Targeting Lcn-2 as a novel strategy to disrupt the iron-trafficking mechanism within the tumor microenvironment

Cancer cells are known to have a dysregulated energy metabolism and exhibit an increased demand for essential nutrients, like iron. Within the tumor microenvironment (TME), cancer cells hijack the iron-trafficking mechanisms for their own benefit, whereby they can educate the tumor-associated macrophages (TAMs) to adopt an iron-release phenotype. Lipocalin-2 (Lcn-2), a 25kDa glycoprotein, acts as a bacteriostatic agent by scavenging iron via binding to siderophores secreted by bacteria. However, in the context of cancer, the Lcn-2/siderophore complex plays also an important role in iron-delivery to cancer cells. Furthermore, Lcn-2 can also form a complex with Matrix metalloproteinase 9 (MMP9) to promote cancer metastasis. Using the preclinical E0771 triple negative breast carcinoma (TNBC) model we found via single cell RNA seq on the CD45+ compartment that a subset of hypoxic macrophages and neutrophils showed an increased expression of Lcn-2. We also addressed the crosstalk between macrophages and E0771 cells in the context of iron- homeostasis and macrophage polarization. Upon coculturing with macrophages the cancer cells were shown to be the main Lcn-2 producers and have an increased FTH1 gene expression, suggesting iron-storage/acquisition. Conversely, macrophages exhibited an increased SLC40A1 (iron-export) and reduced FTH1 gene expression, suggesting iron export, as well as upregulated immunosuppressive M2-markers (Arg1, Chil3). Furthermore, non-immune cells from E0771 tumor bearing mice exhibited a higher cytoplasmic iron level compared to immune cells. Hence, Lcn-2 can be considered a potential novel therapeutic target for TNBC which is characterized by its aggressiveness and resistance to current treatments.