Clodronate-Liposome Mediated Macrophage Depletion Abrogates Multiple Myeloma Tumor Establishment In Vivo

Abstract

Multiple myeloma is a fatal plasma cell malignancy that is reliant on the bone marrow microenvironment. The bone marrow is comprised of numerous cells of mesenchymal and hemopoietic origin. Of these, macrophages have been implicated to play a role in myeloma disease progression, angiogenesis, and drug resistance; however, the role of macrophages in myeloma disease establishment remains unknown. In this study, the antimyeloma efficacy of clodronate-liposome treatment, which globally and transiently depletes macrophages, was evaluated in the well-established C57BL/KaLwRijHsd murine model of myeloma. Our studies show, for the first time, that clodronate-liposome pretreatment abrogates myeloma tumor development in vivo . Clodronate-liposome administration resulted in depletion of CD169 + bone marrow–resident macrophages. Flow cytometric analysis revealed that clodronate-liposome pretreatment impaired myeloma plasma cell homing and retention within the bone marrow 24 hours postmyeloma plasma cell inoculation. This was attributed in part to decreased levels of macrophage-derived insulin-like growth factor 1. Moreover, a single dose of clodronate-liposome led to a significant reduction in myeloma tumor burden in KaLwRij mice with established disease. Collectively, these findings support a role for CD169-expressing bone marrow–resident macrophages in myeloma disease establishment and progression and demonstrate the potential of targeting macrophages as a therapy for myeloma patients.

Targeted Disruption of Bone Marrow Stromal Cell-Derived Gremlin1 Limits Multiple Myeloma Disease Progression In Vivo

“…At the experimental endpoint, femora and tibiae from tumor-bearing, and age- and sex-matched nontumor mice were isolated, and the BM flushed out with PFE buffer (PBS, 2% FCS, and 2 mM Ethylenediaminetetraacetic acid (EDTA)). Collagenase digestion of the cortical and trabecular bone was performed, as previously described [ 51 ]. The digested bone fragments and collagenase-isolated BM stromal cells were co-lyzed in 1 mL of TRIzol TM Reagent (Thermo Fisher Scientific) and incubated on ice for 15 min.…”

“…For flow cytometric analysis, long bones (femora and tibiae) were excised and cleaned. Bones were gently crushed with a mortar and pestle in PFE to isolate BM and compact bone cells were isolated, as previously described [ 51 , 52 ]. Briefly, the resultant bone chips were washed, finely chopped, and incubated with 3 mg/mL collagenase type-I (ScimaR, VIC, Australia) in PBS at 37 °C for 45 min.…”

The Role of Tumor Microenvironment in Multiple Myeloma Development and Progression

“…Despite the positive outcomes obtained in MM patients with bortezomib treatment, results showed that this proteasome inhibitor also promotes the accumulation of pro-inflammatory macrophages and fosters MM cell survival and aggressiveness linked to MM disease progression, which could represent one of the mechanisms associated with MM resistance to bortezomib [ 151 ]. Moreover, depletion of macrophages or blockade of M2-polarization in murine MM models inhibits tumor growth and disease progression in vivo, and enhances survival after stem cell transplantation, providing strong evidence that macrophages are important for myeloma progression and a promising therapeutic target [ 142 , 152 , 153 ].…”

<p>Autologous Fat Grafting Promotes Macrophage Infiltration to Increase Secretion of Growth Factors and Revascularization, Thereby Treating Diabetic Rat Skin Defect</p>

“…Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy 2020:13 4898 for 2 weeks. 25 Every time the AFG+MD group rats injected with Lipo-Clo, the other two groups of rats would receive 100 μL of PBS solution as control.…”