Abstract LB-245: Multiple DNA-damage response pathways are modulated by RANBP9 protein in NSCLC

Non-small cell lung cancer (NSCLC) is the most prominent cause of cancer-related deaths in the world. The most indicated treatment for over 50% of NSCLC patients is represented by platinum-based chemotherapy. These compounds exert their biological effects by inducing DNA damages. Differently from normal cells, cancer cells frequently display a defective DNA Damage Response (DDR), which results in cancer cell death upon treatment with DNA-damaging agents. However, cancer cells up-regulate specific DDR mechanisms to cope with genotoxic stress, leading to resistance to conventional chemotherapies. For these reasons, a better understanding of cellular DDR mechanisms in tumors might help to identify 1) biomarkers predictive of DNA-repair defects and 2) targeted agents to inhibit tumor specific DNA-repair pathways. We have previously demonstrated that RANBP9 is a new phosphorylation target and signaling facilitator of ATM, one of the most important kinases in DDR. We have recently shown that RANBP9 is upregulated in lung cancer vs normal adjacent tissues, and its protein levels correlate with tumor stage. Importantly, low RANBP9 levels were associated to enhanced progression free survival and overall survival upon treatment with platinum-based compounds, in a cohort of more than 130 NSCLC patients. To gain molecular insights in the role of RANBP9 in DDR and sensitivity to genotoxic stress, we generated NSCLC cell lines where its expression was abrogated by CRISPR/Cas9. These models confirmed that absence of RANBP9 results in enhanced therapeutic effects of cisplatin and reduced activation of ATM-dependent DDR. Notably, we also observed that RANBP9 abrogation resulted in increased levels of polyADP-ribosylated chromatin proteins, without affecting total levels of poly(ADP-ribose) polymerase 1 (PARP1), another critical mediator of DDR. Conversely, we found reduced levels of PAR-glycohydrolase (PARG), a negative regulator of nuclear PAR levels, in response DNA-damaging agents. Based on these results, we hypothesized that RANBP9 levels could dictate the preferential DDR mechanism activated by lung cancer cells in response to genotoxic stress. Accordingly, preliminary evidences show that RANBP9-negative cells (PARP-dependent) display higher sensitivity to PARP inhibition. On the other hand, RANBP9-positive cells (ATM-dependent) are more sensitive to ATM inhbition. In summary, our study suggests that RANBP9 could act both as a positive and as a negative regulator of different mechanisms of DDR. These findings pave the way to clinical studies where RANBP9 levels could be used to inform the choice of the most effective genotoxic therapy and prevent resistance. Citation Format: Anna Tessari, Kareesma Parbhoo, Meghan Pawlikowski, Matteo Fassan, Eliana Rulli, Claudia Foray, Alessandra Fabbri, Valerio Embrione, Monica Ganzinelli, Marina Capece, Massimo Broggini, Gabriella Farina, Mirko Marabese, Marina C. Garassino, Carlo Croce, Dario Palmieri, Vincenzo Coppola. Multiple DNA-damage response pathways are modulated by RANBP9 protein in NSCLC [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 LB-245.