Differential p53 signaling in response to 5-FU and Etoposide in modulating toxicity via DPYD and Chk2 in cancer therapy

Open Access
Gokare, Prashanth Ravishankar
Graduate Program:
Molecular Medicine
Doctor of Philosophy
Document Type:
Date of Defense:
November 15, 2017
Committee Members:
  • Wafik El-Deiry, Dissertation Advisor
  • Charles H Lang, Committee Chair
  • Rosalyn Bryson Irby, Committee Member
  • Jin-Ming Yang, Committee Member
  • Nelson Shu-Sang Yee, Outside Member
  • DPYD
  • p53
  • 5-FU
  • chemotherapeutic
  • toxicity
  • DNA damage
  • Chk2
  • etoposide
  • metabolism
Tp53 is a major transcription factor that controls a multitude of processes involved in the response to cellular stress. It plays a critical role in cell cycle arrest and/or apoptosis after DNA damage. p53 downstream effects can impact on cellular metabolism and these are increasingly becoming unraveled. The studies here in highlights previously unappreciated signaling by Tp53 that is relevant to toxicity and efficacy of chemotherapeutic agents. Nucleotide metabolism can influence malignant behavior and intrinsic resistance to cancer therapy. Alterations in pyrimidine metabolism are key to the mechanism of action of the chemotherapeutic antimetabolite 5-fluorouracil (5-FU). The initial study describes a novel role of p53 in controlling the rate-limiting enzyme in the pyrimidine catabolic pathway, dihydropyrimidine dehydrogenase (DPYD) and its effect on pharmacokinetics of and response to 5-FU. P53 binds to a p53 DNA-binding site (p53BS) downstream of the DPYD gene and reduces its expression at both the mRNA and protein level. The reduced expression of DPYD follows the inhibition of thymidylate synthase (TS) and is dependent on DNA-dependent protein kinase (DNA-PK) and Ataxia telangiectasia mutated (ATM) signaling. Overall this study highlights the regulation of DPYD and its implications on toxicity and efficacy of 5-FU. (Chk2) is a serine/threonine kinase that transduces DNA damage response (DDR) signals from the kinases ATM and to some extent also Ataxia Telangiectasia and Rad3-Related Protein (ATR). It plays a critical role in inducing cell death following radiation in a p53-dependent manner. However, the role of Chk2 in toxicity of chemotherapeutics is less well studied with regard to involvement of the ChK2-ATM-p53 pathway. Our experiments addressed the role of Chk2 in Dose Limiting toxicity (DLT) of Topisomearase II (TOP2) inhibitors. We found Chk2 mediates toxicity from TOP2 inhibitors but not with other classes of chemotherapeutics, both in-vitro and in-vivo. Functional screens identified NSC105171 as a novel Chk2 inhibitor. NSC105171 protected from DLT following Etoposide treatment. This study has implications for a potentially effective strategy to preventing DLT. Thus, we have identified a role for p53 in controlling nucleotide metabolism through repression of DPYD following DNA damage through the involvement of TS inhibition. The study highlights different responses to chemotherapeutic agents that signal through p53 activation. In the second study, we described targeting the ATM-Chk2 p53 pathway in the context of Topoisomerase 2 inhibition to preferentially limit toxicity. Depending on the nature and type of damage there appears to be a differential response mediated by p53. Taken together, this research explores ways in which p53 signaling and biology can be used to enhance efficacy and limit toxicity following specific chemotherapy treatments.