Abstract 1598: Epigenetic priming using azacitidine improves cisplatin response in diffuse large B-cell lymphoma cell lines via endogenous retroviruses induced viral mimicry

Abstract Background and purpose Although majority of patients with diffuse large B-cell lymphoma (DLBCL) achieve and complete remission after first-line rituximab-CHOP, up to 40% of patients undergo disease relapse. For those patients, salvage chemotherapy is required, but it has limitations in terms of severe toxicity and insufficient response, an area of unmet needs. In a previous study (Clozel et al, 2013 Cancer Discov), a hypomethylating agent azacitidine, which has been used to treat patients with myelodysplastic syndromes and acute myeloid leukemia, showed a chemo-sensitization effect when primed before cytotoxic chemotherapy in lymphoma cell lines and newly diagnosed DLBCL patients. However, its detailed mechanism and potential to improve outcomes in salvage chemotherapy has not been investigated. In this study, we tried to elucidate the effect of azacitidine as a chemo-sensitizer in cisplatin-included salvage regimen, and its mechanism of action, including viral defense mechanism via endogenous retrovirus (ERV) elements. Methods Six DLBCL cell lines with different cisplatin sensitivity were used in this study. Low dose (0.3 µM) azacitidine was pre-treated to each cell line for epigenetic priming for three consecutive days. Cells with or without azacitidine primming were harvested for RNA sequencing and MBD-sequencing. At the same time, different doses of cisplatin were treated to these pre-treated cell lines for 48 hours to determine their cisplatin sensitivity after epigenetic priming with azacitidine. Results The clinically achievable cisplatin dose was up to 5 µM calculated, reflecting the plasma level of cisplatin in DLBCL patients receiving 80mg/m2 of cisplatin via intravenous injection. OCI-LY1, SU-DHL2, and SU-DHL8 showed IC50 greater than 5 µM and they were defined as cisplatin-resistant cell lines while the other 3 cell lines (OCI-LY3, OCI-LY19, and Toledo) were regarded as cisplatin-sensitive cell lines. Intriguingly, pre-treatment of azacitidine could partially reverse the cisplatin resistance in the three cisplatin-resistant cell lines. Of these, SU-DHL8 showed the remarkably highest restoration of cisplatin response with an IC50 dropped to a similar level with cisplatin-sensitive cell lines. ERVs including MLT1B, ERVL, MER4D and ERV9_1 and viral defense genes including DDX58, IFI6, IFI27 and IFIT2 were upregulated only in SU-DHL8 with azacitidine primming. Consistently, Western blotting results showed that NF-κB pathway was also only activated in SU-DHL8 cells. Conclusion Epigenetic priming using azacitidine could potentially improve the cisplatin response in DLBCL patients. This effect may be attributed to ERV-induced viral mimicry and DNA demethylation. In some of the re-sensitized DLBCL cell lines, the former probably plays a dominant role. Citation Format: Jun Liu, Junshik Hong, Sungsoo Yoon. Epigenetic priming using azacitidine improves cisplatin response in diffuse large B-cell lymphoma cell lines via endogenous retroviruses induced viral mimicry [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1598.