Ralf Bieker

Overexpression of vascular endothelial growth factor (VEGF) and its cellular receptor KDR (VEGFR-2) in the bone marrow of patients with acute myeloid leukemia

Vascular endothelial growth factor (VEGF) and its cellular receptor VEGFR-2 have been implicated as the main endothelial pathway required for tumor neovascularization. However, the importance of the VEGF/VEGFR-2 system for angiogenesis in hematologic malignancies such as AML remains to be elucidated. In 32 patients with newly diagnosed untreated AML, we observed by immunohistochemical analysis of bone marrow biopsies significantly higher levels of VEGF and VEGFR-2 expression than in 10 control patients (P <0.001). In contrast, VEGFR-1 staining levels in AML patients were in the same range as in the controls. Expression of VEGF and VEGFR-2 was significantly higher in patients with a high degree of microvessel density compared to those with a low degree (VEGF: P =0.024; VEGFR-2: P =0.040) and correlated well with bone marrow microvessel density (rs=0.566 and 0.609, respectively; P <0.001). Furthermore, in patients who achieved a complete remission following induction chemotherapy VEGFR-2 staining levels decreased into the normal range. In conclusion, our results provide evidence for increased expression of VEGF/VEGFR-2 of leukemic blasts and correlation with angiogenesis in the bone marrow of AML patients. Thus, VEGF/VEGFR-2 might constitute promising targets for antiangiogenic and antileukemic treatment strategies in AML.

Infarction of tumor vessels by NGR-peptide-directed targeting of tissue factor: experimental results and first-in-man experience.

We induced thrombosis of blood vessels in solid tumors in mice by a fusion protein consisting of the extracellular domain of tissue factor (truncated tissue factor, tTF) and the peptide GNGRAHA, targeting aminopeptidase N (CD13) and the integrin alpha(v)beta(3) (CD51/CD61) on tumor vascular endothelium. The designed fusion protein tTF-NGR retained its thrombogenic activity as demonstrated by coagulation assays. In vivo studies in mice bearing established human adenocarcinoma (A549), melanoma (M21), and fibrosarcoma (HT1080) revealed that systemic administration of tTF-NGR induced partial or complete thrombotic occlusion of tumor vessels as shown by histologic analysis. tTF-NGR, but not untargeted tTF, induced significant tumor growth retardation or regression in all 3 types of solid tumors. Thrombosis induction in tumor vessels by tTF-NGR was also shown by contrast enhanced magnetic resonance imaging (MRI). In the human fibrosarcoma xenograft model, MRI revealed a significant reduction of tumor perfusion by administration of tTF-NGR. Clinical first-in-man application of low dosages of this targeted coagulation factor revealed good tolerability and decreased tumor perfusion as measured by MRI. Targeted thrombosis in the tumor vasculature induced by tTF-NGR may be a promising strategy for the treatment of cancer.

Prognostic Relevance of Increased Angiogenesis in Osteosarcoma

Purpose: The purpose of this work was to evaluate the prognostic relevance of microvessel density (MVD) for response to chemotherapy and long-term outcome in osteosarcoma. Experimental Design: Pretherapeutic tumor biopsies of 60 patients with high-grade central osteosarcoma, who were treated according to multimodal neoadjuvant protocols of the German-Austrian-Swiss Cooperative Osteosarcoma Study Group, were evaluated for intratumoral MVD. MVD was correlated with demographic and tumor-related variables, response, and survival. Results: The median intratumoral MVD was 52 microvessels per 0.26-mm2 field area (interquartile range, 31–77 microvessels per 0.26-mm2 field area). At a median follow-up period of 3.5 years, patients with a high (>median) MVD had significantly higher 5- and 10-year overall survival rates (84%) than patients with low (≤median) MVD (49%; P = 0.0029). Furthermore, increased relapse-free survival for patients with high MVD (P = 0.0064) was observed. In a subgroup analysis of 44 patients with primary high-grade central osteosarcoma of the extremities without primary metastases and good surgical remission, high MVD was associated with 5- and 10-year overall survival rates of 91% compared with 58% for low MVD (P = 0.034). Cox regression analysis revealed that MVD was an independent prognostic factor for survival. A good response to chemotherapy (histologic grading scale of Salzer-Kuntschik) correlated significantly with a high MVD (P = 0.006). Conclusions: Increased angiogenesis is a prognostic indicator for higher survival and response rates to chemotherapy in patients with osteosarcoma. Thus, measurement of MVD might be useful in decisions selecting patients for future neoadjuvant treatment.

