Epigenetic priming improves salvage chemotherapy in diffuse large B-cell lymphoma via endogenous retrovirus-induced cGAS-STING activation

(2023) 15:75 Liu et al. Clinical Epigenetics https://doi.org/10.1186/s13148-023-01493-x Clinical Epigenetics Open Access RESEARCH Epigenetic priming improves salvage chemotherapy in diffuse large B‑cell lymphoma via endogenous retrovirus‑induced cGAS‑STING activation Jun Liu1,2,3,4, Suji Min2, Dongchan Kim2,4, Jihyun Park2,4, Eunchae Park2,4, Youngil Koh2,4,5,6, Dong‑Yeop Shin2,4,5,6, Tae Kon Kim7, Ja Min Byun2,4,5,6, Sung‑Soo Yoon2,4,5,6 and Junshik Hong2,4,5,6* Abstract Background Although most patients with diffuse large B-cell lymphoma (DLBCL) achieve complete remission after first-line rituximab-containing immunochemotherapy, up to 40% of patients relapse and require salvage therapy. Among those patients, a substantial proportion remain refractory to salvage therapy due to insufficient efficacy or intolerance of toxicities. A hypomethylating agent, 5-azacytidine, showed a chemosensitizing effect when primed before chemotherapy in lymphoma cell lines and newly diagnosed DLBCL patients. However, its potential to improve outcomes of salvage chemotherapy in DLBCL has not been investigated. Results In this study, we demonstrated the mechanism of 5-azacytidine priming as a chemosensitizer in a platinumbased salvage regimen. This chemosensitizing effect was associated with endogenous retrovirus (ERV)-induced viral mimicry responses via the cGAS-STING axis. We found deficiency of cGAS impaired the chemosensitizing effect of 5-azacytidine. Furthermore, combining vitamin C and 5-azacytidine to synergistically activate STING could be a poten‑ tial remedy for insufficient priming induced by 5-azacytidine alone. Conclusions Taken together, the chemosensitizing effect of 5-azacytidine could be exploited to overcome the limitations of the current platinum-containing salvage chemotherapy in DLBCL and the status of cGAS-STING has the potential to predict the efficacy of 5-azacytidine priming. Keywords DLBCL, 5-Azacytidine, ERVs, STING, Cisplatin *Correspondence: Junshik Hong 1 College of Medicine, Zhejiang University, Hangzhou, China 2 Center for Medical Innovation, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Republic of Korea 3 Liangzhu Laboratory, Zhejiang University Medical Center, Hangzhou, China 4 Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea 5 Department of Internal Medicine, Seoul National University Hospital, Seoul National University College of Medicine, 101 Daehak‑ro, Jongno‑gu, Seoul 03080, Republic of Korea 6 Biomedical Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea 7 Division of Hematology/Oncology, Department of Internal Medicine, Vanderbilt University Medical Center, Nashville, TN, USA © The Author(s) 2023. 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The Creative Commons Public Domain Dedication waiver (http://creativeco mmons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Liu et al. Clinical Epigenetics (2023) 15:75 Background Diffuse large B-cell lymphoma (DLBCL) is the most common histologic subtype of non-Hodgkin lymphoma (NHL) [1]. Approximately 60–70% of patients with DLBCL achieve complete remission with first-line regimens, such as rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) [2]. However, up to 40% of patients have disease relapse or are refractory to their initial therapy [3]. For those patients, salvage chemotherapy is required, but the majority of patients succumb to their disease or require high-dose chemotherapy with autologous stem cell transplantation (ASCT) because of the limited efficacy of salvage treatment [4]. Newer treatment strategies including targeting B-cell surface antigen CD79 and chimeric antigen T-cell (CAR-T) therapy improved outcomes of those relapsed or refractory DLBCL patients [5, 6]. Polatuzumab vedotin, a monoclonal antibody-drug conjugate targeting CD79, received Food and Drug Agency approval in combination with bendamustine and rituximab (pola-BR), based on an open label clinical trial which showed superior response rate of pola-BR compared to BR [7]. However, the benefit of pola-BR was demonstrated only in transplantineligible patients. In addition, extra-ordinary costs make the wider use of CAR-T difficult. Thus, salvage chemotherapy followed by autologous hematopoietic cell support is still the mainstay of the second chance for cure in relapsed or refractory DLBCL patients. However, salvage chemotherapy and high-dose chemotherapy inevitably cause substantial toxicities, especially in elderly or frail patients who cannot tolerate these regimens [8]. Therefore, potentiating the effect of chemotherapy without significant toxicities is required. Epigenetic modulators, such as hypomethylating agents, have been used to treat patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). The mechanism of action underlying the clinical efficacy of 5-azacytidine remains to be elucidated [9]. To date, most of the focus on the mechanisms of action of DNA methyltransferases inhibitor (DNMTi) has been on the reversal of acquired aberrant DNA methylation of tumor suppressor; however, interest has now switched to the role of activation of endogenously methylated sequences such as the cancer–testis antigens (CTAs) and ERVs [10]. Previous data have suggested 5-azacytidinemediated irreversible inactivation of DNA methyltransferases (DNMTs) followed by restoration of aberrantly methylated tumor suppressor genes (TSGs) as a major mechanism [11]. However, global DNA demethylation by 5-azacytidine is not correlated with clinical objective response [12]. More recently, it has been reported that low-dose 5-azacytidine and its deoxy derivative, decitabine (also known as 5-aza-2’-deoxycytidine), mediate Page 2 of 18 double-stranded RNA (dsRNA) formation, which activates the pattern recognition receptor MDA5 [13]. Specifically, low-dose 5-azacytidine treatment reactivates previous epigenetic silencing of ERV element expression in the human genome. The activated ERV eleme (...truncated)