By Loren N. Delgadillo Llano, Carolina Brooks, Ella Schmidt

Faculty Mentor: Dr. Laura Sipe

Abstract

Triple-negative breast cancer (TNBC) is an aggressive subtype with a 66% five-year survival rate when it spreads to nearby structures or lymph nodes, emphasizing the need for better treatments. One strategy involves depriving TNBC cells of methionine, an essential amino acid cancer cell requires in large amounts. Methionine is converted into S-adenosylmethionine (SAM) a universal methyl donor in DNA methylation, a process where a methyl group is added to a DNA sequence. This process can silence tumor suppressor genes (TSGs) that typically inhibit uncontrolled cell growth via hypermethylation, high levels of DNA methylation. By restricting methionine (MetR), it may reactivate TSGs and slow cancer growth. In an experiment using E0771 TNBC cells, cells were treated with either 3% Methionine restriction (MetR) or complete media (CM). TNBC cells grown with MetR fail to proliferate, have a lower DNA methylation and have a higher TSG expression. We hypothesize that if DNA hypomethylation, low amounts of DNA methylation, is sufficient to induce the anti-proliferative effects of MetR, then by adding SAM will restore DNA methylation, suppress TSGs, and increase cell proliferation. E0771 TNBC cells were then also treated with varying SAM concentrations. Cell viability and fluorescent intensity over 48 hours was assessed via an MTT assay and florescent nuclear staining, respectively. Results showed that in CM, increasing SAM concentrations decreased cell viability and proliferation. While in MetR conditions, cell viability and proliferation increased as SAM concentrations increased. The response to increasing SAM concentrations implies that MetR cells may be able to utilize SAM effectively, but it also shows that the anti-proliferative effect MetR produces against cancer is due to DNA methylation. Some oncogenes in cancer cells are hypomethylated, which allows their aberrant expression. By supplementing with SAM—a universal methyl donor—these hypomethylated regions can become hypermethylated, leading to the silencing of oncogenes and contributing to reduced cell proliferation.