Abstract 5237: Optimizing multiple myeloma treatment approaches by elucidating tumor-stroma interactions in the bone marrow microenvironment

Multiple Myeloma (MM) is a plasma cell malignancy arising in the bone marrow. Despite advancements in therapies, this disease becomes refractory such that relapse and death is inevitable. Immune evasion and drug resistance are partly due to MM-osteoblast cell interactions in the bone marrow microenvironment (BME). We conducted complementary in-vitro and in-vivo studies, each providing insights that converge to a treatment-relevant hypothesis. Several human MM cell lines (MM.1S, U266, NCI-H929, L363) were co-cultured with osteoblasts for two days to assess proliferation in response to two proteasome inhibitors, bortezomib, and carfilzomib. Osteoblasts, represented by the hFOB fetal osteoblast-derived cell line, markedly enhanced MM cell growth and conferred significant chemoresistance determined by a luciferase-based viability assay. We then performed RNA sequencing of FACS-sorted MM.1S and hFOB cells following 1 day of coculture. We found a significant upregulation of Type I Interferon (IFN) signaling pathway target genes (e.g. IRF7, ISG15, p<0.001) in co-cultured MM.1S cells compared to MM.1S cells alone. Two pro-inflammatory chemokines, CXCL1 and CXCL8, were markedly increased in hFOB co-cultured cells compared to hFOB monocultures. A 9-fold increase of CXCL1 (p<0.0001) and CXCL8 (p<0.0001) was validated by qPCR and both chemokines were elevated in co-culture supernatants in a cytokine array. Parallel studies in vivo, using the 5TGM1 MM immunocompetent mouse model, revealed that low-dose decitabine (DAC), a DNA hypomethylating agent known to induce a Type I IFN response significantly reduced MM burden (p<0.0001) and prolonged survival by 9 days (p<0.001), compared to MM-bearing mice treated with PBS vehicle. From these two lines of work, we hypothesize that low-level IFN signaling, mediated by MM cell cross-talk with osteoblasts, is supportive of MM cell proliferation and survival, while hyper-induction of the IFN pathway by DAC may contribute to the therapeutic efficacy of this epigenetic-modifying agent, both alone and in combination with immunotherapies, such as immune checkpoint inhibitors. This postulated biphasic response to Type I IFN signaling in MM cells is consistent with prior reports from other experimental systems. Our findings highlight the utility of epigenetic therapy in MM and suggest that hyper-induction of IFN signaling in MM cells, which already have low-level activation of this pathway from their interactions with osteoblasts, should be further investigated as a therapeutic mechanism. Citation Format: Panteha Behboodi, Angelica Castano, Iriana Colorado, Mauricio Rigo, Martha Salas, Mariam Tariq, Woo Lee, Benjamin Tycko, Rena Feinman. Optimizing multiple myeloma treatment approaches by elucidating tumor-stroma interactions in the bone marrow microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5237.