In vitro and in vivo enhancement of chemoradiation using the oral PARP inhibitor ABT-888 in colorectal cancer cells

Int J Radiat Oncol Biol Phys. 2013 Jul 1;86(3):469-76. doi: 10.1016/j.ijrobp.2013.02.015. Epub 2013 Mar 26.


Purpose: Poly(ADP-ribose) polymerase plays a critical role in the recognition and repair of DNA single-strand breaks and double-strand breaks (DSBs). ABT-888 is an orally available inhibitor of this enzyme. This study seeks to evaluate the use of ABT-888 combined with chemotherapy and radiation therapy (RT) in colorectal carcinoma models.

Methods and materials: RT clonogenic assays were performed on HCT116 and HT29 cells treated with 5-fluorouracil, irinotecan, or oxaliplatin with or without ABT. The surviving fraction at 2 Gy and dose-modifying factor at 10% survival were analyzed. Synergism was assessed by isobologram analysis for combination therapies. γH2AX and neutral comet assays were performed to assess the effect of therapy on DSB formation/repair. In vivo assessments were made by use of HCT116 cells in a xenograft mouse model. Tumor growth delay was measured at a volume of 500 mm(3).

Results: Both lines were radiosensitized by ABT alone, and ABT further increased chemotherapy dose-modifying factors to the 1.6 to 1.8 range. All combinations were synergistic (combination indices <0.9). ABT treatment significantly increased DSB after RT (γH2AX, 69% vs 43%; P=.017) and delayed repair. We found tumor growth delays of 7.22 days for RT; 11.90 days for RT and ABT; 13.5 days for oxaliplatin, RT, and ABT; 14.17 days for 5-fluorouracil, RT, and ABT; and 23.81 days for irinotecan, RT, and ABT.

Conclusion: ABT-888 radiosensitizes at similar or higher levels compared with classic chemotherapies and acts synergistically with these chemotherapies to enhance RT effects. In vivo confirmation of these results indicates a potential role for combining its use with existing chemoradiation regimens.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / therapeutic use
  • Benzimidazoles / therapeutic use*
  • Camptothecin / analogs & derivatives
  • Camptothecin / therapeutic use
  • Chemoradiotherapy / methods*
  • Colorectal Neoplasms / enzymology
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / pathology
  • Colorectal Neoplasms / therapy*
  • Comet Assay / methods
  • DNA Damage
  • Female
  • Fluorouracil / therapeutic use
  • HCT116 Cells
  • HT29 Cells
  • Histones / analysis
  • Humans
  • Irinotecan
  • Mice
  • Mice, Nude
  • Neoplasm Proteins / antagonists & inhibitors*
  • Organoplatinum Compounds / therapeutic use
  • Oxaliplatin
  • Poly(ADP-ribose) Polymerase Inhibitors*
  • Tumor Burden
  • Xenograft Model Antitumor Assays


  • Antineoplastic Agents
  • Benzimidazoles
  • H2AX protein, human
  • Histones
  • Neoplasm Proteins
  • Organoplatinum Compounds
  • Poly(ADP-ribose) Polymerase Inhibitors
  • veliparib
  • Oxaliplatin
  • Irinotecan
  • Fluorouracil
  • Camptothecin