Date of Award

January 2017

Document Type

Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Wendell G. Yarbrough

Abstract

5-azacytidine (5-aza) and its structural analog 5-aza-2’-deoxycytidine (decitabine) are demethylating agents currently used to treat myelodysplastic syndrome and acute myeloid leukemia. In addition to demethylating DNA, they are known to cause DNA damage and activate DNA damage response pathways, but our mechanistic understanding of these processes is incomplete. Given the unique epigenetic profile of human papilloma virus-associated (HPV+) head and neck squamous cell carcinoma (HNSCC), we sought to develop demethylation therapy as a novel, targeted treatment for this subset of cancer that has less morbidity than current treatments. We wanted to characterize the DNA damage and describe the mechanism of damage induced by 5-aza in these cells, as well as the cellular response and effect on metastatic potential in cells, xenograft models, and tumors from patients treated in a clinical trial at the Yale Cancer Center. By using pulsed-field gel electrophoresis, we found that demethylation treatment induces DNA double strand break formation exclusively in HPV+ head and neck cancer cells, and that these breaks depend on active transcription, replication, and expression of a known antiviral enzyme, apolipoprotein B mRNA editing enzyme catalytic polypeptide-like 3 (APOBEC3B). Furthermore, we found that demethylation therapy also reactivates p53, downregulates HPV genes, reduces the expression of matrix metalloproteinases, and reduces the metastatic potential in cells, xenograft models, and in patient tumors.

Comments

This thesis is restricted to Yale network users only. It will be made publicly available on 06/12/2019

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