The Role of Altered Glutamine Metabolism in Breast Tumor Innervation and its Connection to Brain Metastasi

Recent analyses of clinical data have shown that nerve fibers are significantly more present in invasive ductal carcinoma compared to both ductal carcinoma in situ and normal breast tissue. There exists evidence that glutamine metabolism may promote breast tumor innervation and brain metastasis:

1. Breast cancer cells express high levels of glutaminase that initiates glutaminolysis by converting glutamine to glutamate;
2. Cancer-associated fibroblasts upregulate glutamine synthetase expression to meet glutamine demands of breast cancer cells;
3. A synergy between glycolysis and glutaminolysis enhances cancer cell conversion of glutamine to lactate, which stimulates brain-derived neurotrophic factor (BDNF) secretion and drive neurite extension;
4. Brain metastasizing breast cancer cells express post-synaptic marker PSD-95and BDNF receptor TrkB.

Yet, the potential to inhibit these several key metabolic pathways and reduce metastatic phenotypes in triple negative breast cancer have not been clearly elucidated. To this end, we hypothesize that elevated glutamine metabolism by triple negative breast cancer cells promotes breast tumor innervation and brain metastasis. To test this hypothesis, we will bioengineer 3D culture platforms to closely mimic the mammary tumor microenvironment. To do so:

1. We will develop a tissue engineered model of the mammary tumor microenvironment using decellularized mammary tissue as a scaffold to culture 4T1 mouse triple negative breast cancer cells, mouse primary adipose stromal cells (ASCs) and mouse primary dorsal root ganglia (DRG) (Aim 1).
2. We will analyze glutamine metabolic profile of the 3D model of breast tumor innervation by using state-of-the-art metabolism profiling tools and exploiting the endogenous auto fluorescence of metabolic cofactors (Aim 2).
3. Finally we will assess the influence of breast tumor innervation on brain metastasis via immunofluorescence in vitro and in vivo implantation of DRG neurite-conditioned 4T1s and ASCs (Aim 3).

Inhibitors of glutamine synthesis, consumption and glutamate production/function will be tested for their ability to block innervation and the results will be analyzed in the Data Science Core to evaluate glutamine effects on breast tumor innervation in vitro. We will utilize the three cores (Data Science Core for data analysis, Imaging & Spectroscopy Core for 3D volumetric time-lapse confocal and multiphoton imaging, and Bioenergetics Core for metabolic profiling of in vitro cultures) to achieve strong rigor in study design, execution, analysis and interpretation and improve our understanding of breast tumor innervation and brain metastasis. Combined with mentoring by Dr. Tim Muldoon and Dr. Robert Griffin, as well as the AIMRC’s senior mentoring committee and other center leaders, Dr. Song will establish a solid pathway for scientific independence leading to an R01 submission at the end of year 2 that focuses on a full scope study echoing the focus of Aim 3 and the long-term project goals.