Cancer cells possess multiple mechanisms to suppress the cytotoxic effects of DNA-damaging chemotherapeutic drugs that limit their effectiveness with concomitant increases in the mutational burden to all tissues. This added genomic instability is expected to select for chemoresistant cancer cells and foster secondary tumor formation. Since DNA alkylating agents comprise a significant portion of the available chemotherapeutic drugs, knowledge of the spectrum of biologically relevant DNA lesions that are created during therapy and the biological processing of these adducts is critical for the design of more effective treatments. For alkylating agents such as temozolomide, thioTEPA, and nitrogen mustards, the most abundant lesion is formed at N7-guanine, with less abundant, but biologically active lesions forming elsewhere. A similar spectrum of DNA lesions is also formed from exposures to environmental toxicants that have known cancer etiologies. The imidazole portion of N7-alkylated guanines can undergo base-induced ring-opening, yielding stable alkyl-formamidopyrimidine (N5-substituted-Fapy) lesions. The central hypothesis of this program project is that the role of Fapy-dG lesions in modulating genotoxic responses has been overlooked and that the Fapy-dG lesions contribute substantially to the biology associated with the DNA damaging agents. A major reason why Fapy lesions have been under-studied has been an inability to prepare DNAs containing them for biological, biochemical, and structural studies. Insights gained from our multidisciplinary, interdependent approaches will yield fundamental and applied understanding of 1) the identities of stable alkyl-Fapy-dG adducts and their detection in cellular DNA, 2) routes of chemical synthesis for the production and characterization of adduct-containing DNAs, 3) structural understanding of how these modified DNAs not only alter the structure of DNA, but also interface with DNA repair and replication enzymes, and 4) the biological processing of these DNAs by various repair systems to limit cytotoxicity and mutagenesis, or replication bypass to promote damage tolerance and survival, while increasing mutagenesis.

Public Health Relevance

Understanding how exposures to specific DNA alkylating agents contribute to the etiology of cancer, including the development of resistance to chemotherapeutic regimens. Translational endpoints are the identification of chemical functionality that may modulate DNA repair and replication, or facilitate secondary chemistry such as formation of DNA interstrand cross-links. The work should also translate into the identification of new biomarkers of exposure and targets for adjuvant cancer chemotherapy.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Program Projects (P01)
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Special Emphasis Panel (ZCA1-RPRB-O (M1))
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Okano, Paul
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Vanderbilt University Medical Center
Schools of Medicine
United States
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Patra, Amritraj; Politica, Dustin A; Chatterjee, Arindom et al. (2016) Mechanism of Error-Free Bypass of the Environmental Carcinogen N-(2'-Deoxyguanosin-8-yl)-3-aminobenzanthrone Adduct by Human DNA Polymerase η. Chembiochem 17:2033-2037
O'Flaherty, D K; Patra, A; Su, Y et al. (2016) Lesion Orientation of O(4)-Alkylthymidine Influences Replication by Human DNA Polymerase η. Chem Sci 7:4896-4904
Choi, Jeong-Yun; Patra, Amritaj; Yeom, Mina et al. (2016) Kinetic and Structural Impact of Metal Ions and Genetic Variations on Human DNA Polymerase ι. J Biol Chem 291:21063-21073
Egli, Martin (2016) Diffraction Techniques in Structural Biology. Curr Protoc Nucleic Acid Chem 65:7.13.1-7.13.41
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Patra, Amritraj; Su, Yan; Zhang, Qianqian et al. (2016) Structural and Kinetic Analysis of Miscoding Opposite the DNA Adduct 1,N6-Ethenodeoxyadenosine by Human Translesion DNA Polymerase η. J Biol Chem 291:14134-45
Su, Yan; Egli, Martin; Guengerich, F Peter (2016) Mechanism of Ribonucleotide Incorporation by Human DNA Polymerase η. J Biol Chem 291:3747-56
Thiaville, Jennifer J; Kellner, Stefanie M; Yuan, Yifeng et al. (2016) Novel genomic island modifies DNA with 7-deazaguanine derivatives. Proc Natl Acad Sci U S A 113:E1452-9
Patra, Amitraj; Zhang, Qianqian; Guengerich, F Peter et al. (2016) Mechanisms of Insertion of dCTP and dTTP Opposite the DNA Lesion O6-Methyl-2'-deoxyguanosine by Human DNA Polymerase η. J Biol Chem 291:24304-24313
O'Flaherty, Derek K; Guengerich, F Peter; Egli, Martin et al. (2015) Backbone Flexibility Influences Nucleotide Incorporation by Human Translesion DNA Polymerase η opposite Intrastrand Cross-Linked DNA. Biochemistry 54:7449-56

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