THE MECHANISM OF CANCER-MEDIATED CONVERSION OF PLASMINOGEN TO THE ANGIOGENESIS INHIBITOR ANGIOSTATIN

Angiostatin, a potent naturally occurring inhibitor of angiogenesis an d growth of tumor metastases, is generated by cancer-mediated proteoly sis of plasminogen, Human prostate carcinoma cells (PC-3) release enzy matic activity that converts plasminogen to angiostatin. We have now i dentified two components released by PC-3 cells, urokinase (uPA) and f ree sulfhydryl donors (FSDs), that are sufficient for angiostatin gene ration. Furthermore, in a defined cell-free system, plasminogen activa tors [uPA, tissue-type plasminogen activator (tPA), or streptokinase], in combination with one of a series of FSDs (N-acetyl-L-cysteine, D-p enicillamine, captopril, L-cysteine, or reduced glutathione] generate angiostatin from plasminogen, An essential role of plasmin catalytic a ctivity for angiostatin generation was identified by using recombinant mutant plasminogens as substrates, The wild-type recombinant plasmino gen was converted to angiostatin in the setting of uPA/FSD; however, a plasminogen activation site mutant and a catalytically inactive mutan t failed to generate angiostatin. Cell-free derived angiostatin inhibi ted angiogenesis in vitro and in vivo and suppressed the growth of Lew is lung carcinoma metastases. These findings define a direct mechanism for cancer-cell-mediated angiostatin generation and permit large-scal e production of bioactive angiostatin for investigation and potential therapeutic application.