An animal model of MGUS/SMM to investigate the role of cellular senescence in progression to MM.
Authors: Zhang Hengwei , Aljitawi Omar Salah , Zhang Lianping Xing , Conley Thomas , Passero Frank Charles , Lipe Brea 
Published: June 2021

8050 Background: Multiple Myeloma (MM) is an incurable cancer of plasma cells that arises from precursor stages, monoclonal gammopathy of undetermined significance (MGUS) and/or smoldering MM (SMM). Mechanisms for the transformation of MGUS/SMM to MM are not fully known. There is no approved therapy for MGUS/SMM and research is limited by a lack of animal models. Here, we describe the use of a novel animal model of disease progression derived from patients with MGUS/SMM to study the impact of cellular senescence (CS) on the development of MM. Methods: CD 138+ plasma cells and CD138- stromal cells were isolated via magnetic beads from bone marrow aspirates of patients with MGUS/SMM and co-cultured CD138+/CD138- with different ratios. For the animal model CD138+/CD138- cells from MGUS/SMM patients were injected into the tibias of NSG mice (1:10). After 4 weeks, CD138+ cells were harvested and again co-transplanted into the tibia of a 2nd NSG mouse with the CD138- cells (1:10). Mice underwent serial imaging and tibias were histologically examined after 4 weeks in the 2nd mouse. CS gene expression was compared by RNAseq between patients with SMM and healthy older adults. The primary CD138- cells were stained for SA-β-gal. Human mesenchymal stem cells (hMSCs) induced by H2O2 for CS vs control were co-cultured with CD138+ cells. Patient derived CD138- cells were treated with anti-senolytic drugs, dasatinib (D) and quercetin (Q) and cell growth in co-culture with CD138+ plasma cells was measured. D+Q treated patient-derived CD138+/CD138- cells were co-transplanted into our NSG mouse model and followed with serial imaging. Results: CD138- stromal cells from patients with MGUS/SMM support the growth of CD138+ plasma cells (10:1). CD138- cells were found to gain CD138+ expression, suggesting another source for the plasma cell growth. Imaging of our mouse model showed the development of lytic lesions in the tibias of 5/5 mice versus no lytic lesions in mice transplanted with CD138+ cells alone. Staining of the lytic lesions revealed CD138+ plasma cells. Our RNA seq showed significantly increased expression of CS genes, CDKN2A, p16 and p19 (3 fold) in CD138- cells of SMM patients and confirmed by qPCR (8 fold) compared to healthy older adults. The primary stromal cell culture from MGUS/SMM patients showed the presence of SCs by SA-β-gal staining. H2O2 induced senescent hMSCs stimulate cell survival and growth of CD138+ cells. CD138- cells cultured with conditioned media from H2O2 induced hMSCs demonstrated more CD138+ cells than vehicle treated CD138- cells. Conversely, D + Q pre-treated CD138- cells lost the ability to promote CD138+ cells in co-culture. Our animal model treated with D+Q showed less bone erosion in tibias compared to untreated mice. Conclusions: Our work demonstrates a novel animal model for studying disease progression in patients with MGUS or SMM and demonstrates a role for CS in MM disease progression.