67P - PARP inhibition enhances cisplatin sensitivity in cervical cancer by modulating β-catenin signaling

Cisplatin (CDDP) is used in the treatment of locally advanced disease (FIGO stage IIB-IVA) as well recurrent/metastatic cervical cancer. However toxic side effects and acquired resistance limits its efficacy. Enhanced DNA repair is one of the mechanisms responsible for acquired cisplatin resistance. Poly(ADP-ribose) polymerase (PARP) inhibitors have been approved for treating BRCA mutated cancers like breast and ovary cancer, however, little is known about the therapeutic efficacy and mechanism of action of PARP inhibitors in non-BRCA cancer like cervical cancer, either as a single agent or in combination with cisplatin.Table: 67PCombined effect of PJ34 and CDDP on cisplatin sensitivity in cervical cancer cell linesTable: 67PCancer cell parameterOnly CDDP (10μM)Only PJ34 (10μM)CDDP(10μM) + PJ34(10μM)p value/fold differenceClonogenic formation fraction#0.23±0.08 (H) 0.31± 0.06 (S)0.67±0.09 (H) 0.65±0.01 (S)0.13±0.05 (H) 0.15±0.07 (S)* (H) * (S)Fold migration0.71±0.06 (H) 0.75±0.03 (S)0.89±0.07 (H) 0.99±0.08 (S)0.54±0.05 (H) 0.34±0.02 (S)** (H) * (S)Relative invasion43.4±2.25 (H) 47.9±7.07 (S)66.6±5.94 (H) 70.5±5.74 (S)15.8±2.81 (H) 23.4± 4.13 (S)** (H) ** (S)IC50 value##8.25μM (H) 10.8μM (S)31.5μM (H) 33.0μM (S)3.6μM (H) 3.4μM (S)2.29 fold 3.18 fold Effect of PARP-1 inhibition (PJ34/PARP-1siRNA) was determined in vitro on cell viability, apoptosis, cell cycle progression, proliferation, invasion and metastasis, clonogenecity and β-catenin signaling in cervical cancer cell lines HeLa and SiHa. Combination of CDDP with PJ34 or PARP-1 siRNA significantly reduced the cell proliferation and induced cell cycle arrest and apoptosis. Also, a significant decrease in cell survival as well as cell invasion and migration was observed as compared with either CDDP/PJ34 alone. The enhanced CDDP sensitivity by PARP-1 inhibition was determined to be due to inhibition of β-catenin signaling as shown by a decrease in MMP-2 activity, MMP-9, c-myc and cyclin-D1 expression upon treatment with PJ34 and PARP-1 siRNA. Our data provides experimental evidence on the contribution of PARP-1 inhibition in enhancing the cytotoxicity of CDDP in cervical cancer cells. We also present novel findings on the suppression of β-catenin and its downstream signaling components by PARP-1 inhibitor. #: 5μM of CDDP was used both alone and in combination with PJ34; ##: A gradient of CDDP from 0-15μM was used to evaluate the combined effect of PJ34 and CDDP on IC50 value of CDDP. p: *