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Elucidating a role for uracil DNA glycosylase (UNG)-initiated DNA base excision repair in the cellular sensitivity to the antifolate, pemetrexed

Weeks, Lachelle Dawn
http://rave.ohiolink.edu/etdc/view?acc_num=case1386198769

Abstract Details

2014, Doctor of Philosophy, Case Western Reserve University, Pathology.
Antifolates are among the oldest anti-cancer chemotherapeutic agents. Despite decades of research, precise mechanisms of antifolate-mediated cell death remain ill defined. Natural and acquired resistance limits the application and effectiveness of antifolate regimens. In an effort to identify novel molecular targets for improving antifolate efficacy in anti-cancer protocols, I have implicated uracil DNA glycosylase (UNG) initiated base excision repair (BER) as a critical determinant of cellular sensitivity to the multi-target antifolate, pemetrexed. Genomic uracil incorporation is a consequence of pemetrexed inhibition of enzymes involved in the de novo biosynthesis of thymidine nucleotides. Once incorporated into DNA, uracil is removed by UNG to initiate BER. Here, I report that UNG induction–driven in part by c-Myc transcriptional activation of the UNG promoter–contributes to pemetrexed resistance by rapidly and efficiently removing uracil from DNA (AIM 1). Subsequently, using in vitro and in vivo models of UNG deficiency data show that loss of UNG expression sensitizes cells to pemetrexed through a mechanism involving uracil-DNA induced replication fork collapse, DNA double strand break formation and cell death (AIM 2). Moreover, systematic analysis of human lung cancer cells has identified UNG as a novel predictive biomarker of pemetrexed sensitivity in experimental models (AIM 3). Importantly, these data show that in the absence of functional UNG/BER, pemetrexed treatment results in the toxic accumulation of uracil (UNG loss) or the persistence of clastogenic repair intermediates (inhibition of downstream BER). These data therefore rationalize the development of existing and novel BER inhibitors for therapeutic use in combination with pemetrexed and other antifolates (AIM 4). These findings clarify the genotoxic nature of uracil misincorporation and provide clear evidence that the amount of genomic uracil and thus, a cell’s capacity for UNG-initiated BER is a critical determinant of cellular sensitivity to pemetrexed. In highlighting the importance of UNG-initiated BER in the response to pemetrexed, this work provides a solid foundation for future studies, which seek to confirm a role for UNG as both a predictive biomarker and as a novel chemotherapeutic target to enhance clinical response to pemetrexed chemotherapy regimens.
Stanton Gerson, MD (Advisor)
Shigemi Matsuyama, PhD (Committee Chair)
Alexandru Almasan, PhD (Committee Member)
Ruth Keri, PhD (Committee Member)
George Stark, PhD (Committee Member)
Pathology
uracil DNA glycosylase; pemetrexed; antifolates; chemotherapy; DNA repair; base excision repair

Recommended Citations

Citations

  • Weeks, L. D. (2014). Elucidating a role for uracil DNA glycosylase (UNG)-initiated DNA base excision repair in the cellular sensitivity to the antifolate, pemetrexed [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1386198769

    APA Style (7th edition)

  • Weeks, Lachelle. Elucidating a role for uracil DNA glycosylase (UNG)-initiated DNA base excision repair in the cellular sensitivity to the antifolate, pemetrexed. 2014. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1386198769.

    MLA Style (8th edition)

  • Weeks, Lachelle. "Elucidating a role for uracil DNA glycosylase (UNG)-initiated DNA base excision repair in the cellular sensitivity to the antifolate, pemetrexed." Doctoral dissertation, Case Western Reserve University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1386198769

    Chicago Manual of Style (17th edition)

case1386198769
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© 2013, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.