This investigation was aimed to see whether PJ34TM, a PARP inhibitor, could exert cytotoxicity in six nonsmall cell lung cancer cell lines developed from surgically resected tissues. Using various biochemical assays, we have seen that PJ34TM effects are consistent between untreated and treated samples but still somewhat variable between each cell line. Changes in protein expression and mitochondrial membrane potential between treated and untreated cells were indicating the possibility of apoptosis induction through an intrinsic pathway which causes cytotoxicity. Present results open the possibility of elucidating a decisive mechanism and effectiveness of chemotherapeutics specific to a patient.
We have tested PJ34, a potent inhibitor of poly(ADP-ribose) polymerase (PARP), against various lung cancer cell lines (Calu-6, A549, and H460) and normal human bronchial epithelial cells (HBECs). While using WST1 dye assay, lung cancer cells exhibited LD(50) values of approximately 30 μM PJ34 (72-hr assay). Molecular data showed that the effect of PJ34-induced apoptosis on lung cancer cells occurs via a caspase-dependent pathway. The present study has clearly shown that (a) PARP inhibitor can independently kill tumor cells, (b) caspase-3 has modest influence on PARP-inhibitor-mediated cancer-specific toxicity, and (c) a pan-caspase inhibitor decreases the apoptotic effect of PJ34.
Abstract Considering the fact that lung cancer has a high incidental rate among all cancer types, our investigation was aimed to see if PJ34, a PARP inhibitor, could independently exert cytotoxicity in primary lung cancer cells. In the past this PARP inhibitor has been used in combination with other DNA targeted chemotherapeutics or in patients with DNA repair defects (e.g. BRCA mutation), however, based on our published findings we hypothesize that PJ34 can target lung cancer using alternative mechanisms where defects in DNA repair or synthetic lethality are not required. Additionally, we wanted to reveal the specific mechanisms of PARP inhibitor mediated cytotoxicity in lung cancer cells. Anti-cancerous effects of PJ34 were evaluated on six non-small cell lung cancer cell lines developed from surgically resected tissue. Using WST-1 dye and BrdU assay, 30uM (ED50) of PJ34 treatment showed a variable amount of cell survival and DNA synthesis among cultures used herein. Cellular morphological changes in response to the PJ34 treatment were investigated using annexin-V expression, nuclear fragmentation staining, and PARP specific protein in Western blot. Mitochondrial membrane potential changes were measured through JC-1 dye staining and indicated increased stress upon PJ34 treatment. The abundance of Caspase-9 further proves the role of mitochondrial stress in PJ34 treated cells. Immunofluorescent staining for Caspase-3 clearly showed changes towards apoptosis under PJ34 treated vs. untreated conditions. Additionally, a Caspase-3 specific protein band in PJ34 treated cells indicates the possibility of apoptosis through a caspase dependent pathway. Furthermore, lower expressions of PAR in PJ34 treated cells were indicative of PARP inhibition. This study has brought a new paradigm for using PJ34 as a potential therapeutic against lung cancer because of its ability to work regardless of a patient's genetic makeup as well as the possibility of using this group of compounds as independent chemotherapeutic agents. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 257. doi:1538-7445.AM2012-257
