XRCC1 siRNA constructs.

<p>XRCC1 siRNA constructs.</p

Clonogenic survival assays for CH cells treated with cisplatin alone or in combination with NU6027 is shown here (A).

<p>X-axis designates increasing concentration of cisplatin only. NU6027 was fixed at 4 µM. <b>B.</b> XRCC1 deficient CH cells accumulate significantly higher γH2AX foci compared to XRCC1 proficient CH cells upon cisplatin treatment alone or a combination of cisplatin and NU6027. Data represent mean values ±SEM (n = 6). Results were analysed using Students t-test. * p<0.05, ** p<0.01. <b>C.</b> FITC-Annexin V apoptosis assay is shown here. The proportion of cells in early phase as well as late phase apoptosis is higher in XRCC1 deficient cells treated with cisplatin alone or a combination of cisplatin and NU6027 compared to wild type cells.</p

FACS read out in CH cells treated with 24 hours of NU6027 is shown here (A).

<p><b>B.</b> Quantification of various phases of the cell cycle is shown for CH cell treated with NU6027. Data represent mean values ±SEM (n = 6). Results were analysed using Students t-test. * p<0.05. <b>C.</b> FITC-Annexin V apoptosis assay is shown here. The proportion of cells in early phase apoptosis is higher in XRCC1 deficient cells treated with NU6027 compared to wild type cells.</p

Clonogenic survival assays for siRNA transfected OVCAR-3 cells treated with cisplatin alone or in combination with NU6027 is shown here (A).

<p><b>B.</b> XRCC1 deficient cells accumulate significantly higher γH2AX foci compared to XRCC1 proficient cells upon cisplatin treatment alone or a combination of cisplatin and NU6027. Data represent mean values ±SEM (n = 6). Results were analysed using Students t-test. * p<0.05, ** p<0.01. <b>C.</b> FITC-Annexin V apoptosis assay is shown here. The proportion of cells in late phase apoptosis is higher in XRCC1 deficient cells treated with cisplatin alone or a combination of cisplatin and NU6027 compared to wild type cells.</p

Western blot analysis in chinese hamster (CH) cells (CHO9, EM-C11, EM-C12) (A).

<p>Clonogenic survival assays for CH cells treated with NU6027 <b>(B)</b> and VE-821 <b>(C)</b> at indicated concentrations (see methods for details). <b>D.</b> Clonogenic survival assays for EM9-V and EM9-XH cells treated with NU6027. <b>E.</b> Alkaline COMET assay in CH cells treated with NU6027. EM-C11 and EM-C12 demonstrated a higher mean tail moment compared to CHO9 cells. <b>F.</b> EM-C11 and EM-C12 cells accumulate significantly higher γH2AX foci compared to CHO9 cells upon NU6027 treatment. Data represent mean values ±SEM (n = 6). Results were analysed using Students t-test. * p<0.05.</p

Western blot analysis in siRNA transfected OVCAR-3 cells is shown here (A).

<p><b>B.</b> Clonogenic survival assays for siRNA transfected OVCAR-3 cells treated with NU6027 at indicated concentrations is shown here (see methods for details). <b>C.</b> XRCC1 deficient cells accumulate significantly higher γH2AX foci compared to scrambled control cells upon NU6027 treatment. Data represent mean values ±SEM (n = 6). Results were analysed using Students t-test. * p<0.05, ** p<0.01. <b>D.</b> Quantification of various phases of the cell cycle is shown for siRNA transfected OVCAR-3 cell treated with NU6027 is shown here. Data represent mean values ±SEM (n = 3). Results were analysed using Students t-test. * p<0.05. <b>E.</b> FITC-Annexin V apoptosis assay for siRNA transfected OVCAR-3 cells is shown here. The proportion of cells in late phase apoptosis is higher in XRCC1 deficient cells treated with NU6027 compared to scrambled control cells.</p

Ataxia telangiectasia mutated and Rad3 related (ATR) protein kinase inhibition is synthetically lethal in XRCC1 deficient ovarian cancer cells

Introduction Ataxia telangiectasia mutated and Rad3 Related (ATR) protein kinase is a key sensor of single-stranded DNA associated with stalled replication forks and repair intermediates generated during DNA repair. XRCC1 is a critical enzyme in single strand break repair and base excision repair. XRCC1-LIG3 complex is also an important contributor to the ligation step of the nucleotide excision repair response. Methods In the current study, we investigated synthetic lethality in XRCC1 deficient and XRCC1 proficient Chinese Hamster ovary (CHO) and human ovarian cancer cells using ATR inhibitors (NU6027). In addition, we also investigated the ability of ATR inhibitors to potentiate cisplatin cytotoxicity in XRCC1 deficient and XRCC1 proficient CHO and human cancer cells. Clonogenic assays, alkaline COMET assays, γH2AX immunocytochemistry, FACS for cell cycle as well as FITC-annexin V flow cytometric analysis were performed. Results ATR inhibition is synthetically lethal in XRCC1 deficient cells as evidenced by increased cytotoxicity, accumulation of double strand DNA breaks, G2/M cell cycle arrest and increased apoptosis. Compared to cisplatin alone, combination of cisplatin and ATR inhibitor results in enhanced cytotoxicity in XRCC1 deficient cells compared to XRCC1 proficient cells. Conclusions Our data provides evidence that ATR inhibition is suitable for synthetic lethality application and cisplatin chemopotentiation in XRCC1 deficient ovarian cancer cell