Angiostatin generating capacity and anti-tumour effects of D-penicillamine and plasminogen activators

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.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.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.Angiogenesis is an essential step in both tumour growth and the formation of distant metastases. Therefore, inhibition of tumour angiogenesis is currently being explored as a novel anti-tumour treatment [1-5].One class of anti-angiogenic compounds consists of proteolytic fragments of larger parent molecules. Examples of this type of angiogenesis inhibitors are angiostatin and endostatin, that are fragments of plasminogen and collagen XVIII, respectively [6,7]Angiostatin has been shown to possess anti-angiogenic effects both in vitro and in vivo. In vitro, angiostatin inhibited endothelial cell migration, proliferation and tube formation [8-13]. In vivo, administration of angiostatin – either alone, or in combination with radiotherapy or chemotherapy – resulted in potent inhibition of tumour growth and metastasis formation in several animal tumour models [14,14-19].Application of naturally occurring anti-angiogenic molecule