Date of Presentation
5-5-2022 12:00 AM
College
School of Osteopathic Medicine
Poster Abstract
Human uracil DNA glycosylase (UNG2) is responsible for removing uracil bases from DNA and initiates base excision repair pathways. Accumulation of uracil or its fluorinated analogs in DNA is one of the killing mechanisms of thymidylate synthase (TS) inhibitors in cancer cells, and depletion of UNG2 often enhances the toxicity of these anticancer drugs. We tested the effect of UNG2 KO on the efficacy of multiple TS inhibitors (5-fluorouracil, fluorodeoxyuridine, and pemetrexed) and we determined that, except for 5-fluorouracil, all other TS inhibitors were significantly more potent in UNG2 KO cells compared to wild-type HT29 cells. Interestingly, UNG2 protein levels can also be depleted by the HDAC inhibitors SAHA and MS275, providing a pharmacologic strategy to reduce UNG2 activity in cells. Unexpectedly, the HDAC inhibitors synergized with 5-fluorouracil but not fluorodeoxyuridine in both wild-type and UNG2-knockout cells. Similarly, HDAC inhibitors synergized with pemetrexed in wild-type HT29 but not UNG2-knockout cells. This suggested that HDAC inhibitors sensitized cells to 5-fluorouracil through an UNG2-independent mechanism. Interestingly, SAHA depleted the UNG2 level, whereas TS inhibitors alone and their combination with SAHA upregulated the level of UNG2 at 24 hours. This suggests HDAC inhibitors deplete UNG2 but, when combined with TS inhibitors, it did not affect UNG2, at least at a concentration of 100nM. Our future aim is to study these pharmacological drug combinations targeting UNG2 activity in cells and elucidate exact mechanisms of cell death.
Keywords
Uracil-DNA Glycosidase, Thymidylate Synthase, Histone Deacetylase Inhibitors, Cell Death, Combination Drug Therapy, Colorectal Neoplasms
Disciplines
Enzymes and Coenzymes | Laboratory and Basic Science Research | Medical Molecular Biology | Medicine and Health Sciences | Molecular Biology | Neoplasms
Document Type
Poster
Included in
Enzymes and Coenzymes Commons, Laboratory and Basic Science Research Commons, Medical Molecular Biology Commons, Molecular Biology Commons, Neoplasms Commons
Effect of Uracil DNA Glycosylase Activity on the Efficacy of Thymidylate Synthase Inhibitor/HDAC Inhibitor Combination Therapies in Colon Cancer
Human uracil DNA glycosylase (UNG2) is responsible for removing uracil bases from DNA and initiates base excision repair pathways. Accumulation of uracil or its fluorinated analogs in DNA is one of the killing mechanisms of thymidylate synthase (TS) inhibitors in cancer cells, and depletion of UNG2 often enhances the toxicity of these anticancer drugs. We tested the effect of UNG2 KO on the efficacy of multiple TS inhibitors (5-fluorouracil, fluorodeoxyuridine, and pemetrexed) and we determined that, except for 5-fluorouracil, all other TS inhibitors were significantly more potent in UNG2 KO cells compared to wild-type HT29 cells. Interestingly, UNG2 protein levels can also be depleted by the HDAC inhibitors SAHA and MS275, providing a pharmacologic strategy to reduce UNG2 activity in cells. Unexpectedly, the HDAC inhibitors synergized with 5-fluorouracil but not fluorodeoxyuridine in both wild-type and UNG2-knockout cells. Similarly, HDAC inhibitors synergized with pemetrexed in wild-type HT29 but not UNG2-knockout cells. This suggested that HDAC inhibitors sensitized cells to 5-fluorouracil through an UNG2-independent mechanism. Interestingly, SAHA depleted the UNG2 level, whereas TS inhibitors alone and their combination with SAHA upregulated the level of UNG2 at 24 hours. This suggests HDAC inhibitors deplete UNG2 but, when combined with TS inhibitors, it did not affect UNG2, at least at a concentration of 100nM. Our future aim is to study these pharmacological drug combinations targeting UNG2 activity in cells and elucidate exact mechanisms of cell death.