Pilot: The Role of Glycogen Metabolism in Supporting Immunosuppressive TME

Metabolic reprogramming is one of the hallmarks of cancer. It has been known that metabolic reprogramming limits the development of an effective antitumor immune response. Despite notable improvements in colorectal cancer (CRC) treatment, the prognosis of patients with metastatic CRC (mCRC) remains poor, with a median overall survival of approximately 30 months. Immunotherapy such as immune checkpoint blockade (ICB) represents a novel therapeutic approach for a variety of cancers including mCRC with microsatellite instability-high (MSI-H). However, ICB therapy shows little or no clinical activity in approximately 95% of patients with microsatellite-stable (MSS) mCRC. Glycogen is a highly branched polymer of glucose that is used for the efficient storage and release of energy. Dysregulation of glycogen metabolism is integral to cancer cell proliferation and metastasis. Glycogen fuels a range of malignant phenotypes including proliferation and migration, and chemoresistance. Cancer associated fibroblasts (CAFs), the major component of tumor stromal cells, play a critical role in the tumor suppressive TME. However, the roles of glycogen metabolism in CAFs and the impact of altered glycogen metabolism on CAF-integrated TME is not known and represents a major gap in our understanding of the immunosuppressive TME. Our studies have shown that CAFs produce substantial amounts of glycogen from the exogenous glucose supplied. Moreover, In CAFs, the interaction with cancer cells supported glycogenolysis. Treatment of CAFs with conditional medium (CM) derived from human CRC cells resulted in activated glycogen metabolism as noted by elevated protein expression of glycogen synthase, glycogen phosphorylases PYGL and PYGB, and the increased expression of immunosuppressive cytokines and chemokines such as IL6 family members IL6, CLCF1, LIF and CXCL6 in CAFs. In addition, inhibition or knockdown of PYGL or PYGB significantly repressed CAF proliferation and reduced the expression of these cytokines and chemokines. Our studies suggest that glycogen metabolism is crucial for promoting CAF proliferation and tumor immunosuppressive cytokine production. Importantly, our findings suggest that targeting glycogen metabolism in CAFs will reprogram the immunosuppressive TME and may enhance the efficacy of immunotherapy for CRC. A better understanding of elevated glycogen metabolism in CAFs in the TME of CRCs will lead to improved therapeutic strategies to treat CRC. The central hypothesis for our proposal is that elevated glycogen metabolism contributes to proliferation and immunosuppressive functions of CAFs, reprogramming the CRC TME, which leads to ICB resistance and CRC progression. This hypothesis will be tested by accomplishing the following specific aims: (1) to understand the biological significance of glycogen metabolism in regulating CAF proliferation and functional potency in the TME of CRC; (2) to define the impact of targeting glycogen metabolism on the efficacy of ICB for CRC. Our proposed studies will investigate an innovative concept that glycogen metabolism is an essential component of CAF energy homeostasis that is required for supporting effective immunosuppressive functions of these cells, which leads to resistance to ICB and promotion of CRC progression. With this COBRE pilot award, we expect to see that glycogen metabolisms are crucial for CRC TME and resistance to ICB. We further postulate that inhibition of glycogenolysis will enhance the anti-proliferative effect of anti-PD-1 treatment. With these findings, we will generate an R01 grant proposal to further determine the role of glycogen metabolism in CRC progression which may facilitate more rational approaches for improving the efficacy of immunotherapies for patients with advanced CRC. The Biospecimen Procurement and Translational Pathology, Biostatistics and Bioinformatics, Metabolism Core, and Flow Cytometry and Immune Monitoring Shared Resource Facilities will be used in this project.