By Abigail Glenn

Faculty Mentor: Laura Sipe

Abstract

Triple negative breast cancer (TNBC) accounts for 10-15% of breast cancer incidences. These patients have a drastically lower survival rate compared to other breast cancers (1). TNBC lacks receptors for estrogen, progesterone, and HER2. This makes targeted therapies ineffective and limits treatment options to chemotherapy and radiation for most patients (1). As such, increasing the efficacy of chemotherapy is a research area of great importance. A possible mode for this is methionine restriction. Methionine is essential for redox balancing, protein synthesis, and methylation, especially in cancer cells as they perform these processes at high rates. Methionine restriction has been shown to decrease tumor size as well as reduce TNBC viability. In this study, the synergism of methionine restriction with the chemotherapies paclitaxel, 5-fluorouracil, and cisplatin was examined through cell viability and proliferation assays. MTT analysis indicates a lack of synergy between methionine restriction and both paclitaxel and 5-fluorouracil, however, synergy was observed with cisplatin. Methionine restriction reduces the IC50 of cisplatin compared to cisplatin in complete media; less chemotherapy is needed to reduce viability of TNBC during methionine restriction. The mechanism of cisplatin synergy with methionine restriction was further examined through distinction between proliferation and apoptosis. We explored the combination treatment’s effect on proliferation by examining cell cycle arrest. Cell cycle analysis indicates methionine restriction with cisplatin drives arrest in G1 phase at the S-phase checkpoint and decreases overall cell number. To determine if the decrease in cell number was due to decreasing proliferation or increasing cell death, we examined the extent of apoptosis with AOPI. Apoptosis analysis demonstrates combination treatment did not increase cell death compared to methionine restriction alone. To clarify the mode of cycle arrest, we rescued cell viability with N-acetyl cysteine (NAC), which is a precursor to the major antioxidant glutathione, but were only able to recover viability by 20%. This indicates synergy is not due to redox pathways alone. The mechanism of methionine restriction and cisplatin synergy, such as redox disruption or protein production, is of interest for future research.

1. American Cancer Society Medical and Editorial Content Team. “Triple-Negative Breast Cancer: Details, Diagnosis, and Signs.” Details, Diagnosis, and Signs | American Cancer Society, American Society of Cancer, 1 Mar. 2023, amp.cancer.org/cancer/types/breast-cancer/about/types-of-breast-cancer/triple-negative.html.