New insights into PARP inhibitors' effect on cell cycle and homology-directed DNA damage repair.
In preclinical and clinical studies, olaparib and veliparib are the most represented PARP inhibitors (PARPi), which mainly target homologous DNA damage repair pathway-deficient cancer cells. Their off-target effects are not fully understood, especially with regard to cell cycle and homology-directed DNA damage repair. Our objective was to comparatively evaluate olaparib and veliparib in this context and correlate our findings with their therapeutic potential. We used a well-established direct repeat GFP (DR-GFP) reporter assay in U2OS(DR-GFP) and H1299(DR-GFP) cells and measured DNA damage repair activity upon drug treatment. Olaparib-treated U2OS(DR-GFP) cells showed a dramatic decrease in DNA damage repair versus veliparib irrespective of inhibitory potency. We demonstrate that this effect was a result of olaparib's strong effect on the cell cycle. Unlike in veliparib-treated U2OS(DR-GFP) cells, in olaparib-treated cells S-phase decreased and G(2)-phase increased sharply, indicating a G(2)-phase arrest-like state and replicative stress. This was further confirmed by upregulation of p53 and p21 and accumulation of cyclin A. Lack of the same effect in p53-null H1299(DR-GFP) cells suggested that olaparib's effect is p53 related, which was confirmed in p53-depleted U2OS(DR-GFP) and p53-null HCT116 cells. Importantly, we also demonstrate that olaparib, but not veliparib, induced a robust phosphorylation of Chk1, a crucial component of the replicative stress response pathway. Our data show olaparib and veliparib differ in their off-target effects; olaparib, unlike veliparib, mitigates DNA damage repair activity via G(2) cell-cycle arrest-like effect in a p53-dependent manner. These off-target effects may add to PARPis' anticancer properties.
Authors' Affiliation: Gynecology Service, Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, New York.
Petar
P
Jelinic
Authors' Affiliation: Gynecology Service, Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, New York gynbreast@mskcc.org.
Douglas A
DA
Levine
D001562:Benzimidazoles / Q000008:administration & dosage*; D002453:Cell Cycle / Q000187:drug effects*; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D058990:Molecular Targeted Therapy; D010793:Phthalazines / Q000008:administration & dosage*; D010879:Piperazines / Q000008:administration & dosage*; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors
D001562:Benzimidazoles; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C521013:veliparib; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; C531550:olaparib