Bevacizumab reduces VEGF expression in patients with relapsed and refractory acute myeloid leukemia without clinical antileukemic activity

Bevacizumab reduces VEGF expression in patients with relapsed and refractory acute myeloid leukemia without clinical antileukemic activity

Correlation of neuropilin-1 overexpression to survival in acute myeloid leukemia

Neuropilin-1 (NRP-1), a vascular endothelial growth factors and semaphorin receptor functioning as mediator of angiogenesis and neuronal guidance, is expressed by various solid tumors. The importance of NRP-1 in hematological malignancies such as acute myeloid leukemia (AML) remains to be elucidated. Therefore, we determined NRP-1 expression by immunohistochemical analysis of bone marrow biopsies of patients with newly diagnosed, untreated AML. The expression of NRP-1 was significantly increased in AML patients (n=76; median 12.9 arbitrary units (a.u.)) as compared with controls (n=38; median 2.75 a.u.). Survival was significantly poorer in patients with high (>median) versus low (⩽median) NRP-1 expression levels with 5-year overall survival rates of 16.9 versus 49.6% (P=0.050). In conclusion, our data provide evidence of increased NRP-1 expression in AML with significant correlation to survival. Thus, NRP-1 might constitute a promising target for antileukemic and antiangiogenic treatment strategies in AML.

Inhibition of tumor growth by RGD peptide-directed delivery of truncated tissue factor to the tumor vasculature.

Selective activation of blood coagulation in tumor vessels with subsequent tumor infarction is a promising anticancer strategy. To this end, a fusion protein consisting of the extracellular domain of tissue factor [truncated tissue factor (tTF)] was fused to the peptide GRGDSP selectively targeting αv-integrins on tumor endothelial cells. tTF-RGD retained its thrombogenic and integrin-binding activity in vitro. In vivo studies in mice bearing human adenocarcinomas (CCL185), melanoma (M21), and fibrosarcoma (HT1080) revealed that i.v. administration of tTF-RGD induced thrombotic occlusion of tumor vessels resulting in tumor growth retardation or regression in all three types of solid tumors. No apparent side effects, such as thrombosis, in other organs or other treatment-related toxicities were observed. Reduced tumor blood flow in tTF-RGD–treated animals as determined by contrast-enhanced magnetic resonance imaging underlines the proposed mechanism. In conclusion, we consider RGD peptide–directed delivery of tTF as alternative to previously used antibody fusion proteins. Small peptide-directed delivery of coaguligands does not cause immunologic side effects and those caused by accumulation in the reticuloendothelial system. This is the first report to describe the induction of selective thrombosis in tumor vessels by RGD peptide–directed delivery of tTF, which may be a promising strategy for the treatment of cancer.

Circulating angiopoietin-2 is a strong prognostic factor in acute myeloid leukemia

Angiogenesis plays an important role in solid tumors and hematologic malignancies. The angiopoietins act as essential regulators in this process. We investigated the impact of circulating angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2) and soluble Tie2 (sTie2) on overall survival in patients with acute myeloid leukemia (AML). Ang-1, Ang-2 and sTie2 were measured in plasma samples from 68 AML patients and 11 controls using enzyme-linked immunosorbent assay. Circulating levels of Ang-2 and sTie2 (median (range): 1098.0 (361.4–4147.6) pg/ml and 3.40 (1.21–10.00) ng/ml, respectively) were significantly elevated in AML patients as compared to controls (307.9 (199.7–1225.0) pg/ml and 2.88 (1.71–3.29) ng/ml; P<0.001 and P=0.014). In a univariate Cox proportional hazards model, higher levels of Ang-2 and sTie2 were predictive of poor survival. In multivariate analyses, Ang-2 and cytogenetics proved to be independent prognostic factors, with a relative risk of 4.07 (95% confidence interval (CI) 1.88–8.81) and 2.70 (95% CI 1.25–5.81), respectively. The 3-year survival rate for AML patients with Ang-2 levels⩾1495.6 pg/ml was only 14.7% compared to 64.7% for those with Ang-2 levels<1495.6 pg/ml. These data provide evidence that circulating Ang-2 represents an independent prognostic factor in AML and may be used as a prognostic tool in the risk-adapted management of AML.

