Multiple myeloma tumor progression in the 5T2MM murine model is a multistage and dynamic process of differentiation, proliferation, invasion, and apoptosis

Abstract

IntroductionMultiple myeloma (MM) is still an incurable plasma cell cancer, predominantly localized in the bone marrow (BM). Our group demonstrated that the in vivo homing of these malignant cells to the BM is a selective process of directed migration and selective survival in this organ. 1 Once the cells have entered the BM, they have an intensive cross-talk with the BM stromal cells and induce a microenvironment that supports their survival and growth. 2 At time of diagnosis, MM is already a well-established disease. So far myeloma research has been focused on homing and other mechanisms involved in the clinical stage of the disease. The processes involved in the earlier, preclinical, stages are unknown. In this work we took a first step in illumination of the preclinical stages. Since such investigation requires an in vivo model, the 5T2MM experimental mouse model was used. Animals intravenously inoculated with MM cells were analyzed during the entire process of myeloma progression and monitored for 3 markers: CD45, CD138 (syndecan-1), and interleukin 6 receptor (IL-6R). CD45 is a transmembrane protein tyrosine phosphatase, expressed on all B-cells. During maturation toward plasma cells the CD45 expression is gradually down-regulated. Fully matured plasma cells are CD45 Ϫ . 3 In myeloma patients both CD45 ϩ and CD45 Ϫ MM cells have been observed. [4][5][6] More recently, CD45 appeared to be a predictor of therapeutic response. 7 Myeloma patients were grouped according to percentages of CD45 bright , CD45 low , and CD45 Ϫ MM cells, and grouping was associated with clinical outcome: patients with a high percentage of CD45 Ϫ MM cells had the poorest outcome. The significance of this CD45 heterogeneity, from a biologic point of view, is, however, not understood. In the present work CD45 was used as a differentiation marker together with CD138. CD138 is a transmembrane heparan sulfate proteoglycan expressed on sessile B cells. All pre-B cells are CD138 ϩ , but during circulation in the peripheral blood CD138 expression is lost and CD138 is re-expressed on mature plasma cells in the BM. Immature CD45 ϩ MM cells are CD138 Ϫ . CD138 is also proteolytically cleaved and shed from the cell surface, and CD138 Ϫ MM cells appeared to possess a higher invasive capacity. 8 IL-6R consists of 2 subunits: an ␣ chain (gp80, CD126), which specifically binds IL-6, and a shared ␤ chain (gp130, CD130), which is responsible for the signal transduction. 9-11 IL-6 is a growth factor for MM cells, 12,13 and, worthy of mention in this work, it is required in the early stages of plasma cells in the BM to escape apoptosis. 14 We report herein a multistage process of myeloma disease progression based on the evolution of serum M component (paraprotein) and tumor load. Flow-cytometric analysis demonstrated a CD45 ϩ CD138 Ϫ IL-6R␣ ϩ phenotype of the majority of MM cells in the initial stage of tumor progression. Toward the end Materials and methods 5T2MM myeloma model5T2MM myeloma cells originate from spontaneously developed myeloma in elder...

The SCID-rab model: a novel in vivo system for primary human myeloma demonstrating growth of CD138-expressing malignant cells

“…To our knowledge, this is the first report demonstrating the potential of isolated primary CD138-enriched PCs to proliferate, propagate, and produce typical myeloma manifestations in vivo. These results are in contrast to recent study showing the inability of purified CD138-expressing PCs to grow in NOD/SCID mice, 8 but in accord with previous reports demonstrating the ability of human 12 and murine 18,19 mature CD45 À myeloma PCs to grow and manifest in a nonmyelomatous environment.…”

CD45 expression by bone marrow plasma cells in multiple myeloma: clinical and biological correlations

“…3,8,18 During normal development, the marrow is populated predominantly by the CD45 þ population, which represents the early stage PCs. As they mature to terminally differentiated plasma cells, the CD45 expression is gradually lost.…”

“…The expression of CD45 among the PCs in the bone marrow of patients with MM is heterogeneous. 3,8 The weight of evidence suggests the presence of two populations of myeloma cells in the marrow; early PCs with CD45 expression and late PCs with dim or no expression. Important biological differences have been demonstrated between these two populations including their proliferative capability, IL-6 responsiveness and dependence, chromosomal abnormalities and angiogenic capability.…”

Characterization of clonogenic multiple myeloma cells

“…Recent studies have suggested that both human 23 and murine 24,25 MM cell lines can demonstrate heterogeneous expression of several MM-related cell surface antigens. Therefore, we analyzed the expression of CD138 in 2 distinct human MM cell lines, RPMI 8226 and NCI-H929.…”