Download Targeting DNA Base Excision Repair (BER) For Synthetic Lethality

Name: Rebeka Sultana
Email: [email protected]
Thesis Title: Targeting DNA Base Excision Repair (BER) For Synthetic
Lethality
Home institution:
Dept. of Pharmacy
Stamford University Bangladesh
51, Siddeswari Road, Dhaka-1217, Bangladesh
Host institution:
Division of Cancer and Stem cells
School of Medicine, City Hospital Campus
University of Nottingham, UK
Thesis Abstract:
There is an urgent need for novel effective drug regimens for the treatment of cancer.
Current cytotoxic therapy strategies such as chemotherapy and radiotherapy suffer
from narrow therapeutic index and associated toxicities. Emergence of resistance to
such treatments is also a major problem that adversely impacts patient outcomes.
Therefore personalization of cancer therapy based on tumour biology is a high
priority. Synthetic lethality (SL) holds great promise for a personalized therapy
strategy. This phenomenon has been shown to occur between proteins involved in
DNA repair, with most work to date focused on the relationship between poly (ADPribose) polymerase and the BRCA proteins. In this thesis, I intended to identify novel
synthetic lethal relationships among different members of DNA repair proteins.
Firstly, I have evaluated synthetic lethality between APE1 (human apurinic
endonuclease 1) and DNA double strand break (DSB) repair proteins (BRCA and
ATM). To investigate this, I used APE1 inhibitors in a panel of DSB repair deficient
and proficient Chinese hamster (CH) cells and human cancer cells. I also tested for SL
in CH cells expressing a dominant-negative form of APE1 (ED8 cells) using ATM
(Ataxia telangiectasia mutated) inhibitors and DNA-PKcs (DNA dependent protein
kinase catalytic subunit) inhibitors. I found that APE1 inhibitors are synthetically
lethal in BRCA and ATM deficient cells, resulting in accumulation of DNA DSBs
and G2-M cell cycle arrest. The data provides evidence that APE1 is a promising SL
target in cancer and that APE1 inhibitors could have significant translational clinical
applications in patients.
Secondly, I evaluated SL between XRCC1 (X-ray repair cross complementing gene 1)
and DNA damage response and signalling molecules (ATM and DNA-PKcs). A
panel of XRCC1 deficient and proficient Chinese hamster ovary (CHO) and human
breast cancer cell lines and ATM and DNA-PKcs inhibitors were used. ATM and
DNA-PKcs inhibitors were synthetically lethal in XRCC1-deficient cells as evidenced
by hypersensitivity to those inhibitors, accumulation of DNA DSBs, G2–M cell-cycle
arrest, and induction of apoptosis. This is the first study to show that XRCC1
deficiency could be exploited for a novel SL application in breast cancer by blocking
DSB repair using ATM and DNA-PKcs inhibitors.
Thirdly, I have evaluated SL between XRCC1 and ATR (Ataxia telangiectasia
mutated and Rad3 related) protein kinase using a XRCC1 deficient system and ATR
inhibitor. The study was conducted using a panel of CHO cells deficient and
proficient in XRCC1 as well as human ovarian cancer cell lines subjected to siRNA
knockdown of XRCC1. ATR inhibition is synthetically lethal in XRCC1 deficient
cells, as evidenced by increased cytotoxicity, accumulation of DNA DSBs, G2/M cell
cycle arrest and increased apoptosis. I also examined cisplatin chemo potentiation
using ATR inhibitor. Compared to cisplatin alone, combination of cisplatin and ATR
inhibitor results in enhanced cytotoxicity in XRCC1 deficient cells compared to
XRCC1 proficient cells. The data provides evidence that ATR inhibition may be
suitable for SL applications and cisplatin chemo potentiation in XRCC1 deficient
cells.