Abstract

Introduction: Dihydroorotate dehydrogenase (DHODH) inhibitors hold a great potential for breast cancer treatment especially in combinatorial therapy due to their antitumour capability. Brequinar and teriflunomide, the two potent DHODH inhibitors, showed cell cycle arrest in several cancer cells. These inhibitors target DHODH, the key enzyme in the de novo pyrimidine biosynthesis pathway that generates nucleotides essential for cells to proliferate. While the treatment for breast cancer is closely associated with the molecular subtyping (ER/PR and HER2 receptors) that has major implications on the survival of breast cancer patients, yet, the effect on the distinct hormone receptor status by these inhibitors has not been fully investigated. Thus, this study aimed to investigate the differential effects of breast cancer subtypes on the phases of cell cycle preferentially arrested by DHODH inhibitors. Methods: Three breast cancer cell lines with different receptor status were selected to represent each subtype; namely the MCF-7 (ER/PR⁺/HER2^-), SKBR-3 (ER/PR^-/HER2⁺), MDAMB-231 (ER/PR^-/HER2^-, also referred to as triple negative) and one non-tumorigenic MCF-10A (ER/PR^-/HER2^-) cells. Cells were cultured and treated with variable concentrations of inhibitors. Cell cycle analysis was performed by staining with propidium iodide and examined through BD FACSCanto™ II and analysed using Flow Jo software. Results: Results showed that MCF-10A, MCF-7 and MDAMB-231 were arrested at G1/S phase of the cell cycle by both inhibitors. Meanwhile, SKBR-3, the only cell line with HER2⁺, did not exhibit any distinct cell cycle phase arrest between both inhibitors and the control. Conclusion: The present study showed that the phase of cell cycle arrested in DHODH inhibition in breast cancer is independent of the ER/PR status, but may depend on the HER2 status, a finding that warrants further analysis on other cell lines. 

Keywords: Breast cancer, DHODH, Brequinar, Teriflunomide, Receptor subtypes