Combating the Immunosuppressive Tumor Microenvironment in Triple Negative Breast Cancer: The Role of Mitochondrial Dynamics in the Polarization of Tumor-Associated Macrophages

Project Summary/Abstract Triple Negative Breast Cancer (TNBC) is a devastating disease with aggressive growth and frequent metastases. Less than 30% of patients with metastatic TNBC survive beyond five years after their diagnosis. While other breast cancer subtypes have well-defined endocrine markers, TNBC tumors lack such specific therapeutic targets, making cyclic chemotherapy the mainstay of treatment. Immune checkpoint blockade therapy aims to leverage TNBC’s inherent yet limited immunogenicity, though success has been restricted by other immunosuppressive elements in the tumor environment. The overarching goal is to find alternative and/or synergistic methods to enhance immune-mediated cytotoxicity in the TNBC tumor microenvironment. The overall objective of this proposal is to enhance tumor microenvironment immunogenicity by repolarizing macrophages out of a pro-tumor state and into a cytotoxic, anti-tumor state. The central hypothesis is that mitochondrial fusion governs tumor associated macrophages’ (TAM) pro-tumor functions within the tumor microenvironment. The rationale for this project is that macrophage metabolism defines polarization fate. Particularly, anti-tumor macrophages upregulate glycolysis while pro-tumor macrophages depend on oxidative phosphorylation. As mitochondria house oxidative phosphorylation-associated pathways, and as mitochondrial structure impacts oxidative phosphorylation efficiency, manipulating mitochondrial structure could determine polarization fate. This proposal consists of proof-of-principle studies to demonstrate macrophages are flexible and that repolarization can be achieved by manipulating mitochondrial structure in vitro and in vivo. Along this trajectory, the central hypothesis will be tested by pursuing two specific aims. Aim 1 will determine the role of mitochondrial dynamics in macrophage polarization. For this aim, we will culture TNBC tumor macrophages in vitro, manipulate mitochondrial dynamics, and then evaluate polarization. Aim 2 will determine whether TAM pro-tumor functions within the tumor microenvironment are dependent on mitochondrial fusion. In this aim, we will evaluate the effect of macrophages with altered mitochondrial dynamics on T cell cytotoxicity, metastasis, and angiogenesis. The proposed studies are innovative because they will evaluate direct causation between mitochondrial dynamics and macrophage polarization and will also define a relevant in vivo macrophage phenotype. The project is significant because it sets the foundation for manipulation of macrophage mitochondria as a therapeutic strategy to enhance tumor microenvironment immunogenicity for TNBC. Collectively, these studies will lend insight into the mechanisms that govern macrophage fate and make progress towards novel immune therapies for TNBC.