von Willebrand factor fibers promote cancer-associated platelet aggregation in malignant melanoma of mice and humans.

Tumor-mediated procoagulatory activity leads to venous thromboembolism and supports metastasis in cancer patients. A prerequisite for metastasis formation is the interaction of cancer cells with endothelial cells (ECs) followed by their extravasation. Although it is known that activation of ECs and the release of the procoagulatory protein von Willebrand factor (VWF) is essential for malignancy, the underlying mechanisms remain poorly understood. We hypothesized that VWF fibers in tumor vessels promote tumor-associated thromboembolism and metastasis. Using in vitro settings, mouse models, and human tumor samples, we showed that melanoma cells activate ECs followed by the luminal release of VWF fibers and platelet aggregation in tumor microvessels. Analysis of human blood samples and tumor tissue revealed that a promoted VWF release combined with a local inhibition of proteolytic activity and protein expression of ADAMTS13 (a disintegrin-like and metalloproteinase with thrombospondin type I repeats 13) accounts for this procoagulatory milieu. Blocking endothelial cell activation by the low-molecular-weight heparin tinzaparin was accompanied by a lack of VWF networks and inhibited tumor progression in a transgenic mouse model. Our findings implicate a mechanism wherein tumor-derived vascular endothelial growth factor-A (VEGF-A) promotes tumor progression and angiogenesis. Thus, targeting EC activation envisions new therapeutic strategies attenuating tumor-related angiogenesis and coagulation.

Skin melanoma development in ret transgenic mice despite the depletion of CD25+Foxp3+ regulatory T cells in lymphoid organs.

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) known to mediate self-tolerance were also shown to contribute to tumor progression. In mouse melanoma transplantation models, Treg depletion resulted in the stimulation of antitumor immune responses and tumor eradication. To study Treg in conditions close to the clinical situation, we used a ret transgenic mouse spontaneous melanoma model, which, in contrast to transplantation models, resembles human melanoma regarding clinical development. Significantly higher numbers of Treg were found in skin tumors and metastatic lymph nodes at early stages of melanoma progression compared with more advanced stages accompanied by the elevated CCR4 expression on Treg and higher production of its ligand CCL2 in tumor lesions. Numbers of tumor infiltrating Treg inversely correlated with Treg amounts in the bone marrow, suggesting their possible recruitment to melanoma lesions from this organ. The immunosuppressive function of Treg from transgenic tumor-bearing mice was similar to that from transgenic tumor-free mice or nontransgenic littermates. Although anti-CD25 mAb injections resulted in the efficient Treg depletion from lymphoid organs of transgenic mice, melanoma development was not significantly delayed. Furthermore, the treatment of mice with macroscopical tumors also failed to inhibit tumor progression, which correlated with the inability to deplete intratumoral Treg. We suggest that in the autochthonous melanoma genesis, other immunosuppressive cells could play an important role and replace immunosuppressive, tumor-promoting functions of Treg. Therefore, effective melanoma immunotherapy should include the inhibition of Treg migration into the tumor combined with neutralization of other immunosuppressive cells and factors in the tumor microenvironment.

Harnessing high density lipoproteins to block transforming growth factor beta and to inhibit the growth of liver tumor metastases.

Transforming growth factor ß (TGF-ß) is a powerful promoter of cancer progression and a key target for antitumor therapy. As cancer cells exhibit active cholesterol metabolism, high density lipoproteins (HDLs) appear as an attractive delivery system for anticancer TGFß-inhibitory molecules. We constructed a plasmid encoding a potent TGF-ß-blocking peptide (P144) linked to apolipoprotein A-I (ApoA-I) through a flexible linker (pApoLinkerP144). The ApoLinkerP144 sequence was then incorporated into a hepatotropic adeno-associated vector (AAVApoLinkerP144). The aim was to induce hepatocytes to produce HDLs containing a modified ApoA-I capable of blocking TGF-ß. We observed that transduction of the murine liver with pApoLinkerP144 led to the appearance of a fraction of circulating HDL containing the fusion protein. These HDLs were able to attenuate TGF-ß signaling in the liver and to enhance IL-12 -mediated IFN-γ production. Treatment of liver metastasis of MC38 colorectal cancer with AAVApoLinkerP144 resulted in a significant reduction of tumor growth and enhanced expression of IFN-γ and GM-CSF in cancerous tissue. ApoLinkerP144 also delayed MC38 liver metastasis in Rag2-/-IL2rγ-/- immunodeficient mice. This effect was associated with downregulation of TGF-ß target genes essential for metastatic niche conditioning. Finally, in a subset of ret transgenic mice, a model of aggressive spontaneous metastatic melanoma, AAVApoLinkerP144 delayed tumor growth in association with increased CD8+ T cell numbers in regional lymph nodes. In conclusion, modification of HDLs to transport TGF-ß-blocking molecules is a novel and promising approach to inhibit the growth of liver metastases by immunological and non-immunological mechanisms.

