Edwards, Claire M.

Abstract Multiple myeloma (MM) is a clonal plasma cell (PC) cancer that is preceded by the benign conditions monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM (SMM). While MGUS/SMM PCs are not proliferative, many of the oncogenes and chromosomal abnormalities in MM PCs are also present in MGUS/SMM. Since oncogenic stress is known to induce cellular senescence, we hypothesized that MGUS/SMM PCs may be in a senescent-like state. Our analysis of a published human dataset (GSE5900) revealed that compared to healthy PCs, MGUS/SMM PCs had significantly increased expression of senescence markers CDKN1A and GADD45A (FDR<0.05). Gene Set Enrichment Analysis (GSEA) showed significant enrichment in MGUS/SMM PCs of our customized senescence phenotyping gene sets (q<0.25). We next evaluated the KaLwRij MGUS mouse model. 10-mo-old female KaLwRij mice were treated with placebo or senolytics (dasatinib+quercetin, D+Q). D+Q treatment significantly reduced PCs compared to placebo, while restoring B cell number and functional gene expression. PCs isolated from D+Q-treated KaLwRij mice exhibited significant reductions in Myc and Il1b expression (p<0.05) versus placebo and a trend towards reduced Trp53 expression (p=0.13), supporting that senescent PCs are targeted by D+Q. Single-cell RNA-seq and single sample (ss)GSEA of 24-mo-old KaLwRij PCs revealed a PC subset enriched for the ‘Plasma Cell Senescence’ gene set, which included genes from our customized gene sets that were differentially expressed in the human PCs dataset GSE5900. Notably, PCs in this subset showed enrichment for ‘Inflammatory SASP’ (median: 15.26%) and ‘Interferon (IFN) SASP’ (39.36%) gene sets. The IFN-SASP is characteristic of late senescence, driven by the accumulation of transposable elements. In the GSE5900 dataset, we found significant enrichment of ‘IFN-SASP’ in SMM (q<0.25) but not MGUS PCs. Further, whole transcriptome RNA-sequencing showed that SMM PCs had increased expression of LINE1 retrotransposon L1HS in relation to normal PCs (FDR<0.1), but not MGUS (FDR=0.83) or MM (FDR=0.5) PCs. Immunostaining confirmed increased cytosolic DNA:RNA hybrids in SMM (median frequency of cells exceeding the intensity threshold = 33%) versus MGUS (16.4%), MM (4.4%), and healthy PCs (1.5%), which is consistent with cytosolic DNA-mediated activation of the IFN SASP in SMM PCs. When these same patients were redistributed according to disease progression, L1HS was higher in patients with progressing SMM and newly diagnosed MM (NDMM) (FDR<0.1) versus patients with stable MGUS (FDR=0.56) or advanced MM (FDR=0.38). Increased DNA:RNA staining was observed in progressing SMM PCs (median frequency = 41%), but the results for NDMM patients (4.4%) and advanced MM (3%) were comparable to healthy or stable patients (3.5%). These data demonstrate that MGUS and SMM PCs exhibit senescence features, suggest mechanisms that may contribute to MM tumorigenesis, and show that pharmacological ablation of senescent cells may prevent progression from MGUS/SMM to MM. Citation Format: Gabriel Alvares Borges, Angelo Jose Guilatco, Christine M. Hachfeld, Ming Ruan, Sonya Royzenblat, Ming Xu, Claire M. Edwards, Marta Diaz-delCastillo, Thomas L. Andersen, Taxiarchis Kourelis, Tamar Tchkonia, James L. Kirkland, Matthew T. Drake, Megan Weivoda. Pre-malignant plasma cells exhibit a senescence-like phenotype and accumulation of transposable elements [abstract]. In: Proceedings of the AACR Special Conference: Aging and Cancer; 2022 Nov 17-20; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_1):Abstract nr PR012.

Abstract This abstract is being presented as a short talk in the scientific program. A full abstract is available in the Short Talks from Proffered Abstracts section (PR012) of the Conference Proceedings. Citation Format: Gabriel Alvares Borges, Angelo Jose Guilatco, Christine M. Hachfeld, Ming Ruan, Sonya Royzenblat, Ming Xu, Claire M. Edwards, Marta Diaz-delCastillo, Thomas L. Andersen, Taxiarchis Kourelis, Tamar Tchkonia, James L. Kirkland, Matthew T. Drake, Megan Weivoda. Pre-malignant plasma cells exhibit a senescence-like phenotype and accumulation of transposable elements [abstract]. In: Proceedings of the AACR Special Conference: Aging and Cancer; 2022 Nov 17-20; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_1):Abstract nr B020.

ABSTRACT Multiple myeloma is caused by abnormal plasma cells that accumulate in the bone marrow and interact with resident cells of the bone microenvironment to drive disease progression and development of an osteolytic bone disease. Bone marrow adipocytes (BMAds) are emerging as having important endocrine functions that can support myeloma cell growth and survival. However, how BMAds respond to infiltrating tumor cells remains poorly understood. Using the C57BL/KaLwRij murine model of myeloma, bone marrow adiposity was found to be increased in early stage myeloma with BMAds localizing along the tumor-bone interface at later stages of disease. Myeloma cells were found to uptake BMAd-derived lipids in vitro and in vivo, although lipid uptake was not associated with the ability of BMAds to promote myeloma cell growth and survival. However, BMAd-derived factors were found to increase myeloma cell migration, viability, and the evasion of apoptosis. BMAds are a major source of adiponectin, which is known to be myeloma-suppressive. Myeloma cells were found to downregulate adiponectin specifically in a model of BMAds but not in white adipocytes. The ability of myeloma cells to downregulate adiponectin was dependent at least in part on TNF-α. Collectively our data support the link between increased bone marrow adiposity and myeloma progression. By demonstrating how TNF-α downregulates BMAd-derived adiponectin, we reveal a new mechanism by which myeloma cells alter the bone microenvironment to support disease progression. © 2019 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

AbstractThe contributions of the host microenvironment to the pathogenesis of multiple myeloma, including progression from the non-malignant disorder monoclonal gammopathy of undetermined significance, are poorly understood. In the present study, microarray analysis of a murine model requiring a unique host microenvironment for myeloma development identified decreased host-derived adiponectin compared with normal mice. In support, clinical analysis revealed decreased serum adiponectin concentrations in monoclonal gammopathy of undetermined significance patients who subsequently progressed to myeloma. We investigated the role of adiponectin in myeloma pathogenesis and as a treatment approach, using both mice deficient in adiponectin and pharmacologic enhancement of circulating adiponectin. Increased tumor burden and bone disease were observed in myeloma-bearing adiponectin-deficient mice, and adiponectin was found to induce myeloma cell apoptosis. The apolipoprotein peptide mimetic L-4F was used for pharmacologic enhancement of adiponectin. L-4F reduced tumor burden, increased survival of myeloma-bearing mice, and prevented myeloma bone disease. Collectively, our studies have identified a novel mechanism whereby decreased host-derived adiponectin promotes myeloma tumor growth and osteolysis. Furthermore, we have established the potential therapeutic benefit of increasing adiponectin for the treatment of myeloma and the associated bone disease.