Date Available

5-7-2021

Year of Publication

2021

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Medicine

Department/School/Program

Toxicology and Cancer Biology

Advisor

Dr. Christine Fillmore Brainson

Co-Director of Graduate Studies

Dr. Jill Kolesar

Abstract

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death worldwide, 85% of which are lung adenocarcinomas (LUAD). Although molecular studies of NSCLC identified targetable mutations of some oncogenes including BRAF, EGFR and ALK, no targeted therapies exist for most cases. Cancer epigenetics is the study of epigenetic modifications, including histone modifications, that control gene expression in cancer. Recent advances have revealed numerous epigenetic abnormalities in human cancers, and targeting epigenetic regulators could be effective at reversing dysregulated epigenetic programs or driving sensitivity to other targeted therapies.

Inhibitors of the histone methyltransferase EZH2 have recently been approved as single agents for specific solid tumors including lymphoma and sarcoma. In the first project, by using a genetic model to delete Ezh2 in KRAS-driven LUAD, we observed that Ezh2 haplo-insufficient tumors were less lethal and lower grade than Ezh2 full-insufficient tumors, which were poorly differentiated and metastatic. By using three-dimensional (3D) cultures and in vivo experiments, we identified that EZH2 deficient tumors were vulnerable to H3K27 demethylase and BET inhibitors. EZH2 and BET inhibitors also strongly synergized in human lung cancer cells. Mechanistically, EZH2 depletion led to de-repression of the embryonic transcription factor FOXP2, promoting stemness and migration. In human lung cancers, poorly differentiated tumors were enriched for an H3K27me3-low state. Together these data uncover the role of EZH2 activity in the aggressiveness of LUAD and suggest that EZH2 inhibitors will be most effective as low dose single therapies or in combination with drugs including BET inhibitors for LUAD. In the second project, we observed that the PIK3CA-mutant or amplified lung cancer cells were more sensitive to EZH2 inhibition. EZH2 inhibitor had combinatorial synergy with PI3K inhibitor in PIK3CA-mutant or amplified lung cancers both in vitro and in vivo. This study suggested a promising combination therapy in combating the LUAD with PIK3CA mutation or amplification.

Targeting the epidermal growth factor receptor (EGFR) with tyrosine kinase inhibitors (TKIs) is one of the major precision medicine options for LUAD. While first- and second-generation TKIs were plagued by development of drug resistance, third-generation inhibitors including osimertinib and rociletinib were developed. In the third project, we describe a model of EGFR driven lung cancer and a method to develop tumors of distinct epigenetic states through 3D organotypic cultures. We discovered that activation of EGFR T790M/L858R mutation in lung epithelial cells can drive lung cancers with alveolar or bronchiolar features, which can be originated from alveolar type 2 (AT2) cells or bronchioalveolar stem cells (BASCs), but not basal cells or club cells. We also demonstrated that these clones were able to retain their epigenetic differences through passaging orthotopically in mice, and crucially that they had distinct drug vulnerabilities. This work serves as a blueprint for exploring how epigenetics can be used to stratify patients for precision medicine decisions.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.114

Funding Information

This work was supported in part by National Cancer Institute K22 CA201036, Kentucky Lung Cancer Research Program, V Foundation Scholar Award, American Cancer Society Institutional Research Grant IRG-85-001-25, National Cancer Institute R01 CA237643, American Cancer Society Research Scholar Grant 133123-RSG-19-081-01-TBG and American Association for Cancer Research Innovation and Discovery Grant (CFB) from 2017 to 2021.

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