In breast cancer patients, chronic emotional stress accompanies the physiological toll of the cancer and subsequent therapeutic treatment. There is evidence from breast cancer patients that stress can augment breast tumor growth and recurrence, but the biochemical mechanisms are not understood. Sympathetic nervous system release of the catecholamines norepinephrine and epinephrine and activation of adrenergic receptors constitute a major stress pathway in mice and humans. We have observed sympathetic tyrosine hydroxylase-positive nerve fibers adjacent to blood vessels in breast tumors grown in the mammary fat pad of mice. We have also determined that stimulation of breast cancer cell lines with ss-adrenergic receptor agonists dramatically elevates interleukin-6 (IL-6), a molecule that facilitates tumor angiogenesis, invasion and metastasis. In this proposal, we hypothesize that chronic stress exposure stimulates tumor growth, angiogenesis, and metastasis through activation of the sympathetic nervous system. We will characterize the impact of social isolation, a chronic stressor, on tumor growth and metastasis in a mouse orthotopic breast cancer model (specific aim 1) and in a spontaneously occurring mouse model of breast cancer (specific aim 2). In these experiments, we will determine if ablation of sympathetic innervation or blockade of ss-adrenergic receptors prevent stress-induced alterations in tumor pathogenesis.
In specific aim 3, we will characterize the anatomical relationship between sympathetic innervation and tumor blood vessels in vivo. We will use transgenic mice that express enhanced green fluorescent protein (EGFP) under the control of the tyrosine hydroxylase promoter (TH-EGFP mice) and in vivo imaging with multiphoton laser scanning microscopy (MPLSM) to dynamically monitor the relationship between the tumor vasculature (labeled with tetramethyl rhodamine-dextran (red)) and EGFP-labeled TH+ nerve fibers (green) in a growing tumor. These experiments will define the role of the sympathetic nervous system in stress-induced tumor progression. Pharmacological blockers of the sympathetic nervous system have been proven safe and effective in the treatment of cardiovascular disease, offering the possibility of their rapid application to the improvement of current breast cancer therapies.
Our studies will connect stress exposure and the stress hormones norepinephrine and epinephrine to cancer growth and spread in two mouse models of breast cancer. This work will provide immediate insight into how long-term stress exposure influences breast cancer growth and metastasis, and will lead to additional options for the treatment of breast cancer.
