Sensitization to radiation and alkylating agents by inhibitors of poly (ADP-ribose) polymerase is enhanced in cells deficient in DNA double-strand break repair

DA Löser, A Shibata, AK Shibata, LJ Woodbine… - Molecular cancer …, 2010 - AACR
DA Löser, A Shibata, AK Shibata, LJ Woodbine, PA Jeggo, AJ Chalmers
Molecular cancer therapeutics, 2010AACR
As single agents, chemical inhibitors of poly (ADP-ribose) polymerase (PARP) are nontoxic
and have clinical efficacy against BRCA1-and BRCA2-deficient tumors. PARP inhibitors also
enhance the cytotoxicity of ionizing radiation and alkylating agents but will only improve
clinical outcomes if tumor sensitization exceeds effects on normal tissues. It is unclear how
tumor DNA repair proficiency affects the degree of sensitization. We have previously shown
that the radiosensitizing effect of PARP inhibition requires DNA replication and will therefore …
Abstract
As single agents, chemical inhibitors of poly(ADP-ribose) polymerase (PARP) are nontoxic and have clinical efficacy against BRCA1- and BRCA2-deficient tumors. PARP inhibitors also enhance the cytotoxicity of ionizing radiation and alkylating agents but will only improve clinical outcomes if tumor sensitization exceeds effects on normal tissues. It is unclear how tumor DNA repair proficiency affects the degree of sensitization. We have previously shown that the radiosensitizing effect of PARP inhibition requires DNA replication and will therefore affect rapidly proliferating tumors more than normal tissues. Because many tumors exhibit defective DNA repair, we investigated the impact of double-strand break (DSB) repair integrity on the sensitizing effects of the PARP inhibitor olaparib. Sensitization to ionizing radiation and the alkylating agent methylmethane sulfonate was enhanced in DSB repair–deficient cells. In Artemis−/− and ATM−/− mouse embryo fibroblasts, sensitization was replication dependent and associated with defective repair of replication-associated damage. Radiosensitization of Ligase IV−/− mouse embryo fibroblasts was independent of DNA replication and is explained by inhibition of "alternative" end joining. After methylmethane sulfonate treatment, PARP inhibition promoted replication-independent accumulation of DSB, repair of which required Ligase IV. Our findings predict that the sensitizing effects of PARP inhibitors will be more pronounced in rapidly dividing and/or DNA repair defective tumors than normal tissues and show their potential to enhance the therapeutic ratio achieved by conventional DNA-damaging agents. Mol Cancer Ther; 9(6); 1775–87. ©2010 AACR.
AACR