T-Cell Mediated Immune Responses Induced in ret Transgenic Mouse Model of Malignant Melanoma.

Poor response of human malignant melanoma to currently available treatments requires a development of innovative therapeutic strategies. Their evaluation should be based on animal models that resemble human melanoma with respect to genetics, histopathology and clinical features. Here we used a transgenic mouse model of spontaneous skin melanoma, in which the ret transgene is expressed in melanocytes under the control of metallothionein-I promoter. After a short latency, around 25% mice develop macroscopic skin melanoma metastasizing to lymph nodes, bone marrow, lungs and brain, whereas other transgenic mice showed only metastatic lesions without visible skin tumors. We found that tumor lesions expressed melanoma associated antigens (MAA) tyrosinase, tyrosinase related protein (TRP)-1, TRP-2 and gp100, which could be applied as targets for the immunotherapy. Upon peptide vaccination, ret transgenic mice without macroscopic melanomas were able to generate T cell responses not only against a strong model antigen ovalbumin but also against typical MAA TRP-2. Although mice bearing macroscopic primary tumors could also display an antigen-specific T cell reactivity, it was significantly down-regulated as compared to tumor-free transgenic mice or non-transgenic littermates. We suggest that ret transgenic mice could be used as a pre-clinical model for the evaluation of novel strategies of melanoma immunotherapy.

Comprehensive immunohistological analysis of the endothelin system in human kidney grafts.

BACKGROUND: In experimental models of renal transplantation, upregulation of the endothelin (ET) system and amelioration of renal injury by ET-receptor blockers have been documented. In contrast, little information is available on the expression of the ET system in human kidney allografts. It was the purpose of the present study to analyse by immunohistology the expression of ET-1 as well as of the two ET receptors (ET-RA and ET-RB) in the different cells and compartments of kidney grafts and control kidneys. METHODS: Fifty-five graft biopsies were taken from 55 kidney allograft recipients (mean age: 32+/-2.8 years) who were all on a calcineurin inhibitor. The indication for biopsies was delayed graft function or suspected rejection. The underlying diagnoses were acute allograft rejection (n = 14), chronic allograft nephropathy (n = 14), cyclosporin A (CSA) toxicity (n = 10), post-operative acute tubular necrosis (ATN) (n = 11) and recurrent primary disease (n = 6). As control, tissues of non-grafted kidneys with ATN (mean age: 35+/-24 years), of primary glomerulonephritis (mean age: 69+/-10 years) and of non-tumour-bearing parts of eight tumour nephrectomy specimens (mean age: 67+/-5 years) were assessed. The biopsies were scored using the 1997 Banff criteria. Expression of ET-1, ET-RA and ET-RB as well as of vascular endothelial growth factor was evaluated by immunohistochemistry and a semi-quantitative scoring system. Interstitial infiltrating cells were characterized using antibodies against T cells, B cells and macrophages (CD3, CD20 and CD68). RESULTS: Control cases showed only faint expression of ET-1 in glomeruli (in podocytes and endothelial cells), whereas marked expression was seen in distal, but less in proximal tubular cells. The interstitium was completely negative. ET-1 expression was seen in vascular endothelial cells (VEC) and vascular smooth muscle cells (VSMC). Only faint expression of ET-RA and ET-RB was found in glomeruli and tubuli (distal more than proximal). Marked ET-RA and ET-RB expression was seen in VEC and VSMC. In all transplanted kidneys, irrespective of the underlying diagnosis, expression of ET-1, ET-RA and ET-RB was markedly higher compared with control kidneys. ET-1 was strikingly upregulated in glomeruli and tubuli, but surprisingly not in the vasculature of grafts with CSA toxicity. Expression of ET-RB was markedly increased in CSA toxicity in glomeruli, tubuli and vessels. In grafts with ATN and acute rejection, pronounced expression of ET-RA was noted. There was a strong correlation between proteinuria and expression of ET-1 in glomeruli and proximal tubuli and of ET-RB in proximal tubuli. CONCLUSIONS: The above data in human kidney allograft biopsies are consistent with an important role of the ET system in different types of renal allograft damage. This finding extends and clarifies the somewhat contradictory results in animal models.