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Abstract Background Upregulation of endogenous angiostatin levels may constitute a novel anti-angiogenic, and therefore anti-tumor therapy. In vitro, angiostatin generation is a two-step process, starting with the conversion of plasminogen to plasmin by plasminogen activators (PAs). Next, plasmin excises angiostatin from other plasmin molecules, a process requiring a donor of a free sulfhydryl group. In previous studies, it has been demonstrated that administration of PA in combination with the free sulfhydryl donor (FSD) agents captopril or N-acetyl cysteine, resulted in angiostatin generation, and anti-angiogenic and anti-tumour activity in murine models. Methods In this study we have investigated the angiostatin generating capacities of several FSDs. D-penicillamine proved to be most efficient in supporting the conversion of plasminogen to angiostatin in vitro. Next, from the optimal concentrations of tPA and D-penicillamine in vitro, equivalent dosages were administered to healthy Balb/c mice to explore upregulation of circulating angiostatin levels. Finally, anti-tumor effects of treatment with tPA and D-penicillamine were determined in a human melanoma xenograft model. Results Surprisingly, we found that despite the superior angiostatin generating capacity of D-penicillamine in vitro, both in vivo angiostatin generation and anti-tumour effects of tPA/D-penicillamine treatment were impaired compared to our previous studies with tPA and captopril. Conclusion Our results indicate that selecting the most appropriate free sulfhydryl donor for anti-angiogenic therapy in a (pre)clinical setting should be performed by in vivo rather than by in vitro studies. We conclude that D-penicillamine is not suitable for this type of therapy.

Background: Upregulation of endogenous angiostatin levels may constitute a novel antiangiogenic, and therefore anti-tumor therapy. In vitro, angiostatin generation is a two-step process, starting with the conversion of plasminogen to plasmin by plasminogen activators (PAs). Next, plasmin excises angiostatin from other plasmin molecules, a process requiring a donor of a free sulfhydryl group. In previous studies, it has been demonstrated that administration of PA in combination with the free sulfhydryl donor (FSD) agents captopril or N-acetyl cysteine, resulted in angiostatin generation, and anti-angiogenic and anti-tumour activity in murine models. Methods: In this study we have investigated the angiostatin generating capacities of several FSDs. D-penicillamine proved to be most efficient in supporting the conversion of plasminogen to angiostatin in vitro. Next, from the optimal concentrations of tPA and D-penicillamine in vitro, equivalent dosages were administered to healthy Balb/c mice to explore upregulation of circulating angiostatin levels. Finally, anti-tumor effects of treatment with tPA and D-penicillamine were determined in a human melanoma xenograft model. Results: Surprisingly, we found that despite the superior angiostatin generating capacity of Dpenicillamine in vitro, both in vivo angiostatin generation and anti-tumour effects of tPA/Dpenicillamine treatment were impaired compared to our previous studies with tPA and captopril. Conclusion: Our results indicate that selecting the most appropriate free sulfhydryl donor for anti-angiogenic therapy in a (pre)clinical setting should be performed by in vivo rather than by in vitro studies. We conclude that D-penicillamine is not suitable for this type of therapy. [ABSTRACT FROM AUTHOR]

