OGT/CDK5/ACSS2 Axis Regulates Breast Cancer Brain Metastasis Growth.

Onset of brain metastases (BMs) in breast cancer patients is considered an end-stage event, with no effective drug treatment and a median survival after diagnosis measured in months. Thus, there is an urgent need to develop novel treatment strategies. Metastatic breast cancer cells colonizing the brain encounter adverse 'nutritional environment', as the levels of key metabolic fuels such as glucose are much lower, in part because they are avidly consumed by neurons. To overcome this challenge, brain-metastatic cancer cells rely on acetate as a fuel source and convert it into acetyl-CoA via upregulation of acetyl-CoA synthetase 2 (ACSS2) enzyme. We have previously shown that brain tumors increase the nutrient sensing post-translational modification O-GlcNAcylation and O-GlcNAc transferase (OGT) levels to regulate acetate metabolism into acetyl-CoA via increased phosphorylation of ACSS2 on Ser-267 in a cyclin dependent kinase 5 (CDK5)-dependent manner, increasing brain tumor growth. Here, we show that human breast cancer cells selected to metastasize to the brain contain increased levels of O-GlcNAc, OGT and ACSS2-Ser267 phosphorylation compared to parental cells and show that human breast cancer brain metastatic patient samples contain elevated ACSS2-Ser-267 levels. Moreover, overexpression of OGT or ACSS2-S267D phospho-mimetic mutant confer a growth advantage on brain metastatic breast cancer cells in an in vivo intracranial xenograft model, may be due to an increase in lipogenic proteins. Additionally, we show that pharmacologically targeting CDK5 and ACSS2 with small molecule inhibitors reduces tumor growth in a novel orthotopic ex vivo brain slice model. These results suggest a crucial role for OGT/CDK5/ACSS2 signaling in transducing nutritional state to regulate acetate metabolism in breast cancer BM cells and identify CDK5 and ACSS2 as novel therapeutic targets for treatment of breast cancer brain metastasis.