Abstract 2567: Preclinical evaluation of Poly (ADP) Ribose Polymerase (PARP) enzyme inhibitor, ABT-888, in combination with cytotoxic agents in small cell lung cancer (SCLC)
Authors: Owonikoko Taofeek K. , Zhang Guojing , Yue Ping , Ramalingam Suresh , Khuri Fadlo , Sun Shi-Yong 
Published: June 2012

Abstract
The induction of DNA damage underlies the efficacy of cytotoxic chemotherapy agents for the treatment of SCLC. Poly (ADP) Ribose Polymerase (PARP) enzyme plays a key role in the cellular machinery responsible for DNA damage repair. Although inhibition of this enzyme using pharmacological inhibitor is postulated to enhance the cytotoxicity of DNA-damaging cytotoxic chemotherapy, this has not been previously studied in SCLC. The present work evaluated the interaction between ABT-888 and cytotoxic chemotherapy in SCLC.
A panel of SCLC cell lines (H146, H69, H187, H209, and H182) was employed for this work. Exponentially growing cells were treated by continuous exposure for 48-72 h to vehicle, ABT-888 and cytotoxic agents (cisplatin, carboplatin, etoposide) in the presence and absence of ABT-888. Surviving cell fraction and growth inhibition was determined using MTS assay. Sequence dependence interaction was assessed by alternating the sequence of administration of ABT-888 relative to the cytotoxic agents. Western blot assay was performed to assess for PARP inhibition, changes in markers of apoptosis (cleaved PARP and caspase), DNA damage (gamma-H2AX) and other DNA damage repair pathway proteins (ERCC1, DNA-PK, Ku80, ATM, ATR and BRCA1) under different treatment conditions. ABT-888 showed negligible cytotoxicity as a single agent. Co-administration of ABT-888 and chemotherapeutic agents resulted in enhanced cytotoxicity of cisplatin, carboplatin and to a lesser extent, etoposide, in a cell specific and dose-dependent manner. High concentrations (50uM) of ABT-888 produced up to 7-fold reduction in IC50 concentrations of cytotoxic agents while low concentration (5uM) of ABT-888 produced up to 2-fold reduction in IC50 concentrations. There was no sequence dependence interaction between ABT-888 and the cytotoxic agents. Time-course experiments showed down modulation of DNA protein kinase (DNA-PK) levels at 24 hours, which correlated with onset of apoptosis as assessed by PARP and caspase cleavage. Moreover, high basal expression of DNA-PK correlated with reduced potentiation of cytotoxicity by ABT-888 in H128 cell line. These results would support clinical evaluation of ABT-888 plus cytotoxic chemotherapy in patients with SCLC. Furthermore, DNA-PK level may serve as a predictive biomarker of efficacy of PARP inhibitor therapy. Our in vitro finding is currently being tested using in vivo animal model. (This work was supported through the Georgia Cancer Coalition Distinguished Scholar Award to TK Owonikoko, SS Ramalingam, FR Khuri and S Sun and the NIH/NCI Program Project P01 grant CA116676).
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2567. doi:10.1158/1538-7445.AM2011-2567