P02.09 Heteromerization of uPA and PAI-1 enforces pro-tumorigenic neutrophil trafficking to malignant tumors in breast cancer via VLDLr-dependent β2 integrin clustering

Background High tumor levels of urokinase-type plasminogen activator (uPA)-plasminogen activator inhibitor-1 (PAI-1) heteromers independently predict poor survival in early breast cancer. The pathogenetic role of this protein complex, however, remains largely obscure. Material and Methods Neutrophil trafficking was analyzed in orthotopic (multi-channel flow cytometry) and heterotopic (ear; multi-channel in vivo microscopy) mouse models of 4T1 breast cancer, in a mouse peritonitis assay (multi-channel flow cytometry), as well as in the mouse cremaster muscle (multi-channel in vivo microscopy). Cytokine expression in tumors was determined by multiplex ELISA. Phenotypic and functional properties of primary mouse neutrophils, microvascular endothelial cells (cell line bEnd.3), macrophages (cell line RAW 264.7), and breast cancer cells (cell line 4T1) were characterized in different in vitro assays. uPA/PAI-1 expression and neutrophil infiltration in human breast cancer samples were assessed by RNA sequencing, immunhistochemistry, and ELISA. Results and Discussion Here, we demonstrate that uPA-PAI-1 heteromerization multiplies the potential of the single proteins to attract pro-tumorigenic neutrophils. To this end, tumor-released uPA-PAI-1 activates peritumoral macrophages (VLDL receptor- and ERK/MAPK-pathway). This promotes neutrophil trafficking to cancerous lesions (enhanced β2 integrin activation and clustering) and primes these immune cells towards a pro-tumorigenic phenotype (elevated neutrophil elastase expression), thus supporting tumor growth and metastasis. Blockade of uPA-PAI-1 heteromerization by a novel inhibitor effectively interfered with these events and prevented tumor progression. Conclusions Here, we identified an already therapeutically targetable interplay between hemostasis and innate immunity that drives advanced stages of breast cancer as well as characterized the underlying mechanisms of this process. As a personalized immunotherapeutic strategy, blockade of uPA-PAI-1 heteromerization might be particularly beneficial for patients with highly aggressive uPA-PAI-1high tumors. This study was supported by Deutsche Forschungsgemeinschaft (DFG), Sonderforschungsbereich (SFB) 914 Disclosure Information B. Uhl: None. L. Mittmann: None. J. Dominik: None. R. Hennel: None. B. Smiljanov: None. F. Haring: None. J. Schaubacher: None. C. Braun: None. L. Padovan: None. R. Pick: None. M. Canis: None. C. Schulz: None. M. Mack: None. E. Gutjahr: None. P. Sinn: None. J. Heil: None. K. Steiger: None. S.M. Kanse: None. W. Weichert: None. M. Sperandio: None. K. Lauber: None. F. Krombach: None. C. Reichel: None.