Vascular endothelial growth factor and its receptor as drug targets in hematological malignancies.

Angiogenesis is defined as formation of new blood vessels from the preexisting vasculature, a process which is essential for malignant tumor growth. While this has been accepted for solid forms of cancer there is now emerging evidence that progression of hematological malignancies also requires the induction of new blood vessels. Vascular endothelial growth factor (VEGF) is known to be an essential regulator of physiological and pathological angiogenesis. Numerous preclinical and clinical studies have validated VEGF as target for antiangiogenesis and anticancer therapy. With regard to hematological malignancies a stimulating effect of VEGF for proliferation, survival and migration of leukemia cells could be demonstrated. Bone marrow of leukemia patients shows an increased microvessel density as well as VEGF expression. Complete remissions in acute myeloid leukemia (AML) have been reported by targeting the receptor tyrosine kinase system of VEGF. While the pathophysiology behind the contribution of VEGF to leukemia progression is not yet completely understood, VEGF and its receptors may provide promising targets not only in solid tumors but also hematological malignancies such as AML.

Generation of Fusion Proteins for Selective Occlusion of Tumor Vessels

Selective activation of blood coagulation in tumor vessels with subsequent thrombosis and tumor infarction is a promising strategy in cancer therapy. To this end, different fusion proteins consisting of the extracellular domain of tissue factor (truncated tissue factor, tTF) were fused to the peptides GRGDSP (abbr. RGD), GNGRAHA (abbr. NGR) or cyclic derivates of these peptides, which selectively target alpha(v)-integrins or aminopeptidase N (CD13), respectively. Rationale for this strategy is the fact that these surface receptors are preferentially expressed on tumor endothelial cells. The tTF constructs were expressed in Escherichia coli BL21 (DE3). The integrity of the fusion proteins was evaluated by SDS-PAGE, immunoblotting and mass spectrometry. The screening process for the activity contained coagulation assays as well as purified receptor binding assays. The fusion proteins which retained their thrombogenic and binding activity were evaluated further. In vivo studies in nude mice bearing established different malignant human tumors revealed that i.v. administration of tTF-RGD or tTF-NGR induced partial or complete thrombotic occlusion of tumor vessels, which was demonstrated by histological analysis. Furthermore, treatment studies showed that the targeted tTF fusion proteins but not untargeted tTF proteins induced significant tumor growth retardation in human adenocarcinoma of the breast in a nude mice model without apparent side effects such as thrombosis in liver, kidney, heart or lung at therapeutic dose levels. Finally, we illustrate the upscaling process of fusion protein fabrication in order to produce the amounts needed for clinical studies. Thus, generation and screening of active fusion proteins, which induce selective thrombosis in the tumor vasculature, may be a promising strategy for the development of new drugs as cancer therapeutics.

Thalidomide for the Treatment of Acute Myeloid Leukemia

Abstract In analogy to solid neoplasms, accumulating data suggest the requirement of angiogenesis also for the development and progression of hematopoietic malignancies including acute myeloid leukemia (AML). Inhibition of increased microvessel density in bone marrow (BM) might be a promising target for pharmacological interventions aimed at reducing disease activity. Among the putative inhibitors of angiogenesis, thalidomide has demonstrated a considerable efficacy in myelodysplastic syndromes (MDS) and AML with overall response rates up to 56% and 25%, respectively. Responders experienced hematologic improvements with increased hemoglobin and platelet counts resulting in temporary transfusion independence. In AML, partial responses—defined as reduction of the leukemic blast cell infiltration of at least 50% in BM—occurred in four of 20 patients after one month of thalidomide administration in a previous phase I/II study. Additionally, we observed a long-term response in one AML patient of more than 20 months, meanwhile fulfilling the criteria of complete remission. The decrease in leukemic blast infiltration in BM of responders was accompanied by a significant reduction of the microvessel density. Overall adverse events caused by the drug consisted mainly of fatigue, constipation, skin rash and polyneuropathy with a tolerable dose of 200–400 mg p.o. per day. In conclusion, thalidomide as a single agent has significant anti-leukemic activity with some evidence for anti-angiogenic effects in BM, although the precise mechanism of action remains to be elucidated.