The plasminogen activator (PA) content of metastatic malignant melanoma was determined in Triton X-100 extracts of 11 surgical specimens and adjacent normal tissue, using azocaseinolysis with added plasminogen. The mean PA content of the tumors was 8.4 ± 10 (SD) CTA u/g tissue (6 times that of the surrounding tissue), lower than found earlier in lung, colon and breast tumors. Inhibition by goat IgG against purified human urokinase showed that the predominant activator was of the UK type, as was the case with the tumors examined earlier, except those of the prostate. This is in contrast with recent reports which showed that human melanoma-derived cells secrete into the culture fluid almost exclusively the “vascular type” PA (Wilson et al., Cancer Res. 40, 933, 1980; Roblin and Young, Ibid. 40, 2706, 1980). While this type of PA was present in all extracts here examined, in 3 of them only trace amounts (<1%) could be found. The vascular type PA, when present, could be inhibited by rabbit IgG against human melanoma cell culture-derived vascular PA (kind gift of Dr. E. Dowdle). SDS-gel electrophoresis in conjunction with fibrin-agar overlay zymography showed multiple activator bands ranging in mol. wt. from 100,000 to 30,000. All but the 70,000 mol. wt. vascular type PA band were inhibited by inclusion of anti-UK IgG into the fibrin-agar mixture.The discrepancy between the tumor extracts and the culture media may be due to a selective advantage of vascular type PA-secreting cells in culture, or to the turning off of the UK gene in the culture environment. It is also possible that production of vascular type PA is suppressed iii vivo.

The plasminogen activator content of the extracts of excise prostate cancers (25 specimens) was determined with an azocasein assay and found to be on the average 1.7 times higher than that of extracts of excised prostate benign hyperplasias (29 specimens). Both groups contained the same average percentage of human urokinase type activator (approximately 45%) as determined by the inhibition of activity when anti-human urokinase antibody was included in the assay system. The two types of activators were partially purified and found to have distinctly different properties. The most striking difference was the large augmentation of activity o the non-urokinase enzyme in fibrinolysis. The implications of an enhanced fibrinolysis relative to azocaseinolysis (or other) is discussed, particularly with respect to its importance in the quantitation and characterization of activators by different investigators. Highly purified urokinase-like activator was found to be similar to commercial urokinase preparation with respect to molecular weight, isoelectric point, inhibition by the antibody, and inhibition by placenta inhibitor.

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