Dissemination of cancer cells (metastasis) is the leading cause of death in prostate cancer. Emerging data suggest that the cellular composition of cancerous tumors is highly heterogeneous. For example, studies using in vitro colony formation and cancer cell grafts in immunodeficient mice have revealed that tumor formation originates from a small subset of cancer cells that can self-renew in a manner similar to normal stem cells. These cancer stem cells have been prospectively identified in various cancers, including leukemia, tumors of the breast, brain, lung, and prostate.

Stem cell survival, growth, and differentiation are regulated through the integration of signals from stromal cells and their surrounding matrix that form a specific microenvironment commonly referred to as a "niche." Our group has been interested in stem cell trafficking in the bone marrow for many years. Remarkably, stem cells can be forced to migrate into the bloodstream upon stimulation with certain agonists. This process, often referred to as "mobilization," is routinely used in the clinic to harvest hematopoietic stem cells for life-saving transplantation procedures. Our recent studies have revealed, unexpectedly, a major role of the nervous system (in particular, the sympathetic division, responsible for flight or fight responses) in controlling the retention of hematopoietic stem cells in their niche through the regulated expression of an attractant molecule called CXCL12.

Here, we hypothesize that normal hematopoietic stem cells and cancer stem cells share common trafficking mechanisms. In support of this possibility, both normal stem cells and cancer cells express the receptor and respond to the key attractant molecule CXCL12. To track cancer cells in vivo and explore the role of the nervous system in regulating the retention of cancer stem cells into their niche, we will study human prostate cancer cells expressing the firefly (luciferase) and the green fluorescent protein genes in immunodeficient NOD/SCID mice. Expression of these markers will allow us to monitor spreading of cancer cells in live mice using bioluminescent imaging and their mobilization in the blood using flow cytometric analyses of circulating green fluorescent cancer cells. In Specific Aim 1, we will evaluate the spatial distribution of sympathetic innervation and its relationships with CXCL12 expression and the location of putative prostate cancer stem cells. In Specific Aim 2, we will evaluate whether a reduction in the function or expression of the attractant CXCL12 or its receptor CXCR4 in prostate tumors is sufficient to mobilize cancer cells in the circulation. In Specific Aim 3, we will test directly the role of the sympathetic nervous system using pharmacological and genetic gain- and loss-of-function approaches that alter sympathetic nervous activity inside the tumor. These studies will provide novel insights into a potentially important novel pathway regulating the cancer stem cell niche. A greater knowledge of the fundamental processes mediating cancer cell dissemination may have a great impact in the treatment and management of patients with prostate cancer.