Abstract 1548: Pharmacologic inhibition of PAI-1 increases apoptosis and inhibits macrophage migration in cancer.

Abstract The paradoxical observation that elevated blood and tissue levels of plasminogen activator inhibitor-1 (PAI-1) in cancer patients positively correlate with tumor progression supports a pro-tumorigenic function for this serine protease inhibitor. The mechanism by which PAI-1 promotes tumor progression includes a pro-angiogenic function and a protective effect on Fas/FasL-mediated apoptosis in endothelial cells and tumor cells. Here we have tested the activity of TM5275, a newly developed small N-acylanthranilic acid derivative, for its anti-tumorigenic activity in vitro and in vivo. We observed that human fibrosarcoma HT-1080 cells treated with increasing concentrations of TM5275 exhibited markedly reduced cell viability (94.59% when treated with 50 uM, p < 0.01). Similarly, colon cancer HCT116 cells exhibited a 73.10% decrease in cell viability with 75 uM (p < 0.01). This was associated with a statistically significant increase in apoptosis (72.9% for HT-1080 cells treated with a TM5275 concentration of 75 uM and 48.2% for HCT116 cells treated at a TM5275 concentration of 100 uM, p < 0.01). We then made two observations suggesting that PAI-1 may inhibit the recruitment of macrophages by tumor cells. First, we found that tumors derived from HT-1080 cells in which PAI-1 expression was knocked down by shRNA showed a 47.8% decrease in tumor associated macrophage (TAM) infiltration when implanted in PAI-1 null Rag1−/− mice versus tumors from cells transfected with a scramble control and implanted in WT mice (p < 0.01). Second, we demonstrated that TM5275 (at a concentration of 50 uM) inhibits the migration of mouse peritoneal macrophage cells toward tumor cell conditioned media by 37.93% (p< 0.01). We then tested the anti-tumor activity of TM5275 in human HT-1080 cells implanted subcutaneously in nude mice. In a preliminary experiment, we showed that in mice treated with TM5275 (administered orally at 50 mg. /kg. daily from the time of implantation, a dose that resulted in a maximum plasma concentration of 6.9 uM after 1 hr) tumors reached a volume of 1500 mm3 at an average of 33 days in comparison with tumors implanted in mice receiving the vehicle (DMSO) which reached 1500 mm3 at an average of 26 days (p < 0.13). The data thus point to an apoptotic function of small inhibitors of PAI-1 and to the inhibition of macrophage migration as a potentially novel mechanism supporting the pro-tumorigenic activity of PAI-1. Whether small molecule inhibitors of PAI-1 have anti-tumorigenic activity in vivo is being further pursued by our laboratory in preclinical mouse models. Citation Format: Veronica R. Placencio, Toshio Miyata, Yves A. DeClerck. Pharmacologic inhibition of PAI-1 increases apoptosis and inhibits macrophage migration in cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1548. doi:10.1158/1538-7445.AM2013-1548