| Summary: | <p>Abstract</p> <p>Background</p> <p>Upregulation of endogenous angiostatin levels may constitute a novel anti-angiogenic, and therefore anti-tumor therapy. <it>In vitro</it>, 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.</p> <p>Methods</p> <p>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 <it>in vitro</it>. Next, from the optimal concentrations of tPA and D-penicillamine <it>in vitro</it>, 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.</p> <p>Results</p> <p>Surprisingly, we found that despite the superior angiostatin generating capacity of D-penicillamine <it>in vitro</it>, both <it>in vivo </it>angiostatin generation and anti-tumour effects of tPA/D-penicillamine treatment were impaired compared to our previous studies with tPA and captopril.</p> <p>Conclusion</p> <p>Our results indicate that selecting the most appropriate free sulfhydryl donor for anti-angiogenic therapy in a (pre)clinical setting should be performed by <it>in vivo </it>rather than by <it>in vitro </it>studies. We conclude that D-penicillamine is not suitable for this type of therapy.</p>
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