67P - The impact of the uPAR system and its interaction partners as potential therapeutic targets in TNBC

Abstract

Introduction: Triple-negative breast cancer (TNBC) is characterised as an aggressive type of breast cancer with no or low expression of ER, PR or HER2. Yet, it has been shown that certain components of the urokinase-type plasminogen activator receptor (uPAR) system are highly expressed in TNBC. In this study, uPAR and its interaction partners have been evaluated in TNBC model cell lines and by histological analyses of TNBC clinical specimens to explore the possible therapeutic potential of the uPAR interactome. Methods: Stable RNA interference was employed in MDA-MB-231 and BT549 cells to analyse the long term effects of uPAR and/or uPA depletion, on associated proteins, cell proliferation, cell invasion and migration. Protein expression was analysed by Western blot, in formalin-fixed paraffin-embedded (FFPE) cell line blocks and TNBC tumour specimens (n = 180) by immunohistochemistry (IHC). Additionally, the proximity ligation assay (PLA) was conducted to identify effects on complexes formed by uPAR and its interaction partners. Results: The in vitro analyses showed that 8 weeks after the stable depletion of uPAR and uPA by lentiviral vectors, cell invasion and migration was significantly reduced, supported by the decreased expression of matrix metalloproteinases such as MMP2 that are known to be involved in metastasis processes. Proliferation of the knocked-down cells was significantly diminished which was in accordance with induction of p27. IHC and PLA performed on cell line blocks and tumour samples demonstrated the significant association of uPAR with interaction partners uPA, plasminogen, cathepsin B in this TNBC cohort. Furthermore, our results indicated a regulatory effect of uPAR on the insulin-like growth factor 1 receptor (IGF1R) and in vitro experiments as well as statistical analyses indicate that both enhance malignancy in TNBC. Conclusion: Our findings demonstrate that uPAR and interacting partners are potential therapeutic targets in TNBC since the long-term depletion of uPAR and associated molecules does lead to reduced malignant potential in vitro. In particular, combined inhibition of uPAR and its associated partner IGF1R may be considered as a novel therapeutic target in TNBC. Disclosure: All authors have declared no conflicts of interest.