PARP1 and colorectal carcinoma: High-performance liquid chromatography-mass spectrum (HPLC-MS) analyses in His-TOP1 expressing human colorectal carcinoma HCT116 cells also showed that PARP1 is enriched in His-TOP1 pulldown sample even in the absence of CPT (Supplementary Data 1), consistent with the fact that PARP1 and TOP1 are associated under unperturbed conditions22,34, and that PARP1 promptly PARylates TOP1-DPCs without the requirement for replication or transcription.