Date of Award

January 2013

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Robert M. Weiss

Subject Area(s)

Molecular biology, Oncology, Surgery

Abstract

Chemoresistance is a common problem encountered by patients with advanced urothelial carcinoma. Recent studies have investigated the mechanisms of drug resistance in cancer, particularly agents of the DNA damage repair pathway. One major player in this pathway is Ataxia-Telangiectasia Mutated and Rad3-Related protein (ATR), a kinase that becomes activated during nuclear damage yielding a single-stranded DNA break. Due to the fact that many traditional chemotherapeutic agents induce cytotoxicity by initiating DNA damage, ATR is an attractive target for investigating the mechanism behind multidrug resistant urothelial carcinoma.

Using two bladder cancer cell lines, MMCR (a drug-resistant cell line) and RT4 (a non-resistant parental cell line) we were able to create resistance profiles using cytotoxicity assays, which further facilitated in characterizing the extent of cellular resistance to a number of chemotherapeutic agents traditionally used in the treatment of advanced urothelial carcinoma.

We hypothesized that knockdown of ATR expression via RNA interference alone would render cells unstable and induce apoptosis, in accordance with similar studies investigating the effects of downstream members of this signaling pathway. Furthermore, we also hypothesized that by blocking ATR signaling, the cell line would be unable to repair its DNA, rendering the cell line sensitive to other chemotherapeutic agents.

Contrary to the above hypotheses, ATR downregulation via siRNA appeared to increase the cell viability of the MMCR cells, and did not significantly increase the chemoresistance to mitomycin C and doxorubicin across the majority of our treatment arms. These findings, though in opposition to some very early studies regarding ATR expression and chemoresistance in a variety of cancer types, highlight the continued need for elucidation of the role that ATR plays in chemoresistance in urothelial carcinoma.

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