Lindsay Brubaker, MD

2022 Early Career Investigator Grant

University of Colorado – Denver
Targeting Chromobox 2 to Overcome Macrophage-induced Immune Suppression

Project Summary
High grade serous ovarian carcinoma (HGSOC) is the deadliest gynecologic malignancy, thus there is an urgent need to define novel treatment options and improve patient outcomes. Chromobox 2 (CBX2) is an important gene regulator and a component of a large protein complex, known as the polycomb repressor complex 1 (PRC1), which is critical to the development of different organs in the body. Increased CBX2 expression leads to poor survival in ovarian cancer patients and is directly responsible for cancer patients not responding well to chemotherapy. Beyond our existing work, little is known regarding the contribution of CBX2 to the cell make-up of the tumor and the impact on progression of disease. In HGSOC tumors, certain types of immune cells – known as tumor-associated macrophages – correlate with worse outcomes among patients. In prostate cancer, the protein complex PRC1 causes changes in the immune cells in and around the tumor, leading to a muted anti-tumor immune response. This is thought to occur because a secreted cytokine, CCL2, draws macrophages to the tumor. We have found that in HGSOC cells, if we inhibit CBX2 there is a decrease in the cytokine CCL2, raising the question of whether CBX2 may play a role in the influx of macrophages in the tumor. Given what we know about CBX2 and its role in ovarian cancer progression, we have worked with our biochemistry colleagues to develop a CBX2 inhibitor, which shows promise in initial laboratory studies. For the sake of this work, we hypothesize that CBX2 leads to increased expression of CCL2 in the tumor cells, which attracts macrophages to the tumor. This chain of events ultimately leads to a decrease in the anti-tumor immune reaction around the tumor and progression of disease. Conversely, we hypothesize that inhibiting CBX2 will enhance the tumor response to existing immune therapies that attempt to improve anti-tumor immune activity. We will answer these hypotheses in two aims. The first will focus on the relationship between CBX2, CCL2, and the macrophages that respond to CCL2 using both cell culture and mouse models, as well as both genetic inhibition of CBX2 and our CBX2 inhibitor. The second aim will use a mouse model of HGSOC to assess the impact of targeting macrophages and T cells, with and without our novel CBX2 inhibitor. We will comprehensively evaluate how these different therapy options change the immune cells around the tumor. Through this work we will not only define the relationship between CBX2, CCL2, and macrophages in ovarian cancer, but also attempt to improve immune-based therapies using our unique CBX2 inhibitor. As an early career physician-scientist under the mentorship of successful ovarian cancer biologist, Dr. Benjamin Bitler, and in collaboration with macrophage expert, Dr Siddhartha Mitra, we have the experience and drive to complete this work. I expect that the data gathered from the proposed studies will allow us to publish in a high-impact pre-clinical research publication. The research and publication will serve as a critical foundation for my independent career and lead to future clinical and basic science research awards.

Bio
Lindsay Brubaker, MD is an Assistant Professor in the Division of Gynecologic Oncology at the University of Colorado Anschutz Medical Campus. Dr. Brubaker completed her residency in Obstetrics and Gynecology at Stanford University, then moved to Denver, Colorado for Fellowship in Gynecologic Oncology. Upon graduation, she chose to join the University of Colorado Division of Gynecologic Oncology with the goal of providing exceptional clinical and surgical care, as well as building an independent research career focused on platinum resistant ovarian cancer. During her first year of fellowship Dr. Brubaker worked under the mentorship of ovarian cancer biologist, Dr. Benjamin Bitler, to identify drivers of high-grade serous carcinoma dissemination and progression. In the course of this work, she identified Chromobox 2 (CBX2), an epigenetic reader and a component of the polycomb repressor complex, as a regulator of disease progression and chemotherapy resistance. This work found that inhibition of CBX2 re-sensitizes high grade serous carcinoma to platinum therapy and more recently discovered that CBX2 overexpression in high grade serous carcinoma cells is sufficient to promote chemoresistance. Dr. Brubaker’s current focus is to define the impact of CBX2 modulation on the tumor microenvironment (TME) in high grade serous carcinoma. She will use innovative technology, including NanoString and Vectra Polaris multispectral immunohistochemistry, to define the TME with a focus on macrophage recruitment and differentiation. Once the TME is defined, Dr. Brubaker will use syngeneic mouse models to elucidate the role of CBX2 on the TME and explore the potential for CBX2 inhibition alone and in combination with existing immunotherapies. She is hopeful this work will pave the way to bring a CBX2 inhibitor to clinical trial. In addition to her translational endeavors, Dr. Brubaker has a variety of clinical research interests, including decision making in platinum resistant disease and creation of an institutional database of patients undergoing hyperthermic intraperitoneal chemotherapy as part of their treatment for ovarian cancer.