PNKP and malignant colon neoplasm: When low doses of curcumin (2.5 μΜ) were combined with radiation in human colon cancer HT-29 cells, a stronger inhibitory effect on cell proliferation was observed, due to modulation of expression of DNA repair-related genes, including Cyclin H (CCNH), DNA Ligase 4 (LIG4) and Polynucleotide Kinase 3′-Phosphatase (PNKP).