Abstract 2929: GC4419 enhances the response of non-small cell lung carcinoma cell lines to cisplatin and cisplatin plus radiation through a ROS-mediated pathway

Non-small cell lung carcinoma (NSCLC) is the primary cause of cancer-related death in the United States, with a five-year survival rate of only 8-10%. Current treatment methods for NSCLC aside from surgical resection, include platinum-based chemotherapy and chemo-radiation modalities. However, continued poor outcomes necessitate mechanisms to enhance the potency of current therapies but without increasing normal tissue morbidities. GC4419, a novel MnSOD mimetic that has shown promise in clinical trials as a radioprotective agent, may serve as a potential therapeutic adjuvant with these properties. Because MnSOD generates hydrogen peroxide, it can be hypothesized that supplementation of basal MnSOD levels using GC4419 could lead to lethal hydrogen peroxide formation in NSCLC cells and sub-lethal formation in normal cells following therapy-induced superoxide generation, due to differences in hydrogen peroxide metabolism. When H1299 and H460 cells were exposed to either cisplatin for 24h or cisplatin plus radiation, with or without GC4419, GC4419 synergistically decreased clonogenic survival in H460 and H1299 cells. Changes in ROS levels and cell death signatures were analyzed through flow cytometry and western blotting, respectively, following GC4419 treatment. GC4419 was found to reduce intracellular superoxide, increase intracellular hydrogen peroxide, and total cellular ROS in both H1299 and H460 cells, as well as induce early apoptosis. Specifically, across both cell lines, total cellular ROS and intracellular H 2 O 2 was increased with GC4419 treatment by 46% and 54% following cisplatin and platinum chemo-radiation respectively, while intracellular superoxide was decreased by 48% and 42%, respectively. Early apoptosis was also increased with GC4419 across both cell lines on average by 26% following cisplatin, and 34% following chemo-radiation. Furthermore, GC4419 increased PARP cleavage 24h following cisplatin in H460 and H1299 by 83% and 146% respectively, and by 60% and 38% respectively, following chemo-radiation. However, GC4419 did not enhance cellular response to gemcitabine, which unlike cisplatin, does not induce intracellular superoxide formation. To test whether the production of increased cellular H 2 O 2 via GC4419 superoxide dismutase activity was a potential mechanism for this enhanced toxicity, H1299 cells were engineered to express catalase on an inducible doxycycline promoter. In this cell line (H1299CAT), GC4419 enhancement of cytotoxicity was abrogated. Furthermore, in H1299CAT cells treated with GC4419 there was no change in PARP cleavage following either cisplatin or platinum chemo-radiation. As such, GC4419 has the potential to enhance the potency of platinum-based therapies without increasing normal tissue morbidities, leading to improved therapeutic outcomes and better quality of life for NSCLC patients. Citation Format: Ahneesh J. Mohanty, Brock J. Sishc, Kelly C. Falls, Collin D. Heer, Douglas R. Spitz, Michael D. Story. GC4419 enhances the response of non-small cell lung carcinoma cell lines to cisplatin and cisplatin plus radiation through a ROS-mediated pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2929.