APEX1 and neoplasm: Consistent with our observation that acetylation significantly increased endonuclease activity of APE1 (Figure 5A & 5B), extracts of NSCLC tissue samples showed significantly enhanced AP site cleavage activity with respect to matched non-tumor control when tissue extracts with equivalent amount of APE1 were used in in vitro cleavage assay (Figure 5C & 5D; Supplementary Figure S5B).