One-Carbon and Glucose Metabolism in Human Breast and Mouse Mammary Cancers

Breast cancer is a heterogeneous disease. Evaluation of biopsy specimens is essential to determining prognoses and treatment options for patients. Currently approximately 30% of breast cancer diagnoses are for Ductal Carcinoma In Situ (DCIS), a sub-type of breast cancer that is not life-threatening unless it progresses to Invasive Ductal Carcinoma (IDC). To date the relationship between DCIS and IDC is unknown. Therefore, the standard of care is to treat all DCIS as though it were high risk, placing an unnecessary burden on the health care system and the patient.;Metabolic pathways that import, catabolize and synthesize essential cellular components are required for cancer cell survival and proliferation and are often dysregulated. Current chemotherapeutics exploit this metabolic dysregulation and reprogramming. Methotrexate (MTX) and 5'-aza-deoxycytidine (ADC) are two drugs that modulate folate-mediated one-carbon (1-C) metabolism and epidemiological literature suggests that excess dietary folic acid intake may have an effect on 1-C metabolism and breast cancer progression. The increased glucose uptake of cancer cells is already exploited for imaging tumors in vivo. In addition to increased glucose uptake, cancer cells also metabolize glucose by aerobic glycolysis instead of oxidative phosphorylation, which causes them to have a more alkaline intracellular pH (pHi).;This dissertation examines folate and glucose metabolic pathways in cell and animal models of breast cancer: 1) to examine how perturbation of folate-mediated one-carbon (1-C) metabolism with drugs and folic acid may modulate breast cancer progression and 2) to distinguish between low and high risk DCIS based on how pre-cancer cells metabolize glucose.;Chapter 1 presents a review of the literature related to putative models of the relationship between DCIS and IDC, the impact of folate-mediated 1-C metabolism and glucose metabolism on cancer progression. Chapter 2 provides the hypotheses, specific aims and overview of the dissertation project.;Chapter 3 documents the effects of two small molecule inhibitor drugs: 5'-aza-deoxycytidine (ADC) and methotrexate (MTX) on MCF7 breast cancer cell survival, proliferation, migration, gene expression and gene-specific CpG methylation. ADC treatment was associated with decreased CpG promoter methylation and increased mRNA expression of the cancer testis antigens. MTX treatment was associated with an increase in cell migration, a phenotype associated with more invasive cancers.;Chapter 4 explores the effects of log fold increases in folic acid concentration on dihydrofolate reductase enzyme activity and on MCF7 cell survival, proliferation, migration, gene expression and gene-specific CpG methylation. Folic acid excess in cell culture impeded the reduction of 7,8-dihydrofolate to 5,6,7,8-tetrahydrofolate, the biologically active forms of the vitamin. Excess folic acid did not significantly affect DNA methylation but interestingly, the treatment increased cell migration just as MTX exposure did.;Chapter 5 investigates whether cells within pre-cancerous mammary tissue of a mouse model of DCIS (MINO model) metabolize glucose differently using pHi as a surrogate measure. While normal and tumor cells displayed relative metabolic homogeneity in how they metabolized glucose (normal via oxidative phosphorylation, tumor via aerobic glycolysis), the pre-cancer cells (MINO) separated into two groups MINO high (alkaline pHi, aerobic glycolysis of glucose) and MINO low (oxidative phosphorylation of glucose).;Finally, Chapter 6 presents a theoretical model for how glucose and excess folic acid may act synergistically to accelerate breast cancer progression, a summary of the data that supports this model, limitations of the data and future questions that need to be addressed.