Abstract 2799: Multiple myeloma derived mitochondrial DAMPs induce a pro-inflammatory signature in the bone marrow microenvironment to promote pro-tumoral expansion
Authors: Jibril Aisha , Kumar Prakrit , Hellmich Charlotte , Moore Jamie A. , Mistry Jayna J. , Willimott Victoria , Bowles Kristian M. , Rushworth Stuart A. 
Published: July 2021

Abstract
Multiple myeloma (MM) is an incurable malignancy of antibody (Ig) secreting differentiated B cells (plasma cells) characterized by the accumulation and localization of tumor cells in the bone marrow microenvironment (BMM). Mitochondrial DNA (mtDNA) is a damage associated molecular pattern (DAMP), as the mitochondrial genome contains islands of unmethylated CpG nucleotide motifs that have been shown to activate and promote memory B cell proliferation and antibody secretion. Recent studies have indicated that mtDNA is elevated in the circulation of trauma and cancer patients. Here we investigate the functional purpose of elevated mtDNA within the BM microenvironment of MM.We hypothesize that multiple myeloma cells secrete mitochondrial DAMPs into the bone marrow microenvironment promoting a state of chronic inflammation that drives the progression and expansion of multiple myeloma. NSG immunocompromised mice engrafted with human MM1S myeloma cell line showed elevated levels of MM derived mtDNA in the serum, detected by real-time PCR. Next we engrafted C57BL/6 mice with murine 5TGM1 myeloma cell line to establish a syngeneic mouse model. Flow cytometry analysis of the haematopoietic stem and progenitor cell (HSPC) populations showed that 5TGM1 induced an inflammatory expansion of the stem cell niche To determine the role of mtDNA in HSPC expansion we treated C57BL/6 mice with multiple doses of CpG oligodeoxynucleotides to mimic mtDNA export by MM. Results showed similar expansion of haematopoietic stem and progenitor cell populations. To understand the effects of mtDAMPs on the inflammatory cells of the BMM, we show that bone marrow derived macrophages treated with mtDNA and CpG had increased expression of pro-inflammatory cytokines including IL-6. In vivo, isolated F4/80+ bone marrow macrophages from 5TGM1 and CpG treated mice also showed increased expression of pro-inflammatory cytokines. Finally, to understand the role of mtDAMPs in regulating HSPC expansion we used blocking antibodies to TLR9 (toll-like receptor 9 for mtDNA) and FPR1 (receptor for formylated mitochondrial proteins) in 5TGM1 engrafted animals. Blocking these receptors resulted in reduced myeloma tumor burden compared to control animals. Here we establish that MM releases mtDNA into the microenvironment and highlight the involvement of mtDAMPs in creating a pro-inflammatory BMM that aids in MM disease progression. This data suggests the potential for the targeting of TLR9 or FPR1 signaling pathways as a novel therapeutic approach for MM.
Citation Format: Aisha Jibril, Prakrit Kumar, Charlotte Hellmich, Jamie A. Moore, Jayna J. Mistry, Victoria Willimott, Kristian M. Bowles, Stuart A. Rushworth. Multiple myeloma derived mitochondrial DAMPs induce a pro-inflammatory signature in the bone marrow microenvironment to promote pro-tumoral expansion [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 2799.