Prostate cancer (PCa) metastasizes to the bone more frequently than any other tissue site. There are limited options for patients with metastatic disease, which is the major contributor of PCa-associated deaths. A major focus of the Cook Lab is to interrogate mechanisms of the prostate tumor-bone microenvironment that contribute to the progression of bone metastatic prostate cancer (BM-PCa). Our lab previously identified that neutrophils, myeloid immune cells that are generated and stored within bone marrow, are initially protective against BM-PCa that has disseminated into the bone compartment. However, we found that the tumor inevitably becomes resistant to neutrophil anti-tumor responses and suppresses neutrophil function, a finding that can be leveraged for the development of novel immunotherapeutic treatment options. To that end, these initial findings have been developed into several major themes:

Neutrophil impact on Bone Metastatic Prostate Cancer (Theme 1)

Previous analysis of ex vivo tumor-associated neutrophil (TANs; isolated from bone tumors) cytotoxicity revealed that the neutrophil anti-tumoral immune response diminishes as the tumor progresses yet does not switch to a pro-tumor response. In fact, bone tumor TANs were phenotypically altered by four weeks after tumor inoculation. We further identified that neutrophils target PCa androgen receptor expression through inhibition of STAT5.

Project 1 (Role of STAT5 in PCa progression and response to neutrophils):  STAT5 deletion renders PCa cells resistant to neutrophils whereas, exogenous STAT5 expression sensitizes PCa to neutrophil killing. Using bulk RNA sequencing of STAT5-regulated cells, we identified a STAT5-mediated pro-inflammatory response via IL-1-derived neutrophil activation and resultant PCa cell death. We are dissecting the connection between these two pathways that leads to neutrophil activation and cytotoxicity.

Project 2 (Role of Nox2, ROS and redox metabolism in BM-PCa): We identified that targeting PCa redox metabolism combined with neutrophil immunity significantly impairs androgen-insensitive PCa revealing a novel method for targeting bone metastatic castration-resistant PCa. With this project, we will: 1) examine the importance of Nox2 signaling in PCa survival and progression, 2) interrogate Nox2 as a novel therapeutic target for targeting BM-PCa and 3) define its role in PCa resistance to neutrophils.

Prostate Cancer regulation of Neutrophil Function (Theme 2)

Project 3 (Androgen-mediated regulation of neutrophils):  We found that androgen-deprivation therapy (ADT) suppresses bone marrow neutrophil cytotoxicity via increased neutrophil gene expression of the serine-threonine kinase transforming growth factor beta receptor 1 (TβR1). Thus, we hypothesized that anti-tumor neutrophils are suppressed/“switched off” by androgen regulation via TβR1 signaling and this can be leveraged to improve mCRPC outcomes. We are working to define the mechanisms of this phenomenon.

Project 4 (Defining how neutrophils kill prostate cancer cells):  This project will  expand upon key findings that direct cell-cell contact is required for neutrophil-induced death of cancer cells, including prostate, breast, and pancreatic cancer. To investigate these interactions further, we’re performing live cell imaging of prostate cancer cell and neutrophil co-culture with: 1) manipulated STAT5 expression, 2) TβR1 receptor knockout (or wildtype) neutrophils and 3) exogenous manipulation of various granule enzymes and cytokines.

Role of Neutrophils and MSCs in Cancer-induced bone disease (Theme 3)

Project 5 (Characterizing IL-8 regulation of MSCs and PCa-induced osteogenesis):  A major difficulty in treating bone metastatic disease is the impact of cancer cells on surrounding bone stroma, which results in debilitating bone disease and what has been characterized as a “vicious cycle” of tumor progression in bone. Our preliminary data suggests that PCa induces MSC expression of IL8 as a mechanism to induce bone remodeling and we are examining how this change impacts osteogenesis and the role of neutrophils in tumor-induced osteogenesis.