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

Kimberley C Clark,Gareth C.G Davies,Vasilios Panagopoulos,Natalya Plakhova,Krzysztof M Mrozik,Khatora S Opperman,Kate Vandyke,Duncan R Hewett,Daniel L Worthley,Andrew C.W Zannettino,Siddhartha Mukherjee,Alanah L Bradey

doi:10.3390/cancers12082149

Abstract

In most instances, multiple myeloma (MM) plasma cells (PCs) are reliant on factors made by cells of the bone marrow (BM) stroma for their survival and growth. To date, the nature and cellular composition of the BM tumor microenvironment and the critical factors which drive tumor progression remain imprecisely defined. Our studies show that Gremlin1 (Grem1), a highly conserved protein, which is abundantly secreted by a subset of BM mesenchymal stromal cells, plays a critical role in MM disease development. Analysis of human and mouse BM stromal samples by quantitative PCR showed that GREM1/Grem1 expression was significantly higher in the MM tumor-bearing cohorts compared to healthy controls (p < 0.05, Mann–Whitney test). Additionally, BM-stromal cells cultured with 5TGM1 MM PC line expressed significantly higher levels of Grem1, compared to stromal cells alone (p < 0.01, t-test), suggesting that MM PCs promote increased Grem1 expression in stromal cells. Furthermore, the proliferation of 5TGM1 MM PCs was found to be significantly increased when co-cultured with Grem1-overexpressing stromal cells (p < 0.01, t-test). To examine the role of Grem1 in MM disease in vivo, we utilized the 5TGM1/KaLwRij mouse model of MM. Our studies showed that, compared to immunoglobulin G (IgG) control antibody-treated mice, mice treated with an anti-Grem1 neutralizing antibody had a decrease in MM tumor burden of up to 81.2% (p < 0.05, two-way ANOVA). The studies presented here demonstrate, for the first time, a novel positive feedback loop between MM PCs and BM stroma, and that inhibiting this vicious cycle with a neutralizing antibody can dramatically reduce tumor burden in a preclinical mouse model of MM.

Highlights

Multiple myeloma (MM) is a hematological malignancy characterized by the uncontrolled proliferation of antibody-producing plasma cells (PC) within the bone marrow (BM) [1]
In view of the co-localization of the osteochondroreticular stem cell population with sites associated with MM PC growth [17,18], the expression of GREM1 was analyzed in messenger RNA
BM stromal cells (n = 15) had significantly higher expression of GREM1 compared to BM stroma derived from age-matched hematopoietically normal donors (n = 17) (p = 0.0004; Figure 1A)

Summary

Introduction

Multiple myeloma (MM) is a hematological malignancy characterized by the uncontrolled proliferation of antibody-producing plasma cells (PC) within the bone marrow (BM) [1]. Myeloma-defining events include evidence of end-organ damage, such as hypercalcemia, renal insufficiency, anemia, and bone lesions, known as the CRAB criteria [2]. Almost all cases of MM are preceded by monoclonal gammopathy of undetermined significance (MGUS), a benign clonal PC proliferation characterized by less than 10% PCs in the BM and the absence of end-organ damage [5]. While malignant transformation and MM disease progression are believed to occur due to the accumulation of secondary “genetic hits”, recent studies from our laboratory [7] and others [8,9] observed that many of the chromosomal abnormalities and genetic lesions identified in MM PCs are found at the MGUS stage, suggesting that PC-extrinsic factors may be involved in driving the progression from asymptomatic MGUS to malignant MM. While it is well established that the BM microenvironment is critical for MM tumor growth, it remains to be elucidated which stromal cells and factors are required for the continued growth, spread, and survival of the MM PC [11,12]

Methods

Results

Discussion

Conclusion