| Abstract: | A body of evidence has suggested that hormones which modulate plasminogen activator production by cultured tumor explants in vitro may have a qualitatively comparable effect on the growth of the same tumors in vivo. As a test of this correlation and to explore its potential for predicting the in vivo response of tumors to hormones, we have studied here the effect of hydrocortisone on the growth of primary and first generation transplants of mouse mammary tumor virus-determined mammary tumors in BALB/c X DBA/8 F1 (hereafter called CD8F1) mice; hydrocortisone had been found previously to inhibit plasminogen activator production by explants of these tumors. The results were: (a) hydrocortisone reversibly blocked the growth of palpable primary tumors; growth resumed at control rates following withdrawal of exogenous hormone; (b) hydrocortisone inhibited the growth of first-generation tumor transplants when administered either before or after the appearance of palpable tumors; (c) pretreatment with hydrocortisone both delayed the appearance of primary tumors and greatly reduced tumor incidence in susceptible mice; a substantial part of the decrease in tumor incidence was apparently irreversible; (d) hydrocortisone reduction of tumor growth was accompanied by inhibition of tumor plasminogen activator content, and these effects displayed a similar dose dependence (enzyme content of tumor lysates was measured by the 125I-fibrin plate assay); the enzyme present in control and hormone-treated tumors was predominantly of the urokinase type. These findings suggest that plasminogen activator production and mammary tumor growth in CD8F1 mice are coordinately regulated and thus encourage the view that plasminogen activator might be useful as an in vitro marker for predicting the in vivo response of tumors to hormones. |
