Author ORCID Identifier
https://orcid.org/0000-0003-2198-7441
Date of Graduation
5-2024
Document Type
Dissertation (PhD)
Program Affiliation
Cancer Biology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Powel H. Brown
Committee Member
Guang Peng
Committee Member
Khandan Keyomarsi
Committee Member
Stephanie S. Watowich
Committee Member
Xiang Zhang
Committee Member
Traver Hart
Abstract
Abstract
Background: Triple-negative breast cancer (TNBC) is the most malignant subtype of breast cancer, characterized by the absence of estrogen receptor (ER) and progesterone receptor (PR) expression, as well as the lack of overexpression of the human epidermal growth factor receptor 2 (HER2). Unlike ER-positive and HER2-positive tumors that can be treated with hormone therapy or HER2-targeted treatment, respectively, triple-negative breast cancer (TNBC) poses a challenge with limited treatment alternatives for affected women. The currently FDA-approved systemic regimens for TNBC patients remain as conventional chemotherapy and PARP inhibitors (only applicable for a subset of BRCA-mutated TNBC patients). Consequently, our focus has been on the exploration of innovative targeted therapies for TNBC. This study investigated the novel phosphatase, NUDT5, as a potential therapeutic target.
Methods: The mRNA expression levels of NUDT5 in breast cancers were determined using the TCGA and METABRIC (Curtis) datasets. NUDT5 ablation was accomplished through different methods, including siRNA, shRNA, and sgRNA, as well as by employing the small molecule inhibitor TH5427 to inhibit NUDT5. In vivo growth of triple-negative breast cancer (TNBC) was assessed using TNBC xenograft animal models following NUDT5 inhibition. A range of cell biological assays, such as proliferation, apoptosis, and cell death assays, were performed to assess the influence of NUDT5 loss or inhibition on triple-negative breast cancer (TNBC) cells. The effect of decreased NUDT5 on DNA was investigated by measuring oxidative DNA lesions, replication fork progression, and DNA damage response. To investigate the potential clinical applicability of the NUDT5 inhibitor for future clinical studies, in vitro doseresponse assays were utilized to assess the combined effect of a NUDT5 inhibitor with other conventional systemic therapies.
Results: In this thesis, I discovered the importance of an overexpressed phosphatase, NUDT5, in the regulation of oxidative DNA damage in triple-negative breast cancers. My findings revealed that the absence of NUDT5 resulted in the inhibited growth of TNBC both in vitro and in vivo. This growth suppression was not attributable to cell death but rather to a reduction in proliferation. The deficiency or inhibition of NUDT5 caused an elevation in 8-oxoG and ãH2AX lesions in DNA, along with a deceleration in DNA replication, ultimately hindering the process of cell proliferation. The small molecule inhibitor of NUDT5 exhibited synergistic effects with Doxorubicin and PARP inhibitors and also demonstrated, to a lesser extent, synergistic effects with Paclitaxel in suppressing the growth of triple-negative breast cancers in vitro.
Conclusions: NUDT5 plays a critical role in preventing oxidative DNA damage in TNBC cells. Loss or inhibition of NUDT5 suppressed the growth of TNBCs. The NUDT5 inhibitor displays synergistic and/or additive effects when combined with other systemic treatments for TNBCs. These biological and mechanistic studies provide a basic research foundation for the future development of NUDT5 inhibitors for the treatment of TNBC patients.
Keywords
Triple-negative breast cancer, Phosphatase, DNA damage, Oxidative stress