Uncovering the role of tumor-derived LCN2 (NGAL), a systemic mediator of astrogliosis, in facilitating melanoma brain metastasis

Introduction: Malignant melanoma is the deadliest skin cancer with rising incidence worldwide. Melanoma frequently metastasizes to the lungs, bone, liver and brain. Although the development of targeted therapies and immune checkpoint inhibitors has dramatically improved patient overall survival, brain metastases still pose an unmet clinical challenge. The microenvironment plays a crucial role in facilitating metastasis by promoting survival, colonization and proliferation of disseminated tumor cells to distant organs. Therefore, understanding the early changes in the brain microenvironment that precede metastasis is of great clinical importance. Astrocytes are key components of the brain microenvironment. Neuroinflammation is a prominent feature of reactive astrocytes, characterized by the release of pro-inflammatory cytokines and chemokines, increased blood-brain barrier permeability and immune cell infiltration, and is also a hallmark of brain metastatic niche formation. Current models of metastasis indicate that specific organs are predisposed for metastases formation following active modifications by both the primary tumor and reactive stromal cells at the metastatic site.

Lipocalin 2 (LCN2), is a 25 kDa secreted glycoprotein known for sequestering iron as a physiological response of fighting bacterial infections. LCN2 was also shown to be a pro-inflammatory factor, overexpressed in various malignancies. More importantly, LCN2 is a known activator of astrocytes, implicated in numerous CNS pathologies. However, the role of LCN2 in melanoma is largely unexplored.

M&M: Utilizing a transplantable model of spontaneous melanoma brain metastasis in immune-competent mice, recently established in our lab, we compare the metastatic capacity of brain-tropic cell lines to that of the parental cell line. We analyze plasma levels of LCN2 in both human and mouse samples using ELISA, as well as expression levels using qRT-PCR.

Results: We show that plasma levels of LCN2 increase in melanoma-bearing mice and in human patients with melanoma brain metastasis. Moreover, LCN2 is overexpressed in brain-tropic melanoma cell lines both in vitro and in primary tumors of injected mice in vivo, suggesting that melanoma-derived LCN2 facilitates brain tropism and metastases formation by activating astrocytes and instigating neuroinflammation.

Conclusion: Uncovering this systemic signaling pathway may be beneficial for the design of novel therapeutic approaches to prevent early changes in the brain microenvironment, rendering it less susceptible to metastasis.