THE ROLE OF GLYCOGEN ACCUMULATION AND UTILIZATION IN METASTTIC BREAST CANCER PROGRESSION

Breast cancer is a significant public health concern being the second leading cause of cancer-related death in women, with a projected 43,250 deaths in the US in 2022. However, cancer progression to metastatic sites is the primary cause of death in breast cancer patients. A hallmark of cancer is the dysregulation of cellular metabolism. Cancer cells have the ability to hijack their metabolism and drive cellular processes supporting cancer progression. As cancer cells continue through the metastatic cascade, they are challenged with various bioenergetic processes that can be supported by the influx of glucose. Thus, altering glycogen accumulation, where glucose is stored in cells, may be beneficial in supporting cancer progression. In this study, we aim to determine what drives glycogen accumulation in metastatic cells and if it is utilized to support cancer progression. We employed the non-metastatic MCF10A-ras and the metastatic MCF10CA1a cells for these studies. Our results demonstrate that metastatic MCF10CA1a have 20-fold accumulation of glycogen compared to the MCF10A-ras cells. Utilizing 13C6-glucose flux analysis, surprisingly, most of the glucose incorporated into glycogen of the MCF10CA1a cells was in the M+5 glucose labeling pattern instead of the expected M+6 pattern which occurs when glucose is directly converted to glycogen. We showed that glycogen was accumulated due to increased gluconeogenesis through cataplerosis (PEPCK) utilizing inhibitors of the enzyme. Additionally, in a pulse-chase experiment using 13C6-glucose flux analysis, there was an approximate 50% reduction in labeled glucose in glycogen, 3 hours after removing the label, suggesting that the MCF10CA1a cells also have a rapid turnover of glycogen. Glucose can be released through two mechanisms, glycogenolysis or glycophagy. Utilizing siRNAs to a rate limiting steps in each pathway, results suggest both glycogenolysis (PYGL) and glycophagy (GAA) are necessary to support cell migration, a critical step in metastasis of the MCF10CA1a cells. Thus, glycogen metabolism is dysregulated in the MCF10CA1a breast cancer cells such that they have increased glycogen accumulation and that glycogen is required to support cell migration. Further understanding the mechanism by which glucose is accumulated and released in a specific cancer and in specific steps or stressors in cancer progression may contribute to potential therapeutic targets to help mitigate metastasis, and potentially breast cancer mortality.