and other elements of the hemostatic system.

Cutaneovisceral Angiomatosis With Thrombocytopenia

We describe 10 children with multiple vascular lesions of the skin and gastrointestinal tract associated with sustained, minor thrombocytopenia. In some children, there was involvement of the lung (n = 5), bone (n = 2), liver (n = 1), spleen (n = 1), and muscle (n = 1). The cutaneous lesions were congenital, multifocal, discrete, red-brown and variably blue macules and papules; in 3 children, a large dominant plaque was also present. All children developed hematemesis and/or melena and endoscopic evaluation revealed several to numerous small mucosal lesions that involved all levels of the gastrointestinal tract. Three of 5 children with pulmonary nodules had cough and 1 also had hemoptysis. Biopsies of cutaneous, gastrointestinal, and pulmonary lesions showed thin-walled, blood-filled vascular channels and variable endothelial hyperplasia. The endothelial nuclei were elongated, round, crescentic, or hobnailed. Cytoplasmic and extracellular periodic acid-Schiff positive deposits were often present in the zones of endothelial hyperplasia. The platelets were small in some children, suggesting a primary defect, possibly accounting for the thrombocytopenia. Gastrointestinal hemorrhage and hemoptysis required antiangiogenic therapy. The constellation of findings defines a congenital proliferative disorder of blood vessels with a distinctive microscopic appearance. We have termed this relatively indolent or slowly progressive disorder cutaneovisceral angiomatosis with thrombocytopenia because this designation incorporates its major clinical and histopathologic features.