Incorporation and Repair of Epigenetic Intermediates as Potential Chemotherapy Agents
The incorporation of nucleoside analogs into DNA by polymerases, followed by their removal through base excision repair (BER), represents a promising strategy for cancer chemotherapy. In this study, we investigated the incorporation and cytotoxic effects of several nucleoside analogs—some of which a...
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2025-08-01
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| author | Jason L. Herring Mark L. Sowers James W. Conrad Linda C. Hackfeld Bruce Chang-Gu Rahul Dilawari Lawrence C. Sowers |
| author_facet | Jason L. Herring Mark L. Sowers James W. Conrad Linda C. Hackfeld Bruce Chang-Gu Rahul Dilawari Lawrence C. Sowers |
| author_sort | Jason L. Herring |
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| description | The incorporation of nucleoside analogs into DNA by polymerases, followed by their removal through base excision repair (BER), represents a promising strategy for cancer chemotherapy. In this study, we investigated the incorporation and cytotoxic effects of several nucleoside analogs—some of which are epigenetic reprogramming intermediates—in the U87 glioblastoma cell line. We found that two analogs, 5-hydroxymethyl-2′-deoxyuridine (5HmdU) and trifluorothymidine (TFT), are both cytotoxic and are efficiently incorporated into genomic DNA. In contrast, the 5-carboxy analogs—5-carboxy-2′-deoxyuridine (5CadU) and 5-carboxycytidine (5CadC)—showed no cytotoxicity and were not incorporated into DNA. Interestingly, 5-hydroxymethyl-2′-deoxycytidine (5HmdC) was cytotoxic but was not directly incorporated into DNA. Instead, it was deaminated into 5HmdU, which was then incorporated and likely responsible for the observed toxicity. 5HmdU is actively removed from DNA through the BER pathways. In contrast, TFT remains stably incorporated and is neither excised by BER nor does it hydrolyze into 5CadU—a known substrate for the DNA glycosylase SMUG1. We also found that N<sup>6</sup>-benzyladenosine (BzAdo), an inhibitor of the enzyme 2′-deoxynucleoside 5′-phosphate N-hydrolase (DNPH1), enhances the cytotoxicity of 5HmdU. However, the thymidine phosphorylase inhibitor tipiracil hydrochloride (TPI) does not increase the cytotoxic effect of TFT in U87 cells. Together, these findings highlight 5HmdU and TFT as promising chemotherapeutic agents for glioblastoma, each with distinct mechanisms of action and cellular processing. |
| format | Article |
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| language | English |
| publishDate | 2025-08-01 |
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| spelling | doaj-art-3a9ff73997374ea4bc9f1a5e193a618e2025-08-20T03:36:22ZengMDPI AGMolecules1420-30492025-08-013015323910.3390/molecules30153239Incorporation and Repair of Epigenetic Intermediates as Potential Chemotherapy AgentsJason L. Herring0Mark L. Sowers1James W. Conrad2Linda C. Hackfeld3Bruce Chang-Gu4Rahul Dilawari5Lawrence C. Sowers6Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USADepartment of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USADepartment of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USADepartment of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USADepartment of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USADepartment of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USADepartment of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USAThe incorporation of nucleoside analogs into DNA by polymerases, followed by their removal through base excision repair (BER), represents a promising strategy for cancer chemotherapy. In this study, we investigated the incorporation and cytotoxic effects of several nucleoside analogs—some of which are epigenetic reprogramming intermediates—in the U87 glioblastoma cell line. We found that two analogs, 5-hydroxymethyl-2′-deoxyuridine (5HmdU) and trifluorothymidine (TFT), are both cytotoxic and are efficiently incorporated into genomic DNA. In contrast, the 5-carboxy analogs—5-carboxy-2′-deoxyuridine (5CadU) and 5-carboxycytidine (5CadC)—showed no cytotoxicity and were not incorporated into DNA. Interestingly, 5-hydroxymethyl-2′-deoxycytidine (5HmdC) was cytotoxic but was not directly incorporated into DNA. Instead, it was deaminated into 5HmdU, which was then incorporated and likely responsible for the observed toxicity. 5HmdU is actively removed from DNA through the BER pathways. In contrast, TFT remains stably incorporated and is neither excised by BER nor does it hydrolyze into 5CadU—a known substrate for the DNA glycosylase SMUG1. We also found that N<sup>6</sup>-benzyladenosine (BzAdo), an inhibitor of the enzyme 2′-deoxynucleoside 5′-phosphate N-hydrolase (DNPH1), enhances the cytotoxicity of 5HmdU. However, the thymidine phosphorylase inhibitor tipiracil hydrochloride (TPI) does not increase the cytotoxic effect of TFT in U87 cells. Together, these findings highlight 5HmdU and TFT as promising chemotherapeutic agents for glioblastoma, each with distinct mechanisms of action and cellular processing.https://www.mdpi.com/1420-3049/30/15/3239chemotherapyDNAglioblastomaepigenetic intermediatestrifluorothymidineTFT |
| spellingShingle | Jason L. Herring Mark L. Sowers James W. Conrad Linda C. Hackfeld Bruce Chang-Gu Rahul Dilawari Lawrence C. Sowers Incorporation and Repair of Epigenetic Intermediates as Potential Chemotherapy Agents Molecules chemotherapy DNA glioblastoma epigenetic intermediates trifluorothymidine TFT |
| title | Incorporation and Repair of Epigenetic Intermediates as Potential Chemotherapy Agents |
| title_full | Incorporation and Repair of Epigenetic Intermediates as Potential Chemotherapy Agents |
| title_fullStr | Incorporation and Repair of Epigenetic Intermediates as Potential Chemotherapy Agents |
| title_full_unstemmed | Incorporation and Repair of Epigenetic Intermediates as Potential Chemotherapy Agents |
| title_short | Incorporation and Repair of Epigenetic Intermediates as Potential Chemotherapy Agents |
| title_sort | incorporation and repair of epigenetic intermediates as potential chemotherapy agents |
| topic | chemotherapy DNA glioblastoma epigenetic intermediates trifluorothymidine TFT |
| url | https://www.mdpi.com/1420-3049/30/15/3239 |
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