SummaryTumor cell invasion and metastasis formation depend on both adhesive and proteolytic mechanisms. Previous studies have shown that expression of matrix metalloproteinase-2 and integrin αvβ3 correlate with melanoma progression. Recently, direct binding of matrix metalloproteinase-2 to αvβ3 was implicated in presenting activated matrix metalloproteinase-2 on the cell surface of invasive cells. In this study we investigated this, using the highly metastatic, αvβ3-negative melanoma cell lines MV3 and BLM, their β3-transfected αvβ3 expressing counterparts, xenografts derived from these cell lines, and fresh human cutaneous melanoma lesions comprising all stages of melanoma progression. Expression and activation status of matrix metalloproteinase-2 were studied by reverse transcription–polymerase chain reaction, immunohistochemistry, western blotting, and zymographic analysis, respectively. Matrix metalloproteinase-2 protein expression in vitro was similar in both αvβ3-negative and αvβ3-positive cell lines. Remarkable differences, however, exist in the localization of inactive and active matrix metalloproteinase-2. Soluble active matrix metalloproteinase-2 was detectable only in the conditioned medium of αvβ3-negative cell lines and undetectable in the αvβ3-positive cell lines. Conversely, active matrix metalloproteinase-2 was present exclusively on the cell surface of the αvβ3 expressing transfectants. Western blot analysis of other components that are involved in matrix metalloproteinase-2 activation showed that processing of proMT1-matrix metalloproteinase to the activated form was enhanced in β3 transfectants, whereas secretion of tissue inhibitor of metalloproteinase-2 was decreased. In vivo, the presence of functionally active matrix metalloproteinase-2 was significantly higher in xenografts derived from the αvβ3 expressing MV3 and BLM cell lines. In human cutaneous melanoma lesions, neither matrix metalloproteinase-2 nor integrin αvβ3 is detectable in melanoma in situ as determined by immunohistochemistry. In contrast, the number of matrix metalloproteinase-2-positive and αvβ3-positive tumor cells was clearly increased in primary melanomas, and melanoma metastases. Double staining experiments and confocal laser microscopy demonstrated that the percentage of cells coexpressing matrix metalloproteinase-2 and αvβ3 increased in advanced primary melanomas and melanoma metastases. In addition, zymography showed that functionally active matrix metalloproteinase-2 was frequently present in melanoma metastases. In these lesions a high proportion of matrix metalloproteinase-2- and αvβ3-double-positive melanoma cells were detectable. Our study demonstrates that the presence of activated matrix metalloproteinase-2 correlates with expression of αvβ3 in human melanoma cells both in vitro and in vivo, and also in fresh human melanoma lesions. These findings strongly suggest that co-ordinated expression of both factors may be required for melanoma cell invasion and metastasis formation. [ABSTRACT FROM AUTHOR]

PN-E2 is a monoclonal antibody generated against recombinant tumor necrosis factor-α (TNF-α) - treated human umbilical vein endothelial cells (EC). PN-E2 recognized a molecule with expression levels in vitro that could be downregulated by TNF, and in situ PN-E2 showed only weak reactivity with vascular EC in normal skin, as assessed by immunohistochemical staining. The expression of PN-E2 was considerably increased on EC in various pathologic skin lesions, including psoriasis, granulation tissue, and inflamed skin. PN-E2 antigen expression was analyzed in more detail in vitro on cultured EC and fibroblasts by use of enzyme-linked immunosorbent assay and fluorescence-activated cell sorter techniques. The expression level on human umbilical vein endothelial cells and capillary EC was, in contrast to the in situ immunohistologic findings, invariably high. On fibroblasts, a low expression was found. Incubation of the EC with recombinant TNF-α decreased expression by a factor of 2. Incubation of EC with recombinant interferon-γ resulted in a twofold increase in PN-E2 antigen expression, whereas other cytokines [recombinant interleukin (rIL)-1α, rIL-1β, rIL-4, rIL-6], lipopolysaccharide, or recombinant basic fibroblast growth factor had no effect. Immunoelectron microscopy of tissue specimens and EC preparations localized the antigen on the luminal membrane of the endothelium. Immunoprecipitation followed by sodium dodecyl sulfate - polyacrylamide gel electrophoresis analysis revealed a major band at 90 kDa and a minor band at 80 kDa under reducing conditions and bands of 180 and 400 kDa under non-reducing conditions. Molecular weight and expression patterns in vitro on EC after incubation with cytokines excluded most of the known endothelium-specific molecules, with the possible exception of endoglin (the 44G4 antigen). We conclude from our findings that this new antigen could be useful as a marker for endothelial activation in skin biopsy material. [ABSTRACT FROM AUTHOR]

ABT-510 is a small peptide thrombospondin-1 mimetic angiogenesis inhibitor under development by Abbott Laboratories for the potential treatment of solid tumors. ABT-510 is undergoing phase II clinical trials.