Structure-based screening combined with computational and biochemical analyses identified the inhibitor targeting the binding of DNA Ligase 1 to UHRF1.

The accumulation of epigenetic alterations is one of the major causes of tumorigenesis. Aberrant DNA methylation patterns cause genome instability and silencing of tumor suppressor genes in various types of tumors. Therefore, drugs that target DNA methylation-regulating factors have great potential for cancer therapy. Ubiquitin-like containing PHD and RING finger domain 1 (UHRF1) is an essential factor for DNA methylation maintenance. UHRF1 is overexpressed in various cancer cells and down-regulation of UHRF1 in these cells reactivates the expression of tumor suppressor genes, thus UHRF1 is a promising target for cancer therapy. We have previously shown that interaction between the tandem Tudor domain (TTD) of UHRF1 and DNA ligase 1 (LIG1) di/trimethylated on Lys126 plays a key role in the recruitment of UHRF1 to replication sites and replication-coupled DNA methylation maintenance. An arginine binding cavity (Arg-binding cavity) of the TTD is essential for LIG1 interaction, thus the development of inhibitors that target the Arg-binding cavity could potentially repress UHRF1 function in cancer cells. To develop such an inhibitor, we performed in silico screening using not only static but also dynamic metrics based on all-atom molecular dynamics simulations, resulting in efficient identification of 5-amino-2,4-dimethylpyridine (5A-DMP) as a novel TTD-binding compound. Crystal structure of the TTD in complex with 5A-DMP revealed that the compound stably bound to the Arg-binding cavity of the TTD. Furthermore, 5A-DMP inhibits the full-length UHRF1:LIG1 interaction in Xenopus egg extracts. Our study uncovers a UHRF1 inhibitor which can be the basis of future experiments for cancer therapy.

Traditional Chinese Medicine Curcumin Sensitizes Human Colon Cancer to Radiation by Altering the Expression of DNA Repair-related Genes.

BACKGROUND/AIM: The aim of the present study was to investigate the radio-sensitizing efficacy of curcumin, a traditional Chinese medicine (TCM) on colon cancer cells in vitro and in vivo. MATERIALS AND METHODS: Human colon cancer HT-29 cells were treated with curcumin (2.5 µM), irradiation (10 Gy) and the combination of irradiation and curcumin. Cell proliferation was assessed using the MTT assay. Apoptotic cells were detected by Annexin V-PE/7-AAD analysis. PCR was performed to determine differential-expression profiling of 95 DNA-repair genes in irradiated cells and cells treated with both irradiation and curcumin. Differentially-expressed genes were confirmed by Western blotting. In vivo radio-sensitizing efficacy of curcumin was assessed in a xenograft mouse model of HT-29 colon cancer. Curcumin was administrated daily by intraperitoneal injection at 20 mg/kg/dose. Mice received irradiation (10 Gy) twice weekly. Apoptosis of the cancer cells following treatment was determined by TUNEL staining. RESULTS: Irradiation induced proliferation inhibition and apoptosis of HT-29 cells in vitro. Concurrent curcumin treatment sensitized the HT-29 tumor to irradiation (p<0.01). DNA repair-related genes CCNH and XRCC5 were upregulated and LIG4 and PNKP downregulated by the combination of curcumin and irradiation compared with irradiation alone (p<0.05). Combined treatment of curcumin and irradiation resulted in a significantly greater tumor-growth inhibition and apoptosis compared to irradiation treatment alone (p<0.01). CONCLUSION: Curcumin sensitizes human colon cancer in vitro and in vivo to radiation. Downregulation of LIG4 and PNKP and upregulation of XRCC5 and CCNH DNA-repair-related genes were involved in the radio-sensitizing efficacy of curcumin in colon cancer.