Author ORCID Identifier
https://orcid.org/0009-0004-5409-5276
Date of Graduation
5-2026
Document Type
Thesis (MS)
Program Affiliation
Biomedical Sciences
Degree Name
Masters of Science (MS)
Advisor/Committee Chair
Dung-Fang Lee
Committee Member
Hui-Wen Lo
Committee Member
Catherine Denicourt
Committee Member
Yoshihiro Komatsu
Committee Member
Tae Jin Lee
Abstract
Breast cancer is the most diagnosed cancer in American women, and breast cancer brain metastasis (BCBM) exhibits the worst prognoses with a life-expectancy averaging at 6 months. This short life expectancy is largely attributed to the lack of effective treatment. Many challenges remain unsolved, including the limited number of actionable targets for targeted therapy and effective blood-brain barrier (BBB) permeable drugs that are safe without promoting drug resistance. Therefore, there is an urgent call for identification of novel therapeutic targets and development of BBB-permeable drugs. One of the potential targets identified by our lab for BCBM targeted therapy is the Rearranged during Transfection (RET) receptor tyrosine kinase. Recent studies from our lab reported overexpression of RET in BCBM and RET monotherapy significantly suppressed BCBM incidences in mouse models but did not significantly reduce the progression of established BCBM. Thus, in this study, we aimed to identify potential secondary pathways contributing to the observed resistance to RET monotherapy. Through pathway correlation analysis of publicly available breast cancer patient datasets, Truncated Glioma-Associated Oncogene Homolog 1 (tGLI1) activation signature was identified to be positively correlated with RET activation signature. tGLI1 is an alternatively spliced, gain-of-function variant of the GLI1 transcription factor that is overexpressed in and promotes BCBM. In previous studies conducted by our lab, immunohistochemical staining of matched primary and BCBM patient tumors showed concurrent elevation in RET activation and tGLI1 expression in over 80% of BCBM tumor samples. Western blot analysis also suggested increased levels of activated RET and tGLI1expressions in brain-tropic breast cancer cell lines compared to parental counter parts. Building these observations, we hypothesized that there is a potential functional crosstalk between RET and tGLI1 in mediating BCBM progression and co-targeting RET and tGLI1 with FDA-approved orally active BBB-permeable inhibitors overcomes the RET monotherapy resistance and synergistically inhibits BCBM. We observed that mining of patient-derived datasets indicated significantly higher RET and tGLI1 co-activation in breast cancer patients with brain metastasis and the co-activation is associated with worse survival. In vitro cell proliferation assays using tGLI1-overexpressing BCBM sublines demonstrated increased resistance to RET inhibitor Pralsetinib. tGLI1 knockdown in BCBM sublines increased sensitivity of the cell lines to Pralsetinib. Pralsetinib in combination with tGLI1 inhibitor Ketoconazole and with WF-229A, a novel Ketoconazole derivative developed by our lab to counter potential liver toxicity due to potent CYP3A4 inhibition by Ketoconazole, yielded synergistic inhibition on BCBM cell viability, induced significantly higher apoptosis, and inhibited metastasis-related malignant phenotypes including tumor migration, invasion, and stemness in vitro. Together, we report tGLI1 as an important mechanism underlying BCBM resistance to RET monotherapy and targeting tGLI1 sensitizes resistant BCBM to RET inhibition.
Recommended Citation
Cha, Joshua, "Targeting Breast Cancer Brain Metastasis Through Novel Combination of FDA-Approved Orally Active Blood-Brain Barrier Permeable RET and tGLI1 Inhibitors" (2026). Dissertations & Theses (Open Access). 1525.
https://digitalcommons.library.tmc.edu/utgsbs_dissertations/1525
Keywords
Breast cancer, brain metastasis, breast cancer brain metastasis, BCBM, RET, tGLI1, targeted therapy, combination therapy, UTHealth Houston