Abstract 516: Differential in vivo effects of uPA overexpression: role of endogenous tumor PAI-1 expression

We have previously reported that the protease activity of uPA delays tumor progression in a syngeneic model of breast cancer, and that the inhibitory effects are due to the protease activity of uPA (Merchan et. al, JNCI, 2006: 7; 98(11)). We also reported that changes in the uPA/PAI-1 balance favoring the proteolytic activity of uPA are associated with delayed tumor growth and reduction in lung metastases in vivo (Jing, et al, AACR 2009 meeting, #1124). The aim of this study was to extend the above findings in other in vivo syngeneic cancer models and to characterize the changes in gene expression mediated by uPA overexpression. We generated stably uPA overexpressing murine renal cancer (RENCA) and murine colon cancer (MC-38) cell lines using lentiviral vectors carrying m-uPA and selecting high uPA expressing clones for in vivo studies. uPA protein expression and in vitro growth was similar between the uPA overexpressing and control cancer cells. Similar with our findings in the 4T1 model, mice harboring RENCA tumors overexpressing uPA had reduced tumor growth than controls. Conversely, mice carrying uPA-overexpressing MC-38 tumors had significantly enhanced tumor growth compared to controls. To understand the causes for the opposite in vivo effects of uPA overexpressing RENCA and MC-38 tumors, we first compared uPA9s proteolytic activity vs. protein concentration between both cell lines. To our surprise, the uPA proteolytic activity of (uPA overexpressing) MC-38 conditioned medium (CM) was significantly lower (> 15-fold) than that of stable RENCA cell lines even though uPA protein levels were comparable. To assess if the differences in uPA proteolytic activity between MC38 and RENCA transfectants was due to differential endogenous PAI-1 expression, we measured PAI-1 levels in MC38 and RENCA transfectants CM (ELISA). We found that PAI-1 expression in MC 38 was significantly higher (30-fold) than RENCA cells. The above data strongly suggest that in MC-38 tumors, uPA overexpression promoted tumor growth in part due to high endogenous PAI-1 levels. On the other hand, in the RENCA model, uPA overexpression (and low PAI-1 expression) was associated with significantly enhanced proteolytic activity and delayed tumor growth. Gene expression arrays of early murine mammary tumors overexpressing active uPA, showed significant tumor down regulation of several members of the MMP family, which may explain the in vivo antitumor effects. The above data suggest that the pro-or anti tumorigenic/metastatic effects of uPA overexpression depend on its proteolytic activity, and indicate that the status of endogenous tumor PAI-1 may regulate uPA9s effects on tumor progression and metastases. The above data may help reconcile contradictory experimental and clinical findings on the role of proteases and protease inhibitors on tumor progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 516.